ZL1 factored HP and valve springs
 

Couldn't get into factored HP for 1969 ZL1 on NHRA website. Anybody know what it is? It's a stick car. Also, when I was looking at the specs for this engine the other day, it said outer spring with damper. It used to say outer and inner spring with damper. I know the factory used inner/outer with a damper back in 1969.

Re: ZL1 factored HP and valve springs
 

445 for Stock, 476 for Super Stock. Stick and auto. are the same h.p.

Re: ZL1 factored HP and valve springs
 

The configuration of the stock spring no longer matters.

It's a tough and expensive combination.

Re: ZL1 factored HP and valve springs
 

Thanks Alan!

Re: ZL1 factored HP and valve springs
 

When I ordered the cam from Chris at Comp for stock class dual springs with a damper were allowed for the ZL1 in the specs and were sent with the cam. Are you saying I've got to change to a single spring now?


Yes, it is definitely tough and expensive but I got it done. Didn't you run a 427 (ZL1 combo?) at one time?

Re: ZL1 factored HP and valve springs
 

Al, what Alan is saying is that NHRA has changed the rules on stocker valve springs. You no longer have to comply with the specs. listed in the NHRA Blueprint Specs. (pressure, spring style, etc.). You also don't need to run stock style rockers (roller rocker arms permitted). From the current NHRA rule book:

"Any valve spring permitted, provided no modification to head is performed. Steel valve-spring retainers mandatory. Spring cups permitted ONLY if no modification to head is required."

If you got your parts before these rule changes, make darn sure you talk with Comp. Cams to make sure your springs are up to the task. Keeping the lifter in contact with the lobe is critical with these motors. -Al

Re: ZL1 factored HP and valve springs
 

I'm saying the NHRA no longer cares if your spring configuration matches OE spec or the guide. Chris or Tim may have a better spring for you.


Kevin Cradduck and I have the parts for a ZL-1, we set it aside when the new cars entered the picture. We will get it out of mothballs and finish it now. Jimmy Bridges gets after me on a weekly basis telling me it is what should be in Kevin's car. We will start this season (a late start) with a fresh aluminum head 396/375 in both cars. We previously ran the 427/425 in the orange stocker, with the aluminum heads, at 435HP.

Re: ZL1 factored HP and valve springs
 

I appreciate both of you helping me with my questions. I did upgraded to roller rockers a couple of years ago. So I could run a beehive spring as long as I run a steel retainer? It would be nice to run a smaller and lighter steel retainer on the nose for some more ponies!


Jimmy told me years ago about angle milling the 401 head to get it down to closed chamber CCs. .125 off the bottom at 0 on top, redrilling head bolt holes, etc...

Re: ZL1 factored HP and valve springs
 

Al, you can run that spring. I know a few who have tried and do not like the results. I prefer a regular style spring and a tool steel retainer.

How much you might gain by reducing open pressure depends on what cam core you run and what your open pressure is now. We've tried taking spring out, it has not worked for us. You can have too much open pressure, for a cast core cam, that's anything above 525 pounds. You'll get twist, and you'll lose lift. I'd run a steel core cam in a ZL-1. Too many RPM and too much lift for a cast core, in my opinion. Tim will be doing a steel core cam for ours, I talked to him about it the other day. I'd have it in the new 396 if the core would work at 0.520" lift.

You shouldn't have to mill the 401 head a ton to make spec for a 69 ZL-1, since the spec is for an open chamber. You could do a valve job, put the valves and a spark plug in it, then mill it in steps, 0.0" to maybe 0.020" angle, and creep up on it. Then you might have to re-drill, but you'll certainly have to spot face, and correct the intake face.

Re: ZL1 factored HP and valve springs
 

I got the CCs at 117 (min.114.5). I want to leave some meat on the heads in case a head gasket pops someday. Seat is 153, open is 410 on the springs. 580/620 lift. Nice to be able to use head studs! :D. This engine is complete and in the car. Got an iron short block for back up. I remember Kevin with the orange 69, met him in the pits at Norwalk years ago, nice guy. Jimmy still running the 66 Vette?