Squeezing out MPG's

[Johnny Blaze]

So, I am trying to improve milage in the Air Force 69 truck. Yeah, Starting with a brick is not the best for milage, but gotta have some coolness to right? Here are the details.

1969 C10 1/2ton
curb wieght 3300lbs

Truck is lowered 4" front 5" rear

Engine

355
Flat top speed rpos for about 8.9:1 copression
New GM basic 76cc heads
Comp Xtreme Energy Cam

	212 int./218 exh.
Advertised Intake Duration		256
Advertised Exhaust Duration		268
Advertised Duration		256 int./268 exh.
Intake Valve Lift with Factory Rocker Arm Ratio		0.447 in.
Exhaust Valve Lift with Factory Rocker Arm Ratio		0.454 in.
Valve Lift with Factory Rocker Arm Ratio		0.447 int./0.454 exh.
LSA Rams horn manifolds 2 1/4" mandrel exhaust with h pipe and 2.5" 2 chamber Thrush Mufflers Edelbrock Performer Intake Factory Quadrajet HEI ignition M-20 wide ratio Muncie 4 speed 30lb Hays flywheel 3.73 Rear Gears 28" tall tire. Running an electric fan, on a thermostat, engine maintains 190-200F no powersteering. Engine uses 10w30 Brad Penn oil. Trans has Redline synthetic Rear has redline synthetic Right now I am averageing about 14 mpg. My commute is 30miles one way, most of the time cruising at 60 mph. At 60mph I am turning about 2600 rpms. I was thinking about swapping to a 3.07 gear, this will drop my cruise RPM about 500 rpms. Will that make much difference? The carb was built to match the engine. It is a bit rich now, and I am going to start tuning it a little better, but am still reading up on Q Jets. I am running R45TS Plugs at .035". Planning on swapping in new ones and opening them up to about .045" I am going to invest in a wideband o2 sensor and gauge to help with tuning. Open to ideas, suggestions? I have a tpi set up, but figure it would still cost about a grand to swap it.		110

[Johnny Blaze]

Thats weird. Sorry for the graph looking post above!


MY dream would be to knock down 20mpg. I see guys posting numbers like that or higher with bigger truck then mine, but I doubt them.

[19,69camaro]

I would say first get to work with that wideband. Since you are doing a lot of cruising try and tune for lean afr at low load.

[regal454]

Headers would help. I would also look at a T5 from a third gen Camaro. It should survive behind that motor.

[jbake]

How much Mpg do you want to pick up? 14 is good got what you have. Lose all the weight you can. Jack, spare,etc........ how wide are the tires are you running? Width means rolling and wind resistance. Are you running 200 tread wear or running something harder? Harder compounds roll easier and your engine doesn't work as hard to roll down the road.

[Johnny Blaze]

As much as possible. My dream would be 20 mpg.

No jack, no spare, no stereo, no power brakes, no power steering, no ac. Its pretty bare bones now.

Tires are 235/60/17, just about as skinny s I can go. They are hard too.


I can't complain about 14. With the 250 6 cyl, headers, clifford intake and a fine tuned 450 holley, I was knocking down a best of 12mpg. The truck is faster, uses less fluids now and gets better mpg.


I'm wondering what people think about the gear swap, would 500rpm drop at cruising make a lot of difference?

[BonzoHansen]

#1 thing to change: M-20 wide ratio Muncie 4 speed


what kind of shape is that q-jet in? they are great for mpg but they can wear and have leaks causing issues.

[Randy67]

20 mpg should be possible, they are getting that from new trucks which outweigh yours by a good bit (with better engine technology as well). An overdrive transmission would help alot, TPI could help too if tuned properly.

[Johnny Blaze]

#1 thing to change: M-20 wide ratio Muncie 4 speed


what kind of shape is that q-jet in? they are great for mpg but they can wear and have leaks causing issues.

What Trans would you suggest? How much improvement will I get? Spending 2K on an overdrive is a lot, it will take a good bit of a milage improvement to pay for itself.

The Carb is a fresh rebuild, with a few mods to better fit the engine, done by a q jet guy in the Carolinas.

I have not done much to it other then play with the idle mixture screws and idle speed. I have been reading about modding q jets but have not started yet.


BTW, I bumped the base timing up to 12 BTDC.

