Good twin-turbos for 4.0L/stroker?

[ChicksDigWagons]

You're not going to find many turbos that are completely sealed. There is/was one company I know of manufacturing them, and that was primarily for small turbos.

Any turbo you're going to want to use at a reasonable price is going to need both an oil and coolant feed/return. I'd personally stay away from non-water cooled turbos as their life expectancy and functional condition ranges are worse.

You can easily get great spool out of a single turbo, its no more difficult than with twin turbos but you have to make sure you match the turbo to the engine, and consequently, run the appropriate amount of boost. Generally, two smaller turbos with an equal flow capacity as a larger turbo aren't going to spool significantly faster anyhow. Yes the rotating mass is lower, but your input energy will be half. No free lunch in thermodynamics. You'll see a larger benefit in spool time in going to a ceramic ball bearing turbo over a sleeve bearing. But again, thats lots more $$$.

If you went with an appropriately sized turbo (I'd take a wild guess at a light trim Garrett T4 without actually running the numbers), you could easily see full spool at 1000rpm or less, and with the redline you'd have with a 4.0 you shouldn't have a problem running out of steam on the top end at 5 or 6 psi of boost.

A two stage sequential turbo setup brings in an entirely new host of problems as well. Turbo crossover can be tricky. Peoples first thoughts are to just run the small one into the big one or vice versa. This has problems because you're always going to be limited by the flow of the smaller turbo. Also, you run risk of overspinning the small turbo. Running them completely in parallel is counterproductive because in the low end the small turbo has leverage over the big one, slowing its spool, at the same time, on the top end the big turbo is easily overruning the smaller turbo. You lose efficiency. Some cars have sucessfully, with computerized gizmos, gotten this setup to work. But many of them suffer problems with power loss at the crossover, reliability problems because of complexity. Anybody who tunes one of these cars typically swaps to a single turbo setup.

BTW, I run a custom turbo'd Subaru. Jeeps are only half my addiction.
-Brad

 

[Dr. Dyno]

The Duramax in my driveway has ONE turbo - not two. Because it's a variable geometry turbo, it acts like a much smaller turbo at idle and low revs and then opens up as the revs increase. It happens quickly, though, as it redlines at 3200 rpm. With over 500 ft/lbs torque just above idle, you don't need high revs!

I suspect I may have been wrong about the Ford Powerstroke using twin turbos as well. I do like the idea of variable geometry turbos and they have been used to very good effect in modern high performance turbodiesel engines such as Audi, BMW, Mercedes, VW. Some of these engines are producing an amazing 75+hp/liter and 120+lbft/liter from the factory, with potential for even more HP/TQ from chip/injector pump upgrades.

 

[Gary E]

Turbos do not have any parasitic losses, the exhaust is free energy. Lag is very small for a properly sized system, and if you have lag problems you aren't driving right. Lag is what all the stuporcharger guys hang onto to try to think of something a supercharger is better for
A GN turbo would be about perfect or a t3 off of turbocoupe/merkur would produce at lower rpms and would support 300ish rwhp.

There is no logical reason to do twins on an inline 6, you are just causeing space issues. Twins can be a good idea if you have two exhaust banks (V engines) On a V engine the twin versus single debate really just boils down to what side you want more complicated, the hot side or the cold side.

Oh btw what is so hard about T-ing off the Oil pressure sending unit and draining it into the pan, It will cost you like $10 in materials, and will be the easiest part of the install.

 

[krakhedd]

I guess, all things considered, a single should be ok, especially in a stroker application (torque = heat, and heat = energy for the turbo, resulting in faster spool-up - especially down low where the spool would be most noticeable).

I had a 20-minute response typed yesterday, and then the forum killed the message when I tried to post it - I forget everything I said in it!

My ultimate goal is around 400HP at the flywheel. I don't want a blower because you lose at least 10x more power through parasitic losses than with a turbo - and all this power makes it to the rear wheels with a turbo.

Does any company make a good VNT nowadays for a gasoline motor (much larger operating range than diesel)?

GN turbo would be a little small, no? 3.8L vs. 4.6L what I eventually want it for.

Price is somewhat of an object, but again, I'm looking for a bulletproof install. If I can save time and money down the road, expensive parts upfront are not an issue.

Thanks again - appreciate all the responses!

