Cam selection help please

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bb489ss

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Well, a few days ago I finally swapped out the Demon 650 Vac Sec and the Holley Street Dom with an AED 750 DP and Performer RPM and it has made quite a difference in my 9.0-1 383!!!! Throttle response is sick! And the whistling issue has gone away too!!! My combo is:

1971 383 Magnum 9.0-1 comp.
ported 452 heads (milled .060) with steel shim gaskets.
Comp XE 268 hydraulic cam.
Performer RPM
AED 750 DP
long tube headers
MSD 6A box with MP distributor.
727 trans
Dana 60 with 4.10 gears.

I want to go with a bigger cam for some more performance. The car is street driven, and mainly just local, so I plan on keeping the 4.10s. My only concern with cam choice is lift. The motor has stock pistons and since the heads were milled .060, I have to be concerned with piston to valve clearance right? I think my current cam is around .480 lift. I was looking at the Mopar Purple cams (.484 and .509). They have more duration, but not crazy with the lift. Any suggestions would be greatly appreciated. If I can avoid pulling a head to check P to V clearance that would be ideal. Thanks!
 
I see that is one step up from what I have now. I was thinking something in the 280s/ around 240 at .050 no? I read some good and bad about the Mopar 484 cam which is one I am considering. I also was looking at the Comp 285 but that lift might be too much for my milled heads? I guess if I change cams I want to see/feel/hear a difference. My current Comp XE 268 sounds mild, at least to me, in my motor set-up. I think I have plenty of gear (4.10), light car (Dart), and will change converter to whatever I need to. Although my compression is 9.0-1. Plus, when I'm on the road, my RPMS are always 2000-3000 at cruise which is right at the beginning of the power range of some of the longer duration cams I have seen. Again, this is only a local car/show cruiser/stop light bruiser. No long trips here. I've read threads where some say they run the 484 and even the 509 cam in similar setups without problems on the street, then others say they are dogs!! And since a cam change takes a lot more work than replacing a carb, I want to make sure I get one that my motor will like and me as well!!
 
No, this is one step up from yours.

http://www.compcams.com/Company/CC/cam-specs/Details.aspx?csid=708&sb=2

If hearing and feeling is all you want, put a thumper cam in it. You have to take all the specs into consideration when comparing, not just .050". Look at how much more advertised duration the first cam I posted has. Measured from the same .006 point. It's a much bigger cam.
 
Here's a great clip of one in a hot 318. Yours will sound very similar since the 318 and the 383 share a very similar stroke.

[ame="http://www.youtube.com/watch?v=WAhQuKy-I_c"]Mopar HotRod Willys with tuff 318, comp cams Xtreme hi-lift cam and hooker aero chamber mufflers - YouTube[/ame]
 
Fit...as in how? Physically? Yeah it's a big block cam. You might need to upgrade your valve springs though.
 
Sorry, I meant fit as in P to V clearance. However I just found out from original owner that he had valve reliefs ground .040" into the intake side of the pistons and that the piston is .090" in the hole at TDC. He was running a 300 duration cam several years ago, but couldn't remember the lift.
 
Your problem isn't with the piston to valve clearance, it's your static compression ratio. If you go to a longer duration cam you will bleed off too much compression and then you actually make less power.

Every cam has a suggested static compression ratio. If you go above it your motor will ping bad, if you go below it it won't make any power.

If you want max performance without having to change compression ratio (pistons), call someone like Clay Smith Cams and explain what you have and what you're trying to do and they can tell you your best option. I'm guessing it's gonna be to match a cam with your engine to get the most out of it and then go to a different rear gear to take advantage of your engines power band. Right now you have no high speed ability.
 
Oh the hell you say. How many millions of engines have been built outside of those parameters without professional help that made GREAT power overcammed and did NOT spark knock undercammed? TONS.


mopar340dave, I removed the last of what I said. I was havin a piss poor day and that's where it got vented. Sorry buddy. I hope you'll forgive me. For all I know, you've screwed together 10x the amount of engines I have.

Rob
 
Yea, I had two "over-cammed" Chevys (one was a 327, the other was a 496) that ran pretty well. They were both 10-1 motors. But since this is my first venture into Mopar, I'm learning all over again.
 
Well if you look at the description on Comp's site for that cam it says "best all around street performance 9:1 compression....." So see, I was payin attention to your original question. You got 9:1, that cam is suited for 9:1 huh? what? Can we say good match? Sometimes you just don't have to consult the guru of the crystal ball. lol
 
bb489ss said:
Sorry, I meant fit as in P to V clearance. However I just found out from original owner that he had valve reliefs ground .040" into the intake side of the pistons and that the piston is .090" in the hole at TDC. He was running a 300 duration cam several years ago, but couldn't remember the lift.
Click to expand...

