Finally Cosworth Heads!
#61
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Don't confuse STATIC compression ratio as meaningful for anything other than cranking [how much power the starter needs to develop]. All that counts is EFFECTIVE running compression after cam [air flow in/out] is calculated.
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Originally Posted by Q45tech
Don't confuse STATIC compression ratio as meaningful for anything other than cranking [how much power the starter needs to develop]. All that counts is EFFECTIVE running compression after cam [air flow in/out] is calculated.
Originally Posted by Z350Lover
Congrats Joe! You will love those beautiful heads!!! And with a set of 11.1:1 compression pistons and a set of wild cams (Nismo Spec 2 cans suit your needs), you should be at 320rwHP+!
cheers,
richie
cheers,
richie
Last edited by rednezz; 06-16-2006 at 05:56 AM.
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Originally Posted by Q45tech
Don't confuse STATIC compression ratio as meaningful for anything other than cranking [how much power the starter needs to develop]. All that counts is EFFECTIVE running compression after cam [air flow in/out] is calculated.
*EDIT*
OK, I sat and thought about this, and is it really accurate to say that there is "effective" versus "static" compression? Certainly the volumetric efficiency of the engine is going to change based on any number of factors, such as air pressure, temperature, forced induction, cam timing, engine speed, etc. But whatever you put into the cylinder is going to get squeezed based on the mechanical compression ratio of the motor, which should just be a ratio of the total volume at BDC vs TDC.
*/EDIT*
I'm seriously considering using these heads for my build, and want to bore to 100mm, so I'd like to understand as much as I can.
-E
Last edited by -EL; 06-16-2006 at 07:29 AM.
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Originally Posted by rednezz
I have always been told that dynamic CR is lower than static CR because of the valves opening. When adding big duration cams you want to add a higher static CR because the valves will stay open longer reducing CR.
-E
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Originally Posted by -EL
AHHH! Too much to think about. Ok, that makes sense, long duration cams will be open during compression, gonna get some leakage reducing your CR, etc etc. Now I understand what he meant by effective compression while the engine is running.
-E
-E
#67
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Originally Posted by -EL
Could, but it's always a tradeoff... his 8.5 pistons would actually be more like 8.3 with the extra chamber size. Non-boost performance is going to suffer more.
-E
-E
Will
#68
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Originally Posted by -EL
Well, assuming we keep the same cams, increasing the flow through the heads is going to increase the volumetric efficiency, raising the effective running compression? Obviously tough to know what an engineer was thinking when he was working on these heads, but do you think the additional chamber space was meant to compensate for the increase in effective compression due to better volumetric efficiency?
*EDIT*
OK, I sat and thought about this, and is it really accurate to say that there is "effective" versus "static" compression? Certainly the volumetric efficiency of the engine is going to change based on any number of factors, such as air pressure, temperature, forced induction, cam timing, engine speed, etc. But whatever you put into the cylinder is going to get squeezed based on the mechanical compression ratio of the motor, which should just be a ratio of the total volume at BDC vs TDC.
*/EDIT*
I'm seriously considering using these heads for my build, and want to bore to 100mm, so I'd like to understand as much as I can.
-E
*EDIT*
OK, I sat and thought about this, and is it really accurate to say that there is "effective" versus "static" compression? Certainly the volumetric efficiency of the engine is going to change based on any number of factors, such as air pressure, temperature, forced induction, cam timing, engine speed, etc. But whatever you put into the cylinder is going to get squeezed based on the mechanical compression ratio of the motor, which should just be a ratio of the total volume at BDC vs TDC.
*/EDIT*
I'm seriously considering using these heads for my build, and want to bore to 100mm, so I'd like to understand as much as I can.
-E
Will
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Got my Cosworth heads in and veryone I show them too is absolutely amazed of the quality and craftmenship.
Bearings are still on hold.... will have to go with OEM. PITA choosing the right ones, and of course there are none to be found locally.
Will be calling you on Monday Sharif for a rush order
Danny
Bearings are still on hold.... will have to go with OEM. PITA choosing the right ones, and of course there are none to be found locally.
Will be calling you on Monday Sharif for a rush order
Danny
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Wow...no way. Its Dave from Headgames. I didnt know you messed with VQ heads. Anyways, thanks for helping me with the Honda head a year ago. This guy Dave is super nice. I heard you also do 3RZ heads. Is that right? Let me know. Currently Van is doing those for us and he is doing a fantastic job. I'm on the way to E-town as we speak, hope to see you there this weekend. Anyways...thanks for the hospitality.
