effective compression
05-31-2011, 11:33 PM
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effective compression I've been looking over this site for a long time now and I must say that its one of the most informative forum that I ran across in a long time. Alot of good knowledge here, but I guess its time for one of my questions.
If I am running lets say e85 in a 11:7 stock CR engine and want to increase the effective CR to make e85 run more efficiently in return produce more power could I do this by "decreasing overlap"?
I was thinking, if I spread the cams and take out the remainding overlap(remove as much overlap)wouldn't this increase cylinder pressure and in return give my engine more of its effective compression for e85? since knock is not even an issue any longer with e85 increasing cylinder pressure should not even be an issue.
This is just too much to take in all at once but this is what I am thinking.
If I am running lets say e85 in a 11:7 stock CR engine and want to increase the effective CR to make e85 run more efficiently in return produce more power could I do this by "decreasing overlap"?
I was thinking, if I spread the cams and take out the remainding overlap(remove as much overlap)wouldn't this increase cylinder pressure and in return give my engine more of its effective compression for e85? since knock is not even an issue any longer with e85 increasing cylinder pressure should not even be an issue.
This is just too much to take in all at once but this is what I am thinking.
06-01-2011, 05:25 AM
#2
Your effective (dynamic) compression is determined by you static compression and where the intake valve closeS ABDC.....not really overlap.
If you want to raise your dynamic compression you have to either advance your cam (slight gains) get a new cam, and or bump your static compression way up by milling your heads, or getting domed pistons
If you want to raise your dynamic compression you have to either advance your cam (slight gains) get a new cam, and or bump your static compression way up by milling your heads, or getting domed pistons
06-01-2011, 09:32 AM
#4
Not really, the overlap can actually help increase cylinder pressure in the higher rpms due to better scavaging and cylinder fill. Overlap is done long before the intake valve closes, and only when the intake valve is close can you start building pressure.
( I hope I explained that right) lol
( I hope I explained that right) lol
06-01-2011, 10:21 AM
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sorry if I sound too noobish and stupid but I am self teaching myself through articles and alot of reading. so overlap is when 2 valves are open correct?(not sure if im saying this right).
so by tweaking intake and exhaust could I decrease overlap (the time when valves stay closed)and increase cylinder pressure?
Thank you for baring with me
so by tweaking intake and exhaust could I decrease overlap (the time when valves stay closed)and increase cylinder pressure?
Thank you for baring with me
06-01-2011, 10:56 AM
#6
Lol hey man I'm right there with you, I've spent countless hours reading and searching for info.
I'll go through the process real quick in order of events...
1 Your piston gets forced down by the air/ fuel mixture getting ignited.
2 your exhaust valve opens and the piston moves up the cylinder pushing the exhaust out.
3 (this is where overlap occurs) your intake valve opens while the exhaust valve is still opened and exhaust gas is rushing out of the exhaust port...this in turn creates a super low pressure area in the cylinder which pulls the intake air/ fuel into the cylinder.
4 as the piston starts moving back down the cylinder the exhaust valve closes ( the intake valve is still opened letting air/ fuel into the cylinder)
5 as the piston reaches bottom dead center the intake valve is still opened letting air/ fuel flow in.
6 now the piston starts moving back up on the cylinder (with the intake valve opened still)
7 (no "compression" has started yet) now the intake valve closes and compression begins.
8 piston hits 14 degrees before top dead center, spark ignites air fuel mixture and BAM flame front covers the area on top of the piston and it gets forced down for the whole thing to happen again.
Does that help? Lol it sounded good on my head
I'll go through the process real quick in order of events...
1 Your piston gets forced down by the air/ fuel mixture getting ignited.
2 your exhaust valve opens and the piston moves up the cylinder pushing the exhaust out.
3 (this is where overlap occurs) your intake valve opens while the exhaust valve is still opened and exhaust gas is rushing out of the exhaust port...this in turn creates a super low pressure area in the cylinder which pulls the intake air/ fuel into the cylinder.
4 as the piston starts moving back down the cylinder the exhaust valve closes ( the intake valve is still opened letting air/ fuel into the cylinder)
5 as the piston reaches bottom dead center the intake valve is still opened letting air/ fuel flow in.
6 now the piston starts moving back up on the cylinder (with the intake valve opened still)
7 (no "compression" has started yet) now the intake valve closes and compression begins.
8 piston hits 14 degrees before top dead center, spark ignites air fuel mixture and BAM flame front covers the area on top of the piston and it gets forced down for the whole thing to happen again.
Does that help? Lol it sounded good on my head
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06-01-2011, 02:37 PM
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Lol hey man I'm right there with you, I've spent countless hours reading and searching for info.
I'll go through the process real quick in order of events...
1 Your piston gets forced down by the air/ fuel mixture getting ignited.
2 your exhaust valve opens and the piston moves up the cylinder pushing the exhaust out.
3 (this is where overlap occurs) your intake valve opens while the exhaust valve is still opened and exhaust gas is rushing out of the exhaust port...this in turn creates a super low pressure area in the cylinder which pulls the intake air/ fuel into the cylinder.
4 as the piston starts moving back down the cylinder the exhaust valve closes ( the intake valve is still opened letting air/ fuel into the cylinder)
5 as the piston reaches bottom dead center the intake valve is still opened letting air/ fuel flow in.
6 now the piston starts moving back up on the cylinder (with the intake valve opened still)
7 (no "compression" has started yet) now the intake valve closes and compression begins.8 piston hits 14 degrees before top dead center, spark ignites air fuel mixture and BAM flame front covers the area on top of the piston and it gets forced down for the whole thing to happen again.
Does that help? Lol it sounded good on my head
I'll go through the process real quick in order of events...
1 Your piston gets forced down by the air/ fuel mixture getting ignited.
2 your exhaust valve opens and the piston moves up the cylinder pushing the exhaust out.
3 (this is where overlap occurs) your intake valve opens while the exhaust valve is still opened and exhaust gas is rushing out of the exhaust port...this in turn creates a super low pressure area in the cylinder which pulls the intake air/ fuel into the cylinder.
4 as the piston starts moving back down the cylinder the exhaust valve closes ( the intake valve is still opened letting air/ fuel into the cylinder)
5 as the piston reaches bottom dead center the intake valve is still opened letting air/ fuel flow in.
6 now the piston starts moving back up on the cylinder (with the intake valve opened still)
7 (no "compression" has started yet) now the intake valve closes and compression begins.8 piston hits 14 degrees before top dead center, spark ignites air fuel mixture and BAM flame front covers the area on top of the piston and it gets forced down for the whole thing to happen again.
Does that help? Lol it sounded good on my head
06-01-2011, 05:30 PM
#9
That would give you a tighter and make power come in a little earlier....you could leave your exhaust cam where it is, and just retard your intake cam a few degrees to lower your dynamic compression.
Just curious, what type engine are you working with?
Just curious, what type engine are you working with?
