To much cam??

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WARLOCKII

WARLOCKII

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I'm having an issue and would like to get some other ideas. We built a 71 383/727 to install into a 72 Swinger with PS and PB. The engine is bored .030, 9.5 flat top pistons (cast), stock 906 heads (new valves, seats, 3 angle valve job) no port work. Edelbrock dual plane intake w/ 750 carb. The cam is a Comp 284H (484 lift, 104.0 intake centerline, duration @.050 lift 239int, 246 exh, lobe seperation 108.0). 2400 stall conv. and Schumaker headers with dual exhaust. The cam and crank gear marks were aligned when installed and the balancer is 1-2 degrees from being dead nuts on.

The issue is the engine only develops 5-6 in. vacuum at idle (15 deg.initial timing) and 10-12 in. at 3500 (34 1/2 deg. total timing). If I give it more initial timing the vacuum will increase but I end up around 50 deg. total timing. The PB hardly work, it wants to die when put into gear (unless I turn the idle speed up).

I wanted something that had a lopey idle but I need the PB to work. The combo works great above 2500 rpm but I need something a little more streetable. Is the cam to much??? Any ideas, thoughts, comments, suggestions would be great.
 
You need to have more initial with about the total timing you have now. Probably around 20 or so initial with 34.5 total. You may have to modify the distributor by welding up the advance slots depending on which distributor you have.
 
Your combo is out of wack. The easy fix is swap to a smaller cam. A very adjustable distributor would be good.

My buddy did this in a '79 Ram Charger with the same exact results.
For some stupid reason, he refuses to change the cam. I've told him to change it like Um-teen times. His excuses are lame and stands by them. He makes no sense. The engine was built for a super charge with that same cam.

"The cam is where all the engines balls are at.... Right?!"
"I want a lump lump lump idle! And that's final!"
The guy that built it is a MoPar guy and said it would work in my truck!"

After the Um-teenth time, I just said yea it is your right of course how stupid of me!
 
x2 on twenty initial, try to hold or make changes to 36-38 total, Im not sure how on that dizzy but it has to be easier than a mopar dizzy.
 
WARLOCKII said:
The dist. is a Pertronix with the flame thrower coil.
Click to expand...

I am not familiar with them enough to know how adjustable they are. You might try searching their site for some deestruckshuns. If the mechanical advance is adjustable, that should fix your problem....or at the very least greatly improve upon it.
 
You put in cast "9.5:1" pistons. Did you have the block decked? Me thinks your "9.5:1 383" is closer to 8:1. The 383 block is ALWAYS very tall compared to the blueprint spec so you have to mill the hell out of them to get the piston to where it needs to be. Plus, the 906 heads will have much larger chambers than blue print spec especially with a valve job. Were they CC'd to verify the size and mill the heads to correct that? 383s are harder to "get right". Yours is overcammed only because as you describe it - it's about 2pts less static compression that you wanted.
 
moper said:
You put in cast "9.5:1" pistons. Did you have the block decked? Me thinks your "9.5:1 383" is closer to 8:1. The 383 block is ALWAYS very tall compared to the blueprint spec so you have to mill the hell out of them to get the piston to where it needs to be. Plus, the 906 heads will have much larger chambers than blue print spec especially with a valve job. Were they CC'd to verify the size and mill the heads to correct that? 383s are harder to "get right". Yours is overcammed only because as you describe it - it's about 2pts less static compression that you wanted.
Click to expand...

^^^this

Assuming you used a true flat top and .040" (conservative-sometimes as much as .080") under the deck for TDC, an 0.040"x4.4" gasket, and 88cc chambers (typical for 906 based on testimonies on this website), you're probably closer to 8.4:1 at best. And with 8.5:1 and a 284* cam, that may be retarded (dot to dot isn't degreed) on a 108* LSA = usually low idle vacuum.

These guys are telling you correctly. Timing will *help* ameliorate your idle vacuum, but if you're running ~8:1 compression with that cam, you're likely losing a good bit of cylinder pressure at low engine speeds.

If I read your description correctly, you're using a COMP Nostalgia Plus 284H grind 21-671-4; it even recommends at least 2800 stall, with 9.5:1 compression...this also assumes the cam is degreed to a 104* ICL. On many occasions, timing sets are known to actually retard a cam a couple degrees, and that typically softens up your low end.

If you're dead set against changing the cam, take these guys advice; up the stall and work your timing curve. I'd also recommend checking the actual degree on your cam-make sure it's installed as the cam card advertises.

Oh, and what rear gear are you running?
 
Oh...assuming 0.080" in the hole, with the rest being the same as above, it would be closer to 7.8:1
 
Remember too though, that he said the cam is straight up. So advancing it may help a lot.
 
Exactly, Rob-that's where I was driving. He installed it straight up, so advancing it would likely help out. What I've seen is timing sets (what kind, did he use?) that actually retard timing a few degrees-as much as 6* with stock type timing sets or low budget double rollers.

I'm actually kinda waiting for younggun to come on here and say we're all overreatcing. :) since he's running a COMP 294S Magnum grind in his 383 with 84cc Edelbrock heads. But I think he's running more stall and more gear...pretty sure those Eddy heads are about a good 6cc smaller than the 906s too.
 
Comp tends to grind in a couple degrees of advance anyway - but if this is like the MP deal - you can probably go another 4° and it will help.
OP - get a cylinder pressure reading. That will help establish what you're dealing with.
 
I helped a guy put the 508 cam in a STOCK 318 in a 89 W150 years ago. It had 35s on it and 4.10 gears. The truck was stone STOCK. Well, it did have headers. We also did a valve job, but we did no performance upgrades other than matching springs for the cam. I installed it 6* advanced and I couldn't believe myself how much it had down low. He just HAD to have that big joker in there. It sounded good as hell too. lol
 
According to COMP:

284H 284/291 @ 0.006"
239/246* @ 0.050"
104* ICL / 108* LSA
intake opens 38* BTDC
intake closes 66* ABDC

exhaust opens 78* BBDC
exhuast closes 34* ATDC

Hydraulic-Strong midrange with a lopey idle 2800 + stall with 9.5:1 compression replaces the popular 484 cam.
 
I'm not against changing the cam, it could be the least expensive cure. The rear gears are 3.23.
 
Actually the least expensive cure could be to advance the cam and adjust your distributor curve. I think between the two, you would be very close. Close enough to fudge the rest.
 
Try what moper was talking about up there and do a cranking pressure test to see where you're at. If it's just a matter of retarded cam timing, you can probably do just like they're talking about and swing the cam advanced 6-8* and have a much more fun vehicle to drive.

Personally I'd recommend going with a little more gear...like 355 or 373 at least. I guess it depends quite a bit on your intended usage. If you want to drive this thing 20 miles every day, a cam change may be on your horizon. If it's just a weekend toy, bump the cam up, get some lower gears (and maybe some more stall), tune the dizzy, and go from there.
 
If he does the cam advance, gets the distributor curve right AND goes with a 3.55 he'll set it on fire compared to what it is now. Gears oil and gaskets is about all it'll cost.
 
Rob rusty,dead on the money. Had a similar grind in a 396 rat. 6" of vacuum at idle. Threw Rhroads lifters at it,curved the dist to 18 initial,36 total at 3000. Became a pussycat, 12" at idle. Really like advancing the cam 4-6 ,with those 3.23's.
 
How adjustable is that distributor?

The gear set is numerically low. What is the tire size is on there?

Did you mic up the engines slugs and cc the heads etc....
What I'm asking is are you sure your comp ratio is exactly what you state?

I also agree with MTmopars on that converter. Even more so with the rear gear.
 
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