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Old 01-06-2013, 04:51 PM
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Cam question

Can someone explain to me why roller cam with same specs as hyd. Flat tappet have lower rpm operating range. I look at a flat tappet cam and it was .488/.510 and the rpm range was from 3000 to 6500. I look at a retrofit roller .488/.495 and the rpm range is 1000 to 5000. That means if what I read was correct I need to set my heads up for a lot more lift to do retrofit

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Old 01-06-2013, 05:56 PM
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Here's what I was looking at
Summit Racing® Camshafts SUM-1107 - Mobile SummitRacing.com
Howards Cams Retrofit Hydraulic Roller Camshafts 110235-12 - Mobile SummitRacing.com
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Old 01-06-2013, 07:00 PM
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20 degrees difference in duration
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Old 01-06-2013, 07:29 PM
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I guess what I would be asking is what cam to use . The car is an 85 Monte Carlo, has 3.73 rear end and th350 I will run stall converter. The motor is 350 .030 flat top 4 v relief . I was going to use vortec heads that hav been cut and new springs good to .520 lift summit recommended that 1107 cam that I posted the link to that seem like alot of cam for a street car any suggestions.
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Old 01-06-2013, 07:37 PM
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cam choice is tough to pull a number out of the air.what RPM do you want to run? will you consider a roller cam? are you using none modified vortecs? what is the car used for,DD or ss? or both? what else do you have on the engine? what type of exhaust are you using? and so on,,,,
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Old 01-06-2013, 07:54 PM
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The car is goin to be street strip I don't hav any other parts other than what I told you so open to anything . Going to use long tube headers and 2.5 in exhaust. Open to intake and carb suggestions also. The heads are
Summit Racing® Vortec Cylinder Heads SUM-151124 - Mobile SummitRacing.com and the intake I was thinking about is Summit Racing Street & Strip® Stage 3 Intake Manifolds SUM-226019 - Mobile SummitRacing.com
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Old 01-06-2013, 07:58 PM
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I guess I should also say I'm trying to build on a budget that why I was lookin at so many summit brand parts plus there right up the road so parts are readily available and I don't have to pay any shipping
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Old 01-06-2013, 08:01 PM
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Quote:
Originally Posted by Jmszip610 View Post
I guess what I would be asking is what cam to use . The car is an 85 Monte Carlo, has 3.73 rear end and th350 I will run stall converter. The motor is 350 .030 flat top 4 v relief . I was going to use vortec heads that hav been cut and new springs good to .520 lift summit recommended that 1107 cam that I posted the link to that seem like alot of cam for a street car any suggestions.
On the 1107 cam, did you see the part where they recommend a static compression ratio of 10.0:1 to 11.0:1? If you know, specifically, that your static compression ratio is between 10 and 11, great, use that cam. If you have no idea what your static compression ratio is, then you have no business changing out the cam.
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Old 01-06-2013, 08:14 PM
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what Hcompton and tech both said. and I would not use a hydraulic flat tappet cam that big.thats just a personal opinion.
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Old 01-06-2013, 08:24 PM
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Not com controlled using Holley 750 vacuum secondaries . Don't know what static comp is . I also thought that cam was to big.
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Old 01-07-2013, 04:42 AM
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I would use a cam with 110 LSA, not 114. LSA of 114 is more of a n02/blower/efi cam and would reduce throttle response and would lower dynamic compression.

I would recommend a cam one size smaller. 224 to 230 degrees on the intake and 234 to 240 on the exhaust. 10" converter with a 3000 stall.

A holley 3310 750 vacuum secondary is a good carb. I would use a regular rpm intake (not rpm air gap).

Ignition timing is more important when you start messing with the cam. Get a distributor that is adjustable. Use 24 degrees at idle and 34 total. And another 10 degree from the vacuum advance canister.

A 350 with 64cc heads and 4 reliefs should be close 10:1 cr (9.7 or so). You would need to know the piston part number and take a few other measurements to get a more accurate compression calculation.
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Old 01-07-2013, 04:21 PM
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These are really different cams in terms of duration. The lift is only one component that needs to be looked at. Duration has a huge effect on where the power band will be much more so than the lift. The other important component is Lobe Separation Angle (LSA) this is a place where small differences add up to radical and substantial differences in operating behavior.

The Summit cam has an intake duration of 292 degrees at zero or maybe .006 inch lift while having 234 degrees of duration at .050 inch lift where the Howards is 266 degrees at zero/.006 and 213 at .050 lift. This analysis will also fit the exhaust side. But the intake provides much more effect on where the power peaks will be because of where it closes the intake valve in respect to how high the piston has raised in the bore. The Summit cam is a very old fashion lobe shape that holds the valves open a very small amount for a long time. This allows the compression pressure to leak back into the intake until enough velocity is built up within the intake flow to overcome the reverse pumping of the piston against the late to seat intake. This radically pushes the power peaks way up the RPM range and requires a lot of compression ratio both static and dynamic to restore the lost bottom end power. This line of thinking was adequate in the muscle car days but today is incompatible with unleaded premium fuels. Cams today need to act fast, get the valve open, shove it high off the seat and get the damn thing closed. This Mickey Mousing around with long slow ramps is so yesteryear and ineffective today. These old cams are a waste of money, they don't produce the power you want and need nor will it be where an engine short of a competition motor can use it and they guzzle a ton of gasoline while giving you these operating fits. The cheap to buy cam is not the answer as it will cost you in spades down the road in fits, fuel and wear on the cam and lifters.

Bogie
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