"Oldsmobile Diesel" Conversion to gas

[idahovette]

Uh................. that was Taylor @AuroraGirl that posted that GM article Wayne @Turbo4whl

 

[Turbo4whl]

Uh................. that was Taylor @AuroraGirl that posted that GM article Wayne @Turbo4whl

Yeah, when you get old like you and me, we mix up names. Sorry Taylor!

 

[Matt69olds]

Or sell it to someone wanting to build a high HP Olds Small block. The diesel block is more stout than the gas block. But no one is building Hp Olds Small Blocks

Oh yes they are!! The later diesel olds 350 make killer race engines!!

The later ones have larger lifter bores, meaning you can get much more aggressive with the camshaft. There are other advantages, I’m just not all that familiar with them.

Bill Travato in Rochester New York set lots of records with his Olds Star fire. He would buzz the engine to 8800 rpm, making about 1300hp. Definitely pretty stout for a “boat anchor!!

Here is another more recent build.

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[83Stepper]

Did a small amount of reading on the 350 Old Diesel engines as well. Obviously by the time they corrected all the issues they had with them blowing head gaskets and snapping bolts in 84, the damage was already done to the reputation of the engine and they were discontinued being used in the trucks. IMHO it's a lot more than just adding a water separator and rolling it down the road. If you've got a decent amount of knowledge with diesel engines, I'd say go for it. But like Ricko said, you're going to be looking at draining and flushing a lot of fluids from the truck and then starting off with new. That is in case the injection pump, lifters, pistons etc aren't stuck. She's been sitting for 20-ish years and will probably need a lot more attention the anticipated. But I also hope that I'm absolutely wrong and she doesn't need half of what I'm talking about. But at the very minimum, she's going to need that old fuel completely flushed from the system and replaced with new and a water separator.

Something about keeping trucks like that original since it's been in the family so long. It's like paying homage to your grandpa and keeping it going to keep his memory going. Wish you the best with it and keep us updated, would really love to see how it's coming along for you!

 

[Matt69olds]

I agree, see if it will run before doing anything. It’s been my experience with those engines that they will either run forever, or die a quick death.

My 81 GMC was also my grandfather’s truck. He died in 1991, several of my cousins occasionally used the truck. Not long after he died, it developed a water pump or thermostat leak, instead of fixing it, my idiots cousins kept adding water. No big deal, until wintertime. I remember starting it, only to find cracks in the side of the block big enough for Stevie wonder to see, and a radiator swollen so bad it split the side tank.

Dad tells me “fix it! Do it as cheap as you can!” Since all I had was 455 olds stuff, that’s what went in it.

The 350 to 455 swap is probably the easiest engine swap possible. A 455 is nothing more than a tall deck small block olds. Probably 90% of the brackets and hardware are a direct interchange. The hardest part about it is the wiring, and that’s not difficult. If I remember correctly, the heavy pink wire that would normally plug into a HEI distributor plugged into the injection pump, and the glow plug timer, control box and related wiring plugged into a firewall connector just behind where the distributor went. There was a single wire from the glow plug box that plugged into the fuse box, I assume that was a “wake up” wire for the glow plugs. I would definitely swap the torque converter, the factory diesel converter has a very low stall speed. No doubt a byproduct of the 3000rpm redline of the diesel engine!!

Not long after getting the truck on the road, it developed several leaks from the Hydraboost brakes. I fixed that by bolting on a vaccum brake booster from a gas square. Problem solved!!

The biggest hassle will be finding a good running 455. They aren’t nearly as common as they once were. If you do find one that runs, don’t even think about it out installing it until you replace the stupid nylon covered timing chain, and clean out the oil pump pickup.

If you put a mild camshaft in it, even with the lame compression ratio it’s hard to not make 470-500pounds of torque. Olds engine don’t really have a torque curve, they start high, reach the peak, and then slowly drop back to the previous high point. What they don’t do is make a bunch of hp, the truck is not fast. I have no doubt headers and a more aggressive cam would solve that, but it’s a truck. The engine is basically stock, it definitely has its tongue hanging out by 4800 rpm. Even with the stock 3.08 gears, it would effortlessly pull my 69 cutlass to all the races I attended years ago.

I’m done with my 455 endorsement speech!!

 

[AuroraGirl]

I agree, see if it will run before doing anything. It’s been my experience with those engines that they will either run forever, or die a quick death.

My 81 GMC was also my grandfather’s truck. He died in 1991, several of my cousins occasionally used the truck. Not long after he died, it developed a water pump or thermostat leak, instead of fixing it, my idiots cousins kept adding water. No big deal, until wintertime. I remember starting it, only to find cracks in the side of the block big enough for Stevie wonder to see, and a radiator swollen so bad it split the side tank.

Dad tells me “fix it! Do it as cheap as you can!” Since all I had was 455 olds stuff, that’s what went in it.

The 350 to 455 swap is probably the easiest engine swap possible. A 455 is nothing more than a tall deck small block olds. Probably 90% of the brackets and hardware are a direct interchange. The hardest part about it is the wiring, and that’s not difficult. If I remember correctly, the heavy pink wire that would normally plug into a HEI distributor plugged into the injection pump, and the glow plug timer, control box and related wiring plugged into a firewall connector just behind where the distributor went. There was a single wire from the glow plug box that plugged into the fuse box, I assume that was a “wake up” wire for the glow plugs. I would definitely swap the torque converter, the factory diesel converter has a very low stall speed. No doubt a byproduct of the 3000rpm redline of the diesel engine!!

