3400 turbo.

Maybe I'm wrong but can't a waste gate controller get him a similar feel? I hesitate recommending supercharging unless with the newest Eaton super chargers as used on the CTS-V or ZR-1. These new units have CFD optimized air paths that have efficiencies on par or surpassing turbos. They heat the air less, require less power to run and have bypass valves that help with fuel economy.

Boost controllers are not designed that way, at least not most. There are some that will allow a bit of a slope to the onset of boost, but there has to be pressure to control. In order to open the wastegate, there has to be positive intake pressure, to provide pressure to the wastegate actuator (be it internal or external wastegate they all work the same way). To delay the onset of boost pressure, a huge turbine A/R, large turbine wheel, large compressor housing, or a combination all are required. This will make it hard to achieve solid boost pressures once the RPM is achieved. This could also cause the turbo to be run outside of it's efficiency, actually this is almost a definite, especially at such a low desired boost and power level.

To open a wastegate without boost pressure requires some technology that is never seen on street cars, and requires the use of stepper motors or actuators, to directly control the wastegate. I have not seen a consumer product like this so it would need to be custom made, not really worth it, when there are better options available. A variable nozzle turbo in theory could be made to work like this, but again, I haven't seen any aftermarket controllers for these, again, there are better options.

Why does the the supercharger need to be the latest technology? A simple centrifugal charger will work fine, and give that linear onset of power, when sized well.

For the amount of power he wants why not go NA? 327 HP is obtainable with all motor. Get a good pair of heads and port everything...

I kinda agree. I do like to use forced induction, simple because the engine can be built a little more "mild" to promote good driving manners, and then when power is needed, get into the boost.

[NateD4]

Maybe I'm wrong but can't a waste gate controller get him a similar feel? I hesitate recommending supercharging unless with the newest Eaton super chargers as used on the CTS-V or ZR-1. These new units have CFD optimized air paths that have efficiencies on par or surpassing turbos. They heat the air less, require less power to run and have bypass valves that help with fuel economy.

For the amount of power he wants why not go NA? 327 HP is obtainable with all motor. Get a good pair of heads and port everything...

The Borg Warner Diesel works great on my 2.8L Nissan I6. Maybe a tad on the large side, since the boost threshold is a little later in the RPM range than I would like, around 3200 RPM to get full boost (I've seen 20 PSIG, but keep it around 15 to 16, until I get some time to tune the 20 PSIG level.) Using it on a 3400, or maybe even a 3100 would pretty decent, due to the better flowing heads of the 3100 and 3400 and the slight displacement increase.

I've already recommended that the OP go with a supercharger based his his desire to have boost come in late, and that boost and therefore power increase would be more linearly tied to RPM, possibly keeping any traction that he already had in tact.

What should really be done is forgetting about adding any more power and concentrate on the suspension and chassis, since he is already complaining about traction issues, which is why he mistakenly believes that a late boost threshold and low boost will help with traction.

[NateD4]

Oh I was referring to the Duramax turbo packaging wise it is a chore. Rather than a traditional flange the header 2:1 style inlet GM cast onto these adds almost 2" in turbine section diameter. It physically won't fit in my car. I'm going to end up either cutting that inlet and making a new one or casting/gabbing a new housing to make it my way.

The size of the Duramax turbo vs your 6.5L makes sense. If I'm not mistaken the 'max turbo is about the same physical and flow size as a T68 or T70 sized turbo. Might flow a bit les but the duty and power range they are designed for is larger than a 6.5L original design.

In my case my target is a minimum of 350 HP max possible 700. I'll probably be 'very' happy with 450-500.

How does that 6.5L turbo work on a gas engine?

As far as the OP I think with a bit of know how he can get what he wants from it. No idea why he's concerned with late spool and sub 350 HP numbers.... Generally high HP and lag go together.

If I were him I'd focus on the resulting torque curve... Or build the thing with the cheapest t3/t4 hybrid I can find with a square t3 flange and see how it runs. Learn and refine with a better turbo. Then sell the old turbo on eBay.

I'm slightly fascinated by this post. I tend to 'think' most t3/t4 sized turbos put you in the 200 to 400 HP range. a/r helps dial the spool rpm and trim the peak power. My vote is put something on and go with it.

BTW there used to be a lot of Solstice-Sky/Cobalt SS turbos cheap on eBay.

I've seen dyno pulls to the 300-350 range from them. I originally looked at two of those to hit my 600 HP goal. But decided a single Duramax turbo was easier to plumb. To bad I didn't realize how large the housings are.....

