Valvetrain control issue?

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Johnny from Chicago

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I have a problem in my powerband from 5400 to 5800 it doesn't want to rpm but after that it will rev cleanly again. I have a 383 with a purple 484 cam advanced 4 degrees ( I know that's not right - had wrong spec sheet on install ) stock 516 heads 9.5 compression, stock rockers, MP electronic dist. locked out at 35 degrees and an Edelbrock rpm intake with a holley vacuum 750 with no spring in the secondary ( I tried springs but to no avail ). I have rejetted and no luck, I changed valvesprings to MP heavy springs 250 seat 350 open (way more than this cam needs)no luck either. A racer friend says I may have lifter pump up, but the solution it adjustable rockers $$$ and maybe different lifters too. If I do all that I may as well blow even more money on a monster cam, which I don't want to spend all that now - I need heads first.
 
Hi Johnny, welcome. What did you mean by
"has no spring in it"? It sounds like you have a few issues there. One at a time. Was the .484 degreed, or just installed with the 4* advanced keyway in the timing set? Your timing needs a curve, no a welding job (IMO anyways), the valve springs are now way off, replace them before your cam gets eaten, and BTW, they shouldnt have 250# anywhere near the seats. "normal" would be like 140# on the seat, 350 open. The MP springs are junk to bigen with, so I'd use Comps, p/n 911-16 will work fine. The heads will work, but you can do much better on cam choice. The small exh valve and bowl area is killing a bit of power. It should still work, but in reality, the 484 is not meant for 6500rpm. The peak if things are right is more down around 5800. Just out of curiousity, how did you come to have 9.5:1?
 
well, with your persistant difficulties, should you be saying anything?lol.
and whats up with that sig pic? lol
I told you try a different distributor too, if you remember..
 
I have a friend who races stock eliminator and is forced to use a vacuum secondary (national record holder) and he recommends removing the spring for actuation similar to a double pumper. Tried it and the car really leaves the line now - I bought the quick change kit of springs and tried them all - the problem still exists and the car slows down with all of the spring choices. The cam was installed without degreeing on the +4 keyway (thought I had a different centerline). I locked the distributor centrifigal advance out and set the timing to a total of 30-40 degrees in two degree increments (it likes 36). This was done to eliminate the advance as the problem. The problem is still there - this was done with the screws provided inside the dist. I welded the vacuum advance plate because it is able to flop around and change the gap on the reluctor if it does so (don't know if it does flop but again I'm hunting for a problem and I don't drive it on the street anyway so I don't need vacuum advance.) I don't expect the cam to make power to 6500 but I need it to make it smoothly to the 5900 that it advertised, as now I have to shift at 5400 and I'm leaving e.t. on the table. The compression - KB hyper pistons with a valve relief 5cc, zero deck, 516 closed chamber heads 79cc. These are actual measured with the whole burette thing by a competent machine shop. The spring were also a wild quess because it feels like valve float - no better. I got a few suggestions about lifter pump up, but I don't like the cost of the solution = adjustable rockers and anti pump up lifters. Any help appreciated.
 
Mike in the words of Cartman "shweet"..


Johnny, As far as the carb goes, run the white spring, and put the check ball back in if you took it out. That's of course just a suggestion..lol, but the secondaries only pull fuel thru the boosters when air is flowing fast enough. With a double pumper, there is a secondary fuel source (the squirtor), so there is no lean spot. The real fix is a swap meet DP carb.
Witht he ignition, you can run with things set tight, but it will foul plugs (or at minimum make the plug reading unreliable for tuning). Id keep the vaccum can disconnected, but reset things so you have like 20* initial, and 16-18* centrifical. The compression is a tad low for that cam, and the chamber is closed, but it's no quench engine..lol.
Now, aboutt he cam. If this thing was bought in the last five years or so, you really need to take the time and degree it. For $50 plus a timing cover set and valve cover gasket you can spend a quality afternoon doing it. It's not hard, and the cams MP produces are terrible in terms of accuracy. Of all the cams I use, the MPs are consistently off the most in terms of installed centerline. The worst I had to move like 9* just to get to the recommended installed CL. The I had to advance it to get it where I wanted to run it. There wasnt enough bushing to get the timing gear that far. I had to use an offset crank keyway too. yuk. I think it's springs/head setup, but the cam cant be helping. I am curious about what your cylinder pressures are tho.
 