Not long after getting the truck on the road, it developed several leaks from the Hydraboost brakes. I fixed that by bolting on a vaccum brake booster from a gas square. Problem solved!!

The biggest hassle will be finding a good running 455. They aren’t nearly as common as they once were. If you do find one that runs, don’t even think about it out installing it until you replace the stupid nylon covered timing chain, and clean out the oil pump pickup.

If you put a mild camshaft in it, even with the lame compression ratio it’s hard to not make 470-500pounds of torque. Olds engine don’t really have a torque curve, they start high, reach the peak, and then slowly drop back to the previous high point. What they don’t do is make a bunch of hp, the truck is not fast. I have no doubt headers and a more aggressive cam would solve that, but it’s a truck. The engine is basically stock, it definitely has its tongue hanging out by 4800 rpm. Even with the stock 3.08 gears, it would effortlessly pull my 69 cutlass to all the races I attended years ago.

I’m done with my 455 endorsement speech!!

I wish the short deck oldsmobile (260...) (just saying short deck as figure of speech) shared accessories with the regular or tall deck..

I have 2 boat anchors that are worthless essentially except if you wanted a block to machine up to 307, 350, etc but its not like olds owners are crying for new blocks often.

The intakes are worthless, heads are worthless, and the accessories only will mount to a 260 combination. Even a 307 at least shares stuff with the other olds engines ;(

 

[Matt69olds]

The water pumps, oil pans, and bolt on accessory brackets all interchange between the 260,307, 350, and 403 engines.

I have owned a couple of 260 powered G body cars, driving a 260 will make you wish for the rompin stompin power of a 307!

 

[AuroraGirl]

The water pumps, oil pans, and bolt on accessory brackets all interchange between the 260,307, 350, and 403 engines.

I have owned a couple of 260 powered G body cars, driving a 260 will make you wish for the rompin stompin power of a 307!

Are you sure, a lot of the online things suggest the bolts in the heads dont allow accessory brackets to change? If thats true then there is value in at least harvesting the 1979 and 1980 (different from each other) brackets for another oldsmobile engine with AC

 

[Matt69olds]

Are you sure, a lot of the online things suggest the bolts in the heads dont allow accessory brackets to change? If thats true then there is value in at least harvesting the 1979 and 1980 (different from each other) brackets for another oldsmobile engine with AC

Yes, the bolt pattern on the ends of the heads are identical between all olds engines from 64-1990. The head bolt diameter changed on a couple engines, I think the late 70s 350 and 403, and the diesels. There is plenty of meat to drill the heads to accept the larger head bolts.

 

[AuroraGirl]

Yes, the bolt pattern on the ends of the heads are identical between all olds engines from 64-1990. The head bolt diameter changed on a couple engines, I think the late 70s 350 and 403, and the diesels. There is plenty of meat to drill the heads to accept the larger head bolts.

so its smaller diameter meaning the brackets would just need to be possibly increased in size with a drill to fit the larger ones?

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Both 1979 and 1980 (respectively) have a nice layout for the accessories and are matched since they are OEM (alignment and everything) so would be nice to repurpose someday to someones 307 or 350

 

[peats]

Even though I have the 6.2 in mine, I'd give that 350 a shot before moving on, as long as you're not in a hurry to get somewhere!

 

[Matt69olds]

so its smaller diameter meaning the brackets would just need to be possibly increased in size with a drill to fit the larger ones?

You must be registered for see images attach

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Both 1979 and 1980 (respectively) have a nice layout for the accessories and are matched since they are OEM (alignment and everything) so would be nice to repurpose someday to someones 307 or 350

The bolts that hold the cylinder head to the block changed, not the accessory bracket mounting bolts. The mounting bolts have always been 3/8x16.

If I remember correctly, the later 350,403 and diesel engines used 1/2 or 9/16 head bolts.

 

[AuroraGirl]

The bolts that hold the cylinder head to the block changed, not the accessory bracket mounting bolts. The mounting bolts have always been 3/8x16.

If I remember correctly, the later 350,403 and diesel engines used 1/2 or 9/16 head bolts.

oh, well im pretty sure the geometry of where the brackets attach to the head face are different, but i could be wrong it seems the consensus tho

 

[Camar068]

I've just taken over my grandfather's '79 Chevy SB with the 350 "Olds diesel" engine. It ran when it was parked 20 years ago, but hard to guess what all would need to be done now. I'm considering whether to work on the stock motor or just find a 350 / 403 / 455 gas motor and move on, hopefully sourced from an Oldsmobile.
Welcome thoughts on the question, as well as sourcing ideas for the "Replace" option.
Thanks in advance.

Read up on this before you ditch it....not just this article....others as well.

https://www.hotrod.com/how-to/wise-performance-engineering-465ci-oldsmobile-engine

 

[JBswth]

I've just taken over my grandfather's '79 Chevy SB with the 350 "Olds diesel" engine. It ran when it was parked 20 years ago, but hard to guess what all would need to be done now. I'm considering whether to work on the stock motor or just find a 350 / 403 / 455 gas motor and move on, hopefully sourced from an Oldsmobile.
Welcome thoughts on the question, as well as sourcing ideas for the "Replace" option.
Thanks in advance.

This engine, while not a good diesel, is an excellent base for a gas engine. You need gasoline heads, maybe pistons, not sure, and of course a distributor and a carb, and the proper camshaft and lifters. It might work with the present cam, but probably won't have as much horsepower, but will have more low-end torque.

J. B.