I am trying to better understand how to go about tuning for higher compression. I know that changing the compression will alter the entire VE of the motor so i assume everything (timing, fuel, MIVEC) will need to be re-optimized for a change in compression. But where do you start, more then that, how would things be adjusted (advance, retard, add fuel, subtract it)? Obviously the physical change in compression is also a factor going from stock (8.8) to 9, 9.5 or 10:1.

While i am not changing pistons anytime soon I am just looking to expand my personal knowledge on the subject as well as spark some good discussion for others questioning the same thing.


-Mike

 

Bump for good question. I had seen similar evo with bigger piston size (I think 87mm) and metal gasket running on stock un-tuned rom. His peak came early about 500rpm. Is this a good setup?

 

Lucas @ English racing may chime in on this when all the daywalkers wake up.....haha. I know he's running 10:1 right now. Kind of in the experimental stage i guess.

 

I would start by making sure your AFR is where you want it. Then dial back timing as necessary. Realize that your upper boost threshold will be lower. So say you run 25psi right now, I would:
A. Turn it down to 22psi
B. Tune AFR to where you want it (for 9.5:1 and higher I'd stay in the 11.5 range)
C. Get timing where you want it.

Technically, you really could closely calculate the before and after peak cylinder pressures and try to match them. That's what you're really doing by playing around w/ AFR/Timing/Boost. It really should be no different from starting any other tune. Just realize you can't run the boost you used to (and won't need to).

On the Mivec, I don't have a good feel, but I'd guess you won't need to adjust that too much. Perhaps pull back the aggressive areas just a tad. I'd start w/ the JDM and go from there.

 

MIVEC will stay about the same, boost drops about 4 pounds as pointed out and timing seems to drop about 5-6* on pump gas.

We have a customer car with 10:1 that is E85 only and the few times he has had to limp home on gas, anything more than 16psi with "standard" timing seemed to want to knock.

Basically its like you already figured out though, you need to just back everything off and start over somewhat. As far as AFR's I dont think they are gonna change a whole heck of alot looking at Lucas' 8.8 map and his 10:1 map.

 

Thanks guys for the info.

 

looking for more spool/torque?

 

I am. I mean upping the compression always helps with efficiency as well. I would like to eventually go with a 9:1 or 9.25-9.5:1 setup even though i love almost tacking out my boost gauge