Here is the problem....as strange as it may sound. I have a BBC w/ 13.8:1 compression, 800" roller, super victor intake...and a pile of high RPM parts (should make peak power at 8800 revs). I have tried a number of things (msd box, good wires of course, good coil, gap plugs a .020). I would like to keep the factory remote coil HEI. But no matter how hard I try, this thing will not rev past 5300 / 5500. It makes no power their...makes great power at 5000 (when the convertor locks up) but shortly their after...it dies.....WHAT IS THE DEAL!!!! somebody had to have one of these distributors in a car that spins 6000+ rpms... PLEASE HELP... I am running out of hair!

Thanks
Dennis

 

what are you using for fuel and air delivery? Is there a rev limiter on it? Tell us more about your set up? Are you using rocket fuel to power that thing with that compression? lol

 

do you have heads and valve train to support that much HP if this isn't . i'd open the plug gap up just a bit. i ithnk it's foolish to run any factory hei stuff on an engine like your's

 

Just to be certain, R U using the magnetic pickup to trigger the MSD box and the factory ignition module is out of the loop?

 

Ok...here is the deal.. It is injected (gen 7 + dfi). I am still using the factory pickup and module (so I can have advance). The heads flow over 420 and spring pressure is 385 on the seat 1050 open.....so I think I gots all that covered. This is not BS and I am very frustipated...I have heard of "rev limits" in these distributors...I would like to know if this is true and if their is a way around it!

Thanks
Dennis

 

I think you need to drop that stock HEI module. I know they're not good for much more than 5000 RPM's. The system wasn't designed for the high RPM's that you are planning to run!

Unfortunately, I'm not sure what to tell you to get though!

 

IMHO the difficulty with an HEI coil at that rpm is spark energy. You can find a simulation for a single-coil energy curve here, to see the scope of the problem first-hand:
http://www.bgsoflex.com/igncoil.html

(For a stock coil you can use 0.5 ohm primary R; 8 mH primary inductance; 90* dwell.)

As you see, the stock coil drops below 100 mJ (0.1 Joule) of energy someplace after 4500 rpm. To run a single coil @ 9000 rpm requires a coil with << 2ms saturation time, i.e. substantially more coil current.

Common solutions that may work:

1. MSD 7- or 10-series ignition boxes (with a proper coil) are adveertised for that rpm range, IIRC.
2. Both FAST & MSD now offer multi-coil packages, I believe.

HTH

 

Hmm...all interesting information... just to bring everyone up to date... I replaced the ignition module with an accell piece...no change. I just replaced the pickup coil now and will try it, but the pickup coil seemed OK. I understand what you are saying about the single coil at High RPM's, but I have worked with many high RPM engines (8000+ Revs) with single coils before...never having a problem. The only difference being this small cap remote coil HEI. I must have the timing control through the DFI, and this distributor makes a nice easy and neat job of doing it. A couple more questions on the subject!

1. What is the highest RPMS anyone has turned with the factory HEI?

2. Is it safe to assume that the Holley style module that is rated to 9000 RPMS will deal with a motor like this?


Sometimes it seems that a crank trigger is the only way to fly!

Thanks
Dennis

 

The coil issue does seem pretty logical. What kind of coil are you running? Stock? That could very well be your issue!

Good luck!

 

I was running a stock replacement (HO). I just purchased an accell super coil and installed this morning. That did not seem to make a difference... So to point, I have all the good parts in the distributor, and an accell coil. I am going to try another MSD box and see what it does...It sure would be nice to know what is going on!

Thanks
Dennis

 

If you want to do a little light reading I put a summary of some GM HEI info here, including coil & module design equations:
http://forums.corvetteforum.com/zerothread?id=419893

IMO to run a single inductive coil @ 9,000 you need something with much lower primary R & L. You will also need a module that can swing 10-12 amps. I don't think that kind of module will fit in an HEI distrib, nor have I seen anyone selling one like that commercially.

To put that into perspective, the bigger MSD boxes have been measured to pull 20-40 amps at high rpm. Your HEI module pulls 6-7.

FWIW, I haven't seen any tests of an HEI VR pick-up running at that rpm - but there is nothing in the basic design to say it won't work there.

 

Here is a link to MSD's site and it shows that with an HEI, the module is not used. Only the magnetic pickup is used.

MSD for a 4-pin HEI

 

That is for the older 4-pin module, I believe he's using a 7-pin module, where he has to wire it the other way (Using the points/trigger option) That would be the ideal way to go if using a vacuum/mechanical advance dist.

Is there any way you can run vacuum/mechanical advance with that setup? I know it would take the computer control off the timing, but is it an option to explore (I wouldn't personally on my own, just thought I'd throw the idea out there, possibly to troubleshoot what's messing up!)

 

Doctor J, Thanks for the info! I need to atleast get this thing working to 8 grand ....that would be enough...

I am using a 2 plug style module. I am installing the new MSD box as we speak...If this does not work, would it be safe to say that I need to install a little hotter MSD box?

What is a VR module?


Thanks
Dennis

 

You're welcome.

Dunno what MSD box you have. MSD is pretty honest in their specs as far as I have seen. See what they rate your box at for a V-8 application.

VR = variable reluctance (magnetic) pick-up.

 

IT WORKS!!!! A special thanks to everyone that helped with the problem. Here is the deal. I replaced the Module, Pickup, and coil with accell pieces. I also installed another new MSD box. With all pieces installed it works. If you replace ANY of the pieces with stock, it does not work. You must replace all of the components to work...And boy does it work.


Thanks Again!
Dennis

 

Awesome! Thanks for the update that it works now!