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need help choosing cam
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bigtizzles
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PostPosted: Sat Jan 15, 2011 1:59 am    Post subject: need help choosing cam Reply with quote

Good news, the 327 made it through the boring machine and all the rust is gone from the cylinders. Its gonna be .060 over when finished. Anyway the old man says I need to pick out a cam and he could get me the correct springs lifters and cam in a kit so all the stuff will work together for a good price. I want to put this thing in an S-10 or some other small vehicle. I want to run it on the street and maybe drag race it on the weekend. I don't wanna have to buy an expensive stall converter and I want to stay away from additional machine work. The heads are Vortec 906's. How do I go about deciding on a cam? What kind of RPM power range should I shoot for to make it a good street and strip motor? How about lift and duration numbers? So many cams, how the hell does anyone pick one out?
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SMOKEmUP
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1979 Chevrolet Camaro

PostPosted: Sun Jan 16, 2011 1:21 pm    Post subject: Reply with quote

Lift wise you're limited to .420" with the stock springs. Did you machine the heads for aftermarket springs?

I like to use dynamic compression ratio to pick the cam. Assuming a tight quench of around .045" then you should be able to run 8.0:1 DCR. So pick a cam that will give you a DCR of 8:1 with an RPM range of 2000 - 6000. Lobe sep I'd go with 110 or 112.

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squeeezer
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PostPosted: Sun Jan 16, 2011 1:27 pm    Post subject: Reply with quote

X2^^^^^^^^^ with the exception of a lsa of 108 to 110 with same dcr
then you can getthe torque in quicker and across the board

spray it if not satisfied Laughing

you dont even have a doner vehicle for it yet so you really dont have a tranny picked for it if you end up with a stick you need not worry about a converter

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clay
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PostPosted: Sun Jan 16, 2011 10:29 pm    Post subject: Reply with quote

Quote:
Lift wise you're limited to .420" with the stock springs. Did you machine the heads for aftermarket springs?

This is pretty much the most important question right now. I've read between 0.430" limit and 0.480" limit. Which piston did you wind up running? I have a plan to maybe get more clearance for a Vortec setup (+0.050" locks and aftermarket retainers) as their looks like there is plenty of valve tip exposed and clearance to the rocker arm (self guided). You'll have to give me a week or two to have time to get to it though. I'll measure what lift you can get away with on the factory stuff too. Clay

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bigtizzles
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PostPosted: Mon Jan 17, 2011 12:59 am    Post subject: Reply with quote

I haven't bought anything to speak of yet. I did not get the guides machined, but the heads are still at the shop, waiting for the new valves so I can get the valve job done. Even if I got the guides cut down, how radical of a cam would I really need? I want to run this thing on pump gas probably mostly on the street. I don't even think there is a drag strip around here within 200 miles. I will most likely run an automatic. How do you determine dynamic compression ratio? I plan on buying springs, lifters and cam all together, as a package if possible. I think I can get away with .45 .46 with a stock style spring. NOS is a definite possibility.
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squeeezer
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PostPosted: Mon Jan 17, 2011 9:36 am    Post subject: Reply with quote

you want a z-28 spring at the very least .500 lift-ish
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SMOKEmUP
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PostPosted: Mon Jan 17, 2011 3:49 pm    Post subject: Reply with quote

You can calculate DCR here http://www.smokemup.com/auto_math/dynamic_compression_ratio.php

I've heard mixed things about how much lift you can run on Vortec heads. I quoted 0.420" since it's on the conservative side. You might be able to get away running more. Those heads with a good valve job flow well to 0.500" lift. If you have the money I recommend you machine the heads to run larger cams. That way down the road if you change your mind and want to run a bigger cam you don't have to pull the heads off and machine them.

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af2
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PostPosted: Tue Jan 18, 2011 8:35 pm    Post subject: Reply with quote

SMOKEmUP wrote:
You can calculate DCR here http://www.smokemup.com/auto_math/dynamic_compression_ratio.php

I've heard mixed things about how much lift you can run on Vortec heads. I quoted 0.420" since it's on the conservative side. You might be able to get away running more. Those heads with a good valve job flow well to 0.500" lift. If you have the money I recommend you machine the heads to run larger cams. That way down the road if you change your mind and want to run a bigger cam you don't have to pull the heads off and machine them.


Smoke, I remember the Vortec being .485 lift?? My 2 sons used that cam and went to the LT4 at over .510.

I am also wondering?

I used KMotion springs at 130/350 on Mikes build and have been happy after the installing the LSX lifters.
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SMOKEmUP
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PostPosted: Wed Jan 19, 2011 12:11 pm    Post subject: Reply with quote

I'm sure you can get away with running more because some are a little different than others. I think 0.485" is more than I've seen run and I haven't heard anyone getting away with 0.510" stock. With that said if anyone can make it work I'm sure you can.
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bigtizzles
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PostPosted: Wed Jan 19, 2011 1:56 pm    Post subject: Reply with quote

I think i'm gonna shoot for around .50 lift with a longer exhaust duration. Try to achieve this with springs, retainers and locks rather than machine work. Who would be the best deal and would have all this stuff available and know what they are talking about. Summit? It doesn't look like they deal much in springs?
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bigtizzles
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PostPosted: Wed Jan 19, 2011 2:35 pm    Post subject: Reply with quote

so what if I go with a summit cam, they don't have springs in their kits like comp offers. How do I select a set of springs to go with one. For example, say I go with the summit 1103 cam and lifter kit. What springs do I need to run. Will summit be able to tell me ?
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af2
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PostPosted: Thu Jan 20, 2011 12:08 am    Post subject: Reply with quote

Are you going flat tappet???

Summit ( BULK ) springs suck no matter what you run!
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ericnova72
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PostPosted: Thu Jan 20, 2011 1:03 am    Post subject: Reply with quote

A good source for good valvetrain parts at good prices is Competition Products/Howards Cams at www.competitionproducts.com. Good folks to deal with and quality parts, they specialize in the dirt track market but most of that transfers over to street/strip work as well. First place I look when I need parts.
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bigtizzles
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PostPosted: Thu Jan 20, 2011 3:07 am    Post subject: Reply with quote

The machinest measured my retainer to guide boss clearance on one set of valves using a stock retainer and valve seal, he got .520 on the intake and .480 on the exhaust, that was allowing for .050 clearance. Thats not bad. With performance retainers he said it would buy me a little more clearance. I think i'm gonna go ahead and have the guide boss ground down a bit, he said he'd do it for 4 dollars a boss. Of course the stock valve seals I bought won't work then. That sucks cause its like the only part I have bought so far. Then I can run a bigger cam and not regret not having the machine work done when I had the chance. Anyway I have been considering trying to "cheat" by using the comp cams beehive springs, but they would definitly cost more than just doing the machine work. I have also been looking at this kit. Do you think it will work if I stay with a cam no bigger than .510 or so? I can't find alot of reviews of this guy. Let me know what you guys think. http://www.alexsparts.com/products/VALVE-SPRING-KIT%2C-SB-CHEVY-VORTEC%2C-HI%252dPERF-HYD-FLAT-TAPPET%2C-MILD-HYD-ROLLER.html
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af2
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1933 Willys Coupe

PostPosted: Thu Jan 20, 2011 1:01 pm    Post subject: Reply with quote

Comp springs are no longer made by PAC and I have heard horror stories since.

I would use PAC behives.


http://www.pacracing.com/Street_Strip_Springs-PAC_1218_Set_of_16.html
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