Fox351

Will I need to clearence the pistons if I use a stock head with an F-303 cam??? Sorry if this seems like a dumb question a buddy of mine has a b-303 and wants more lopey sound so he asked me about it and I said I would ask you guys.

FoxGT

What year engine?

I'm running the x303 with stock pistons & stock heads (for the most part) in my '89. I've helped put an x303 in a '91 aswell with no problems. By all means I should upgrade my rockers & springs, but haven't yet. So far about 30k miles with the x303 on stock heads, rockers, & springs. Puts alot of stress on them though so i wouldn't advise.

Not sure about clearance on the '86 5.0's though because of not having reliefs cut in the piston.

tyler72

Im about 99% sure that you wouldn't have PTV clearance issues. MJR46 touches on this all of the time. However, That cam in a stock motor would be stupid. It wouldn't run correctly. You would definately need to change all of the valvetrain components, upper and lower intakes (unless its carbed), add headers, and probably different MAF sensor and injectors (assuming its actually injected).

FoxGT

Why wouldn't it run correctly?

I ran stock maf & 19lb injectors with my x303 with no problems. And i'm still to this day running stock valvetrain parts with over 30k miles since the cam went in & this is my daily driver. idle sits dead still at 400rpm with no surging whatsoever. I could even get a video to show

I helped a friend put one in his 91 lx & it was quite a good gain for the money with everything completely stock other than exhaust. I don't see why the f cam would give him any trouble, but idk perhaps there's something different with it which is why i'm asking so i'll know in case anyone I know tries to install one.

Fox351

Hey has a cobra upper and lower with headers but as far as injectors and maf....no hasn't spent that money yet....thanks fellas for all your help. I can't wait to give him the good news.

wrenchturner75

the reason they say it wont run right is because factorye e7te heads just dont have the flow numbers to get the full effect of the cam, basically you toss in the cam without changing any other parts like heads or intake your choking the engine, the cam wants to produce more power but the heads and intake say uh uh no can do. you can get more power with a cam change dont let anybody here fool you, but do it with a dual pattern cam that favors the exhaust side. straight up cams just dont work as well as they could on factory head/intake motors. remember it may run better with a cam change but youll never get the "full effect" with the factory setup.

FoxGT

You just mentioned the effect of every single part that see's any kind of airflow on the engine... That's the same concept with everything. Think about it, you change the heads & keep the stock intake/cam/exhaust then you can say the same thing, you won't see the "full effect" because of the intake/cam/exhaust will be choking it.

You're always going to have a bottleneck somewhere when modifying a stock engine. If it's not one thing it's another. e7 heads aren't the only thing restricting airflow. I'm still running e7's on my '89 & I can walk on my friends '90 Gt with gt40x heads, e303, & full exhaust, but he also still has the stock intake, i don't.

You have to start somewhere. I went with the x303 because it was extremely cheap & offered the highest power gain over stock of the letter cams that would fit, but i don't have to worry about emissions. I'd definitely recommend a dual pattern, but i'd decide what you want at the end before picking it so you don't have to buy another down the road. my x303 was a cheap cam that I could put in while building the 351.

1992gt400hp

on the stock springs? damn... it chop much at idle? i may be going to use the x303 in my build...

FoxGT

Has a very lovely idle. I get quite a few comments about it actually. I definitely wouldn't recommend using the stock springs with it, but all the same I've been using mine for a rather long time & I still have no ticking sound in my engine. Other than the exhaust & elec fan it's fairly quiet as far as the engine goes.

PJC Racing

Stock E7 springs are only good for a stock cam. The spring rate needs to be matched to any cam used. To run an "F" cam in stock heads you should replace the springs and retainers with FRP B-50 springs and A-50 retainers. FoxGT I am willing to bet you have valve float at high rpm and are probably at coil bind or very close to coil bind on the exhast valve.