Boost Question

[Beej]

Just for the sake of argument, what would it take to run 15psi of boost on a fuel injected stroker?

Lets say single turbo or twin parallel turbos, or some kind of supercharger.

If you were going to build this and make it last, and money were not really an object, how would you build it?

If you would be so kind, please discuss...

:yap:

[Dr. Dyno]

If you want the motor to last with 15psi of boost, you'll need to build it with forged Eagle rods & custom forged pistons. You'll need to nitride harden the crank, o-ring the cylinders, and use a copper head gasket. Upgrade the fuel pump so the engine doesn't run too lean.
Since the engine is an I6, it's easier to install a single turbo (I'd go for a TO3/4 hybrid to get good boost from as little as 1500rpm).

[goodburbon]

Would it be an alternative to have an auxilliary injector in a tb spacer to prevent lean conditions under boost?

[Michaelarchangelo]

No, aux injectors are more of a bandaid then a permante solution. If you were going to do it the correct way, you would run larger injectors with at least a piggyback system.


15 psi on a stroker would need a lot of other parts to survive besides just the motor. Tranny, rear end (I wouldn't even really think about using a TC) would all need to be upgraded or replaced with better units.

[ricot83]

you would need a different vehicle basically.

[BBeach]

What about a centrifugal supercharger in the place of the A/C? I think i've seen this before with the xjarmor.com setup but does anybody know of what model supercharger they used and such or have any idea of how to make a custom one?

[Beej]

Remember, this is just an exercise in navel-gazing. Thanks for the replies so far.

A few more parameters:

Consider the build for the engine only, nevermind the vehicle, tranny, etc.

Which block, any special treatment?
Head?
Intake?
Throttle body?
Header, downpipe, exhaust?
Pistons, rods, crank, cam, lifters, springs, bearings, etc...

Any special treatments for anything else?

[Beej]

What about a centrifugal supercharger in the place of the A/C? I think i've seen this before with the xjarmor.com setup but does anybody know of what model supercharger they used and such or have any idea of how to make a custom one? Vortech and Paxton both make centrifugal superchargers, maybe it was one of them?

[Seiler]

What I wanted to do, and someday hope to do, is get the hesco 4.7L stroker kit and then have a avenger supercharger installed. However, that's probably down the line and would also need other after market parts already discussed.....

Scott

[RWKHausSupply]

wow the 4.0 is that weak of a motor? 15psi is not all that much, depending on static comp ratio that is.

At a 8.5:1 (isnt that about stock?) I would figure that a sturdy block and inners like the 4.0 would survive without much issues up to 15psi. O-Ring the head or block? at 15psi? daym that sucks..

just as a side note. The SRT-4 that is just a basic dodge 2.4 lower end, nothing more fancy then just a basic stratus,cirus, or neon 2.4 lower end, we can push 20-22 psi to it with no needs to change much in it, and up to 25 with only the need for a piston change.

I would agree that just a Good piggy back system would be needed. I would also look in to a good water/methenal injection system though.

And a TO3/4 for lower quick boost or a GT40 for max hard boost.

[Michaelarchangelo]

Remember, this is just an exercise in navel-gazing. Thanks for the replies so far.

A few more parameters:

Consider the build for the engine only, nevermind the vehicle, tranny, etc.

Which block, any special treatment?
I would go with a late model block, and just do the normal check for cracks, hone walls, etc.
Head?
Def. clean up the bowl, go with larger valves
Intake?
If it were me, I would custom build an intake for a turbo. Go with something with a larger plenum, and that points the TB to the front of the jeep. Most superchargers are their own intake manifold.
Throttle body?
See above, but it would need to be much larger (mustang?).
Header, downpipe, exhaust?
With a turbo, you won't have headers. I would run a min of a 3" downpipe and exhaust.
Pistons, rods, crank, cam, lifters, springs, bearings, etc...
Forged, Forged, Forged, most of the time stock cams work well with turbos, lifters should be fine, you might need stiffer springs (if you go too stiff, you might as well change it all out anyways). Stock replacement bearings should be ok.
Any special treatments for anything else?
Might want to upgrade ignition and fuel system, go full standalone.



There are also a few diffrent factors that determine what boost to run. Outside temps, fuel, static comp ratio, if you have an intercooler, what timing you are running, where your turbo is efficent at, etc...

[RWKHausSupply]

There are also a few diffrent factors that determine what boost to run. ..., if you have an intercooler, ....where your turbo is efficent at...