[Johnny Blaze]

20 mpg should be possible, they are getting that from new trucks which outweigh yours by a good bit (with better engine technology as well). An overdrive transmission would help alot, TPI could help too if tuned properly.

Years ago, I had the JTR tpi swap book, and they said tpi alone will not give you an improvement, its the fact that TPI allows your engine top run better under load at low rpms, which means you can then run an overdrive.

I would like to swap an overdrive, but again its a lot of cash.

A rear swap is much cheaper.

[Johnny Blaze]

According to the calculator at 60 mph I should be turning 2686 rpms.

A swap to a 3.08 rear will drop it to 2218rpm

Keeping the 3.73 and swapping to an overdrive, say a 700r4 would change it too 1552rpm

So, a trans would make a much greater change, however it would be a much greater investment.

[Johnny Blaze]

I do have a WC T5 sitting on the shelf, but its for the iroc! I think the Camaro t-5s aren't good for the trucks because of the shifter location, most go with s 10 trannys.

The worst part is, my IROC with a much more modified engine will probably still get better mpg then the old truck. I have thought about trading the truck for a car, got a guy with a nice g body wanting to trade, but my daughter has already layed claim to the truck, she doesnt want the camaro or the 55 belair, she wants the old truck!

[BonzoHansen]

Years ago, I had the JTR tpi swap book, and they said tpi alone will not give you an improvement, its the fact that TPI allows your engine top run better under load at low rpms, which means you can then run an overdrive.

I would like to swap an overdrive, but again its a lot of cash.

A rear swap is much cheaper.

what is 1st gear in your current trans? dropping the rear gear may hurt local mpg, especially with 28" tall tires, and can be tough on a clutch. how many miles a year? you can do the math on return on investment if you have good estimates on mileage and costs.

make sure the carb is 100% and the tune up is good.

[Johnny Blaze]

First gear is 2.52 as far as I know.

about 12000 miles a year.

Carb is fresh, base tune, as stated I have not yet started fine tuning as Q jets are greek to me, but the baseline tune should be fairly close, the guy that did it is a pro.

[Johnny Blaze]

Running a 14"x3" open k&n filter. Thinking about trying to fab a cold air intake, wonder if it would make much difference?

[48prerunner]

I'd swap the t-5 in just pick up a t-5 from an s-10 and the shifter well the whole tail end of the tranny will swap over to your iroc t-5 and take care of the weird tranny mount and give you good shifter location. I ran a t-5 in my 37 with 4:11 gears for a bunch of years till it died then I swapped to a tko much nicer tranny but like you said 2 grand. We have a t-5 in a 72 chevelle behind a gm 350 crate motor runs nice. Maybe look into a simple front spoiler/ air dam to clean up the air flow under the truck would look cool and could be made on the cheap from some aluminum or maybe an old conveyor belt or something. Have you tried tail gate up tail gate down? or even a piece of plywood in like a rear wedge? maybe a bed cover. Check the toe if its off can hurt mileage.

[48prerunner]

gm part number for air dam 15569084 4x4 have lower ones think it could be made to fit older trucks junk yard or rock auto they are cheap.
shifter swap with pics http://www.inliners.org/Jack/T5tech.html

info on rpm drop http://www.chevytrucks.org/tech/s10t5.htm

here is the shifter swap http://www.flatheadv8.org/ernie/ernie-t5.htm

[MonzaRacer]

