I enjoy mechanics and trucks, but I'm also a realist. I am not a mechanical engineer. I know the basics on how everything works and will be attempting to build my own new rebuilt motor. I know how a camshaft works, and I know what it does, but I am not well-read enough to understand what lift and duration I need for my application.

I dropped the heads off at the machine shop today, so I'm gathering parts and going to be building as my budget and time allows. I need help picking out a cam, and here's my situation:

I have GT40 heads off a 93 Mustang Cobra. I have instructed the machine shop to keep them fairly stock. They are planing them, making sure all the springs are fine, and making sure all the valve nonsense is functioning normally. Basically, I will be getting back reconditioned heads.

When I get around to pulling the block, I will also take it to the machine shop. I will not be changing the stroke and will bore it over as little as possible. Long story short, it's going to stay a 351 (or maybe a little more depending on the bore.)

I want to retain the stock fuel injection system. I don't know all of the constraints of the system, and that's part of the reason I am asking for help. I don't want to retune the truck. It's a 1994, which I have been told is a roller block. I was also told it's a hydraulic roller, but I can't attest to that (maybe another question someone can confirm).

Anyway, I just want something that will work with what my setup will be, and not do any (major) fuel system changes, and have a smooth enough idle. I want as much power as I can get out of this puppy but don't want to push it.

Ryan

on edit: Does anyone know what the stock lbs/hour rating the injectors were on the 351 in 1994? How much power are they good for?

Im in the same boat as you on this bro. but i heard if you call the guys at comp cams they can help you figure the best approach with some basic info.

the stock injectors are 19# injectors. mine did ok when i did my engine.. but struggled at the high end.. badly..

Hydrualic roller cam setup is what you have.

If 19 is stock, do you figure I can get away with the 21 pound, or should I jump to the 24 pound?

Ryan

O'Rattlecan said:

If 19 is stock, do you figure I can get away with the 21 pound, or should I jump to the 24 pound?

Ryan

Click to expand...

don't you have Mass Air Flow?

No, it's speed density

Ryan

being speed density when you up the poundage on the injectors the computer wont help at all.

if im not mistaken the computer will recognize its running rich and shorten the pulses on the injectors relegating it back to the equivalent of 19# injectors..

I found a cool site to help calc injector size.

http://mustangpartstech.com/FuelInjectorMath.html

Estimated (absolute maximum) of 350 horsepower (will end up being lower, realistically)

(350hp x .5 bsfc) x (8 injectors x 80% load) = 27.34 lb injectors

That's a worse case scenario, assuming I get more HP than I will, and with only an 80% load rating. More realistically it will look like:

(325hp x .5 bsfc) x (8 injectors x 80% load) = 25.39 lb injectors

99% of the time, that will be 'enough' injector. If I decide to go full throttle, there should be enough headroom left on the injector to absorb more load and be in spec.

I'll look into the crap to swap to mass air flow after I get this thing built.

Ryan

a mass air flow swap aint bad actually..

im going to do one on the Flareside when this 302 goes down..

cause the plan is that it'll either get a 331 or 347 stroker. probably 331 for the reliability.

Check out Iskys 371257 cam. Theres a Desktop Dyno graph over on FSB that indicates a real nice torque curve with this cam.

I wouldn`t worry about the injectors. If you`re keeping the stock intake and not going forced induction, they wont be slowing you down.

I don't want to choke it. My calcs say that ideally I would want a 24 for full throttle if I managed to get a motor to put out 325hp. I would say my GT40 heads and a nice cam could probably pull that off.

Ryan

it will as long as its a good cam..

custom ground cam is the way to go..

along with some headers.

Ryan....you could always give TMI a call as well, he is also well versed in the W's.

Are you changing the intake? That will be your biggest cork. 325 hp with just GT40 heads and a cam, regardless of how good it is, is optimistic at best.

Consider how Lightnings were equipped and what they were rated at.

And just to throw this out there, in 99 Hot Rod built a junkyard jewel engine with GT40ps, Performer RPM intake with a 750, and a Comp Extreme Energy cam with 224/230 @.050, and made 330 hp.

Not trying to be a spoiler, just saying.

O'Rattlecan said:

I found a cool site to help calc injector size.

http://mustangpartstech.com/FuelInjectorMath.html

Estimated (absolute maximum) of 350 horsepower (will end up being lower, realistically)

(350hp x .5 bsfc) x (8 injectors x 80% load) = 27.34 lb injectors

That's a worse case scenario, assuming I get more HP than I will, and with only an 80% load rating. More realistically it will look like:

(325hp x .5 bsfc) x (8 injectors x 80% load) = 25.39 lb injectors

99% of the time, that will be 'enough' injector. If I decide to go full throttle, there should be enough headroom left on the injector to absorb more load and be in spec.

I'll look into the crap to swap to mass air flow after I get this thing built.

Ryan

Click to expand...

See how easy a carb looks now?

primetime said:

Are you changing the intake? That will be your biggest cork. 325 hp with just GT40 heads and a cam, regardless of how good it is, is optimistic at best.

Consider how Lightnings were equipped and what they were rated at.

And just to throw this out there, in 99 Hot Rod built a junkyard jewel engine with GT40ps, Performer RPM intake with a 750, and a Comp Extreme Energy cam with 224/230 @.050, and made 330 hp.

Not trying to be a spoiler, just saying.

Click to expand...

not actually if you have the correct pieces all together and a GOOD cam. you can do just bout anything.

351W in my other Flareside i had put down 321 HP and 394 ft. lbs of tq at the wheels. on speed density, custom ground cam, GT40 heads, shorty headers, hot tuneup, new injectors, and stock intake.

5.0Flareside said:

not actually if you have the correct pieces all together and a GOOD cam. you can do just bout anything.

351W in my other Flareside i had put down 321 HP and 394 ft. lbs of tq at the wheels. on speed density, custom ground cam, GT40 heads, shorty headers, hot tuneup, new injectors, and stock intake.

Click to expand...

Any details on the tune? What were the cam specs? Got a dyno sheet?

primetime said:

Any details on the tune? What were the cam specs? Got a dyno sheet?

Click to expand...

got the came from a buddy. cam card went with truck when sold it. it'll be later tonight before I can see if I can find the scan of the dyno sheet.

it was not tuned.

Should I get stock valve springs for the GT40 heads?

Ryan

no...... remember mine Broke 200 miles after stock rebuild on heads. cause of the cam