These are Very accurate statments.

im my experiences with the SRT's. A stock setup can run a boost controller and get 21psi from the stock system that is ran stock at 12-14psi. Well at 14-15psi, and then to 19-21 psi (no other mods except boost controller) the HP only goes up maybe 20hp, but the torque I have see jump from around 290 to 350 peek.

But taken that same car/setup, and done a Huge front mount intercooler on and the HP jumped like around 40 hp gains (20 HP add with the larger Int.) But if you take the stock setup and just add the intercooler with no added boost, still around 12-14psi, the gain is around 1-5 HP at most.

That is mostly due the the stock SRT turbo not being very effecicent above around 17psi, and the stock intercooler not being able to keep up with heat soak above like 15 PSI.

Water/meth inj will bandaid fix the lower quality fuel, timing issues, and heat soak and even build much better HP/TQ#'s though... And nitrous will double the benifits of the water/meth inj, but its not a consistant. Not to mention Nitrous will jump your 15PSI up to around 20-22PSI with no other mods, other then spraying such a cold mixture.

[Michaelarchangelo]

I thought the SRT4s were limited to 18psi before it starts to retard ignition?

[5-90]

Gimme a bit - let me kick this one around a little.

First of all, tho, I'd run a blower rather than a turbo - but I just don't much care for turbos. I can build systems to run on them - I just don't like doing it...

Besides, I've got to get back to you about that other thing...

5-90

[RWKHausSupply]

I thought the SRT4s were limited to 18psi before it starts to retard ignition?

Thats all a matter of case by case, Yes the stage 2 kits that use the stock turbo limit the output to 18-20PSI. But Ign. is only a issue with to low of a octane or high heat / knock sensor read.

One major acces. that most will run is a map clamp though. Not only does the computer then not see anything above around 17psi, but you also dont throw codes from "high boost" with one. Only issue there though is fuel delivery is cut back, so the more knowledgable will run a piggy system of some form to allow inj correction also so that you dont go lean.

[Michaelarchangelo]

Gimme a bit - let me kick this one around a little.

First of all, tho, I'd run a blower rather than a turbo - but I just don't much care for turbos. I can build systems to run on them - I just don't like doing it...

Besides, I've got to get back to you about that other thing...

5-90

Why a blower? The 4.0 has plenty of off the line power, with a turbo you can help it breathe at higher RPMs, less parastic loss, plus it should fit without making a huge hole in the hood :D

[Michaelarchangelo]

Thats all a matter of case by case, Yes the stage 2 kits that use the stock turbo limit the output to 18-20PSI. But Ign. is only a issue with to low of a octane or high heat / knock sensor read.

One major acces. that most will run is a map clamp though. Not only does the computer then not see anything above around 17psi, but you also dont throw codes from "high boost" with one. Only issue there though is fuel delivery is cut back, so the more knowledgable will run a piggy system of some form to allow inj correction also so that you dont go lean.


Ive never owned one (wouldn't mind it) but I have a buddy and he was asking me a lot of questions about his. Electronics today take all the fun out of trying to blow up a turbo motor (ask me about my XR4ti).

[5-90]

But a Whipple/Lysholm/"twisted rotor" blower has greater adabiatic (sp? I'm never sure...) efficiency, meaning less need for an intercooler. Also, a Whipple can be laid on its side, meaning low-profile mounting (you'll want a better intake anyhow,) and it isn't as hard on oil as a turbocharger.

And, you get more boost at lower RPM - meaning you're getting 15psi at 2000rpm, while the turbo is still spooling. It doesn't "surge," and it doesn't "lag."

I'll admit that turbos have their uses, but it's generally more difficult to plan and build a turbo setup than a blower setup - at least, it has been for me. Also, if you don't get your turbo sized just right, you're going to end up "lagging" right when you need it...

Another advantage? You can plan a blower to be cut in and out at will - I used to set up GMC -71 (mainly 4-71's and 6-71's) series blowers to do that on SBChevvies for week-end warriors. Use a magnetic clutch pully, and you can either drive the blower, or just allow it to freewheel - and build the engine to run well either way (you're still going to lose some NA performance - but that's more of a tradeoff for working well with a blower than anything to do with the minimal restriction of airflow through a freewheeling blower.)

Running a full atmosphere of boost is going to take some compromise anyhow - but it should be doable, and I'd prefer to do it with a blower than with a turbo. Personal preference, but that's just me...

