Is it worth replacing valve springs @ adding roller rockers? - Team Camaro Tech
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post #1 of 14 (permalink) Old Feb 12th, 07, 08:34 PM Thread Starter
 
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Is it worth replacing valve springs @ adding roller rockers?

I am going to throw a lot at you here... I have a 69' 350 CI, book says 9:1 CR. Looking at putting in either a Lunati 60102 , 3 or 4. Heads are stock 73' z-28 2.02/1.6 I was thinking about replacing springs, and going to roller rockers 1.5. Car is a 73' z-28 with 4spd, headers and dual (exhaust not ordered yet - so flexible) 3.73. Looking for street application with attitude not strip.

1. Which of these cams???
2. Replace valve springs +components and What pressure rate/spec?
3. Stay with stock rockers or rollers? and 1.5? 1.6? or combo?
4. Also shopping intake/carb (looking to stay 600-670cfm) recommendations

Thanks, want to do it right first time, but do not have unlimited $$$
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post #2 of 14 (permalink) Old Feb 12th, 07, 09:16 PM
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Re: Is it worth replacing valve springs @ adding roller rockers?

For a hotter strip set-up I would suggest 60103 no bigger with Comp Magnum roller tip rockers. You won't see a big benefit from full roller rockers on your set up, and us the springs to match the cam. If there stock springs change them out for sure. As for intake I would go with Weiand Stealth or if you want to try a little more more radical then the Weiand Stealth Air Strike . Before I built my 427 with 60105 and 1.6 full roller rockers and a Team G. I was running a 350 with a basically stock bottom end reworked 65cc heads with 2.02/1.6 ss undercut valves a Comp extreme 274 cam that is pretty close to this and 1.5 magnum roller tip rockers a Stealth intake and 600cfm 4160 Holley, and 3.73 rear gears. It was a total blast to drive. Although the carb did hold me back on the top end to go flat at @ 5k. So there I would say go 650 or 700 cfm vac sec carb.


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post #3 of 14 (permalink) Old Feb 12th, 07, 10:25 PM
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Re: Is it worth replacing valve springs @ adding roller rockers?

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Originally Posted by HarleyD67 View Post
Although the carb did hold me back on the top end to go flat at @ 5k.
At 5000 rpm in a 350 you aren't drawing anywhere near 600 cfm. A 600 cfm carb won't make the engine 'go flat' at 5000.
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post #4 of 14 (permalink) Old Feb 13th, 07, 01:02 AM
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Re: Is it worth replacing valve springs @ adding roller rockers?

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Originally Posted by onovakind67 View Post
At 5000 rpm in a 350 you aren't drawing anywhere near 600 cfm. A 600 cfm carb won't make the engine 'go flat' at 5000.
I didn't think so either until I dropped a 700 DP and it started to pull up into the 6k range. The 700 was down jetted 64/68 and the 600 was running stock. I know the 600 flows enough air to feed a mild 350 so maybe it just needed to be leaned up a bit.


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post #5 of 14 (permalink) Old Feb 13th, 07, 04:20 PM Thread Starter
 
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Re: Is it worth replacing valve springs @ adding roller rockers?

Spring replacement... a stock type spring or perhaps an edelbrock performer type spring or other make? Any suggested specs for this application?
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post #6 of 14 (permalink) Old Feb 13th, 07, 05:16 PM
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Re: Is it worth replacing valve springs @ adding roller rockers?

This 60102 is one knotch under the "268" cam which I consider better but for your application, I see nothing wrong with what you have. I would use the spring recommended or the stock Z28 springs to arrive at the recommended spring valve seat pressures. You need to check out coil bind issues also. If you can't get 80-110# closed seat pressures out of these Z28 springs (and I think you can) I would look for the recommended springs. Really need to look at your cam card on this , especially if you are breaking it in. The magnum roller tip rockers are a preventive for valve guide wear and they give you a true 1.52 rocker ratio.

Don
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post #7 of 14 (permalink) Old Feb 13th, 07, 05:51 PM Thread Starter
 
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Re: Is it worth replacing valve springs @ adding roller rockers?

The "268" cam is that a comp cam unit? Please provide an stock number if available.
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post #8 of 14 (permalink) Old Feb 14th, 07, 05:57 PM
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Re: Is it worth replacing valve springs @ adding roller rockers?

I think we are still talking hyd flat cam and the comp extreme # is 12-242-8 or XE268H. This is a workhouse cam. Ultradyne has their own Voodoo series in this also.

