Pistons and Compression

[azgtx]

As far as I know..... I have a set of 7.8's in .50 over

[rbrown]

As far as I know..... I have a set of 7.8's in .50 over

You are running the stock CR pistons?

[azgtx]

Nope I have 2 GTX's both running the 9:1's from automatic tranny Capri's and using VJ14/11 hybrids. I will go back the the 7.8's and use a bigger turbo.

[bhearts]

Nope I have 2 GTX's both running the 9:1's from automatic tranny Capri's and using VJ14/11 hybrids. I will go back the the 7.8's and use a bigger turbo.

That's pretty low though. Couldn't you adjust for that compression with some methanol

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[azgtx]

Yes but no need to for my use. Stock cr is 7.8 and they run just fine.

[FestYboy]

And what's wrong with a "high" compression turbo engine? SCC built a 11:1 turbo civic @ 8 psi on Cali high test (91 oct)...

[bhearts]

And what's wrong with a "high" compression turbo engine? SCC built a 11:1 turbo civic @ 8 psi on Cali high test (91 oct)...

Fueling. Pretty much. You could run tons of compression but without a good fuel no timing advance, so no power. Here's the big issue though. Think about how hot your air is coming from your turbo at 15psi. Maybe 200f warmer than ambient air. That's a 2:1 compression ratio. Now imagine 11:1 compression and how much it's going to heat the air up. Hot pockets for everyone.

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[FestYboy]

Most turbos run low advance anyway... Also the temp increase is related to the turbo efficiency at the given a/r more than the boost level itself. Also, what's the combustion temp of fuel vapor? Now keep in mind that for every psi of pressure, the vaporization temp of most liquids increases...
It's not as bad as you think then add an after cooler and meth or water injection...

[FestYboy]

My point is, if you want better driveability off boost, you need compression, and you can get it and have your boost too. More compression allows the same power to be made at a lower boost pressure (lower intake temps too).

[bhearts]

My point is, if you want better driveability off boost, you need compression, and you can get it and have your boost too. More compression allows the same power to be made at a lower boost pressure (lower intake temps too).

Im not arguing. E85 main fuel with water meth injection on top of that sounds lots of fun

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[bhearts]

I guess if cylinder pressure equals cylinder pressure at different cr and psi, the same power should be getting put down.

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[bhearts]

An article I read about Chevy 350 engines noted ~4~ percent hp increase with every point increase in compression.

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[bhearts]

So it really doesn't equate a huge deal going from b6ze miata compression up to 11:1, that may only be worth 10hp peak, but maybe only 3-4 at off boost cruising rpms.

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[FestYboy]

Just supporting my initial statement. Just did some research on an engineering forum: according to one of the members (supported by maths), adjusting a high c/r engines timing to achieve similar cylinder pressure while under boost, there is a significant increase in torque, I'll provide the link: https://www.physicsforums.com/thread...ngines.646362/

[bhearts]

With that being said, I'm shaving my head 50 thou plus. Plus it'd be the cheapest valve deshrowd known to man. Are there mil limits on b6 heads?

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