Spark control for an old chevy?

Imho you could never save enough fuel to pay for the parts. A 3/4 ton truck is never going to deliver very good mileage because of weight, big tires, rear end ratio, and maybe your driving style. An HEI ignition is not any better than a well maintained points type, but the HEI doesn't require much maintenance.

Randy

Joe,

I think the HEI's main strong point from a functional view is that it can deliver more power at higher RPMs...at least that's what I've understood. The maintenance required with HEIs is almost nonexistent except when parts break or go bad.

That knock sensor / ESC combo is known to be a performance killer, not an enhancer. It's main purpose is to stop knocking, and it does it by decreasing timing quite a bit (5 or 10 degrees). I don't know it'd help much.

My long term plan is to acquire a cheap, 2nd vehicle to drive at some point. Then I can dedicate some time to removing the carb and 4/5 pin HEI setup, and replacing the whole deal with a '87 and later TBI setup. That'll include a more modern 7-pin HEI, and the carb will be gone. Maybe that might help with mileage some. When I do this, I'm going to be trying to tie in some digital gauges into one system that'll let me view all aspects of the engine over a time period on a PC, to aid in tweaking. I'll probably be swapping in a RV-style cam as well. I don't need mid-to-upper RPM horsepower as much as I need low-end torque. This will probably also require a custom ECM chip.

It'll be a neat project. Hopefully, by lowering the RPM range where peak power is produced, I'll save a little gas too.

Good luck, and post the results if you try anything new.

~jp

Group: alt.trucks.chevy Date: Tue, May 16, 2006, 11:34pm (EDT-3) From: snipped-for-privacy@webtv.net (Joe=A0Cougar) =A0=A0=A0=A0I was just reading Jon's post about "carb and HEI" and it got me thinking. I have a 1969 restored GMC 3/4 ton with the 350 CI 4V engine. It has the stock points distributor. I have seen kits advertised that manage the spark advance with a knock sensor and some electronics ( Jakob) but it sells for $800 I believe. I know I can swap in an HEI distributor but I wonder if there's a way to adapt the spark management system from a vehicle like his ( 1986 ) That would surely save me gas (currently 10 MPG!) and increase power. Any of you guys ever done this or know where I can find a plan? I guess the tough part would be finding a suitable location for the knock-sensor. =A0=A0=A0=A0Thanks

You could save yourself a ton of money by just getting an HEI distributor out of a 1970's era pickup because they didn't use knock sensors or computers. The beauty of the GM HEI system is that the power line on it is relatively flat from low RPM to high RPM but I seriously doubt that installing an HEI system on your truck will increase your gas mileage.

%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% "Sometimes, when you're up to your butt in alligators, it's hard to remember that the intial objective was to drain the swamp." ~ Unknown ~

Back in the "good old daya" (before HEI existed) I changed several cars over to after market capacitor discharge ignitions. The improvement in fuel economy and performance was significant.

The improvement came because we were then able to run plugs gapped at up to .125 which threw a much fatter spark and resulted in more complete combustion. In one car I specifically remember, we had tried everything and the exhaust was always sooty black (inside the pipe) but when I changed the ignition it became soft gray in color, the mileage increased and the performance jumped.

Modern cars don't have the room for improvement that the older cars had. Those cars were carbureted not injected and the increase was typically 3 to 4 mpg. Didn't mean much when fuel was 50 to 75 cents a gallon. Now I would jump through hoops for a 3 to 4 mpg increase.

HEI should provide the same benefit on an older, carbureted engine. YMMV

Group: alt.trucks.chevy Date: Fri, May 19, 2006, 11:45am (EDT+4) From: snipped-for-privacy@sbcglobal.net (George)

Back in the "good old daya" (before HEI existed) I changed several cars over to after market capacitor discharge ignitions. The improvement in fuel economy and performance was significant. The improvement came because we were then able to run plugs gapped at up to .125 which threw a much fatter spark and resulted in more complete combustion. In one car I specifically remember, we had tried everything and the exhaust was always sooty black (inside the pipe) but when I changed the ignition it became soft gray in color, the mileage increased and the performance jumped. Modern cars don't have the room for improvement that the older cars had. Those cars were carbureted not injected and the increase was typically 3 to 4 mpg. Didn't mean much when fuel was 50 to 75 cents a gallon. Now I would jump through hoops for a 3 to 4 mpg increase. HEI should provide the same benefit on an older, carbureted engine. YMMV

I had a Capacitor discharge system on two cars. The first system, I build from scratch using plans that I found in Popular Electronics Magazine and the second was a kit I bought from Allied Electronics (later became Radio Shack). The systems worked very well for improving engine performance and also, the points did not burn as quickly because of the low voltage being passed over them. I actually had a set of ponts that lasted so log that the plastic rubbing block on them wore out and the contact were still good.

