15 MPG ... WooHoo - The 1947 - Present Chevrolet & GMC Truck Message Board Network

mikep · 07-22-2002, 08:05 PM

I decided to build the new motor more for low end torque and mileage . Got it in yesterday and drove it around a bit today in and around town. The new motor specs are

9.4: 1 compression . Using 34 degrees total timing, no vacuum advance I'm able to use 87 octane.

Edelbrock performer plus cam 204/214 duration, .420/.444 lift.

New World Product S/R heads 1.94/1.50

Early cast iron intake-HEI distributor

Rebuilt 4ME marine quadrajet . Damned near perfect condition.

3.54 gears / 285-75-16 tires / manual close ratio 4 spd/ heavy 3/4 ton chassis

In driving around town somewhat light on the throttle I'm able to get 14.8 MPG and this is with only 90 miles on the motor. I'll have to flog it out on the highway once its well broken in to see what sort of mileage I can coax out of this thing. Its certainly not lacking power especially low end torque. I can maintain 15 MPH in 4th Gear without surging at all.

*Randy70C-10* · 07-22-2002, 09:22 PM

Wow, that's damn good!

vfrdude · 07-23-2002, 11:40 AM

Any specific reason for not using the vacuum advance??? You would probably get even better mileage by using it - especially around town/stop and go type driving. If you're getting some pinging under load with the vacuum advance connected, I would suggest installing an adjustable type advance, and follow the directions - You can adjust when the advance comes in, and limit the amount of vacuum advance....

mt Al · 07-23-2002, 02:31 PM

Did you use your stock block, pistons, crank, etc.?

A freind of mine has a '71 short bed 4x4 with a very similar setup, 4 speed manual, with 3.08 gears and gets almost 19 on the highway.

Awesome!

68 Suburban · 07-23-2002, 02:33 PM

I just got mid 14's going 80-85 mph this past weekend. I wonder what I would get if I went 70-75?

Stock 350 with 3.08.

hanssolo · 07-23-2002, 02:37 PM

Know what you mean on the mech. only advance. I have 10:1 and no pinging.

mikep · 07-23-2002, 03:48 PM

The block is a fresh .030 over with a steel crank, scat rods, moly file to fit rings set tight , and domed hypereutectic pistons. with the 76 cc chambers I'm right around 9.5:1 compression. On the vaccuum advance since I'm not pinging even under load I prefer to get all the advance in by 2000 rpm with light advance springs and run 20 degrees off idle for a total of 34 degrees at 2200 rpm which is about perfect for that design of chamber. The extra initial advance gives me more lower end torque and a snappier throttle on the lower end.

This one isnt but Ive run quite a few engine with the advance entirely locked out. Really picks up the throttle response if you are running gas that can handle the extra spark lead. I'm running a late model gear reduction permanent magnet starter and it doesnt even strain under the extra load.

Once this thing is broken in I'd expect 18-19 ( or better? ) on the hiway. we'll see in a few weeks.

Besides all that mumbo jumbo I have a marine carburetor with no vacuum ports so even if I wanted to run vacuum advance ( which I dont ) I would have a hard tme hooking it up. I'll probably have to take the carb off to drill the baseplate for a PCV valve vacuum port though.

68 Suburban · 07-23-2002, 04:54 PM

I am planning for a gear vendors underdrive (not overdrive) unit and a 2.76 rear gear. This will give me the 2.76 gear on the highway and 3.45 around town. I would go with the overdrive unit, but I can get the underdrive unit a lot cheaper.

Mike C · 07-23-2002, 09:11 PM

Nice work! Gotta love that torque, huh? I wish I could convince everybody that trucks need cams with 210 degrees of duration at .050 or less. That's an excellent combo you've got.

mikep · 07-23-2002, 10:14 PM

I did an experiment today where I kept in 4th gear at all speeds over 15 miles per hour basically driving it like an automatic. I wanted to see how it affected the mileage . It ran fine and didnt lug the motor at all but I wont do it again ! The mileage went to hell. I dropped to 12.5 miles per gallon over the 75 miles I drove like that through town and a little on the hiway.

Longhorn Man · 07-23-2002, 10:19 PM

Quote:

Originally posted by mikep
I dropped to 12.5 miles per gallon

Poor baby... ONLY 12.5 MPG....
LOL, I would love to get that right now!

