302Ci Horsepower

Trent K. · Oct 22, 2019

So if I have a 1977 302 going into my 67 mustang how much horsepower would I be getting, just a guess, from the specs list below?

Block: Stock
Rotating assembly: Stock
Heads: Stock
Cam: Some sort of ford performance cam from the '80s or late '70s
Intake: Edelbrock performer 289 with 1/2 inch spacer
Carb: Holley 650cfm
Headers: Tri-Y long tube
Exhaust system: Dual pipes with chambered or glass pack mufflers

01HellionGT · Oct 25, 2019

77 302? out of what? I'm guessing its s aftermarket 4bbl carb n intake with stock 2bbl heads? auto or stick? Some unknown performance cam from unknown yearS (between 1980 to 1979 - bout 20 year difference) don't help. Horse power wise, especially from a 77? not much. 135 to 140 tops fly wheel for stock. Then you can go from there. All together just guessing n giving the benefit of the doubt 125 rwh stock on a 77 Mustang, then with the slight power parts 155/65 (maybe 175 if you're lucky) to the wheels? Take it to a dyno and let them do their work, this is just guessing.
Had one 70 Grande and a 69 with a 302 2bbl, no smog restriction or built for saving gas - just plain jane 302 2bbl. Put a 4bbl vac sec with an Edelbrock torker intake n nothing else and it did wake it up, just to no great horse power levels. Fun to drive, just no where near 12 sec quarter mile. Looking if maybe at mid 14's.

rustaddict · Nov 24, 2019

Trent, Im not giving you a hard time but I am gonna be honest. Your 77 302 will have that 70's era low compression and the heads are gonna be worthless as far as performance is concerned. Really anything you bolt on to the rest of the engine is gonna be held back by the stock heads. I get the idea from your other threads that budget is an issue and it is with most of us. If you want to pick the performance up, I would try to find some GT40 or GT40P heads from an Explorer and add them to the other things you describe.

rbohm · Nov 24, 2019

without the cam specs, its hard to say what kind of power your engine is going to make. however an educated guess would be something like 175 with the average aftermarket cam and intake. but that is about it.

Trent K. · Nov 25, 2019

rustaddict said:
Trent, Im not giving you a hard time but I am gonna be honest. Your 77 302 will have that 70's era low compression and the heads are gonna be worthless as far as performance is concerned. Really anything you bolt on to the rest of the engine is gonna be held back by the stock heads. I get the idea from your other threads that budget is an issue and it is with most of us. If you want to pick the performance up, I would try to find some GT40 or GT40P heads from an Explorer and add them to the other things you describe.

Do you think the factory 289 heads would help me any more, power wise? Or are the stock heads just going to be worthless no matter what?

rbohm · Nov 25, 2019

Trent K. said:
Do you think the factory 289 heads would help me any more, power wise? Or are the stock heads just going to be worthless no matter what?

the stock heads are limiting factor here. you can get only so much flow out of the stockers. you can pick up between 20-50 hp by porting the stock heads though.

Trent K. · Nov 26, 2019

rbohm said:
the stock heads are limiting factor here. you can get only so much flow out of the stockers. you can pick up between 20-50 hp by porting the stock heads though.

Someone told me to take a dremel to the exhaust ports on the factory heads and that would increase power. If I were to do this which set of heads should I do it to? The 289 heads have a 49.2cc combustion chamber and about the same flow as the 302 heads which have either a 73 or a 79cc combustion chamber. I am thinking since the engine will be naturally aspirated that I want smaller combustion chambers, correct?

rbohm · Nov 26, 2019

Trent K. said:
Someone told me to take a dremel to the exhaust ports on the factory heads and that would increase power. If I were to do this which set of heads should I do it to? The 289 heads have a 49.2cc combustion chamber and about the same flow as the 302 heads which have either a 73 or a 79cc combustion chamber. I am thinking since the engine will be naturally aspirated that I want smaller combustion chambers, correct?

i dont know of any stock 289 heads that have 49cc chambers, most have between 53-56cc. measure yours to be sure. smaller chambers are better because you get a better compression ratio.

as for porting, yes you can pick up some power by opening up the ports. you want to match the port opening with the gasket on both the intake and the exhaust. you dont want to try and open the ports up all they way down though as you may run into the water jacket and ruin the heads. but you can open up the ports and blend back and 3/4" or so into the port without issue, and use the dremel to clean up the rest of the port to improve flow. there are articles and videos around to show you how this is done, though you will have to find them.

with a decent job you can pick up 25-30hp with about 8 or so hours of work for basically the cost of the dremel and some dutting heads and some sanding rolls.

a few things here;

1: safety. wear some breathing protection, since you are grinding on cast iron and that will damage your lungs to breath in that dust. surgical masks do a good job.

2: take your time. remember that the port walls get thinner the closer to the valves you get. to be careful. if oyu do break through the port wall, dont panic. often times you can use some high temp epoxy to seal the breach.

3: let the tool do the work, dont force any thing to happen. you will only break tools.

4: do not polish the ports, engines make better power with a slightly rough port wall so the fuel mixes better with the air.