(Besides, have you ever seen what a turbocharger can do to engine oil? They've gotten better, but just imagine something spinning about 90Krpm without a supply of fresh oil. There's a reason they have "Turbo Timers" - and it's not for "bling" factor...)

5-90

[RWKHausSupply]

Ive never owned one (wouldn't mind it) but I have a buddy and he was asking me a lot of questions about his. Electronics today take all the fun out of trying to blow up a turbo motor (ask me about my XR4ti).

Yes todays ECU's and tech. do make it hard. I have not heard of one case of motor failier with less then like 40K on a SRT4 yet. I havent been in that arena though for 7 months. In any case I personally been to the track and street with a SRT4 running completly stock long block and a GT40 with all custom int, full stand alone, about a 100HP shot after the intercooler, and 25hp before. all running on 110oct, and 24psi peeking to 27 with the spray on. front wheel HP at I think the best was 655hp..

Never did the long block have an issue. It was though broken down and rebuilt with all higher end stuff after maybe 100 passes and numerous dyno pulls... And thats nothing more then a neon 2.4 long block.

[Michaelarchangelo]

Ya turbos are known to be harsh on oil. As for surge and lag, those can be taken care of very easy by today's newer designs in turbos (variable vane turbos are awesome). Picking the proper one for a specific app isn't that hard either. I had at one time a spreadsheet to help determine the best turbo based upon various inputs, I will have to see if I can dig it up.

I think it really depends on the backround you come from, and what you feel comfortable working with. I myself have never put a blower on anything, so I really wouldn't have the first clue on how to set it up. I didn't even know you can get a clutch for them (don't know why that didn't dawn on me). I wouldn't mind putting a blower on a SBC on day, just to do something diffrent (for me).

[5-90]

Ya turbos are known to be harsh on oil. As for surge and lag, those can be taken care of very easy by today's newer designs in turbos (variable vane turbos are awesome). Picking the proper one for a specific app isn't that hard either. I had at one time a spreadsheet to help determine the best turbo based upon various inputs, I will have to see if I can dig it up.

I think it really depends on the backround you come from, and what you feel comfortable working with. I myself have never put a blower on anything, so I really wouldn't have the first clue on how to set it up. I didn't even know you can get a clutch for them (don't know why that didn't dawn on me). I wouldn't mind putting a blower on a SBC on day, just to do something diffrent (for me).

"Something different?" I've probably done a couple dozen by now. Hell, I've even managed to setup a "staged boost" setup - did a 454 running a pair of turbos into an 8-71 (I think - that notebook is 2500 miles from me right now...) for something like 4atm of boost. Boy, was that ever fun to set up!

Staged boost isn't that uncommon tho - think Diesel pulling tractors, and you're on the right track. You end up feeding air under boost into a fixed displacement blower, and then cramming it in even more. You can't do staged boost unless the last stage has fixed displacement tho - as I recall.

Having seen coked oil, I'm about as likely to put as much work into oiling mods as I am into the forced induction proper - I did have a couple of ideas that worked rather neatly, tho (and didn't require any "user intervention," either...)

5-90

[5-90]

First of all, I would probably not want to run that boost level on a stroker (with OTS parts) - at least, not without some serious charge air cooling. Most forced induction engines (especially turbocharged gasoline engines) are "destroked" slightly to make up for the increase charge air temperature. Air/Air charge air cooling is of limited utility - water/air cooling can be more effective, but you'll need to plumb a separate circuit and not use the engine coolant to make that work. Point to remember - "If it doesn't make you go faster, it slows you down."

I'd select a supercharger for the reasons I mentioned - no lag, no surge, and better boost at lower RPM (where the AMC242 thrives.) Losses are comparable - whether it's crankshaft loss due to the string-driven thing, or pumping losses due to the exhaust turbine. Besides, plumbing a supercharger is usually easier (and not as large of an exhaust pipe is required. 1ATM blower going into a 4.7-ish stroker should only need a 3" exhaust, while 1ATM turbocharge will want 3.5-3.75" as a minimum. Superchargers benefit from exhaust tuning, turbos just want the biggest damn pipe you can fit.) And, you can run a supercharger as a "switchable" setup, as I'd mentioned before.

Another advantage of a blower over a turbo? No need to design a new manifold to make the turbo work at or near its best - and no turbo mass hanging off of the exhuast manifold, or to account for bracing up.

