1988 suburban with cummins 4bta and ford zf5-s42

[Edahall]

I would not be surprised if you can squeak 40 mpg at 60 mph out of this rig with the 2.73 rear end and manual transmission.  Does your Cummins 4BT use a VE pump?  And have you advanced the timing?  Advancing the timing can get you a bit better fuel economy.

For better MPG's, consider installing a BHAF (Big Honkin Air Filter) like what I've got on my 1990 Suburban.

[wildcatjason]

I think 40 mpg might be a little bit of a pipe dream, but I am hoping for high 20's. Everyone says to advance the timing and I should gassers run better that way and this is my first experience with a diesel so I was a little nervous to screw with the pump to much. Yes it is a ve pump. I did put a 3200 spring in it. I will advance it. Just haven't done it yet. I have the industrial air filter on it from the frito lay truck. It's a least a foot in diameter if not better plus a 3 in exhaust in the back and 4 in the front (plans for a he341 in the future) with a flowmaster muffler (it might be to loud for my taste but I wanted flow).

[wildcatjason]

I would not be surprised if you can squeak 40 mpg at 60 mph out of this rig with the 2.73 rear end and manual transmission.  Does your Cummins 4BT use a VE pump?  And have you advanced the timing?  Advancing the timing can get you a bit better fuel economy.

For better MPG's, consider installing a BHAF (Big Honkin Air Filter) like what I've got on my 1990 Suburban.

I see your running the vacuum booster. Does your vacuum pump work pretty well to stop it? Do you prefer that to a hydroboost? If you hit hydroboost hard enough it feels like you could bit your head on the windshield.

[Edahall]

I've also got a 1982 6.2L diesel Suburban with the factory hydroboost brakes so I can comment on both setups.

Yes, the vacuum pump works plenty well to stop it unless I'm trying to stop a trailer loaded with 10k load behind that has no brakes.  The vacuum pump on the Cummins seems to put out a lot of vacuum so it's plenty adequate for running a vacuum booster.  Besides, the 1st generation Dodge's that came with the Cummins ran a vacuum booster as well.  However, I will say that the hydroboost stops faster because there is less lag time.  I've had sports cars behind my Suburban who had to run off the road to avoid the bumper because those brakes are so quick.  The vacuum booster brakes just don't engage as fast.

For your reference, I'm getting 26 mpg with the 1990 Cummins powered Suburban.  It's 3/4 ton, 4x4, has a 4" lift, oversize tires, manual transmission and 3.73 rear end.

The 1982 Suburban with the 6.2L and my tweaking gets 30 mpg on the freeway.  It's 1/2 ton, 2 wheel drive, 30x10.50 tires, 700R4 and 3.08 rear end.  

[wildcatjason]

I've read about small trucks and Jeeps getting low 30s with a 4bt. If you comb through 4bt swaps you read alot about the gas mileage guys are getting and I can't see this brick getting over the 30 mark, but when I get to drive I will definitely post numbers. I did the math over the OVERALL gear ratio between a 700r4 with a 3.42 and a zf5 and a 2.73. If I ever tow anything relatively heavy it will have to be in third. That will be a 3.88:1 The first four gears of the zf5/2.73 combo would be relatively close to the 700r4/3.42 that I had with a 2.02 5th. I have a 28 in tire. I used a rpm calculator on the internet that said I would turn 1680 @ 70mph. It will be a road trip machine for sure.

[wildcatjason]

Here is a link to all the photos I took of my swap. Feel free to ask questions. I love gabbin about my truck. http://www.flickr.com/photos/66727529@N03/

[wildcatjason]

I would not be surprised if you can squeak 40 mpg at 60 mph out of this rig with the 2.73 rear end and manual transmission.  Does your Cummins 4BT use a VE pump?  And have you advanced the timing?  Advancing the timing can get you a bit better fuel economy.

For better MPG's, consider installing a BHAF (Big Honkin Air Filter) like what I've got on my 1990 Suburban.


Do you have your stock gauges in the truck? When I drove this rig the oil pressure would run high most of the time (60's or greater warmed up) and then suddenly go to 30-40 and fluctuate in between and it would always show over 250 degrees when it warmed up even though you could pop the radiator and stick your finger in it. (New water pump and thermostat) I wonder if I should switch to mechanical gauges. Did you have any problems like that with your 6bt?

