Tell Me About 317 Heads
12-12-2009, 02:30 PM
#1
Burning Brakes
Thread Starter
Tell Me About 317 Heads
I have a 99 FRC I bought used. It has 317 heads, a Cam (don't know specs) and long tubes. Makes 390 RWHP and 380 lb-ft.
I know the 317 heads are basically LS6 heads with a larger chamber (71cc I think).
Normally these heads would lower the compression ratio due to the large chamber. The seller told me the compression ratio is ~11:1 and given the HP that seems to be true.
My question is - what would the builder have to do to these heads or to the pistons (Seller told me the engine has forged internals) to get that high of a ratio?
Any info would be much appreciated. Thanks, Brad
I know the 317 heads are basically LS6 heads with a larger chamber (71cc I think).
Normally these heads would lower the compression ratio due to the large chamber. The seller told me the compression ratio is ~11:1 and given the HP that seems to be true.
My question is - what would the builder have to do to these heads or to the pistons (Seller told me the engine has forged internals) to get that high of a ratio?
Any info would be much appreciated. Thanks, Brad
12-12-2009, 03:04 PM
#2
Tech Contributor
I have a 99 FRC I bought used. It has 317 heads, a Cam (don't know specs) and long tubes. Makes 390 RWHP and 380 lb-ft.
I know the 317 heads are basically LS6 heads with a larger chamber (71cc I think).
Normally these heads would lower the compression ratio due to the large chamber. The seller told me the compression ratio is ~11:1 and given the HP that seems to be true.
My question is - what would the builder have to do to these heads or to the pistons (Seller told me the engine has forged internals) to get that high of a ratio?
Any info would be much appreciated. Thanks, Brad
I know the 317 heads are basically LS6 heads with a larger chamber (71cc I think).
Normally these heads would lower the compression ratio due to the large chamber. The seller told me the compression ratio is ~11:1 and given the HP that seems to be true.
My question is - what would the builder have to do to these heads or to the pistons (Seller told me the engine has forged internals) to get that high of a ratio?
Any info would be much appreciated. Thanks, Brad
12-12-2009, 05:16 PM
#4
Race Director
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St. Jude Donor '03
Taking a stock 6.0l head and achieving the necessary chamber size to achieve that CR via milling would require at least .070" stock removal, and that's not a good idea if you have any hopes of bolting up the intake manifold.
Most likely answer:
Patriot used to take the 6.0 (317 & 035 casting #s) heads and welded the chambers up to get them down to 59cc volume. They called them "LS6 style" heads, and because they were in the low-budget price ballpark, were quite popular. These would put an otherwise stock LS1 around 11:1.
Only way to know for sure what your actual CR is would be to ID the pistons (if not flat), cc the head chambers, measure deck height and head gasket thickness. Anything else at this point is just guesswork.
Most likely answer:
Patriot used to take the 6.0 (317 & 035 casting #s) heads and welded the chambers up to get them down to 59cc volume. They called them "LS6 style" heads, and because they were in the low-budget price ballpark, were quite popular. These would put an otherwise stock LS1 around 11:1.
Only way to know for sure what your actual CR is would be to ID the pistons (if not flat), cc the head chambers, measure deck height and head gasket thickness. Anything else at this point is just guesswork.
12-13-2009, 03:17 PM
#5
Burning Brakes
Thread Starter
Thank you for the responses.
Y2Kvert4me - very good information. You are always so knowledgeable and helpful, I'm sure I speak for many folks on here in saying I appreciate your posts.
Y2Kvert4me - very good information. You are always so knowledgeable and helpful, I'm sure I speak for many folks on here in saying I appreciate your posts.
12-13-2009, 06:29 PM
#7
317s are roughly equivalent to 243s with the exception of the larger chamber size as already mentioned and *different valves*. You do not get the sodium filled exhaust valves, nor the hollow intake valves with 317s, you get solid ss valves.
With that much compression, I bet either the chambers were welded, or you have some domed slugs and some thin head gaskets.
With that much compression, I bet either the chambers were welded, or you have some domed slugs and some thin head gaskets.
12-13-2009, 10:46 PM
#8
Melting Slicks
The 317's came on a 6.0 truck motor I bought. I think on that motor they were 9.5 to 1 on the lq4's. They had a dished piston if I recall correctly to bring down the comp. ratio on that motor and I think the lq9 motors were 10 to 1 ratio with a flat top piston. So, they definetly had some work done.
12-14-2009, 08:12 AM
#9
The 317's came on a 6.0 truck motor I bought. I think on that motor they were 9.5 to 1 on the lq4's. They had a dished piston if I recall correctly to bring down the comp. ratio on that motor and I think the lq9 motors were 10 to 1 ratio with a flat top piston. So, they definetly had some work done.
12-14-2009, 08:16 AM
#10
Melting Slicks
Thats about what I thought, I'm getting ready to port the set that I have in case something happens to my ported ls1 heads or I'll sell them once I get them done. Nobody seems to want them stock.
