454 will not start help!!! Opinions needed!!!
 

I have a stock short block 454. I have 781 large oval port heads that I had ported an 2.19 in, 1.88 exh valves added an milled .020 . The cam is a 629 lift with 260 duration at .050( cam specs http://www.compcams.com/Cam_Specs/Ca...?csid=459&sb=2 ) The car will not start, it trys but just will not run. I did compression test showing 90 psi?? I know thats very low, cause of cam or flat top not going to work? :?:

First thing i would check is cam timing, if you have multiple keyed timing gears it may not be set on the right combination. The compression is way too low even for flattop pistons. It should have 160 to 200 lbs. of cranking compression even with that cam.

JMO

Zip.

I agree with Zip. One time I put a cam in one that was otherwise all stock and decided to advance it 4 deg...didn't degree it and I didn't do it at the cam I used the key on the crank pully. That thing never would fire.Not even close.I finally put it back to "straight up" and it fired immediately....I guess the cam was probably already ground with advance in it to begin with.

Has it run with the current setup, or are the heads & cam something new?

I put the cam in straight up dot to dot.
Yes the car ran fine before tear down, ran 8.16 in 8th with stock motor. I just had the heads done then added the 629 lift cam. The car will try to run but only after I pump the gas million times.

The motor turns over fast like theres no compression, same as it did when no plugs where in? I did notice when I kept double checking to make sure it was on compression stroke, there was hardly any pressure blowing out the cycl like it should.

If you are running he 781 heads w/119cc chambers and a flat top piston, your compression should be around 8.5:1 and on the cam specs it calls for a 11:1 for this cam. Is it possible that the cam is too big and your bleeding off what little cylinder pressure that there is? This is a pretty stout cam for a flat top engine. JMO.

Won't start
 

I would adjust the valves again. Sounds like they are too tight and bleeding off compression.

I agree with tcarda. With that cam, the intake valve closing a 79 degrees after BDC, you have an effective stroke of 2.70 inches. If you only have a static compression of 8.5:1 your dynamic compression is going to be about 5.86:1. Something to think about.

TS1955

Re: Won't start
 

x2

did you put new lifters in? if so are they hyd? the valves might be to tight due to not pre oiling the lifters? JMO

Re: Won't start
 

...yep check the valves adjustment again.... :wink: :wink:

Overcammed for application.

Just because you put it in Dot to Dot doesnt mean that cam is in @ 106 either. A degree wheel is the only way to fly ...


Just went over this, this weekend, lined up a new chain the same as the old chain suppose to be 110 like the old, came in @ 101. 9 degrees.

Sounds like you put open chamber heads on already low compression piston. It takes 80 to 90psi of compression just to fire an engine. If you have hydrolic lifters and you set them not pumped up they maybe to tight and trying to pump up as oil pressure comes up while your turning over the engine, causing the valve to stay open.

Sorry about the edit, but I wanted to ad that if you timing chain is not on the right centerline, and is retarded to much you can loose 50 to 60 psi.

According to the cam card in the original post, this is a solid lifter cam. Unless the valves were not adjusted with a feelers guage, valve adjustment shouldn't be a problem.

TS1955

I think the valves are set wrong myself and bleeding off to much compression.
I'd verify that you have the valves set right before I did anything else.

Turn the motor over by hand, set the intake lash on each cylinder just as the exhaust valve begins to open, set the exhaust lash just before the intake valve closes.

There are other ways to do it, but this is the most accurate and foolproof method I have found, and I always do mine COLD and set the lash on both valves the same.
For instance on my BBC 496 which has a 722 lift solid roller > I set them cold @ .022 A good friend of mine who used to be a R/D guy for Lunati said this will work on most solid lift and solid rollers cams, it may not work for you but it does for me and should get you in the ball park.
Goodluck, Cp