Have 78 L48 with 4spd.
Thinking of replacing stock HEI with Mallory or MSD, one of the $150. ones from Summitt.
Whats good and bad about the change.

 

i guess i would ask why???? the stock HEI units are pretty good perhaps just shim it and replace the coil and module to a higher voltage one if you feel like spending some dough

 

What's good is that Summit makes 150 bucks. What's bad is you're out 150 bucks.
The real question is: Given that it's going into what I assume is a stock L48, what are you expecting to get for your time, trouble and money?

 

$150 is too much!!!!!!
Add a 50,000 volt coil, a performance modual and gap your plugs about ..010 more than normal(.050), spend your extra money on good wires and GGGGOOOOOOOOO!!!!!!!!!!!!

 

If you do buy a new HEI don't get the Summit one I did that and it cost me nearly $1,000 in problems several tows and I finally replaced it with a GM unit.

 

I baught the MSD HEI ProBillet unit for about $350,but only because my stock 250,000 mile on the clock unit needed to be recurved,and was very worn.For my engine I needed the advance curve to be modified in order to keep my lumpy cam idling. For your stock setup,if the HEI you have is still in fair shape,get a Crane advance kit,cap and rotor,and wires and call it a day.For a stock distributer,you can't beat an HEI.

 

Another CF member (78 L48 4 speed) and I (79 L82 Auto) bought these as direct replacements. I was shopping around for parts to refit the original unit and it became clear that this was the way to go. It works beautifully..totally satisfied and big improvement for low cost.

http://cgi.ebay.com/ebaymotors/CHEVY...spagenameZWDVW

 

That seems awfully cheap, sorry, low priced for that unit. Almost to good to be true.

I'm glad to hear you're happy with it. Kind of makes me wanna purchase one now.

 

Thanks for the advise, I was hopping to get an improved advance curve by buying a new unit. I think that I will try an advace kit and coil pack.

 

I recently bought the MSD Streetfire HEI. It's a really nice distr for about $170. My stcok '79 Hei was determined through some research here and elswhere that this stock distributor was limiting my centrifugal advance. The advance curve through the timing light was eratic.

With this new one, timed correctly, I can really feel a seat of the pants difference. But don't forget ALL HEI's drop in voltage after 4000 RPM, that's why most of the 6000+ rpm motors people run here, switch to a MSD 6AL set up. It give you consistent voltage through 6000rpm.

 

You have nothing to gain by replacing the stock HEI with an aftermarket Summit HEI. The aftermarket units have horrible advance curves in them. Just re-curve what you have and you'll have an unbeatable system.

 

Hi Lars,

What do you think of the Propcomp units I referenced above...too good to be true, or a decent unit being sold at a good price? It curved perfectly in line with your recommendations.

Just curious,
Steve

 

I haven't tested one of the PropComp units, so I can't make specific comment on them. But here are some general thoughts:

Super-high voltage systems are neat, but you don't need more than that which is required to "light the fire." Over-kill is common in the aftermarket ignition system market, and it doesn't gain you anything. High compression engines, and engines with very good volumetric efficiency (producing high dynamic compression ratios) need higher voltage at the plugs in order to get the spark to jump the gap. But once you have enough voltage to fire the plugs reliably, adding voltage doesn't do anything for you. You can get enough voltage to do the job (with a .035" plug gap) with a stock points-style system and a good coil in most street-type applications. And the stock HEI is more than enough for any modest performance engine.

What's more important than impressive coil secondary voltage numbers is the advance curve and the total timing setting. To demonstrate this, we recently ran one of my re-curved, stock points-style GM distributors (with a good aftermarket coil) against 2 out-of-the-box aftermarket systems: One was a capacitive discharge system and one was an HEI. The re-curved, stock points system produced more average horsepower than either of the two aftermarket units, even though both aftermarket units had significantly more secondary voltage. This was on a 500-horse engine. All 3 distributors produced identical peak horsepower numbers, since all 3 were set to 36 degrees max total timing. But the mid-range went hands-down to the recurved stock unit.

Obviously, the aftermarket units could have produced the same mid-range and average numbers if we had re-curved them to match the points distributor, but the point is that you don't need an aftermarket unit to perform well: The key is in the curve and the precision you build into the distributor.

 

Thanks, re-curve was my ultimate goal, buy a new unit Like a Mallory with springs and stops and see if with a timing light get a smoother engine. Engine stumbiles untill you get to 2500 to 2800, retard the timing and the RPM goes up 3000 to 3300, advance the timing and the the engines is strong to about 3000, then it must be over advance. Just tying to have fun and learn something in my old age.

 

Other than that, anything wrong with them? I bought one to carry as a backup to events with me. I figured in a crunch I could just swap advance springs quick enough and get in the same ballpark quickly as what I've got normally.

On another note, it seems like I've been killing ignition modules lately; Saturday I lost spark from a module that's been in for about a month and a half. It had the grease too; are GM modules much more reliable than a Hong Kong unit that I bought in a crunch?

 

No, there's really nothing wrong with them - you just don't have anything to gain unless you do some work to the curve, which can just as easily be done to the stock unit.

As far as the modules go, I would assume there are some quality and reliability differences in them. When GM first released the HEI, they had reliability issues which were fixed with a revised, heavy duty module design. So design and manufacture quality does affect reliability.

 

GM modules use a ceramic hybrid technology for the electronics. Very reliable under vibration and temperature. Some, I haven't seen all aftermarket manufactured modules so I can't say all, use printed circuit board technology. PCB boards are limited in temperature range compared to ceramics, and the heat gets trapped easier in pcb parts. Not a good thing. I don't know what switching transistors are used in your Hong Kong modules, but the transistors used in the GM modules are quite robust, and are mounted on very efficient internal heat sinks. I personally would rather run a used module that I got out of a greasy swap meet distributor than a new module purchased at some of the major parts stores.
JMO

 

OEM's do extensive engineering development on their components and have to stand behind multi-year warranties. They make them to last (at least as long as the warranty). Aftermarket suppliers (China, etc.) make components that "look like" the originals. But the materials, reliability, etc. are usually far short of what you bought originally. There are many components that have newer designs and can be better...if made properly. New distributors aren't really any different in basic design. Some of the electronic modules are better...but that's if you have high revving engines that need something "better". Most street engines won't know the difference (except when that chinzy metal drive gear on the $45 eBay distributor wears out in 6 months).

 

Procomp specs show they use "4340 Chromoly steel bottom gear, for use with cast and steel billet cams" for the drive gear. Is this considered "chintzy"? What are the OEM gears made of?

Just curious

 

I replaced mine with a MSD HEI. My original distr. was on the way out because of wear, so I decided to do it right. The advantage of the MSD is that you can recurve it easily, plus it has the module to go to higher rpm.