1988 C3500 Dually - BBC to SBC Swap - Req'd Brackets, etc..?

[88dually454]

Greetings Gentlemen:

Odd as it is.... I'm considering going the opposite direction, BBC to SBC.

BACKGROUND

I have a 1988 C3500 Dually, single cab restoration / mod project.
The stock 454 had a nice mild performance/towing rebuild, converted to Carb.
Turbo 400 transmission was also professionally performance rebuilt.
Rear gear ratio is stock 4:10. It's all pretty fresh, less than 10k miles on rebuild.

My intended purpose for the truck is to tow 24-27' boats short distances to boat ramp. I will likely never tow anything over 6-7k pounds and on occasion enjoy cruising the truck (non-towing) on the highway 250 miles, each way, back and forth to the lake. With the TH400 and 4:10 gears I'm at about 3400 rpm @ 65mph.

Spinning 454+ cubes at 3400 is simply a waste. The engine could be repurposed for a friends boat.
I'm very interested in purchasing a GM crate HT383 motor to use with the existing TH400 and 4:10 gear ratio. Seems the HT383 torque curve would be well suited for my needs. The truck is emissions exempt.

INPUT PLEASE

I believe mating the TH400 to a SBC will pose no problem.

My concern is frame mounts and drive pulley/mounting brackets. The truck has A/C and hydroboost power steering / brakes.

I'll love to get feedback regarding what bracket changes / mod's are required for the BB to SB swap.

Unfortunately, I will have little time to find a junkyard donor for components.
I'd entertain an "off the shelf" serpentine belt pulley/bracket kit, just haven't found one for a SBC with hydroboost.

Are components from 3/4ton (c/k 2500) trucks interchangeable? Do they use hydroboost?

I will genuinely appreciate any time you could devote towards guidance.

Thank you kindly.

 

[Christian Steffen]

So, just a thought and its not what you're asking for so by all means tell me to F off if you wish, but it might be easier to 4l80 swap, or regear to a numerically lower set? OR slap some giant tires on it lol or gear vendors

As far as brackets go.. Maybe look for stuff off a 3/4 ton - 1 ton that had a 350 in the later years? Should have all the same stuff as the 454 trucks just for the 5.7, this is a guess though.

 

[Stumpy]

Probably an easier swap than you think. My 96 regular cab dually came stock with a SBC, so I wouldn't be surprised if it dropped right in, same mounts and all.

 

[stutaeng]

Greetings Gentlemen:

Odd as it is.... I'm considering going the opposite direction, BBC to SBC.

BACKGROUND

I have a 1988 C3500 Dually, single cab restoration / mod project.
The stock 454 had a nice mild performance/towing rebuild, converted to Carb.
Turbo 400 transmission was also professionally performance rebuilt.
Rear gear ratio is stock 4:10. It's all pretty fresh, less than 10k miles on rebuild.

My intended purpose for the truck is to tow 24-27' boats short distances to boat ramp. I will likely never tow anything over 6-7k pounds and on occasion enjoy cruising the truck (non-towing) on the highway 250 miles, each way, back and forth to the lake. With the TH400 and 4:10 gears I'm at about 3400 rpm @ 65mph.

Spinning 454+ cubes at 3400 is simply a waste. The engine could be repurposed for a friends boat.
I'm very interested in purchasing a GM crate HT383 motor to use with the existing TH400 and 4:10 gear ratio. Seems the HT383 torque curve would be well suited for my needs. The truck is emissions exempt.

INPUT PLEASE

I believe mating the TH400 to a SBC will pose no problem.

My concern is frame mounts and drive pulley/mounting brackets. The truck has A/C and hydroboost power steering / brakes.

I'll love to get feedback regarding what bracket changes / mod's are required for the BB to SB swap.

Unfortunately, I will have little time to find a junkyard donor for components.
I'd entertain an "off the shelf" serpentine belt pulley/bracket kit, just haven't found one for a SBC with hydroboost.

Are components from 3/4ton (c/k 2500) trucks interchangeable? Do they use hydroboost?

I will genuinely appreciate any time you could devote towards guidance.

Thank you kindly.

Yes, find a C2500 or K2500 with a big block or diesel (truck or Suburban.) Both of those had hybroboost, as well as any C3500 or K3500 (regardless of engine.) The C/K2500 SBC did not have hydroboost, unless it was like a government-optioned truck (fire department?), at least I haven't seen a civilian truck in person that had the SBC with hydroost in that class truck.

But I'm sure you can drop a SBC in there with no issue. I mean, 3500s with SBC were made like that off the assembly line. My 2000 K3500 CCLB SRW has the 5.7 Vortec (also with 4.10s.) I'm sure you can find a 5.7 Vortec and mate it to a 4L80e and drop it in there without much headache.

Otherwise drop a SBC, save some coin and let her rip.

 

[Frank Enstein]

The rpm looks kinda high unless it's a low rider. Should be more like 2800. What size tires?
SBC should drop right onto the BBC mounts. All the accessory brackets will need to be changed so look for a complete engine that has the same AC compressor that your truck takes.

 

[stutaeng]

The rpm looks kinda high unless it's a low rider. Should be more like 2800. What size tires?
SBC should drop right onto the BBC mounts. All the accessory brackets will need to be changed so look for a complete engine that has the same AC compressor that your truck takes.

Good catch! Yes, that does seem off...by a lot!

I just just a quick check. 4.10 with LT245/75/R16 (diameter = 30.5") and transmission gear ratio of 1.0, 62 MPH gives around 2,800 RPM:

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See here: https://spicerparts.com/calculators/transmission-ratio-rpm-calculator

 

[Frank Enstein]

Add maybe 300 RPM for converter slippage aannnd it's still too high!

 

[88dually454]

So, just a thought and its not what you're asking for so by all means tell me to F off if you wish, but it might be easier to 4l80 swap, or regear to a numerically lower set? OR slap some giant tires on it lol or gear vendors

As far as brackets go.. Maybe look for stuff off a 3/4 ton - 1 ton that had a 350 in the later years? Should have all the same stuff as the 454 trucks just for the 5.7, this is a guess though.

Hello Christian:

Thank you for your reply. I recognize the wow factor for the BBC, it is a lot of fun to drive the torque..... Really a big factor for me is the under hood heat. I designed the engine without EGR. Exhaust temps are high and the header heat is scary. Tried header wrap, etc. white paint on firewall is turning brown. Also, during the 100 deg summer days loath any idling time at the boat ramp or heaven forbid traffic jams. PS - New radiator, A/F gauge etc.. Just interested in roller -cammed SBC. Kind thanks ...

 

[88dually454]

Probably an easier swap than you think. My 96 regular cab dually came stock with a SBC, so I wouldn't be surprised if it dropped right in, same mounts and all.

Appreciated, thank you..

 

[88dually454]

Add maybe 300 RPM for converter slippage aannnd it's still too high!

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