RB28 High Comp ratio question

[RB335]

Hi Guys.  

This question is for any people who've built a 2.6 or 2.8 with a high compression ratio or tuned it.

My CR is currently 9.6:1 on a Nitto 2.8.  I want to go higher while still being able to have it be a pump gas
motor for street purpose.  I have flex fuel and a Haltech Elite.

The highest my tuner has done is 9.5:1 with no problems on both.

I've heard of a few running 10:1 but no idea if they are E85 dedicated or not.

Any higher I've been told is a try it and see how it goes sort of thing.

I've been told having the CR too high can upset the engine in the way that it can't be tuned
as aggressively on higher boost and as a result may be more tame than a lower CR engine which
can be tuned "all out" in the higher boost levels.  

I've heard of many big power 2J's running high comp but not many RB's

It's a 800-1000hp car.

Any advice appreciated if anybody here has built one or tuned one.

Cheers.

[joshuaho96]

10:1 is GDI territory. Unless you run massive duration cams to lower dynamic CR I would be skeptical that you can get great power.

Just my opinion though. 9.5:1 is already very high for port injected turbo engines and I would expect to be running E85 full time with that kind of CR.

[sneakey pete]

9.5 with 98 is possible, as the OP said he's done it, i've also done it. 260*11 cams probably helps. but also its not making anywhere near the maximum possible power for the setup on 98 either.

Honestly, i'd question how often you'd actually need the ability to run 98 on it, and if its worth actually worrying about?

just turn the boost waaay down for 98, and go for gold with 10:1 would be my strategy, though its still an interesting question to hear answers on.

[GTSBoy]

I think that 10:1 on 98 should be perfectly doable. It's the same as any other (more) modern engine. It comes down to getting the fuel-air mixing right and having top notch management. You should be able to make the same power either way (lower CR, more boost, or vice-versa). Even if you can't quite make the same peak, the high CR engine is going to do everything else better (off boost, spooling) and will be a good thing.

Then there's WMI. The answer to most problems.

[burn4005]

this is the perfect use case for a V-cam system. you can purposely run shitty cam timing to keep VE low on lower octane fuels.

[SiR_RB]

Mines been built at the moment at 10.1 compression

 

have seen afew others also at this compressions but only on dedicated e85