Good twin-turbos for 4.0L/stroker?

Hey guys, I just wanted to get some of your opinions on something I've been thinking about.

There are a lot of twin-turbo kits for 4.6L V8 Fords. It occurred to me that a 4.6L stroker kit, of roughly the same displacement, should also have roughly the same operating range as the 4.6L V8 (in terms of RPMs).

Now, obviously, the headers wouldn't work at all, but those can be custom fabbed. But I could theoretically purchase/acquire a pair of turbos matched to the Ford motor, and they should work equally well on the I6, correct?

FYI - supercharging is on the table, but turbocharging is far more preferable!

Thanks!

I would say, if your going to turbo, just run one. therse not real reason to run 2 turbos, expecially on an inline engine. Granted, 2 smaller turbos would spool up faster. But its much simpler to just run one. After all, every big diesel truck runs 1 turbo, even the v-8's.

"All the kids want twin turbos untill they realize how many problems they have with one"

Granted that both motors have the same displacement, the heads flow differently and also the displacement per cylinder is different. Both of thoes will be a factor in where the turbos spool up at. You must look at what what the typical running RPM as well as redline for both motors. Also where do you plan on putting TWO turbos under the hood of an XJ? Just one will be a tight squeeze especially if you plan on running an IC.

One day I too will be boosted. If you go through with this, take good notes and please share :sunshine:

AARON

Well, it's certainly going to be expensive. I'll need an external computer which plugs in through OBD2 (I have an '01), and that, coupled with a laptop and dyno, should lead to no problems. (and larger injectors, ported/polished heads and intake, turbo-friendly cam)

As for space, well....I don't know exactly how big the turbos will be! I've seen some pretty compact installations with twins before, but only in pics, never in person, so I have only an estimate/rough idea of how large they'd be. I know it will be tight, be I think it should be doable.

As for an IC, I could mount one in front of the AC condenser and the radiator with some more cutom fab. Maybe even no A/C since she will be for offroad use only once she's totally built. The radiator would be replaced with a GDI 3-core, which I've heard lots of good stuff about, and the water pump would be replaced with a MOPAR high-flow unit. Along with hood vents a la '98 ZJ 5.9 Limited, that should prove to be a good combination for heat dissipation underhood. Maybe twin electric fan conversion too.

I still have only a rough sketch in my head of what I want to do, and until I have another vehicle for a daily driver, I won't be able to really get down and dirty, and see what there's room for. I also am approaching this from a theoretical perspective ("by the numbers"), and want to make sure I don't miss anything.

Buffalo eh? Whereabouts?

hillbilly_jeeper said:

After all, every big diesel truck runs 1 turbo, even the v-8's.

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The trick to getting good full-range performance from one big turbo is to use variable geometry. My Duramax and the Ford Powerstroke both use VG turbos and both will flat smoke a Dodge Cummins off the line while it's big fixed turbo gets itself spooled up.
Seems awfully ambitious and terribly expensive. What do you plan to do with it if/when you get it all done?

thinking that an I-6 is going to have the same RPM band as a 4.6 V8 is not correct.
While the V8 has good low end torque, it was also designed to rev fairly well. The I-6 is all about torque and trying to lift the RPM band much higher usually ends up with a host of problems and/or failures with very few positive results.

Going with two small turbos and splitting the header is possible, since smaller turbos will spin up faster and therefore kick in at lower RPM - but I'd prefer to use a supercharger with the XJ/Offroad applications than a turbo.

Going with two small turbos and splitting the header is possible, since smaller turbos will spin up faster and therefore kick in at lower RPM - but I'd prefer to use a supercharger with the XJ/Offroad applications than a turbo.

The main issue I have with turbos is their maltreatment of oil - especially when you shut the engine down. When you kill the engine, the turbo is still spinning, and the oil isn't moving. If you don't idle for a couple minutes before you kill the engine, you're going to have the turbo going full speed - and that's typically upwards of 100Krpm! That will generate enough heat to make coke particles in your oil, and that will wreck bearings in a hurry!

The nice thing about a supercharger is that it is crank-driven via a belt; when the crank stops, the blower stops. Also, blowers spin a lot slower (~10,000-16,000rpm for Roots/Eaton/Whipple) and can usually run on engine oil under pressure or from their own internal oil supply.

Also, the supercharger will kick in a little quicker for boost power, and you don't have to wait for it to "spool up" like a turbo, since it's driven directly.

Any other questions?

(Seems to me my book should be selling a little better by now... Look at all the questions we get!)

5-90

If you were to use two small mitsu turbos that were used on the Chrysler 89+ 2.5 Turbo engines (Mopar FWD Turbo engine info, keep boost level down and use 3 cylinders to run them you would get very quick respons and they should be reasonable to purchase. NO one wants them because they are restrictive in the 2.2/2.5 applications above 4500 rpms. The stock garrett on the TI/TII would also be a viable option.

Also the VNT 25 turbo used on the 90/91 VNT 2.2 would be great as it really improves low-end torque but are hard to mess with and EXPENSIVE to replace. Somewhere I read that VW uses a VNT on the TDi engines.......

VNT General info

More VNT info from the aussie world
Aussie VNT info

If you are serious about turbos then do some browsing and reading over here atTurboDodge.com before you dive into this. Read what is involved and the consequences of turbos gone bad. Most of these guys use stock parts (turbos) and made dependable, drivable power.

