Help with blown bbc

An intake opening of 50 degrees BTDC at 0.005" does not seem reasonable. According to your basic specs of 286 at .050", and a desired intake centerline of 106 degrees, go for an intake opening at 0.050" lifter rise of 37 degrees BTDC. With 60 pounds cranking compression, it's suprising that it runs well at all. Regards, Chase

 

I get 120 lb cranking on my 540 with 11.2 calculated compression an blower cam. To me 120 is low, 60 is Briggs & Stratton territory.

maybe you had the cam in wrong before - off 2 teeth or whatever. now you align the marks and it aint happy. dis you write down any piston to valve clearance numbers at the last assemble?

maybe just keep advancing it (double checking PVC) till it makes over 100 psi cranking.

GK www.MotorSportsInnovations.com

 

i still think its timing issue like for some reason the cam is in wrong

 

When I ran a chevy it did the same thing on a rebuild. Ended up taking the motor apart and rebuilding it from scratch. Only had about 60 lbs of cranking compression... my engine builder woundn't admit it but I'm pretty sure the cam was in wrong. afer the rebuild it ran fine....for six passes.... but that is another story

 

pull the cover off put the cam in straight up and see if it isnt better quick way to check

 

.005 is 5 thousand not .050 thousand. (.050 )

 

To clarify, I was initially responding to post #9, that mentioned an intake opening of 50 BTDC at .005 (five thousandths). The timing figures presented in post #20 of 50-86, result in 316 degrees, which is the advertised duration figure, but with no checking lift specified. If the duration at .050" is actually 286 degrees and the cam has 108 degrees lobe separation, then using intake timing figures at .050" tappet lift of 37 degrees opening BTDC, and a closing of 69 degrees ABDC, should put you at a good starting point (2 degrees overall advance). Make sure that you are degreeng the camshaft using the same type of lifters that you run on it. Regards, Chase

 

the saga continues

cknight:

I took your suggestion and checked the cam at 0.050. It rolled in at 36 deg straight up. So, my cam timing is very close. I suspect that my static gauge is hosed. I have not used it in years. More info: I took all my jet cans to someone that could check when they activate. All is good there. However, when we pulled the feed hose off, it kind of fell apart. It is possible that my inlet hose was sucking air or worse, collapsing? One more thing. I mentioned that I did not change ANYTHING. Well, I did not change anything with the motor, but I did have to change a return spring location for hood clearance. (we were not running a hood before) If the BV was not opening all the way, how much would flow be affected?

 

a lot if its sucking shut its not going to run if the barrel valve barely opens the throttle barely opens it would be a pig

 

That would be my guess too. If the timing is way retarded, it could possibly put some flame out of the pipes. Back in the Jurassic period (1979) we had the timing way retarded (looked at the wrong mark on pulley) and the car (Rodeck TAD) slowed .5 in the 1/8 mile on a night run with flames coming out of the headers. Another racer asked if we had some nitro added to the tank. Embarrassing to look like we were cheating and still run like a herd of turtles.

 

Chase sent u a pm cool can u get back to me thx crane cam questions.

 

Is the front cam button there and the appropriate distance from the cam? If the cam button is missing or incorrectly spaced with the timing cover the static ignition timing could check fine with the engine not moving or at idle, however as soon as the distributor gear got loaded enough by the oil pump, it could concievably push the cam forward and move the ignition timing. Totally a theory but....

 

I guess the same could be possible if the rear cam plug is not properly seated in the block...

 

Never mind, I see you're using a crank trigger wheel for timing, lol