10:1 compression FI build - Opinions wanted

**Hi-Po** · 03-24-2010, 05:56 PM

Alright, well I'm betting my stock shortblock is toast. I really need to get another engine going together, but hate the idea of spending money on a NA engine build with FI long term goals. On the other hand, I really want to get the TA running so I can at least go to the track this year and race. I'm currently looking at a LS2 402 with ~500 miles on it. This engine has some badass parts on it.

LS2 aluminum block.
Callies 4" stroke forged Crank and rods.
Diamond custom pistons
Katech billet main caps, fully pinned.
ARP main studs.
ARP 2000 rod bolts.
ARP L19 head studs
ETP 245 heads, with PSI ML1225 Valve springs. Valve springs alone cost over $900.
242/248 hydraulic cam (Slowhack specked cam for centrifugal setup)
Morel lifters
Smith Brothers pushrods.

Motor comes with valve covers and oil pan, so I may be able to reclaim a tad of money there. The engine is semi local to me, and seems to be a great deal. Anyone think this CR is too high for a turbo application? I really like the idea of a Procharger, but Modular Turbo is coming out with a sweet turbo kit.

My thoughts were that I could run this engine this season and make 450-475ish RWHP until I get the funds for FI. Guys/girls that have a FI car or knowledge, feel free to chime in on the matter. Would the 10:1 CR make you stay away if you weren't sure on what FI road you were going in the future? Thanks for your opinions

**Frost** · 03-25-2010, 06:55 AM

It's not too high, you will just have to keep the boost in check to keep it pump gas friendly. At 13-ish PSI it should make nearly 800rwhp. I don't think that's the best cam for a turbo, but it may be ok. That kind of setup is sort of mismatched though... At around 900-950rwhp it's gonna lift the heads. You may get a few more out of it before it happens. The lame part is, when you get a turbo spec'd for that many cubes, the turbo is going to be good for 1600-1800HP... much more than the engine. To keep from having backpressure issues, you will have to run a T6 turbo and probably at least 90mm worth. Good luck finding a 'kit' that will do that. A stock cube 346 can make over 700rwhp on pump gas with a T4 76mm turbo. Strokers and big cubes become a headache for turbo setups at the level you are looking at. There is no way I'd a build a 400-cube turbo engine unless it was a 6-bolt block that could do something with the power potential of such a setup.

FWIW, I'm tuning a 10.3:1 SCR 408 with ETP heads and an F1c blower on it today actually...

**Hi-Po** · 03-25-2010, 08:42 AM

Originally Posted by Frost

It's not too high, you will just have to keep the boost in check to keep it pump gas friendly. At 13-ish PSI it should make nearly 800rwhp. I don't think that's the best cam for a turbo, but it may be ok. That kind of setup is sort of mismatched though... At around 900-950rwhp it's gonna lift the heads. You may get a few more out of it before it happens. The lame part is, when you get a turbo spec'd for that many cubes, the turbo is going to be good for 1600-1800HP... much more than the engine. To keep from having backpressure issues, you will have to run a T6 turbo and probably at least 90mm worth. Good luck finding a 'kit' that will do that. A stock cube 346 can make over 700rwhp on pump gas with a T4 76mm turbo. Strokers and big cubes become a headache for turbo setups at the level you are looking at. There is no way I'd a build a 400-cube turbo engine unless it was a 6-bolt block that could do something with the power potential of such a setup.

FWIW, I'm tuning a 10.3:1 SCR 408 with ETP heads and an F1c blower on it today actually...

Ive been following that build closely, I'm pretty sure I know which one your referring to, and was wondering what CR he was at. He didnt say in his thread. I get what your saying, its easy to get in over your head power wise... only to have problems with 4 bolt heads. So are you saying you think the combo your tuning today is slightly 'mismatched'? I'm very anxious to see the results of your tuning today on that car.

Thanks for your input Steve.

**Frost** · 03-25-2010, 09:38 AM

No, the combo today (which is having cooling issues, so WOT may not get done) is matched well. I think if you max-ed out that F1c that it would probably make 1100rwhp on an M6 car where as a turbo sized appropriately for 400 cubes will make much more than a 4-bolt block/head arrangement can work with. A Precision T76GTS turbo (T4, too small of an exhaust housing for 400" setup) can make 900rwhp on a stock-inch LS1 and should have a shade of room left in the turbo. A T6 90-ish mm turbo that you would need for the 400 is enough turbo to go deep 8s.

If you HAVE to have a stroker and a turbo, I would keep it to 370-ish cubes. It will still want a T6 frame unit. Someone will jump in and tell you how their 370 is fine on a 76-78mm turbo, but look at their dyno graphs after 6K RPMs... Ask them what the pressure ratio is from feed to intake (high!). High back pressure will gets the heads lifted earlier as well. My mismatched reference was to using a turbo that can make almost twice what the motor can handle in order to have the needed exhaust flow.

**Hi-Po** · 03-25-2010, 10:05 AM

Originally Posted by Frost

No, the combo today (which is having cooling issues, so WOT may not get done) is matched well. I think if you max-ed out that F1c that it would probably make 1100rwhp on an M6 car where as a turbo sized appropriately for 400 cubes will make much more than a 4-bolt block/head arrangement can work with. A Precision T76GTS turbo (T4, too small of an exhaust housing for 400" setup) can make 900rwhp on a stock-inch LS1 and should have a shade of room left in the turbo. A T6 90-ish mm turbo that you would need for the 400 is enough turbo to go deep 8s.

If you HAVE to have a stroker and a turbo, I would keep it to 370-ish cubes. It will still want a T6 frame unit. Someone will jump in and tell you how their 370 is fine on a 76-78mm turbo, but look at their dyno graphs after 6K RPMs... Ask them what the pressure ratio is from feed to intake (high!). High back pressure will gets the heads lifted earlier as well. My mismatched reference was to using a turbo that can make almost twice what the motor can handle in order to have the needed exhaust flow.

Gotcha. This motor was spec'd out for a S/C build. I'm not trying to break any land speed records, as much as I would like to

Would this motor still be mismatched in your eyes if kept to a supercharger and not a turbo? The motor itself seems to be a great deal, with top notch parts. The whole thought in buying this motor is to put some kind of FI on it later, down the road. But run it NA this season. I'm not really liking the idea of being limited to one form of FI or the other really, and do understand your point on a stroker plus a properly sized turbo not working with most 4 bolt setups. I'm in need of a motor, soon... but cant for the life of me decide which avenue to go down with long term goals in mind.

**GORILLAVETTE** · 03-25-2010, 10:47 AM

Well...at a 10:1 compression ratio you will be limited on the amount of boost you want. If your goal is somewhere between 8 to 12 pounds you should be fine. You start moving into 15 to 20 pound range and your asking for problems quick!