[Edahall]

Do you have your stock gauges in the truck? When I drove this rig the oil pressure would run high most of the time (60's or greater warmed up) and then suddenly go to 30-40 and fluctuate in between and it would always show over 250 degrees when it warmed up even though you could pop the radiator and stick your finger in it. (New water pump and thermostat) I wonder if I should switch to mechanical gauges. Did you have any problems like that with your 6bt?

Yes I have stock gauges in the truck.  My oil pressure stays pretty much constant at 60.  And my engine temperature stays pretty constant at 180 degrees.  However, the temperature will climb pretty fast if I'm pulling a 10k load up a 7% grade and try to maintain 65 mph.  I don't ever let it go above about 210 degrees when pulling.

I wonder if the 250 degrees is actually half of that, 125 degrees since you said you can stick you finger in the radiator.  Using a voltmeter, test the resistance on the engine temperature sensor and see how it compares to a Chevy.

[Edahall]

I was also wondering if you have any issues with noise and vibration from the 4BT.  How loud is it in the cab compared to the gas engine?

[wildcatjason]

It's quite abit louder and shakes pretty bad I have a flowmaster to now. I found some factory sound deadner between the carpet and the floor when I've been installing the stick shift. I'm going to spray the heck out of it with lizard skin and have an idea about using a modified motor mount for the rear tranny mount to cut down the shaking. I was also running it without a hood for awhile. Thanks for the advice on the sensor. I think that might do it. I don't have the old chevy sensor anymore because I sold the 350, but my haynes might say something. If anything I could put a reducer in the block and put a chevy sensor in it. There is no way it is running that hot. It feels like hot tub water and at 250 it would be blowing anti freeze. I was afraid the wiring ran through the computer. I do have a youtube video I will get up of my truck running.

[wildcatjason]

I have tried and tried to post pics and get video up. Here is a link to hear it run. http://youtu.be/F806XvqMrOk

[Edahall]

Yes, I bet the sensors have different resistance values which is throwing your gauge off.  However, there are option here.
1.  Use a reducer so you can run a chevy sensor
2.  Hook a resistor so that resistance matches to a Chevy sensor
4.  Put a different face on the temperature gauge

But first off, find the resistance of the sensor when the engine is cold (say 70 degrees) and after the engine is fully warmed up.

Regarding mufflers, here's the muffler you want.  This muffler is free flowing and quiet and I don't think you'll find a better price for it.  If you're running a 3" exhaust, use a reducer to get the size down.

http://www.ryderfleetproducts.com/ryder/af/ryder/core/content/product/srm/oid/78183/erm/productDetail.do

[wildcatjason]

Thank you. I just bought this flowmaster, so for I gotta put up with it for now. I will bookmark that for future reference because this suburban has a regency package and it was built for comfort. I would love to keep it that way. I will experiment with the sensor first and probably go with the chevy sensor. I wish I would have kept my old one. It actually may be lying around somewhere, but I doubt it.

[Edahall]

I have tried and tried to post pics and get video up. Here is a link to hear it run. http://youtu.be/F806XvqMrOk

The engine sounds nice and healthy like my Kubota tractor.  Thank goodness it has the VE pump on it.  It would be significantly louder with the newer style P pump.  From what I've seen, the noise and shaking from the 4BT is the biggest complaint of this conversion.  There is not much you can do about the shaking but you can do quite a lot with the noise.

If you want to understand more about the science of noise control in a vehicle, read the following:

http://www.sounddeadenershowdown.com/cgi-bin/index.cgi

You can buy the MLV for a better price here:

http://www.soundproofing.org/infopages/flooring.htm

For areas you can't get to with the MLV, mix up some cheap house paint with a bunch of sand and apply a very thick coat of the slurry.

[wildcatjason]

As far as the shaking I though putting the transmission mount on a hinge to allow it rock back in forth with rubber pads on both sides of the mount pushing it into the crossmember to keep the tranmission from getting to wild. I've got some 1/8" I'll make it out of and reinforce it. I think I want something spray on for most of the undercarriage for the sound. I don't want to start tear up all my carpet. The headliner needs replaced, so I'll buy some lay out stuff then. I think after the hood and firewall I should be good. Thanks again for the advice. It does kind sound like a turbocharged tractor. It will be fun to put around with that 5spd knowing I'm not breaking the bank at the pump.