FYI About Stock HEI - The 1947 - Present Chevrolet & GMC Truck Message Board Network

1-PU70 · 02-11-2005, 01:29 PM

I started to do some reserch on the total advance of a stock HEI and this is what I found. The stock centrifugal advance for a HEI is only 15 degress. I checked the HEI I have in my truck witch is just a stock pull out it only has 15 degress of centrifugal advance. The original points distributor I pulled from my 402 has 28 degress. So my point is if you use a stock HEI your total advance might not be where it needs to be. Your tatal advance without vacume advance conecterd should be around 36 degress acording to all the info I found and my 402 with the original points distributor had 32 degress of total timing without vacume advance.You might be loosing some power this way. I always thought my 402 was not up to what it should be so I will be looking to do some curve work on it soon. I you think any of this info is wrong or misleading speak up you wont heart my fealings. I just want to spread the truth.

stelth2002 · 02-11-2005, 01:40 PM

Good find, but i think that it depends alot on what engine you get the donor HEI out of. Where did you get yours?

1-PU70 · 02-11-2005, 01:49 PM

I dont remember but I think most came that way. I talked to a teck at Acell and he said that there performance advance curve kit #31041 will give 28 dagrees of centrifugal advance. Thats right where I want to be. 1 more point the centrifugal advance is controlled by the shap of the weights in a HEI so with a little gringing you could DIY but I think I will get the kit.

Longhorn Man · 02-11-2005, 10:25 PM

The GM HEI was pretty much set to the vehicle...each engine/gear/tranny/vehicle got it's own advance rate.

ezernut9mm · 02-11-2005, 10:50 PM

hmmm... would this explain stumble on initial exelleration?

86SILVERADO · 02-11-2005, 11:11 PM

This is an area where I know I could use some work so I will give my input and anyone who has a better grasp please let me know. I am pretty sure that motor was a high compression motor 9:1. It was designed to run on premium grade fuel and with the higher compression AND the use of high octane fuel it allows you to use much more advance without knock. Your motor would have been setup for alot more mechanical and vacuum advance than most anything else as far as SBC trucks go. If you pulled an HEI out of a smog era truck (Wait a minute, all HEI"S are from smog era trucks) you are guaranteed that it will have no wheres near the mechanical advance that your points dist would have had. I am pretty sure you could swap out the weights and springs and put them in the HEI. That would be the best way to get the proper mechanical advance for that motor with your new HEI.

1-PU70 · 02-13-2005, 05:25 PM

The advance rate could be different but the total mechecal should only be 15 degrees.

**special-K** · 02-13-2005, 08:20 PM

Lighter springs and heavier weights are the best improvements I`ve seen for the HEI.It may not allow more total advance,but will give the advance quicker for greater response and effective spark.

ddsmith · 02-13-2005, 08:27 PM

Here is some food for thought from the FAQ. http://67-72chevytrucks.com/vboard/s...d.php3?t=62040
It may help some of the understanding with regards to advance.

02-11-2005, 01:29 PM	#1
1-PU70 Registered User Join Date: Apr 2000 Location: Bradenton, FL Posts: 1,036	FYI About Stock HEI I started to do some reserch on the total advance of a stock HEI and this is what I found. The stock centrifugal advance for a HEI is only 15 degress. I checked the HEI I have in my truck witch is just a stock pull out it only has 15 degress of centrifugal advance. The original points distributor I pulled from my 402 has 28 degress. So my point is if you use a stock HEI your total advance might not be where it needs to be. Your tatal advance without vacume advance conecterd should be around 36 degress acording to all the info I found and my 402 with the original points distributor had 32 degress of total timing without vacume advance.You might be loosing some power this way. I always thought my 402 was not up to what it should be so I will be looking to do some curve work on it soon. I you think any of this info is wrong or misleading speak up you wont heart my fealings. I just want to spread the truth. __________________ 1970 CST/10 402,700R4,3:73 posi,AC,PS,PB,TLT,PW,Buckets with heaters

02-11-2005, 01:40 PM	#2
stelth2002 Young Gun wth Fast Inline Join Date: Jan 2002 Location: Idaho Posts: 1,475	Good find, but i think that it depends alot on what engine you get the donor HEI out of. Where did you get yours? __________________ 1967 Chevrolet LWB with built 292! 415 ft. lbs of torque, 4 speed :O with 27% overdrive too, 3.73 Posi. Frame and body done... getting painted!!!

