Thread: Cam For 383 Vortec

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What cam is working for those of you that are running a 383?

My Vortec 383 TBI build is shaping up as follows:

Modified 50mm 670 CFM TBI
GMPP Vortec TBI manifold w/50mm Venturi ports
18cc D-cup Pistons ~9.6:1cr
Stock 64-65cc Vortec Heads w/Polished Chambers
No porting other than intake matching
Upgraded valve springs good for ~.520 lift
~.039-.040 Quench
OE Roller Lifters
At least roller tip rockers
Edelbrock Headers with EGR
Single large tube Exhaust with Cat
ECM Controlled
Stock Torque Converter
Upgraded 700 Transmission
3.42:1 Rear End Gear
1994 K1500 Suburban
Cruise RPM @ 60mph = ~1680rpm
Vehicle seems to start moving at around 1000-1200rpm and doesn't likely see above 4500rpm before shifting

I have been considering Comp Cams Extreme Energy line for computer controlled vehicles originally equipped with OE Roller cam, either;

08-500-8 206/212 @.050, .480I/.488E, 112LSA
08-501-8 212/218 @.050, .488I/.495E, 112LSA

I'm looking for grunt towing torque for my service vehicle used to pull boats out of the water and up hills - highway performance appreciated but secondary (probably the smaller cam huh?).

I am not experienced enough to know how 383's react to cam specs so any advice would be appreciated.

I'm sure you will get many suggestions from all the sbc guys here. My only suggestion would be to fill out a Comp Cams Tech Sheet and see what they recomend. Works for me !!!!

You know, I did fill out the online form at Comp Cams but never received a reply - been several weeks now. I'll do it again sometime to see what they have to say but would also like to here from those that are running them.

Originally posted by MainCap
You know, I did fill out the online form at Comp Cams but never received a reply - been several weeks now. I'll do it again sometime to see what they have to say but would also like to here from those that are running them.

I sent them the same on-line form, 2 weeks and no answer. I called them and they took care of me....G/L

Yup, I get the sheet filled out, then do the phone call thing. Sorry, should have specified that in my post. Never been disappointed in the results.

For your application, you can't go wrong taking Dave's advice and letting the cam tech line help with your selection. There computer takes all variables into account to come up with the best cam possible. It's impressive sometimes because it's not always a part no. cam that they come up with. I have called and they built a custom cam for me by their suggestion.

You could just call them. The number is 18009990853. Becauese you're going to use it for towing, I would recommend something smaller in the XR264H or smaller catagory, but you have a fairly high compression ratio for towing and you'll want to keep your dynamic compression ratio down at low rpms to hold off detonation. In that case, I would recommend the XR270H. Because the motor is a 383, it should lower the powerband of that cam a little so it might come on at 1200 rpm instead of the advertised 1600. All of these cams will require aftermarket valve springs be installed and may require the valve guide be machined to clear the lift.

76GMC, I appreciate the comments on compression ratio. I'm trying to keep it down but there is not much of a selection of pistons with a greater than 18cc dish (64cc chambers) - unless I drop to well below 9:1cr. So I am going to use a D-cup dish, an .039-.040 quench, and polish the combustion chambers in an effort to reduce potential detonation. I'm also trying to use as thin a head gasket as posible to reduce the deck to head gap for carbon buildup.

I found an upgraded spring and retainer kit from Crane that increases valve lift clearance to ~.520 on Vortec heads without machining - this option is a little less costly than machining for larger springs and replacing seals and retainers.

Both of the Comp Cams I listed are in the grind families you have mentioned, though the LSA's are at 112 and are intended for use with ECM controlled engines.

I will get Comp Cams on the phone next week to see what they advise and will pass on what I learn to the group.

old thread, but my suggestion for a 383 truck motor is this

http://www.sdpc2000.com/catalog/989/...r-Camshaft.htm

looks like "what the doctor ordered"

I don't know so I am asking,Can you use a thicker head gasket and lower compression?

Originally posted by BigTruckDriver
I don't know so I am asking,Can you use a thicker head gasket and lower compression?

Yes you can, but you will alter the piston to head clearance (squish) at the same time. Also called "quench", this is the calculated distance between the top of the piston and the bottom of the cylinder head at top dead center. It has been found that if this distance is minimized to a distance just short of allowing a piston/head collision, that the motor will become more detonation resistant and can be run on lower octane fuels and with more spark lead. A generally respected figure is 0.040", although some will tell you that you can run closer and some will tell you that you have to run a little wider than that. My personal opinion is that with lightweight steel rods and light pistons and keeping the rpm's in check, a guy can get away with much closer.

What you want to do when you build a motor is to pick your pistons and cylinder heads to establish your static compression ratio, then pick the right thickness of gasket to set the squish at around 0.040". An iron head motor can run as high as 11.0:1 on pump gas with a tight squish.

So you see, if you, for instance, changed an 0.040" gasket for one with a 0.060" thickness, yes you would lower the c.r., but you'd be going the wrong way to control detonation (the reason for changing the gasket in the first place).

the very last thing you pick is the camshaft, after you have dialed in the rear gear, tire size, converter and all the above.

Originally posted by techinspector1
...It has been found that if this distance is minimized to a distance just short of allowing a piston/head collision, that the motor will become more detonation resistant and can be run on lower octane fuels and with more spark lead. A generally respected figure is 0.040"...

... then pick the right thickness of gasket to set the squish at around 0.040". An iron head motor can run as high as 11.0:1 on pump gas with a tight squish.

Tech: You mean LESS spark lead, don't you?

Are you saying that I could get away with a static CR of 9.6:1 on pump gas with iron 64cc Vortec heads for a towing motor if I keep my "squish" between .035 - .040?

Originally posted by MainCap
Tech: You mean LESS spark lead, don't you?

Are you saying that I could get away with a static CR of 9.6:1 on pump gas with iron 64cc Vortec heads for a towing motor if I keep my "squish" between .035 - .040?

I should have said "normal" spark lead. The first thing that happens when a motor detonates is that timing gets pulled out of the motor. What I mean is that with tight squish, you can run pump gas and a normal load of ignition timing such as 34-36 degrees total without detonation.

I don't know if ....YOU.... can get away with it, but I have and several of my friends have. Now, we weren't building for a specifically towing application and we weren't using EGR. But we've run up to 11.0 on pump gas without detonation and I've read on several other forums that other have done the same. It's all about balancing the static c.r. with the intake closing point of the cam to achieve the proper cylinder pressure for the fuel being used.

Don't pick a cam out of thin air, call the cam grinders and tell them what you want to do. They'll help you by grinding the cam with the proper timing to achieve the highest cranking compression possible on your fuel. Be sure and tell them about the EGR. That will pollute the mixture and make a difference in the pressure the fuel will tolerate.

I've been building motors of all different kinds for over 40 years and I NEVER choose a cam without talking to the techs at Crane. I can normally get a youngster pretty close so he can budget for a spring change if necessary, etc, etc, but the final decision should be made by the professionals.