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View Full Version : 78 K30 to 6.5 conversion



irspiff
07-08-2009, 17:21
I have a 1978 Chevy K 30 crew cab 1 ton 4x4. I am seriously thinking of changing out my 454 big block in it for a 6.5 turbo diesel. Mostly for the fuel savings. The big block gets 6 mpg loaded, unloaded, uphill, downhill, sideways it don't care 6 mpg is what it gets. I pull a 28ft fifth wheel with a bike trailer behind it carrying 2-3 quads. I can make it up most hills with only the long steep ones slowing me down to 35mph smaller hills only about 55. Since it is an older truck with the th400 I keep it under 65 mph while cruising. As far as I know the motor is stock other than the fuel injection and a Holley intake and super coil. I decided on the 6.5 because it is nearly a complete bolt in. A Duramax would be nice but to pricey and too much work right now.

Since it is a one ton truck some issues normally associated are not a problem. Such as it already has the hydraboost brakes, has the heavier frame and heavy duty dana 60 up front so it can easily handle the weight and torque. It originally came with a 400 small block and I believe it even has the heavy duty th400. I also just recently put fuel injection on it and doing so had to install a 5/16th return line.

I have read as much as I could find here and I still have these questions before I commit to the conversion.

1. What mod/s do I have to do to the A/C system and exhaust to accomodate the turbo? Any info or links would be appreciated.

2. Can I run 65 mph with the th400 with 4.11 gears and 35" tires and keep the rpm under 2000 on the 6.5 TD? Or would it be the same where I would be running 2900 rpm like the 454. Can the 6.5 do that for long periods without harm? Other than fuel economy of course. Any thing better than 6 mpg is still better right?

3. If I can run the th400 for now what governor and torque converter do I need. Part #'s if possible or where to get them.

4. If I can't run the th400 will any 700r4 for a 4x4 work or is there a special diesel model? If not what mods does it need to work?

5. Is the 5/16th return line I just put in big enough for the 6.5?

6. I have the option of a 93 or 98 donor truck right now in my price range which should I get? Stick with the 93 and manual pump with little or no electronics or go with the 98 and figure out all the electronics? Both donor trucks are 2wd and both have about 165,000 miles on them.

Thanks in advance!

HH
07-09-2009, 09:46
1. What mod/s do I have to do to the A/C system and exhaust to accomodate the turbo? Any info or links would be appreciated.

If you have a complete donor truck you can use all the components from it for the AC and turbo. There will be an interference problem on the passenger side. Someone else here who has done this should chime in.



2. Can I run 65 mph with the th400 with 4.11 gears and 35" tires and keep the rpm under 2000 on the 6.5 TD? Or would it be the same where I would be running 2900 rpm like the 454. Can the 6.5 do that for long periods without harm? Other than fuel economy of course. Any thing better than 6 mpg is still better right?

When I tow I get about 15mpg with my K3500 dually, but that is with an OD, I am turning about 2200 rpm on highway. Not towing I get 18-19mpg regularly. 4.11 gears, 235/85R/16 tire - about 32".



3. If I can run the th400 for now what governor and torque converter do I need. Part #'s if possible or where to get them.

Yes governor and TC will need to be changed.



4. If I can't run the th400 will any 700r4 for a 4x4 work or is there a special diesel model? If not what mods does it need to work?

You will need to change the TC and governor on 700R4 also. You also need the TV cable and bracket.



5. Is the 5/16th return line I just put in big enough for the 6.5?

This should work for the return.



6. I have the option of a 93 or 98 donor truck right now in my price range which should I get? Stick with the 93 and manual pump with little or no electronics or go with the 98 and figure out all the electronics? Both donor trucks are 2wd and both have about 165,000 miles on them.

Depends what you want, the mechanical injection is easier for the conversion, but the electronic is probably smoother and slightly better for mileage.

irspiff
07-09-2009, 21:09
Thank you for the reply HH. I would sure appreciate anyone expanding on the A/C mods.

Can anyone tell me how the 6.5 will compare to the 454? Will it tow better? I am sure it will get better fuel mileage but will it pull as good or better than the 454?