Gas Milage And Timeing Question??? - The 1947 - Present Chevrolet & GMC Truck Message Board Network

sam's 72 · 12-12-2002, 09:50 AM

I need a little help from you guys. I want to try and squeze another 2 to 3 MPG out of my truck, how can I ? Reset timing, lean out carb? I have a LWB 72, with a 86' 305 all stock,( I dont want to add mods to this engine) I have an HEI already, 700r4, 308 gears withg 31" tires. I am getting 11 MPG right now, would like to get just a little more. Is it possible?
Sam

beautimus · 12-12-2002, 10:13 AM

remove tailgate, add a couple of pounds more of air to the tires,
should be good for a point or so...., but there should be a
fix, 10 or 11 mpg with 3.08 gears sounds kinda low to me.....
just my 2 cents............

Huck · 12-12-2002, 10:27 AM

Your mpg is real low for what you are running---. Timing will help a bit --try a little less advance and see how that goes---. I suspect that either your carb is junk or your 305 is not pushing enough hp to take advantage of the 700R4 with the 308 gears. The only other sure fire way to get more mpg would be to let that little sucker breath a bit with some headers. My 350 with edlebrock 1406, performer, HEI, headers, 5speed & 308 give me 20mpg on the highway. GORDO has a Short bed running a 350, HEI, Edelbrock, 700R4 and 373 gears and gets 20mpg on the flats as well. Headers are probably good for 15-20hp and 2-3 mpg and most sbc motors. Good luck~~Huck

slam33 · 12-12-2002, 10:37 AM

Sounds like your working the motor a bit too much. You have all the good stuff but that 305 might not have the power and torque to drive it all. The 3.08 are great on the highway when your rolling but around town you need to push it a bit to get it going, add the 31's which take more grunt to get going, the 700 is good. There is a point when cubes are needed and it looks like you might be there. Leaning the carb might not be a good idea. Read the plugs and if they look good then leave the mix alone. A nice 350 would do you much better. I'm getting around 15 with mine and I run a TH350 with 3.73
's and 31's. Thing is the 350 is set up for low end power (carb, manifold, headers, ignition ), I spin 2600 at 60mph on the highway and I have the power around town so that I don't have to lean on it.

sam's 72 · 12-12-2002, 11:11 AM

Huck,
I am running with the timming way advanced, I will back it down a bit, have any ideal how much to back off, I think I am running 36 or 38 total advance. I hate this 305 in this truck, I am building a 383 right now, but I don't see it being ready till June or July, that is why I really don't want to add any mods. like headers, to this 305. all of my driving is on the high way. I drive 35 miles to work one way, all high way. I have thought about adjusting the timing down, I have to run 93 octane fuel, any thing else cause pinging, and the truck wants to keep running once you turn it off with lower octane fuel. Just don't know how much to retard.
any ideals?
Sam

jku72 · 12-12-2002, 11:27 AM

The way I got the best timing for my truck was by results, not any set timing number. In other words, since it seems clear that the engine is way too advanced, try backing it off some, check mileage, if it improves a little, keep going until the mileage starts dropping again, then go back to where you got the highest. An 86 305 *should* be able to run the cheap gas no problem.
I have a 68 half ton suburban with a 70 350 and a 4 speed, 3.07 rear gears and 31 inch rear tires and I get 19-20 mpg on the highway. I know the 305 is quite possibly the worst small block ever offered, but still, 11? Maybe you have a hole in your gas tank. That timing will do it, and can really damage things over time.

sam's 72 · 12-12-2002, 12:14 PM

jku72,
I thought the same thing man! I like DAMN! I have got to be leaking gas some where. Ok I will start with moveing the timeing on it, your right, a 86 305 should run on what ever gas I put in it, hell should run on a mixture of gas and water huh! J/K. sounds like I have something to play with this weekend.

any other things other then timeing let me know guys, dont want to remove tail gate or over pressure my tires, will be glad when the 383 is ready, I hate this engine, can you say NO POWER!!
Sam

cableguy0 · 12-12-2002, 01:07 PM

well even if you do get a set of headers and a nice dual exhaust it wont go to waste the headers would bolt right up to that 383 when u get it done

dmec · 12-12-2002, 01:12 PM

when you installed 700r4 did you have your speedo calibrated? if you didnt you probably arent getting the right information to calculate fuel mileage.