 

[Gary E]

VNT? I am guessing thats a varriable vane dealy. I think you are just looking at a $1500 turbo versus a $300 one. I do not think the returns would be worth it, unless you are a bench racer, performance increase would be minimal. I am not to familar with the GN turbos but a 60/63 turbocoupe t3 will support approximatly 325 rwhp, which is 390 crank hp. A GN turbo will do more than that from my understanding. Also a T3 can be upgraded to give you all the airflow you want.

You are looking at more than displacement here. Those smaller motors work at higher revs, you need to be focusing on airflow, thats all a turbo cares about. Personally on a 4.0 I would want about 4-5 psi of boost at 2000 rpm so I could pull any hill in overdrive with bigger tires.

Also I would either stroker or turbo not both. If you are doing a budget stroker detonation will kill you. I personally find the returns on a stroker high$/hp. If you have fab skills a turbo could be thrown on for less than $1000 and smoke any stroker out there.

One day I held up a t3 and figured it would fit under the manifolds, I looked another day I looked and decided I was smoking crack the first day. The other negitives are an allready sub par cooling system and no room for an intercooler. At the end of day I decided I would leave the go fast to my go fast car and the going slow to my going slow car. I am happy with that decision so far.

There are 3 or so manufacturers of turbo 4.0 kits all use t3 turbos and from what I could gather they were 60/48 types.

 

[5-90]

Turbos do not have any parasitic losses,

Partly correct. Turbos do not have parasitic drag, but there is a pumping loss associated with the restriction in the exhaust system. At low boost levels, it should also be borne in mind that the forced induction assist to scavenging is reduced significantly by the restriction in the exhaust getting past the turbo (you don't get work out of gas - or anything else - unless it stays for a bit.)

TANSTAAFL.

Part of the reason I like superchargers over turbochargers - apart from the ease of lubrication and increased oil longevity - is that the pumping losses are actually reduced due to the positive intake pressure and the lack of restriction in a well-designed exhaust system. While there is parasitic drag invovled with the belt drive, it's in the same league as a high-output alternator or a middlin' air conditioning system, and is therefore acceptable.

I'm not trying to dissuade you from using a turbocharger setup if you really want - just letting you know what I think and why. Take with appropriate grain of salt...

Always remember the Three Laws of Thermodynamics (Simplified Form):
You Can't Win
You Can't Break Even
You Can't Quit the Game

(You can't get more out of something than you put into it. You can't get out of a system what you put into it, and there's no way around the first two Laws.)

5-90

 

[krakhedd]

No way! Superchargers use at LEAST 30HP from the crank. Assuming 100% efficiency (ie: impossible), 30HP of loss from an alternator would be somewhere around (30HP x 742W/HP) = 22000 watts! I think I heard most alternators are around 50-60% efficient, so that's still upwards of 10k watts. Assuming 14,400W, that's around 1000 amperes. Stock XJs come with either a 130 or so amp alternator, or (with the towing package), a 190 or so.

Anyway, I'd just prefer a turbo anyway. I've just always been fascinated with the process of turbocharging, and all the thermodynamics associated with them.

The one other question I had in my response that got lost yesterday/2 days ago, related to using a hybrid turbo/super setup. I know they've been built before, but I can't see the benefit, unless you're racing. I see all sorts of potential pitfalls also. Anybody know the advantages/disadvantages of such a hybrid setup?

 

[Gil BullyKatz]

No way! Superchargers use at LEAST 30HP from the crank.

SPOBI!!!

You can't post a comment like that in a room full of gearheads and not back it up...

prove it...

There's different forced induction applications (screw type, centrifugal, turbine, etc) for varied purposes...

I'm a big fan of building according to it's use...

You cant build a formula grand prix engine and compare it to a top fuel dragster...

So again... I'd like to know how you arrived at this "at least 30hp from the crank" figure...?

 

[krakhedd]

Ok, I'm a poseur!

I've heard (yes, just heard) that blowers take a lot of power to make it (somewhere on the order of 40-50HP). Obviously, the power increase is far greater than what they use, otherwise they'd be useless.

But blowers cause parasitic loss, whereas the energy used to spool a turbo comes from the heat of the exhaust. I don't know the exact numbers, but around 2-3HP sounds like a reasonable loss for a turbo (due to backpressure), maybe even 5. The rest of the power they make comes from the heat.

