Does anyone know if i need to do any modifications to put GT40P heads on my 85 351w? I thought about putting cleveland heads on it but i know you have to rerought the cooling exit.

 

To bolt them on you do not have to make any modifications. However, to bolt the exhaust manifolds or headers on you have a problem as, from what I've read, the spark plugs were moved such that the wire will be against the header/manifold unless you use a short spark plug and a 90 degree boot, and even then it is very close so you may have ignition problems. I'm told there are headers available for our trucks with that head, but I've not been able to find them with a quick search.

But, your problems won't stop there. Assuming your 85 351W has the same heads on it that my 85 351W did, D8OE's, you'll be going from 69 cc combustion chambers to 59 cc ones. That'll take your compression ratio from ~8.5:1 to 9.26:1. And, from what the experts on here have told me, since you won't have any "quench" area your chances of getting it to run on 87 octane gas are nil and it may well not even like high test.

So, you'll have to retard the ignition timing to get it to run properly. How much I don't know, but maybe not so much that it will hurt your power. On the other hand, it may kill all the advantage you'll get from the added compression ratio. However, you will have significantly better flow on both intake and exhaust, although if you don't have an after market intake and headers you may not be able to take advantage of the flow.

IMO you'd be far better off with F1ZE-AA GT40 heads from a 96/97 Explorer. They flow well, don't have the relocated spark plug, and their 64.5 cc combustion chamber should give you a compression ratio of 8.8:1, which I believe will run nicely on 87 octane gas in that engine.

(Finally, someone asked a question I've thought about!)

 

I wouldn't bother with P heads due to the goofy spark plug angle. No point in doing a Clevor anymore since you'd spend as much as getting a good set of aftermarket heads. It's a small block, heads are cheap. Just put a set of AFR or Trick Flow heads on it, cam to match what you want to do and an intake and carb along with headers and you'll be golden. Good time to pull the bottom end apart and check/freshen up if necessary.