Strange Problem Revealed at Dyno

[cdog]

Hi all.

I cured the detonation and pinging issues with a trip to the dyno. Got the timing and jets straight, car runs good...Thanks for everyone's input. Relays on fan/ignition to stop run-on.

However, the horsepower curve goes up to 5,000 rpm then levels off until 6,200 rpm where it drops. More of a wavy plateau than a curve. This is a built 514 that should have power through 6,000 rpm easy. Bhp at wheels was 492.

Dyno guy suspects that the valves may be floating over 5,000 rpm. I have Edelbrock performer 460 heads with the stock springs (the ones they came with). The cam is somewhat hot (i.e. rump-rump) and it has 1.8 roller rockers.

Will the stock edelbrock springs work with this setup? Dyno guy says to go to Endurance Race Triple springs....

Also, this motor ate its last cam. I wonder if the springs were a cause of that?

Thanks.

[427sharpe]

1:8 rockers?? should be 1.73:1 if using the 429CJ/SCJ set up, and 1.75:1 if using 'plain' 429/460 parts. If you are using 1:8's, you should be using a slightly shorter pushrod. The 1.8:1 are actually BB chevy ratio. I double checked mine, and are 1.73:1. This may be the source of valve problem--not float, but bind. Can be VERY damaging to a motor--esp the camshaft & lifters. I found a couple of cam mfgs that sell 1.8 rockers, but a footnote says you MUST use thier pushrods?

[cdog]

I know that the engine builder gets all of the pushrods custom length for various applications. This was discussed at the time.

I will ask him to make sure he figured in the 1.8 ratio when determining length.

These rockers were used due to the 35 hp boost that they gave in a super ford mag test some months back. With a hydraulic flat cam these offer a good boost.

The question is do these rockers change the valvetrain dynamics (lift) to the point where the valve springs are not keeping up.

[hford]

Have you checked your installed spring height to see that it is adequate for 1.8 ratio? Especially if these are the stock Edelbrock springs. Also are you sure the rocker clears the stud when at full lift? Just a couple of thoughts -- I could be all wet!!

[DAVID GAGNARD]

Cdog;

All good info so far. I would also check valve spring pressure......First check installed height and then valve spring seat pressure at that height. I would not run less than 125 # for a 6000 rpm motor or you may well have valve float as well as valve bind,check out these things and I think you will find your problem.....

David

[dalola]

I think all your answers are in your cam specs, and spring specs. Assuming everything is assembled correctly, cam profile most directly affects power band. Since you didn't give that info, it's hard to guess. Also, unless this is a monster cam, these springs should be ok. Again, check the specs and match to your cam. Your HP figures sound good, so I'm going to guess that's the power band of the parts you used. What does your engine builder say? Also, don't over look fuel delivery. As far as wiping out the first cam, the reasons already stated, or improper break-in, could be the cause.
Dave

[Coloradocobra]

My brother-in-law used assembled Edelbrock heads out of the box on his SBF and he floated the valves at 5,000 rpm. Many engine builders will not buy the assembled heads because they have to throw the springs away anyway. If your cam is more radical than the matching cam that Edelbrock would sell for that application, you may indeed be floating. Get the spring recommendations from the cam grinder first but don't go overboard with too stiff springs.

Gary

[cdog]

Attached is the JPEG of the DYNO sheet.

Please let me know your thoughts about the fluctuations after 5000 rpms.
Thanks.

[dalola]

cdog,
Basically, that looks good. I believe, judging from this, it's valve float you are experiencing at the upper rpm range. Unless you want to rev it that hard, I see no other problems based on this.

Dave