: GM HEI Mod for improved power and fuel economy

08-26-05, 01:14 PM
Obtain a EMR Ingition module from a early 80's GM car, I have seen them in 260 Olds powered cars, and I have read about them in Olds 350's in 1980 also. As per Jim Hand, use a GM module, not a garden variety parts store replacement.
This module is a direct replacement for the 4 pin std 990 module, only it has an additional termal marked "R". This terminal when grounded, reduces ignition timing by 10 degrees. High compression engines have problems with starting when the initial ignition is too high. But with this "mod" the module will allow you to start the car with ease (and less abuse to the starter) with the flip of a switch. GM used this with a vacuum switch to at certain times it would pull timing back 10 degrees, or run normally. But this was done with a fixed timing distributor.
You can install this, then increase your initial timing by 5-10 degrees, use the EMR Pin "R" to retard timing at start, and then return to higher timing for cruise. This will now require modifications to the overall mechanical timing curve. As now it is advanced what you cranked up initial base timing, now needs to be removed from the mechanical timing curve. Once removed you will have a much tighter timing spread and have a overall much faster curve and more repsonsive engine. The area under the curve is fuller and will have overall higher combustion efficiency.
Base timing:-->10 degrees
Mech Adv:--->24 degrees
Total Adv:--->34 degrees
Modified with EMR
Base timing:-->20 degrees
Mech Adv:--->14 degrees
Total Adv:--->34 degrees
Now WOT power is unchanged, and part throttle power is up by upwards of 0-10 degrees (in the above example) so your overall timing curve is faster and you are doing most of your driving with higher base timing, improving fuel economy and throttle responsiveness. Higher compression engines will need to be adding possibly less than the full 10 degrees, but low compression cars will welcome the full 10 degrees. I have found most lower compression cars enjoy as much base timing as possible while limiting the overall total timing, but still increasing it.
I recommend that cars with vacuum advance, that you use the timed vacuum port and do not use full time vacuum (which always was the crutch for many cars with limited low rpm timing). This is due to excessive timing at idle which will be too high, wil linvite pinging off idle, and will cause an unstable idle. I also highly recommend that you find a vacuum advance can that has only around 10-15 degrees advance now (GM cans are marked, the last part of the P/N is the max advance), as this coupled with the higher base timing, will invite part throttle pinging. Some vacuum advance cans on low compression engines are as much as 25 to 30 degrees vacuum advance! You will need less, so this vacuum advance is reduced, you will reduce your part throttle pinging. You can install a Crane adjustable vacuum adv can and have full adjustability here.
These mods are excellent for any HEI GM V8, V6, or 4cyl with the mechanical adv (sorry CCC guys you are left out...learn to burn EPROMS!)
Overall this should not have an adverse effect on emissions, although it is remotely possible that the higher timing may increase some NOx emissions, but should overall reduce CO and HC emissions due to more complete combustion. So nothing is implied here about using this on the highway, off road or whatever, this information is for entertainment reference only.
Thomas Martin

08-28-05, 02:31 AM
Excellent tip! Keep the neat electrical tips coming! :cool:

09-06-05, 02:15 AM
This could help to keep my 75s starter from getting its ass completely kicked by 12.5:1. Excellent tip.

09-06-05, 02:35 AM
I figured it out by reading the FSM and having a problem with some crap pistons in a boneyard 400 Pontiac I picked up. With my 87cc heads (10:1 with flattops) on these junk pistons (dual valve relief, for 1966 and older heads and 1967 and newer) I am netting maybe 7.5:1. So to get some decent power, I was running upwards 60 degrees timing at cruise! (36 degrees mechanical and 30 degrees vacuum), and I found best drivability with FULL time vacuum on the can. But with as much base timing as I needed, it was hard to start. So, enter the EMR module. It made all the difference in the world.

Now, to get some 67 cc heads and try to get me up to 9:1 and see if I can have a normal motor. Or ditch it and get back to the 455....

10-10-05, 12:42 AM
Just some info; a new unit (spendy compared to the ol' 4 pin) can be found with the following part numbers at your local friendly auto parts retailer:

Niehoff: DR406
Borg/Warner: CBE22
GP Sorensen: EL119

All about $70-80 :ill: Very sweet modification... I wonder if you could set a potentiometer up to vary the amount instead of just an "on/off" type setup (probably would damage the module).

