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Cam selection ideas

hunt2elk

hunt2elk

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I had my 383 rebuilt several years ago and have never been satisfied with the performance. It seems the engine builder put in a cam that isn't ideal for my setup. So I am looking at replacing just the cam and lifters. The car is a 69 Road Runner, 4-speed, 3.91 gears, 28" tall rear tires. The block was bored .030 and JPW KB162 030 pistons were used with the stock rods. Stock intake manifold, stock HP exhaust manifolds with 2 1/4" pipes no h-pipe. Stock 906 heads with no porting. 750 Edelbrock carb.
I am looking for a decent running car with a catering to in town stop light to stop light fun. I called Comp and was told the XE268H would be a good choice and I should be ok with reusing the springs I already have. Anybody running this cam or have another recommendation?
 
I try not to get lost in marketing names. When the "Xtreme energy" series came out, everybody went nuts about them. I honestly think the dual energy grinds are better suited for exactly what you're doing. I think this would be abetter choice.

http://www.compcams.com/Company/CC/cam-specs/Details.aspx?csid=715&sb=2

From what it sounds like, you're running a pretty stock setup but want better snappyness but not overboard on the cam.
 
You might do well with the 268 or even better with the one Rusty mentioned but that depends on your compression ratio. If you have low compression then the smaller one might be a better choice. Also, you don't have to be confined to Comp Cams. Crane makes some really good cams as well as the MoPar purple shaft line or Edelbrock and a few others.

What cam do you have now? If you go smaller you should go a bit taller with the gears. 383's are not torque monsters but can respond very well to a high overlap cam (108 lobe separation grinds) but you will use all of that 3.91 gear and have low vacuum, use more gas, etc. Those are not street cams. And perhaps this is where you are now and what prompted the change.
 
The cam in it now is a Comp CRB 268H which I don't think is even made anymore. gross valve lift in .464 ex .464 / duration @.006 in .268 ex .268 / lobe separation 108 / duration @ .050 in 222 ex 222.
When I talked to Comp yesterday, they said the cam installed now would work better with headers and aluminum intake-exhaust manifolds.
I cant get anymore than 10 inches of vacuum and have to run 23* initial timing. I did a compression test with a warm engine and all cylinders were between 132-137. Someone on this site thought this would translate to a 9.2 compression ratio. We did take the front of the motor apart to check the cam timing and found it is at 0.
Yes RRR I do want a little more snappiness for in town driving. The car originally had 323's and was a total dog - hence the change to 391's which made a world of difference, but I think it could be better.
 
No way can you equate cylinder pressure with static compression ratio. There are simply too many variables. 108 degrees LSA. That's a large part of it, I think. Honestly, I think the Road Runner cam would make you more happy. .......and I'm dead serious. It's either 114 or..I think even 115 LSA. See, that makes for a much more street happy cam. All the charts and books and such say wider LSA bleeds off cylinder pressure.......but I'm ready to argue that point with lower compression ratios. I've seen it too many times and I don't know why. But when I've used a wide LSA with like 9:1 and lower, the cylinder pressure goes up each and every time, and the engine runs like fire RIGHT where you want it for a street motor. 112 works about as well. That's why I recommended the smaller cam above.......even though it's on a 110, the smaller duration @ .050 kinda gives the same result as the wider LSA. Kinda. Sounds like your engine is pretty much stock. That's why I believe there's room for improvement is because the cam is somewhat of a mismatch with that 108. I think this could be another good choice.

http://www.summitracing.com/parts/cro-32242/overview/make/dodge
 
Last edited:
RustyRatRod said:
No way can you equate cylinder pressure with static compression ratio. There are simply too many variables. 108 degrees LSA. That's a large part of it, I think. Honestly, I think the Road Runner cam would make you more happy. .......and I'm dead serious. It's either 114 or..I think even 115 LSA. See, that makes for a much more street happy cam. All the charts and books and such say wider LSA bleeds off cylinder pressure.......but I'm ready to argue that point with lower comprassion ratios. I've seen it too many times and I don't know why. But when I've used a wide LSA with like 9:1 and lower, the cylinder pressure goes up each and every time, and the engine runs like fire RIGHT where you want it for a street motor. 112 works about as well. That's why I recommended the smaller cam above.......even though it's on a 110, the smaller duration @ .050 kinda gives the same result as the wider LSA. Kinda. Sounds like your engine is pretty much stock. That's why I believe there's room for improvement is because the cam is somewhat of a mismatch with that 108. I think this could be another good choice.

http://www.summitracing.com/parts/cro-32242/overview/make/dodge
Click to expand...

