Last summer I had a 355 built for my Z28. I spent most of the last part of summer just breaking in the engine. Problem is I have never raced this car yet, and I was always breaking rocker arms when I gave it some gas (never went over 5000 RPM) so what I did was replace the stamped steel rockers with COMP CAMS roller tipped rockers. No the rockers are not breaking, but the pushrods are bending !!

Can anyone help me. My engine specs are as follows.

355 4 bolt
10.5 to 1 compression
flat top pistons with valve reliefs
Crane Cam Energizer 302H cam
(advertised duration 294 degrees .500" lift)
1970 1/2 Z28 heads with 2.02" intake and 1.60" exhaust valves.(Blended bowl & ported)


Thanks for all your help
Jaret

 

Jaret,

The one thing you didn't mention was teh valve springs. What springs are you using, and at what installed height?

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Later,
Vader
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"What a Day..."
Adobe Acrobat Reader

 

I am using a set of Crane Cams single coil valve springs with dampeners. The pressure at checking height is 100 LBS. and 1.940 inches.

The pressure at opening height is
375 LBS. and 1.380 inches.

The bind height is 1.320 inches
Thanks for the help Vader.

 

Did you have the valve guides milled? The reatainer may 'just' be hitting the guide, especially during high rpm blasts which you said never happened. I assume you have screw in studs because the stud will pull out before the pushrod bends (I know!)

Also if you are running higher ratio rockers and have guide holes milled in the heads, the pushrods may be binding in the holes (because a higher ratio moves the pushrod closer to the rocker)

DONT DRIVE THE CAR!!!!

You may be damaging your valve guides which will require head removal..

Since you are close to the border (actually over for stock on reatainer to guide interference) you may get away with having the retainers cut (surface milled)

If you replaced the springs and never removed the shims and checked the installed height I could think of instances where this could come in.

 

Those springs should work if they were installed correctly. Thats where the problem comes in, that installed height is much higher than stock. This means you will for sure need different pushrods as well. Do you have all of this stuff?

 

O.k. then. My rockers ratio are 1.52 with of course a 3/8" stud.

If you say that it's a pushrod length problem then give me a suggestion as to which kind I should be using? Something like stock height + .100 with guideplates? I am afraid to go to a chromemoly pushrod until all this is fixed. As I don't want to ram a valve though a piston. Thanks

 

I cant really answer that as is. I dont know how much the heads have been cut, if at all, what the deck height is, and what the valve installed height is. If I guessed, it would be the approx. diff from 1.94 and 1.78 (that right guys?) which leaves about +.16, barring anything else and assuming that your installed height is actually 1.94, which I really question. I would not recommend using that number, you need to check your own engine as to how much it needs.

 

Wow....guys, this was a great thread. Very informative, no sarcasm, kindness. This is a "textbook" way that questions here should be answered. To those involved.....I applause you.
Alex

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Alex (A.K.A chevyboy) '91 RS 327c.i., ported, polished, & gasket matched heads & intake. Competition cams camshaft, trans-go shift kit(stage 3)> manual valve body, cat-delete, MSD (ignition, coil, 2-step, timing retard/ advance), T.C. lockup switch, Flowmaster exhaust, Edelbrock Pro-Flo open element, Edelbrock shocks, struts and lowering springs. CRAGAR drag wheels w/BFG T/A tires. Lowered 2.25" in front and 1.5" in rear....Best E/T 12.84 @109 mph. Newest mod= Nitrous Express adjustable nitrous kit. "I survive for your survival" -me- LT2 U.S.M.C. Demolition

 

push rods are fairly cheap (not moly) i go +.100 up to about .550 cam. sorry to say i don't own a length checker which would be the best way to go. there is a rule that goes something like this for every .150 more of cam you need .100 more push rod, nut milling heads and other factors figure in to it.

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ICON Motorsports

1st & 3rd
MM Black Diamond 538 F&AM

 

I would like to thank everyone for helping me on this question. To all those involved I have gained extremely valuable info.

Now I have alot of checking to do. Also I think I should buy a pushrod lengthg checker!

Thanks