Increased compression. Input wanted on those running more CR

[grimreaper]

Fresh build under way, using wiseco pistons. These pistons bump up compression to 9:1.
Who is or has ran a bit higher compression with the stock ecu/piggy back setup? Outcome? Likes/dislikes?

Car is a street car, no plans for 30psi or race gas. 15-17psi planned for pump and 20-25psi for 93+meth/water injection. Turbo currently is an SP61. I know i can make more power with boost over compression. Peak power is not my goal, the area under the curve is where i spend most of my drive time.


Any thoughts on this or why to or not to? maybe a 8.7:1 instead?

pros:
more power at same boost level as lower CR (assuming no detonation)
increased spool
increased off boost response

cons:
more heat
less room for error
closer to detonation threshold
less peak power

 

[boostcraver]

You need to look at your cons list again, specifically items one and two. From what I have gathered from others on here and my own experiences, heat + 7m= boom. These engines already have a small margin for error. Doing anything that narrows that margin any further is a bad idea IMO. What if you blow a radiator hose during a high speed run on the freeway? By the time you realize it, pull over an shut it down, you have overheated and possibly popped your newly built motor. I might just be conservative but I'd rather be safe than sorry. Mine was built with stock CR Ross forged pistons and pulls very hard with just a 60-1 modded ct and no other power adders in place right now. Just my two cents...

 

[shaeff]

jblmk3 used to run higher compression 7mgte's with good success. John B. Lunsford.

 

[grimreaper]

^ his and a few others posts is what gave me the impression its beneficial with a moderate boost street car. Him and marcum also ran stock ecu's from the information i could gather as well. I'v conservative with my tunes, I can pull timing where I need to if needed as well.

Still undecided. The difference in effective compression ratio at 15psi: static 9:1= effective 18.18:1 static 8.4:1 = effective 16.97:1

Dynamic at 15 psi : static 9:1 = dynamic 16.79:1 static 8.4:1= dynamic 15.68:1 (using stock cams at 38*ABDC)
any input?

 

[Nick M]

heat + 7m= boom. .

Complete nonsense. There isn't anything different about this engine than others, other than the 7M family is more robust than just about everything else from its era.

9:1 is hardly playing with fire.

 

[suprarich]

As nick said, 9:1 is not even close to something to worry about. There is nothing but benefits for a near stock motor with 100% correct tune and maint. to run some higher compression.

 

[grimreaper]

cool, 9:1 it is.

 

[radiod]

I calculated out what my compression ratio would be when I was doing my engine build because my buddy had given me a 1.2mm Cometic MLS gasket for Christmas and wanted to make sure that it would all still be fine with the block having had 0.008" taken off and the head being prepped for the MLS vs. composite gasket. I believe I worked out the ratio to be 9.1:1 (can't remember for sure), but it's been boosting 11psi (stock ecu/fuel/electronics, CT-26 57) and haven't had a problem yet. I know it hasn't been a super long time, but I've driven it a good 3,000 miles and done a couple oil changes (was super paranoid about the gasket not sealing and making sure there was no coolant leaking in to the oil at all...) and it's been great so far.

 

[87ttsupra]

im going to be running 9 to 1 compresion as well. with map ecu piggyback so when it gets running hopfuly in two weeks il let you know what happens.