#73
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increasing the displacement of the engine via boring or stroker kit I don't think has an effect on compression ratio. The compression is the same, there's just more volume of it being pushed. If the piston was the diameter of an oil drum, it would still compress the air to the same compression. There's just more air being compressed overall
I'm curious too about if the heads have more volume how that might change the compression ratio.
I've actually been thinking of going with something like 10.5 or 11:1 CR when I do a built engine with my vortech setup considering I run water/meth injection and 96-101 octane gas anyway.
I'm curious too about if the heads have more volume how that might change the compression ratio.
I've actually been thinking of going with something like 10.5 or 11:1 CR when I do a built engine with my vortech setup considering I run water/meth injection and 96-101 octane gas anyway.
#74
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Originally Posted by sentry65
increasing the displacement of the engine via boring or stroker kit I don't think has an effect on compression ratio. The compression is the same, there's just more volume of it being pushed. If the piston was the diameter of an oil drum, it would still compress the air to the same compression. There's just more air being compressed overall
I'm curious too about if the heads have more volume how that might change the compression ratio.
I've actually been thinking of going with something like 10.5 or 11:1 CR when I do a built engine with my vortech setup considering I run water/meth injection and 96-101 octane gas anyway.
I'm curious too about if the heads have more volume how that might change the compression ratio.
I've actually been thinking of going with something like 10.5 or 11:1 CR when I do a built engine with my vortech setup considering I run water/meth injection and 96-101 octane gas anyway.
2. less head chamber cc's = increased compression, more head chamber cc's = lower compression. Cosworth heads slightly drop the stock compression (vs, say NISMO heads, which raise compression)
#75
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I dunno, I can see how the cc's in the heads completely affect compression because the air being compressed has more room to expand into with bigger heads
but for the short block with a larger bore and stroke, more air is naturally going to fill the (larger) cylinder chamber and more gas is obviously called for to balance the A/F
I guess what I'm wondering, is if you proportionately increase everything, why would the compression would change??
but for the short block with a larger bore and stroke, more air is naturally going to fill the (larger) cylinder chamber and more gas is obviously called for to balance the A/F
I guess what I'm wondering, is if you proportionately increase everything, why would the compression would change??
Last edited by sentry65; 05-04-2007 at 03:00 PM.
#76
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http://www.chevyhiperformance.com/te...ression_guide/
easier for me to post that article rather than post myself
Both bore and stroke have an effect on compression....stroke moreso than bore
easier for me to post that article rather than post myself
Both bore and stroke have an effect on compression....stroke moreso than bore
#77
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thanks for the link
so when you buy a stroker kit with 11 CR that was intended for stock heads and I went and got some huge high flowing heads, that'd then lower the CR by whatever amount. So I guess people just need to factor that into their build
so when you buy a stroker kit with 11 CR that was intended for stock heads and I went and got some huge high flowing heads, that'd then lower the CR by whatever amount. So I guess people just need to factor that into their build
Last edited by sentry65; 05-04-2007 at 03:06 PM.
#78
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if coming from a reputable manufacturer, just the opposite..the compression should be EXACTLY what they quote, as they've taken the other variables into account.
Obviously, if you toss that stroker onto an aftermarket head with more or less combustion camber cc's, varying deck heights (can't vary it by much on this motor or it won't bolt together), then compression can be expected to vary slightly
Obviously, if you toss that stroker onto an aftermarket head with more or less combustion camber cc's, varying deck heights (can't vary it by much on this motor or it won't bolt together), then compression can be expected to vary slightly
#79
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^^Correct^^
For instance, when we make our 100mm Arias ED pistons, this results in a 3.8L displacement, so the CR of the piston is set to 9.0:1, and the piston is constructed to acheive this CR, given the CC of the heads, headgasket thickness, etc..etc..
Like Z1 mentioned, CR can vary ever so slightly with different combinations of HG's, combustion chamber shaping/porting, but usually not in a huge way.
Manufacturers will do these calculations for you, so no worries.
For instance, when we make our 100mm Arias ED pistons, this results in a 3.8L displacement, so the CR of the piston is set to 9.0:1, and the piston is constructed to acheive this CR, given the CC of the heads, headgasket thickness, etc..etc..
Like Z1 mentioned, CR can vary ever so slightly with different combinations of HG's, combustion chamber shaping/porting, but usually not in a huge way.
Manufacturers will do these calculations for you, so no worries.
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