Timing on 350 HEI - The 1947 - Present Chevrolet & GMC Truck Message Board Network

TC70C10 · 04-24-2002, 08:10 AM

What do you guys have your timing set on your 350 with HEI. Truck is running great but I'm getting about 9 - 10 mpg. I've been through my truck this past winter, front end, plugs, wires, u joints, brakes etc. Opened gap up to .45 on new plugs. Sure would like 11 or 12 since gas is going up and I live about 18 miles from work.

------------------
1970 Chevy C-10 350,3 spd
1998 Pontiac Firebird
1999 GMC Envoy

Harvest,AL 35749

tom hand · 04-24-2002, 10:03 AM

I have owned several of these trucks and every one got 10mpg, even one I had with a 6.
Without going to an overdrive trans or a wimpy rearend gear,your best bet would be to install a big vacuum gauge in the cab. You use the vacuum gauge to teach yourself to drive like a grandma. If you keep the vacuum on the gauge as high as you can,you will get better milage. Every time you give it gas you will see the needle drop and know that is money flying out of your pocket. You will probably be surprized how much your milage improves. Also get out on the highway and check your speedometer,if it is not correct your odomometer will be wrong also so you will never know what your true mileage is. I always get on the highway and use the mile markers to see if they jive with my odomometer.

------------------
72 GMC Sierra SWB almost finished---- 84 Softail
Olive Branch MS

TC70C10 · 04-24-2002, 10:07 AM

Thanks Tom,

My ddometer is right on. There's probably not anything else I can do. 3 speed with 4:11's runs high rpms. I was thinking about swapping intakes and running a 4 bbl but that would probably make matters worse.

**MJN** · 04-24-2002, 10:09 AM

I get around 11 or 12mpg with the timing set at 8 and gap set for HEI .060". That is the gap at which the HEI spark will perform best. I also run 35" tires and a 3:08 rear. The hills around here don't help with all the down shifting, we took the truck out to Nebraska and all the flat land gave great mpg.

71402BB · 04-24-2002, 10:58 AM

Dad and I just put HEI in my burb the other day. I have the timing set at 8 deg before topdead. I belive my plugs are gaped at 45. I get 10 around town and 13-14 on a trip. I have a rebuilt 350 with about 6,000 mi's on it with a 2bbl carb and 4.11's out back. I run her at 65 down the hiway.

------------------
71 SWB Stepside, was a 250, now is a 402 Big Block with 4 speed and 3.73's

72 LWB 4x4 350 4-speed 3.08's posi wearing army olive drab green (SOLD!)

68 BURB 50TH LOOKALIKE with built 350 4-speed 4.11's and posi

69 longhorn · 04-24-2002, 11:08 AM

I usaully try a 10btdc setting on a stocker(if it will handle it without spark rattle). The longhorn is set @ 16btdc,but hotter cams tend to like more initial timing. Gas milage,whats that? I get 9mpg with my combo,& dont think thats too bad considering a 383/loose converter,& 4.10 coggs.......69

TC70C10 · 04-24-2002, 11:15 AM

Thanks guys,

I appreciate the replies. I should just look at the bright side, It's paid for.

O'l Buck · 04-24-2002, 12:12 PM

mine gets 12, timed at 8 btdc, dad's 67 K-20 geared lower than low gets 12 and he's timed the same, both 350's, mine's hei, his is points. he as a 2bbl, mines a quadrajet.

------------------
Ol' Buck: '72 Chevy 1/2T 4x4 shortbox stepside 350/350auto on '84
ralleys and 31/10.5s

Angel girl: 67 Cutlass convertible
330, 3spd stick

Greener: 90 GMC Jimmy
350/auto
Chad Stephens
Orleans,NE

no name yet: 72 442 under serious construction

superchevy · 04-25-2002, 07:45 AM

My stock 350's set at 6 degrees with a stock quadrajet on an edelbrock intake. Starts, runs, idles perfect at 650 rpm. SC

Scott Menzies · 04-27-2002, 01:50 PM

If you have a stock harmonic balancer on your engine a timing light will not be accurate. The outer ring will slip on the elastomer damper creating a false reading with a timing light. Top tuning profesionals don't use timing lights unless there is a new balancer.