I'm starting to think my cam is the whole problem. I'm considering scrapping the heads for Edeldbrocks and then having comp cams tech help with the cam selection. I originally wanted more compression when it was built but I was told piston to valve clearance was an issue with these heads(im told i can only run a 510 max lift cam as the engine is assembled-by the machine shop.)I dont know if thats because the cam is ground all wrong and installed too advanced or what. I am sort of happy about the low comp now though because I want to put on a procharger p1sc with a small nitrous blast to cool the charge.(50-100) Of course I'll be squirting c16 to keep it from shredding itself. Thanks for such quick responses, I'm working on it this weekend and am gathering data as quickly as possible.
 
well, the 440 I run my 516s on is a factory part. No valve reliefs. I run the MP .528 solid, and Crane Iron arms. My heads were milled .100" (yes, really) and I run the steel head gasket. I have not looked, but I'd assume there are some tiny eyebrows on the pistons now. If you have the hyd .484 lift, and uncut heads, you have enough room in there by a long shot. The XE268 would rock in that thing. The 516s can work, but they do need a little modifying to get it out of them. Either way, the cam has to be in RIGHT for it to work. It is a good cam, just not a great one IMO.
 
I was reading an article which prompted me to build a 383 in the first place (it being a free good core also helped) and they used the xe285hl with stock 906's and it put 50 horse on the motor, a 9.2:1 zero deck with the same pistons as mine. They said it wouldn't reach it's full potential without heads, but what an increase for a cam not running at it's potential. What's your thoughts on that one. ( My springs are already good enough and they(them) used the stock rockers as well.)
 
Hi Mike, IIRC, you're ok. I think there was well over .1" on the intake, and exh was like .250. Obviously, and as a discalimer, you should recheck piston to valve clearance to be sure, but i think there's room. Didnt we check into that a long time ago?
 
Well, the 906 exhaust port is much better than a stock 516 with the small valve. I dont think it would work as well. Just for curiousity's sake, what is the short block, head gasket, and the rest of the powertrain? Gear, convertor, exhaust, body style, type of racing?
 
yes but i just wanted to be sure!!!....i think it was something like .100 int and .120 exh??
and YES your right..we should of writen it down!! :crybaby:
 
The block is a 67 383 with the forged crank, stock rods, kb hyper pistons, .048 gasket, 3000 converter and a Pro-trans, 4:56.1, 3" exhaust from 1 3/4 headers (2" propart headers going in soon). 1970 Dart SHWinger! Drag Racing only - occasional street use 3-5 miles. 29.5x9x15 et drags.
 
Im not sure about your head ccs, but I'm assuming by "stock" you mean not milled, or milled like .010" to clean up the surface. I think the convertor and gears allow it to rev, I dont think the 2" headers will help with these heads, but future plans they 'll be OK. Just dont lower the gear ratio. They'll hurt low end on a 383. I'd stick ina cam to work with the heads you're running right now. For these, Id use run one of these 2 Crane numbers. p/n 680591 is a little smaller, 284/290, 228/234 @ .050, .480/.490 lift. The second choice is a bit larger, and piston to valve should be checked. It may also run stronger with a 4-4500 convertor, but again, 4.56s will let it go decent now. Its p/n 680701 - 314/324, 242/252 @ .050, .528/.552 lift.

Notice both have more lift and duration on the exh side, and the second one closes the exh valve 4* after TDC. The 516 exh port just cant move air well, and there is very little scavenging. No sense keeping that valve open when there's nothing that's going to go out thru it, and it allows the cam to idle a little better for it's size.

I think the XE285 will not work as well in a head that is that handicapped on the exh side. That's my opinion anyways..a smaller comp will work much better than that MP also.
 
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