Yes, that would lower the compression by about a point and you could adjust accordingly with the head gaskets.
Iron heads, pump gas 93
- Thread starter Jeff_383
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Jeff_383
Well-Known Member
516 been milled to 76cc
Closed chamber you could gain 2 or 3 cc by unshrouding the valves, to help get you closer to running on pump gas.
IMHO a 516 is the last head I would run on a 499 even w serious upgrades. Maybe yours have lots of time and upgrades into them.... But from my time working them over on a flow bench, a very mild port job on a later head 906,346,452 will run with a all out port job on 516, and it takes a lot of port work to get a 516 to run with a stock 906 especially on the exhaust. Stock a 516 intake port is fair... but it has no short side radius compared to later heads and the exhaust has very limited potential with the two bumps. I am not a 516 fan. We spent lots of time porting with sub par results compared to the other heads....a bit frustrating
. In some applications where you have quench the 516 has its place for pump gas. Sorry, probably not what you want to hear.
IMHO a 516 is the last head I would run on a 499 even w serious upgrades. Maybe yours have lots of time and upgrades into them.... But from my time working them over on a flow bench, a very mild port job on a later head 906,346,452 will run with a all out port job on 516, and it takes a lot of port work to get a 516 to run with a stock 906 especially on the exhaust. Stock a 516 intake port is fair... but it has no short side radius compared to later heads and the exhaust has very limited potential with the two bumps. I am not a 516 fan. We spent lots of time porting with sub par results compared to the other heads....a bit frustrating
. In some applications where you have quench the 516 has its place for pump gas. Sorry, probably not what you want to hear.
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Jeff_383
Well-Known Member
No, that's the stuff I want to hear.
Just for comparison, I just had my 516 heads checked. As far as I could tell they were original and had never been apart. They came in at 77 cc's.
The cam will help at low RPM. But what about high RPM when it doesn't have time to bleed off cylinder pressure. I can tell you a [email protected] doesn't like 9.7-1. 906 heads with all combustion chamber depths matched. It has .040" piston to head with KB deflector dome pistons. Polished chambers. Slow curve in the distributor. It'll rattle at 36 total in hot weather.
Doug
Doug
Nate S
Well-Known Member
This matches my experience exactly. I’m 215 @ .050 with 9.25 and just get away with 93. Timing at 36 total mech and another 16 or so of vacuum (for part throttle). Some hot days going up hill at part throttle I get a tiny tick. 89 and it’s a total mess.
F4R/T
Well-Known Member
Don’t forget to keep engine temp around 180 to help with detonation... there are some ways to make it work but don’t ignore the warning signs, you may put it on a dyno for tuning..I’ve heard of some guys running 160 with high compression. That was from Mr six pack and he also like to run as close as possible to 40degrees timing .. tuning! Good fuel is a must!
Jeff_383
Well-Known Member
Well, I ended up getting a pair of e-street heads new for an extremely good price off of someone. The 75cc ones. So with .051 gaskets, I should be at 10.67.
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