1ATM boost, either way, will definitely want charge air cooling (I think the optimax for non-cooled forced induction is about 6psi - not quite 1/2ATM.) Due to the heat of compression, you'll start negating the effect you're trying to get from compressing the charge air in the first place - 1ATM, non-cooled, works out to be about equivalent to 1ATM cooled, I'm wanting to recall (I'd have to check - a lot also depends upon the adiabatic efficiency of the compressor you're using.) Also, bear in mind plumbing in general - if it gets in the way, it's going to cause a flow loss. If it makes the flow change direction, it's going to cause a flow loss. TANSTAAFL.

All that aside, on to the core question - how would I build it?

I'd probably make sure the block and head deck are dead flat in the machine shop. I can always have a head gasket milled out of thin copper and annealed (I'd save the head gasket for last anyhow - since I'd want a finished bore size, and I'd want to play with some numbers and some "compression tests" to figure out how thick I want it to end up, and how thick I'd have to make it to get there.) I'd also o-ring the block deck, and make the final bore for the copper gasket the same as the final bore size for the block (-.000"/+.005") Quench would be very much a factor (since running 1ATM boost on pump gas is tough enough...) and I'd probably have custom pistons (and rods?) made while I was about it. The pistons would have a large round dish in the top (the better for quench turbulence,) and the rods would be as long as I could safely make them ("piston dwell" is also a factor in making torque - longer rods mean more piston dwell, and that means more developed pressure for the heat engine to use.)

Cylinder head would have polished chambers (maybe larger valves - depends on flowbench numbers,) and the ports would be polished and "gasket-matched" to the manifolds. I'd probably also install "anti-reversion cones" into the exhaust manifold entries - even with the mild flow restriction, they can help with scavenging (which can actually reduce pumping losses slightly. More flowbench work.) I might also have the combustion chambers enlarged slightly - via CNC, so I could also get consistency.

Exhaust? Equal-length headers, split by cylinder banks (as I recall, that means the front three on one pipe, and the back three on another.) Maybe have a wye joint right before the catalytic converter, maybe not - haven't decided yet. If not, I'd probably want to run two pipes all the way back - or as far back as I could.

Intake? Definitely not OTS - fab up to allow for "side-mounting" the Whipple blower. I'd probably split the intake in half as well (why not, if I'm going this far) so that I could run two smaller throttle bodies in tandem, rather than one large one. Charge air cooling either directly UNDER or directly OVER the throttle bodies, probably water/air.

Fuel? High-volume pump with a "rising rate" pressure regulator, or a "MegaSquirt" system to allow for more open FAR curve programming. 1ATM boost is WAY past anything the factory thought of doing - so why try to use factory gear (hey, you said "money wasn't a factor...")

Ignition? While I'd vastly prefer a Vertex Magneto (which I've used on SBChevvy with great results,) they don't make them for AMC I6, at last recall. I'd select MSD next - and I'd go with "coil packs" if I could, to increase saturation and per-spark energy over the single central coil. Three coils and a variation of the GM "Waste Spark" setup would be nice - six coils with one for each plug would be ideal. "Waste Spark" would probably be easier, tho.

I'd have to chew and dig a little deeper to give you an even better answer, but does this answer your question?

5-90

[BlueCuda]

Why the magical number of 15psi? Depending on setups you could make more with 10 or less with 20 depending on the parts and how efficient your setup is. Myself I would run a turbo, just because I like them. I have helped some friends with some blow-thru systems and they work well. The fab part would be tough with a non crossflow head but I am sure it can be done without putting the turbo on the hood lol.

Some friends of mine with blowers(a couple Eatons and 1 novi 2000) always bitch about belt slippage. There is not much room to play with wider or cog belts in an XJ thats for sure. I am sure belt slippage would not be an issue at low psi but that blower gets hard to turn the higher you go. Just my .02.

[5-90]

Probably just a though experiment, knowing him. I'd probably want to do a LOT more work than I said to make 1 bar of boost, but I think that's what he was after - just a "what if" or a "clean sheet of paper" build more than anything else.

With the restrictions of underhood space, even with fabbing up an intake, I'd probably not want to go more than about 1/2-bar of boost, for the reason you gave.

5-90

[MaXJohnson]

...I'd probably split the intake in half as well (why not, if I'm going this far) so that I could run two smaller throttle bodies in tandem, rather than one large one. Charge air cooling either directly UNDER or directly OVER the throttle bodies, probably water/air...
split the intake in half? "why not"
why?
throttle bodies in tandem?
where?

