Hey everyone! I’ve got a ‘95 F-150 351w, and id like to add a little extra horsepower by adding some GT40 heads. I’m looking to go to the junkyard to see if I can find some, any idea what models these heads came on? Will they bolt right on to my stock 351? And also, if I come across a vehicle that’s got these heads, is there anything else I should take from it, like an intake, for my truck? Thanks a lot guys!

 

GT40 heads are a nice upgrade from the E7's but they are not really necessary. The stock E7s you have now will support as much power as you can make with the stock injectors and computer. Your best gains on the truck roller 5.8 while staying within the limits will be in replacing the whole exhaust, replacing the intake manifold, and maybe throwing in some roller rockers. If you want to replace the heads you can throw some GT40's on there and it won't hurt. Everything mentioned can be done with the engine in the truck. Most of the upgrades worth doing are not going to be "cheap" for a lot of folks, and you will never get your money back. I think you should focus on getting what you have running right before you start throwing mods at it.

 

Thanks a lot, I appreciate the insight. And definitely, it’s hard not to think about and plan for the better part of the project, haha, but yes, I’ve got to focus on it running right first. Thanks again.

 

GT40 heads and an intake based around the 5.0 truck intake design are what all of these 5.8 motors should have come with IMO, there wasn't enough of a difference between these two engines from the factory and all the "289 parts" they used really hold it back.
If you want a set of these heads you have to find a '96-97.5 Explorer, a Gen1 Lightning, or one of the super rare 5.0 Cobra Mustangs. Later Explorers used the GT40p head which actually performs slightly better but requires special headers or the stock manifolds but those limit their potential. If you find a lightning the intake(both upper and lower) would be worth grabbing too but none of 5.0 versions will fit a 5.8.

If you just put GT40 heads on your truck motor that will add some power but not as much as it should, the exhaust and intake need upgrades to get the most from them. The exhaust is easy just take it all off and replace it with just about anything aftermarket and include at least shorty headers. The 5.8 truck intake isn't the best or worst thing in the world but the lower portion is definitely the bottleneck, if you have it off to do the heads port the blazes out of it and open up the exits to match the heads as much as possible.

The last piece that will really wake it up is a cam change, something like the Comp 35-349-8 would complete the package and make it a solid 300+ hp motor, this last part gets complicated and expensive though as it will exceed the limits of the factory fuel supply components requiring upgrades to those parts and the EFI computer at the same time.

 

Might have to drill out the head bolts for the 1/2" size for the 5.8. If the heads came from the 5.0, they used 7/16" head bolts.

 

Hey conanski, just want to say thanks a lot, I know you’ve really been putting in some helpful input in some of my other threads. I just took the Gt40 heads to the machine shop to get them inspected, magnafluxed, and have the head bolt ports drilled out to fit the 351w.

I’d really like to stay around no more than $400 (budget $ for right now), and I am debating on what’s more important, 1.7 rockers, shorty headers, or trying to find a cheaper intake manifold.

Any guidance? I wanted to get the most done since my top end is already apart, but I just don’t have too much dough to spend for right now. I do still need to buy some replacement lifters which are going to run at least $120 or so. Thanks in advance!!

 

And I’m sorry, but what do you mean by porting the blazes? I asked the machine shop guy and he said it’d cost quite a bit to port the heads. Do you mean porting the lower intake?

 

Hey guys, I don’t have the tools to do any porting (yet), but my machinist said he’d port both intakes for $250 on the high side. Is that gonna help the GT40s and make a noticeable difference? Thanks!

 

Both intakes? You mean upper and lower? The lower is the bottleneck so have him spend all his time on that, there really isn't much that can be done with the upper.

 

Okay, do you think I should even bring the upper one in to him? Or just the bottom? Thanks

 

Don't bother unless he specifically asks for it. Extrudehone is the only way to do anything with this upper but it's not worth the cost and it doesn't have any glaring bottlenecks anyway. The lower on the other hand is nothing but bottlenecks.

 

okay thanks a lot man, he quoted me $150 to port the lower intake. Gonna drop it off tomorrow, I appreciate it, saving me a couple bucks for my budget build.

 

Hey Conanski, when I install my GT40 heads, obviously the thermactor tube won’t be hooked up to them because the heads don’t have the ports. Can I just leave the tube hanging there disconnected or what do you recommend? I know about smog deleting, but I’d rather not at this moment if I don’t have to, want to stay on a clean slate with emissions. Thanks

 

Air injection is for the cat. If you're using the factory cat or a factory-type replacement, it needs air injection. This allows the cat to function properly. Without air injection, the catalyst reduction reaction in the cat won't be very efficient and the end result will be a plugged cat.

However, catalytic converter tech has improved significantly since the 80s (when these trucks were designed) and modern cats generally don't need air injection. So if you've got a modern replacement cat installed that is specifically designed to not need air injection, then you can leave the air injection disconnected. Exactly what is legal here varies by state (which is why certain replacement cats are legal in some states but not others), so be careful to follow the rules for your state.
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thanks for the information. What about the guys that do AIR/smog deletes? Do they have to buy new cats or can they just run stock?