351 Port Size
 

I replaced an exhaust manifold on my 1992 F-150 5.8 a couple of weeks ago and noticed that the exhaust ports (and I assume the intake ports as well) are extremely small. I always thought this engine ran out of steam really early in the RPM band, and now I know why. The ports seem freakishly small. I can't imagine ever being able to make any kind of power using these heads.

Not that I'll ever modify the truck from stock, but what do you that modify these engines use for heads? From what I can see, and head swap must be the foundation of any performance build for these engines.

If I ever run into head issues with this engine, I'll be on the hunt for something better than a direct replacement for these bricks.

Just wondering what everyone does.

Thanks,

JD

Yes the heads are WAY too small for this motor, but the stock cam is a TQ grind and the 5.8 intake becomes restrictive pretty early too, so even with an upgraded cam the motor runs out of steam at around 4500rpm. The heads are one of the major reasons why it produces such low power numbers, but larger heads are of no use without a larger volume intake and higher capacity fuel system(injectors, pump), and then to make all that cooperate the computer needs to be upgraded and/or reprogrammed, so this isn't exactly a simple change. I have most of the parts collected to do this with my 5.8, the cam has already been upgraded, I have Dart Iron Eagle heads that flow about double what the stock E7TEs do, I have a Typhoon intake system, 24lb injectors, a mass air EFI system and a tuner. All totaled there is $3000+ in it so far not counting the basic engine and I still need a throttlebody and some other small parts to make it work, but when it's done it should make about 350hp.

bout to port and polish mine. they are extra on the garage floor so im not out anything. we'll see if there's much improvement.

Thanks for the feedback on the heads. I'm glad to hear I don't still have issues with my engine. I just spent a few weeks and a few bucks correcting all the drivability issues on my truck, so I'm happy (I guess) to hear "that's just the way they are". I just can't believe how early in the RPM's it starts to lay down. I can readily see that it would take re-vamping the entire intake and exhaust side to get flow and horsepower.

I fool with Thunderbird Super Coupes, and was amazed at how much better the heads are on their 3.8L V-6 than on my big 'ol 5.8! Those heads look like they can make decent power, and they do for the size of engine. But, I guess with a blower, they need to handle more airflow.

Conanski, it definately sounds like you're on the right track to making power with your 351. You seem to have all the right pieces in place. I'm sure it will be a "night and day" difference.

mean green 91, good luck with your porting project. You're right, I don't think it will hurt anything. At least you can add better parts to the upstream and downstream sides if needed once the heads are done.

Thanks!

JD

well i already have some shorty headers (not the best i know but the price, free, was right) and they make a noticeable difference just themselves. the heads would im sure make some more help but the 2.5" into 2.5" single has to just kill it.

These motors were always heavily restricted from the factory to meet emissions and noise restrictions, but because of that there are lots of ways to get a little bit more power here and there in incremental steps, you don't necessarally have to go whole hog and replace the complete top end. Despite the size of the heads they do flow enough for about 275hp and the stock EFI system will support that without any mods. And getting to that power level which is quite a jump from stock and very noticable by the seat-o-the-pants dyno simply involves opening the valves more and removing the gases from the engine. Depending what version of this engine you're dealing with you could add 1.7 rockers or replace the cam, and all of the stock exhaust is restrictive so replacing any part of it pays dividends. The timing can also be advanced more than stock too, and high voltage ignition parts will also work better. I had my 5.8 modified to this level and it was definitely much more fun to drive, it really pushed the truck around with authority.

275 would be perfect. i'm planning on port and polish and the 1.7 rockers. i have the ho coil, i just need the wires and cap. from what i understand you just use autolites and gap em to 55 then set the timing to about 14? from there i just need a decent exhaust and i should be good to go. id like to do maf conversion but i dont know if its even necessary with 275 hp. does the torque curve stay low with all this stuff? i like torque

i need to keep it emissions legal so the exhaust might be tricky