Will TBI mods help or hinder my fuel mileage?

[Jamesd]

I just recently purchased a 95 350 GMC Z71 with 3.73's and it is completely stock. Just tuned it up but besides that if I do the ultimate TBI mods will it help my fuel mileage? If their is a way to increase it, what certain mods should I do? I know the stock exhaust system is restrictive but my goal is to pick up some extra power and fuel mileage.

I do not want a race truck or anything like that I just want something that has a little more passing power going up hills. Right now the truck feels like my 93 with a 305, it runs great but not 350 TBI great. The catalytic convertor has been changed before I bought the truck. It has 190k on it but a new Jasper engine has been replaced two years ago with roughly 20k on it. Transmission shifts beautifully with no issues. Checked the timing and it is advanced 3 degrees so I left it alone. Everything runs great and works and I even changed the original 3 wire oxygen sensor as well. Like I said it runs beautifully but does not have the power of a 350 TBI. I have drove many of these TBI trucks 305 and 350 so I know what to expect from them. I know the TBI trucks aren't the most powerful but something is holding this truck back maybe 15-20 horses. Thanks for your help.

James

[DylanC]

How many mpg are you getting ? TBI mods really only help with a bit of HP not really gas mileage your fuel mileage is what it is simply because you have a 350 lol

in my 93 gmc swb / 305 v8 i hit near 18mpg highway

i mean depending on the mileage engines do loose there natural humph after so many miles

[cancritter]

every little bit helps and adds up..is worthwhile

[Jamesd]

I'm not looking for miracle gas mileage maybe 1-2 at the most. I do not want to put all the money into it and find out I achieved 40 horses and 3-4 miles per gallon less. I have a Mustang for that kind of stuff. If the exhaust is my best bang for the buck and it helps fuel economy and power then that is all I will do.

James

[Jamesd]

Just for a comparison my 2wd 01 6.0 HD averaged around 12-13mpg, roughly what I'm getting now so I know there is a small room for improvement. I did not buy the truck for fuel mileage per say but any amount helps at the pump with gas being so high.

James

[cancritter]

ld look into doing a taurus fan swap..can be done for cheap and will help milage

[OttoVonMerz]

fwiw...

I run a taurus fan on my jeep. worked great.

However on my truck I swapped in a Mark VIII fan and run it with a painless F5 controller for a single fan. gained roughly 2mpg the mark 8 fans can be found on ebay anywhere from 50-100 bucks. the cheapest i found the f5 controller was jegs for around 250.

i truly think the electric fan was the best mileage mod. plus a/c is a helluva lot colder.

[cancritter]

ya ment any electric fan realy...got 2 taurus for 30$ with all fuses ect...things up here are limited..cant remeber last time l seen a mark 5 at the wreckers...ticks me off sometimes when l read a post and someone got a good score from thier local wrecker down south...anyway like the fact that the fan is rarely on durring winter driveing and quick warmups durrin winter,,,imo best all around mod

[GreaseDog]

How many mpg are you getting ? TBI mods really only help with a bit of HP not really gas mileage your fuel mileage is what it is simply because you have a 350 lol and this is why you don't listen to every yahoo you come across on the internet. my 92 C1500 (with its 5.7, and 170K on the clock), vs my uncle's identically equipped 94 C1500 (with 4.3, 70K)... the 92 always came out on top, by about 3-4mpg.


in my 93 gmc swb / 305 v8 i hit near 18mpg highwayi was getting a pretty consistent 20.

[davo727]

One thing I noticed on my 95 5.7 truck is the y- pipe is a lot smaller diameter than on my 93 5.7. And with both stock the 93 ran circles around the 95.

[helo]

It has 190k on it but a new Jasper engine has been replaced two years ago with roughly 20k on it

So you probably have a 250,xxx engine that got a couple of new lifters...:sorry::naughty:

Make sure you're tuned up, timing chain isn't worn out, dizzy gear is good, etc..

If your fan clutch is still good, an efan won't really do anything for you except strain your alternator.

Don't waste $$$ on changing the exhaust. MAYBE a new cat (cause we have inspections 'round here), but headers are a total waste in NY unless you go with stainless everything (salty roads for months). Doing full stainless exhaust would probably be more than you paid for your truck, so..

[Jamesd]

So you probably have a 250,xxx engine that got a couple of new lifters...:sorry::naughty:

Make sure you're tuned up, timing chain isn't worn out, dizzy gear is good, etc..

If your fan clutch is still good, an efan won't really do anything for you except strain your alternator.

