Cam timing help!

[68suprB]

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?

 

[RustyRatRod]

Praise God from whom all blessings flow. Finally somebody with some SENSE That asks a question and gives ALL info. Instead of "I need help with my timing, my car is red."

YES. It is normal to have significantly higher timing requirements with a non stock camshaft. Especially with low compression ratios. I know, I know. You said it is an HP so that means 10:1. Wrong. That means Chrysler advertised it at 10:1. You're lucky if it's really 9.25.

So, what's all that mean? It means with that particular camshaft, it's gonna bleed off a good bit of cylinder pressure requiring a lot of initial timing to get it back. It is actually a little big, but you can work around it. 244* @ .050. That's pretty big. Specially talkin about a hydraulic.

You might even experiment with locking out the distributor. Maybe try 34* and see what happens. BUT, it probably won't like it, because again of the lower compression. Lower compression engines usually like higher total timing figures. I bet it'll like 38* total, inital plus mechanical. You say 46.8". Is that with or without a vacuum advance? If it's with, then that's pretty low. It's not uncommon to have 60* including the vacuum advance. It's simply something you're going to have to play around with to see what it likes best. But again to reiterate the answer to your question, higher initial and total timing is normal in your situation.

You will likely have to end up modifying the distributor so you can have less mechanical advance and more initial. This is acheived by brazing up the slots in the advance plate and filing them to the right spec. It helps to find someone with a distributor machine. Essentially where you are now is not enough initial and too much mechanical.

I hope all that made more sense to you than it did me. lol

 

[68suprB]

Thanks for the reply rusty.
Yes the 46.8º total is with vacuum advance at about 3000 rpm read with a digital timing light. Like I said I don't know too much about cams, kinda learning as I go along and wanted to make sure I wasn't going to mess anything up with that much advance. I was hoping not to screw with the distributor but I guess it is what it is. The next thing I was looking at changing is the intake manifold this winter. Would a single plane intake be more suited to take advantage of the high rpm cam or would that put the final nail in the coffin and totally kill the low end power?

 

[RustyRatRod]

I would go with a good dual plane of some sort. The edelbrock RPM comes to mind. The DP4B is another excellent chioce, as is the Weiand 8008. A single plane will work, but if it is mostly a street car, the dual plane will help bottom end a little more.

 

[Garys1969RR]

My son has a similar set up. 1970 Super Bee, 383, Comp Cams .491 lift, 284 duration I believe. Street dominator intake. We did like Rusty said, braze up the dist mech advance to limit total advance from the dist weights. Then total advance of about 38* all in by 3000 RPM. 3.91 gears. Auto. It does the same thing, decent low end, but comes on real strong about 4000 RPM. Wont spin the tires in first, but some chirp when it hits 2nd. And they do like alot of initial advance, like 20* or more. These figures are all concerning mech advance only. Vacumn advance is a whole other subject, but follow Rustys thoughts there. Good luck.

 

[Meep-Meep]

I would change the cam. What you have is too much for your compression ratio, or more specifically, too late of an intake closing point. All the above suggestions will help, and are typical in this situation, but really it's just too much cam. Find one with about 270 deg duration and 112 lobe separation. Everything will work better.

As a side note, I did run an Isky 280 deg 108 LS cam back in the 80's in a 383 with "stock" compression, and it ran well, but also had similar symptoms though not as bad as you describe.

 

[Garys1969RR]

Oh yea, forgot to mention on our 70 383 in the Super Bee, we are running dome pistons and 915 closed chamber heads. Gets us a C/R of 12 to 1. And the combination works pretty well. So like Meep Meep said, you need more compression, or less cam. And less cam is easier to change. Also, on a bigger motor, like a 440 or 451, I think you can get away with more cam for the C/R. Correct me if I'm wrong. But with the longer 3.75" stroke, that allows for more low end torque. So the later closing intake event doesn't doesn't kill the low end as bad. You can also try advancing the cam 4 to 6*, that tends to help low RPM torque, due to an earlier intake valve closing in relation to piston position on the compression stroke. That traps a little more mixture in the cylinder at lower RPMs for better torque. And I dont think in this case it would hurt your top end performance.

 

[Meep-Meep]

I'm not sure if it's the stroke or just displacement that soaks up camshaft, but of course more stroke usually means more displacement. I suppose the RB 383 vs. the B 383 would be an interesting experiment. Advancing the cam will help too, and I was going to suggest that, but then thought if you have to go that far on the OP's combo just change the cam to something smaller.

12:1!!?? Damn Gary, that thing must have been a hoot!

 

[Mebsuta]

I used a 270 Isky Mega Cam in 383 HP RR, 4 spd for a little while years ago. I liked the way it sounded, but thought it was a little too much. Switched to factory 383 HP cam and like that better. Right now it is advanced 4 degrees at the crank. Initial is 15 degrees BTDC. Idles with 16 inches manifold vacuum at 700 rpm or so. I use Edelbrock 1405. 3.91 with 255/60/15 in back. It's real easy to drive, but it doesn't have the Dairy Queen idle. It's fine for what I want to do, which is cruise around, enjoy the night and not worry about it.

Sometimes I think about trying a Comp 268H or something like that to close intake valve a little earlier and raise cylinder pressure, but probably won't touch it.