02-11-2005, 11:11 PM	#6
86SILVERADO Registered User Join Date: Dec 2002 Location: Hills of Western Mass Posts: 626	This is an area where I know I could use some work so I will give my input and anyone who has a better grasp please let me know. I am pretty sure that motor was a high compression motor 9:1. It was designed to run on premium grade fuel and with the higher compression AND the use of high octane fuel it allows you to use much more advance without knock. Your motor would have been setup for alot more mechanical and vacuum advance than most anything else as far as SBC trucks go. If you pulled an HEI out of a smog era truck (Wait a minute, all HEI"S are from smog era trucks) you are guaranteed that it will have no wheres near the mechanical advance that your points dist would have had. I am pretty sure you could swap out the weights and springs and put them in the HEI. That would be the best way to get the proper mechanical advance for that motor with your new HEI. __________________ 86 Silverado C10 back to 305 power! 67 C30 Dually Dump, with 350 transplant, Rockhauler 05 Duramax 3500 "If at first you don't succeed, try a bigger hammer" Member of the 1-Ton club! Last edited by 86SILVERADO; 02-11-2005 at 11:14 PM.

02-13-2005, 05:25 PM	#7
1-PU70 Registered User Join Date: Apr 2000 Location: Bradenton, FL Posts: 1,036	The advance rate could be different but the total mechecal should only be 15 degrees. __________________ 1970 CST/10 402,700R4,3:73 posi,AC,PS,PB,TLT,PW,Buckets with heaters

02-13-2005, 08:20 PM	#8
special-K Special Order Join Date: Nov 2004 Location: Mt Airy, MD Posts: 85,852	Lighter springs and heavier weights are the best improvements I`ve seen for the HEI.It may not allow more total advance,but will give the advance quicker for greater response and effective spark. __________________ "BUILDING A BETTER WAY TO SERVE THE USA"......67/72......"The New Breed" GMC '67 C1500 Wideside Super Custom SWB: 327/M22/3.42 posi.........."The '67" (project) GMC '72 K2500 Wideside Sierra Custom Camper: 350/TH350/4.10 Power-Lok..."The '72" (rolling) Tim "Don't call me a redneck. I'm a rough cut country gentleman" R.I.P. ~ East Side Low Life ~ El Jay ~ 72BLUZ ~ Fasteddie69 ~ Ron586 ~ 67ChevyRedneck ~ Grumpy Old Man ~

02-11-2005, 01:49 PM	#3
1-PU70 Registered User Join Date: Apr 2000 Location: Bradenton, FL Posts: 1,036	I dont remember but I think most came that way. I talked to a teck at Acell and he said that there performance advance curve kit #31041 will give 28 dagrees of centrifugal advance. Thats right where I want to be. 1 more point the centrifugal advance is controlled by the shap of the weights in a HEI so with a little gringing you could DIY but I think I will get the kit. __________________ 1970 CST/10 402,700R4,3:73 posi,AC,PS,PB,TLT,PW,Buckets with heaters

02-11-2005, 10:25 PM	#4
Longhorn Man its all about the +6 inches Join Date: Jan 2001 Location: Hilliard Ohio Posts: 2,693	The GM HEI was pretty much set to the vehicle...each engine/gear/tranny/vehicle got it's own advance rate.

02-11-2005, 10:50 PM	#5
ezernut9mm Registered User Join Date: Feb 2005 Location: kansas city, mo. Posts: 224	hmmm... would this explain stumble on initial exelleration?

02-13-2005, 08:27 PM	#9
ddsmith Glowing since 1978 Join Date: Mar 2001 Location: Lusby,MD,USA Posts: 532	Here is some food for thought from the FAQ. http://67-72chevytrucks.com/vboard/s...d.php3?t=62040 It may help some of the understanding with regards to advance. __________________ 66 Chevy C30 Stakebody Dump, PS,PB, 327cu in 71 Corvette Coupe 454 4 speed 69 Chevy C20 Custom Camper

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