sam's 72 · 12-12-2002, 01:25 PM

yes the speedo is correct. I know the headers will fit the 383, I already have duel exhaust with flow masters, 2 1/4' pipe, I have a set of headers already, they are ver big primary tubes, did not want to use them on this Bull Sh!t 305 engine.
Sam

lukecp · 12-12-2002, 01:41 PM

A 305 isn't that bad of a motor. A friend of mine has a '88 up 305 (has centerbolt vc's) in a '76 Chevy C10. The 305 is stock, with a allumium intake off a caprice cop car, a quadrajet, and HEI. The truck moves pretty damn good, even with 3.08 gears. It has a TH400 in it, and if you leave it in first gear and floor it, it will leave a 3-4 ft black mark when it hits second. My 350 beat it, but it is pretty impressive for how small of an engine it is.

**tkeduk8r** · 12-12-2002, 06:33 PM

man hearin you guys talk bout your 350's with 1:1 final drive transmissions and 3.73's gettin 15-20 mpg on the highway, man and in my 74 c10 with a 250,1 bbl, 3 on tree, and 3.73's and 30 inch tires and im lucky to get 13... ive got initial timing at 8 BTDC, and 22 Hg/in vaccum with rebuilt carb (starts and accellerates good) new exhaust and all the approprriate filters.... guess i need a 350.... I did have a 80 K5 4x4 with 3pd n creeper, 373s and 31" tires and got 19... but im getting at ly limits with this thing... very puzzling...
--mike

**MikeB** · 12-12-2002, 06:43 PM

If you don't already have them, dual exhausts will make a big difference in power and economy. My original 307 went from 11 to 13 mpg and ran a lot better by simply adding 2" duals and generic turbo mufflers. I'm not sure if 86 trucks had these, but make sure your heat riser valve and air cleaner valve (in the snorkle) are open when the engine is hot. And check your timing to make sure the mechanical and vacuum advance work properly.

**tkeduk8r** · 12-12-2002, 06:50 PM

speedo checks out with milage markers on side of the highway.. the ONLY thing i can see happnin is I have a VERY slight miss at times, but idle and acceleration are very smooth...i have capped off all the vac lines off the carb cept for vac advance to eliminate and chance of vac leak and theslight miss didnt go away so i figured my valves may a little carboned up, although it still holds even compression across the board....
--mike

12-12-2002, 09:50 AM	#1
sam's 72 Senior Member Join Date: Nov 2001 Location: Pasadena, Texas, USA Posts: 1,005	Gas Milage And Timeing Question??? I need a little help from you guys. I want to try and squeze another 2 to 3 MPG out of my truck, how can I ? Reset timing, lean out carb? I have a LWB 72, with a 86' 305 all stock,( I dont want to add mods to this engine) I have an HEI already, 700r4, 308 gears withg 31" tires. I am getting 11 MPG right now, would like to get just a little more. Is it possible? Sam __________________ 72 LWB chevy truck. Pasadena, Texas

12-12-2002, 10:13 AM	#2
beautimus Registered User Join Date: Mar 2002 Location: woodstock, alabama, usa Posts: 938	remove tailgate, add a couple of pounds more of air to the tires, should be good for a point or so...., but there should be a fix, 10 or 11 mpg with 3.08 gears sounds kinda low to me..... just my 2 cents............ __________________ i survived cancer and kidney stones, but my kids are killing me.

12-12-2002, 10:37 AM	#4
slam33 Registered User Join Date: Aug 2001 Location: Long Beach, Ca Posts: 1,432	Sounds like your working the motor a bit too much. You have all the good stuff but that 305 might not have the power and torque to drive it all. The 3.08 are great on the highway when your rolling but around town you need to push it a bit to get it going, add the 31's which take more grunt to get going, the 700 is good. There is a point when cubes are needed and it looks like you might be there. Leaning the carb might not be a good idea. Read the plugs and if they look good then leave the mix alone. A nice 350 would do you much better. I'm getting around 15 with mine and I run a TH350 with 3.73 's and 31's. Thing is the 350 is set up for low end power (carb, manifold, headers, ignition ), I spin 2600 at 60mph on the highway and I have the power around town so that I don't have to lean on it. __________________ 71 LWB 350/350still working on it but it's going tp be sweet. www.geocities.com/stevemau/slam33page.html " TARGET=_blank>http://www.geocities.com/stevemau/slam33page.html?1004806705410 </A>

