compression ratio
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Tuned
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From: Eastern Virginia
compression ratio
I am doing the 360 to 390 conversion. Figuring on paper with my setup it looks like I will have between 9.5 and 10:1. I've heard that higher compression raises horsepower. Does this hurt torque? The reason I ask is because most of the big truck motors run very low compression. I am going to use the motor i'm building mainly for daily driving or towing/hauling. Not really for drag racing. Just wondering.
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From: Evanston, WY
Compression will not lower torque, it will raise it. The most compression you can get, without detonation, with any given cam, is where you will create the most power. The reason someone might associate high compression with low torque is that typically a high compression engine will also have a long duration cam. It is the cam, not the compression, that lowers torque. With a short duration cam compression can't go very high before the dreaded ping starts. Still, as long as it is appropriate for the fuel you use, compression is a good thing.
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-Scouder
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From: Sun River St. George
9.5 is pushing it on iron heads and rv cam. 9.0 is better or 10.0 with aluminum heads. It is so easy to wind up with a rattling engine on a truck. I used silvolite 1130's with a crane 901 at 12 initial advance and get away with 87 octane. If I am pulling or hauling I use premium.
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Tuned
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From: Eastern Virginia
Thanks for the replies. Fordeverpower, what compression/engine/cam are you running just out of curiosity?
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Postmaster
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i have a 390 .030 over, rv cam (do not know the specs yet), and about 9 to 9.5 to 1 comp. I burnt up a valve before because of to much total timing. It was at like 55 degrees total. I thought i did the same thing again but it turned out to be the valve seat came out.
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From: Iowa
Originally Posted by fordeverpower
i have a 390 .030 over, rv cam (do not know the specs yet), and about 9 to 9.5 to 1 comp. I burnt up a valve before because of to much total timing. It was at like 55 degrees total. I thought i did the same thing again but it turned out to be the valve seat came out.
Post Fiend
Joined: Feb 2001
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From: Missouri
The FT was a low compression engine because they wanted an engine that could take a severe beating, run sub-standard gas and live forever. They got exactly what they were going for.
Upping compression will up torque across the board unless you are lacking enough octane and can't advance the timing at low RPMs to make it work right.
Upping compression will up torque across the board unless you are lacking enough octane and can't advance the timing at low RPMs to make it work right.
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