Trent K. · Nov 26, 2019

rbohm said:
i dont know of any stock 289 heads that have 49cc chambers, most have between 53-56cc. measure yours to be sure. smaller chambers are better because you get a better compression ratio.

as for porting, yes you can pick up some power by opening up the ports. you want to match the port opening with the gasket on both the intake and the exhaust. you dont want to try and open the ports up all they way down though as you may run into the water jacket and ruin the heads. but you can open up the ports and blend back and 3/4" or so into the port without issue, and use the dremel to clean up the rest of the port to improve flow. there are articles and videos around to show you how this is done, though you will have to find them.

with a decent job you can pick up 25-30hp with about 8 or so hours of work for basically the cost of the dremel and some dutting heads and some sanding rolls.

a few things here;

1: safety. wear some breathing protection, since you are grinding on cast iron and that will damage your lungs to breath in that dust. surgical masks do a good job.

2: take your time. remember that the port walls get thinner the closer to the valves you get. to be careful. if oyu do break through the port wall, dont panic. often times you can use some high temp epoxy to seal the breach.

3: let the tool do the work, dont force any thing to happen. you will only break tools.

4: do not polish the ports, engines make better power with a slightly rough port wall so the fuel mixes better with the air.

The casting number on the heads off of the 289 is C6OE, which means they have a 1.67 intake valve, a 1.45 exhaust valve and a 49.2cc combustion chamber. Not trying to seem rude or anything lol just letting ya know that those are the facts I've found on the heads. I believe that if I took a day or two to port them myself it would be worth it. I'm not looking for insane power I really just want to get to that 300 rwhp mark.

2Blue2 · Nov 26, 2019

Trent K. said:
just letting ya know that those are the facts I've found on the heads.

My book lists it as follows, but take it with a grain of salt. Ford has always had some castings with odd/wrong numbers as well as one offs.
C60E = 54.5cc,

The only head with 49.2cc was a 1963 hipo head casting

Mild porting and gasket matching is a good way to go on 289 heads

rbohm · Nov 26, 2019

the problem with accepting what is written about ford combustion chamber size is that often times they are wrong. so until you actually measure the chambers, you have no real idea what you have. heck it has been found that chamber volume varies not only from head to head, but cylinder to cylinder as well.

rustaddict · Nov 27, 2019

What was the CC volume on the 87-93 5.0 GT head ? people almost give those away sometimes. I would definitely use the 289 heads over the 70s 302 heads. Don't forget to check the deck for straightness and the valve guides for wear. If you have a way to get the valves out, I would polish off and casting flash or sharp edges in the bowl area too.

rbohm · Nov 27, 2019

rustaddict said:
What was the CC volume on the 87-93 5.0 GT head ? people almost give those away sometimes. I would definitely use the 289 heads over the 70s 302 heads. Don't forget to check the deck for straightness and the valve guides for wear. If you have a way to get the valves out, I would polish off and casting flash or sharp edges in the bowl area too.

a guy on another forum cc'ed his 87 heads and got 60.5 cc. the range seems to be 60-63cc

southcross2631 · Dec 14, 2019

Amateur porting can hurt power. That's why porter's get bucks for doing what they do. Any more than gasket matching and minor bowl blending should be left to the pros.
70's smog heads are worthless . Pick up some aluminum heads from Pro Maxx. For what you will have in some junk smog heads you can have some real heads that will outperform the old style heads and you don't have to deal with 50 year old castings.
I made 510 horsepower from a set of off the shelf CNC'd Promaxx heads with a set of .040 over flat tops and a solid roller cam . You don't need that much head ,but they do have less expensive quality heads.

bartl · Dec 16, 2019

My GROSS horsepower estimate (at the flywheel) would be 160-180 depending on the camshaft used. You have a few issues to overcome, the first being a piston with a large dish. Also, if the engine has been previously rebuilt and bored oversize the chances of having "destroked" pistons with a 1.585" compression height are large. That adds to the low compression and potential detonation aspect. The 3rd is the '77 cylinder head, with a 69cc combustion chamber. All things considered, you could, potentially, have a static compression ratio of 7.5 to 7.75 to 1, depending on the pistons installed. Factor #2 is the cylinder head design, which is very poor on the exhaust side. Moving along, any sort of "performance" camshaft, other than an "RV grind" is most likely going to kill low rpm torque. Sure, it might produce 15-20 more horsepower, but at a higher rpm. A 650 cfm carburetor on an otherwise stock-headed 302 is about 150 cfm too large and will result in a poor vacuum signal. A Summit M2008VS500 would be just about right.

With the '66 heads, you could do some mild work on the exhaust ports to remove the Thermactor "bump" and port-match to the exhaust manifolds/headers but, unless you've done so before, I'd find someone who has done this (successfully) and watch them do a couple ports before you take this on yourself. There are some additional tasks you can perform such as smoothing the valve guide bosses, removing some material from the "short side" radius of the port where it turns to exit the head, installing over-sized valves and so forth and with some aggressive work you CAN get a SBF iron head to flow close to that of an off-the shelf aluminum piece.

If you were going to consider using the '66 heads, I wouldn't do so without changing pistons to a Silv-O-Lite 3165HC, which will bring your static CR to around 9.75:1 and with decent flowing heads and a strong low-end cam will be quite snappy... capable of the 300 flywheel horsepower range.

302Ci Horsepower

Trent K.

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will be trying this sex one when I can find it

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302Ci Horsepower

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