I'm going to have to get off my ass and get some books to read about blowers and turbos, and all the advantages/disadvantages (so I'm not such a big poseur). Anybody have any recommendations?

 

[BrettM]

if a supercharger was pulling 30hp off the belt, wouldn't the normal belt slip?

 

[renegade_z71]

the turbo idea is can produce alot of power and to your comment on losing 30 hp i think i have read that on top fuel cars they drag only a 100 or 200 hp on the s/c and they have a much more massive supercharger than you can would run in a jeep. to awnser you question originally though no a turbo from a 3.8L motor isnt to small. just because a turbo is in a package for a 4.6 dosent make it the right turbo set up for another different configuration of 4.6. you are looking completely at what type of boost you need and what rpm band you need the turbo to work in. a diesel turbo is designed to spool faster than a car turbo... i have friends pulling 22+lbs on modified power stroke diesels and the top end of one of those motors are well below 5500 rpm... keep in mind though that when you buy a super charger for a 4.3 chevy from whipple they use the exact same compressor for the 5.0, 5.7. 7.4 and so forth. they may mount it different but the supercharger it self is the same. what you need to find is that type of flow charcteristics you want and when you want the turbo spooled up.. then look at your engines internal drag i.e. fly wheel weight in a standart or torque converter in a auto.... these things will increase you turbo lag. and also heat will be a big issue as you will most definately need to ceramic coat everything, put in vents possible fans to dissapate the heat as well as find a sutiable place to put the i/c to get a good colder charge. fuel mapping and posible fuel managment, after market ignition because withe a stroke and the increased compression of the turbo your engine will not take detonation as well as a naturally aspirated enigne and most stock ignition systems seem to loose power as the heat increases and as then also get older. the next thing in line other than drive train part like axles to think about is the transmition can it handle all that power you are wanting at the wheels? you will spend alot of time trying to build this mythical setup and see if it works. if it were me i would start with a 350 and a set of vortec heads find a good cam possible stroke it and run a tune port set up. you can get brackets from advanced adapters, a whiring harness from painless and build a stout turbo350 tranny or 700r4 and then you would have 400+ hp and it would be alot more relable... turbos are cool but a nice shinny tpi system still has a great wow factor and the cost to do that would probably be either more reasonable or about the same

 

[Gil BullyKatz]

Not all blowers are built the same either...

Kenne Bell's twin screw intercooled units for the 4.0 run at 90% efficiency and add 80 ft/lbs Torque at 1600 rpm....

I've owned a few turbocharged street rockets and I'll tell ya that's pretty damn good torque that low...

of course the fun part of my turbocharged toys was feeling the punch in the kidneys at about 3k rpm and holding on...

apples and oranges...

for crawling gettting over obstacles... turbo's probably not the way to go...

for making ricers nervous?

definately yes

 

[renegade_z71]

turbos also dont make horsepower from heat.... they spin at like 10k rpms and create heat.... heat kills power that is why a i/c is used to lower the discharge air. just wanted to clear that up ive seen it posted to many time and no corretions

 

[krakhedd]

Well, I meant, the heat in the exhaust is where they get their energy from.

I fully intend to use an i/c to bring the boost temp back to as close to ambient as possible, obviously within the packaging restrictions (space constraints).

What about the hybrid setup? Any biters? I've only seen 1 such setup on the Internet, and it was not at all an in-depth explanation of what they did, only something along the lines of, "You could go with a s/c and a turbo, like my friend did with his car. But he doesn't have a website or anything."

That would be the best of both worlds, assuming I could find a reliable, inexpensive, and easy way to clutch the s/c, once the turbo is spooled.

 

[renegade_z71]

space confinements, plus the compression ratio would probably be astromical with both. if you did run a clutch set up i think u can do something similar to that car from mad max it believe it had a clutch on the s/c. but why go to the expense of a turbo and a s/c? i think that is plain silly go one direction or the other.. btw you still dont get it... heat is the result not the power source. a turbo works on air pressure not heat. heat is a parasite. i think depending on the type of turbo you are to use you could gain more or the same hp from a s/c. simply by running all electric fans, a electric water pump and susch then using a ball bearing supercharger like a vortec or a ati type setup. those are basically a the same design as a turbo yet they use a pully inplace of air pressure.

