How much can a set of heads be milled to reduce chamber and increase CR safely?
I mean no major problems like rough idle or pre-ignition, I am not looking for high CR just some extra to get better performance out of my 1989 50 FI, I will go for 93 and 108 octane fuels but it is a dayli driving vehicle.
Set of heads are stock today (61cc I think).
Also a guy toldme not to mill heads since it can lead to a really rought idle and computer will not work properly then, is it correct?
What would you sudgestme to do?
You input is higly appreciated as always.
You can probably reach a reasonable C/R increase without milling the heads. Your current piston volume is 6.5cc and your current head gasket thickness is .046. This gives a C/R of about 8.9/1. (I'm assuming your engine is currently stock). If you would install a Fel-Pro 1011-2 head gasket which is .039 compressed thickness then your C/R would bump to 9.2/1. If you would install an aftermarket piston like the Keith Black 115,which has a piston volume of 3cc, along with the .039 head gaskets then your C/R would increase to about 9.4/1. This would be a reasonable increase without worrying about pinging. Depending on many other variables a 9.5/1 C/R is acceptable on pump gas.
I have World Windsor JR's going on my 89 which have a 58cc combustion chamber. According to World, these heads would have to be milled .070 to gain a full point in C/R. The combustion chambers of the World heads are similiar to your E7TE heads. So if your convinced to mill the heads to get the C/R bump then you would need to mill about .042 to reach a 9.5/1 C/R.
Increases in C/R should not affect the speed density system on your truck. Things that change actual volume of air passing thru the engine (better flowing heads, larger throttle body etc) and a erratic vacuum (lopey cam) will goof up the system tho. A change in C/R does not change the volume of air thru the engine. Going too high would cause pinging.
Reason why I am asking is because I have receive an offer for a set of GT40 P heads with the following specifications.
FORD GT-40 "P" Hi-Flow cast iron cylinder heads (M-6049-P303) for use on 289, 302, or 351W engines. Their casting numbers are F77E-AA. This head features a much improved air flow over production GT heads. To increase the airflow, we have enlarged the valve sizes from 1.84"/1.46" to 1.90"/1.60" using NEW stainless steel undercut race-flo valves. They also feature four angle competition valve seats (30-45-60-75), and the combustion chambers machined for increased performance. The intake ports have 18% greater volume than E7TE (GT) heads.The ports measure 1.910" x 1.180" for the intakes and 1.350" x 1.100" for the exhausts. The flow numbers with the original valves are - Intake 58.0 @ .100", 121.0 @ .200", 159.0 @ .300", 186.0 @ .400", 190.0 @ .500" - Exhaust 45.0 @ .100", 88.0 @ .200", 112.0 @ .300", 125.0 @ .400", 127.0 @ .500". This is a 20-32% improvement over E7TE (GT) factory heads without the enlarged valves. The heads have been milled to reduce the chambers to approx 54 cc's. This will result in a 1/2 to 1 point in crease in compression. This package also includes positive stem seals, custom valve springs, 4130 steel retainers, and HD keepers. The springs are rated at 110 lbs @1.800" and 280 lbs @1.250" and will handle cam lifts to .600".
Also during the upgrade I will add a cam (nothing wild) and roller rockers.
What can you tell me about this heads? And about my project set up?
The gt40p heads should work with a stock cam. Checking valve clearance prob. isnt a bad idea though. I have a set of those that have been milled .060 and run a cam with .512 lift and havenot experienced any problems. A side note: you may have to buy headers for the "p" heads because of the relocated plug angle. Milling the heads shouldnt affect the computer although the cam may depending if you have speed density or mass air. Also check for proper intake sealing depending on how much the heads have been milled, you may need to mill the bottom of the intake also.
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