need help with picking a cam

[redcamaro72]

the cam I have now is a competition cam part number 12-502-5
valve lift .530 intake .540 exhaust
duration at .50 250 intake and 254 exhaust
lobe seperation 106.
my set up is a 383 stroker with vortec heads, rpmperformer intake, pro systems 750 hollycarb, turbo 350, 373 posi rear.msd distributor and 6a box.

I don't think I'm getting everything I should out of this setup and I need help to pick the right cam.

[Dirt Reynolds]

That's a pretty stout combo. In my notes on Vortecs, I came across a 383/Vortec combo making 518HP with unported Vortecs (518.6HP @ 6600 RPM 505 TRQ @ 3200) using a Comp solid with 256/264 @ 0.050", .605" lift with 1.6 rockers, 2.02/1.60 valves. The bigger valves aren't an absolute must, as the stock 1.94/1.50 valves are back-cut from the factory and feature a super 3-angle valve grind in stock form.

My suggestion would be to look at your cam profile a little closer. It might be better to use a cam with around 10 degrees more exhaust duration than intake, especially with unported Vortecs, due to the less than optimum flowing exhaust port. It might be an idea to have the exhaust lobe reground for 260 degrees @ 0.050", and leave everything else as is.



------------------
'Silver Bullet' 1977 Z-28 413" SB
11.73 @ 115.10 and dropping...
Old Vortec combo:
12.15 @ 110.52
1989 GTA L98
Daily driver

[redcamaro72]

the vortec heads have 202 intake and stock exhaust. milled down around 10 thousand. I'm able to run about 550 max on cam. So what is your suggestion. I know there alot of guys with the 383 stroker so I'm hoping they could give me some good advice.

[Rick WI]

That is a lot of camshaft and tight lobe sep. if you are not running a lot of compression. What is your compression?

What are the symptoms that make you think it's not giving you everything you think it should?

------------------
70 SS 454 CI Dynoed 684 HP, 702 TQ All Aluminium Fuel Injected Small Block , plus 200 - 500 HP NX nitrous system.

[redcamaro72]

Rick Wi, thanks for the response. I haven't taken a compression test on the motor, it idles like shit, pings even with 94 octane gas, the engine builder built alot of dirt track motors here in Pa and I think he just threw this one in and wasn't sure of the outcome. I have little vac. so one shot for the brakes and thats it. I really dont mind but it just doesn't seem to have the power that he bragged it would. I'm new at this so I take every suggestion very seriously. Should I stay with a solid cam? any Suggestions?

[redcamaro72]

MWilson. thanks for the advice on Howard cams. I talked with John and he was very helpful. He doesn't have a cam in stock but would have to grind one for my application. He adviced me to get the lobe seperation from 106 to 110. I'll have to think about it and hopefully other stroker builders can help me on this.

[Rick WI]

Those symtoms smack of a camshaft way too big. With the camshaft way to big combined with low compression and no carburator signal due to no vacuum you won't have any power until way up the rev band. With a Vortec and the small ports that head will give up before the cam comes into it's power range.

The simple answer is to take the motor back to the builder and tell him it runs like doo doo and fix it. I think though you may not have that option. The next step would be to have the builder give you the specs on the pistons so at least we could estimate the compression. If he remembers the deck height that would be great as well.

For a street car I'd keep the lobe sep around 108-110. 106 will give you that blubbery sound we all like but the 108-110 tends to idle more stable. It's a balancing act. Bottom line though you can't buy a camshaft unless you know the compression.

Now if he doesn't and he is a big circle track guy then he has to know soemone that has a whistle. A whistle is what you use to verify compression for spec classes.

The ping can simply be caused by a poor distributor that's way too advanced. It should not ping on top of not having any vacuum. I'd take the distributor out and make sure it is in good condition. Is it new or old? With a vortec head you should only need 32-34 degrees of advance total.

------------------
70 SS 454 CI Dynoed 684 HP, 702 TQ All Aluminium Fuel Injected Small Block , plus 200 - 500 HP NX nitrous system.

[This message has been edited by Rick WI (edited December 06, 2004).]

[cattmann1]

I was under the impression that vortecs petered out at about .500 lift. Is it possible to port them enough to obtain flows to justify having lifts this high.I was thinking of swapping mine out for flow reasons after .500.