Chevy409 · 07-24-2002, 09:59 PM

I'm with longhornmail. I went to vermont the other day, mostly interstate, and scored my record high of 8.5 MPG.

Longhorn Man · 07-24-2002, 10:19 PM

Ouch, I just read what I posted last night...without the smiley face, it looks like I was being an A-hole.
Sorry, it was only sarcasim.

mikep · 07-24-2002, 10:51 PM

Its like my first wife once told me...

"When I first met you I thought you were an asshole but I thought it was an act ...Then I found out it wasn't."

Of course she was the one who also said ...

"Marriage isnt like this on television"

**ThreeQuarter** · 07-24-2002, 11:01 PM

Hmm...sounds like the results I'd like to have from my '67 when it's up and running.

[Ben is writing down the specs...]

07-22-2002, 08:05 PM	#1
mikep Used to have a truck Join Date: May 2002 Location: port orchard WA Posts: 1,552	15 MPG ... WooHoo I decided to build the new motor more for low end torque and mileage . Got it in yesterday and drove it around a bit today in and around town. The new motor specs are 9.4: 1 compression . Using 34 degrees total timing, no vacuum advance I'm able to use 87 octane. Edelbrock performer plus cam 204/214 duration, .420/.444 lift. New World Product S/R heads 1.94/1.50 Early cast iron intake-HEI distributor Rebuilt 4ME marine quadrajet . Damned near perfect condition. 3.54 gears / 285-75-16 tires / manual close ratio 4 spd/ heavy 3/4 ton chassis In driving around town somewhat light on the throttle I'm able to get 14.8 MPG and this is with only 90 miles on the motor. I'll have to flog it out on the highway once its well broken in to see what sort of mileage I can coax out of this thing. Its certainly not lacking power especially low end torque. I can maintain 15 MPH in 4th Gear without surging at all. __________________ No truck :-(

07-23-2002, 11:40 AM	#3
vfrdude Registered User Join Date: May 2002 Location: Oakley, Ca. USA Posts: 137	Any specific reason for not using the vacuum advance??? You would probably get even better mileage by using it - especially around town/stop and go type driving. If you're getting some pinging under load with the vacuum advance connected, I would suggest installing an adjustable type advance, and follow the directions - You can adjust when the advance comes in, and limit the amount of vacuum advance.... __________________ Rudy Fierros '95 Honda VFR750F Used to have a '71 Chevy Stepside, Guards Red, Lowered 4" rear, 3" front, White Oak bed wood, 700R4 w/373 gears until some low life stole it!

07-23-2002, 02:31 PM	#4
mt Al Registered User Join Date: Aug 2001 Location: Bozeman, Montana Posts: 243	Did you use your stock block, pistons, crank, etc.? A freind of mine has a '71 short bed 4x4 with a very similar setup, 4 speed manual, with 3.08 gears and gets almost 19 on the highway. Awesome! __________________ '72 GMC 1/2T 4x4 1500 Super Custom pickup (current) past rides were: '70 Chev 2wd farm truck '71 GMC 2wd 1/2T 402 nice! '72 Chev 2wd 1/2T 396 '72 GMC 3/4T 4x4 2500 Super Custom suburban. Bozeman, Montana

07-23-2002, 02:33 PM	#5
68 Suburban Registered User Join Date: Oct 2000 Location: From Chicago, Live in Phoenix, AZ Posts: 6,802	I just got mid 14's going 80-85 mph this past weekend. I wonder what I would get if I went 70-75? Stock 350 with 3.08. __________________ Just sitting here contemplating contemplation.

07-23-2002, 02:37 PM	#6
hanssolo Registered User Join Date: Sep 2001 Location: central Ill. USA Posts: 447	Know what you mean on the mech. only advance. I have 10:1 and no pinging. __________________ 69 C10 longbed: 357c.i. /TH400/3.73s/AC/ beige primer/saving $ for paint ______________________________

07-22-2002, 09:22 PM	#2
Randy70C-10 Account Suspended Join Date: Mar 2001 Location: Virginia Beach, Va. U.S.A. Posts: 15,320	Wow, that's damn good!

