Th400/NP208 to 700R4/NP208 Conversion V2500 Suburban

[v2500burb]

Even with a stage 4 clutch pack kit, bigger fluid pan, and a cooler?


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[bucket]

Even with a stage 4 clutch pack kit, bigger fluid pan, and a cooler?


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It's less than ideal. It lugs the motor too much, the trans constantly wants to go out of lockup, and the fluid gets hot quickly. It does work though, but a trans temp gauge is HIGHLY recommended so you know when to back off the throttle.

After having two 3/4 ton Burbs with 3.73's and 33's, one with a built 700r4 and the other with a stock th400, I'd take the th400 any day of the week.

Also, I've put 70-80K on that built 700r4 and it still works fine, but I will be removing it because it has seen so much stress in that time, I just don't trust it anymore. I'm putting a th400 in it.

 

[v2500burb]

What would you suggest?
I would really like that overdrive.... With freeway speeds at 70-75mph
I would never tow anything heavy....
This is meant to be the family travel vehicle
Would love to be able to set the cruise control at 70-75mph and not have the motor scream in agony


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[bucket]

It's not screaming in agony, it's spinning with delight

Unless you are constantly driving at 75mph all day long on a very regular basis (like everyday), going with an overdrive isn't really going to gain you much considering what the upgrade will cost. The truck was designed to see those high speeds, it's just uses a little more fuel. And I mean just a little. It's NEVER going to be efficient pushing a 3 ton brick through the air at high speeds.

 

[v2500burb]

Ok
Sorry guys I'm so new to these trucks
I come from an import truck world.
With you having had a bunch of these
What is the best mod you have done
Best bang for the buck


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[350runner]

700r4 for my highway miles.. Mine's just for a daily commute as well

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[bucket]

Don't be sorry, it's mostly a matter of opinions anyway.

For me, by far the best bang for the TBI buck is simply advance the timing beyond the factory 0* spec. Next best is a good free flowing exhaust, most stock replacement type mufflers are very restrictive. The single 3 inch exhaust works well, but a performance type muffler is needed, as well as a better catalytic converter (factory is the pellet type).

Beyond basic simple things like that, it's going to start costing some money.

 

[bucket]

700r4 for my highway miles.. Mine's just for a daily commute as well

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But is it a 3/4 ton 4x4 Burb?

 

[350runner]

It's for sure a c10, but honestly does it really matter if it's just used to commute? And no serious off-road venture?

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[v2500burb]

I have a high flow car and a Flowmaster 40 series
3"
Thinking about hedders in the future....
Any thoughts of CFM technologies TBI rebuild kits?



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[bucket]

It's for sure a c10, but honestly does it really matter if it's just used to commute? And no serious off-road venture?

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Yes!!! Weight and large tire sizes are key here. Off road doesn't matter one bit, it's highway use that kills a 700. They are fine with the weight of a 1/2 ton pickup and a 235/75 tire. But a heavy 3/4 ton Burb with 33's and relatively tall gearing, they just plain aren't happy. Steeper gearing like 4.10 or 4.56 would help out a bunch, but that takes away from having overdrive to begin with.

 

[bucket]

Also, I find it funny that the 700r4 was put in use to help out with freeway speeds, but those freeway speeds are what helps kill them.

 

[skysurfer]

CFM has some good products. The spacer that goes under the throttle body is a nice upgrade, so is an adjustable fuel pressure regulator set to 13 psi, but don't expect any "OMG" power gains from them.

They offer a ported throttle body, but with an engine that's nearly stock it's not necessary, your stock tb can provide all the air a 5.7 needs. Besides, even if you did get a larger tb the intake manifold then becomes the choke point unless it's also ported.

Headers are a good call, long tubes if you don't have emissions inspections.

 

[skysurfer]

Steeper gearing like 4.10 or 4.56 would help out a bunch, but that takes away from having overdrive to begin with.

In a perfect world he could switch to 4.10 gears coupled with a 700r4 for a loafing 2000 rpm's at 68.4 mph. Problem is the the cost of doing both diffs and trying to build a 700r4 that's as durable as a T400, he would never recoup the investment in fuel savings.

My solution is to slow down and enjoy the ride. It's kinda nice cruising in the slow lane and seeing passengers check out my square as they go by.

 

[MadOgre]

My motor is quite happy at 2500 rpm. There is no sluggishness to it and can get up and pass when ever it wants.

I have a 700r4 33s and 3.42s and I leave it in 3rd pretty much all the time even on the highway. I really don't get much of a chance to use OD unless im doing 75-80 mph.

If I could scrounge a set of 4.10s I would keep it but next year when I swap in the new frame the th400 is going back in with 33s and 3.42s I can live with 2500 rpm as I do any way and I will have peace of mind when towing any thing I wish.