[5-90]

Throttle bodies in tandem (each one feeding three cylinders - 1-2-3, and 4-5-6. Exhaust probably split the same way) between the supercharger and the intake. Linkage could work like the old 2x4 setup, with carburettors in tandem (primary/secondary on each carburettor going progressive - but no need to do tha there.)

Running two smaller throttle bodies would effectively provide more flow area than a single large throttle body, and should also be easier to package underhood (the idea is to make things compact, no? That's why we are - presumably - starting with a clean sheet of paper.)

At least, that was my interpretation of the whole exercise - what would you do if you had a clean sheet of paper to work from, effectively unlimited funding, and naught but a basic long block to work with...

5-90

[MaXJohnson]

Throttle bodies in tandem (each one feeding three cylinders - 1-2-3, and 4-5-6...

Running two smaller throttle bodies would effectively provide more flow area than a single large throttle body, and should also be easier to package underhood (the idea is to make things compact, no? That's why we are - presumably - starting with a clean sheet of paper.)

At least, that was my interpretation of the whole exercise - what would you do if you had a clean sheet of paper to work from, effectively unlimited funding, and naught but a basic long block to work with...
5-90
your description of splitting the manifold into two, three cylinder pairs implies that you would be placing the throttle bodies on the compressed side of the Whipple. This would be alot of extra work for no gain; plus added headaches for fitting everything in what is already a limited amount of space. Besides that, the desired throttle cross section can be achieved with a single throttle body which would take up less space than two smaller units.

If I had a clean sheet of paper and a pocket full of money and a 4.0 long block, I wouldn't hesitate to drop in a SBC crate engine. The 4.0 long block would make a nice anvil for fabbing brackets and mounts.

[shortxjdoug]

15 psi on a stroker would need a lot of other parts to survive besides just the motor. Tranny, rear end (I wouldn't even really think about using a TC) would all need to be upgraded or replaced with better units.

i know this is piping in a little late on this post but tranny and rear would be the last of my worries. the aw-4 is the same unit that came in mk3 supras both naturally aspirated and turbo if it was in the auto flavor, im not sure what auto came in the mk4's but i can only assume that it is something similar, but the basic idea is that the a-dub platform at its basic design can handle a 280 hp plus boosted engine

[Beej]

I think its been bandied about quite a bit that the AW4 could handle upwards of 400hp in stock form. (IIRC) At any rate, the tranny and vehicle need not matter, this is just a mental exercise in what it would take to build the engine. I didn't say anything about it being in a Jeep. :D

I'm interested in 15psi because it equates to ~1ATM. From what I'd read in theory, just about any engine can at least be modified to handle this level of boost. I was just wondering what it would take as I'm not so schooled in such matters. Its just a clean sheet thinking build as 5-90 inferred.

Anyone have thoughts on what kind horses one might expect?

[5-90]

I think its been bandied about quite a bit that the AW4 could handle upwards of 400hp in stock form. (IIRC) At any rate, the tranny and vehicle need not matter, this is just a mental exercise in what it would take to build the engine. I didn't say anything about it being in a Jeep. :D

I'm interested in 15psi because it equates to ~1ATM. From what I'd read in theory, just about any engine can at least be modified to handle this level of boost. I was just wondering what it would take as I'm not so schooled in such matters. Its just a clean sheet thinking build as 5-90 inferred.

Anyone have thoughts on what kind horses one might expect?

If you've got some baseline specs in mind for the core engine build, pass them along. If not, I can come up with some goodies on my own - but once I've got specs, I can sim it for you and see what we can come up with...

5-90

[Flip94ta]

My 355 LT1 has 14 psi though a Vortech V-1 and an aftercooler. The static compression is 9.2-1 and the cam is 220-230 114 lsa .544-.544 The heads have cnc chambers, a must for high boost, and ported exhaust ports. It also has 1-5/8 headers, 3 inch borla exhaust. M6 tranny and a 12 bolt. It puts down 540hp at the rear wheels and 515 ftlbs. For the jeep your would probably need a stand alone fuel controller and atleast 42lb injectors. I am using the stock computer and an aftermarket tuning program on my laptop.

I would not do a stroker because it would make the side of the piston too short and blown motors need alot of thickness in the crown to keep the heat away from the rings. Centrifugul blowers are a little nicer on the drivetrain because they bring the power up gradually with rpm. There is still some low end torque though, I put down 380 ftlbs at 2500 rpm.

