Impressed with increase in gas mileage with square body!

[turbo350]

Originally Posted by chevymotocross

Thanks everyone!

2badgn, forgot to mention that. After deployment, a cover will be the first thing I get for the truck! Also, beautiful looking truck! I remember seeing a thread with some more pics of yours, I love the factory look of your rig!

Another thing I forgot to mention. The EGR system. I currently have it blocked off. I replaced the OEM gummed up EGR a few years back. I wrote the factory EGR numbers on the new EGR, but I remember there was no P or N at the end of the numbers to represent positive or negative backpressure type. After removing the cats and dumping the exhaust, I was getting code 32 on the freeway. Also, my truck was stalling occasionally after highway use at the exit ramps. I don't think the EGR was closing properly causing a vacuum leak. Come to find out, the replacement egr says POS on it. I believe I need a NEG backpressure EGR especially since I have no cats and the exhaust is dumped.

Since I plugged the current EGR, there is no more stalling but a properly working system will probably yield better mileage.

Sweet rig!

I had an '87 350 tbi in a 3/4 ton conversion van. Best that van ever saw was 12, maybe 13 mpg even when it was new. Had 700r4 and 3.08 rear and of course the heft and bulk of the van. Using that for a very loose comparison I'd say you are doing a heck of a job and squeezing out the max amount of economy out of what you have.

[pig rig]

Ive got an 88 with the 454 tbi in it Ive done a lot to get more power out of it and in the process of that I went from around 10 mpg to 12 mpg then we took atrip to socal in it and on the way home the clutch fan went out so I pulled it off and for the last 600+ miles I got just short of 16mpg out of it.
so I put electric fans and I did some reading on the advantages to running an MSD 6al spark box so I added a 6al and an MSD distributor and new injectors
but Ive developed engine problems and I still havent been able to do a few hundred mile road trip to see if its improved.

[franky69c10]

Originally Posted by bustedknuckles

Blocking the egr system is definitely better for your mileage.

i have a stock 87 350 tbi it does lag when i press the gas how do i go about blocking the EGR system and when i do will i throw any codes, is good to block the EGR system
Posted via Mobile Device

[bustedknuckles]

I used the egr gasket to cut a plate to block it off, then used a vacuum cap to cap off the egr solenoid. Left everything else hooked up and it never threw a code, and ran great.

[franky69c10]

Originally Posted by bustedknuckles

I used the egr gasket to cut a plate to block it off, then used a vacuum cap to cap off the egr solenoid. Left everything else hooked up and it never threw a code, and ran great.

Sweet gonna try it out, oh what about the computer won't it know that it's been blocked off or sumthing
Posted via Mobile Device

[bustedknuckles]

As long as the solenoid is plugged in and the vacuum capped it will still think its pulling on the egr valve.

[Hotrodrobert]

All you have to do to disable the EGR is pull and plug the vacuum hose.
If you want max economy, a Q Jet set up and a properly curved vacuum advance non ECU distributor will beat the throttle body every time. Deal with the throtle body is the electronic controls to limit some emissions
Tuning can be an issue, but it can be done. The ECU tries to maintain 14.7AFR no matter what until a certain throtle position is reached-near WOT. Best economy is always a little leaner than that, usually 15-16AFR.
Don't forget-warmer air is better economy, cooler air better power.

[bustedknuckles]

Originally Posted by Hotrodrobert

All you have to do to disable the EGR is pull and plug the vacuum hose.

Not always true.

I had to remove and block my egr because it was stuck open.

[chevymotocross]

I disabled my EGR by capping both the EGR itself and the port on the solenoid. I still trip the SES light on highway trips. From what I've heard, Brian Harris can burn a chip to support this and the light won't trip a code 32.

[franky69c10]

Originally Posted by bustedknuckles

Not always true.

I had to remove and block my egr because it was stuck open.

Would u mind taking couple of pics of how u blocked it off
Posted via Mobile Device

[bustedknuckles]

Man I would, but those trucks are long gone. It's really simple. Just cap the vacuum port on the solenoid (the tube that hooks to the egr valve itself). Then remove the egr valve and use the gasket to make a template and cut a piece of steel or aluminum and put it in place of the egr valve.

I found this also.

http://www.custombilletworks.com/products.php

from this:

http://67-72chevytrucks.com/vboard/s....php?p=4819805

[ProStreet83C10]

ive seen 21.5 hand calculated out of my 83

[chevymotocross]

Squeezed out 19 on today's fill-up! This time, I am trying mid-grade. If there are no knock issues, I will try low-grade next fill up. Not sure if I will get as good of mileage but atleast I won't be paying as much per gallon.

I don't see why there would be an issue with the low grade fuel and the performance chip. With the performance chip, base timing had to be set at 0. When I was running the stock chip, I was running the base timing at +4 with no knocking on low-grade.

[Cue-Ball]

I'm not very familiar with the workings of the TBI engines (I prefer carbs), but 0* base timing? Seriously? I don't think I've ever run a smallblock engine - Chevy, Ford or otherwise - with base timing less than 10* BTDC. Usually more in the neighborhood of 12-14* BTDC. Is there a particular reason for running the base timing so retarded? I would think that would be a power and mileage killer. Are you setting the base timing at 0*, then letting the computer advance it so that "true" base timing is much more advanced?