Secondly, what gauge wire are you using to get power to the HEI system? If you have switched over from a points style ignition system the stock wire will not be sufficient to allow the HEI to power fully. If you are using the stock wire try and get a proper guage for the HEI system.

Longhorn Man · 04-27-2002, 02:38 PM

A 4 bbl will get you better MPG if you keep your foot out of it. The primaries are smaller than that of a 2 bbl.
45 is a littls excessive for a stock HEI...all that will do is burn up coils and wires.
Harmonic ballancers that are old ate still fine if they are in good shape, find TDC and see if it corrosponds to the damper.
Out of the 2 trucks I have had on the road, the Longhorn got 14 -15 on the highway at 75 MPH, and the GMC gets about 11.
If you have a stock motor, I would ditch the 4:11's, and go with a 3:73 or even a 3.07 set. If you have a cam that is sleepy untill 3000 RPM, stay with the screamer gears. This is why my Longhorn got better MPG than the GMC...it was the exact same engine and tranny.

------------------
'69 G.M.C. 350/350. Trying to clean up the left over damage from the Dope-Smokin-Old-Man
I've been dubbed the Longhorn Freak/Fanatic/Expert, I just hope I can live up to it.
FINALLY got the HORNIAC...a '70 one ton Longhorn with a Pontiac 350/350 and lots of 'personality'. Check out The Longhorn Webite.
If you need a pic posted, E-mail me at longhornmail@yahoo.com
Andy, in Columbus Ohio

04-24-2002, 08:10 AM	#1
TC70C10 Registered User Join Date: Nov 2001 Location: Harvest, AL 35749 Posts: 337	Timing on 350 HEI What do you guys have your timing set on your 350 with HEI. Truck is running great but I'm getting about 9 - 10 mpg. I've been through my truck this past winter, front end, plugs, wires, u joints, brakes etc. Opened gap up to .45 on new plugs. Sure would like 11 or 12 since gas is going up and I live about 18 miles from work. ------------------ 1970 Chevy C-10 350,3 spd 1998 Pontiac Firebird 1999 GMC Envoy Harvest,AL 35749 __________________ 1981 K5 Blazer 305, 4spd, 4x4, 4" Lift, custom bumpers, Warn 9.5 Ti Winch 1995 T10 Blazer 4.3L 4x4 (Son's) 2004 GMC Envoy 4.2L 2WD 2005 GMC Sierra Crew Cab Z71 4x4 5.3L 240 Fun Finder Travel Trailer Harvest, AL 35749

04-24-2002, 10:03 AM	#2
tom hand CCRider Join Date: Feb 2000 Location: Olive Branch,MS,USA Posts: 2,232	I have owned several of these trucks and every one got 10mpg, even one I had with a 6. Without going to an overdrive trans or a wimpy rearend gear,your best bet would be to install a big vacuum gauge in the cab. You use the vacuum gauge to teach yourself to drive like a grandma. If you keep the vacuum on the gauge as high as you can,you will get better milage. Every time you give it gas you will see the needle drop and know that is money flying out of your pocket. You will probably be surprized how much your milage improves. Also get out on the highway and check your speedometer,if it is not correct your odomometer will be wrong also so you will never know what your true mileage is. I always get on the highway and use the mile markers to see if they jive with my odomometer. ------------------ 72 GMC Sierra SWB almost finished---- 84 Softail Olive Branch MS __________________ 72 GMC Sierra SWB almost finished---- 84 Softail Olive Branch MS

