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Discussion Starter #1
high compression such as 12-13:1 and high boost 30 psi.

do we see this combination?


will high compression and high boost make more power?
 

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The tuning window will be VERY NARROW! Don't slip up
 

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You would also need a very large turbo to run 30lbs at 12.5 to1 comp.

I have a GT500 with compound boost(stock blower and twin billet 64's) and run 8.5 to1 and 40lbs and am building a new motor with 9.5 to 1 and hope to pick 100-150rwhp at the same boost level.
 

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My friends old Big Cheif 540 had 11-1 with up to 43psi of boost on Alcohol..But is had a 14-71 kobelco on it..
 

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You would also need a very large turbo to run 30lbs at 12.5 to1 comp.

I have a GT500 with compound boost(stock blower and twin billet 64's) and run 8.5 to1 and 40lbs and am building a new motor with 9.5 to 1 and hope to pick 100-150rwhp at the same boost level. It's on E85.....The fuel is incredible....I don't know why they won't allow it in X275????? Cheaper for the racer and a lot less breakage!!!
 

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It's on E85.....The fuel is incredible....I don't know why they won't allow it in X275????? Cheaper for the racer and a lot less breakage!!!
It really pisses me off that I will have to switch back to gas this year to run X275. I will miss my cheap racing fuel.
 

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Discussion Starter #11
I wish there was some solid data such as:

- dyno graps with low compression vs high compression

- drag race results low vs high comp engine


When the compression is raised, the piston turns the cranshaft faster.

There "is" or "should be" a point where more compression will trigger detonation whichever fuel we run.

It is hard to find that sweat spot.
 

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I wish there was some solid data such as:

- dyno graps with low compression vs high compression

- drag race results low vs high comp engine


When the compression is raised, the piston turns the cranshaft faster.

There "is" or "should be" a point where more compression will trigger detonation whichever fuel we run.

It is hard to find that sweat spot.
If you search on google, there are some back to back tests that were done with dyno sheets.
 

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check out the diesel engines. HIGH compression and TONS of boost. its all in the fuel and tune for gas. also, without a long drawn out post, " just an example" if you were to run 8.5:1 engine with say.... 12lbs of boost and make 400rwhp. now, if you were to run a 10.0:1:1 engine and want to make the same rwhp you would be able to run less boost to get the same result. but you need to be more carful with the tune. like they say, the window for tuning is shorter. The 8.5:1 engine might be able to run on 89octane fuel, but the 10.0:1 would need to be on 93 octane.
 

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If you search on google, there are some back to back tests that were done with dyno sheets.
The only tests I have ever seen are low compression ratio vs high compression ratio with constant boost. Surprise surprise the high compression engine makes more power....

The back to back tests with dyno sheets I would like to see are low compression ratio vs high compression ratio while maintaining the same BMEP, i.e. increase boost pressure with lower compression to create the same BMEP as the high compression engine.

If you search on google you will also find some interesting information on the benefits of low compression/high boost:
http://www.modularfords.com/forums/showthread.php/51059-increasing-static-cr-vs-boost-pressure
http://forum.e46fanatics.com/showthread.php?t=726637

Cheers,
Glen
 

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The back to back tests with dyno sheets I would like to see are low compression ratio vs high compression ratio while maintaining the same BMEP, i.e. increase boost pressure with lower compression to create the same BMEP as the high compression engine.
Well said. That's what it's all about. We just need to find some one with the coin$ to afford us this information. One method could require less octane or greater efficiency at the same BMEP.

There are also a lot of factors to consider with each cylinder head design and such.
 

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Diesel engine CR is pretty high and boost is above 40, runs very well. looking to push even more boost this year.
 

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I guess if gas had the same properties as diesel it would be easier to run high compression/high boost.
 

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The reason diesels run high boost and compression successfully is not the fuel so much. Diesel's research octane is only around 25.;)

The real difference is that the fuel does not enter the combustion chamber with the air thru the intake valve. It is injected directly into cylinder. This gets around detonation. You cant have detonation if their is no fuel in the hole to burn!

I really think the next big step for boosted engine will be when we see performance direct injection for gas engines.
 

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I'm not sure what the relationship between octane and flashpoint is, but I know diesel's is a heck of a lot higher.
 

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You can not really compare it like that. Again the big difference is the way the fuel enters the cylinder.

The flash point of diesel is 125*F. Regular Gas -45*F.
 
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