HEI advance curve ? - Page 2 - The 1947 - Present Chevrolet & GMC Truck Message Board Network

mikep · 07-29-2002, 02:49 PM

I should state that I am running a late model delco gear reduction permanent magnet starter and I dont have any problem turning over my engine even with 9.5 :1 and loads of initial advance.

**MikeB** · 07-29-2002, 02:56 PM

Mikep -- that's an interesing subject you brought up. The engine's running at idle with initial mechanical and max vacuum advance. Then you stomp on it and all the vacuum advance goes away just when you need it. Sure, mechanical comes in, but not until the revs start to build a little. Where's an MSD engineer when we need one?

Jesse 67 c-10 · 07-29-2002, 06:39 PM

This is where an electronicly controlled dist with a computer and knock sensors would be nice, runs max advance engine can take without detonation or pinging, adjusts in real time to suit the current conditions. But, who has the cash! a question though, I have an accel hei with an adjustable vac advance and a 1406 carb. should I hook the vac adv up to ported or full vacume? I have it on ported vac, seems ok but I don't want to be cutting myself short in milage or power or something. What are some advantages/dissadvantages of either? Another, when you guys are setting your timing, are you using a timing tape on the damper or some sort of special timing light?
Thanks!
Jesse

crazy longhorn · 07-29-2002, 06:45 PM

I use a timing tape on the balancer to set mine. as far as the advance , you will hear both ways......go for what the eng wants. With hotter cams,& fat carbs, I like to run on a full manifold source at the carb. some of the leaner setups seem to like ported spark better. try em both,& see what works best for your combo. good luck......Al

mikep · 07-29-2002, 08:35 PM

I use an advance timing light. Works great. I keep it in my tuneup bag along with a tachometer, a vacuum gauge, a dwell meter, an infrared pyrometer, assorted tools, and a fluke multimeter .

I dont use vacuum advance and I havent in years so cant help much there. In fact with lighter cars for hi performance use I dont use any at all . Get the advance in and get it in fast .

robby · 07-29-2002, 11:03 PM

this is great discussion. But lets say I was just a normal Joe who wanted the engine to run with some pep and soem decent gas mileage what would I do woth the curve on an HEI? Should I eye ball the stock springs and go with the ones that are close in strength? shoot for middle and call it good?

robby · 07-29-2002, 11:10 PM

man I gotta go to bed, ,I caint herdly spel no mo.

Denny · 07-30-2002, 12:15 AM

I run a timing tape and I use the full vacuum not the port. I have a vacuum gauge in the car that is connected to the same line as my vacuum advance. Port vacuum on the Holley and the Demon comes in when I don't want vacuum underload. Port vacuum is an emission thing for cars running not much advance.

crazy longhorn · 07-30-2002, 10:50 AM

Robby, if you pick up a Crane vac advance, they will have a good suggested starting point,with a chart on springs,& adjustments. I would try to start in the 2800 "all in" range(beaware that the lighter aftermarket weights will change the listed range). start by selecting springs,& setting the timing 2 degrees faster than stock setting. then make a full throttle run with out the vac advance. If it doesnt ping, bump the timing a little more,or go 1 step lighter on the spring. if it pings, go 1 step heavier on the spring. I would suggest about 10-12 BTDC as a starting point. Once you have the max timing,with no ping(full throttle run), then start on the vac advance. With a heavy truck,I would use the limiter plate set the the max amout of limitation(should give in the range of 12 degrees vac timing). now take it out for a part throttle run,pull a few hills,& check for spark rattle under lite throttle/ heavy load. if she rattles, adjust the screw in the port on the vac can CC 2 turns at a time till the rattle is eliminated. as far as hooking the vac advance, I like to run to a full manifold source at the carb,but you may find that your combo will respond better hooked to ported spark.........try em both, & use what the engine likes. good luck........Crazy Al

07-29-2002, 02:49 PM	#26
mikep Used to have a truck Join Date: May 2002 Location: port orchard WA Posts: 1,552	I should state that I am running a late model delco gear reduction permanent magnet starter and I dont have any problem turning over my engine even with 9.5 :1 and loads of initial advance. __________________ No truck :-(

07-29-2002, 02:56 PM	#27
MikeB Senior Member Join Date: Jul 2000 Location: North Texas Posts: 3,475	Mikep -- that's an interesing subject you brought up. The engine's running at idle with initial mechanical and max vacuum advance. Then you stomp on it and all the vacuum advance goes away just when you need it. Sure, mechanical comes in, but not until the revs start to build a little. Where's an MSD engineer when we need one? __________________ Mike 1969 C10 LWB -- owned for 35 years. 350/TH350, 3.08 posi, 1st Gen Vintage Air, AAW wiring harness, 5-lug conversion, 1985 spindles and brakes. 1982 C10 SWB -- sold 1981 C10 Silverado LWB -- sold, but wish I still had it! 1969 C10 (not the current one) that I bought in the early 1980s. Paid $1200; sold for $1500 a few years later. Just a hint at the appreciation that was coming. Retired as a factory automation products salesman. Worked part-time over the years for an engine builder and a classic car repair shop. Member here for 24 years! This is the very first car/truck Internet forum I joined. I still used a dial-up modem back then!