If you don't recommend a turbo what should the OP put in?

As for earlier discussions... Diesel turbine housings are huge.... And packaging tough.

A generality that is not always true. The Borg Warner I use from a 6.5L Diesel, has a turbine housing that is physically about the same size as a T3 turbine housing, though the turbine wheel would be closer to a stage 4 T3 wheel if I remember the sizing of the T3 wheels correctly. It actually has a T3 inlet flange on it, which made it easy to use in my application.

It sounds like the OP is on the right track with a properly sized turbo.....

I WHOLEHEARTEDLY disagree. With the end desires the OP laid out from the start, a turbo is not the right choice here.

[TGP37]

Is that a hint of sarcasm I detect?

No, I was serious. We had a discussion in this forum regarding turbo, flow, egt's over time. Unless I got you mixed up with someone else. Your one of the handful I trust on this site regarding engines/boosting.

I did not see it as sarcasm. But I'm afraid to mention what I was considering for a turbo build. I have to find the right wording for the question, lol

Pressure Wave Supercharger? They don't spin as fast as a turbo/SC and provides boost off the start. Interesting little device it is, I try to find more information about it but it is an uncommon way to boost up. It seems some exhaust recirculation would be a minor issue (tune around it) and higher temps IAT's. But the boost response is much better then a standard turbo as far as Ferrari tested in the 80's.

[NateD4]

As for earlier discussions... Diesel turbine housings are huge.... And packaging tough.

It sounds like the OP is on the right track with a properly sized turbo.....

[NateD4]

Yeah I'm not sure how Holset turbos compare... But considering everyone seems to size turbos on A/R ratio and the VGTs have variable areas that approach full close (giving A/R probably down to .3 or less)... And about 400 CFM of air @3500 RPM for 6.6L displacement I'd say the turbine side should be just fine. For reference a 3.4L at 6500 RPM uses 389 CFM.





Compressor side...



This is from a 94mm 48 trim compressor wheel (stock is 88 mm for an LLY). The 77% island happens at @55lbsm/min and a 3:1 pressure ratio.

That gives similar single point performance as a Garret GT35R @55lbsm/min and a 3:1 pressure ratio except at the 72% island and near the top of the boost graph.

I've never known diesel exhaust temps to be any less than gas exhaust temps, especially when pushed.

It doesn't matter anyway, the original topic at hand will prove that the turbo is a bad idea, and not work like the OP expects it to, but you know, those of us that actually have turbocharged cars don't know better.

[TurboGTU]

Most diesel vgt turbos are tolerant to high exhaust temps.

[AleroB888]

Is that a hint of sarcasm I detect?

I did not see it as sarcasm. But I'm afraid to mention what I was considering for a turbo build. I have to find the right wording for the question, lol

[NateD4]

Is that a hint of sarcasm I detect?

[TGP37]

You didn't read my post, otherwise you would have seen that I said the diesel vg turbos aren't designed for the hotter exhaust gasses from a gasoline burning engine instead of the cooler exhaust from a diesel engine.

Diesel vg turbos were not made for that.

I also already stated that the Porsche does use a VG turbo for the 996 but at about $5k a pop, and you needing two of them, who is going to buy those just to claim they have vgt?

NateD4 is really wise about this stuff. His knowledge of forced induction is extensive. If he says the diesel turbo will work, it will.


Lots of gas boosted engines run diesel turbos. It is all about the size of the inducer/exducer of the compressor/turbine. Match that to the engine and it will work, diesel or gas. Heat energy is heat energy regardless of the fuel used. The turbo utilizes heat energy to boost the engine.


But it is your car, just saying. You could get some great advise here.

[NateD4]

That might be the case for Holset turbos... But take a look at what some of the Duramax guys are running for EGTs. I've found numbers as high as 1400 F from guys making 500-600 HP on stock turbos.

There's nothing wrong with VG turbos. Porsche uses two of them on a few of their cars. What matters is matching characteristics to your engine. There is a reason they are on both Porsche and diesel trucks. Unfortunately the Porsche ones are quite pricey on eBay.

You didn't read my post, otherwise you would have seen that I said the diesel vg turbos aren't designed for the hotter exhaust gasses from a gasoline burning engine instead of the cooler exhaust from a diesel engine.

Diesel vg turbos were not made for that.

I also already stated that the Porsche does use a VG turbo for the 996 but at about $5k a pop, and you needing two of them, who is going to buy those just to claim they have vgt?