The Stovebolt Site Forums The Shop Area The Electrical Bay New tech tip - HEI conversion

For those of you who have been wondering how to put a later model GM HEI in your stovebolt, I have written this tech tip. Red58 was kind enough to provid the picture for me so I wouldn't have to pull mine back out for a snapshot. Thanks Bill.

HEI conversion

How about V8s ?

Inky05, Any idea about the part number for this HEI distributor (250 version). Where did you pickup the split collar clamp? Thanks.

taz - to convert a V8 to HEI, just get an HEI out of a newer V8 and put it in your older V8 [pre-HEI] - no real difference for the V8, the difference will be in if you have to modify the firewall for it to fit in, as the HEI is much bigger diameter than the points dist

Bill

Inky, could you elaborate a bit re. this 'split collar' with a photo? Would the retainer off the old 235 dist. work?

now that were on the hei topic, is there a smaller hei distributer verion available other than than the huge, bulky ones that came in 76 and on? i love the convieance of the intregrated coil in cap as well as the simple wiring, but the cap is just so big. it would be nice if they had the hei technology, but in the size of the original points and condenser distributor.

I assume you're talking about V-8. Mallory has a small HEI distributor that requires an external coil. Check them out at any performance site (e.g., Summitt or Jegs)

It would have to come from a sraight 6. 78 up is the best but 75-7 will work good. If you want to keep the small dist. in a v-8, Crane has a real neat conversion. Very easy to put in. I get them from Summit.

You can get a 6 cylinder HEI distributor from Tom Langdon.

That HEI in the tech tip shouldn't be a first choice. The extention is slightly undersize(.007") and doesn't support the gear as well as a solid shaft. This example happens to be in an external-coil unit.
[img]http://home.earthlink.net/~roadruner/Dist2.JPG[/img]
The one on the left has a much smaller, lower shaft and shouldn't be used either. The .012" step down on this one is hidden when the gear is in place.
[img]http://home.earthlink.net/~roadruner/Dist1.JPG[/img]
The only one that should be considered, is one with a .489-.490" shaft, the entire length, such as the stock point dist on the right, above.
[img]http://home.earthlink.net/~roadruner/Dist5.JPG[/img]
The internal-coil and the external-coil housings have a different key slot for the cap. The external-coil housing has the slot, next to the vacuum advance. The slot on the internal-coil, as seen on the lower one, is much farther away. I'm using a internal housing, with external-coil and cap, with no problems.

Richard, What should be used to replace the collar once removed? Thanks

Jim,

Keep asking...someone will hear you!

Richard, great tech info and pictures, but I am not sure I follow what you're saying. I am a little challenged, could you clarify a tad..thanks.

Stuart

Don't know.
I'm familiar with the 250/292 distributors and just wanted you to know there are several variations and that some should be avoided. One of those reman, small housing, with HEI shaft units tore up the oil pump and cam gear on a 235 on this forum a couple of years back. I thought most of the problem was an undersize shaft.
There is also the issue of cam gear and dist gear compatibility. I've read that after 1954 the cams are all cast iron, so the HEI works OK. The pre 1954 dist used either a steel or bronze gear.
Do a search on the clamp by searching tony or #107. He has built a bunch of these 235/HEI and I think he used the stock clamp.

automarc
All I'm saying is that when you pull your old 235 dist out, you are going to find a one piece shaft that's .489-.490". Find a HEI that has the same size shaft.

Richard,

Thanks...


Stuart

Apparently the undersize shaft, whether one piece or two piece wobbles around enough to distroy the gears. Sounds like a disaster waiting to happen, which usually happens to me ruining an otherwise fun trip. The unit I was going to use measures .484" and slightly smaller on the lower shaft.

You'd think there would be stalled stovebolts piling up on the backroads of America. And as these inline six HEIs don't seam to grow on trees then the better solution would be to turn to Pertronix and keep the stock unit, NO?

Jim/Richard,

I'm still foggy on this issue. Is the problem that the HEI shaft, if not correct, is a smaller OD than the gear that must be put on it..OR the OD of the shaft where it goes into the oil pump is a tad bit smaller which allows the shaft to slop around and destroy the distributor drive gear.

I was under the assumption, when installing these GM HEI's in stovebolts, the case was modified, but the gear etc was fine. I don't want to confuse anyone, but I am confused now.


Stuart

The 6cyl HEI gears are all the same. It's the shaft below where the gear sits that is sometimes different. The engine that the stepped shaft(blue rotor) came out of, could not use either of the other two distributors pictured. They would not fit into the pump bushing.

Inky05 you might want to mention in your Tech Tip that the HEI is a smog distributor and as such the performance will not be the same unless recurved. As an example 63 292 six distributor is 0@600, 14@1500, 28@3700, vac adv 6@4-7 pounds, 23@13-14 pounds a 1976 distributor is 0@1100, 6@2000, 14@2300, 24@4100, vac adv 0@10-12 pounds, 10@13-14 pounds. I would have the HEI recurved to the original distributor. If your compression, cam, carb have been changed then the curve needs changed for best perforance.
Larry

Larry-

Here's an article I found on Google regarding a Datsun recurve kit that talks about 'smog distributors'.

http://www.datsunroadster.com/PIC_PAGES/NEW_PARTS_PIC_PAGES/221-10_24.htm

To recurve the HEI for the stovebolt you'd just have to change the hook shaped weights, springs and centerplate. Recurve kits come with a variety of springs. Here's a link to a picture of a 'HEI recurve kit':

http://www.moroso.com/catalog/categorydisplay.asp?catcode=41012

The question is which weight/spring combo is best for this applaction?