[Lowend]

I am with Rick, that is a ton of cam and the lobe seperation is WAY too tight for a street car. I don't like going tighter than 108 on anything that sees street use.
You could be having some of your problems if the heads have not been properly prepped for this cam. You NEED screw in rocker studs and different valvesprings than what come on the heads stock (stock stuff limits to .480 lift)
If these items have not been replaced than what you think it a ping might actually be the valvetrain destroying itself.
Have the valvesprings and studs been changed?

------------------
1971 Camaro
383 stroker ~500HP
M21 4spd
12" brakes
16x10" Wheels
Autocross competitive
Sales / Tech - The Speed Merchant, San Jose, CA
1-800-994-0930
mailto:BrettK@speedmerchant.comBrettK@speedmerchant.com</A>
http://www.speedmerchant.com/

[Dirt Reynolds]

Is this car for track use (my initial assumption based on the posted cam profile), or is it more a street car? The 106 degree lobe sep angle is great for midrange power at the track, but will provide very low manifold vacuum for power brakes, be a bitch to tune for the street, and have low bottom end power until the RPM's rise enough to where the cam begins to work, ie, when it 'comes on the cam'. Tight lobe sep angle cams of this duration are usually only used for a primarily strip car. Widening the lobe sep angle will give better vacuum and idle manners, broaden the torque band and be a lot easier to tune for the street. You should also get a vacuum gauge and see what you have at idle. Your power valve might need to be changed out in the carb. A real tight lobe sep cam and a lot of duration can spell big headaches to sort out for street use. For a street/strip car, I would not use that cam.

What is the stall speed of the converter? You need a high stall converter to make this combo work properly. My guess would be a 10" 3800-4500 stall would be a good starting point.

I find it strange the machinist guy would install a 2.02 intake but leave the exhaust stock. The exhaust is the relative weak point on the Vortecs; the intake is the strong suite. I'd get the 1.60 exhaust valve installed and some mild bowl work (a clean up will do) to help with the flow and get a better intake/exhaust airflow ratio.

catmann: just my opinion, but I would do a little home porting work to your Vortecs before thinking of changing them out for other heads. If you look at Gary Penn's Vortec 355" build-up, he is making a lot of power (480HP)with only a .485" solid cam. My Vortec/400 combo worked very well with a .488" street hyd. cam. Easy on the valvetrain and a lot of fun on the street. You don't need a ton of cam lift to make great power with these heads.

------------------
'Silver Bullet' 1977 Z-28 413" SB
11.73 @ 115.10 and dropping...
Old Vortec combo:
12.15 @ 110.52
1989 GTA L98
Daily driver

[Mwilson]

My lobe sep angle is 105? Ilove it
jumps like a frog at any speed!
no traction on the 295 15's under 40 mph!

[Mwilson]

My lobe sep angle is 105? Ilove it
jumps like a frog at any speed!
no traction on the 295 15's under 40 mph!
You do need good compression
but my heads are factory 186 casting (i ported) they seem to match well with
the cam

[This message has been edited by Mwilson (edited December 07, 2004).]

[cattmann1]

Dirt I was just discussing this with rust bucket. I am running a XE274 which I beleive is about .490 exh and .485 int. my heads have been machined to accept 981 comp springs and the guides have been cut down.I have guide plates and screw in studs also.I am at the point that I have to decide whether to invest more money into these heads or upgrade.Presently I am running 12.90 at 106 with a 4000 stall with my 355. Rust feels the same as you do .I might unbolt them and have the porting done .

[redcamaro72]

the heads have been worked on, able to run up to a 550 lift, screw in studs, crane gold racer rocker arms, 2800 to 3000 stall converter, keith black silv-o-lite pistons flat top, the builder said tht the compression is around 10 to 1. How can I determine what compression I have? 3.75 stroke with 6.0 rod. Should I pull the heads off and have 160 exhaust valves put in? will it make that much difference? Or should I try to sell the vortecs and move up to a better head?

[redcamaro72]

dirt reynolds: my vacumn is 6 at idle. It is basicially for street use, for a 383 stroker I think it's a dog, no power on the low end, doesn't idle for sh-, very hard to get tuned, I feel tht i'm on my last leg before I get frustrated and sell her.