.090 in the hole won't ever have trouble with cams like we're talkin about....and it is the duration you have to worry about.
 
You're pretty funny StrokerScamp. Sometimes I just need things spelled out for me to see the light! Remember I am an ex-Chevy guy right?! So I guess you have sold me on this XE275 HL cam. 1st questio: Do you think I can keep the springs that are already in the heads? (previous owner states they are single springs and seat pressure of those is 300 lbs). The ones that I saw Comp recommends are dual springs at 350lb. I may have answered my own question, but then I guess I'll have to have the heads machined to accept the dual springs? 2nd question: What kind of gains do you think I will see switiching from what I have now to this new cam (7 degrees greater duration on intake and exhaust and .045 greater lift) from what i have now? Thanks
 
No, they require a different spring. These:

http://www.compperformancegroupstor...Store_Code=CC&Screen=PROD&Product_Code=924-16

You know what? Now that I think about it, I believe one of the owners of the trans shop where I'm helpin out, HAS that cam in a 383 in one of his rat rods. I'll ask Rodney since he built the engine and if that's the cam, I'll get some video. How would that work? That way, you can hear it in a sho nuff 383.....and it's not a stroker, but a 9:1 383, just like what you're talkin about. I can run by Charles' house because he doesn't drive them a lot but that won't be a problem. If you aren't in a hurry, just hold off until I get a chance to get the video.

And as far as power, yes, I really think it'll make a difference. Those xtreme high lift cams are sorta like grinding for the .904 lifter diameter because they have more lift per duration, so they work well in Mopars. Just let me know and I'll get you some video, ok?
 
Sounds great!! I am not in a big hurry. Will probably pick up the cam and lifters this week. I suppose I will also need the springs, retainers, and locks as well? Probably a new timing chain too right?? Hopefully Comp makes a kit with all of this. I have an engine shop in my area that I am going to use for the cam change, especially since I forsee some possible machine work needed to accomodate the new springs. And I also don't want to mess it up myself. I've only ever installed cams straight up in my Chevy. I appreciate all of your help. I did hear a video on Youtube of a 360 dart with that cam and it did sound pretty nice!! I'd love hear that video of your friend's 383 with that cam.
 
They do make a kit. Remember the dual spring cam break in though. Install the outer springs ONLY for cam break in. Then go back and install the inner springs once the cam is broken in. You might call Comp and see if they have a compatible single spring that'll work. They should....it's only a small hydraulic. Even if they don't, it's still worth it.
 
I was wrong about which cam was in Charles' rat rod. It's this one:

http://www.compcams.com/Company/CC/cam-specs/Details.aspx?csid=716&sb=2

But, the two cams are very similar duration wise and will sound very close. That 275 extreme high lift I linked to first though will make more power. If you're still interested, I'll get a video. They'll sound very close.
 
Ok. I will get some video of it this weekend. I'll swing by and see him.
 
A couple things here - That 268 is an excellent cam for a street 383. I run them too and they are hard to beat.
Here's a couple stats for you -
You have a static compression that is uber-low. Like if you're lucky it's 7.5:1 depending on the heads and gasket choices. That's based on an 85cc chamber (open chamber that was milled a little, or as-cast closed chamber) and any of the flat top replacement pistons that dont come with reliefs.
The heads you have are more-than-likely not cut for dual springs. older model cams did not require the higher spring loads a fast rate does. So the previous owner could run a number of much larger cams with signle-w-dampner springs. In order to run true duals, you will need to have the guides cut and the spring seats cut on your heads. If you look at the springs now with a flash light you should be able to tell if the seats and guides were cut. If not, prepare to pull the heads.

I dont think a bigger cam will get you more power than that xe268. I run them with 9.8:1 in 383s and they make past 400hp. You may want to look into heads with smaller chambers to get you more compression rather than cam. Cam without compression is more detrimental than helpful when compared to compression without cam. I really would advise against this until you have a better understanding of what you have, and can manage the weak points first.
 
He said in his first post he has a 9:1 motor.
 
Yeah, I know. He doesnt have a 9:1 motor with flat top pistons .090 in the hole. He has "9:1 pistons" in a non-blueprinted 383 block, which means when you take into account the way tall deck height, plus the thick (replacement) head gasket, and assuing it has the closed chamber heads... It's less. If it's got open chamber heads it's MUCH less. Remember, if you run the domed pistons in a 383 that isn't decked a lot it still only gets up to about 9.5:1.
 
I was going on the assumption that he's done work to get it there. He didn't say he had not.
 
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