3100 and 3400 intake manifolds

[Jbrogan]

I just wanted to make sure that a 3400 upper intake manifold will bolt up to the 3100 lower intake manifold. Or do i have to do more than just swap them? also i was wondering if the 3400 and 3100 use the same lower intake manifolds, considering in the 60degreev6 store it shows a ported lower intake for the 3100 and 3400.

[19Cutlass94]

The ports on the 3400 LIM are bigger than that of the 3100 LIM, ( stock ) although both will bolt up to 3100 heads. Depending on what yr 3400 plenum you use, it may just bolt up or you might need an adpater for the EGR

[ihatemygrandamg]

99 and previous manifolds should work for ya.

[bszopi]

99 and previous manifolds should work for ya.

Huh?!?

A 3400 plenum will NOT bolt to a 93-99 3100 manifold. A 00+ 3100 manifold is identical to all 3400 manifolds, therefore a 00+ plenum will bolt to a 3400 manifold.

Besides the port size, the easiest way to tell is by the number of mounting holes. The older 3100s use 12 bolts whereas the 3400s and newer 3100s use 6 bolts for the plenum.

[Jbrogan]

so if i get a 99 or ealier 3400 upper plenum i can swap it with my 3100 upper plenum without porting or modifying?

[FallenZ24]

so if i get a 99 or ealier 3400 upper plenum i can swap it with my 3100 upper plenum without porting or modifying?

No.

None of the 3400 manifolds will fit on your "small-port" LIM. You will have to swap the lower and upper manifolds to either a 00+ 3100 setup or any 3400 setup. Depending on the year, you may have to adapt your egr.

-Joseph

[Jbrogan]

alright

[Z3R0]

So correct me if im wrong but a 1996 3100 block can have a year 2000+ 3400 LIM bolted to it w/o modification except maybe the egr...then a 2000+ 3400UIM will just bolt right onto that LIM. Ported perfection?

[ihatemygrandamg]

Huh?!?

A 3400 plenum will NOT bolt to a 93-99 3100 manifold. A 00+ 3100 manifold is identical to all 3400 manifolds, therefore a 00+ plenum will bolt to a 3400 manifold.

Besides the port size, the easiest way to tell is by the number of mounting holes. The older 3100s use 12 bolts whereas the 3400s and newer 3100s use 6 bolts for the plenum.

Sorry forgot he wasnt using the 3400 heads also. i said 99 and previous just to mention the differences in the egr and heater plug.

[Z3R0]

SO, the 3100 block and head can or cant bolt to the 3400 LIM?

How bout the 3100 block and 3400 heads

[bszopi]

All the heads will bolt to any block (even the early 80s blocks). All Gen3 manifolds will bolt to all Gen 3 heads, but there are issues with port alignment between the years. 93-99 3100 plenum and manifold are compatible. All 3400 and 00+ 3100 plenum and manifold are compatible.

[Jbrogan]

so if i find a 3400 that is a 99 or Earlier, then i can put the LIM and UIM on my 96 3100, correct?

[bszopi]

No. Reread what I wrote...

93-99 3100 plenum and manifold are compatible.

All 3400 and 00+ 3100 plenum and manifold are compatible.

[Jbrogan]

so i cannot in anyway put a 3400 intake manifold on my 3100.

[IsaacHayes]

Jbrogan hehe sorry if this is confusing you. Let me try to help.

You have a "small port" 3100. To swap to a large port manifold, you must swap both the upper and lower to a large port. Here is a listing of what are large and small ports:

94-99 3100 (like what you have) Small Port.
2000+ 3100 Large Port.
All year 3400 Large Port.

To get them on your car, you will use the LIM gasket for the year of your heads not the intake manifold. Of course you'll need the UIM gasket from the large port years.

Issues:
1) You can use a late 3100/3400 large port LIM but the attachment for the coolant pipe is not threaded like your old one. Work around: get a NPT tap, and tap it.

2) The UIM from a 2000+ has a different way the EGR mounts. Since you are a 1996, you have the wiring connector to use the new 2000+ EGR. Work around: You could swap to the 2000+ EGR, and you will need the tube that goes to the EGR to the exhaust manifold.

OR you can do this: Find LIM and UIM that works with your "connections" already. These will be direct bolt on pretty much.
A 3400 LIM from a mini-van will have the coolant pipe fitting threaded already. 96-98 I believe were the years. I got a 97 from a Venture van to put on my car for example. Then you need the UIM from the same era, and I think even a 99 3400 UIM still has your style EGR. Then you can just bolt your existing EGR on without change to the newer one.

Adapting the newer manifolds is more work but you might find some lower mileage ones. The other way it all bolts up but you don't know the condition of them (mainly the lower) and some pitting might be around the cooling ports. So you can use pretty much any year large port and get them to work, or go for certain ones to save you some time and trouble.

Also A good idea since you will be putting on a new LIM gasket, is to get the metal Fel-pro ones for your car. That way you won't ever have to worry about a stock style plastic LIM gasket leaking coolant into your oil. You will need to buy a seperate large port UIM paper gasket too as mentioned above. They are like $6 for that.

(This info below you don't really need to know, but if curious..) Since yours is a 96 you have roller fulcrum rockers which clear large port manifolds. A 94-95 doesn't, and requires grinding on the lower manifold to clear. This is what I ran into. Just something to know, but you are in the clear with your car.