Where do I find this Road Runner cam? 91 octane gas is what I run in my cars, is this good enough for an older style cam? I do remember reading in one of the Mopar engine books that they recommended a lobe separation of at least 112* for a stock 383 build. And no, I am not married to Comp by any means.
 
I just wanted to throw this out there. Have you gone through all the basics like making sure that when the gas pedal is all the way down to the floor the carb is full open? Have you tried advancing the timing more and or looser springs in the advance. My 2 cents worth.
 
I never try to figure out MoPar cam specs. I've mapped um before and they don't come out regardless which method you use. They say they use .850 to figure duration @ .050 but it doesn't come up either. Whenever I used MoPar cams in the past, I just build the engine around it like the book says and it works just like it was intended. I forget about the specs and just go with it. lol
 
eric383 said:
I just wanted to throw this out there. Have you gone through all the basics like making sure that when the gas pedal is all the way down to the floor the carb is full open? Have you tried advancing the timing more and or looser springs in the advance. My 2 cents worth.
Click to expand...

I've spent a lot of time with the carb. The throttle plates are fully opening when the pedal is down. I had originally used a rebuilt 750 Edel, but listened to a consensus saying I had to much carb. I then bought a 650 Thunder and tried that for a year. Nowhere near the performance I had with the bigger one. So I bought a new 750 and found it ran the best when I went down 2 sizes on the primaries. I don't feel as though I gain anything by advancing the time anymore. I have not tried different springs in the advance, but it is all in by 1900 rpm. In my opinion I have it running as well as possible with this cam.
 
The best way to get alot of torque and horse power (without going more cubic inches) in your 383 is increase cyl head airflow, and raise C/R. We have a 383 in a 1970 Super Bee, runs really strong. We have the XE 274 hyd grind. .488 int and .491 ex lift. 274/286 total duration. Dome pistons, 915 heads unported. Street Dominator intake, Holley 750 CFM carb, stock ex manifolds. If you were to install a Performer RPM intake, and headers, that will help airflow alot.

- - - Updated - - -

And my 451 with 13 to 1 C/R, ported 915 heads, 2.14 intake and 1.81 ex valves, headers, Mopar 509 cam, fries the tires in 2nd gear at 5200 feet above sea level.
 
Garys1969RR said:
The best way to get alot of torque and horse power (without going more cubic inches) in your 383 is increase cyl head airflow, and raise C/R. We have a 383 in a 1970 Super Bee, runs really strong. We have the XE 274 hyd grind. .488 int and .491 ex lift. 274/286 total duration. Dome pistons, 915 heads unported. Street Dominator intake, Holley 750 CFM carb, stock ex manifolds. If you were to install a Performer RPM intake, and headers, that will help airflow alot.

- - - Updated - - -

And my 451 with 13 to 1 C/R, ported 915 heads, 2.14 intake and 1.81 ex valves, headers, Mopar 509 cam, fries the tires in 2nd gear at 5200 feet above sea level.
Click to expand...

On this car I am trying to keep everything stock, but want the most I can get out of it. I'm thinking I will build my 440 Charger motor a lot stronger - and yes RRR this probably means headers lol.
 
Notice that the OE RR cam is simar to the extra long duration of the Comp Cams Rusty mentioned. There designed with use with exhaust manifolds in mind.
 
Using stock heads, manifolds, keeping everything stock, its going to be difficult to get alot more perf than you already have. More cam lift/duration will help, but will tend to sacrifice low end torque, while increasing top end power.
 
Right on Gary. That's why I was tryin to make mild conservative suggestions. lol

Oh and you really like them 915 heads, dont you? Hows that 383 run with them?
 
The 383 runs really strong with the 915 heads. 2.08 int 1.74 ex valves. No porting on this set. He could almost keep up with my 451 RR equipped with 906 heads. We had same intake, carb, HP ex manifolds and ignition. But now with my 915 heads on the RR, he doesn't have a chance! Those 915s really work well.
 
i'm a little reluctant to get into this but i don't think there's a cam problem. that cam has 108lsa, probably 4 degrees advance, short duration, closes the intake valve very early and only 130psi,...? too many other things to look at here.
 
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