Cam timing help!

[68suprB]

That's what I was thinking. I like the idea of putting a "stock" profile Magnum Muscle in but the comp cams rep said the xtreme energy cam will make more power with my relatively stock setup.

 

[1948 santa]

Hey 68suprB from your original post,I have a 69RR 4speed with exactly the same problems and have the Comp cam #21-223-4 have been told and been working with a machine shop the way to fix it is with a Holley carb#4778 or 4779.I have an Edelbrock carb on my car right now but getting an AVS carb reworked,should have it back before long and will post results.Trying to keep car as original as possible the reason I chose to put AVS on car instead of Holley.

 

[68suprB]

You're having the same problems as me WITH the 21-223-4? Its a substantially less aggressive profile than the one I'm running now, I would hope it ran alot better with the 21-223-4 in it

 

[SwedCharger67]

You're having the same problems as me WITH the 21-223-4? Its a substantially less aggressive profile than the one I'm running now, I would hope it ran alot better with the 21-223-4 in it

It probably runs better but in a very low compression engine even that cam might be a bit of trouble.

 

[64 Post]

We like alot of C/R in the rarified air of Denver. Lol. And my 451 is at about 12.2 C/R. Thats with 906 heads. Well just got a set of 915s to put on it. With 1.81/2.14 valves installed. So will put those on this winter which will make it about 13 to 1. Then I will have to go to E-85 fuel. So should be interesting. C Ya

Kinda doubt you'd need E85. Remember, the D/A knocks a minimum 20% off the compression/cylinder pressure. Your 13.1 is really 10.5 at 6,000 ft. I ran 12.4 on the street with 5 gal. of 110 and the rest pump gas.

 

[Scatransit]

Ok here goes- for all you cam guru's:
I have Comp Cams Part # 21-242-4
292 duration
501 lift
Grind # CRB 292H-10
1968 Dodge Super Bee
4 Spd transmission
383 HP V8
Pertronix electronic conversion in stock dist.
Edelbrock 750 CFM Carb
Bored .30 over, stock intake & exhaust manifolds
3.73 rear
My question- is it normal to have significantly higher timing with this cam over the stock one? The engine was rebuilt with this cam prior to me buying it, and the owner had it at only 8º BTDC. It had no power on the bottom end at all. I now have it set at 21º initial with 5-7" of vacuum and 46.8º total at 3000 rpm with 18.5" of vacuum (vacuum gauge hooked to manifold port). After advancing the timing the bottom end power has improved a little along with throttle response but it still lacks alot of bottom end power, but doesn't ping or knock with the high timing. Kinda just stumbles if you open it up fast, then pulls ok once it's wound up. (with this newly rebuilt motor and a 3.73 rear I thought it would be able to smoke the tires just stomping on it in 1st while rolling) My main concern is advancing it too much and damaging something. Would the cam be causing the need for high timing and the low vacuum? It says RPM range is 3000-6200 so am I just stuck with more or less high end power?
Thanks for any input guys, I don't know alot about cams, is this a super agressive one? maybe too much for this motor?

It is possible that with the set-up you describe, that the cam may be a tad much. Regardless, when comes to ignition timing using a non-stock cam, typically it will require more timing - that is, more advance. In all cases, when tuning these cars in our driveways, we must first find a good timing baseline. From there you can fine tune in 2 degree increments (+/-) until the engine is happiest. In the absence of a dyno, the best way to find this baseline or "sweet spot" is this: Install a vacuum gauge to a manifold source. The lower port on your Edelbrock carb is perfect. Start the engine and warm it up. Loosen the distributor and rotate it fore or aft until you achieve the highest steadiest vacuum reading. Adjust the idle (and air/fuel mixture) accordingly as you go - usually around 700-800 RPM is best, as we do not want the mechanical advance weights to skew our efforts. Keep at it until you have the highest steady reading and decent idle in the above range. From there, retard the timing about 2 inches of vacuum +/- and lock down the distributor. You have just found your baseline. Next turn off the engine and see if it starts OK. Does it turn over normally & smooth? If so, great, we're almost done. If not, return the vacuum reading to highest steady reading and re-start, OK now? Good...With your timing light, make a note of where the timing is on the balancer. The reading is not important (well it is, but not for the purposes of this discussion). Drive the car, does it accelerate smooth? Does it ping? Advance the timing 2 degress and test again. Starts good? Accelerates smooth? Doesn't ping? Keep playing with the timing until you get a drop in any of those areas and then back up. Be sure to do this with the fuel you intend to use primarily. Yes, over-advancing will potentially damage the engine, BUT, as long as it 1). Starts smooth, and 2). Accelerates without hesitation or pinging, you should be just fine. This has always worked for me, in my nearly 35 years doing this sort of thing for a living. Good luck with it!