Don't waste $$$ on changing the exhaust. MAYBE a new cat (cause we have inspections 'round here), but headers are a total waste in NY unless you go with stainless everything (salty roads for months). Doing full stainless exhaust would probably be more than you paid for your truck, so..

No I called Jasper and gave them the serial number on the engine. They told me the date it was replaced so a high estimated guess is that if the person drove 10k a year for 2 years it has roughly 20k miles on it. Everything works fine and is good. The cat has been changed already. The truck is from Texas and has absolutely no rust on it. The only rust on it is the surface rust on the exhaust. The truck will most likely be put away for winter since I hate to drive it through the salt. I'm not bothering on a electric fan swap, not worth it. I highly doubt I would gain 3 mpg. The reality is more like .5 mpg.

James

[Jamesd]

One thing I noticed on my 95 5.7 truck is the y- pipe is a lot smaller diameter than on my 93 5.7. And with both stock the 93 ran circles around the 95.

Do you have any pictures by any chance? I was told they are the same.

James

[RichLockyer]

No I called Jasper and gave them the serial number on the engine. They told me the date it was replaced so a high estimated guess is that if the person drove 10k a year for 2 years it has roughly 20k miles on it. Everything works fine and is good.
What he's saying is that when Jasper "rebuilt" the engine, it was a 250k core and they just dropped in enough lifters to make it run "well enough"
They didn't completely tear it down and blueprint it.

Contact them again with the serial number and ask specifically what work was done to that core. Dollars to doughnuts, it compression checked within spec and the oil pressure was in spec so the heads and bearing caps never came off.

[whitelightnin92]

jasper is hit or miss. i would say it was completely rebuilt. but done correctly is another story.

[SierraDan]

Just go ahead and do the mods, more power means less engine stuggle which means better mileage. So it's the same for an e-fan swap and headers/exhaust, do it all. Go for longtubes, and you can buy regular painted headers as long as appearence doesn't matter. It'll surface rust but won't rust all the way through. After a few months my Flowtech's on my old 86 looked like they rusted out but lasted for years and never leaked.

[whitelightnin92]

yeah if you do headers get longtubes. shorties arent worth the money.

[Jamesd]

What he's saying is that when Jasper "rebuilt" the engine, it was a 250k core and they just dropped in enough lifters to make it run "well enough"
They didn't completely tear it down and blueprint it.

Contact them again with the serial number and ask specifically what work was done to that core. Dollars to doughnuts, it compression checked within spec and the oil pressure was in spec so the heads and bearing caps never came off.

Oh trust me, I believe you when it comes to Jasper engines but this engine has been in the truck for 2 years and it was a daily driver. It does not burn oil, make any abnormal engine noises, has very good oil pressure, timing chain is tight verified by a timing light and runs very well just low on power. That could be because of the factory tune being it is a 95 or maybe the RPO codes say it has 3.73 gears and it may have 3.08 gears, who knows but as of right now it is a good solid engine but that can change tomorrow with a Jasper engine.

James

[Jamesd]

Just go ahead and do the mods, more power means less engine stuggle which means better mileage. So it's the same for an e-fan swap and headers/exhaust, do it all. Go for longtubes, and you can buy regular painted headers as long as appearence doesn't matter. It'll surface rust but won't rust all the way through. After a few months my Flowtech's on my old 86 looked like they rusted out but lasted for years and never leaked.

That is not necessarily true. You may be burning more fuel depending on the modifications that you do.

James

[RichLockyer]

Oh trust me, I believe you when it comes to Jasper engines but this engine has been in the truck for 2 years and it was a daily driver. It does not burn oil, make any abnormal engine noises, has very good oil pressure, timing chain is tight verified by a timing light and runs very well just low on power. That could be because of the factory tune being it is a 95
You just described my 200k '95 engine.

My boss has a squarebody and he always comments on how good mine sounds... his sounds like it's going to blow up at any minute.

I'll go through about a half quart in 6000 miles.

[whitelightnin92]

That is not necessarily true. You may be burning more fuel depending on the modifications that you do.

James

with tbi trucks simply boosting the fuel pressure from the stock 11-13 up to 13.5-14.0 actually increases fuel mileage because theyre so lean in stock form. especially when running E10 in them. the tbi mods will always improve mileage unless you seriously screw up

[whitelightnin92]

95s were about the worst for the factory tuning. you can easily pick up some hp/tq and mileage with a tune. i would diy, but if not tbi chips is ok

[Jamesd]

I think my first modification will be exhaust. Long drops into a single 3" all the way back with a Super Turbo muffler. I do not want a loud truck.

James

[whitelightnin92]

dyno max mufflers arent loud and i hear alot of good things about them flowing very well