HEAD: How much shaved = how much compression ratio?
11-08-2005, 09:10 AM
#16
Race Director
Originally Posted by david fracolli
As an FYI with .045 removed my cam timing was retarded by almost 3 degrees.
PS, nice to see that you moved from "HELL" to upstate NY, the climate must be far better there. The 968 clock I bought from you looks great in my car, BTW.
Thanks for being so easy to deal with.........
11-08-2005, 09:22 AM
#17
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Originally Posted by tod84944
The reason for the 951 head, according to Jim Pasha, the 951 head flows so much better, and more than the 944 head.
11-08-2005, 09:23 AM
#18
Three Wheelin'
Yes, actually I did purchase an adjustable cam gear. The cam that I was running had quite a bit of duration so torqure was pretty non exsistant below 3,000 rpm. Retarding the cam 3 dgrees made things even worse. The engine pulled great all the way to red line but had nothing under 3,500 rpm. Great for a track car but it sucked on the street. I ended up running the cam 4 degrees advanced to help bring the torque curve back down.
I have no idea what just rasing the compression did as I did it at the same time i installed the cam. I will say though that even with the aftermarket cam I still very light pinging with 91 octane in the summer.
Happy you are enjoying the clock and you are welcome. I have a feeling though that come Jan. or Feb. that I am going to wish I was back in hell. Minus 30F is not my idea of good weather.
I have no idea what just rasing the compression did as I did it at the same time i installed the cam. I will say though that even with the aftermarket cam I still very light pinging with 91 octane in the summer.
Happy you are enjoying the clock and you are welcome. I have a feeling though that come Jan. or Feb. that I am going to wish I was back in hell. Minus 30F is not my idea of good weather.
11-08-2005, 09:30 AM
#19
Race Director
Originally Posted by david fracolli
Yes, actually I did purchase an adjustable cam gear. The cam that I was running had quite a bit of duration so torqure was pretty non exsistant below 3,000 rpm. Retarding the cam 3 dgrees made things even worse. The engine pulled great all the way to red line but had nothing under 3,500 rpm. Great for a track car but it sucked on the street. I ended up running the cam 4 degrees advanced to help bring the torque curve back down.
I have no idea what just rasing the compression did as I did it at the same time i installed the cam. I will say though that even with the aftermarket cam I still very light pinging with 91 octane in the summer.
Happy you are enjoying the clock and you are welcome. I have a feeling though that come Jan. or Feb. that I am going to wish I was back in hell. Minus 30F is not my idea of good weather.
I have no idea what just rasing the compression did as I did it at the same time i installed the cam. I will say though that even with the aftermarket cam I still very light pinging with 91 octane in the summer.
Happy you are enjoying the clock and you are welcome. I have a feeling though that come Jan. or Feb. that I am going to wish I was back in hell. Minus 30F is not my idea of good weather.
11-08-2005, 09:41 AM
#20
Three Wheelin'
It was a custom made cam from Elgin. I don't remember the exact specs but IIRC the lift was stock, the duration was 230 at .050 lift and it had around 50 degrees of overlap.
11-08-2005, 01:45 PM
#21
Three Wheelin'
Originally Posted by david fracolli
I hate to throow a wrench into this but the 944 cylinder head is not symetrical. What I mean is that the first .010 inches removed will reduce the volume of the head by 2cc but the next .010 will only reduce the volume by 1.8cc.
When I did by N/A engine I used the 88 10.2/1 pistons and had my head shaved .045 inches. The mesured compression ration was a tad over 10.7/1.
When I had the headwork done I had my machinest measure the stock head and then remeasure the volume after every .010 inches removed. If I can find the information I will post it but it might take a while to find as this was done over 4 years ago.
I wanted to remove .060 inches but was not able to go more than .045 due to piston to valve clearance problems since I was running an aftermarket cam. As an FYI with .045 removed my cam timing was retarded by almost 3 degrees.
When I did by N/A engine I used the 88 10.2/1 pistons and had my head shaved .045 inches. The mesured compression ration was a tad over 10.7/1.
When I had the headwork done I had my machinest measure the stock head and then remeasure the volume after every .010 inches removed. If I can find the information I will post it but it might take a while to find as this was done over 4 years ago.
I wanted to remove .060 inches but was not able to go more than .045 due to piston to valve clearance problems since I was running an aftermarket cam. As an FYI with .045 removed my cam timing was retarded by almost 3 degrees.
Dave, since you are working from memory, is there any chance that you may be remembering the measurement units wrong? If I run the numbers for planing 0.045" and getting a 10.7:1 CR, I calculate a cylinder head combustion chamber diameter of 62 mm, which just doesn't seem reasonable. HOWEVER, if I calculate CR using a planing value of 0.45 mm (NOT 0.045"), I calculate a CR of 10.71:1, which sounds very close to your measured CR.
11-08-2005, 02:44 PM
#22
Three Wheelin'
I am 100% positive that the amount of material removed was .045 inch. The reasons I remember is that one I was there when the work was done and 2 I had been told by numerous people that the maximum you can safely remove with the stock cam was .060 inch.
I have said this in the past and I will say it again, the only way to be 100% sure what the actual compression ratio iis is to measure everything. This means cc'ing each combustion chamber, deck height, gasket thickness and the dish in each piston.
I think if more people did this they would be very surprised at what the actual compression ratiio was compared to what they calculated it to be.
I have said this in the past and I will say it again, the only way to be 100% sure what the actual compression ratio iis is to measure everything. This means cc'ing each combustion chamber, deck height, gasket thickness and the dish in each piston.
I think if more people did this they would be very surprised at what the actual compression ratiio was compared to what they calculated it to be.
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