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Author Topic:   high rpm miss
dode
Member
posted June 30, 2002 09:16 PM
We run a fairly stock 9:1 350 with a mild cam, and we end up running about 5300 rpm at the end of the straights. We could probably run more, but above like 4500 rpm, the engine starts to stutter. I have heard this is common with the HEI sometimes, but some people have no problems with them. This is an older unit, so it could have some wear, but it runs like a champ up to that point. What is it about the HEI that causes problems at high rpm? Is there anything I can to to try and help the one we have? We are required to run it by rule, so we can't change it. We are running 36 degrees of total timing and 91 octane fuel. Could there be another problem that I am missing? We are running a box stock quadrajet with the choke plate removed as well. We really need to try and figure this out, but I can't replicate it in the garage, so I don't know what to do. Thanks.

John

AC156
Member
posted June 30, 2002 09:23 PM
Hmmm...that could be...I hadn't thought of the module. How much end play is there supposed to be in the shaft? Could any excessive endplay cause a problem, and if so, how would you fix that? Also, where would I get parts for it, because O'Reilly really couldn't get much for me. Thanks.

John

LUBEGUY07
Member
posted June 30, 2002 09:36 PM
dode, summit sells new distributors with cap coil and modules for 150 dollars i bought one after the first couple races and hit helped alot 1500 rpms more, try it they look completly stock too



racer2
Member
posted July 01, 2002 09:12 AM
i had a pickup coil go bad and miss like you explained,its next to the module. you'll have to remove the shaft to replace it.


dode
Member
posted July 01, 2002 09:45 AM
pickup coil? I am not famaliar with that part I guess...I have had the distributor apart before, so that isn't a problem.

John

Racer14K
Member
posted July 01, 2002 05:28 PM
This is a common problem with the HEI disributor with the stock module. Can you use an MSD box in your class? I used to crew chief for a friend and I threw the module away, wired the MSD box directly to the pickup assembly in the distributor and we would run at 8300 rpm. If you cannot run the MSD box, MSD does make a replacement module thats works real good. I put one of these in another friends car with a stock coil and he runs it around 6200 rpm with no problem. If you can get ahold of the August 2002 issue of Speedway Illustrated, they have a writeup on HEI Hop-Up.


#49
unregistered
posted July 01, 2002 10:43 PM           
Before you start spending money replacing things, Check your spark output. You can a get a spark output checker at most parts stores. (under $10) Should be reading at least 25,000 volts. If the reading is below, do you run an altenator? Is your battery charged enough? Then go to coil, module etc. If the reading is above then it is not an ignition problem. Then it may be fuel problem, or valve spring problem. What are your plugs gapped at?


dode
Member
posted July 02, 2002 12:08 AM
No, we don't run an alternator, YET. This seems to happen even when we first go out, and the battery is brand new, so I know it has the voltage. As for the spark checker, I have never seen one of these. For the plugs, don't quote me on this but I think they are like .040. I just checked them the other day, and they all gapped out just as my manual said. Should I open them up or close them? Also, now that I think about it, when I was checking the timing, I noticed it missed a couple of times, even at idle. Would this seem to point more toward the coil? Thanks.

John

racer17j
Member
posted July 02, 2002 01:03 AM
have you replaced anything in the hei ie the old weights or have you welded it i had a mis like that in mine one time it was a weight bushing was bad and was coming off also a new modual might help cure it i run an accel mod and mine will turn 6500 before it flattens out and that is way over what your turning so it should work for you too


dode
Member
posted July 02, 2002 01:08 AM
No, I have not changed anything yet. I thought about getting a new set of weights for it while I was in there. What kind of ramp should I look for? This is a bone stock HEI, not using the vaccuum advance.

John

BayouGent
Member
posted July 02, 2002 02:32 AM
I agree with racer2. If the pickup coil is going bad it can't read when to send the spark properly, especially at higher RPM's. Since you aren't running the vacuum advance, installing a curve kit wouldn't be a bad move either. I've seen engines turn up quite a bit with stock HEI's but they do wear down. My experience with the modules is that when they go bad, you have NO spark at all. Then again that may just be MY luck.


dode
Member
posted July 02, 2002 09:06 AM
Which part exactly is the pickup? I am unfamaliar with that. Is that in the coil itself, the module, or another part? Thanks.

John

#49
unregistered
posted July 02, 2002 09:15 AM           
Get those plugs gapped down to .032-.034!


dode
Member
posted July 02, 2002 09:27 AM
Is that smaller than normal plug gap? I gapped them per the manual for what the engine was out of, a 75 C10 Chevy. Thanks, and still learning guys.

John

#49
unregistered
posted July 02, 2002 03:02 PM           
Stock HEI won't work with plugs gapped at .040! Maybe,this might be your only problem.
Back to your battery quickly. I know you said it was new, but how many nights do you have on it? With the bumping around and vibration from racing, we've found that around 5 nights and we are charging the battery before racing everytime. (if you don't run an altenator) Not enough charge and your going to get a miss.
P.S. always start with the simple stuff before spending money & taking things apart.



dode
Member
posted July 02, 2002 03:06 PM
The battery has like 6 nights on it, but doesn't take much to charge it when we work on it the next day. It never drains more than like 25%. I am all about the easy stuff. That is what I am going to try for this week, and if that doesn't work, try something else next week.

I will most definitely check the plug gap and see what it is. As stated before, is like .032 what we should be running? Thanks.

John

#49
unregistered
posted July 02, 2002 09:57 PM           
John,
Try .034. That should be alright. Make sure the battery is fully charged right before racing and see what happens. (if possible, check to see right away when your done just how much the battery was drained)If your miss is still there at least we've eliminated two possiblities at no cost.


csracing
Member
posted July 13, 2002 01:30 AM
Normally a stock HEI will not work very well beyond 4500 rpm..it was designed this way as most street people don't drive their cars above this..change out the ign module(inside the dist)to an aftermarket type thats designed for this,,Oreilly's carries one under Accell(used to work there)and they can also special order just about any other types.Or you can get a kit that has all the springs weights and module plus cap and rotor with nylon screws(eliminates spark scatter)..update to a good coil also.....



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