Low Compression Vs High Compression - Discuss
#161
Caraholic
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Bore and stroke size, rod angle, piston speed etc. If you change any of these, they have a knock on effect (no pun intended ) of their ability to be resistant to det or not. You cannot compare different engines to their ability to run high compression - it absolutely has to be like for like - just because it is an in-line four of the same capacity, doesn't mean that it will respond in the same way to a compression hike. A good example of this is the Evo engine, which due to it's configuration, can take a much higher compression as standard (8.5:1 compared to the Cossies 8.0:1), as well as modified.
#163
Caraholic
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Originally Posted by NEIL A
So what is the lowest comp that has been openly tried on a cosworth, i know 7.2:1 is what's normaly considered as low. Lowest i have been in was a 6.8:1 and didnt feel any different to my old 7.2:1 engine.
#164
PassionFord Post Whore!!
iTrader: (6)
Not the engine you think im on about Mike but was a ava build, dont know what comp Euan is running these day but sure it will be low and his car is responsive as any like for like and takes big boost with ease. Will be good to compare others i have been in to my new LOW comp engine soon
#174
high compression
escrstJust noticed you are building zetc hc engine, who's the builder? I ask as i'm in the same process. Sounds more sense to me if you are not after high hp to run hc engine
cheers Richard
cheers Richard
#181
Happily retired
707bhp on Optimax from mine . Can I ask what MikeR considers HC in a YB engine producing near 800bhp, over 7.5:1 or maybe even 8:1 . Genuine question after Knowing what Mark now builds.
#183
PassionFord Post Whore!!
Mark
#185
Caraholic
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Rod,
I know you can do it - if you're prepared to accept an engine that doesn't make full boost until 5000rpm. However, driveability is what I want, rather than outright numbers, so for me achieving a a high power figure with a huge turbo is complete and utter waste of time for a track car .
My engine makes 0.7 bar at 3000rpm and 2.2 bar by 3500rpm, which it holds all the the way to the limiter and due to this, I personally wouldn't want to run any higher than the 7.3:1 that I am running, as I want good ignition values to keep engine heat at bay.
A top speed run lasts 35s? A lap of the Ring lasts 8mins.... .
Obviously you build an engine to its desired remit. To say it is stuck in the past is completely missing the point .
I know you can do it - if you're prepared to accept an engine that doesn't make full boost until 5000rpm. However, driveability is what I want, rather than outright numbers, so for me achieving a a high power figure with a huge turbo is complete and utter waste of time for a track car .
My engine makes 0.7 bar at 3000rpm and 2.2 bar by 3500rpm, which it holds all the the way to the limiter and due to this, I personally wouldn't want to run any higher than the 7.3:1 that I am running, as I want good ignition values to keep engine heat at bay.
A top speed run lasts 35s? A lap of the Ring lasts 8mins.... .
Obviously you build an engine to its desired remit. To say it is stuck in the past is completely missing the point .
#188
Too many posts.. I need a life!!
Compression Ratio Dynamic vs. Static
Static compression ratio is calculated from swept volume and combustion chamber volume etc, etc... We come up with a value of 7.5:1 or 9.5:1, or whatever we want.
Camshaft timing - specifically when the intake valve closes is much more important.
Dynamic compression ratio is the important factor. Japanese engines ( or most modern designs) have variable intake camshaft timing - where the intake camshaft is advanced or retared wrt the crankshaft. This changes the dynamic compression ratio. Much higher static CR's are used when variable or late intake closing camshaft timing is used.
On a Cossie the camshaft position is not variable, and is not a late closing profile, therefore CR's of 7.5:1 and lower are used for high boost applications.
Honda engines with variable camshaft timing (phasing) and an efficient combustion chamber
can use a much higher compression ratio before detonation takes place.
One cannot make a blanket statement regarding compression ratio in a turbocharged engine. There are many more variables than just static compression ratio alone.
Just a thought from a Canadian ERST fan.
Cheers
Camshaft timing - specifically when the intake valve closes is much more important.
Dynamic compression ratio is the important factor. Japanese engines ( or most modern designs) have variable intake camshaft timing - where the intake camshaft is advanced or retared wrt the crankshaft. This changes the dynamic compression ratio. Much higher static CR's are used when variable or late intake closing camshaft timing is used.
On a Cossie the camshaft position is not variable, and is not a late closing profile, therefore CR's of 7.5:1 and lower are used for high boost applications.
Honda engines with variable camshaft timing (phasing) and an efficient combustion chamber
can use a much higher compression ratio before detonation takes place.
One cannot make a blanket statement regarding compression ratio in a turbocharged engine. There are many more variables than just static compression ratio alone.
Just a thought from a Canadian ERST fan.
Cheers
#189
Rally nut
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I have 425lb/ft of torque at 3000rpm and my engine is not a low CR one.
And without all Mike's Mountune inlet and other stuff. Thanks Harvey Gibbs !
And without all Mike's Mountune inlet and other stuff. Thanks Harvey Gibbs !
Last edited by Mad Matt; 13-05-2008 at 05:20 PM.
#192
cannock is a race track
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bmw f1 car! 1000 bhp from a 1.5! high comp turbo! if you got the internals and the octain then its better. i kno its an F1 car but thats where it all starts
#193
DEYTUKURJERBS
they was NOT high comp, 7s and 6s.
and they ran on mega race fuel, on pump fuel high comp is a whole different ballgame...
#194
#195
Happily retired
Well Mike mine made 3.2bar of boost at 4400rpm on 8.4:1 on a GT42.
#198
cannock is a race track
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#200
Wahay!! I've lost my Virginity!!
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The F1 Turbos used 8.0-8.5:1 in CR and used ~85% toluene and 15% heptane fuel = poison!
I run 10.88:1 in CR on my WRC escort rallycar engine. Anyone want to argue if it works proper?
I run 10.88:1 in CR on my WRC escort rallycar engine. Anyone want to argue if it works proper?