Olds64

I browse our forum, the internet and diesel forums most of the day at work... still haven't found the end of the internet.

Anyways, I found this recently and thought some folks would be interested.

http://www.dieselhub.com/idi/5.7-olds-diesel.html

Aside from the few posts on our site about this most infamous of Olds engines, there isn't much info on the Olds diesels out there. For instance, I had no idea the Olds diesel was an IDI engine.

Here's another site I figured would be useful for anyone that digs up this thread in the future.

https:/oldsjunction.classicoldsmobile.com/oldsfaq/ofedsl.htm#EDSL%20DieselEngineDetail

wr1970

You are not involved with this engine enough to know what information is out there. The diesel 350 has been for a long time a great foundation to make a drag racing engine. Russell Hunt's Twin engine dragster in a example. There are many others out there. I am hoping to convert one myself as i own a 350D block diesel. Wished i knew more myself. Thanks for digging up the link.

joe_padavano

Have you seen this one?

http://a350diesel.tripod.com/newmain.html

Here's a Fiero with an Olds V6 diesel swap.

http://a350diesel.tripod.com/dieselfiero.html

wr1970

I had some info on my Diesel engine build but lost it. What info i am looking for is how much material i need to remove off the 425 crank counter weights.

wr1970

I think this is the info .375 is the amount i need to remove off counter balance weights. I am not sure that is correct. I think my wife tossed all my paper work by accident on this engine. I was collecting info for two possible builds. One with 4.09 stroke 425 crank. The other was a 4.19 stroke 425 crank.

Olds64

Thanks for the links Joe. I had seen the first website in the past. I haven't ever seen the Fiero though.

I did know there were folks that used the diesel blocks for racing engines. I was wondering more about modifications to the motor as a diesel.

Are head studs available for the motor? If so, are they just the same studs used on a gas 350 block?

Does the diesel 350 have an exhaust crossover like the gas 350? If so, why? There isn't a carburetor and choke to heat at start up.

Besides the exhaust crossover, can the diesel heads be improved by filling the exhaust divider? Plus, why not run an aftermarket intake if it will fit? All it's doing is providing air to the engine since the injectors provide the fuel. I've heard of folks running headers on their non-turbo IDI engines to improve performance (I've never heard of intake changes to diesel engines though). Why not on a diesel 350?

Was the injector pump timed at the back of the engine where the distributor was on the gas block? Was the diesel 350 an interference engine? If not, why not run an aftermarket cam to improve the performance (apparently a gas Olds cam can fit in the diesel block).

​​​​​Ultimately, depending upon the answer to some of these questions I am convincrd that the diesel 350 engine is litte more than a gas 350 with bigger mains, different rotating assemblies and diesel heads. I know I've read otherwise in the past (even on the link I provided above). But how much different does an engine need to be to be a separate engine altogether?

wr1970

Olds64 i can tell one thing.I have never seen a 350 gas motor in race form go as fast as Paul Testers 434. The Olds diesel is in a league of there own in my opinion. No doubt that not the same as a gas block 350 factory engine. I seen Paul's car run in the 8.60's before he changed car front end frame and added the carbon fiber front end. Paul ran i know some where in the 8.30's before switching to a chevy motor. No turbo,no nos, just a n/a engine and a door slammer. Now there may be faster door slammers using Oldsmobile diesel engines but i haven't seen or heard of one in a A body car. I also don't know who has the fastest 455 converted race engine right now. BTR built a 5.38 ci but i know nothing more about it.

Olds64

That's cool!

I was giving this some thought over the weekend and while the Olds 455 and Pontiac 455 use the same distributor cap and coil that doesn't make them the same engine.

It's cool if folks can use an Olds diesel block as a foundation for a race engine. At the same time, it's a shame that Olds missed the mark with the Olds diesel engine.

joe_padavano

Diesels used the same 1/2" head bolts as every 1977-1990 Olds gas engine, so studs would be the same also.

No, for the reason you cite. There is no fuel in the intake, it's injected at the heads, so no reason to heat the intake.

As with any internal combustion engine, improving the flow of air in and out of the motor increases performance.

The stock diesel intake is already a single plane design that is pretty low restriction. Since there is no fuel flowing in the diesel intake, there is no need for dual plane design or other features common to a gas engine. The Olds diesel intake has several unique provisions that mount to the intake, like the vacuum regulator valve that modulates vacuum from the vacuum pump in response to throttle position to mimic the vacuum vs throttle curve of a gas engine. This kluge was primarily used to operate the vacuum modulator on the TH350. This is also why GM got away from the vac modulator on their later transmissions and went to a TV cable, to avoid this problem.

No, it's in the valley under the intake and driven off the cam. There is a large mounting boss on the block that can be machined out for weight savings in a DX conversion to gasoline. There was a vacuum pump mounted in the distributor location that both generated vacuum for accessories and drove the oil pump.

No idea, but the cam profile is obviously unique to the diesel engine and you'd need a custom ground "performance" cam. I can't begin to tell you what the parameters of a performance diesel cam would be.

​​​​​Contrary to what you may read, the Olds diesel was a dedicated diesel design that was fit within the existing gas engine architecture. This was done mainly to allow assembly on the existing gas engine lines without expensive retooling and to also allow it to be fitted to existing vehicles without major redesign. The D and DX blocks were brand new with much beefier sections to handle the stresses. Cranks, rods, pistons, etc were all dedicated diesel parts. The basic geometric architecture of the gas engine line was retained (bore spacing, mounts and hard points, head bolt pattern, overall dimensions) but within those constraints this was a dedicated diesel design.

The biggest problem with the Olds diesel wasn't the motor itself, it was that GM cheaped out and didn't incorporate a water separator in the fuel system.

Olds64

Very cool! Thanks for the info Joe.

I suppose the few Olds diesel engines left in the world are probably bone stock (hopefully with fuel/water separators). I was just curious about the Olds diesel engine after I read that article at DieselHub.

joe_padavano

Ironically, the Olds diesel wasn't the first GM diesel derived from a gas engine architecture. The GMC V6 truck motor (NOT the Buick V6) from the early 1960s was also used as the basis for a diesel. Called the Toro-Flow, it also had problems in production and was not long-lived.

http://6066gmcguy.com/toroflow.html

Olds64

A GM diesel V6 from the 60s. Very cool!

I browsed that site, I've seen info on the GMC twin-six V12 before.