i am curious as to how much boost a 6.9 can take? i may be able to get a truck with a 6.9, and do a tri-turbo compound setup for about $2,700. two garrett 25mm turbos, one on each bank, into a single 4 inch garrett spooled by both banks. i have been told the 4 incher is capable of nearly 30 PSI by its self. would it be able to handle that kinda pressure without throwin new gaskets and ARP studs at it?

 

maybe 15-18 psi

 

how much pressure do you think i could make with that setup anyway?

 

Without studs 30psi would pop the top right off. You would have to swap those out.

 

so how much will it handle before i get into a danger zone?

 

12 psi is the generally accepted limit in factory form, 15 if it was a 7.3 cause of the larger head bolts.

 

so if i ran, say 20 psi, id be pushin the hell outta things?

 

Yup! Tho it's possible, IIRC Dave S here (our mod) can bring his up to 25 psi, but it definitely ain't no stock engine.

 

Hi Trey

Studs cost about $250 and thats actually cheap compared to studs for a stroker or cummins. You need to use them for anything sustained over 10 PSI (or 15 PSI for a 7.3 IDI), and they are rated at well over twice the tensile strength of the original.

So far, only one diesel like this that used a compound turbo setup and he used a dual setup. First turbo was a banks turbo kit made off the shelf for the engine and the second turbo was mounted under the front of the cab that orignally came out of a powerstoke. That engine made up to 25 PSI before a wrist pin started knocking. To this day we are still not sure what really went wrong with that engine since the builder decided to start focusing more on his family and threw in the towel with his diesel building. Truck is now a non turbo

The best dyno run to date that has been documented was a 7.3 IDI that ran a hot pump AND hot injectors with a run of the mill aftermarket turbo kit again, made for the engine. He topped out at about 205Hp at the wheels. Depending on how you figure for losses between the crankshaft and the dyno, thats between 250-290 Hp which was pretty darn good. What was really impressive is the engine Hp peaked at a mere 2300 RPM instead of 3000 where the pump starts cutting fuel back.

My guess is the fact that ALL the aftermarket turbos loose efficiency above 10 PSI combined with the fact that he did not have an intercooler contributed to his Hp ceiling.

My take on all this is you don't need compound turbochargers to get into the 300Hp range. However you will need some mods to whatever turbo kit you are building on if you start with an off the shelf setup. Unfortunately figuring out what turbine and compressor combo that would work is a problem since hardly anyone that owns an IDI can afford to experiment with expensive turbochargers. I tried swapping the compressor to a slightly larger one but the difference in performance was not very big.

One final thing to mention is these are high compression engines compared to powerstrokes or other direct injected diesel engines. You simply can't stuff the same kind of turbo boost in a 22.5:1 engine as you do in a 18:1 CR engine.

Best guess is you should be safe to hit 20 PSI with studs and no other mods (like dropped compression ratio, for example), but to my knowledge, there are only 2 engines that ever reached that kind of boost level. And as for the truck that pumped out 205 Hp? that one peaked out at 15 PSI while on the rollers - go figure. I don't remember if the compound turbo truck was ever dynoed. The other 20 PSI+ truck is owned by our very own Dave Sponaugle (moderator) but he doesn't live near any dyno shop and despite our pestering has yet to put his truck on the rollers.

Basically, you are entering uncharted territory but deep down we would all like to go there too.....

 

thanks for the input LCAM and dave. think i could get what i want effectively out of twin garrett T25s, or would it be better to run the single garrett T04R?

 

The other thing you need to remember is if you get a turbocharger too big, the engine won't be able to spool it, or will only kick in right near governed speed. We discussed this on OBN a little while back and of the choices out there, the guys figured it was between the Garrett T61 or the T04E with 60 trim. Both boost well within the efficiency range up past 20 PSI with the T4E being more efficient since its a later generation of turbo. For turbine side, they said something with a 0.8:1 AR ratio for a good compromise between max flow and reasonable low end spooling. My wussy ATS non wastegated turbo for example has 1.0:1 AR ratio which is great for keeping EGTs down but it always seems to be spooling about 3 PSI less than what the engine is begging for.

 

yeah, i know how the dynamics of it work. i might need to do some barterin to get the combo i need. lol.

 

ok. so i can get three garrett GT2554R turbos for $200. two are good and workin, and one is seized. i already know im gonna buy em. im thinkin bout just usin one on each bank right now. think thisd be feasable, and generate adequate, but not excessive boost?

 

Man if I had a nickel for every time I heard some one say they were going to set up a true twin turbo pack on an IDI, I probably could have done it myself. Don't get me wrong, I would love to see it done but everyone that has tried just gave up and moved on to something else. The problem is the engine is really shoe horned into the truck and making everything fit is a huge undertaking. I hate to be the one poopooing the idea but its no small feat.

If you pull it off you will command some serious respect from all of us though. Please don't let me stop you because we could all learn something.

I don't know if this would help you at all but this is a handy turbo calculator that can give you a VERY basic idea for how the engine can handle different compressors:

Squirrel Performance

I assumed 3.4L and 150Hp per turbo since you will be running 2 of them - not sure if thats the right way to go about it. The plot shows it near the surge line across the map.

 

heres what im thinkin:

-build manifolds that go strait up to mount the turbos on each side.
-get a cowl hood.
-find an intercooler that the hood can close around.
-run the pipin from the turbos around to the "back" of the intercooler.
-the front of the intercooler will run strait to the intake.
-use two small fans to either push or pull air though the intercooler. (a second cowl can be made of fiberglass to go under the intercooler so that cool air comes in underneath and hot air goes out the top.)
-use recirculatin blow-off valves to prevent surge, and the turbos are already wastegated.
-before installing the turbos, replace head bolts with ARP studs and better gaskets to handle 20 to 25 lbs of boot.

considerin that the combined cost of the truck, turbos, gaskets, studs, and intercooler is still under $3200, i think that can be classified as a budget build. you?