My Vtec Gives Hugs mmmbah
Join Date: 2007-12-13
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Posts: 4,537
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I went from a 9.3:1 to a 8.5:1. I like the boost friendliness of the lower compression. And boost seems to come on a bit harder and faster, even with the bottom suffering just a tad. The higher compression is great with a large turbo and cams though. But you can't really go wrong with either one. I can safely push about 4psi more boost on the 8.5:1 motor on pump gas, which is more power than the higher compression would do. On low boost the high compression worked great, but I didn't notice much loss in response or power when dropping compression. But I did notice the bottom end was lacking a little bit more, but the dyno still showed about 200rpm quicker spoolup on the lower compression. Perhaps the extra timing I was able to toss into the bottom end helped with the spool while keeping things safer.
Right now I only run about 14psi at the most on my setup now on pump gas 91. Any more than that and I tend to get a bit of light detonation. By light, I mean extremely light. And this is just from reading plugs.
I could push 14psi on the higher compression, but I had to back the timing off 2* and that lost a lot of power.
The higher compression looks like a good route to go for future builds though. I don't really like pushing the boost too much. I'd like to make around 500whp on 20psi one day with just my JWT tune. Perhaps she can do it, but at least I know that 20psi isn't really pushing the setup too hard.