Fuel Economy + Power • 3100 GP Project

[Futures Passed]

As fuel got to be a larger and larger percentage of my overall budget, I decided to invest some time into both driving style and engine improvements which would help increase my MPG. However, I still enjoy my ability to pass cars quickly (most of my driving is on one-lane roads) so power-reducing mods or trading in for a small car weren't appealing options, and I've started a project to improve the engine's efficiency without doing so in ways which would notably reduce power.

One power/driving style combination I've found is that since my vehicle shifts based on speed and throttle position, if I increase the power (without doing so through displacement increase/forced induction) I can reduce the amount of throttle required to get up to speed, keeping the RPM down/forcing an early shift. Perhaps it was other factors I didn't note/observe, but I have seen MPG gains with this technique.

The most recent upgrade I have been working on is a ported/polished upper intake manifold. I was going to save up for a WOT-TECH Ported Upper Intake Manifold, but the cracks in my current one kind of forced my hand, and I've been porting/polishing one myself over the past few days. I'll have pictures of the finished job later.

The most recent modification I've done isn't an engine modification, but here's a picture anyway:

That modification also had the bonus effect of reducing wind noise at highway speed. I'm pretty sure the noise was air hitting the tire tread, which is what I designed those to reduce in the first place, but just for drag-reducing purposes.

Ending this on a question: When porting/polishing, is it best to polish as much as possible (so it's completely smooth), or is some roughness good for flow? I vaguely recall reading something about this but I can't find it.

[pocket-rocket]

I found shifting my truck at 2000 rpm helped quite a bit. A slower turning engine takes in less air per minute which means less fuel is required.

As for porting, smooth on exhaust only (to prevent carbon sticking and reduce friction). On intakes you want a slight texture left behind. Reason being smooth surfaces can cause fuel to fall out of suspension. Also the airflow will behave differently by the walls. I don't remember the specifics of it in that aspect right if hand, but I know it hinders airflow to a point. Hope this helps.

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[robertisaar]

One power/driving style combination I've found is that since my vehicle shifts based on speed and throttle position, if I increase the power (without doing so through displacement increase/forced induction) I can reduce the amount of throttle required to get up to speed, keeping the RPM down/forcing an early shift. Perhaps it was other factors I didn't note/observe, but I have seen MPG gains with this technique.

yes, increasing an engine's VE in the RPM range that you drive in normally WILL benefit fuel economy.

could always go the 00-05 MC vs 00-03 GP route... MC got 3400 but 2.86 gears, GP got 3100 but 3.05 gears. MC was rated for 21/32, GP rated for 20/29. IIRC, they pull similar 1/4 and 0-60 times too.

[Futures Passed]

As for porting, smooth on exhaust only (to prevent carbon sticking and reduce friction). On intakes you want a slight texture left behind. Reason being smooth surfaces can cause fuel to fall out of suspension. Also the airflow will behave differently by the walls. I don't remember the specifics of it in that aspect right if hand, but I know it hinders airflow to a point. Hope this helps.

That sounds like what I read, thanks!

Due to the polish level being a fuel-based concern, would this mean that the entrance opening can be more polished than the six ports, since fuel is less likely to get to that point (near the throttle body)? I'll probably just have that to do, and then I'll be ready to put it on the engine once the gaskets arrive.


As for gearing, my friend has an Oldsmobile Regency with a 3800, which I believe has the same transmission as mine. He busted something in the transmission, and ended up getting an entirely new one. If the top gear is recoverable in that, would it be worth getting? (In other words, did the Regency transmission come with that 2.86 gear?)

Either way, although I have the tools required to do it, I doubt I'll be able to pull out the engine/transmission any time soon.

[TGP37]

Fuel efficient cars are just an expensive throttle stopper. Not sure, I think bumping up the ATF line pressure should help fuel economy. I tried a lean cruise trick and works well.

Set these tables...
Engine>Fuel>Power Enrich
...>Delay vs TPS: Set 5-20% TPS to 3-4 seconds (the rest should be normal settings)
...>Add vs TPS: Set 5-20% throttle tables as to hit 15.7 AFR during PE only. 25%+ set normally

Throttle will rarely ever remain within 5-20 for more then 4 seconds unless cruising on the highway. When you are cruising, the AFR will hit 15.7

The moment the throttle goes past 20-25%, normal AFR for PE will still remain.
It's a simple fuel saving mod but it works. I have a manual and 3 sec delay worked just right, automatics may want 4-5 second delay times.

