The Stovebolt Site Forums The Shop Area Engine Shop Big Bolt Re-Power Questions...

The 58 450 GMC Dump with Howe Coleman Conversion in the Photo Gallery is me... I posted here about repowering it & the recomendations were to keep the inline 302. I REALLY was gonna do that until today.... Brought home a 4 Speed Allison Automatic from a bus camper conversion. Came with the shifter console & cables/linkages, external filter AND an adapter plate & Torque Converter for a Chevy 350 V8 that was installed when they converted the bus to a Camper/Commercially done conversion... The conversion used a late 70's carberated 350CU V8. Now the problem.. I'm really a 50's -70's Ford guy/GM illiterate....
My limited knowledge of Small Block Chevy's tells me the preferred engine for torque is the small block 400.
First Question: will a small block 400 from an automatic donor vehicle bolt up to where the 350 did? 1 friend mentioned there may be differences on outside balancers on the 400 making spacer issues in the adapter plate?
Second Question: Are there different generations of 350 or will any 350CU Block bolt up to that adapter?
Third Question: Has anyone ever tried using the original radiator with the modern V8/is there enough cooling there or do I need to change the radiator too?

One thing I do know/I think, I will need to put a low rpm torque band cam in this conversion?

The 400 small block & 86 up 350,s use balance weights in the flywheel. They will work if you use the corresponding flyweel. The weight should not interfere with anything. The 400 has overheating problems & would not work well in something like that. The bolt pattern is the same plum up into the 90,s. You may want to look at a big block. They bolt up the same. I believe it should have a big enough radiator for a 350.

The 400 uses a 4 1/8" bore, and a 3 3/4" stroke. The center cylinder walls are siamesed together due to the large bore size, and there must be a couple of extra holes in the cylinder heads and the block deck to allow coolant to circulate past the cylinders. An alternative that gets used often is putting a stroker crankshaft into the 350, a special-order item that puts the 400 stroke into the more reliable 350 block. I think the resulting displacement is about 375 cubic inches. The 400 crank is not a bolt-in swap into the 350 due to different main bearing diameter.

The flywheel and harmonic balancer for the 400 is different, but the stroker crank for the 350 is internally-balanced. Check out Scat or Eagle crankshafts for the long-stroke 350 shafts. Of course, you could buy a NASCAR crank from King's in North Carolina, with any stroke you specify, but his price is about $2,800.00 for a basic setup, with an extra thousand for rods, and another grand for pistons! Nothing like a $5,000.00 rotating assembly!
Jerry

I agree with all the others here and would only add that your best bet may turn out to be a 383 crate motor from GM Performance Parts. Reliable, powerful and comparitively inexpensive. One model is made for high torque truck applications right out of the box. Since it is abasic 350 block darn near anything is available to bolt on it.

I would shy away from a small block 400 in a application like this. Finding a good solid block when the motor has now been out of production for 30 years could be difficult, and overheating was a problem with those motors when they were new.

You've described the truck and the transmission, but said nothing of desired usage and performance. A 350 built for low end torque might be perfect, but a stroker 383 will be better. Dave's suggestion is a good one.

But if you want a strong performer while loaded you want a bigger motor. A GMC 450 is a big truck and pretty heavy. I'd be thinking 454 big block or maybe one of the bigger stroked versions of that motor if you want hot rod performance.

Where Ford seemed to design a new bellhousing pattern for every series of motors, Chevy motors are far more interchangeable. Your adapter will bolt to any Chevy V-8 made starting in 1955 up to sometime in the 90's. I don't know the details of the most recent Chevy motors. For about 40 years they shared bellhousing patterns, and starting in '58 those motors all shared the same motor mounts.

Can I add another thought?

GMC didn't use Chevy motors in '58. I believe a V-8 powered GMC would have had a Pontiac motor. A 455 Pontiac won't fit your adapter, but would be an interesting and more powerful choice compared to a small Chevy. It also could be dressed to look close to original.

My suggestion would be to pick up a donor vehicle - Suburban or 2500/3500 pickup with a big block. This way you get all the accessories. Lots of them out there cheap. More than adequate power for a big truck.
Fred

Consider the speed you want to drive at, the RPMs that the engine will enjoy running at, tire size, transmission high gear ratio, and your axle gear ratio.

I believe that proper gearing should come first, sure beats having a truck you can't drive how you want, or can't afford to feed.

I'm almost certain your Allison is not an overdrive, this could be a big problem if you are stuck with the axle gears you have now, as they are probably really slow.