04-24-2002, 10:07 AM	#3
TC70C10 Registered User Join Date: Nov 2001 Location: Harvest, AL 35749 Posts: 337	Thanks Tom, My ddometer is right on. There's probably not anything else I can do. 3 speed with 4:11's runs high rpms. I was thinking about swapping intakes and running a 4 bbl but that would probably make matters worse. __________________ 1981 K5 Blazer 305, 4spd, 4x4, 4" Lift, custom bumpers, Warn 9.5 Ti Winch 1995 T10 Blazer 4.3L 4x4 (Son's) 2004 GMC Envoy 4.2L 2WD 2005 GMC Sierra Crew Cab Z71 4x4 5.3L 240 Fun Finder Travel Trailer Harvest, AL 35749

04-24-2002, 10:09 AM	#4
MJN Registered User Join Date: Feb 2000 Location: Maquoketa, Ia/ Orr, Mn Posts: 3,045	I get around 11 or 12mpg with the timing set at 8 and gap set for HEI .060". That is the gap at which the HEI spark will perform best. I also run 35" tires and a 3:08 rear. The hills around here don't help with all the down shifting, we took the truck out to Nebraska and all the flat land gave great mpg. __________________ '51 South Bend Model "9A" '56 Chevy 3600 NAPCO '74 Chevy Cheyenne Super K20-restored on 37's '72 GMC Sierra Custom K2500- in progress '08 GMC Envoy Denali '12 GMC Sierra 2500HD Denali '17 GMC Yukon XL VCCA member #58596 http://www.nohrco.com

04-24-2002, 10:58 AM	#5
71402BB now thats a true COON DOG Join Date: Nov 2000 Location: Franconia, NH Posts: 1,977	Dad and I just put HEI in my burb the other day. I have the timing set at 8 deg before topdead. I belive my plugs are gaped at 45. I get 10 around town and 13-14 on a trip. I have a rebuilt 350 with about 6,000 mi's on it with a 2bbl carb and 4.11's out back. I run her at 65 down the hiway. ------------------ 71 SWB Stepside, was a 250, now is a 402 Big Block with 4 speed and 3.73's 72 LWB 4x4 350 4-speed 3.08's posi wearing army olive drab green (SOLD!) 68 BURB 50TH LOOKALIKE with built 350 4-speed 4.11's and posi __________________ current project 67 402BB stout th350 3.08's with a locker. Plan on tubs 18.5's out back! (thanks Burnsman!) 71 SWB Stepside, was a 250, now is a 402 Big Block with 4 speed and 3.73's ( was crushed by a tree, bed sold, motor pulled) was my first truck!... oh well... 72 LWB 4x4 350 4-speed 3.08's posi wearing army olive drab green (SOLD!) 68 BURB 50TH LOOKALIKE work in progress, soon to have 250-I6 with a 3-speed on the tree 4.11's and posi ( currently sitting in back yard tarped awaiting time, $$$, and lots of love!) 67 1 TON- work truck 396 sm 420 4-speed, flat bed 4.57 gears "big red" (my first landscape truck, very rusty and crusty! but still gets the job done when needed!)

04-24-2002, 11:08 AM	#6
69 longhorn Registered User Join Date: Aug 2001 Location: rock island,il,usa Posts: 5,382	I usaully try a 10btdc setting on a stocker(if it will handle it without spark rattle). The longhorn is set @ 16btdc,but hotter cams tend to like more initial timing. Gas milage,whats that? I get 9mpg with my combo,& dont think thats too bad considering a 383/loose converter,& 4.10 coggs.......69 __________________ http://community.webshots.com/user/hotrodhorn

04-24-2002, 11:15 AM	#7
TC70C10 Registered User Join Date: Nov 2001 Location: Harvest, AL 35749 Posts: 337	Thanks guys, I appreciate the replies. I should just look at the bright side, It's paid for. __________________ 1981 K5 Blazer 305, 4spd, 4x4, 4" Lift, custom bumpers, Warn 9.5 Ti Winch 1995 T10 Blazer 4.3L 4x4 (Son's) 2004 GMC Envoy 4.2L 2WD 2005 GMC Sierra Crew Cab Z71 4x4 5.3L 240 Fun Finder Travel Trailer Harvest, AL 35749

