Have a 73 Comet with it's original 302 motor in it, what's the comp ratio of this motor and what heads and what's there cc's , have a set of 68 4v heads that are 53 CC's and closed chamber to bump up my comp ratio I want to put on the motor, any idea what the comp ratio would roughly be with these heads, heads have been ported and freshened up
I have read where the compression ratio is 8:1 and 58 cc heads were used on a 73. Some info shows 138 hp and some shows 140 hp so I am not sure how accurate that info is. I recently had a set of 53 cc 289 heads refreshed and the shop said I should see about .5 to 1 point gain. I think the 73 302s had the deck height increased also so the compression drop from 71 was not just because of the heads.
The main reason HP figures dropped after '71 was switch from gross to net hp, knocked aprox 25-30% from figures. Gross rating is engine on dyno with open headers, optimum tune etc. Net HP is as installed in vehicle, operating accessories, water pump, alt etc. Chances the '71 engine made 210Hp through asthmatic, single exhaust are zero & none. On a good day, maybe 155-160Hp. Lower compression, retarded timing, lean carbs and so on were responsible for another 20-25HP loss on '72-up models.
Things must have gotten progressively worse into the mid and late seventies when all the smog components were added. My girlfriend (wife now) bought a new 74 Comet with 302 auto. At the time it ran nothing like my 71 Grabber 302 3 speed. After she wrecked the Comet, she bought a 1975 Mustang ii with a 302 auto. The performance of that car was anemic to say the least. In 79 I bought a new Ford F100 with a 302 3 speed on the column. Not very impressive either.
The period of '72 through '81 were dark ages for performance. That and ugly ass snow plow bumpers are reasons I bought my '69 in March '73. Ford breathed some life into hot rodding again with the '82 Mustang GT, from there the races were on.
To my knowledge the deck height of the 302 has never changed, always be 8.2". It is possible the compression height of the piston was reduced to lower compression. Chrysler did this to the 440 for that reason, the pistons stopped .150 short of the deck at TDC.
The low compression engines had I believe a .030 or so taller deck. Nothing that could not be handled in decking block. Somewhere Ford stopped leaving extra material and went with large combustion chamber heads.
According to George Reid in his book about Ford v-8s the deck height for the 1973-76 302 was increased from 8.206" to 8.229". The heads on my 73 are D20Es and have the 58 cc combustion chambers. I do not think installing the 289 C6AE heads on my car are going to help that much but I have gone too far to turn back now. One chart I found shows a cr increase from 8:1 to 8.4:1. BTW removing the heads with the engine still in the car has been an adventure to say the least.
Pulling a motor just to swap heads lots of extra work. If you decide to pull motor great time to refreshen it up. Do a compression test first. Rear main seals, freeze plugs, timing chain, camshaft and so on.
While clearance with the shock towers on our cars is always an issue, swapping heads with the engine in place is far less work than pulling the engine. The biggest problem I had was the head bolts. I used every possible combo I had with my sockets and extensions. At this time my engine is o.k., cylinders looked fine and oil valley clean so it is not the time for a full refresh. At some point I may pull the engine but for now the heads are swapped. Still have to button everything up before a test drive.