 

[krakhedd]

Trust me, I understand what's at work. To spin the compressor, the impeller uses the heat from the car's exhaust. In the process of compressing the air, it is heated up as well. This is Boyle's law (PV=nRT, aka "Pivnert").

I know you get higher thermodynamic efficiencies with higher CRs, and you are limited by octane rating as to how high CR you can go (assuming your mechanicals are all strong enough). There must be some other inherent reason to go with a combo setup though........?????

I definately want something nobody else has - I suppose I should have mentioned that in the first place!

 

[renegade_z71]

if you are dead set on something interesting then do as follows.... paint it to match a taco cabana building, get a isuzu diesel out of a chevy luv stack a fewy toy transfer cases and put a hyundi logo on the hood. lol jk but are you building a off road machine a cool to look at vehicle or a show machine?

 

[krakhedd]

Looks on a Jeep to me are knicks and dings.....there is absolutely no point in a show Jeep (or a show anything, for that matter).....no, she'll eventually be all about offroading. But for now, she has to double as daily driver.

I just found some great info on the Internet about s/c's and turbos. Read the stuff here:
http://www.lextreme.com/Turbo.htm
and here:
http://www.superchargersonline.com/content.asp?ID=19

There's a link on the first page to the second.

Makes me wonder about a centrifugal-style blower + a turbo, except they don't make boost until higher RPMs (according to the article). I'm sure that with a clutch and smaller pulley (to drive it faster), I could mate this type of blower with a turbo quite easily.

But still, anybody for advantages of s/c + turbo setup?

PS - Renegade, if you've got Yahoo IM, send an IM to PaulyVD - I'll be online for a bit - no need to keep this discussion going in the forum (not that I mind, I just don't think everybody else wants to read it)

 

[Gary E]

No I am entirerly correct Turbos use waste energy (heat, exhaust energy)from the inefeciency of the IC engine. There are NO pumping losses pumping energy is when you do something to increase pressures like in an IC engine pumping work is done by changing the volume in a cyl. Turbos do not do that, the pressure is equal on both sides of the exhaust housing of the turbo, thus no pumping work. Additionaly exhaust backpressure is insignificant. I have taken college level Thermodynamics and IC engine classes as well, it was difficult for me to grasp at first that turbos don't cause a loss due to exhaust restriction. More energy does have to be put into a turbo motor for more hp, but that extra energy is just in the form of fuel, which is proportional to hp.

I think Krakhedds # of 30 hp used to spin the blower on a 4.0 is very realistic and maybe conservative. Blowers use the crank energy lower hp setups can get away with a little extra belt tension but when you start adding more hp you need cog belts and lots of extra belt tension that your balancer and crank aren't really designed for.

hybred turbo + SC setup is not at all practical in a 4.0 engine bay and is gee wizz stuff at best.

Turbos do not really create heat, very small amounts when the cold side compressor compresses air. Heat is generated by fuel burning in the engine, Heat is what makes the turbo spin, thats why its important to keep the Turbo as close to the engine as possible.

Partly correct. Turbos do not have parasitic drag, but there is a pumping loss associated with the restriction in the exhaust system. At low boost levels, it should also be borne in mind that the forced induction assist to scavenging is reduced significantly by the restriction in the exhaust getting past the turbo (you don't get work out of gas - or anything else - unless it stays for a bit.)

TANSTAAFL.

Part of the reason I like superchargers over turbochargers - apart from the ease of lubrication and increased oil longevity - is that the pumping losses are actually reduced due to the positive intake pressure and the lack of restriction in a well-designed exhaust system. While there is parasitic drag invovled with the belt drive, it's in the same league as a high-output alternator or a middlin' air conditioning system, and is therefore acceptable.

I'm not trying to dissuade you from using a turbocharger setup if you really want - just letting you know what I think and why. Take with appropriate grain of salt...

Always remember the Three Laws of Thermodynamics (Simplified Form):
You Can't Win
You Can't Break Even
You Can't Quit the Game

(You can't get more out of something than you put into it. You can't get out of a system what you put into it, and there's no way around the first two Laws.)

5-90

 

[olympicgold]

1 turbo should be enough......psshaw heat just put the turbo outside