You're right though, one way to improve gas mileage (and power) on an engine is to step up the voltage going to the plugs (install a hitter coil), install low resistance spark plug wires (500 ohm maximim) and then open the gap on the spark plugs. The biggest disadvantage to doing this is that you have to maintain a close watch on the plugs to make sure the gap doesn't end up so wide that you create a miss in the engine at driving speeds. I run a .055 inch gap on my '90 Suburban (.035 is the norm). You should not only get better gas mileage but there should be a noticeable power increase as well. As for plugs, I've found that AC platinum work as well as any and better than most other brands. BTW I think that MSD still makes CD ignition systems (check Summitt Racing).

%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% "Sometimes, when you're up to your butt in alligators, it's hard to remember that the intial objective was to drain the swamp." ~ Unknown ~

The CD systems I used were marketed by a company known as Delta Electronics. They had the Mark 10 and the Mark 10-B. The difference was the Mark 10-B had a switch on the end that you could depress and instantly change from CD back to conventional ignition. I believe the kit marketed by Allied was the Mark 10-B sold under their name. Did it have the button on the end of the box that disabled the CD system??

They had little "tabs" with wires and stud attached that you placed on the coil and moved the resident wire over to the stud?? Same??

I actually saw one, an Allied version of a Mark 10-B, just yesterday. On a 67 Chevy C-10, a 292 6. Not in use though, still mounted but not hooked up.

Group: alt.trucks.chevy Date: Fri, May 19, 2006, 3:59pm (EDT+4) From: snipped-for-privacy@sbcglobal.net (George)

The CD systems I used were marketed by a company known as Delta Electronics. They had the Mark 10 and the Mark 10-B. The difference was the Mark 10-B had a switch on the end that you could depress and instantly change from CD back to conventional ignition. I believe the kit marketed by Allied was the Mark 10-B sold under their name. Did it have the button on the end of the box that disabled the CD system?? They had little "tabs" with wires and stud attached that you placed on the coil and moved the resident wire over to the stud?? Same?? I actually saw one, an Allied version of a Mark 10-B, just yesterday. On a 67 Chevy C-10, a 292 6. Not in use though, still mounted but not hooked up.

My unit had no brand name but I think it was the first one offered by Allied Radio. Mine came as a kit that you had to assemble (lots of soldering involved) and it did not have a bypass switch in it but I rigged up a polarized plug on the connecting wires so that I could bypass the unit if necessary (or to set the dwell). I believe I bought mine in 1968 and I ran it on several different vehicles up until about

%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% "Sometimes, when you're up to your butt in alligators, it's hard to remember that the intial objective was to drain the swamp." ~ Unknown ~

Thanks for all the replies. Some interesting information.

I once tried a pointless spark replacement unit that went in in place of the points but I noticed no difference in mileage or power,and I left the ignition on (engine off) once and it ruined the thing.

My main concern is the timing advance curve. I had the engine replaced with a lower compression one and the distrib advance is way off (won't advance far enough,knocks at certain RPMs etc.,even with an adjustable Vac Adv.) and I just thought there must be a quick and easy way to get the spark advanced to the "just before knock" point electronically,which I am convinced would boost performance. Talking used,junk-yard parts here. I'll post my results here in case there is anybody else driving a gas swilling relic from the past.- Joe

If the coil isnt hotter, it wont make a difference.

Not enough advance is not the issue, but rather too much advance. I would go with an HEI distributor and coil. That said, cheap cap, rotors and wires are a no-no because GM HEI eat them for lunch. No champion, nor Bosch spark plugs. Its really hard to beat an AC Delco plug.in a GM product. I do like the Delco Rapid Fires. Points are a constant issue (and it took years for me to move away from them) They limit RPM because they bounce, make the spring stiff enough to keep them from bouncing and the block wears fast requiring constant dwell resets(at least it was easy with GM and the little window and allen wrench) and frequent replacement. Moisture is always an issue. And hot coils burn them up to fast. Carb makes a lot of difference. Rochester can be made to work as well as any on the market, but Eldebrocks work fine out of the box and require little maintenance. And the secondaries need to be set right. A daily driver I wouldn't want them opening before 3/4 throttle. Rochester used to make a 450 or 500 cfm 2 barrel. Finding them, and the manifolds was hard 20 years ago. The base was larger, as were the bores. You know Holly says a 350 cid doesn't need any more than 550cfm unless it turning more than 7,500 rpm. But they sure are happy to sell you a 650, 750, even

Whitelightning

This is something I don't understand... What determines the CFM of a carb??? Is it the size of the plates that determines the maximum flow?

How would that relate to driveability and fuel/air mixture? By that I mean, if a 600cfm carb can flow way more air than I'm ever going to need on my 350ci, (likely, since I don't foresee breaking 4000rpm) could it be a cause of the rich-running condition that I've never been able to cure?

Just curious, and trying to understand carbs better...

~jp