[EDIT: Image added]

The upper left pin (tiny one) is the "R" pin:

10-10-05, 02:26 AM
AFAIK it is strictly on or off. But the ESC module will vary up to 15 degrees retard. BUT, I don't know the input to the module. They are found in Buick Turbos (w/HEI), Pontiac 301 Turbo 80-81 (1981?? Might be the 7 pin module for EST), and 1981-1983(?) ESC 305's Chevy Full Size Trucks.

I have my 1980 Original ESC module still functioning. So they are solid at least. The delay is on the "D" terminal, same place only slightly larger pin.

Some comment on the EMR module, the thin "R" pin is for a connector that plugs in and goes directly outside the HEI. It went directly to a vacuum switch that apparently was grounded when whatever vacuum condition GM wanted was met, and it pulled the overall timing down by 10 degrees only. Same Mechanical and Vacuum advance, just offset. If I can find one of my GM books, I will look it up and see if I can figure it out.

If anyone has a GM FSM, 1980-81 with Olds 350, 260 or 307 in it and finds the EMR module, read up on it for us and give us a summary.

11-12-05, 11:29 PM
anybody know how emr works with vacuum switch?

11-13-05, 02:25 AM
According to my 1980 Pontiac FSM, the operation of the EMR module is part of the C4 Computer Controlled Cataytic Converter system.

1980 Pontiac FSM Page 6E-33, referring to Fig 6E-47 (which is only a picture of the ECM mounting in the car), reference only the 5.7L "R" (Olds) 350 V8.
"...The EMR module has the capability of retarding the engine timing 10 degrees during certain engine operations to reduce exhaust emissions. During other engine operations, the module functions the same as a standard HEI module. The terminal "R" on the module is connected to the ECM and retard is accomplished by an internal ground. The timing is retarded 10 degrees only when engine coolant temperature is between 19C (66F) and 54C (130F), with thottle opening position below 45% and the engine speed above 400 rpm...."

As I think I noted above, the car I snagged my EMR module was a 260 Olds V8 powered Cutlass, 1980. I got the vacuum switch as well, but could not determine it's operation, so I assumed it was defective. My guess would be OEM operation non ECM was strictly to reduce timing at high vacuum conditions to reduce N2 emissions. Being Pontiac didn't use the 260 (they were stuck with the Pontiac 265), I don't have any info on the 260 usage (anyone with an 1980 Olds FSM??). Being the 260 was a lower cost car, likely they were able to make it work ultra cheap with a vacuum switch only. If they got it certified, in 1980, ECM's weren't required yet. 1981, they were. And IIRC the 260 died in 1980, none in the 1981 model year.

12-19-05, 12:52 AM
So, which engines does this apply to? Will it work on the 4.9L? Any downside?
Is it easy to install?

Very cool tip!

12-19-05, 03:34 AM
No, sorry, only non computer control engines with large cap HEI. The ones with the 4 pin module. 4.9's have the 7 pin "EST" module.

No drawbacks that I have found. It helped my ultra low compression 400 (7.5 est) a lot by allowing additional timing and still be able to start.

12-21-06, 08:36 AM
I was wondering if this will work on my '92 305ci Brougham motor. I believe it has the HEI distributor but I didn't know that the newer 4.9's had that. Like anyone, I would like to increase power and economy.


--tech tips is not for questions, please post in the proper forum for your car - urbanski

12-21-06, 11:47 AM
Nope, this mod is for GM cars up to 1980, after 80 all cars were computer controlled. Trucks were non computer for a little while longer, but not much. Maybe 84-85 before they got sacked with a PCM.

The vacuum switch when high vacuum I think pulled timing down 10 degrees to help with NOx emissions. Pretty much all it was used for. But what I have listed is a much improved way to manage a tighter timing curve that will benefit most cars without a PCM. PCM's do it for you already. Just not necessarily optimal for power.

