Valve lash, how much is to much?

[Mesik Motorsports]

I am looking to gain as much low end TQ on a 580 BBC with 12 degree spreadport heads to help with the 60' times. Running a Comp Cam custom solid roller that calls for I-.024" & E-.026" lash. Rockers are: Int 1.8 and Ex 1.7 ratio. How loose can I "safely" run this setup to find more lower RPM TQ without hammering the cam or valve train to a point of damaging it? I will be checking back as time allows to answer any questions that maybe required to get your answers. Thanks in advance for any real world feedback, Walt

[user-30257]

I am looking to gain as much low end TQ on a 580 BBC with 12 degree spreadport heads to help with the 60' times. Running a Comp Cam custom solid roller that calls for I-.024" & E-.026" lash. Rockers are: Int 1.8 and Ex 1.7 ratio. How loose can I "safely" run this setup to find more lower RPM TQ without hammering the cam or valve train to a point of damaging it? I will be checking back as time allows to answer any questions that maybe required to get your answers. Thanks in advance for any real world feedback, Walt

I wouldn't use lash to Increase torque

Increase launch rpm, and or converter flashpoint.

Radial or slick?

@580 inches you should be making plenty of torque.

[E.R. Racing]

I am looking to gain as much low end TQ on a 580 BBC with 12 degree spreadport heads to help with the 60' times. Running a Comp Cam custom solid roller that calls for I-.024" & E-.026" lash. Rockers are: Int 1.8 and Ex 1.7 ratio. How loose can I "safely" run this setup to find more lower RPM TQ without hammering the cam or valve train to a point of damaging it? I will be checking back as time allows to answer any questions that maybe required to get your answers. Thanks in advance for any real world feedback, Walt

Can you advance the camshaft?

[engineguyBill]

I wouldn't deviate from the recommended lash settings. If you are seeking more low end torque, change the cam. Advancing or retarding the cam will confirm that the cam is wrong for the application . . . . . . that is all.

[Mesik Motorsports]

It is a slick tired rear engine dragster. Agree it is not the ideal method, however it is an option to learn and a HELLUVA lot cheaper and easier than swapping converters if not subjecting anything to damage. The converter will be re-stalled eventually, the run graphs show a downward hook in the launch (flashes 6400 and drops to 6300 @ .4 -.5 into the pass) where the converter "grabs" and the effort is to flatten the graph to see the ET gains, not run it there forever.

[user-30257]

I am looking to gain as much low end TQ on a 580 BBC with 12 degree spreadport heads to help with the 60' times. Running a Comp Cam custom solid roller that calls for I-.024" & E-.026" lash. Rockers are: Int 1.8 and Ex 1.7 ratio. How loose can I "safely" run this setup to find more lower RPM TQ without hammering the cam or valve train to a point of damaging it? I will be checking back as time allows to answer any questions that maybe required to get your answers. Thanks in advance for any real world feedback, Walt

Can you advance the camshaft?

Advancing the cam or loosening lash will not have a big enough impact to change the 60. He needs more launch rpm or to short stage.

Assuming he has a cam in the mid to late 280s@.050 it should be making north of 800lbft.

It could be chassis, rollout, gearing or launch rpm. If it's doing a wheel stand and blowing past the 60 on the rear tire, it will show a slower 60.

Or get a better converter, you may be blowing through it.

[Mesik Motorsports]

Can you advance the camshaft?

Already advanced 4 degrees and will need to go through the entire P to V clearance checks again. When building it I did not check P to V clearances at anything beyond 4 degrees ADV. My notes indicate OK to 4 ADV with nobody to blame but me for not documenting data rather than OK...

[Mesik Motorsports]

Assuming he has a cam in the mid to late 280s@.050 it should be making north of 800lbft.


Camshaft is 288/308 @ .050" 328/348 adv with 114CL

TQ is 905 @ 6000

Myself, I did not completely buy into the cam data. The cam to me is better suited if the combination was a 632 using the 4.75" stroke. I am a 4.53 bore with a 4.500" stroke.

Whats your thoughts on a camshaft vs what I have?

[user-17438]

Assuming he has a cam in the mid to late 280s@.050 it should be making north of 800lbft.


Camshaft is 288/308 @ .050" 328/348 adv with 114CL

TQ is 905 @ 6000

Myself, I did not completely buy into the cam data. The cam to me is better suited if the combination was a 632 using the 4.75" stroke. I am a 4.53 bore with a 4.500" stroke.

Whats your thoughts on a camshaft vs what I have?

sounds like a great choice to me. Thats what i would run for an engine of that size. I agree with the maybe you are blowing through the converter.

[Stan Weiss]

It is a slick tired rear engine dragster. Agree it is not the ideal method, however it is an option to learn and a HELLUVA lot cheaper and easier than swapping converters if not subjecting anything to damage. The converter will be re-stalled eventually, the run graphs show a downward hook in the launch (flashes 6400 and drops to 6300 @ .4 -.5 into the pass) where the converter "grabs" and the effort is to flatten the graph to see the ET gains, not run it there forever.

Why don't you post up the graph?

Stan

[F-BIRD'88]

If you want to know the valve lash workable range you need to know the lash point lift where the lash ramp ends. Ask comp cams for this design spec on your 2 lobes. Multiply by rocker ratio, deduct .002".

Why not first try tighter lash to see if the car slows.
Less risk in that try .016"--- .018" say.....

[F-BIRD'88]

With a real 6400 stall speed on launch you don't need more low end torque, you want more top end torque. 6000++ rpm.
You may want more converter stall torque ratio.
It will then hit harder at launch, if the tires can use it.
Tires are a big factor. Smaller tire dia= more launch torque.

[F-BIRD'88]

You may be getting a bit of converter cavitation on launch.

[Mesik Motorsports]

Why don't you post up the graph?

I will do my best... have to figure out how to get it from the Racepak software to an image for posting. It will be a few days before I can make anything happen, we are heading out for a race shortly.

[F-BIRD'88]

If you want to know that you still have enough vtp clearance if you advance the cam then first advance it a LOT, say 10 MORE DEGREES. now set lash at 0 on #1 and #6.. Now By Hand turn the crank slowly by hand.
Thru 2 complete cycles. If the valves don't touch the piston, you can now reset the cam advance to say +4 or +6 and reset the running lash.

As you advance the cam the intake valve gets closer to the piston and the ex gets further away.