This site is great for figuring speeds
http://www.drivetraindirect.com/t_gear_calculator.htm
and this one I just found, and I may like it better...
http://www.onlineconversion.com/bigger_tires.htm

Grigg

WOW! Interesting....Lotsa information in the posts above. I'm not looking to go any faster than the original in line 302 would have taken me. I've got 1/3+ of a mile of difficult terrain driveway that a 1 ton 90's 4x4 dump currently handily plows but I'd like to have this truck as a backup. When I was gonna keep the 302 I was just short of getting a HEI distributor for it on E-Bay/one of the goals is I want it to reliably start. For off road there is the low range 2 speed transfer case that should make the 350 pull OK there. Gravel pit only 6 miles away, Stone Quarry, 10 miles. Not at all concerned about hi-way speed vs as much as I am about feeding it ga$. I'm kinda set with the idea of donor vehicle with good running engine. I might put 100 miles a year on it. I border Mass. & vehicles won't pass inspection over there with rust issues so if one is patient good running vehicles appear for parts over there. I think I'll shy away from the 400CI's based on the advise above. If they overheat in light duty trucks, I believe I'm sure to have heat issues in a heavy dump truck sometimes loaded up to 5 yards... Big Block comes with those ga$ concerns. My 67 400CI Pontiac got 10mpg's with a light foot in a Firebird. I see aftermarket wiring harness' advertised for Chevy 350's pulled from vehicles with fuel injection. I think that may help the ga$ thing... I really don't want to put a lot of money in the truck. My goal is a good running occasional WORK vehicle that looks good enough to run down the road without getting stopped by every cop car I pass.... For example, I pulled the factory painted grill, had it all stripped and painted Powder Coat Chrome. Will look good at 30mph & 1/20th the cost of chrome.... The 4 Speed Allison I picked up is not overdrive & should have adequate fisrt gear being from a full size bus....?

Sounds like you should leave the engine alone and drive it.
You don't need more power, as you won't be driving it much, fast, or far.
Fuel consumption will be reasonable as is, and 100 miles a year is nothing.
The cost of an engine swap and all the little things that it takes will add up really quick.

I say drive it as is, or rethink your plans for it.

Grigg

Driving it 100 miles a year I'd ignore fuel cost concerns but if it runs as is I'd not go to the trouble of a swap for that few miles either.

Well, likely logically I should leave it alone. But..... Everybody needs a hobby... I did buy the thing to keep me from getting underfoot around the house in retirement... Reasonable $'s for fixing her up with near unlimited manhours will be available..if I live that long..

One more question though... I can pick up an 80's C60 Chevy with rebuilt 366 V8 for the price of scrap DELIVERED to the house. I think everything I may need for the conversion project is on the C60 intact with the exception of an auto transmission flywheel. My only concern.. Is the 366 truck engine the same bolt pattern as a 350? My Allson adapter plate is set up for a Chevy 350.... Without the Allison I would leave the drivetrain alone. Everbody with bad knees & shoulders/elbows wants automatic?????? don't they?

The 366 pattern is the same as the 350.

The 366 is a big block. Are you familiar with the Ford truck 330 and 360 motors that are are externally very similar to a 390/428? The Chevy 366 is a big block based truck motor externally very similar to the Chevy 396/402/427/454.

Might be a better choice than running a used 350 in your Jimmy.

If the 366 is running good - then use it if the pricee is right. Its a high torque low rpm truck motor. If you need/want more power later then you can bolt in a 502HT crate motor. To get better driveability and mileage try and find a complete 454 TBI setup and bolt it on. It'll add about 15% milage compared to a carb.

I have a complete 454 TBI setup and have been considering taking it off. I get terrible mileage with that setup. Granted it might be worse without it, but I've not been impressed by it.

F100Panel... can I have your 302?

A couple of questions..

1) have you replaced the 02 sensor lately?
2) are the injectors dripping?

TBI should be 10-15% better mileage than a qjet.

I agree with Pauly - Can I have your 302???

The tbi intake from the 454 will not bolt up to the 366. The 366 is a Tall Deck engine, so the heads are actually spaced wider apart on the block due to the extra block hight. The intakes on the 366 and the 427 Tall Deck engines are wider that the Short Deck blocks. There are adapter kits from Jegs and Summit to adapt them, though. It would probably be easier to use a Holley Pro-Jection than adapt the 454 intake.

I bought a new O2 sensor for it recently, but the truck was wrecked before I got it installed. I don't know if the injectors are dripping, but I'll check.

When I started thinking about removing the TBI I had also begun thinking about transplanting this motor from the wrecked truck into something else, and while I've not been impressed with the fuel economy a significant driver behind that thought was relunctance to figure out the E part of the EFI.

Steve, The TBI engine is one of the simplest E engines to figure out. Check Here and buy the book . Only 5 wires needed: +B, Ground, Ignition, Idiot light and power to the 1-Bar (15 psi)fuel pump. Just grab the whole engine harness and ECM. The dash harness is a bonus.

Scott