BBC Conventual Head Cam Help?

540ci BBC Conventual head motor with 38 to 42#s of boost, cam help needed. As I have gone up with the boost, I have started having valve train problems breaking intake rocker adjuster nuts and also have increased cylinder pressure and started stretching intake valves. I want to start with a milder cam and lower compression to get better service from the BBC parts. I know that 150#s cranking compression maybe be high, but worked great with the lower boost. I may lower it as I have the heads off now for service. Any help with recommendations for roller cam specs or cam numbers that work for you would be appreciated. Our Hemi does not seem to mind what boost we put on it, it just keeps on ticking, but the BBC is really finiky for us! THANKS for the help! Jim

 

Just a thought, as you go up on boost you need to go up on vavle spring pressure on the intake side. On a typical BBC chev intake vavle you will be adding 180 lbs of pressure trying to keep the vavle off the seat at 42 lbs of boost.

Richard Gavle

 

We run 400 psi had the same problem went to a stronger spring no more problems. The valves were hopping on the seats that is hard on all of the parts. we were running 300 psi at 25 psi no prob went to 38 psi stretched the valves in two quarter track passes

 

lbs spring valves is weight .the psi is per square inch psi or lb/in2 that have not at all like it did not influance lot of pressure on the spring.

 

It appears to me that too weak of valve springs limit RPM (valve float) and also heat warp valves. Since they are bouncing, they are not on the seat, when they are not on the seat they are not transfering heat away from themselves. This is my opinion/experience.

I used to heat warp intakes all the time. I couldn't burn a piston because as I would sneek up on leaning down a cylinder, the first thing to go was the intake valve. Until I put more spring psi at it.

Now when I slightly warp/tulip a valve there is enough spring psi where a leakdown won't show this because the valve is being centered back in the seat and sealing. I don't like this side effect but love the extra spring psi.

 

Knowing that happens what do you do to check you don't have a warped/tuliped valve? Is it simply a case of manual inspection?

 

Titanium or Stainless Steel valves?

Are still talking about running Stainless Steel Valves with 400#s of seat pressure, or has everyone had to go to Titanium valves to keep from stretching/tuliping them? THANKS, Jim

 

They used to show up in a leakdown test, but now only if the valve is out and you spin it.


Does titanium deal with the heat better?

 

i know we bent some titanium valves, and the springs seated them back with 0 leakage

 

Blown 540,

On my BBC's with conventional heads on nitrous I always ran titanium on the intakes because of the extra size of the intake vavle. This helped control the vavle action as I revved my motor to 8-9 grand the exhaust side being smaller the wieght was not quite as critical.

As far as the adjuster breakage deal I assume you are running either T&D's or Jesel rockers either one of them is very sensitive to overtorque of the jam nut on the adjuster follow the specs for this and you may find your problems dissapear, if you have someone going through your vavles that may be a little heavy handed LSM

http://www.lsmproducts.com/tq1003.htm

makes a adjusting tool with a preset torque wrench built in to set the torque on the jam nut.

My 2 cents

Richard Gavle

 

For time machine

When we have tuliped valves the first thing to show up was the valve clearances reducing. Any time anything changes there is an explanation! Wish I had known of this website when I was wrecking parts by the truckload!
JC