[robertisaar]

upping line pressure should hurt economy... pressure = resistance to flow.

obviously you want enough line pressure to stop any slipping that could be going on, but otherwise, higher would be detrimental to fuel economy.

[Futures Passed]

Fuel Levels @ Throttle Positions & RPMs

Set these tables...
Engine>Fuel>Power Enrich
...>Delay vs TPS: Set 5-20% TPS to 3-4 seconds (the rest should be normal settings)
...>Add vs TPS: Set 5-20% throttle tables as to hit 15.7 AFR during PE only. 25%+ set normally

Throttle will rarely ever remain within 5-20 for more then 4 seconds unless cruising on the highway. When you are cruising, the AFR will hit 15.7

The moment the throttle goes past 20-25%, normal AFR for PE will still remain.
It's a simple fuel saving mod but it works. I have a manual and 3 sec delay worked just right, automatics may want 4-5 second delay times.

I need to get that $500 computer thing for this sort of tuning, right? It's on the to-get list.

Is there any way to modify fuel injector output based on RPM levels? It seems like running lean in the range just above idle and below 3K would also be beneficial to fuel economy, especially when casually driving through a neighborhood or other twisting 30-45 MPH roads. It may hinder high speed, low RPM driving mileage, though, since the throttle would have to open up more to keep the power high enough to overcome the drag.

The idea came to me looking at a modern car's horsepower/RPM chart, where there were two peaks on the chart, and the valley was what looked like the normal driving RPM range.

[pocket-rocket]

Adjusting the fuel pressure to do this would be led than ideal and probably get you no where. I say this Barclays the pcm is always going to try to keep the afr art what it is programmed for with given rpm vs airflow/load. The best to get this done correctly and reliably is to get HPT and program the afr for the given rpm/load range to a leaner setting, otherwise you will be fighting your computer, and it will always tend to win since it controls your injectors.

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[TGP37]

Adjusting the fuel pressure to do this would be led than ideal and probably get you no where. I say this Barclays the pcm is always going to try to keep the afr art what it is programmed for with given rpm vs airflow/load. The best to get this done correctly and reliably is to get HPT and program the afr for the given rpm/load range to a leaner setting, otherwise you will be fighting your computer, and it will always tend to win since it controls your injectors.

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Fuel pressure? Or ATF line pressure.....lol.

I agree 150% about the tuner. Looking back I can't imagine how I could have lived w/o it.

[pocket-rocket]

Fuel pressure? Or ATF line pressure.....lol.

I agree 150% about the tuner. Looking back I can't imagine how I could have lived w/o it.

Fuel pressure.

Also in my last post led=less...

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[TGP37]

Fuel pressure.

Also in my last post led=less...

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I was correcting you, I mentioned ATF line pressure increase, for less slip. But Rob corrected me stating it may hurt performance/economy. Nothing about fuel line pressure :P lol

[pocket-rocket]

I was correcting you, I mentioned ATF line pressure increase, for less slip. But Rob corrected me stating it may hurt performance/economy. Nothing about fuel line pressure :P lol

But above the post you first quoted me on he asked about adjusting the fuel pressure vs rpm to adjust the fuel pressure

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[TGP37]

But above the post you first quoted me on he asked about adjusting the fuel pressure vs rpm to adjust the fuel pressure

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haha...I see where I goofed. Carry on

[Futures Passed]

It's been a while since I've posted here! I'm getting back to work on this project.

1: Is there any easy way to add an oil cooler to a 3100? On top of its regular benefits, my recent experiences with the engine getting close to overheating have gotten me interested in the idea of having a little back-up.

2: Has anyone had any experience with running synthetic oil in a 3100? I'm coming up on the time where I need to change it, and I work at a place that sells the stuff. I think they have Royal Purple there, too. I'll run some more seafoam through it before I make the switch, if I do.

3: I'm replacing a few small parts in the next few days, including the thermostat, PCV valve, and the grommet for the PCV valve. If there are any other little things that I should check (due to being unreliable on these engines), let me know.

[robertisaar]

i don't see why an early LQ1 oil cooler wouldn't work(from what i can tell, they mount on top of the oil filter boss)..... however, you would either need a radiator with the ports on it already or get an external heat exchanger.