4bt conversion in 84 gmc crew cab

[JacksonJ]

I've finally decided to go full tilt and drop the 454 gas out of my 1984 gmc 3500 and convert to a 4bt. I've found a doner motor from a bread truck with a chevy adapter that should fit the bill nicely. Currently my GMC has a NV4500 behind the gas-sucker that I'll definitely keep. If the bread truck has a chevy 4-sp manual transmission behind it, what will I need to change to bolt it up to the NV4500? Any gotchas in this conversion that you guys have run into? Motor mounts, oil pan interference, etc? Any and all input it welcome. Thanks!



--Mike

Greenville, SC

 

[JacksonJ]

I know this has been asked before, but I won't be getting the whole P-30 chassis (it's about 300 miles away), just the engine, the extra parts that I need after talking with you guys, and the 19. 5" wheels from it.



I've read that I can use the p-30 mounts since the 3500 is 2wd, what about the lift pump, throttle cable, and radiator? Any other parts I should get from the chassis? The 3500 has hydravac brakes, so I think I can use the pump that's on the 4bt already, with some plumbing adjustments.



I'd also like to convert over to a hydraulic clutch from the current cable clutch that the 3500 is using (sloppy linkage). Should I also grab p-30 parts for that, or use late 80s suburban clutch parts?



--Mike

Greenville, SC

 

[TBowles]

Mike, I have an 85 K30 with a 6bta if you are interested in looking at it to maybe get some ideas on motor mounts etc. Truck and engine have been together for 10 years now working almost flawlessly the whole time. Also i would like to look at the parts that you get off of the p30 just to stimulate the ole mind for new ideas. Located in Travelers Rest, work in Greenville.

 

[DKarvwnaris]

Mike,

if the P-30 was a straight 1 ton GM frame as many are, you can use the motor mounts from it. I've swapped the 454 engines directly out for the 4bt's with little fabrication issues. They were designed for this application, the only issue is the oil pan on the 4wd models, but a lift will take of that.

Since you already have a big block in the truck, you should be very close in weight to the 4bt, that takes care of the spring issue for you.

When you get the 4bt in your hands, have the pilot bushing replaced in the flywheel with an actual bearing. It will stop alot of the hop you'll get with the pilot bushing issue.

If you drive it sensibly and remember the clutch is your weakest link under low RPM and high torque conditions, you'll be fine. You can always go back later and use Dodge bellhousing parts to get the big Cummins flywheel and pressure plate. Then you can really put some fuel to the setup.

With the NV-4500 you should be close to a happy interstate speed, if not, I'd just install a gear vendors overdrive unit behind it and leave the rear end alone. Max RPM you'll get with the 4bt is about 2800 rpms.

 

[JacksonJ]

That's great information on being able to use the motor mounts. Do you think I'll have any trouble changing over from a manual clutch to a hydraulic with the chevy bellhousing?



Also, I currently have an external electric fuel pump mounted on the outside of the passenger side frame rail. What kind of pressure does the injection pump require for proper cooling and fuel flow? Should I scavenge the pump and filter setup off the p-30, or do ya'll have a preference for a better setup?

 

[JacksonJ]

d-day (delivery)

So tomorrow is the day to pick up the 4bt from the recycler. I asked him to make sure that the trans adapter, motor mounts, air cleaner, 2 ft of exhaust pipe, starter, electrical connectors, and front accessories (fan, alt, ps pump) stay with the engine. Hopefully that'll be most of what I need to drop it in... (crossing fingers)

 

[bgilbert]

4b in a 1 ton truck is gonna be a dog. Why not a 6b?

 

[JacksonJ]

Bill,



Ease of installation, price, and availability. I'm not pulling 14k pounds of trailer, just want to pull my 17ft boat to the lake and drive around town without paying for the 14mpg that I'm getting with the 454.

 

[ECannady]

This is off topic but how are you getting 14mpg with a 454? my 2000 454 only gets 10 if I'm very lucky. :--)

 

[DKarvwnaris]

That's great information on being able to use the motor mounts. Do you think I'll have any trouble changing over from a manual clutch to a hydraulic with the chevy bellhousing?



Also, I currently have an external electric fuel pump mounted on the outside of the passenger side frame rail. What kind of pressure does the injection pump require for proper cooling and fuel flow? Should I scavenge the pump and filter setup off the p-30, or do ya'll have a preference for a better setup?

I can think of NO reason to disrupt the 4BT's fuel system, the lift pumps are on the block just like the 6bt's are. Don't waste your time trying to rethink a wheel into a cube, the 4bt's lift pump is designed for the 4bt. I have yet to have to change the lift pump on my 6bt 12 valve in over 270,000 miles. My older 4bt powered rig was well over 250,000 miles on it before I pulled it out of the bread van it was in. It ran perfect on the original lift pump in my last conversion.



Some issues may be firewall clearance on the downpipe from the turbo depending on the manifold type used on your 4bt. Most I have stumbled across are center position turbo's which alleviates mandrel bent custom down pipes to fit it in there.

 

[JacksonJ]

ECannady,



I actually got 15-16 when I drove the truck back from Kansas to South Carolina. I'd attribute the economy to the NV4500 5-speed and my light foot. Additionally, it's got and edelbrock 650cfm carb, and I try to stay on the primaries and out of the secondaries.

 

[JacksonJ]

DKarvwnaris,



I didn't know if it was on the block or not. If it's mechanical and on the block, I'll definitely just use that (the less electrics, the better). Does anyone have a diagram or service manual for the 4bt? I'm leaving for NC at 11:00am to pick up the engine from the boneyard 3 hours away.

 

[JacksonJ]

Picked up all the parts at the yard today, including the starter, downpipe, air cleaner / plumbing, motor mounts, and 6 19. 5" chip truck wheels that fit on my 8 lug axles. I'll take some photos tomorrow and post for laughs, my little 86 toyota cargovan was REALLY loaded down.

 

[JacksonJ]

TBowles,



I've got the 4bt engine out of the back of the toyotavan, and on the engine hoist now. I pulled the clutch (which measures 12" across the pressure plate), the flywheel, and the trans adapter to start cleaning it up for maintainance and paint.



Who can I go to locally to pick up front, rear, valve cover, and side cover seals? Also, would it be worth while to have the flywheel cleaned up? If so, who would you recommend?



I'm over on East North Street by Bob Jones if you'd like to come over and visit for a while.



--Mike

 

[TBowles]

I have used several different places: Christopher White Trucks on White Horse Rd. & I-85 269-2131, Carolina International on Hwy. 14 & I-85 848-0050, or ordered parts from Cummins Atlantic out of Columbia (800) 695-5383 usually will have part next day via UPS ground. For machine work I use a small machine shop up here near the house in the Blue Ridge community, but I understand there are some competent machine shops in Greenville, you just have to be very judicious in selecting one.

 

[kurgan]

JacksonJ if you don't mind me asking, can I get some details on the bone yard you got your 4b from?



--kurgan