3100 High Compression/Fuel Economy Build

[Superdave]

then the only logical solution is ITB's

[SappySE107]

Its decided, phil must install ITBs!

[3400-95-Modified]

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.

I know its not a difinitive answer But when I was at the dragway I was able to get 14.0's with the 3500 stuff, but when I put my 3100 large port on I dropped 2 tenths, but then again I also got some 14.2's with the 3500 upper, it was really sensitive to wheel spin having street tires and all... so I guess unless I were to dyno it and see a power gain with the 3500 the whole which is better is still up in the air here...

Ironically enough tho, on my old 3400 that was getting spray, Cylinder #5 is the one that blew the headgasket... I wonder if thats because it got a majority of the nitrous spray. But #2 also looked like it was leaking, and both of those cylinders are ones where the waterjacket is like RIGHT next to the fire ring and there isn't much gasket material separating them so if the fire ring loosens up from the cylinder slightly warping it will seep coolant.

[IsaacHayes]

Instead of boring out a 3100 to fit 3500 heads, how about destroking a 3400 with a 2.8 crank? Then you'd have quick reving small motor which would get good mileage, and also the shorter stroke would help resist detonation with the higher compression. If I was to build a HO economy V6 that's what I'd do with a 3500 top end, and a decent cam. A cam can give you MPG too. Power logs or a factory style manifold like the 3500/3800/3900 would help a lot. I would go with the 3500 upper still though. It does seem to take some of the peakyness out of the power band, making it more broad. You don't get that "VTACK!" kick at 3,000 rpms so hard, but you are overall faster, and have a more streetable powerband I feel. Having more plenum air space helps too.

But either way, a destroked 3400/3500 hybrid, or what you are building now it sounds cool. A cam will help you run that high compression and can help with mpg too. I don't know what your RPMs are at cruise speed, but I'm sure they are way higher than mine so a mild -med cam should be just fine with your car.

[onefastV6]

Instead of boring out a 3100 to fit 3500 heads, how about destroking a 3400 with a 2.8 crank? Then you'd have quick reving small motor which would get good mileage, and also the shorter stroke would help resist detonation with the higher compression. If I was to build a HO economy V6 that's what I'd do with a 3500 top end, and a decent cam. A cam can give you MPG too. Power logs or a factory style manifold like the 3500/3800/3900 would help a lot. I would go with the 3500 upper still though. It does seem to take some of the peakyness out of the power band, making it more broad. You don't get that "VTACK!" kick at 3,000 rpms so hard, but you are overall faster, and have a more streetable powerband I feel. Having more plenum air space helps too.

But either way, a destroked 3400/3500 hybrid, or what you are building now it sounds cool. A cam will help you run that high compression and can help with mpg too. I don't know what your RPMs are at cruise speed, but I'm sure they are way higher than mine so a mild -med cam should be just fine with your car.

After test fitting a 3500 head on a stock 3100 block, it appears that if I have it bored .060" the combustion chamber on the 3500 heads is still going to be too big. Even on a 3400 it would be wise to have the block bored for the 3500 heads even though I did have 3500 heads on a standard bore 3400 block in the past.

The reason I wanted to use the 3500 heads was because of the design characteristics (better flow and velocity), which should have helped with fuel economy. The 3100 block also needs to be bored due to a little imperfection in one of the cylinders. At this point I will probably have the 3100/3400 heads ported, use a 3400 equinox LIM, and a 3500 plenum.

I would love to use a 2.8L crank, however that would require custom pistons in a 3100 block (someone correct me if I am wrong).

[SappySE107]

the 3500 heads overlap a 3400 bore about as much as your 3100 heads did, so with the .060 head gasket I don't see stock 3400 bore being an issue for 3500 heads. I don't see the 3500 heads fitting a 3100 though without the .060 overbore and notching the top of the deck above the rings for the larger combustion chamber size.

So back to a 3500 plenum now?

[onefastV6]

the 3500 heads overlap a 3400 bore about as much as your 3100 heads did, so with the .060 head gasket I don't see stock 3400 bore being an issue for 3500 heads. I don't see the 3500 heads fitting a 3100 though without the .060 overbore and notching the top of the deck above the rings for the larger combustion chamber size.

So back to a 3500 plenum now?

Wouldn't hurt to try the 3500 plenum.... they are easy to swap between.

[onefastV6]

Pics of the 3500 heads on the stock 3100 bore.





And my rendition of modding cars:

[SappySE107]

20s? Thats budget modding!

[IsaacHayes]

Yeah those wont work on that bore.

I really think if you want something cool do the destroked 3400 with 3500 top end, cam and high compression. It would be a beast and I bet get great MPG. There has been one or two people talk about it and even start to gather parts but never do it.

[Superdave]

I have a spare 3400 block, it's yours if you come get it out of my garage. iirc it's got 30K on it..

[onefastV6]

Yeah those wont work on that bore.

I really think if you want something cool do the destroked 3400 with 3500 top end, cam and high compression. It would be a beast and I bet get great MPG. There has been one or two people talk about it and even start to gather parts but never do it.

I agree, I just don't want to get custom pistons made.

[torq455]

Dave, is that 3400 block bare?

[montess408]

i have a bare 3400 block along with the rest of the stuff but it's all disasembled

[Superdave]

Dave, is that 3400 block bare?

it's got cam bearings, that's it

it deffenetly needs to be hot tanked, but it's in decent shape otherwise. There was a hint of surface rust in the lifter bores but they appear to be fine after i cleaned them out with a crossbuff and some WD-40.