And intercool it if you are using stock compression.....

aperwork

krakhedd said:

There are a lot of twin-turbo kits for 4.6L V8 Fords. It occurred to me that a 4.6L stroker kit, of roughly the same displacement, should also have roughly the same operating range as the 4.6L V8 (in terms of RPMs).

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A 260hp 4.6L stroker will certainly have a similar operating rpm range as a 260hp '99+ Ford modular 4.6 V8 but there are two differences:

1. The I6 configuration with its longer stroke and larger displacement per cylinder has more grunt at lower rpm than a V8 of identical displacement. It also produces better gas mileage and has seven larger main bearings instead of five smaller ones for reduced NVH and longer engine life.

2. The V8 configuration with its larger valve area and shorter stroke does better than the I6 at higher rpm.

Does this matter? The answer is yes.
Since the V8 produces less torque at lower rpm, it needs a smaller turbo that spools up faster so a twin turbo set up here makes a lot of sense.
The I6 already produces abundant torque at low revs so it can get away with a single larger turbo to produce a bigger torque boost at higher rpm where it's relatively lacking.
Now you know why the Dodge Cummins 5.9 I6 has a large single turbo whereas the Chevy Duramax 6.6 V8 and new Ford 6.0L Powerstroke V8 have two smaller ones.

All the simi trucks i get parts for all day have one big turbo. And still make 20-50psi of boost below 2,000 RPM. So, one big turbo can make low RPM boost, not that you want 40psi of boost, though.

Dr. Dyno said:

Now you know why the Dodge Cummins 5.9 I6 has a large single turbo whereas the Chevy Duramax 6.6 V8 and new Ford 6.0L Powerstroke V8 have two smaller ones.

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Uhh I don't recall Ford or GM selling any twin turbo diesels

what about twin with one big and one small? I thought that was a common config

Yeah - something like that was done with modded Celicas so you'd have less turbo lag and a wider powerband.

Bear in mind that the Celica is also designed to rev a lot higher - and being a street car, lived at higher rpms than we do.

I'd still like to know what your idea is for doing the turbo setup - not that it's not a valid idea, just that I'm highly inclined to think that there's an easier way to get where you're going than using a turbocharger or twin turbocharger setup - plus, with a supercarger you're going to be doing a lot less plumbing and it will be easier to set up. Toss in the increased underhood temperatures you typically get with turbos (due to heat retention upstream of the turbo in the exhaust system) and the already high operating temperature of the 242, and I just can't help but try to think of another idea...

What's your plan?

5-90

hillbilly_jeeper said:

After all, every big diesel truck runs 1 turbo, even the v-8's.

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Just to clarifiy....They don't all run one turbo. In the small world of hotrod semis they have been upgrading to twin turbo systems forever. Also the new 625 HP Cat is running twin turbos. And they flat scream!

Dr. Dyno said:

Now you know why the Dodge Cummins 5.9 I6 has a large single turbo whereas the Chevy Duramax 6.6 V8 and new Ford 6.0L Powerstroke V8 have two smaller ones.

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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!

DrMoab said:

Just to clarifiy....They don't all run one turbo. In the small world of hotrod semis they have been upgrading to twin turbo systems forever. Also the new 625 HP Cat is running twin turbos. And they flat scream!

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Granted, i'll give you that. Just like every really fast dodge cummuns runs 2 turbos. But is that for the same reason, being able to get good boost low and high, or because you reach a point where one turbo just dosent make enough boost period? How aboout a v-12 detroit? i think its either 2 superchargers and 4 turbos, or 4 superchagers and 2 turbos. Cant remeber what my dad said for sure.
But personaly, for ease of instilation, i would still do one single turbo on my jeep.

Wow - lots of responses!

Well, again, I would go with a blower, but I don't want the parasitic power loss. It takes power to make power, whereas a turbo uses waste energy (exhaust heat) to make it.

Why 2 small turbos? Because I want as little lag as possible. I'm not particularly worried about higher RPMs - I only plan to build the stroker to run up to 5500 or so.

Newer ball-bearing turbos are completely sealed, and have their own oil supply. Maintenance free.

I've thought of using older Mopar/Shelpby turbos (my first car was a '92 Sundance with the 2.2 - wow I miss that bugger), but again, they need to be plumbed for oil, and have a slower spool-up, and are not maintenance free (as far as coke particles in the oil). Also, VNTs from that series (the Turbo III option) are notorious for the nozzles getting clogged quickly. Granted, this will eventually be exclusively an off-roader (as opposed to its current daily driver status), but I don't want to tear the motor down every oil change to make sure everything's still in order.

My main question, about similar displacement and similar operating ranges, is correct though, is it not? I mean, 4.6L I6 vs. 4.6L V8 still uses the same volume of air, right? I realize there are differences in the flow of the heads and the intake and all, but those things excluded, I should be able to use the same turbos, right?

Thanks again guys - I'm notorious for overlooking obvious things, so I just want to make sure that all the assumptions I've made are correct. Please continue to point out anything you see wrong, or think I'm wrong about!

Oh yeah Storydude - I think you're on JU, aren't you? - I'm in Amherst.

"Parasitic Power Loss" is still a bit of an issue with a turbocharger, since there's a significant increase in exhaust backpressure due to the turbine restriction.

Like I said before, "What's your plan?" This is an excellent example of a case where it requires dispensing information to get information. The more you tell us, the more we can tell you!

Hell, if you're that worried about parasitic drag, why not just go with nitrous and eliminate the issue?

5-90