This is what happens to stock motor with comp 278's

SonicStangGT · Apr 10, 2008

Installed cams about a month ago and after starting found out that something wasn't right. So I called comp and they said that it was ptv issues. So I took my motor out and just got finished tearing it down and found that it was hitting just a little bit. So know I got 96 cobra pistons(higher comp) that are getting some flycuts, and the heads are getting a valve job and porting. Cant wait to get everything back for machine shop and put back together. Check out pic below.

BurningRubber · Apr 10, 2008

Really cant see much with that small pic, but this isnt the first time ive heard of the 278's having issues smacking the pistons on an otherwise internally stock 4.6...

Hope it all works out for you, down time sucks.

tank_567 · Apr 10, 2008

We need a BIGGER pic!!!

shallowreef · Apr 11, 2008

SO if you were to go with the next size down from 278s this wouldn;t have happened? Just curious because i was planning on putting 278s in my stock 4.6 but i am not looking to have to tear apart my engine 2 months later. Are there certain cams from comp that give you a rough idle that won't give you any headaches?

Sorry to hijack

COramprat · Apr 11, 2008

Any cam swap should be degreed but 278 is pretty stout no matter what you do. Stick with 270's. I'd get adjustable cam gears for 270 or bigger.

StangYellow · Apr 11, 2008

Where did your other 6 cylinders go!!??? Im never buying 278's!

SonicStangGT · Apr 11, 2008

I only took pics of the first 2 cylinders. The good thing is I did'nt run it much at all, so no valves were bent. I heard the stage 2 and they did'nt sound bad. Working on a bigger pic.

joshheat25 · Apr 11, 2008

I have heard only crap about those cams!

SonicStangGT · Apr 11, 2008

View attachment 322637

SonicStangGT · Apr 11, 2008

Every cylinder has the same marks in the same spots. I was glad that only one valve per cylinder was hitting. I almost got away with it. But I'am glad the heads had to come off. I was told that the 278 were to big for stock heads. So thats why there off. I was going to just fix the pistons but then decided to have some work doon. Also I know that 96-01 cobras comp. is around 9.8, I was wondering what kind of comp I would have with my 44cc heads. Would it be the same or more. Thanks

SonicStangGT · Apr 11, 2008

I just hope it gets better. SOunded so good running in the back of car, but when you walked to the front, it sounded awlful. I'am hopeing to get close to the 275-300 hp mark on motor and about 425-450 on nitrous.

BurningRubber · Apr 11, 2008

I cant tell if thats a reflection or if the contact marks are on the cylinder walls also? If so you might be screwed out of a block if they are deep and boring the cylinders out will not remove them.

Either way, it must not have been too severe of contact if you didnt bend the valves, or pop a piston. That sucks though, hopefully it all works out for you.

SonicStangGT · Apr 11, 2008

There is a reflection on the cylinder walls, but there's no damage to them, just the tops of piston. Its very little, so will not have to get real big flycuts in the pistons.

BurningRubber · Apr 11, 2008

Sounds like you got pretty lucky then.

Seeing as how they were hitting hard enough to eat away at the piston id have the crank checked to make sure it didnt get beat up or anything... dunno if you are re-using the rods not, but id suggest to make sure they arent stress damaged if you do so.

Best of luck.

SonicStangGT · Apr 12, 2008

Yeah everything is at the machine shop getting checked. I just hope I get it back together with no more problems. Then I have to get to the dyno for a couple of tunes. 1 for motor and 1 for nitrous.

Mustang92 · Apr 14, 2008

joshheat25 said:
I have heard only crap about those cams!

The problem is the Comp Cams have a build it advance already and they must be degreed or they will hit and most people out there just don't degree them and end up with damage.

Bill

shallowreef · Apr 14, 2008

So what is the next step down from 278s that you can put in your stock motor that still ha a noticable idle? I hate cars that have cams in them and you can hardly even notice. Sorry to hijack.

ProCharger GT · Apr 14, 2008

What is the lift on the 278's?

SADL-UP · Apr 14, 2008

ProCharger GT said:
What is the lift on the 278's?

Comp XE278AH specs (as provided by Summit Racing):

Basic Operating RPM Range: 2,200-6,200
Intake Duration at 050 inch Lift: 242
Exhaust Duration at 050 inch Lift: 246
Duration at 050 inch Lift: 242 int./246 exh.
Advertised Intake Duration: 278
Advertised Exhaust Duration: 282
Advertised Duration: 278 int./282 exh.
Intake Valve Lift with Factory Rocker Arm Ratio: 0.550 in.
Exhaust Valve Lift with Factory Rocker Arm Ratio: 0.550 in.
Valve Lift with Factory Rocker Arm Ratio: 0.550 int./0.550 exh. lift
Lobe Separation (degrees): 113

Check out my sig for a vid clip

SonicStangGT · Apr 14, 2008

Since I'am flycuting pistons, due I need to degree cams still or will it be alright. Thanks for info.

This is what happens to stock motor with comp 278's

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