SUPRIZE SUPRIZE !!! a little confuzed
 

i bought a 1966 Mustang Fastback 3 years ago. it was a 19 yr old kid who owned it, his parents had the whole car completely redone(paint-interior-suspension-gas tank) everything including being told it was a 302 including all new 302 emblems. i just finished tonight tearing the engine down by pulling the manifold and heads off to upgrade the cam to a roller cam and redo the heads. i just decoded all the numbers off the block and heads because i also pulled the starter off so i could see what year 302 it was. its a 1966 289!!!! a little suprised. i am wondering does anybody know what the performance of these heads are???? and what exactly needs to be done to the heads to add some performance for my new roller cam set-up. i am also going to have to by new emblems for a 289 lol.:icon_chickendance:

Well, on the plus side you apparently have the correct block for that car. Get a set of heads from a V-8 Explorer or a set of '69 351W heads if you want it to look stock.

Why are you surprised it was a 289?...302s didn't hit the scene until midway through the 1968 production. had it been a 302 someone would have swapped engines at some point. most people here say 289 heads suck and by the time you are done machining them to not suck, you have spent almost as much as a new pair of aftermarket heads would cost.

nothing can be done to these heads??? port matching? better springs? not looking to race just bump it over stock.

HELLO !! as in my original post i stated that i was told a 302 was in the car when i bought it! thats why the suprise of the 289.

the exhaust ports are the weak link in the heads, search around and you will find pics and info on porting your exhaust ports for better flow

You can improve the performance of stock heads. Like Silverblade mentioned, you can gasket-match the exhaust ports for much improved flow. It'll help, but they still won't flow anywhere near as well as a set of aftermarket heads. A full port job will get them close, but IMO, unless you want it to look 100% stock, anything more than port-matching isn't worth the money you'll put into them.

If you can find a set of GT40 heads off of a 95-96 Exploder (not GT40P's from later models), those are a good economical upgrade. They're essentially small-chamber 351W heads. Again, not as good as aftermarket, but better than what you've got.

If you decide to run the 289 heads, you need to make sure you have the heads machined for threaded rocker studs. You'll also need some valve springs that can keep up with your roller cam.

The exhaust ports of the 66 heads have the dreaded 'emissions hump' in them. So it will take a fair amount of porting to clean them up.

Your block can't take standard roller lifters because the bores are too short.You didn't mention if you got the short lifters.
You can get expensive, over $400, short rollers though.

If I am not mistaken, wouldn't a 302 crank make it a 302? Maybe it's bored out like .060 over? Either way, if your not happy with the seat of the pants feel I would start with an entirely different motor. Save this one for the 'all original guys' and bolt in a completely different motor from air cleaner to oil pan.

Dont do crap to the existing heads unless you have to. your best bet is to get a new set of AFR or trick Flow heads.

I kept me stock heads and worked them over. port, polish, screw in studs, guide plates, valve springs, and roller rockers. It made a difference but i have had a ton of trouble with them. Just get new aftermarket heads and do it correctly.

Learn from others mistakes.