cummins swap, adapter or transmission?

[MaxPF]

What do you mean by torque fluctuations? and in the other thread you said you're conserned about vibrations, can you elaborate on that some. I'm finding it hard to grasp what you find to be a problem. Thanks.

All reciprocating engines have torque fluctuations in their crankshaft output. That is, the crankshaft accelerates when a cylinder fires, and then decelerates as the next piston approaches TDC on it's compression stroke. In other words, the crank doesn't rotate at a smooth RPM like an electric motor, but speeds up and slows down as it rotates. An engine with more cylinders will have less torque fluctuation due to more overlap in the firing events. Diesels have more torque fluctuations than gassers due to their higher compression. A 4 cylinder diesel like the 4BT has a good deal more torque fluctuation on it's output than an 8 cylinder like the 6.2 - heck, the 6.2's were bad enough that they went to a rubber-isolated crank pulley to dampen the fluctuations imparted to the accessory belts. Anyway, it will effectively act like an impact driver turning the transmission. The torque converter will soak up much of it, but I can't help but think it will still be harder on the tranny than a smoother V8 diesel.

The vibrations I spoke of are are related to the 4 cylinder's torque output, and the fact that inline 4's aren't inherently balanced like inline 6's and v-8's. Put simply, the motor shakes quite a bit. Go put your hand on the hood or fender of a running bread truck and you will see what I mean.

Once again, I have no direct experience with a 4BT in a K5 or hooked to a 700. I would suggest checking out a running bread truck with a 4BT to get an idea of the noise and vibration before making your decision. Lots of guys actually like the clatter and shake - it gives em more of a "big diesel" feel . Some don't like it. At least that way you can make an informed decision.

 

[DEMON44]

I totally understand what you're talking about......its the number of power strokes in 720 degrees of crankshaft rotation. Thats sort of a basic principle.

My question was why do you think its a problem?


with the number of 4 cylinder turbo diesels in service in dirt equipment with not much of a problem?

I see no consern what so ever. See I'm just not seeing the problem is all.

 

[MaxPF]

I totally understand what you're talking about......its the number of power strokes in 720 degrees of crankshaft rotation. Thats sort of a basic principle.

My question was why do you think its a problem?


with the number of 4 cylinder turbo diesels in service in dirt equipment with not much of a problem?

I see no consern what so ever. See I'm just not seeing the problem is all.

Like I said, I think the crank output would act like an impact driver on the tranny, and accelerate wear on items like the sprag and planetaries at low RPM (where the torque pulses are most severe). Yes, a lot of construction equipment uses 4cyl diesels, as do a lot of delivery trucks and such (think of all thise Isuzu box vans out there). However, they usually have pretty burly trannys behind them. Once again, I may be totally wrong and a 700 may be perfectly fine. Unless I already had the 700 I would get myself a 4L80E instead. Especially if you plan on tweaking the 4BT for more power

 

[DEMON44]

I'm pickin up what your laying down.

don't think its a problem though. A 4bt isn't exactly a powerhouse to start with, and the fluid coupler that is the torque converter can't transmit the "impact driver" as you describe to tranny hard parts. unless of course there is a functioning lockup.


but I think you give the mighty 4 banger way too much credit. sure its slightly less smooth at idle, but power outputs of a 4b are about half that of a 6b even though its only down 2 holes............

but a 700 is a 700..........and I'd never own one no matter how built it was.

 

[u2slow]

Forget a TH400, it's a non locking 3 spd......
....Go with a 518 or 47RH Dodge trans....
....You want a lockup 4 spd auto if at all possible....

That's my thinking also. These already have 205 behind them in the 90-93 CTD trucks.

FWIW, I could not stand the TH400 that came behind my 6.2L diesel. I would imagine its even worse with the lower rpm band of the Cummins.