12-21-06, 10:39 PM
OK so we have low compression engines this will work on and high compressions too.
BUT as a tuner and having many many years experience tuning engines and if you use ported vacuum you will increase the tendencies to loose so much mileage and your power curve will suffer.
I would prefer to taylor the spark curve to the running characteristics of the particular engine rather than kill my mileage.
I ran a 400 Pontiac with milled heads and 10.5 to 1 and a very short duration cam. This engine would spark knock anywhere over 3500 to 3800 period. BUT I still ran a fast curve and vacuum advance hooked to manifold vacuum but used an adjustable advance can.
The mileage was DEPLORABLE when it was hooked to ported vacuum and power sucked.
I prefer to use un worn distributors, the light or medium curve springs or a mix of light and medium to get a fast centrifical advance (and I use the stock weights as I find the stock type curve pretty much satisfactory for just about any car on the road, racing is different can of worms) that will be all in by cruise (you can tighten it up and limit it at cruise speed too but you muxt understand it will cause advance farther up in the rpm range and takes some testing and research) and vacuum advance hooked to manifold vacuum.
I like to run the base timing up as most engines will use anywhere from 5 to 15 degrees more intial timing than stock, I also try to get as much accelerator pump travel as I can in carbs.
Another thing is that if you advance timing it makes the engine "see " a richer mixture. Another thing tayloring a curve in my way is it gives you the chance to (if you feel comfortable) adjust the adjustable part throttle on Qjets (adjusting this is best done with a A/F guage and shoot for the 13.8 to 14.0 to one (14.7 to 1 is stoichometric but will cause it to buck,jump and lean misfire.
A good thing this allows is as you advance the timing it allows you to close the throttle blades more(ie reduce idle speed) and gives you more pump shot to get a heavy car off the line (ie moving).
I have my 355 in my truck running right now 16-18 degree intial it advances to its limit to just under cruise rpm and use around 42 total less vac, and my distributor is running around 58-62 deg total and running loaded most times, on hilly roads to work it still gets 14-15 miles to the gallon and has no overdrive and the engine had an 800 spreadbore holley, holley intake and SR Torquer heads with 202/160 valves and LT4 HOT Roller cam.
Went to Missouri to deliver a buddys 68 Nova and ran around 70 all the way there and since my buddy wasdriving hiscar with accurate speedo we used his trip readings and I averaged 18 mpg with no OD there and back to southern Indiana.
OH and as for tip in spark knock , if you actually read the GM manuals it has been documneted (I hope my friend still ahs his tech training manual) this is normal and will not do serious damage unless youare seriously lean or super high compression.
Several of the best engine tuners (now pasted away) found many years ago that even in the best engine you will have some detonation which will be compounded by lean mixtures (hot ones too so if you make a cold air package it can help).
And if you do have a slight tip in ping simply add on a performance water injection as it helps with bad quality fuel, keeps carbon levels lower and simply helps an engine perform more efficiently.
I am sotrting out the parts to make a simple WI unit that can be built on the cheap and you can simply use plain old blue washer fluid as its only methanol and water,both of which wont hurt the engine. But you can buy comercial units with good results, me I just like to tinker.
Hope I dont piss anyone off but some people are just too conservative on timing. OH and this little mod listed can help on the tiop end if you dragrace as it may(depends on tune of engine) give you some more MPH if you retard your timing above 4500-5000 rpm. IT does work on some engines.
Lee Abel

12-24-06, 12:09 AM
Something, at least on my LT1, I have been experiementing with timing and I am finding that less timing is actually proving improved mpg.

The beauty of this mod is that it allows you to tighten up the timing range, so it allows you have a much faster curve than without it. In most all engines the base timing is set so you have a comprimise of ease of starting and a decent initial timing ramp.

So now you can have a say 10 degrees cranking advance, once the engine is running, it can idle at 20 degrees, and at WOT you can ramp very quickly up to 32 degrees (or whatever peak power ends up at) and then vacuum advance handles the rest. Sure you can do it with a mech only adv, but you can never get the advance rate I can get with the EMR module. You will have to have such loose springs you will have unstable timing at idle (been there done that). Running vacuum advance to full time vacuum is still inherrently unstable timing. This brings you a very stable timing curve.

HEI's from 75-81 (car) all have lame mechanical advance limits. With this we can capitolize on that without having to mod the distributor. We can use an adjustable vac advance can to limit the vacuum advance to keep within 45 degrees too.

My experience is anything over 45 degrees of timing is too much (I tried over and over, higher isn't better). We have a 90 degree engine, more than 45 degrees is beyond mechanical limits of 1 cyl and doesn't help economy or emissions, it actually hurts.

Think of this as a tuning aid. It allows much faster timing curves and flatter cuves. Learn to tune with it and you will find improved power and economy. If you have ever tuned with a PCM, this can get you much closer to PCM similar timing.

And for pinging, my 301 Turbo can show you that pinging is bad.... REAL bad.... It beat the TAR out of my rod bearings! I have a 460 Ford piston that within 1000 miles pinging shattered the upper and middle ring lands. If you have see how agressive GM is on ping control today you would be amazed.