OK, lets talk heads for a second...a while back I was gona sell a set of 66 model closed chamber 289 heads. Since then I rethunk (yeah I know) my plans and now I want to rebuild, and open these heads up.my .040 over 302 compression is 9.1. If I ported the exhaust side of the heads and gasket matched the heads and cleaned up the intake ports, my compression should come up to say at least 10 to1?? Also adding new valves and seats and beefer springs to run a bigger cam. I know aftermarket heads are the way to go but being on a shoestring budget, could this help my lil motor wake up a bit more...thinkin on a comp 278 magnum cam. I just bought a weiand stealth intake today and I have a new 600 edelbrock carb. Somewhere in my closet are the hooker headers that once graced the 302 in my red 73 mav. Any thoughts?? Jim
Jim, for street use, that should be a fine set-up. If it's not too much out of budget, you could have your machinist put bigger valves in the heads. You could clear out some material in the intake tunnels, but the exhaust ports are the most important. Ford made a Hi-Po 289, once upon a time, that was about what you will have (with a little hotter - solid cam) and it made 270 advertised HP. The ones in the Shelby's were more.
Just don't spend more than you could buy a set of aftermarket heads for! New valves/seats, and other services really add up. My Nephew spent $800.00 for used, cracked World Product heads, with worn out roller rockers, when the heads new with springs were only $800.00! You small block guys are lucky, my 460 heads were $1950.00, SB heads are lots cheaper.
heads well so far I been lucky, most of the parts I have gotten cheap, the new carb I traded stuff for, the intake was a deal, so right now I am doin pretty good. the heads will be the most expensive thing I do. I got the NEW cam lifter combo set at a swap meet near here for about half price.
Here's one thing to consider: What size are the combustion chambers on the heads you have on the engine now? You stated you have 9:1 now but with what size chambers? The early 289 heads have very small chambers and can really increase compression ratio. Also, you can't really run over 10:1 with an iron head on today's gasoline. The reason you see some better compression ratios on later model engines is due to aluminum heads. The aluminum dissipates heat better so there is less chance of detonation. I used a set of these heads years ago on an '85 302 HO engine and the compression ratio went from 9.4:1 up to 11.25:1 with no other changes. Something to consider. On the "bigger valve" issue....do not go larger than 1.88" on the intake valve or 1.55 on the exhaust valve unless you rework the chambers. Anything bigger with no work on the chambers will shroud the valves and ruin the flow path. A good mix is to use a 1.85" 351 Windsor intake valve and a 1.55" Chevrolet exhaust valve. I also have the measurements for porting the bowls and templates for the exhaust runners for the heads I used to do. Or I could do them for you if you'd like. However, like everyone else is telling you, price all this out before you do it. You could end up spending more on these than a good set of GT40 heads. Let me know and good luck! You small block guys are lucky, my 460 heads were $1950.00, SB heads are lots cheaper. Yes they are......the Blue Thunder heads we did for my dad's 512" engine ended up at $3300.
heads When I bought the car the last owner had bored the block .040 over. he is the one that told me about the compression. He is a good friend and I saw no reason not to believe him. As far as the size of the chambers they are the stock 72 302 heads, so you got me. thats why I am asking ??? Thats why I wanted yalls imput. If and when I pull the motor down then I'll know all this. I just needed to know if it is a feeseble build. the 66 closed chamber heads do have very small chambers...
72 heads.....wow. If that thing has 9:1 with those heads you'll end up with around 11.5:1 compression with the 289 heads. If you can find out what piston he used I can tell you what the compression is now and what it will be with the 289 heads.
Shadowmaster; I have a stock '74 engine, and have '72 heads. Can you calculate the compression ratio of this combo? Also, if I put on the '66 heads, what would it be? Just some options, but need to know. Thanks, Earl
With the .040 overbore you'll end up with anywhere from 10.5:1 to 10.8:1 compression. This will depend on piston-deck clearance, compressed thickness of the head gasket and duration/centerline of the camshaft you're using. Personally, I'd open the chambers up a bit.
i have a extreme energy 484 lift cam.... i will be getting the 268h 512 cam... i have 3 friends that have it in their 289-302 and they love it... the stock 302 heads have a 56cc chamber (well at least mine is that size) i have heard that a porting job on the stock heads will get ya an increase of 20 HP..... i will do mine when i change the cam over... my pistons are 9.5:1 flat top hyper pistons....the shop i got them from ordered them so i guess i have to take their word for it (since i used them last they disappointed me so i wont be using them again) so i dont know for sure.... i also bored mine .040" over....and i think it runs a little hot because of it....
Earl, The '72 and '74 heads have the same combustion chamber size so you're at stock. I believe (don't have all my reference material handy here at work) that you're at 8.8:1 compression. With a standard bore and the early 289 heads you would be 10.1:1 up to 10.4:1 depending on clearances and the head gasket.
i'm a little confused. you talk about porting the intake & exhaust ports & it will raise comp ratio to 10:1. nothing you do to the ports & passages, or gasket matching for that matter will increase or decrease compression ratio. it only affects the flow of the heads. head gasket thickness, grinding on chambers, decking the block or heads, sinking or raising the valves on the seats, or boring and/or stroking will affect the comp ratio. obviously different heads would change these things, too. mid 70's 302s also had the piston deeper in the bore which doesnt help build the ratio. installing the cam advanced in relation to the crank will help build cylinder pressure. using a pre 72 (i think, or 73) timing set or a racing timing set will also help cylinder pressure. ford retarded the crank gear slots in 1972 or 73 to help with emissions. degreeing in the cam will also insure that the cam is installed where you want it. while manufacturers have gotten better, sometimes you still get a cam that wasnt ground quite right in relation to the pin on the front for the cam sprocket.
ShadowMaster; thanks so much for the information. Might be a good trade up, if I had the cam and converter to go with it. I have them, so I might port them out and clean them up. Thanks again, Earl