[jeepnuts311]

just poking my head in for a sec,

i am wondering if you introduce boost to the intake in the amc242, wouldnt you lose all the vacuum in the intake manifold?

i know it has been done before, but how do you make the map sensor, etc. work if you are totally changing the vacuum?

or am i totally missing something?

-Tim

[5-90]

just poking my head in for a sec,

i am wondering if you introduce boost to the intake in the amc242, wouldnt you lose all the vacuum in the intake manifold?

i know it has been done before, but how do you make the map sensor, etc. work if you are totally changing the vacuum?

or am i totally missing something?

-Tim

No, you're more or less spot on. These things have to be considered...

A larger vacuum reservoir is indicated (anything below ambient "normal" pressure is vacuum - you could build up enough, given time - but only at 1/2-atm boost or less...) or install a vacuum pump. Also, this is a case where HydroBoost brakes would be indicated - simply so you're not relying upon relatively low manifold vacuum at idle and low RPM and non-existant vacuum at speed.

MAP sensors can be had that read vacuum and pressure. A "1-bar" MAP will read from 0m/m Hg to 760m/m Hg (one atmosphere,) a "2-bar" reads from 0m/m to 1520m/m Hg, and so on. I've seen 3-bar and 4-bar MAP sensors, but not much past that.

Most other vacuum-driven accessories (like HVAC controls) can be supplied with a fairly small engine-driven or electrcally-powered vacuum pump, if you want to have a thoroughly reliable vacuum source. For brakes, tho, I'd prefer HydroBoost (which uses hydraulic pressure from the power steering pump, in case you haven't heard of it. It's common on large GM trucks) rather than manifold vacuum to boost pedal pressure into the master cylinder.

Most OEM engine management systems aren't programmed from the factory to handle more than about 1/3- to 1/2-atmosphere of boost, which is why I (should have!) brought up the MegaSquirt system.

Just a few more thoughts...

5-90

[MaXJohnson]

No, you're more or less spot on. These things have to be considered...

A larger vacuum reservoir is indicated (anything below ambient "normal" pressure is vacuum - you could build up enough, given time - but only at 1/2-atm boost or less...) or install a vacuum pump. Also, this is a case where HydroBoost brakes would be indicated - simply so you're not relying upon relatively low manifold vacuum at idle and low RPM and non-existant vacuum at speed.

MAP sensors can be had that read vacuum and pressure. A "1-bar" MAP will read from 0m/m Hg to 760m/m Hg (one atmosphere,) a "2-bar" reads from 0m/m to 1520m/m Hg, and so on. I've seen 3-bar and 4-bar MAP sensors, but not much past that.

Most other vacuum-driven accessories (like HVAC controls) can be supplied with a fairly small engine-driven or electrcally-powered vacuum pump, if you want to have a thoroughly reliable vacuum source. For brakes, tho, I'd prefer HydroBoost (which uses hydraulic pressure from the power steering pump, in case you haven't heard of it. It's common on large GM trucks) rather than manifold vacuum to boost pedal pressure into the master cylinder.

Most OEM engine management systems aren't programmed from the factory to handle more than about 1/3- to 1/2-atmosphere of boost, which is why I (should have!) brought up the MegaSquirt system.

Just a few more thoughts...

5-90

dude, you need to google some more before trying to answer these questions. Turbo motors still produce vacuum under normal driving conditions.

[jeepnuts311]

dude, you need to google some more before trying to answer these questions. Turbo motors still produce vacuum under normal driving conditions.

were talking about the amc242 here, an engine that is pretty picky when it comes to vacuum. i know on my renix 4.0s that if one vacuum line comes loose, the whole engine runs funky. this seems like something that should be adressed to me.

-TIm

[goodburbon]

What if you just tie your vac system to a point just upstream of the turbo/blower in the intake tube? Is this just not done?

[jeepnuts311]

What if you just tie your vac system to a point just upstream of the turbo/blower in the intake tube? Is this just not done?

i dont think you would have much vacuum there. most of the vacuum lines connect to the intake manifold because it is a closed chamber almost. the engine is sucking down air and (at idle) the throttle body is mostly closed. there wont be much vacuum upstream from the throttle body.

sometimes when im driving at speed, my a/c controls will slowly creep back to default (defrost) cuz of low vacuum, if i let off the gas the throttle body closes and sucks lots of vacuum and my a/c controls go back to how i had them set.

