Sorry not sure if this is the right place to post this but Im wondering if someone can tell me roughly what the stock ignition module on a TBI 350 can run for RPM before crapping out. Im thinking that this may be my problem. I have richend and leaned out to no avail, and it seems to cut out at the same RPM all the time. Right around 5000rpm. Just wondering if someone can relate to this or if I should replace it with something from the aftermarket?? Thanks for any help. Its on a slightly modded 350 heads/cam/intake etc with a Msd coil and wires. Thanks again.

 

What's your plugs gapped too? You could be putting out the fire.

I have ran the stock GM dist. and coil to 5500rpm multiple times in my old TBI engines.

 

Plugs are at .45 I figure that should be fine but you never know!! Im just thinking it may be time for a new module, not sure. Trying to narrow down the problem. THanks though

 

Is it the actual original module or a cheapo parts store unit? I've run the stockers upwards of 6 grand without a problem. I also havent' had much problem if I buy one of the better parts store brands. Luck with the cheaper aftermarket brands had been erratic at best.

 

I've taken engines to over 7K RPM with a GM small cap distributor. JY unit from a Caprice, including the coil.

RBob.

 

Yep I have been to 6500+ w/ stock small cap hei stuff

 

When a coil and module run out of steam depends on the amount of cyls and rpm.

On a V8, the stock GM HEI coil and module run out of juice at 4800-5000 RPM. Every test ever done on them have shown this to be true. My stock coil and module also dies of at around that RPM.

It comes down to the inductance, turns ratio, and resistance of the stock coil and the resistance of the module driver. RPM and cyls determine the amount of charge time. At 5000 RPM on a V8, there is almost 24ms/8 = 3ms to charge the coil between spark firings. That is how long it takes to charge the stock coil using the stock module. On a V6, this comes out to be around 6800 RPM. RBob was probably referring to a V6.

Overall, to reliably light the air/fuel on a V8 with an HEI above 5000 RPM then you need a better coil to start with. If you need more than that then get a better module later on.

 

Stock HEI coil and module on a V8 at 6500 RPM? If it did rev without misfiring then the VE was so low that the plugs would fire easily. This means little HP was being made and the engine was out of it's range of usable HP.

 

Ok thanks for that again guy's but Im running an MSD Blaster TBI coil with the correct connections. I gues that maybe I should try a new module. Im not sure if it is the O.E one or if it is aftermarket but I will look into it.

 

woops I spoke too soon. Stock module, accel super coil (remote). This is a MAF Holley stealth rammed 327 w/ big cam and aftermarket heads. Not a slug stock TBI/TPI 4500 rpm tug motor. Peak HP with this setup is north of 6200 rpms.

 

6500 RPM, 327ci, stock module with super coil sounds right. A stock coil wouldn't do it.

 

I would guess that it is something else. FWIW, I run up to 6000 RPM with a stock GM HEI small cap with a stock HEI module and MSD Blaster 2 coil on a 355ci at 8 PSI of boost on 8.7:1 compression. At 11.9 AFR it runs fine, at 10.5 AFR, it has spark blow out. Spark plugs at .032".

What do you mean by cut-out? Does it fall on it's face or just stop pulling? When I had spark blow out it was like the fuel shut off and nosed over until the RPM dropped. Stock TBI heads run out of wind at around 5000 rpm? What kind of cam do you have in it?

 

Its a dynoed 300hp engine even with the basic mods that I have plus I do my own tuning. Its not a firebreather by any means but it gets up pretty good in my 4000lbs P.U. What do you think??

 

If you have a WBO2 then you might see the misfires if they are truly happening (not enough ignition). I am not good at guessing, but if I had that setup I would guess it is the cam first (street cam), then the heads. Can you hear it misfire?

 

Yes you can hear it miss. The funny thing is that this engine in a similar truck with a carb ran and pulled fine to 5500rpm no problem. Of course it was running out of power there but would just like to beable to shift at about 5300 or so when needed.

 

Stock AC Delco GM Coil, Stock AC Delco Replacement GM module, Stock style cap and rotor. Made 379 RWHP @ 6,400 rpm

 

Nope, a V8 SBC.

RBob.

 

"Stock AC Delco GM Coil, Stock AC Delco Replacement GM module, Stock style cap and rotor. Made 379 RWHP @ 6,400 rpm"

Fellas, as usual thanks for all this useful info, I had the same questions about my stock TBI ignition system.

Fast355, what year ignition and type ignition are you talking about there, the one with separate coil or coil on the distributor?

Thanks,

Paul T.

 

Must have been an external HEI coil.
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What kind of VE, CR, timing, etc was it setup for?

I have revved a stock V8 HEI coil and module to 7K RPM before also. The thing is that to build an engine to make power reliably at 7K+ requires decent parts. In doing so it will also be setup for high rpm power so the logical path is to put the proper ignition on it to take advantage of all the expensive high RPM parts.

EDIT: info here: cyberdave.org/HEICoilInfo.html. The title Coil Saturation Time and data below has the most useful information for the original poster.

 

Large cap HEI in a TBI application. The small cap will rev just as high.

 

The original of the HEI information is posted here: http://www.corvetteforum.net/c4/doctorj/heicoilinfo.htm

The other site is my personal page(s).

Re the module information, the description was written years ago and the prose
isn't very good. The equations are correct however, AFAIK.

The highlight is that spark energy is proportional to the SQUARE of the module
CURRENT. Aftermarket coils don't make any more energy than is already there
from the stock module. They only gain saturation time by reducing spark
energy.

BTW, a joule is one amp-volt-second. I neglected to mention that in the write up.


Have fun.