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PostPosted: Fri Dec 19, 2014 5:45 pm 
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EFI Slant 6
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Joined: Sun Jun 10, 2012 3:54 pm
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Location: Terre Haute IN
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Simple HEI boost retard.

When running boost it is often recommended here to limit your total timing to 18*. Well that's all and good except for when your not in boost it takes away from your total timing for better mileage. Or let's say you want more timing taken out for higher boost levels. Well it's quite simple and I'll detail how I done mine.

First this applies if you are running GM HEI setup. If not there is a great write up by Dan. Located here: http://www.slantsix.org/forum/viewtopic.php?t=15779
And it also has links for the discussions etc.

First some parts:
GM HEI module DR137, picked mine up at autozone. List price is $42 but I get a military discount. Just ask for 1980's Oldsmobile Toronado, 5.7 V8 4bbl. Once they order it, verify that it has a smaller 5th pin.
Image
Next up is your choice of E-core coil: mine is a factory one from a junk yard.
Hobbs switch: got it on amazon prime ASIN B00GBW3ZTY. Or search lefoo LF20. Cost $15. It is adjustable. 3 prongs: NO, NC, and C.
Image
Your choice of dizzy: mine has a 9R slot length and light springs. More I for on springs, slot length, and timing can be found here:
http://slantsix.org/forum/viewtopic.php ... lot+length
Coil wire: 15N autozone $5.
And misc pcs of wire, connectors and your choice of heat sink.

So now to building. First I made an all new bracket for my coil and HEI module out of a thicker sheet of aluminum. Cutting a square for the coil and then drilling holes for it and the module. Keeping most of the wires etc hidden by mounting them to the under side. The module and coil wire up like normal per the HEI write up by Dan. But what about the 5th pin!? You ask, we will get there. No pics during the build but a pic of it installed before my 15N coil wire.

Image

Next up the hobbs switch. I took my to the bench w a 10psi gauge and some fittings. I used an 1/8" tee, 1/8" nylon line fitting, and 1/8" plug. Assembled it so a feed line on one end, hobbs on other and plug in the bottom in case I need a port later. Then I used a hand pump and multimeter to adjust it to 2-3# and it closes the NO (normally open) contacts. This tee setup will be plumbed in with your boost/vacuum gauge. It needs to see what the plenum sees. You then run a wire from the 5th pin of the module (the wee lil one) to the "C" or common on the hobbs switch. From the "NO" normally open you run a short wire to ground.Installed mine on the fender above the HEI/coil mount as seen here.
Image
Don't mind the mess, I'm yet to clean up all that.

Now the dizzy. Mine has an advance of roughly 15* mechanical. Which I measured w calipers. So out to the garage I went, once warm etc etc I set it for 8* initial. So now I know most of you are like me and figured out that's 8+15 for 23* timing before any vacuum. But we won't talk of vacuum here bc we are talking about boost (insert evil grin here) now that's 5* more than we are shooting for so that's where we have the module and hobbs.

To the rescue they come. Once this is all setup timing is normal, 23* and mines all in by 2k I think. It's got really light springs. So now when I mash the pedal my 23* is a problem until about 2# of boost. That 2# then closes my hobbs switch which in turn grounds out the 5th pin on the module. When the 5th pin sees a ground it retards timing by 5* crank! Now we are back to 18* where we want to be!!

This has all been verified w my timing light. 8 initial, revved up w 23*, ground out the pin and I see 18. Now your set ups will need tweaked since we don't all run the same initial, or slot lengths, etc.

_________________
225, Offenhauser, Holley 350, A833OD, 3:55, GM HEI,99 Durango starter
BOOSTED! WH1C, BIG FMIC, 10#
Operation Noble Eagle 03-05
Operation Iraqi Freedom 05-07
Operation Enduring Freedom 12- 13


Last edited by Ssg Pohlman on Sat Dec 20, 2014 6:37 am, edited 8 times in total.

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PostPosted: Fri Dec 19, 2014 10:16 pm 
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TBI Slant 6

Joined: Fri Sep 20, 2013 12:50 pm
Posts: 211
Location: Bay Area, California
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fascinatingly simple. It makes me want to undo my governed 18* timing distributor and try this out.