04-24-2002, 12:12 PM	#8
O'l Buck Recovering Truck Driver Join Date: Mar 2002 Location: Orleans, NE USA Posts: 1,883	mine gets 12, timed at 8 btdc, dad's 67 K-20 geared lower than low gets 12 and he's timed the same, both 350's, mine's hei, his is points. he as a 2bbl, mines a quadrajet. ------------------ Ol' Buck: '72 Chevy 1/2T 4x4 shortbox stepside 350/350auto on '84 ralleys and 31/10.5s Angel girl: 67 Cutlass convertible 330, 3spd stick Greener: 90 GMC Jimmy 350/auto Chad Stephens Orleans,NE no name yet: 72 442 under serious construction __________________ 67 K-20 350, SM465, Eaton rear, 4.56 no spin option 00 Dodge 2500 4x4, 24V cummins, 5 speed Chad South Central Nebraska

04-25-2002, 07:45 AM	#9
superchevy Got big-block? Join Date: Jul 2000 Location: Austin, Texas Posts: 2,453	My stock 350's set at 6 degrees with a stock quadrajet on an edelbrock intake. Starts, runs, idles perfect at 650 rpm. SC __________________ '68 CST SWB factory 396/T400 buddy buckets, a/c, ps, pb '72 Corvette convertible 454/4spd/ac, ps, pb '73 GMC Sierra Grande short wide 454/T400 ps, pb, ac '77 K5 Blazer black on red, 350/T350/NP205 ps, pb, ac all original '78 GMC Sierra Classic short wide 454/T400 ps, pb, ac '72 GMC Sprint SP454. 1 of 38 built. '73 GMC Sprint SP454. 1 of 71 built. '75 GMC Sprint SP454. 1 of 25 built. SOLD! '72 GMC K25 4x4 468/4L80e/NP205 build thread http://67-72chevytrucks.com/vboard/s...23#post4324423 SOLD!'55 Chevy gasser 496/4spd build thread http://67-72chevytrucks.com/vboard/s...96#post4324396

04-27-2002, 01:50 PM	#10
Scott Menzies Registered User Join Date: Apr 2002 Posts: 3	If you have a stock harmonic balancer on your engine a timing light will not be accurate. The outer ring will slip on the elastomer damper creating a false reading with a timing light. Top tuning profesionals don't use timing lights unless there is a new balancer. Secondly, what gauge wire are you using to get power to the HEI system? If you have switched over from a points style ignition system the stock wire will not be sufficient to allow the HEI to power fully. If you are using the stock wire try and get a proper guage for the HEI system.

04-27-2002, 02:38 PM	#11
Longhorn Man its all about the +6 inches Join Date: Jan 2001 Location: Hilliard Ohio Posts: 2,693	A 4 bbl will get you better MPG if you keep your foot out of it. The primaries are smaller than that of a 2 bbl. 45 is a littls excessive for a stock HEI...all that will do is burn up coils and wires. Harmonic ballancers that are old ate still fine if they are in good shape, find TDC and see if it corrosponds to the damper. Out of the 2 trucks I have had on the road, the Longhorn got 14 -15 on the highway at 75 MPH, and the GMC gets about 11. If you have a stock motor, I would ditch the 4:11's, and go with a 3:73 or even a 3.07 set. If you have a cam that is sleepy untill 3000 RPM, stay with the screamer gears. This is why my Longhorn got better MPG than the GMC...it was the exact same engine and tranny. ------------------ '69 G.M.C. 350/350. Trying to clean up the left over damage from the Dope-Smokin-Old-Man I've been dubbed the Longhorn Freak/Fanatic/Expert, I just hope I can live up to it. FINALLY got the HORNIAC...a '70 one ton Longhorn with a Pontiac 350/350 and lots of 'personality'. Check out The Longhorn Webite. If you need a pic posted, E-mail me at longhornmail@yahoo.com Andy, in Columbus Ohio



Register or Log In To remove these advertisements.

Register or Log In To remove these advertisements.