-TIm

[goodburbon]

I know it would be opposite of a standard vac, and that lowest pressure would be at full boost, I think it could be done with a good reservoir, check valve and venturi style inlet.

[jeepnuts311]

I know it would be opposite of a standard vac, and that lowest pressure would be at full boost, I think it could be done with a good reservoir, check valve and venturi style inlet.

oh, that may be true.

-Tim

[MaXJohnson]

were talking about the amc242 here, an engine that is pretty picky when it comes to vacuum. i know on my renix 4.0s that if one vacuum line comes loose, the whole engine runs funky. this seems like something that should be adressed to me.

-TIm
what engine isn't picky when it come to vacuum. They all run funky with a vacuum leak. The 4.0 is no different in this respect.

Just because an engine has a turbo or super charger, doesn't mean you're going to be up on the boost all the time. Under normal driving conditions when load demand is low, you should see pretty normal vacuum levels. Spark ignition engines, boosted or otherwise are throttled by controlling the air supply. Unless you are asking for more power, the throttle blade will be mostly closed and the pistions will be pulling for air, creating a vacuum.

5-90 is sounding like Chicken Little yelling "the sky is falling"; thinking you need custom built rods, auxilliary vacuum pumps, de-stroke kits and hydro brake boosters.

[5-90]

Not at all - just trying to come up with the most effective setup.

Also, note that I didn't say there would be no vacuum - just that you wouldn't have as much, and there are better ways to do things. Since you're planning on running about 15psig boost, even at idle, you're not going to have much (boost is progressive, 1 bar of boost is 1 bar of peak boost.)

Also, most "bolt-on" kits for production engines are designed for 1/3- to 1/2-bar of boost - go much beyond that, and you're going to be running into some work. I know - I've done it.

The auxiliary vacuum pump also wasn't mandatory, it's just a good idea (since it would increase reliability of the vacuum source, and therefore increase reliability of vacuum-driven accessories.)

Mainly, I'm just trying to highlight some of the concerns that should be brought to mind. Again, most "production kits" are designed for 1/2-bar or less (a typcal figure is 6psig of peak boost - or about 2/5-bar) which reduces the need for charge air cooling, and increases vacuum at idle. Break the 1/2-bar mark (7.35psig @ STP) and you're going into another ballpark.

I'm hardly saying "The sky is falling!" but I'm not going to let everyone know it's raining soup, either. Don't grab your buckets just yet...

5-90

[goodburbon]

Ok simple vac system solution is to plumb both upstream and downstream of pressure induction device with check valves for vac, then there is never a need for an aux vac pump, since the vac at idle demands will be met by the mainfold pressure and the vac demands at WOT would be met upstream of the blower.

Long story short on the block is build the shorter stroke 4.0 to take the beating of a 1atm+ boost. Then Use custom programmable piggyback sys with large enough injectors to handle consumption demands at WOT as well as lean enough mixture at idle and off-idle conditions. With the right combination of rods, pistons, computer, injectors, MAP and torque converter it should be a cake walk. Nothing but time and dollars stand in the way.

Does the computer address detonation/timin issues? Or am I just drunk posting again?

[BlueCuda]

Don't Forget that there is 0 vaccuum at WOT, if you have vaccuum at WOT you need a bigger TB.

Also, don't worry about the piston skirt on a 4.0L stroker, since alot of them use a STOCK 4.0 piston. I don't think the skirts will get any smaller than stock with a 258 crank. The SBC strokers have shorter piston skirts to clear the crank, not as much of a problem with the 4.0 setup.

[j99xj]

Don't Forget that there is 0 vaccuum at WOT, if you have vaccuum at WOT you need a bigger TB.

Also, don't worry about the piston skirt on a 4.0L stroker, since alot of them use a STOCK 4.0 piston. I don't think the skirts will get any smaller than stock with a 258 crank. The SBC strokers have shorter piston skirts to clear the crank, not as much of a problem with the 4.0 setup.

Sorry to nitpick. But there is no such thing as a true vacuum in an engine. It's all a matter of higher vs. lower pressure.

Low pressure in the cylinder (from a falling piston) causes the higher pressure gas in the intake manifold to flow into the cylinder. When the higher pressure gas flows out of the intake into the cylinder, this creates a lower pressure, causing the higher pressure gas in the atmosphere to flow past the throttle body in to replace the gas that just left.