12-12-2002, 11:11 AM	#5
sam's 72 Senior Member Join Date: Nov 2001 Location: Pasadena, Texas, USA Posts: 1,005	Huck, I am running with the timming way advanced, I will back it down a bit, have any ideal how much to back off, I think I am running 36 or 38 total advance. I hate this 305 in this truck, I am building a 383 right now, but I don't see it being ready till June or July, that is why I really don't want to add any mods. like headers, to this 305. all of my driving is on the high way. I drive 35 miles to work one way, all high way. I have thought about adjusting the timing down, I have to run 93 octane fuel, any thing else cause pinging, and the truck wants to keep running once you turn it off with lower octane fuel. Just don't know how much to retard. any ideals? Sam __________________ 72 LWB chevy truck. Pasadena, Texas

12-12-2002, 11:27 AM	#6
jku72 Registered User Join Date: Jan 2002 Location: cornville, maine Posts: 659	The way I got the best timing for my truck was by results, not any set timing number. In other words, since it seems clear that the engine is way too advanced, try backing it off some, check mileage, if it improves a little, keep going until the mileage starts dropping again, then go back to where you got the highest. An 86 305 should be able to run the cheap gas no problem. I have a 68 half ton suburban with a 70 350 and a 4 speed, 3.07 rear gears and 31 inch rear tires and I get 19-20 mpg on the highway. I know the 305 is quite possibly the worst small block ever offered, but still, 11? Maybe you have a hole in your gas tank. That timing will do it, and can really damage things over time. __________________ jku Cornville, Maine 68 C10 burb 42 Willys MB 46 Dodge WF-32 1.5 ton 53 & 56 Olds' 60 Cadillac 22 Dodge Brothers

12-12-2002, 10:27 AM	#3
Huck Senior Member Join Date: Jun 2001 Location: Shelbyville, KY Posts: 3,261	Your mpg is real low for what you are running---. Timing will help a bit --try a little less advance and see how that goes---. I suspect that either your carb is junk or your 305 is not pushing enough hp to take advantage of the 700R4 with the 308 gears. The only other sure fire way to get more mpg would be to let that little sucker breath a bit with some headers. My 350 with edlebrock 1406, performer, HEI, headers, 5speed & 308 give me 20mpg on the highway. GORDO has a Short bed running a 350, HEI, Edelbrock, 700R4 and 373 gears and gets 20mpg on the flats as well. Headers are probably good for 15-20hp and 2-3 mpg and most sbc motors. Good luck~~Huck

12-12-2002, 12:14 PM	#7
sam's 72 Senior Member Join Date: Nov 2001 Location: Pasadena, Texas, USA Posts: 1,005	jku72, I thought the same thing man! I like DAMN! I have got to be leaking gas some where. Ok I will start with moveing the timeing on it, your right, a 86 305 should run on what ever gas I put in it, hell should run on a mixture of gas and water huh! J/K. sounds like I have something to play with this weekend. any other things other then timeing let me know guys, dont want to remove tail gate or over pressure my tires, will be glad when the 383 is ready, I hate this engine, can you say NO POWER!! Sam __________________ 72 LWB chevy truck. Pasadena, Texas

12-12-2002, 01:07 PM	#8
cableguy0 Senior Member Join Date: Apr 2000 Location: Delta,Pa Posts: 14,948	well even if you do get a set of headers and a nice dual exhaust it wont go to waste the headers would bolt right up to that 383 when u get it done __________________ Owner of North Point Car Care in Dundalk Md. We specialize in custom exhaust on both modern and classic vehicles. We are a full service auto shop from classics to modern vehicles. Feel free to contact me with questions. I will give a 10% discount to any board member.

12-12-2002, 01:12 PM	#9
dmec Senior Member Join Date: Jun 2000 Location: yucaipa ca Posts: 580	when you installed 700r4 did you have your speedo calibrated? if you didnt you probably arent getting the right information to calculate fuel mileage.