Here's a how-to and why article on 'recurving' your distributor:

http://www.442.com/oldsfaq/ofign.htm#IGN%20Tuning

NM51, Thanks for the reply

First I'd like to say I hope I'm not under estimating all the folks switching to an HEI distributor. The HEI is a great distributor, faster starts, more spark, and no points. Well worth the effort to recurve it.

NM51, This 442 link is a good one,

http://www.442.com/oldsfaq/ofign.htm#IGN%20Tuning

A pretty complete discussion on recurving including how to check the results yourself and adjust.

The distributor data in my previous post is part of what I have from my shop manuals, and I'd like to add a few more. I've put the data in a spread sheet and looks pretty obivious that starting in about 1968 GM starting limiting the centrifrugal advance and vacuum advance in some years the vacuum advance was increased. That's why just putting in an HEI may not get what you want. If your performanced minded then the HEI needs to be recurved. Just putting in a recurve kit is not the answer, it could do more harm than good. The 442 link is a must read. I have a distributor machine and intend to some more work with distributors as soon as I get done with my 292. The 292 is the next project on my list.
Larry

Larry- I think what we are all saying is that just like changing carburators, when you change distributors, you need to fine tune it to your engines to get the most out of it. In many cases just bolting on the carb or distribtor will improve things, but maybe not as much as it could if it were tuned properly.

The advance specs Larry posted illustrate the point very well by showing that the original distributor produced spark on a certain advance curve which is different from the HEI distributor's stock curve. The vaccum advance is different too. The factory distribtor was set and designed for factory specs. If you've got a different cam you'll produce different amounts of vaccum (generally less with a bigger cam at WOT, wide open throttle) so you may need an adjustable vaccum advance.

Here's a brief summary of the articles I posted as a starting point for research on the topic of recurving.

The Datsun article says is that due to emission regulations the advance curve was restricted on all distributors at just about the same time the HEI came out, so all HEI's are restricted in their factory configuration, and people looking for performance out of a car that cam with HEI can improve the performance of their engine by recurving their distributor too.

Fine tuning an HEI distributor is called "recurving it" and adjusts two things: Mechanical or Centrifucal advance and Vaccum advance. To adjust the Mechanical/Centrifucal advance you play with the weights, springs and center plate until you get the right combo. A recurve kit contains several sets of springs, one set of weights and one center plate. The newer weights are lighter than the originals and the center plate limits the amount the weights can close towards the center of the distibutor. Your perfect combo may be the stock weights and lighter springs, it may be new weights and the original springs, it may be one light spring and one medium spring... The point is, you can't just swap the weights and be done with it.

Vacuum advance is adjusted using an adjustable vaccum advance cannister on the distibutor. You might check to see if you got lucky and the stock one is perfect, otherwise you'll have to buy an adjustable one, take vaccuum readings on your engine and fine tune the distibutor to get it just right.

ANOTHER OPTION for recurving the vaccum and mechanical advance on the distributors while on your engine is to use a machine/computer. I think one of the classic machines for that is the SUN machine.

PS-

Recurving your distributor will not only improve performance it can seriously improve your fuel efficiency.

Holy crap ,I've been ripped off!!! I was making HEI's for Chevys and GMC's 6 years ago, described the modification with photos here on Stovebolt a few times.

I spoke with Tom Langdon, who sells an HEI converted for the I-6s and he said the curve they come with is pretty agressive and the vaccum cannister uses a soft enough spring so that it'll advance a lot with the I-6 216/235/261 since it was made for an engine that produces less vacuum.

I found that a moderately modified 235-261 gives sharper throttle response,especially off idle, when the initial timing is set at around 12-14 crankshaft degrees.You have to limit the mechanical advance to 20 crank degrees by brazing or welding the weight stops ,stock advance springs are ok.This gives a total mechanical advance of about 34 degrees.You can set the timing with a fancy set back timing light if you are using the stock 5 degree timing mark.The vacuum advance may need to be limited to about 2/3 it's normal travel if the engine detonates on part throttle.
You don't need a distributer machine to do this,done carefully on a bench,with a protractor and a pointer rigged to the distributer cam if using points.Using an electronic unit will reqire a distributer machine however.

Has anyone used Tom at 12 bolt.com for hei recurving. They have a great site with some good info.

For 6 cyl owners, use your own distributor so it looks correct in your vehicle. The cost of doing it yourself is pretty cheap.

http://devestechnet.com/Home/HEIgnition

Its not easy, but works flawlessly. Here is a link to a friend of mine who used the old voltage regulator to hide the module:

http://talk.classicparts.com/threads/deves-hei-kit-with-help-from-bilbo.22233/

Hardest part is machining a round reluctor to go on a Hexagon distributor shaft, then making a mounting wafer for the pickup. I used rudimentary tools to do my first one. Fun project when its cold outside if you have a warm place to work.

There is less mystery about this than people think. They have 6 cylinder and 8 cylinder modules and reluctor systems that you can modify yourself if you are up for a challenge.