I do not know the compression ratio, the engine is a stock '77 model rebuilt to factory specs about 20,000 miles ago. The only numbers I found on the intake were on the rear runner behind the carb pad. TheyI know are RF-E4ZE-9425-GA. I know there are a ton of variables I was just looking for some input. Cary I've never heard of any '77 model 302 in stock configuration with more than 8:1 compression ratio @142 H.P. Even with the "closed" chamber smog era truck heads, which I have owned a set of in the past(boat anchors), with 81/2:1 c/r. All you have to do is look in the older Chilton manuals,and Motors manuals, and you will see that compression ratios dropped from 9:1 to 8:1 after 1971. I don't believe they climbed back up to 9:1 until 1983 in the mustang GT. With all that said, it is very easy to over cam 8:1 c/r with stock smog era cylinder heads. Too "BIG" of a cam (too high lift, too much duration) will make a "weak" engine that sounds good to the ear. In my opinion,I would stay around 260 degrees duration, if you have a bone stock '77 model 302, and around 450" lift, because you also have to take into consideration the stock valve springs that can't handle more lift than that. Although, I would change the valve springs before I upgraded the cam. That's if everything in your motor is stock.
The comp ratio change in 72 was due to the use of pistons with a large, deep dish (aka grand canyon). In 77, Ford went back to a flat topped piston (with reliefs and possibly a slight dish) and went with the D8OE heads with their huge combustion chambers (70 cc vs the earlier 58 cc heads). If he's got the flat topped pistons (also depending on which flat topped pistons are in there as the pin height varies from 1.585 to 1.620 for 302's, which translates to as much as 4.5 cc volume in the mix ) the actual ratio is going to depend on what heads and chambers they've got. Could be as little as in the 7's, way up to 10.5 to 1. That's a huge variance.
You can't show me a factory Ford car with a production line "run of the mill" 302 in the '77 era that came with 10 1/2:1 c/r, because there was'nt one. Everything was smogged down, low compression, weak, boat anchors, and the engine in question will be no acception, unless someone somewhere along the way rebuilt it with different parts than what he thinks he has. Yes, the wrist pen location, connecting rod length, piston dish/dome,and combustion chamber volume all factor greatly into the compression ratio, but let's face it, Ford Motor Company was'nt mixing all those variants in that era like they were in the 1963-1971 time frame. None of the above really does'nt matter to the guy asking the question about the cam. If he has a stock 1977 Ford 302 engine, he has an 8 to 8 1/2:1 c/r engine, because that is what they were building at that time. Check your 1969-1977 engine manuals, they will verify. But I agree, he does need to find out for sure exactly what he's got so he can see what cam he is even able to run. Everything I have said here is based on madbaverick stating that he has a '77 model 302 built to stock specks., and in no way am I trying to quarrel with anyone. " I've been proved wrong before."
Re: Guy's I appreciate all the input. I am leaning alot I didn't know. The engine I have was low mileage when I pulled it. I was short on time when I had it rebuilt and was only looking for reliability. I am sure the shop simply re-ringed it and it still has all originall hardware (pistons,rods,ect). I do recall they had to bore it 10 over. If I had to guess it is probably in the 8 to 81/2 range based on all the ford literature I have seen on that era engine. Oh and the engine,heads and all came out of a '77 Mustang II ghia not a truck. Cary
Pretty good advice posted here on the cam selection. In a mild 302, that would be about as big as you would want to go until you get the compression up. There might be some drivability gains with slightly less duration. With the headers and 3:55 gear, I would think this would be a combo that would make a very fun car. If using that Edelbrock Performer, they usually respond to the addition of a carb spacer. If you can get one of the newer air-gap manifolds, they seem to work well overall on engines that are mild all the way through most street/strip mods, and it should still fit well under the hood with an air cleaner change. That is what I will be going to next ...
i will be working on my mav this week end if ya need a hand let me know i may need to run to BA any way. ps. im in the 51 and mingo area every monday through thursday about 4;30- 5:30. im just sayin. 812-6166
I NEVER said there was. What I said was the ratio could vary from in the 7's to 10.5 to 1, DEPENDING ON WHAT HEADS AND CHAMBERS ARE ON IT.
It seemed to me that you were probably confusing Cary, with your technical expertise. I was just trying to speak to him in every day language, seeing that the range of compression ratios of the Ford 302, in 1977 was so very narrow. No offence intended. My appologies to those more learned than I. This guy , made me laugh.
Re: Guy's thank you so much for all the input. Based on your opinions I think I may drop down to the smaller cam. I dont have the specs handy but it was good for 1500-4500 rpm. The consenses seemed to be that the cam I wanted would need new valve springs, That is not in my current budget, plus I do not want to pull the heads right now in order to change said springs. I also am going to run that Ford intake since it is the same as the Edelbrock becouse it is laying in the garage doing nothing anyway. Thanks again I will let you know how it goes. Cary
Look at your heads. Are there any of these letters in the lower front corner of the head, next to the valve cover ? (S, T, P, or GT) If there's not, remove the valve cover and look and see what the rockers look like. Are they stamped steel, held down with a 1/2" headed bolt ? Or is there a stud and nut holding down a cast iron rocker ? If you truly have the stock pistons and heads, then you can move up to as big a cam as a Comp Cams 268H and still use the stock springs. This cam also works with the stock comp ratio (from 8 to 9.5 to 1) And you don't have to pull the heads to change the springs, these can be changed on the motor, with a few special tools (that can be rented or bought) Mainly just an air compressor and a valve spring removal tool. (plus attention to detail in seating the valve locks in the retainers)
I'm running a Crane H-272-2 with stock springs in an otherwise stock 85 302 non roller block with the 85 heads. Lift is 484 and 512, RPM range 1800 -5400 with a stock converter. It has a nice lope and seems to make good power, but I haven't taken it to the strip yet. Something in that range works good for a multi purpose engine. I don't know if they are available new anymore unless somebody has one in stock since Crane went belly up and was bought out.
