3100 High Compression/Fuel Economy Build

[onefastV6]

I was at the yard and picked up a large port 3100 core motor for $150, and will be working on the build this winter.

The plans are as follows:
Bored 0.60
Camaro 3.1L pistions
3500 heads
3500 LIM
Large Port 3100 UIM
SBC Cam Bearings
Stock Cam
TCE Single Roller (If finished by the time it is ready)
Scorpion Rockers (If finished by the time it is ready)
2.5" down pipe

I am still unsure if I will be using the stock exhaust manifolds, however I might try to fab something that flows a little better than stock while I have it on the stand. Something like the ZZP power log that is available for the dreaded 3800's.

I am shooting for 40 MPG on the highway with tuning, as I was able to get 33.6 MPG on a 3400/3500 hybrid.

Has anyone else built or considered building a more fuel efficient motor?

[95Grand-Am]

40 mpg is alot to shoot for, with a 0.060 overbore your not much smaller than a 3400. But the compression is a lot more steetable with that combo. I have a few questions why not use the 3500 UIM. What gear ratio are you going to run in the trans? Is this for your Grand-Am? I like the Idea, It should make decent power too.

[onefastV6]

I agree 40 MPG is a lot to shoot for, but 35 MPG should be easily attainable if I was able to get 33.6 MPG on a 3400/3500 hybrid. Worst case I get about the same mileage and learn something new with a fresh engine.

As for why I am using the large port 3100 plenum (same as the 3400 plenum), from what I have been told it flows more evenly across all the ports as compared to 3500 plenum.

The tranny will probably be the stock 4t45e gearing 3.29 gear ratio (If I recall correctly)

Depending on this build the 3400 that comes out will probably be built similarly, with a larger cam and some other goodies for my 2000 Grand Am. That will run the 4T65E HD tranny that was in the Grand AM GXP concept car. I have the the .bin, wiring harness, axles, tranny and two of the mounts.

[DarkWhoppy]

Just out of curiosity, is this a 95 - 99 3100 SFI?

[Superdave]

the 3500 plenum flows more evenly to all 6 ports due to the plenum "neck" actually running inside and stopping by the middle ports. the middle 2 cyls still get more flow but the other 4 get even flow VS the 3100 where cyl 1 and 2 get the short end of the stick.

should be a decent build, the 3500's "header" manifolds will work great for power and economy as long as you keep the downpipes at about 1 7/8"-2".

I managed to get over 30 MPG highway with my built 3500, city MPG is terrible though.. around the 12's.

[onefastV6]

Just out of curiosity, is this a 95 - 99 3100 SFI?

The LIM is stamped 00 so I believe it is out of an 00 W-body.
I will be running it off the stock 01 grand am PCM, and tuning it with DHP tuning software

[onefastV6]

the 3500 plenum flows more evenly to all 6 ports due to the plenum "neck" actually running inside and stopping by the middle ports. the middle 2 cyls still get more flow but the other 4 get even flow VS the 3100 where cyl 1 and 2 get the short end of the stick.

should be a decent build, the 3500's "header" manifolds will work great for power and economy as long as you keep the downpipes at about 1 7/8"-2".

I managed to get over 30 MPG highway with my built 3500, city MPG is terrible though.. around the 12's.

Ben was the one that told me that the large port 3100/3400 manifolds flow more evenly across all the cylinders..... I am sure he could get into more detail on that.

I will look into using the 3500 header style manifolds, if there is enough room for them in an N-body.

[torq455]

Dave, cruising at 50 MPH on the highway doesn't count! I've gotten 30 highway cruising around 60-65 before my wideass tires. I got 27 with the wider tires, tranny swap, and cruising 70-75. I haven't been able to do normal daily driving exclusively to check city mph, but, with tuning for 50-80 kPa at higher rpm and a lot of wot 1-2 (top of 2nd), some 3-4 shifts, I've been getting 23 mpg!!

[johnnymossville]

I am loving my 11.5:1 CR, but I have to admit it prefers Shell 93 octane gas. lol

[Superdave]

Ben was the one that told me that the large port 3100/3400 manifolds flow more evenly across all the cylinders..... I am sure he could get into more detail on that.

I will look into using the 3500 header style manifolds, if there is enough room for them in an N-body.

i'm sorry but i have to dissagree with Ben there. If the old design was better than GM would have used it on the gen 4 engines.

[torq455]

according to the CR calculator, the CR will be ~13:1???? did i do that right?

[torq455]

i'm sorry but i have to dissagree with Ben there. If the old design was better than GM would have used it on the gen 4 engines.

agreed. the 3500 upper is more efficient due to it's equal air distribution.

[95Grand-Am]

@11:1 CR When you calculate it use 32.4 cc for the head. 3.75 for the head gasket width because the 3.1l fire ring is too small and goes into the comustion camber. I think I would use the gaskets ment for the iron heads. I would also deck the block to get a 0 deck height to get the squish to where it would help you the most. 12.5-13 is what you end up with when building a 3400 with 3.4L pistons.

[torq455]

i used the 3100 since that's what he had + .060 over, 3.69 bore, and mid 90s camaro pistons.

[SappySE107]

You have more shrouding around 4 of 6 runners, and you have a 180 degree turn for 2 of 6. The Equinox upper drops down from the top but still has flow issues due to the shrouding in the design. I don't see how either design could flow more evenly than the 3400. It makes more sense to me that they wanted less air to 5/6 since they are the hottest cylinder and already get their own oil squirters if the others don't.

You can create a larger powerband from a non vvt intake by creating a different tuned setup for different cylinders. For peak power, you want them all the same. For a broad powerband, you would have some cylinders setup for lower RPM, some for the middle, and some for top end. Or 3 low and 3 high. Considering how the most common reaction to the 3500 upper intake is that the powerband is better, I find this to also follows with the flowbench testing.

To tune for optimal MPG, I want each cylinder as even as possible to start with. That is my thinking on it right now.