Your valvetiming has a lot to do with the amount of compression also. If you are running cams with say less than 220' @ .050 and a short exhaust duration ( like Comp Cams in the catalog ) for a good N/A aspirated combo. You may want to stay around 11:1 for a good safe and sane tune. If you step up to say 235' @ .050" you could easily run 11.5 - 12:1. Remember these engines do not need a lot of exhaust duration like the old pushrod engines did/do. And, the higher the compression the faster a four valve head loses internal exhaust pressure once the valve leaves the seats. If you run a dual pattern cam ( more exhaust duration ) like say a crower cam ( as stated in their catalog ), you could feesible get away with a little more compression. But, you may lose some torque down low and more horsepower upstairs in comparison to a cam set that is either single pattern or dual with a slightly less duration exhaust cam. Another note to consider for cams. Too much valve lift on the four valve heads ( not GT or GT500 heads ) can be hard on the valve springs. Our short installed height ( 1.42" - 1.47" )can cause valve spring over heating and breaking. That is why FRPP chose to raise the retainer on their valves , thus adding more spring material. Lending it to more long term reliability and less heat in the spring.
N/A highest compression on pump gas
- Thread starter 99vertcobra
- Start date
heads are being completely redone with all new springs valves guides you name it its new. and the cam is gonna be a custom spec
11-11.5 to 1 is safe with 93 octane, anything higher will require the timing to be retarded.
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so i could have a tune so i can drive on a street and a tune so i can run race fuel right?
I know they are complete different motors but I was just stating a fact my good sir :beer: It can be done on our cars though.
id just like to say that this is a great thead!:beer: iv been planing a build similar to this. the info on here is great guys. i wanted to get as much as i could staying N/A. but for now i just blew the rear up sooo yea. but thanks for the info guys. :thumbsup:
im running 11.5:1 on 91
if you dont mind could you tell me what kind of setup your running and what power range your in? heads, cam, intake, CI?
sure. Its a 97 cobra with stock heads (only a valve job done on them)stock cams, stock intake and its 5.1L. On a stock h-pipe and stock intake tube I made 309hp and 322lbtq.
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