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Old 04-19-2013, 06:08 AM
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Dirt oval .450 lift rule camshaft

A friend wants me to build a SBC for his Pure stock race car. I need to choose a hydraulic flat tappet camshaft with no more than .300 lobe lift.

Need to pull 14 inches at 1200 rpm.

Other rules:

2 barrel carb
Can run headers
1.94/1.50 valves
175 psi max cranking compression
flat top 4 eyebrow pistons
No Vortecs or small chamber heads
72cc minimum chambers

Doubtfull but, woukld the old Crane 274 H06 pull 14?

It is 218 at .050 274 at .004 106 LSA .450 lift

What about the ISKY 264 mega? 214 at .050 264 at .007 108 LSA

Too small?

Thanks

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Old 04-19-2013, 07:23 AM
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all the cam manufacturers make .450 lift rules race cams.Contact the tech line.These cheap engines end up costing a few extra bucks by the time you get the cam/carb combination correct
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Old 04-19-2013, 08:16 AM
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We had tremendous success with Comp's "lift rule" cam in Charger Div., similar engine rules. We had a .410" lift rule, but the cams are in the same group. 12-522-5 (242/255 @ .050, .450" int., .453 ex, 106 LSA) looks right for your application. I'd think, with a hydraulic lifter, they (inspectors) wouldn't bark at .003" lift. Leave a little "lash" when they check it, and you'll pass.

By retarding the cam (put the intake on a 110 CL) he was able to "flat-foot" coming off the corner, and it would pull the length of the straight (1/3 mile). Used this setup in several cars with similar results. Setting the cam "straight up" would create too much bottom-end power and blow the tires coming off.

Be sure to use "Z/28" valve springs. No more than 120 lbs. at the seat, though.

FWIW

Jim
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Old 04-19-2013, 08:35 AM
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Quote:
Originally Posted by Mr. P-Body View Post
We had tremendous success with Comp's "lift rule" cam in Charger Div., similar engine rules. We had a .410" lift rule, but the cams are in the same group. 12-522-5 (242/255 @ .050, .450" int., .453 ex, 106 LSA) looks right for your application. I'd think, with a hydraulic lifter, they (inspectors) wouldn't bark at .003" lift. Leave a little "lash" when they check it, and you'll pass.

By retarding the cam (put the intake on a 110 CL) he was able to "flat-foot" coming off the corner, and it would pull the length of the straight (1/3 mile). Used this setup in several cars with similar results. Setting the cam "straight up" would create too much bottom-end power and blow the tires coming off.

Be sure to use "Z/28" valve springs. No more than 120 lbs. at the seat, though.

FWIW

Jim
You probably won't hit 14" vacuum with that cam, its a little too long.

the 268-MEGA cam from Isky with a set of Rhoads lifters should get you by just fine with a good set of headers. If you don't have good headers then have the LSA spread to as much as 110. A 107LSA is on the shelf version and may not make your vacuum rule even with Rhoads lifters- it'll depend a lot on tune and exhaust. What RPM is your vacuum checked at? If they don't specify on then just raise your idle up to 1500rpm or so and you should be able to get the vacuum you need.
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Old 04-19-2013, 02:31 PM
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You can bet your....umm....hat that the front runners at the track you plan to run at have this camshaft timing thing dialed in to a gnat's eyebrow and maybe even have an inside track with the tech inspector(s). This will behoove you to talk with all the camshaft tech guys at all the cam grinding facilities you can think of in order to get anywhere close to running with those guys. Even being off by one degree one way or the other on the open or close of the intake and exhaust valves will make the difference in running at the front or in the middle of the pack.

I would approach this problem by getting every rule written down and running it past the track tech inspector(s) before ever beginning the search for a cam or any other parts for that matter. You should ask the inspector if anything has changed since the rules were written and if so, can he give you the exact verbage of the rules so you can find the right parts and be legal. If you talk with him in this way, you will have begun to establish a good relationship with the tech inspector and believe me, it will help you tons when the rubber meets the road. The inspector will recognize you as a good guy who wants to do the right thing and will give you some slack. Trust me on this. There were racers at Firebird where I inspected that never went through technical inspection because I knew them well and I knew that their car was legal. I would just sign off their tech card at every race and leave them alone.

CompCams
http://www.compcams.com/
Crane
http://www.cranecams.com/
Crower
http://www.crower.com/
Howards
http://www.howardscams.com/
Iskenderian
http://www.iskycams.com/
Lunati
http://www.lunatipower.com/
Sealed Power...cannot find a link to the factory engineers....
Melling
http://www.melling.com/Aftermarket/H...Camshafts.aspx
Edelbrock
www.edelbrock.com
Chevrolet (Scoggin-Dickey Parts Department)
https://sdparts.com/
Elgin
http://www.elgincams.com/
Engle
http://www.englecams.com/
Colt
http://www.coltcams.com/
Delta
http://deltacam.com/
Schneider
http://schneidercams.com/

There are others, I'll leave it to you to find them.....Good Luck.

Last edited by techinspector1; 04-19-2013 at 02:48 PM.
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Old 04-20-2013, 09:30 AM
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where else are you going to find horse power?
pistons,rods,crank,windage tray,scraper,remote parallel oil filters,valves,carb,intake,headers& extensions, ,,
you need to read all the rules,many times,,,
you did not say what the cubic inch maximum rule is?
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Old 04-20-2013, 01:50 PM
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GMC boogie, I've raced with engines under similar rules over the years. With 2 barrel carb rules the cams that worked the best for me stayed with moderate duration and 108-110* LSA's (but I never had to meet a vacuum rule). With your flat top piston/minimum 72cc chamber rules you won't be able to make much over 9:1 static compression ratio so you will want to keep your durations on the mild side. Isky and Howards both have .450 vacuum rule "off the shelf" grinds that I believe would work well. The Isky 268-Mega cam mentioned by AP72 is available in a vacuum rule version with 114* LSA, Howards #112431-12 is their equivalent with a 112* LSA, I believe either of these would make a good starting place. With the "smogger" heads that will meet your rules, I would consider running a little more duration on the exhaust, consider the Howards #112931-12 or the Howards #111241-12. There are cams, especially in the Howards listings, with plenty of duration to do whatever you would want to do in a pure stock class. The Isky 264-Mega you mentioned seems a bit small, but it's intake is slightly "bigger" than the intake on the GMPP #24502476 used in the CT 350 "602" street stock crate engine, so it might work well, especially if you run moderate rpm. I wouldn't be afraid to try one, especially since it's very moderate duration would help keep the dynamic compression up.

ISKY lift rule/vacuum rule grinds:


The Howards .450 lift rule/vacuum rule cams are in these listings:



Crower only lists 1 .450 lift vacuum rule cam, but I think the duration is too much for your compression rules.

Last edited by BigEd36; 04-20-2013 at 02:16 PM.
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