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PostPosted: Sat Dec 20, 2014 4:16 am 
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Joined: Wed Oct 23, 2002 7:57 pm
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Location: Waynesboro, Pa.
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That sounds like a nice simple set-up! Great

Would you be able to leave the pics a little larger. I am unable to see them and when I click them it only shows the link. Maybe it is just me. I am pretty much a computer moron! :lol: :lol:

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2 Mopars come with Spark plug tubes. One is a highly refined, record setting, world class, racing machine. The other is a 426 CI. boat anchor!
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PostPosted: Sat Dec 20, 2014 6:40 am 
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EFI Slant 6
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Joined: Sun Jun 10, 2012 3:54 pm
Posts: 344
Location: Terre Haute IN
Car Model*:
Updated per Ricks request. :lol:
Had to remember how to type it to do that. Looked up old posts on my slixxer gallery and good to go.
Also added pic of module for reference
And one of the hobbs switch.

Will continue to edit and critique as needed.

_________________
225, Offenhauser, Holley 350, A833OD, 3:55, GM HEI,99 Durango starter

BOOSTED! WH1C, BIG FMIC, 10#

Operation Noble Eagle 03-05

Operation Iraqi Freedom 05-07

Operation Enduring Freedom 12- 13


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PostPosted: Mon Dec 29, 2014 5:38 pm 
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Turbo EFI
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Joined: Tue Jan 17, 2006 4:57 am
Posts: 1567
Location: Oslo, Norway
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Ssg Pohlman, what an excellent and well documented writeup on a simple, cheap and easily duplicated solution to a known problem! :bow:

Olaf

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PostPosted: Tue Dec 30, 2014 3:21 am 
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EFI Slant 6
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Joined: Sun Jun 10, 2012 3:54 pm
Posts: 344
Location: Terre Haute IN
Car Model*:
Thank you, I can not take full credit for it as I read about it in one of the hundreds of pages during my research. However, I did want to take the time and spread the help to try and give back to the slant community for all that I have received.

Is there a way to make this a sticky as a how to? Or do we add it to the electrical as well since it would help for other things.

_________________
225, Offenhauser, Holley 350, A833OD, 3:55, GM HEI,99 Durango starter

BOOSTED! WH1C, BIG FMIC, 10#

Operation Noble Eagle 03-05

Operation Iraqi Freedom 05-07

Operation Enduring Freedom 12- 13


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PostPosted: Tue Dec 30, 2014 7:10 pm 
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Turbo EFI
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Joined: Tue Jan 17, 2006 4:57 am
Posts: 1567
Location: Oslo, Norway
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This should definitely be a sticky, send a pm to Guido, he'll fix that.

BTW, some Pontiacs (Fiero?) in early '80's used a similar module with app. 10° retard, but from what I understand, it is very hard to find now.

Olaf

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PostPosted: Tue Dec 30, 2014 7:35 pm 
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EFI Slant 6
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Joined: Sun Jun 10, 2012 3:54 pm
Posts: 344
Location: Terre Haute IN
Car Model*:
The olds module like I have is seen at 10* retard but one has to be careful because that is 10* cam which results in 5* crank. Small but tricky part. Ill look into the fiero module and verify which 10* it is.

_________________
225, Offenhauser, Holley 350, A833OD, 3:55, GM HEI,99 Durango starter

BOOSTED! WH1C, BIG FMIC, 10#

Operation Noble Eagle 03-05

Operation Iraqi Freedom 05-07

Operation Enduring Freedom 12- 13


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PostPosted: Tue Feb 27, 2018 11:07 am 
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EFI Slant 6

Joined: Thu Jun 24, 2010 12:30 pm
Posts: 266
Location: GYMPIE,QLD,AUSTRALIA
Car Model*:
Sorry to dig up such an old thread .
I have seen mention on other forums to use a Stewart Warner #78628 Hobbs switch.
Would a Honeywell #76575 be suitable ?
Apparently it is adjustable from 1 to 10 psi .

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