[Hotrodrobert]

Originally Posted by Cue-Ball

I'm not very familiar with the workings of the TBI engines (I prefer carbs), but 0* base timing? Seriously? I don't think I've ever run a smallblock engine - Chevy, Ford or otherwise - with base timing less than 10* BTDC. Usually more in the neighborhood of 12-14* BTDC. Is there a particular reason for running the base timing so retarded? I would think that would be a power and mileage killer. Are you setting the base timing at 0*, then letting the computer advance it so that "true" base timing is much more advanced?

The computer can adjust the timing throughout the rpm range and the "0" timing is seldom correct but because of the chip tuning may be necessary in his case.
A carbed SBC usually will run much better between 10 and 18 base, depending on compression, combustion chamber design, cam, timing curve,.................
You have to tune your engine for best performance as every one is a little different.

[406 Q-ship]

You know the performance chip may actually be taking MPG's away from you. It will be set for a more agressive timing curve (good for mileage) but also it will try to keep the A/F richer than 14.7. Now the stock chips in GM vehicles typically put the A/F to the richer side too, it was to keep the warrenty issues of burned pistons to a minimum. I would call one of the chip manufactures and tell them what your doing to get a special MPG chip. Vacuum gauge, a Tach (lowest RPM is usually the best for MPG), and even consider going to slightly narrower tires (rolling resistance) are good areas to look at. You have seen a good pick up in driving style to improve mileage, to add to the driving style, press down on that accelerator like there is a raw egg between the petal and your foot. Small tube headers (1 1/2" primary to 2 1/2" collectors) in tri-y design would be a good addition. Get the engine to build the most torque efficently in the lowest RPM, so you can press the throttle a little less hard to get to speed. Good luck on getting better mileage and thanks for the service to the country.

[Edahall]

To get 20 mpg or higher you're probably going to have to focus on aerodynamic mods since most likely, your engine has already been just about maximized for fuel economy.

Regarding aerodynamic mods, here are some ideas.

I would first start off with extending the front bumper down to almost the ground and installing a cover that angles downward from the cab down to the tail gate. You can use thick rubber to bring that bumper down. There are a bunch of other things you can do such as using pizza pans as hub caps or rear fender skirts but then the truck starts to look silly. Also, make sure you are using low resistant tall and skinny tires. If your truck is 1/2 ton, go with a 30x9.50 and if it's 3/4 ton, go with a 235/85/16.

Here are several truck that were ecomodded to the extreme to give you an idea what I was explaining. Pay particular attention to the slopping canopy and the front bumper. These guys also smooth out the bottom of their trucks with a pan so they don't need to extend the bumper so far down.

--And oh by the way, that 1994 Toyota T-100 went from 23.3 mpg to 32 mpg at 75 mph. And that truck was a lot more aerodynamic than our trucks so there's even more gain to be had on our square bodied trucks.

[TheManInBlack]

I suggest 225 tires, sweet truck dude.

[legendman]

Chevymotocross, first nice looking truck, second what are you running for tires and what pressure?

[TJBrown]

Im installing my TPI with Megasquirt 2 this next weekend. Im hoping to have some numbers on how mine has improved. On the high way last weekend (all highway miles) i got 15.2.

355 (.30 over 350) stock everything
882 smogger heads.
Exhaust manifolds
duals with no cross over and Thrust Turbos dumped before the rear end.
2.73 gears with 700R4
255-50-15's @ 35lbs a pressure.

will take a few weeks to get data as i am going to take fuel first and spark second with a week in between.

[chevymotocross]

Originally Posted by legendman

Chevymotocross, first nice looking truck, second what are you running for tires and what pressure?

Thank you. 255/60/15 Front and 275/60/15 rear set to 35 PSI. I check the pressure weekly especially in the colder weather here.

[Smoke_Dog]

Chevy motorcross, that's a nice truck!!!

[Fan2zee]

Very Clean Truck... Do you have pics of the installed Throttle Body Spacer?
Posted via Mobile Device

[chevymotocross]

I filled up my 1992 s10 blazer 4.3 TBI today after driving it on the same routes as my square body and driving it in the same manner. I got the same exact mileage.... 18mpg

I realized that the 6 cylinder is IMO (besides the sweet straight 6 ) useless. The 305 feels like night and day in terms of torque and power and gets the same mileage. I couldn't imagine towing with the 4.3. Actually, I did tow with the blazer once, a small open utility trailer with some dirt bikes and it was AWFUL. It's in good running tune but I think it is geared for highway use. I would never even consider a 6 cylinder in a full size truck. If I were to buy another small-size pickup or suv, it would have to be a 4 cylinder. I bet the 4 cylinder (properly geared) can do the same work as a 4.3 with lots less gas consumption.

I think the 6 cylinder, the more modern 6 cylinder (overhead cams etc) work well in today's cars. The old style pushrod V6 although pretty reliable, doesn't deliver good power to match it's fuel economy IMO.

[sethv]

I could get ~18 mpg out of the old Chevy when it had the original 350 engine, and a finely tuned Quadrajet. Timing was advanced a few degrees, and it ran 93 octane. Also had dual thrush turbo mufflers that dumped before the rear axle. Had an Edelbrock open element air cleaner, and 245/75R16 tires.

Since I blew that up and put another 350 in it, with an Edelbrock 1407 carb, it gets about 13 mpg highway.

It's not hard to make them get good mileage, just gotta keep them maintained, and not getting in the fun pedal too much helps the most.