Compression vs Pump Gas
12-05-2009, 11:23 PM
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Compression vs Pump Gas Alright...so I realized that my cam swap isn't going to be so simple...since I'd have to fly cut a decent amount I decided just to go with a set of pistons. Now my question rises....I'm looking at getting the diamond high comp dome pistons. I'd also like to mill my heads, now without milling my 66cc heads I'd be at 11.5:1 if I milled them to a 62cc I'd be 12.2:1, will the 12.2:1 still be streetable? Can I still run pump gas efficiently? With that compression would I see gains running a higher octane? I'd like to get answer to these questions before I make up my mind. Also if anyone has any input on bumping the compression in a stock bottom end motor please let me know....
-Dave
-Dave
12-06-2009, 11:30 AM
#4
When your cutting it that close it depends on more than just the static CR.
Is the pump fuel in your area 91 or 93? What will your quench be? A tight quench helps to ward off pre-ignition.
Also keep in mind there will be a line that you can cross where higher compression with pump fuel will require a softer timing table which will cost you potential power.
I personally ran 11.34-1 on a stock bottom end heads/cam setup for nearly 3 yrs. It never saw an ounce of race fuel or fuel additives, and it never had any issues with 93 pump fuel with 28 dgrees of timing. My quench was tight at .032-.033 and I also ran the proper heat range plug (imo), which was a TR6.
What do you use the car for? Daily driver? Weekend car?
Is the pump fuel in your area 91 or 93? What will your quench be? A tight quench helps to ward off pre-ignition.
Also keep in mind there will be a line that you can cross where higher compression with pump fuel will require a softer timing table which will cost you potential power.
I personally ran 11.34-1 on a stock bottom end heads/cam setup for nearly 3 yrs. It never saw an ounce of race fuel or fuel additives, and it never had any issues with 93 pump fuel with 28 dgrees of timing. My quench was tight at .032-.033 and I also ran the proper heat range plug (imo), which was a TR6.
What do you use the car for? Daily driver? Weekend car?
12-06-2009, 06:53 PM
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When your cutting it that close it depends on more than just the static CR.
Is the pump fuel in your area 91 or 93? What will your quench be? A tight quench helps to ward off pre-ignition.
Also keep in mind there will be a line that you can cross where higher compression with pump fuel will require a softer timing table which will cost you potential power.
I personally ran 11.34-1 on a stock bottom end heads/cam setup for nearly 3 yrs. It never saw an ounce of race fuel or fuel additives, and it never had any issues with 93 pump fuel with 28 dgrees of timing. My quench was tight at .032-.033 and I also ran the proper heat range plug (imo), which was a TR6.
What do you use the car for? Daily driver? Weekend car?
Is the pump fuel in your area 91 or 93? What will your quench be? A tight quench helps to ward off pre-ignition.
Also keep in mind there will be a line that you can cross where higher compression with pump fuel will require a softer timing table which will cost you potential power.
I personally ran 11.34-1 on a stock bottom end heads/cam setup for nearly 3 yrs. It never saw an ounce of race fuel or fuel additives, and it never had any issues with 93 pump fuel with 28 dgrees of timing. My quench was tight at .032-.033 and I also ran the proper heat range plug (imo), which was a TR6.
What do you use the car for? Daily driver? Weekend car?
12-06-2009, 07:22 PM
#6
Its not so much static compression that you have to worry about for running pump gas. Dynamic is what your worried about. Dynamic compression is measured once the intake valve is closed. For example, lets say the intake valve closes 25* after bottem dead center. That means the piston is on its way back up on the compression stroke before the intake valve is fully closed. The A/F mix is not being compressed until the intake valve is closed so that means your dynamic compression is always gonna be lower than static.
Quench is the measurment between the piston and the cylinder head when the piston is at TDC.
Quench is the measurment between the piston and the cylinder head when the piston is at TDC.
Last edited by BarneyMobile; 12-06-2009 at 07:30 PM.
12-06-2009, 11:20 PM
#7
The valve events of your cam play a major role in your DCR. Do you know the cam that you are going with and it's specs? Post them up and someone on here that can use the calculator can punch in the numbers for you.
As far as quench goes, since the LS1 pistons, at least stock ones, come out of the hole ~.007-.008, you have to subtract this value. So with .040 gaskets, you'd be at .032-.033 for your quench.
The tight quench helps by forcing the air/fuel charge into the combustion chamber, which helps to even out the temps and hot spots. It also helps to mix the air/fuel charge making it ignite easier.
As far as quench goes, since the LS1 pistons, at least stock ones, come out of the hole ~.007-.008, you have to subtract this value. So with .040 gaskets, you'd be at .032-.033 for your quench.
The tight quench helps by forcing the air/fuel charge into the combustion chamber, which helps to even out the temps and hot spots. It also helps to mix the air/fuel charge making it ignite easier.
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12-06-2009, 11:55 PM
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The valve events of your cam play a major role in your DCR. Do you know the cam that you are going with and it's specs? Post them up and someone on here that can use the calculator can punch in the numbers for you.
As far as quench goes, since the LS1 pistons, at least stock ones, come out of the hole ~.007-.008, you have to subtract this value. So with .040 gaskets, you'd be at .032-.033 for your quench.
The tight quench helps by forcing the air/fuel charge into the combustion chamber, which helps to even out the temps and hot spots. It also helps to mix the air/fuel charge making it ignite easier.
As far as quench goes, since the LS1 pistons, at least stock ones, come out of the hole ~.007-.008, you have to subtract this value. So with .040 gaskets, you'd be at .032-.033 for your quench.
The tight quench helps by forcing the air/fuel charge into the combustion chamber, which helps to even out the temps and hot spots. It also helps to mix the air/fuel charge making it ignite easier.
12-07-2009, 12:56 AM
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e.g.
Intake Opens @ ....* ATDC, Int Closes @ ....* ABDC
Exhaust Opens @ ....* BBDC Exh Closes @ ....* ATDC
Someone will be more than happy to help you out.
12-08-2009, 04:23 AM
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My cam sheet gives me a bunch of ATDC and ABDC numbers...which ones do I use?
Also quick side question....do you have to clearance an LS1 block for a 4.000" crank?
Also quick side question....do you have to clearance an LS1 block for a 4.000" crank?
12-13-2009, 12:22 PM
#13
DCR is the key. If the valves dont close the compression preasure is O. Did you advance that cam?? Your sheet points out a 112 +4. I am saauming it is advanced. If so that is not what you want to do. The cam is pritty up there so i think you will be OK. TOM