07-29-2002, 06:39 PM	#28
Jesse 67 c-10 Registered User Join Date: Feb 2000 Location: Edmonton, Alberta, Canada Posts: 599	This is where an electronicly controlled dist with a computer and knock sensors would be nice, runs max advance engine can take without detonation or pinging, adjusts in real time to suit the current conditions. But, who has the cash! a question though, I have an accel hei with an adjustable vac advance and a 1406 carb. should I hook the vac adv up to ported or full vacume? I have it on ported vac, seems ok but I don't want to be cutting myself short in milage or power or something. What are some advantages/dissadvantages of either? Another, when you guys are setting your timing, are you using a timing tape on the damper or some sort of special timing light? Thanks! Jesse __________________ Edmonton, Alberta, 67 c-10, Long fleet, front disks, 5 lug rear end, 327 with Vortechs, edlbrock manifold, comp cams XE 256, 600cfm carb. Backed by a getrag 5 speed and 1 piece driveshaft. 1993 Dihatsu Hijet Jumbo cab 4x4, currently converting to battery electric power.

07-29-2002, 08:35 PM	#30
mikep Used to have a truck Join Date: May 2002 Location: port orchard WA Posts: 1,552	I use an advance timing light. Works great. I keep it in my tuneup bag along with a tachometer, a vacuum gauge, a dwell meter, an infrared pyrometer, assorted tools, and a fluke multimeter . I dont use vacuum advance and I havent in years so cant help much there. In fact with lighter cars for hi performance use I dont use any at all . Get the advance in and get it in fast . __________________ No truck :-(

07-29-2002, 11:03 PM	#31
robby Semper Fidelis Join Date: Dec 2001 Location: Cedar City, Utah Posts: 654	this is great discussion. But lets say I was just a normal Joe who wanted the engine to run with some pep and soem decent gas mileage what would I do woth the curve on an HEI? Should I eye ball the stock springs and go with the ones that are close in strength? shoot for middle and call it good? __________________ 72 Chevy C 20 with 402 For sale 85 GMC K2500 83 Trans Am Cedar City, Utah (Missouri Native)

07-29-2002, 06:45 PM	#29
crazy longhorn Fabricate till you "puke" Join Date: Jun 2002 Location: Ill Posts: 9,403	I use a timing tape on the balancer to set mine. as far as the advance , you will hear both ways......go for what the eng wants. With hotter cams,& fat carbs, I like to run on a full manifold source at the carb. some of the leaner setups seem to like ported spark better. try em both,& see what works best for your combo. good luck......Al

07-29-2002, 11:10 PM	#32
robby Semper Fidelis Join Date: Dec 2001 Location: Cedar City, Utah Posts: 654	man I gotta go to bed, ,I caint herdly spel no mo. __________________ 72 Chevy C 20 with 402 For sale 85 GMC K2500 83 Trans Am Cedar City, Utah (Missouri Native)

07-30-2002, 12:15 AM	#33
Denny Registered User Join Date: Jul 2002 Location: Cedar Hill, MO Posts: 426	I run a timing tape and I use the full vacuum not the port. I have a vacuum gauge in the car that is connected to the same line as my vacuum advance. Port vacuum on the Holley and the Demon comes in when I don't want vacuum underload. Port vacuum is an emission thing for cars running not much advance. __________________ 1969 Chevy C10. Dakota Digital Gauges, 383 Votex Engine, MSD 8361 Distributor, MSD 6A Unit, Demon Carb, Phoenix Transmission 4L80E trans, 3:73 Posi Rear End Early Classics 6 Lug Disc Brakes and Spindles All Stainless Lines

07-30-2002, 10:50 AM	#34
crazy longhorn Fabricate till you "puke" Join Date: Jun 2002 Location: Ill Posts: 9,403	Robby, if you pick up a Crane vac advance, they will have a good suggested starting point,with a chart on springs,& adjustments. I would try to start in the 2800 "all in" range(beaware that the lighter aftermarket weights will change the listed range). start by selecting springs,& setting the timing 2 degrees faster than stock setting. then make a full throttle run with out the vac advance. If it doesnt ping, bump the timing a little more,or go 1 step lighter on the spring. if it pings, go 1 step heavier on the spring. I would suggest about 10-12 BTDC as a starting point. Once you have the max timing,with no ping(full throttle run), then start on the vac advance. With a heavy truck,I would use the limiter plate set the the max amout of limitation(should give in the range of 12 degrees vac timing). now take it out for a part throttle run,pull a few hills,& check for spark rattle under lite throttle/ heavy load. if she rattles, adjust the screw in the port on the vac can CC 2 turns at a time till the rattle is eliminated. as far as hooking the vac advance, I like to run to a full manifold source at the carb,but you may find that your combo will respond better hooked to ported spark.........try em both, & use what the engine likes. good luck........Crazy Al



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