Can anyone tell me the most power and torque I can pull out of my stock engine? I have a 96 f250 with a 351W, I did a header back exhaust (no cat), I removed all smog/EGR equipment and dropped in a K&N filter. I know that the speed density FI is pretty limited and I am pretty sure that Im at the end of its limits.

I just want to know where I stand before I convert to mass air.

 

You might have picked up 5-10 hp. But might have lost that too as the computer is now reading things into the performance and trying to compensate for those readings.

 

I read somewhere that by opening up the exhaust and intake it will be about 300hp and 400ft.lb. but I dont remember and I wanted to see if anyone has done all of that and dyno'd or anything

 

I did a GT40 head swap, along with Cobra roller rockers, plus a completely new full 3" exhaust system with shorty headers on my 96 E150's 351 and I'm 90% certain it doesn't put out those numbers, nor near it. It does have more power and better mileage, but it doesn't put out 300 hp/400 tq

 

I have to agree, no 300 HP! The '95 Mustang Cobra R which used a 351 was rated at 300 HP but only 360-365 tq. It used the Cobra/Lighting GT40 intake. But the cam in that engine was different then used in the truck 351 so you would have to change cams. The good thing is that you have a roller cam or at least a roller ready block so swapping to a bigger roller cam should be easy.
With long tube headers, a proper cam, GT40 heads, and the good intake manifold you can make those numbers. The stock truck 351 intake will never allow you to achieve that power level however.

 

The only info I have on the GT40 Cobra R motor lists it as having the HO roller, if that's so the power numbers aren't that much different than having the F4TE truck cam. Certainly not 50 hp worth over the Lightning 351.

 

Thanks for the info guys. Aren't these trucks rated at like 250hp and like 300ftlb stock? Im not sure, thats just hear/say. A very knowledgeable friend/engine builder told me not to bother with a cam until I convert to mass air. He said that I would loose a lot of drivability with any cam no matter how mild with the speed density fi.

 

You don't have mass air on your 96 ? The cam you've got now is a pretty decent cam, just needs 1.7 rockers on it. The specs with 1.7's are this: 256/266 advertised duration, .445/.473 lift, 116 LSA.

 

You can run a cam with SD, I had comps 31-255-5 I believe in my 89 5.0 with ported heads and rockers and lost no drive ability and gained some good power

 

The numbers for the Lightning motor were 240hp/340 tq. Yours would be 210/325

 

Its an F250 so no not likely it does. The Cobra 351 made peak HP at only 4800rpm and wore the same old GT40 heads as the Lightning so it's not likely it has a real big cam.. the stock Mustang HO grind is a good possibility as a little more intake duration is all it would take.

The relatively low peak TQ numbers all factory engines seem to get is no doubt due to the stock exhaust systems and the manifolds or "headers" they wear, a proper set of longtubes will produce much better results in this regard.

 

Well I'm not too sure about any of the published numbers for the EFI motors, especially the 351's. I got those numbers from my Chiltons Ford van manual. And the vans never had a lightning engine option. Then take into account the cam change in the roller 351's from the flat tappet engines, then too the two different roller 351's in 96-97 (SD and Mass Air) Same deal with the cam change from 93 to 94 with the 5.0 pickup van 5.0, the numbers stayed the same. I figured I'd post that just to give him some idea of where he was at.

 

There were no internal engine changes made when these trucks got MAF in '95 or OBD2 in '96, changes were in the EFI control systems only.


But in that case the later cam is much larger and I'm sure I'm not the only one that has owned or driven several of these trucks over the years and knows that the later motors definitely made more power, so yeah can't trust the printed specs so much.

 

No, nothing internally, but there was a difference in smog equipment (some like my 96 E150 came with no smog pump) that could possibly change the power output. The 97 F250 I pulled a roller 351 out of had a dual exhaust or at least the forward part of the system was (the rear part was missing) Definitely different than the Y pipe that my van came with.

 

Thanks for all the info guys. I'm actually working on a set of headers and a custom Y pipe.
And no its not mass air. I'm guessing its an early '96 because its OBD1 also.

So from what im reading, all I need to do is slap on some 1.7 rockers and it will breath better...... Is there any extra pro-cations I need to take doing that? (ie; piston to valve contact)