gt500pwr

I've got a '91 camaro with l03 right now, stock distributor and msd 6 box and msd coil. Is there a better setup? I'm not quite sure about the differences between this setup and the HEI setup. I believe HEI can run independent of the ecm so it's ideal for carbed engines but what about a TBI?

Thanks.

sofakingdom

iTrader: (1)

Sorry to hear that.... we'll see if we can take care of that....

HEI is GM's trade name for "electronic ignition". So, take off your MSD stuff, which is doing essentially nothing whatsoever for a stock L03 except for lightening the car, with the weight savings concentrated in the region of the driver's wallet, and what you're left with is ..... HEI.

The "original" HEI sysem was of course not computer controlled.

The HEI systems used in conjunction with computer control, including any form of FI, are computer-controlled HEI. (duh)

I can't quite see how it would be possible to use a non-computer-controlled ignition system with any form of EFI, including TBI. The ECM needs to know, SOMEHOW, how fast the engine is spinning; otherwise it has no clue whether to inject fuel, let alone how often or how much. So I think the short answer for that question would be "no"; although it might be possible if you used some other ECM for the FI part besides the stock one, that got its "tach" signal by some means other than how a stock ECM is set up.

Streetiron85

There's a company called Howell that makes kits to convert carbed trucks to TBI using GM parts, and they have kits that use a centrifugal/vac advance along with a TBI. So it isn't an impossibility.
I dunno if the TBI ECM needs an input signal from the dizzy to control the fuel flow.

gt500pwr

So the old school HEI with the coil in the cap was used pre-computer? Now with the ECM controlling the distributor that is essentially HEI (is what your saying correct?).

So why would someone invest in an MSD box when running fi?

sofakingdom

iTrader: (1)

Right; HEI has been around since 74. I saw most of the 74s come out new with points still, but on toward the end of the model year, we started seeing them come in with HEI. I guess it was around April or May of 75 that I saw the first HEIs come out.

The first series of computer-controlled HEIs, from 80 to about 86 or 87, were coil-in-cap. They went to the smaller external-coil type after that.

I didn't know that Howell "made" ECMs. Last I knew, he was doing the burn-the-chip-over-the-phone deal; and selling stock ECMs and Holley TBs, IIRC, for conversions. Maybe that's changed? But the fundamental problem remains the same: the FI system has to inject a pulse of fuel per every x number of cyl firings (could be 1 pulse per cyl if it's SPFI, could be one every 4 or 5 or even more if it's a large TBI like one of the 4-barrel ones), so it HAS TO know when the cyl firings are. That info comes from the distributor. The stock ECM needs a logic-level signal for that, and additionally, controls the ignition timing. Therefore it's TOTALLY INCOMPATIBLE with an original style HEI. But of course the stock ECM and the later HEIs are designed to work as a team.

Iunno.... I'm not the one that's doing that.... I would think, maybe you could tell me?

Streetiron85

The MSD throws a different type of spark than the factory unit.
MSD stands for multiple spark discharge (I think) It means that each time the spark fires, it fires numerous times. The first time anyone sees the spark from an MSD, they're usually amazed. A regular spark goes Snap Snap Snap but an MSD spark goes Peep Peep Peep. Don't let it bite you either - OUCH!

gt500pwr

Strange, seems to be quite common for people to invest in an msd box but what you say makes sense, why would you need an external device for spark control if it's done by the ecm? But what about the amount of spark itself? Since the wiring from the msd box connects to the stock harness for the coil and then a separate harness for the coil, wouldn't you think the msd box helps to create a better spark voltage? That was the understanding I had, but I must admit, this past summer I removed the box for a couple of weeks (cleaning up the engine bay) and I really didn't notice any difference.

What about dist. advance and so on? Are there any mods to a stock distributor to improve it?

Thanks again.

Streetiron85

I don't think Howell does make ECMs, just conversion kits, wiring harnesses etc.
But I swear that I saw a kit for a TBI vac/centrifugal setup last time I looked on their site.

I hope I wasn't hallucinating, cause I'll feel like a moron if I was.

Streetiron85

I didn't notice much difference when I replaced a stock ign system with MSD on a stock TBI engine. But when I upgraded a stock HEI with an MSD box on a carbed engine the difference was noticable.
I'm sure there's an explanation for that, but I don't know what it is.

Sonix

iTrader: (1)

great, now i've gotta clean the hamburger helper off my monitor screen... nyuk nyuk

sofakingdom

iTrader: (1)

Sorry about that!!

Seems like the stock system is fine for a stock motor, and then some, IF it's working right. Sometimes even with a properly working one, people report that their car starts and idles better with MSD or other hot-rod ignition; but it's not going to give more HP or anything.

My late little brother used to work at RHS, when RHS had actual physical stores (2 of them) around town. I'd go to the store and hang out with his sometimes at closing time. Autotronics had just released the amazing new MSD, and they had this display fixture for it; had 2 pointy electrodes, one of them that you could screw toward and away from the other; and a switch where you could flip it from "stock" ignition to MSD, and it would make sparks between the electrodes. They had this one other salesman working - well, on the payroll - there, who was too busy trying to be California cool and impress all the customers' girlfriends to actually do any work. He smoked. In those days, this was right after the Civil War mind you, you could smoke just about anywhere; even in gas station parking lots. Well this smarta$$ would impress the chicks by lighting his cigarette in the MSD display. So one day, after the store closed, when he went to the bathroom or something and left his cigarettes sitting on the counter, we took out a couple of them and drew a line down the side with a pencil and put them back. Sure enough, after a few of his smokes, he went to light the next one on the MSD (even though he didn't have a female audience), and got one of the "loaded" ones. Damn near blew his lip off. The rest of us laughed for about 3 hours on that one.

So they're definitely good for SOMETHING... even if it's only some 10th grade humor at the expense of a buffoon.

Seriously though, the hotter spark makes a BIG difference in a higher compression, higher RPM setup; but has very little or no effect in a stock low-perf motor like TBI, compared to the system that's already there. Certainly not usually a bang-for-the-$$$ type of improvement. Which is why I was kind of hoping you could tell us why somebody would do that.

Sonix

iTrader: (1)

hahahahahahaha!
That's awesome!
But how the heck does a pencil line do anything? Flammable graphite?

sofakingdom

iTrader: (1)

Graphite is conductive.

Streetiron85

That is Cuh-Lasssic! I'd have LOVED to been there to see that one. The guy just tazered himself right in the mouth!