No matter what our logic says, the engine doesn't "suck" gas in. Pressure always flows from high to low. This is exactly how the wind works.

[MaXJohnson]

Sorry to nitpick. But there is no such thing as a true vacuum in an engine. It's all a matter of higher vs. lower pressure.

Low pressure in the cylinder (from a falling piston) causes the higher pressure gas in the intake manifold to flow into the cylinder. When the higher pressure gas flows out of the intake into the cylinder, this creates a lower pressure, causing the higher pressure gas in the atmosphere to flow past the throttle body in to replace the gas that just left.

No matter what our logic says, the engine doesn't "suck" gas in. Pressure always flows from high to low. This is exactly how the wind works.
you didn't realize that BlueCuda's reference to "0 vacuum" was in reference to the reading on a typical automotive vacuum gage that is designed to indicate the difference between the manifold pressure and atmospheric pressure???

Everyone else did ;)

Look up the definition of suck and you'll see it means to draw in by creating a partial vacuum. Sounds like a perfectly appropriate term for this discussion.

[j99xj]

you didn't realize that BlueCuda's reference to "0 vacuum" was in reference to the reading on a typical automotive vacuum gage that is designed to indicate the difference between the manifold pressure and atmospheric pressure???

Everyone else did ;)

Look up the definition of suck and you'll see it means to draw in by creating a partial vacuum. Sounds like a perfectly appropriate term for this discussion.

I know what your saying. It's all relative. There are two ways of measuring pressure: gage pressure and true pressure.

The bottom line is the more molecules of air you can allow into your engine by any means, the more fuel you can add, and the more horsepower you can make.

The only thing limiting any engines performance is the material properties of the engine itself.

The trick is to select components with a high enough strength so that under load the metal will remain in the "elastic region." This way the part will return to its original shape when the loading is removed. If stress in a particular part exceeds the elastic limit, the part will permanently deform and will continue to deform until complete failure. (when your pistons shoot through the hood of your Jeep and connecting rods make your oil pan into swiss cheese)

I'm not a big fan of forced induction on engines that weren't designed for it. It's too big of a risk imho. The best engines to mess with boost are diesels because they are overbuilt to begin with and can take a lot of punishment. I've seen Duramax and Cummins diesels really kick some ass, even if they are hauling around a 3 ton truck.

[MaXJohnson]

The trick is to select components with a high enough strength so that under load the metal will remain in the "elastic region."
yeh, I use that philosophy for rubber hoses and belts too...




... and underware

[j99xj]

yeh, I use that philosophy for rubber hoses and belts too...




... and underware

So do I. :cheers:

[BBeach]

http://cgi.ebay.com/ebaymotors/T3-T4-hybrid-turbo-SVO-Turbocoupe-Turbo-Ford-5-BOLT_W0QQcmdZViewItemQQcategoryZ33742QQihZ005QQite mZ150044895472QQrdZ1

Is it just me or does that seem pretty cheap?

[neonrog]

Just to throw some more tech out, this might be for the Chrysler Turbo crowd (Pre-SRT4), but the tech is good for basic mods...

[Beej]

Just to throw some more tech out, this might be for the Chrysler Turbo crowd (Pre-SRT4), but the tech is good for basic mods... More information please? I'm not sure what you are talking about...

[Hellbent]

http://cgi.ebay.com/ebaymotors/T3-T4-hybrid-turbo-SVO-Turbocoupe-Turbo-Ford-5-BOLT_W0QQcmdZViewItemQQcategoryZ33742QQihZ005QQite mZ150044895472QQrdZ1

Is it just me or does that seem pretty cheap?

i think that thing looks like a pos. plus that seller's got a TON of negatives. more than likely it's cheap junk that'll seize up in a few thousand miles....but i've been told that i'm negative. :dunno:

[BBeach]

i think that thing looks like a pos. plus that seller's got a TON of negatives. more than likely it's cheap junk that'll seize up in a few thousand miles....but i've been told that i'm negative. :dunno: Yeah idk, i just typed in T3/T4 cause i heard dyno say it was a good choice and picked any random one. I dont think i would buy much from ebay because what my friend has bought so far for his car has turned out to be junk.

[87manche]

just a thought. was crusing that thar intarweb and found this.
http://www.jpmagazine.com/techarticles/engine/154_0508_jeep_4_0l_turbo/
which led to this
http://www.505performance.com/
which seems to have most anything you'd need. including a forged 4.7L stroker kit.