Don
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post #9 of 14 (permalink) Old Feb 14th, 07, 10:41 PM
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Re: Is it worth replacing valve springs @ adding roller rockers?

Like I said I am a big Comp Cam fan, and both are great options. The only reason I run the Lunati is they offered the higher lift I was looking for for my bigger inch motor without the long duration of some of the all out drag or circle track profiles.


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post #10 of 14 (permalink) Old Feb 15th, 07, 05:41 AM
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Re: Is it worth replacing valve springs @ adding roller rockers?

From the looks of your combo , I dont see a lot of compression for a drag motor, so if you use a larger cam, I think you will see some compression loss due to greater amount of over lap. Thats what I see when running Pat's DCR program as well as some paper dyno runs. I would still lean to the smaller cams , 268 is good but if you have some options to go larger rocker arm ratios to increase lift,, try that. .550 lift should be plenty . I am basing this on the combo you listed . Need to make sure you have good valve springs also to keep this motor spinning . I have seen small motors buzz well with small cams and heads and heard what PDQ has run with simple stuff and it works so I think you can do the same but you need to keep all compression you can . Think you said you were running 9.1? Would also help if you went to solids.

Don
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post #11 of 14 (permalink) Old Feb 15th, 07, 08:00 AM
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Re: Is it worth replacing valve springs @ adding roller rockers?

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Originally Posted by zdld17 View Post
From the looks of your combo , I dont see a lot of compression for a drag motor, so if you use a larger cam, I think you will see some compression loss due to greater amount of over lap. Thats what I see when running Pat's DCR program as well as some paper dyno runs. I would still lean to the smaller cams , 268 is good but if you have some options to go larger rocker arm ratios to increase lift,, try that. .550 lift should be plenty . I am basing this on the combo you listed . Need to make sure you have good valve springs also to keep this motor spinning . I have seen small motors buzz well with small cams and heads and heard what PDQ has run with simple stuff and it works so I think you can do the same but you need to keep all compression you can . Think you said you were running 9.1? Would also help if you went to solids.
What does overlap have to do with compression? Overlap occurs at the end of the exhaust stroke. Pat's DCR calculator uses the following variables:

Variables used:

* RD = Rod horizontal Displacement in inches
* ICA = advertised Intake Closing timing (Angle) in degrees ABDC
* RR = Rod Distance in inches below crank CL
* RL = Rod Length
* PR1 = Piston Rise from RR in inches on crank CL.
* PR2 = Piston Rise from crank CL
* ST = STroke
* 1/2ST = one half the STroke
* DST = Dynamic STroke length to use for DCR calcs
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post #12 of 14 (permalink) Old Feb 15th, 07, 08:30 AM
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Re: Is it worth replacing valve springs @ adding roller rockers?

From what I am seeing with Pat's program, too much overlap tends to decrease cly volumne sweep , thus resulting is less volume. It tends to bleed off compression which sometimes will allows you to run high compression and get away with running pump gas. You have to run the program to understand what I am seeing. don't you see it that way? Am I looking at it wrong? I am looking at it from the intake to compression stroke. When I input cams specs with less overlap, i notice the cly volume increases.

Don
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post #13 of 14 (permalink) Old Feb 15th, 07, 09:22 AM
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Re: Is it worth replacing valve springs @ adding roller rockers?

Overlap occurs at the end of the exhaust stroke, where the intake valve opens before the exhaust valve closes. It has no direct effect on the calculated DCR, you could add 50 degrees of overlap and have the same calculated DCR. Overlap will have some effect on the actual cylinder pressure by allowing exhaust scavenging of the intake mixture, increasing the VE.
The only event in the cam cycle that will change the calculated DCR is the intake valve closing point. The fact that many cams with later intake valve closing points also have more overlap may contribute to the misunderstanding that overlap affects compression. Cams with a large exhaust lobe will generally have more overlap, but the exhaust lobe has nothing to do with the DCR.
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post #14 of 14 (permalink) Old Feb 15th, 07, 09:52 AM
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Re: Is it worth replacing valve springs @ adding roller rockers?

Thanks, letting this soak in , I am currently selecting cams with Pats program and maybe looking at it the wrong way but when my cly sweep volume comes up and thus my dcr comes up as well as desktop dyno curves are higher to a point, than the larger cam I am running, this tells me I am going in the right direction. Thats where I am getting these assumptions. Using these programs are new to me as in the old days, we installed it, run it and make a determination. Thanks for trying to explain this. Hope I dont throw too many people off with my remarks and comments.

Don
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