OK so here goes my suggestions:
first of all pop the carb off, remove base bplate and make sure the jet well plugs are sealed with JB weld,, not the quick stuff, regular, all of the seal plugs in bottom of main body.
Now you need to look and see where the adjustable part throttle adjustment is. Olderones are inside I believe (gotta go look at my spares) newer Chevy Q jet it is a seal plug facing forward and you remove that and adjust the needle in or out to raise or lower the main hanger.
Thiss allows you to lean it or richen it at cruise, shoot for 13.5-14.0 AFR or higher (listen for lean rattle, feel for surging) with wide band. Yes headers and wideband can help tuning.
On HEI, open gaps t o 0.045 to 0.050, I take open chamber flat top headed Chevys and run 14 to 16 initial, basically if your timing tab is at 2 oclock standing in front of truck I have even ran the timing at top of timing tab(this varies up to 18-20 degrees, as long as it doesnt buck starter hot its ok. I use advance kits for the light springs, use stock weights and mix and match the springs dependent on cruise characteristics and AFR. THEN I add in the vacuum advance hooked to manifold vacuum. Most chevy engines with open chambers and moderate not short cams can like as much as 45 to 50 deg total down road,,,also dependent on fuel quality. After adding vacuum advance you WILL have to readjust the idle speed and mixture, also you MAY need to address the closure of rear throttle blades too.
I cooked my 4000lb 71 Monte, 355sbc, Qjet, cast iron intake, headers and duals, 2.73 and it would run 18mpg running hard 75-80 on 98 Power tour, totally stock 89 350 roller short block from truck LT4 HOT cam with 1.5 rockers, 992 heads,,and ran around 45-48 total IIRC.
As for the TPI, swap in a 7 pin HEI thats locked, Look at a MicroSquirt (small version of MegaSquirt) OR use it as fuel only and no timing control. Those are pretty sheap and moding your tank for a in tank pump shouldnt be hard, I have done several and rad shops can solder you in a 1/4 NPT bung like a rad drain fits into, and simply screw in a 5/16 elbo with barb fitting for return.
That rich condition might get little better if you just open up the gap some. Also 3.08 might be little extreme depends on first gear of trans, what you really need is an OD.
Get your cruise at 60 down to about 1800-2000, the mileage will get better. 700R4 would be better, or one of the ODs from a newer 1/2 ton truck.
Just some rules, no rattle, keep it lean, give it timing, watch AFRs idle, cruise, and WOT.

[Randy67]

Cheap way to lower rpms: Taller gear like 3.08 or 2.73 and get a SM465 (granny gear) transmission. Will give you good takeoff and decent cruise rpms. An overdrive trans would be better, but SM465s are cheap and came in trucks. I had an 83 4x4 with SM465, 3.08 gears and 30" tall tires, was a pretty good all around truck. Mileage was 15-16 mpgs when driving nicely.

[MonzaRacer]

OK so here goes my suggestions:
first of all pop the carb off, remove base bplate and make sure the jet well plugs are sealed with JB weld,, not the quick stuff, regular, all of the seal plugs in bottom of main body.
Now you need to look and see where the adjustable part throttle adjustment is. Olderones are inside I believe (gotta go look at my spares) newer Chevy Q jet it is a seal plug facing forward and you remove that and adjust the needle in or out to raise or lower the main hanger.
Thiss allows you to lean it or richen it at cruise, shoot for 13.5-14.0 AFR or higher (listen for lean rattle, feel for surging) with wide band. Yes headers and wideband can help tuning.
On HEI, open gaps t o 0.045 to 0.050, I take open chamber flat top headed Chevys and run 14 to 16 initial, basically if your timing tab is at 2 oclock standing in front of truck I have even ran the timing at top of timing tab(this varies up to 18-20 degrees, as long as it doesnt buck starter hot its ok. I use advance kits for the light springs, use stock weights and mix and match the springs dependent on cruise characteristics and AFR. THEN I add in the vacuum advance hooked to manifold vacuum. Most chevy engines with open chambers and moderate not short cams can like as much as 45 to 50 deg total down road,,,also dependent on fuel quality. After adding vacuum advance you WILL have to readjust the idle speed and mixture, also you MAY need to address the closure of rear throttle blades too.
I cooked my 4000lb 71 Monte, 355sbc, Qjet, cast iron intake, headers and duals, 2.73 and it would run 18mpg running hard 75-80 on 98 Power tour, totally stock 89 350 roller short block from truck LT4 HOT cam with 1.5 rockers, 992 heads,,and ran around 45-48 total IIRC.
As for the TPI, swap in a 7 pin HEI thats locked, Look at a MicroSquirt (small version of MegaSquirt) OR use it as fuel only and no timing control. Those are pretty sheap and moding your tank for a in tank pump shouldnt be hard, I have done several and rad shops can solder you in a 1/4 NPT bung like a rad drain fits into, and simply screw in a 5/16 elbo with barb fitting for return.
That rich condition might get little better if you just open up the gap some. Also 3.08 might be little extreme depends on first gear of trans, what you really need is an OD.
Get your cruise at 60 down to about 1800-2000, the mileage will get better. 700R4 would be better, or one of the ODs from a newer 1/2 ton truck.
Just some rules, no rattle, keep it lean, give it timing, watch AFRs idle, cruise, and WOT.


shoot dude your pretty close too me if you need hand tuning it,,,,