I'm looking at rebuilding the 302 in my '86 bronco. It's got almost 300k miles on it, low on power, has a knock, leaks oil from everywhere, and is basically just living on borrowed time.

I'd like to rebuild it and get about 250 horsepower out of it. (300 would be awesome) it's just a truck. Weekend driver/ off road/ camping rig. Light towing from time to time.

My only ideas so far,
-bore it, as much as needed.
- bump compression up. Pistons/ deck height
-convert to roller cam. F303 maybe?

I'd try to find a set of GT40 or GT40P heads. Which ones are better?

Any input on what to do? I'm not very well versed on what's allowable with the EEC-IV control system. If I have to convert to aftermarket EFI then that opens the door to anything. And jumps the price up quite a bit.

 

Rebuild with pistons that produce 9-9.5:1 cr, use GT40 heads with the Comp cams 35-349-8, install a full exhaust with headers, add an adjustable FPR and electric pressure gauge to the fuel rail and put a wideband O2 in the drivers side header(stock sensor in passenger side). That is 300-320hp, use the wideband to monitor A/F ratios to see if it goes lean at higher rpms, and if it does bump fuel pressure up 5psi at a time until A/F ratios are good or you run out of fuel pump. If the fuel pump can't keep up(pressure begins to drop at high rpm) install a higher volume pump... a 155l/hr should do.. stock is 90-100l/hr if I'm not mistaken.

 

I've read that the GT40P heads are about the best factory small block heads that Ford ever made (Conanski may say differently), but they have an awkward spark plug angle that makes header fitment complicated, and spark plug changes difficult. Some guys just live with burning spark plug boots and frequent plug wire changes. On the upside, they're pretty easy to find. Back when I was looking, I found a half a dozen sets of GT40P heads locally. GT40 heads by comparison are 100% plug-N-play and use the same spark plug angles that Ford heads used for decades. By "plug-N-play", I mean that they will work with your existing exhaust or whatever headers you want to use. The downside is that they are much harder to find (at least they were back when I was looking), and you don't get much of a compression bump with them compared to the GT40P heads. If I recall correctly, my GT40 heads measured out at 65-66cc. Mine were early Explorer GT40 heads as they did not have thermactor ports.

I'm now working on a different truck and recently rebuilt a 5.0/302 for it. Having learned a few things from my first 302 build (with the GT40 heads) I decided to do something different this time and basically went with a stock 1996 F150 302. Stock E7 heads, and stock roller block bored out 0.040" (I think the block is an 88-89) and stock 1996 F4 roller cam. I think the stock 1996 F150 5.0 was somewhere in the 200-220HP range. My goal here was to have a 5.0 that worked as good as possible between 1500-3000 RPM. Having a 302 that performs its very best between 3000-5500 RPM is not much benefit to me.

Anyway, do lots of research (like you are) and you'll come up with the best options. Conanski is a subject matter expert, so you won't get much better advice.

I still believe that when it comes to trucks, the best performance enhancing thing you can do with the 302 is to replace it with a 351 LOL. And I say that as a guy that loves the 302. If that is not an option, then there's lots of things you can do with the 302. Just don't get carried away spending money to improve the HP at 5000 RPM if you don't plan on being up there.

 

I would find a good local machine shop and talk with them. It's not like they haven't rebuilt these for people before. Here's a old family friend that is one of the best shops around here.
Eastwoods Auto Machine - Homepage


You should be able to find something like them around you.

 

Good information so far. Keep it coming.

I have considered a 351 swap. That option is still on the table, but I don't necessarily need that much power in this bronco.

I already have a 3" exhaust on it from the Y pipe back. No cats. But I'd probably put short tubes on it if I build a good engine.

 

Remember most power gains from a 302 will be in the upper rpm range. With all your modifications you will have to wind it out to get all the power out of it. That is the advantage of a 351w, more power in the lower rpms. Or stroke the 302 to do the same thing. If you have a heavy Bronco with 4x4 and large tires, you need low end grunt to get it moving. If you stick with the 302, you might have to consider a gear change to take advantage of the higher rpm power it makes when modified.

 

Already has 4.56 on 33s. Lower than most people deem necessary but I think it's perfect.

 

Looks like you are ready as far as the driveline. How is it at a stoplight? Do you find yourself pressing on the brake a little harder than you should to keep it from moving? If you build a firebreather engine, the idle speed may need to be higher and would make holding it at a stoplight even worse. If you feel this might be a problem you might need a torque convertor with a little higher stall. I am assuming you have a automatic?

 

Definitely not looking to build a fire breather. Like I said, it's a pretty "basic use" vehicle other than Off-Road. It has plenty of torque down in low range. Low end is important, but mid-range is where it could really use the most improvement.

It was advertised at 180hp when it was new, and I doubt it makes more than 150 now. It's awfully slow. Even with the low gears. So 300 would be a night & day difference. And more than it needs.


I'm looking at the option of buying a separate engine, building it on a stand, and then swapping it out in a weekend. As to minimize downtime and still be able to use it to run parts around. What would be the "best" block to start with? Does it really matter?

 

Found a 1996 Explorer being parted out. Engine is said to run. Maybe I'll buy it and swap cams, stick it right in.

 

They are supposed to have the good factory heads correct? I keep hearing about sparkplug clearance problems if it has those heads with the angled plugs.

I am always leary of using aftermarket cams in a stock Ford engine. The stock engine valvetrain is not adjustable, so if the valvetrain does need some adjustment after the cam swap you are stuck sometimes and have to shim or buy different length pushrods.

 

Yeah. From what I've read, Up to 97 1/2 had the regular GT40 heads with straight plugs. 97-1/2 and newer had the GT40P heads with angled plugs.

 

The one way you can ID the early Explorer GT40 heads is that they had no thermactor ports. A few people have found out the hard way when buying GT40 heads for a vehicle that needs to have it's smog system intact and working. The only other ones will be from a Mustang GT...'93-'95 Cobra?...I forget which years had them, and also the first gen Lightnings.

I think the GT40P heads are quite good if you can find headers that will work with them. The stock header/manifolds from the Explorers are wild looking things, I can't imagine anybody wanting to use them, but maybe they are OK. There were companies that did make headers for the P heads...I think for Foxbody Mustangs, but last time I looked (couple years ago) they were no longer available.

 

I also read on another forum that factory compression on a '96 explorer was 9:1. If that's the case, I'm very much inclined to just degrease this engine, swap the cams, and stick it in.

I'm hopefully going to look at it tomorrow afternoon. And hopefully I can see/hear it run.

 

That engine actually has a really good cam from the factory by the way. That's what I'm running in mine.