Will a 96 DOHC PCM/Wiring run a 95 3100 4T60E?

[lkurek]

Guys....OK, my quick look through the wiring diagrams/shop manuals says it should be a plug and play. HOWEVER...I have heard that the 3400 DOHC trans is different than the 3100 trans. True? I assume the ratios may be different...but the PCM should still control it ok, no? I assume the inputs to the PCM from the trans are the position switch, speed sensor, and RPM..... I can see a disconnect with the RPM vs MPH....but is it THAT bad? Is that a showstopper?

HELP! I need to drop a new motor in the Old Lumina, and I'm thinking the DOHC is the motor I want to use.... I have that available, AND a 3400 OHV, but the DOHC is a sweeter choice, I would guess....

Any opinions?

[3100 MPFI]

my opinion is go with the 3400. That will save money on PARTS, and SUSPENSION. The 3.4 DOHC is heavier so you will need to beef up the front suspension. Each cam carrier with cams is almost 50 lbs.

The connector is the only difference. You can use a 3100 tranny with a DOHC ecm, and a DOHC tranny with a 3100 pcm. The wiring for the connector is just in different places (basically). The 3.4 DOHC and 3100 SFI tranny is pretty much the same, just with minor differences.

In fact, I was using a 1993 3.4 DOHC tranny with my 3100 in my 1988 Cutlass Supreme.

For the engine choices, I would go with a 3400 or a 3500 over the 3.4 DOHC. I am in the process of rebuilding a 3.4 DOHC for my 1995 Cutlass Supreme, and so far I think this has been the worst mistake I have EVER made. With as much money as I have spent in just parts for my 3.4 DOHC, I could have bought a RUNNING 3500 and swapped it out.

[lkurek]

OK...so you are the second person to tell me to ditch the DOHC motor. Hmmm.....this is a tough one for me.

I have BOTH motors complete....a 3400 and a 3400 DOHC. I have all the front parts for the belt on the DOHC motor, so that is going to be changed with it out of the car.

That being said.....

Assuming you had two good motors, no other expenses needed really, which would you put in the car? The suspension isnt a big deal as I have upgraded that already.

As for the trans.....I do see that two wires need to be repinned on the range selector switch, but otherwise...looks the same.

Sigh......decisions decisions....

THANKS!

[3100 MPFI]

if I were you, I would go to any parts site (I recommend ROCKAUTO.COM) and look at the prices of parts.

Just about every part for the twin cam will cost more than the 3400. Don't look at what you have, but look to the future (as far as maintainence goes). Right now, I can get 3400 parts for about HALF of the twin cam parts.

Also, the 3400 is smaller and more compact, so it gives you more room to work on it, as well as future possible upgrades (easier to fit a turbo in the engine compartment of a 3400, but not as easy for the 3.4 DOHC).

I am only fixing my 3.4 DOHC because I figured I might as well, since I talk trash about it so much. So far, I think my decision to fix it has been one of the worst that I have ever made.

[SappySE107]

3400 would work better with that ECM. The 3.4 DOHC is a nice motor when its running, but its more maintenance, less gas milage, heavier, etc. Ive been thinking about pulling my 96 DOHC out of the GTP for a 3400 or 3500 this year. Or I may sell the car. I have 2 other DOHC cars and a project car that I had a DOHC/5 speed in. Unless you have some serious performance goals and love working/tweaking engines, the 3.4 DOHC isn't for you.

[lkurek]

Thanks Sappy....

OK, so you guys really don't like the DOHC motor? I'm suprised. As I see it, that engine puts out what, 40+hp more than the 3400? And that isn't a good reason to keep it?

As for PCM's..... I have the PCM from both motors....and also the wiring, etc. That isn't the issue. My issue was that I had feedback that the gear ratios in the 3100 trans are different than the ones in the 3400 DOHC trans, and that either trans needed to be matched with its engine/PCM to work properly. I see where I need to repin one connector on the trans range switch....and it should work fine.

Now, you say the motor is heavier.....I agree. But 40+hp would offset that. I mean I'm not looking for the best autocross car....just a good daily driver. The parts cost/availability are not issues....as I can find TONS of both motors in the local boneyards. I also have a good inventory of the one off parts of the DOHC in storage in my basement

Now....what really has my attention is the lower gas mileage. As I drive my car primarily for commuting.....mileage is important. If I drop 1-2mpg, I'm not going to sweat it....but if the thing is a pig.....I may have to reconsider. With the 3100, I averaged (mostly highway driving) 22-23mpg. How bad would the DOHC motor be?

As for dropping in the OHV 3400....it seems to be such a lame little boring motor. Even so, I would guess it also has the LIM gasket problem as the rest of the 60 degree OHV motors....

[SappySE107]

3.43 DOHC fdr vs 3.33 of the pushrod. All else is the same, though torque converter might not be.

gas milage isn't even close. 22-23 with a 3100 is horrible. My 3.1 got 35-40 highway. I thought the 3100 was high 20s low 30s minimum. My 3.4 DOHC cars are all mid 20s highway max. high teens in town. They also use more oil, as the PCV system sucks straight up the middle of the block. Catch can would be a good idea.

[lkurek]

Well, I guess I won't worry about the trans then That's not enough to have a major impact...

WOW! So you say you were getting near 40 on the highway in a 3100? NO WAY! How did you pull that one off??? If I look at the stats:

http://www.fueleconomy.gov/feg/bymodel/1995_Chevrolet_LuminaMonte_Carlo.shtml

The 3100 gets 17/26 and the DOHC gets 15/24....and those are usually optimistic. Hear near Chicago, they pretty much have E10 everywhere too, and that knocks another 2-3 off the ratings. I thought I was doing pretty damn good for combined mileage on a car with 285K miles

Oh, and FWIW.....I don't know why this is such a hard decision for me! I have the choice between easy (3400) or not as easy but still not bad (DOHC), and then the difference between 170 hp and 220..... Dunno.....

[SappySE107]

No, I said my 3.1. 1991 pontiac grand prix 3.1 4 speed auto. I was getting 40+ all highway between texas and arizona.

The 3400 makes 175, not 170. 185 in minivans. If you don't use a MAF and your exhaust is better than stock, 190+. The DOHC never made 220 either. 215 in 1996-1997. 95 is 210.

[3100 MPFI]

mild work to the 3400 will give you the same power that the 3.4 DOHC makes.

The 3.1 MPFI in my 1990 Grand Prix STE averages mid to high 40's on the highway. The 3100 I had in my 1988 Cutlass Supreme with a 4T60-E and running off of a 3.4 DOHC ecm with custom chip was getting low 50's MPG on the highway. My 3100 was also faster than a stock 3.4 DOHC, BUT IT WAS NOT STOCK. I had done quite a bit to it.

The 3400 is not a boring motor. Do not confuse simplicity with boring.

The only advantage the 3.4 DOHC has over the 3400 is the 2 extra valves. But when you add an extra 100-120 lbs of just metal to the car, then that takes away some of the gains. You might get 190 HP out of the 3400, and you might get 210 HP out of the 3.4 DOHC, but 20 HP alone will not counterbalance the extra 100 lbs.

Forget about if you are a fat-ass like me.