07-23-2002, 03:48 PM	#7
mikep Used to have a truck Join Date: May 2002 Location: port orchard WA Posts: 1,552	The block is a fresh .030 over with a steel crank, scat rods, moly file to fit rings set tight , and domed hypereutectic pistons. with the 76 cc chambers I'm right around 9.5:1 compression. On the vaccuum advance since I'm not pinging even under load I prefer to get all the advance in by 2000 rpm with light advance springs and run 20 degrees off idle for a total of 34 degrees at 2200 rpm which is about perfect for that design of chamber. The extra initial advance gives me more lower end torque and a snappier throttle on the lower end. This one isnt but Ive run quite a few engine with the advance entirely locked out. Really picks up the throttle response if you are running gas that can handle the extra spark lead. I'm running a late model gear reduction permanent magnet starter and it doesnt even strain under the extra load. Once this thing is broken in I'd expect 18-19 ( or better? ) on the hiway. we'll see in a few weeks. Besides all that mumbo jumbo I have a marine carburetor with no vacuum ports so even if I wanted to run vacuum advance ( which I dont ) I would have a hard tme hooking it up. I'll probably have to take the carb off to drill the baseplate for a PCV valve vacuum port though. __________________ No truck :-( Last edited by mikep; 07-23-2002 at 04:21 PM.

07-23-2002, 04:54 PM	#8
68 Suburban Registered User Join Date: Oct 2000 Location: From Chicago, Live in Phoenix, AZ Posts: 6,802	I am planning for a gear vendors underdrive (not overdrive) unit and a 2.76 rear gear. This will give me the 2.76 gear on the highway and 3.45 around town. I would go with the overdrive unit, but I can get the underdrive unit a lot cheaper. __________________ Just sitting here contemplating contemplation.

07-23-2002, 09:11 PM	#9
Mike C Registered User Join Date: Dec 1999 Location: Austin, TX, USA Posts: 7,723	Nice work! Gotta love that torque, huh? I wish I could convince everybody that trucks need cams with 210 degrees of duration at .050 or less. That's an excellent combo you've got. __________________ 44 Willys MB 52 M38A1 64 Corvette Coupe 68 Camaro 'vert LT1 & TH700 69 Z/28 355 12.6's @110 69 Chevy Short Step 4 1/2"/7" drop 72 Jimmy 4WD 4spd 4" & 35's 02 GMC 2500HD 4x4 Duramax

07-23-2002, 10:14 PM	#10
mikep Used to have a truck Join Date: May 2002 Location: port orchard WA Posts: 1,552	I did an experiment today where I kept in 4th gear at all speeds over 15 miles per hour basically driving it like an automatic. I wanted to see how it affected the mileage . It ran fine and didnt lug the motor at all but I wont do it again ! The mileage went to hell. I dropped to 12.5 miles per gallon over the 75 miles I drove like that through town and a little on the hiway. __________________ No truck :-(

07-24-2002, 09:59 PM	#12
Chevy409 Giddy up giddy up... Join Date: Feb 2001 Location: US Posts: 483	I'm with longhornmail. I went to vermont the other day, mostly interstate, and scored my record high of 8.5 MPG. __________________ 72 with 69 grille and custom 73-87 stepside. BIG BLOCK 409, SM465, NP205, 3/4 axles slung under a 5" lift, 3"bodylift, 112" frame, and 35inch Pro Comp X-terrains... "BUILT NOT BOUGHT" Here's the site...

07-24-2002, 10:19 PM	#13
Longhorn Man its all about the +6 inches Join Date: Jan 2001 Location: Hilliard Ohio Posts: 2,693	Ouch, I just read what I posted last night...without the smiley face, it looks like I was being an A-hole. Sorry, it was only sarcasim.

07-24-2002, 10:51 PM	#14
mikep Used to have a truck Join Date: May 2002 Location: port orchard WA Posts: 1,552	Its like my first wife once told me... "When I first met you I thought you were an asshole but I thought it was an act ...Then I found out it wasn't." Of course she was the one who also said ... "Marriage isnt like this on television" __________________ No truck :-(

07-24-2002, 11:01 PM	#15
ThreeQuarter Senior Member Join Date: Jun 2000 Location: Texan in Iowa Posts: 2,522	Hmm...sounds like the results I'd like to have from my '67 when it's up and running. [Ben is writing down the specs...] __________________ Ben '68 Chevy C10 Custom LWB 327/TH400 2nd owner '16 GMC Sierra 1500 SLE Dblcab 4wd 5.3



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