1985 k20 and back pressure through mufflers??

[Nasty-LSX]

I have an 85 k20. It has a 350 with 400 trans.

It is has true dual exhaust from the manifolds to back bumper. The mufflers are glass packs that look like they been there forever. The truck has no back pressure due to straight through exhaust. Am i wasting gas driving around
with almost straight pipes? will taking off all the smog stuff help with gas mileage, including smog pump belt. Thanks

I was thinking of getting new exhaust, 2.5 pipe, x pipe, magnaflow mufflers, all the way to back bumper. the most important thing i
need to do is get rid of the TH400

 

[MadOgre]

Why do you need to get rid of the TH400? What are you gonna replace it with?

The air pump does nothing for power or fuel economy except that it is a drive accessory robbing power thus increasing fuel consumption.

The EGR doesn't exactly promote the most efficient Combustion

 

[Nasty-LSX]

Why do you need to get rid of the TH400? What are you gonna replace it with?

The air pump does nothing for power or fuel economy except that it is a drive accessory robbing power thus increasing fuel consumption.

The EGR doesn't exactly promote the most efficient Combustion

I want to use this truck as a daily driver. I have a 700r4 for it. Need 4x4 shaft and spacer. I need overdrive

 

[89Suburban]

I want to use this truck as a daily driver. I have a 700r4 for it. Need 4x4 shaft and spacer. I need overdrive

Did you already start gathering parts? Why not go with the 4L60E?

 

[Nasty-LSX]

Did you already start gathering parts? Why not go with the 4L60E?

Yes, I have all new parts for Trans. Just can't put it together till I find a shaft and spacer

 

[MadOgre]

Input shaft for the transfer case? and adapter?

 

[Nasty-LSX]

Input shaft for the transfer case? and adapter?

Yes. I cannot find a used 4x4 transmission shaft, (because my 700 came out of a 92 trans am) have to change tail end. I think ill need a spacer also because ADVANCED ADAPTERS sells a shaft and spacer kit. Im trying to hold out on buying from them because its almost $500.00 bucks

 

[MadOgre]

Buy a new 4x4 out put shaft. Its got to be cheaper than $500. Those guys always try to milk everyone.

You will also need to change the input gear on the transfer case unless you get a used one from a 700r4. And then just use a stock adapter. No need for an adapter from those crooks. They make good stuff but their out to lunch on their pricing.

Th400 uses a 32 spline out put shaft and the 700r4 uses a 27 spline

The transfer case will end up in exactly the same spot. so no need to worry about drive shaft length.

 

[MadOgre]

What gear ratio are you running in your diffs?

 

[Nasty-LSX]

What gear ratio are you running in your diffs?

Not sure, but its very peppy with 33's. moves as quick as a car without giving much gas. On the freeway, motor sounds like its doing 2500 or more RPM at 55

 

[Nasty-LSX]

Buy a new 4x4 out put shaft.

From who??

 

[MadOgre]

http://www.gearcentregroup.com/

These guys can sell you one

 

[MadOgre]

With a stock 4x4 out put shaft and a matching input gear on the transfer case a stock adapter is all you need. Probably cost $10-20 for a used one.

The other thing is if your Th400 set up as the straight flat crossmember then you will have to find a newer style that's kinda like an S. im thinking your 85 probably has the S type already.

 

[Nasty-LSX]

With a stock 4x4 out put shaft and a matching input gear on the transfer case a stock adapter is all you need. Probably cost $10-20 for a used one.

The other thing is if your Th400 set up as the straight flat crossmember then you will have to find a newer style that's kinda like an S. im thinking your 85 probably has the S type already.

Cool man. In order to swap the spines on the TC from 32 to 27, does the TC need to be opened up?? or this this an easy swap. Where do I find the 27 spline input for the TC? thanks again!!

 

[MadOgre]

Cool man. In order to swap the spines on the TC from 32 to 27, does the TC need to be opened up?? or this this an easy swap. Where do I find the 27 spline input for the TC? thanks again!!

Unless you can find a transfer case that was originally behind a 700r4 then yes you would have to open it up to replace the input gear.

A complete rebuild kit with bearings, shift fork pads and seals is about $125 the gear is probably about $100. The chain is a bit more if it is stretched.