12-12-2002, 01:25 PM	#10
sam's 72 Senior Member Join Date: Nov 2001 Location: Pasadena, Texas, USA Posts: 1,005	yes the speedo is correct. I know the headers will fit the 383, I already have duel exhaust with flow masters, 2 1/4' pipe, I have a set of headers already, they are ver big primary tubes, did not want to use them on this Bull Sh!t 305 engine. Sam __________________ 72 LWB chevy truck. Pasadena, Texas

12-12-2002, 01:41 PM	#11
lukecp Formerly yellow72custom Join Date: May 2001 Location: Austin, TX Posts: 7,531	A 305 isn't that bad of a motor. A friend of mine has a '88 up 305 (has centerbolt vc's) in a '76 Chevy C10. The 305 is stock, with a allumium intake off a caprice cop car, a quadrajet, and HEI. The truck moves pretty damn good, even with 3.08 gears. It has a TH400 in it, and if you leave it in first gear and floor it, it will leave a 3-4 ft black mark when it hits second. My 350 beat it, but it is pretty impressive for how small of an engine it is. __________________ '72 Chevy C10 Mild 350/TH350/3.07. Ochre/White. Old high school ride. '70 GMC C2500 '62 327 4bbl/SM465/4.56-geared Dana 60. White/White. Project or parts truck. '97 Saturn SL DD. 1.9/5-speed. 40+ highway mpg

12-12-2002, 06:33 PM	#12
tkeduk8r Senior Member Join Date: Apr 2001 Location: Alexandria, MN Posts: 1,462	depressing man hearin you guys talk bout your 350's with 1:1 final drive transmissions and 3.73's gettin 15-20 mpg on the highway, man and in my 74 c10 with a 250,1 bbl, 3 on tree, and 3.73's and 30 inch tires and im lucky to get 13... ive got initial timing at 8 BTDC, and 22 Hg/in vaccum with rebuilt carb (starts and accellerates good) new exhaust and all the approprriate filters.... guess i need a 350.... I did have a 80 K5 4x4 with 3pd n creeper, 373s and 31" tires and got 19... but im getting at ly limits with this thing... very puzzling... --mike __________________ 63 C20 2WD, 230/SM420/4.11 73K 68 C30 dump truck, 327,SM425,4.56 66K original 68 C10 2WD SWB Stepper, 250/3-tree/3.73 66K.... Wifes 68 Buick Skylark Custom Conv., 350/TH400/2.56 In our family since '79 69 GMC 1500 SWB 2WD, 350/TH350/3.73 posi... 70 K10 SWB 4X4 4-sp,ps, pb, tilt, buckets, console, sliding back window (Need AC parts) WIP 72 Chevy K20 4x4 350/350/205/4.56 donor 72 Vette 350/M21/3.70 posi, triple black and super fast 84 Olds Cutlass Brougham 350/2004r/4.11 was Dad's

12-12-2002, 06:43 PM	#13
MikeB Senior Member Join Date: Jul 2000 Location: North Texas Posts: 3,597	If you don't already have them, dual exhausts will make a big difference in power and economy. My original 307 went from 11 to 13 mpg and ran a lot better by simply adding 2" duals and generic turbo mufflers. I'm not sure if 86 trucks had these, but make sure your heat riser valve and air cleaner valve (in the snorkle) are open when the engine is hot. And check your timing to make sure the mechanical and vacuum advance work properly. __________________ Mike 1969 C10 LWB -- owned for 35 years. 350/TH350, 3.08 posi, 1st Gen Vintage Air, recent 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!

12-12-2002, 06:50 PM	#14
tkeduk8r Senior Member Join Date: Apr 2001 Location: Alexandria, MN Posts: 1,462	speedo checks out with milage markers on side of the highway.. the ONLY thing i can see happnin is I have a VERY slight miss at times, but idle and acceleration are very smooth...i have capped off all the vac lines off the carb cept for vac advance to eliminate and chance of vac leak and theslight miss didnt go away so i figured my valves may a little carboned up, although it still holds even compression across the board.... --mike __________________ 63 C20 2WD, 230/SM420/4.11 73K 68 C30 dump truck, 327,SM425,4.56 66K original 68 C10 2WD SWB Stepper, 250/3-tree/3.73 66K.... Wifes 68 Buick Skylark Custom Conv., 350/TH400/2.56 In our family since '79 69 GMC 1500 SWB 2WD, 350/TH350/3.73 posi... 70 K10 SWB 4X4 4-sp,ps, pb, tilt, buckets, console, sliding back window (Need AC parts) WIP 72 Chevy K20 4x4 350/350/205/4.56 donor 72 Vette 350/M21/3.70 posi, triple black and super fast 84 Olds Cutlass Brougham 350/2004r/4.11 was Dad's



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