Thoughts on this built engine for my Turbo FRS

[Conman]

https://www.rallysportdirect.com/par...ru-short-block

Looking to build my engine. The shop I would take it to is recommending this engine. Any thoughts?

[86TOYO2k17]

Originally Posted by Conman

https://www.rallysportdirect.com/par...ru-short-block

Looking to build my engine. The shop I would take it to is recommending this engine. Any thoughts?

how much power are you trying to make?
What turbo are you going to be running and at how much boost?

[Conman]

Originally Posted by 86TOYO2k17

how much power are you trying to make?
What turbo are you going to be running and at how much boost?

400ish... Gt2860rs...I dunno; what ever is safe for E85 and occasionally 91.

[Grady]

You can make 400whp on E85 without dropping the compression ratio.

[Conman]

That’s jus what they recommend... Why would or wouldn’t you use a different compression ratio? The IAG described it as being safer for boost... I don’t care what hp number I make. I just want my engine to not blow up.

[Joveen]

IAG is a great company. Do it!!

Sent from my SM-N960U using Tapatalk

[Irace86.2.0]

Originally Posted by Conman

That’s jus what they recommend... Why would or wouldn’t you use a different compression ratio? The IAG described it as being safer for boost... I don’t care what hp number I make. I just want my engine to not blow up.

Dropping compression will allow for more power and especially more power on pump gas, but you may find there is less fuel economy and less power down low or off boost with slightly more turbo lag. It is definitely not necessary for modest goals and isn’t too necessary if you have easy access to E85. Unlike a supercharger, the turbo can have its boost modulated better with an electronic boost controller to adjust for 91 or for doing boost by gear or progressive boosting. If you want to go further than 400whp then definitely drop compression.

[Grady]

Originally Posted by Irace86.2.0

less power down low or off boost with slightly more turbo lag

Exactly why I would not drop compression at 400hp. With good rods, pistons, tune and E85 you will be safe at 400.

[86TOYO2k17]

Originally Posted by Conman

400ish... Gt2860rs...I dunno; what ever is safe for E85 and occasionally 91.

I’m not a turbo expert. But isn’t that turbo on the smaller side? Not sure if it can flow enough air to hit 400whp with 10:1 compression. If it can I bet it’ll be maxed out.

350whp on 91 and 425whp on E85 should be perfectly fine and safe on stock compression with forged rods/pistons. It’s largely on the tune and boost controller for safety once you have forged internals.

The trade off is lower compression requires more boost to make the same power So you’ll have more turbo lag/spool up and less low end torque/throttle response, worse MPG, and less off boost power. but assuming your turbo can pump enough air you’ll have more top end potential. But with sub 425whp goals your probably better off with stock compression. Or do 12:1 or 11.5:1 for a happy medium.

[Irace86.2.0]

Pump gas is really the deciding factor, besides power potential and reliability. I would rather be able to make big power on pump gas than be concerned about low end power.

Are there many people making more than 300whp on 91? 350whp on 91 seems sketchy, even on a built motor. A built motor can help avoid failure from higher power, but not from preignition/detonation.

[86TOYO2k17]

Originally Posted by Irace86.2.0

Pump gas is really the deciding factor, besides power potential and reliability. I would rather be able to make big power on pump gas than be concerned about low end power.

Are there many people making more than 300whp on 91? 350whp on 91 seems sketchy, even on a built motor. A built motor can help avoid failure from higher power, but not from preignition/detonation.

You may be right. 350whp on 91 may be pushing it. I’ve seen 350whp on 93 though. So maybe 315whp on 91. (Disclaimer dyno #s vary a lot dyno to dyno)
But not really anyone with a built block that kept stock compression and runs 91 that’s posted a dyno that I’ve found. Usually either lowered compression, or uses E85.

Personally if I had E85 and only wanted sub 450whp i would keep stock compression, or only slightly drop it. And just keep the boost low if I ever had to resort to pump.

[Scjacob827]

Well that took a turn

[Irace86.2.0]

Originally Posted by 86TOYO2k17

You may be right. 350whp on 91 may be pushing it. I’ve seen 350whp on 93 though. So maybe 315whp on 91. (Disclaimer dyno #s vary a lot dyno to dyno)
But not really anyone with a built block that kept stock compression and runs 91 that’s posted a dyno that I’ve found. Usually either lowered compression, or uses E85.

Personally if I had E85 and only wanted sub 450whp i would keep stock compression, or only slightly drop it. And just keep the boost low if I ever had to resort to pump.

The other option is lower compression and have more power on pump and e85, but deal with a slight drop in low end, but I’ve seen dynos with lower compression, and there doesn’t seem to be a huge difference. This is also why high compression and FI is just not done. It is better to raise the effective compression ratio than to start with a high static compression ratio.

I would run 10.5:1

[Irace86.2.0]

Also, this post of this thread had this link, which showed the dyno below for a slightly modded WRX throwing down decent numbers on 93 octane.



That post led to this response, which I'll quote anyways:

For what it’s worth and more from a holistic perspective... the final tuning work was recently completed on my engine. Since I was going to use 91/94 octane (no e85 in my location) The builder/tuner had decided to proceed with 10:1 to maximize long term reliability and detonation protection. I was initially concerned about how this could affect off boost performance, however Final tuning dissipated all my doubts, the car performs amazingly, with power delivery being just as gradual as before, with essentially no lag at all. The car is simply mind boggingly fun to drive, and they we able to bring TQ about 400rpms earlier than before in the low end, as well as achieving a higher tq plateau (up to +60lbft @crank) across the entire mid/top end as well, resulting in lots of extra “area under the curve”. The garrett gt2871 was able to maintain steam to 7500rpm. Note that I was not seeking maximum top end power, but just more usable tq across the entire range for daily driving with the odd hpde. My low boost 91 map now has higher tq across the entire rpm range than my previous stock engine high boost 94 map, with the rest of the setup and unchanged. So for those not going towards higher octane fuel, my feedback on those considering lowering to 10:1 cr would be that very satisfactory results (for my goals) was achieved.