Friend just had his 383 rebuilt, and something ain't right. putt 11-5 to 1 pistons, heads ported and new valves, springs, etc (906's) a 292 513 hydraulic cam that was degreed when installed, air gap intake, and a 750 carb. msd ignition. 727 tranny. Shows about 350 hp to rear wheels. Running mid 14's in the quarter. Compression check shows 110 psi per cylinder. His engine builder told him the psi didn't matter, as long as they were all even. Block was decked and cylinders were 10 0ver. Running open headers. this thing should run alot better, any idea where to look?
At first look I think the cam is way big. The low cylinder pressure could be a result of lots of valve overlap. Where did you get the hp number? What converter? What rear gear? Do you have the timing card ? .
That cam shouldn't be bleeding of 80-90 psi, it's not that big. I've got 10:1 in my 440 and cylinder pressure is 165 with a similar cam. Rings are gapped way too loose maybe?
I built a similar 383 for my buddies 69 super bee with a 4spd and 4.11 diff.we had a split duration cam 270-280ish I think and about 480 lift on a 108 centerline.That bee would run 12.8 all day shifting at 6k.
Check the timing card for the amount of overlap, or call the grinder if you know the grind number. Big cams can have big overlap. .
i've got that same cam in my 10.15:1 compression 415 inch smallblock. It's not that big of a cam (yes i know it seems bigger on fewer cubes) but 110 psi sounds a little low but not the end of the world i ran 13.ohs in 4100lb Fury with a 3.23 gear and a deep first planetary. i run an 850 double pumper though, he may need to step up the carb. with 350 to the tires, it should run much better, sounds like driver mod is needed....
The cam is too big, as others have said. Is it the reason the compression is low? Might be, your next step is to do a leakdown. A 383 with ported iron heads will need a smaller cam than a 440 with similar mods. The carb may be a bit too small too. It sounds like the combo was built for mid to high range (3000-6000 RPM). What does the car weigh? What timing and ignition?
Where are you guys coming up with the cam is too big? 3000 stall, 4.10 gears and ported heads, that cam is just about right. Just look at some builds like the Resto to Rad 383 build that Mopar Muscle did a few years ago, .545 inch lift with stock 906's and they made 450 at the flywheel.
That cam is way too big for a mild 383. Put something like a .480/280 "Comp Magnum 280" or comparable and watch that little 383 wake up. That hydraulic 292 in a little 383 won't even wake up until about 4500 rpm.
I cannot speak for the others who agree with me that the cam seems too big, all I can say is that, to me, it sounds big. No, I do not know all of the cam details, but I have asked for more info... I have used alot bigger sticks in 354 Hemis but since every cam is different and responds differently to the particular engine in which it is (assumed to be correctly) installed, all that is left is that 'ol gut feeling. .
http://www.moparmusclemagazine.com/techarticles/mopp_0209_383_engine_restore/index1.html rated at 285/297 degrees gross duration and spec'ing out at 241/247 degrees duration at .050 inches, with .545/.545-inch lift on a 110-degree lobe separation. The cam was degree'd in at four degrees advance and topped with a set of matching Comp lifters. His still sounds big (292 dur/513 lift), especially considering the duration is the same, which is what kills low end. That article also used an 850 carb, so my thoughts on that are backed up. If you have a cam that is soggy down low but works up high, and a carb that only works up to say 5K it will never be really happy. Leakdown will answer some of it, and it may need some good old fashion tuning.
Overlap has no effect on psi. Your cam is retarded, should pick up nicely advanced 4-6° as a test (but 383 has fairly tight piston to head clearance so unless the pistons have deep notches, be careful).
I say the cam is not to big, I have built many 383 and 440's I allways run the MOPAR purple cam 292-509 it is a great old school cam. What size headers are you using? I allways run 1 7/8 the 2" seems to kill low end to much. Yes I know so will a big cam but with a stall and 4:11 gears you should be ok. Is the dizzy tuned? 12 initial 38 total. Are you spinning your tires 1/2 way down the track ? That could be slowing you down..
Elpolacko, thanks for digging up that thread. Don has alot of experience and glad that he continues to share it. Perhaps he will weigh in here. .
What are the part number for the pistons that were used. I'm willing to bet you don't have 11.5 to 1 like you think. Those 906's are an open chamber head. Stan
It's making 350 to the rear wheels, probably around 425 at the flywheel. That is plenty of power but it probably has a very narrow power band. The problem is 383's are not torque monsters like 440's are and like to rev. A 383 with a hyd. 292 cam, ported 906's and 11.5 to 1 compression is going to be a pig until about 4500. If it had a 4 speed or a 4500 converter the car would ET a lot better, but 4500 converters are not very street friendly. I have built and raced many B/RB Chrysler's and had good success with them. And yes, you could advance the cam and it would help some but the cam is still too big for the combination.
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