 

[Garys1969RR]

I'm not sure if it's the stroke or just displacement that soaks up camshaft, but of course more stroke usually means more displacement. I suppose the RB 383 vs. the B 383 would be an interesting experiment. Advancing the cam will help too, and I was going to suggest that, but then thought if you have to go that far on the OP's combo just change the cam to something smaller.

12:1!!?? Damn Gary, that thing must have been a hoot!

Yea his 383 runs great on 100 Sunoco. 3.91 gears. 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

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Another thing, my 509 cam has the same duration as yours, 68 supr b. That is 292* . In a low compression 440 (like 8 to 1 at the most), that motor had no low end, and not alot on top. But with that same cam, heads, carb, exhaust, and just raising C/R to 12 to 1, and a new bottom end, in a 451, it is a screamer! The 509 cam is very similar to yours, just a little more lift. And that cam likes compression, gears and a loose converter. Also was running an Eddy 750 carb. Put on a 700 Holley and went 1/2 second quicker in the 1/4 mile. Have since gone to a 780 vac secondary, and it runs even better! So experiment to see what works. You said you running a stock cast iron intake? Maybe try an alum one like the RPM Performer. Keep us posted!

 

[Meep-Meep]

Oh yeah, mile high. Makes sense now!

 

[Moparmatt72]

Wow after reading all the posts I really can't wait to see what my new motor does. I have the risky mega 292 509 lift had it on a basically stock 440 with 906 heads with bigger valves and a torker intake. Ran well never had a stumble, had to pump the brakes due to little vacuum lol. Dang I need to get my Dana done.

 

[Garys1969RR]

Wow after reading all the posts I really can't wait to see what my new motor does. I have the risky mega 292 509 lift had it on a basically stock 440 with 906 heads with bigger valves and a torker intake. Ran well never had a stumble, had to pump the brakes due to little vacuum lol. Dang I need to get my Dana done.

What are the specs on your new motor? 509 cam and 906 heads? What C/R? Still usin the Torker? When I put my 509 in my 440, Power brakes would only work if I down shifted it and pulled alot of vacumn. So I changed over to manual brakes, not too hard to do. I like them better, and have more room in the engine bay.

 

[Moparmatt72]

Its a .060 over with at the time 10:1 for the 88cc chambers but I went with a set of ported stealths that have 76 cc chambers. I also have a ported m1 with a 850dp but also a 1050. I also have a set of 1.7 roller rockers. So I'm thinking my over all compression will be bumped up to what atleast 11:1 maybe 11.5:1 or am I wrong. I actually am planning on converting to hydraboost just need to mount everything.

 

[Garys1969RR]

Using a 76cc head chamber volume, bore of 4.380, head gasket of .040, and pistons at .020 below deck, the calculator says 11.19 to 1 C/R for your motor. But I am guessing on head gasket thickness, and piston height.

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Oops, that is for a 3.75 inch stroke. With a 383 its a 3.38 stroke which makesC/R at 10.18 to 1

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And the bore is 4.310? Makes C/R at 9.98 to 1. If you go to a .020 head gasket, you can get to 10.42 C/R

 

[m79ded]

I agree 100 % with a cam change and the range that Meep-Meep suggests is right on the money.Look at this crower grind 222 intake 234 exhaust @50 or Lunati 60303. Those would be alot better

 

[68suprB]

Thanks for all the input guys! It's gonna suck to tear apart a freshly rebuilt motor, so I guess I have a decision to make...get a new intake manifold and hope it helps the bottom end a bit...or get a new cam...obviously I would rather go the easier route and get an intake, but do you think a dual plane would be working against the cam in the higher rpm's?

 

[SwedCharger67]

Thanks for all the input guys! It's gonna suck to tear apart a freshly rebuilt motor, so I guess I have a decision to make...get a new intake manifold and hope it helps the bottom end a bit...or get a new cam...obviously I would rather go the easier route and get an intake, but do you think a dual plane would be working against the cam in the higher rpm's?

I'm afraid a new intake won't help, go with a cam change. More cylinder pressure is what you need. My 383 is very similar to yours, and the engine is a pain, surely much less hp than a stock engine!

 

[68suprB]

Ok, I've decided to just go with a new cam, I've been talking to a guy at comp cams and we've narrowed it down to these 3: Let me know what you guys think:

1) 21-305-4 Magnum Muscle 1600 to 5600rpm Duration- 268 intake 276 exhaust Duration@ .050 intake 222 exhaust 226 valve lift .464 (basically a stock 383/440 cam with magnum lobes)

2) 21-222-4 Xtreme Energy 1300-5600 rpm Duration 262 intake 270 exhaust Duration @ .050 intake 218 exhaust 224 valve lift .462, .47 (smoother idle with good response)

3) 21-223-4 Xtreme Energy 1600- 5800 rpm Duration 268 intake 280 exhaust Duration @ .050 intake 224 exhaust 230 valve lift .477, .48 (little more aggressive than #2, broader power band)
My engine specs are at the top of this thread....thanks for any input, no power brakes so vacuum isn't a huge issue, looking for a broad power range and a choppier than stock idle...thinking I should stay away from the magnum profile with my stock compression, just wanna see if anyone has any experience with any of these cams...He says I'll need new lifters springs retainers and keepers with the new install...[FONT=Garamond, serif][/FONT]

 

[RustyRatRod]

#3.