350 D/DX gas conversion guideline

crazymathlefou

New member
Mar 23, 2020
5
3
3
Hello everybody,

i'm curious about olds 350 diesel conversion. we have many engines here in europe but nobody really dives into how their works what are their weakness.

So the idea could be to do a gas conversion for a barn find. But i don't really find any guidelines, only some talks about it.

Someone had done it by past ?

best regards
 

Olds 307 and 403

Active member
Oct 4, 2018
597
212
43
Melville, Saskatchewan
One thing you need is gas heads, #8 heads will give mid to high 8 to 1 compression and work with regular gas and the mild diesel camshaft. Early 330 and 350 heads, 72 and older will give 9.5+ to 1 compression, it may have pinging issues. Also a gas 4 bbl intake is needed, either an Olds 330, 350 or 80 to 84 Olds 307 intake, avoid the 260 and 85 up Olds 307, both tiny ports, heads are no good either. The starter and flexplate are unique on the diesel due to the massive starter to crank over 22.5 to 1. The diesel timing chain is unique and like a bicycle chain, if the injection pump boss is ground down, a regular gas timing set can be used. Also a fuel pump eccentric must be added to the cam gear if running a mechanical pump, I believe there is a spot in the block.
 

crazymathlefou

New member
Mar 23, 2020
5
3
3
One thing you need is gas heads, #8 heads will give mid to high 8 to 1 compression and work with regular gas and the mild diesel camshaft. Early 330 and 350 heads, 72 and older will give 9.5+ to 1 compression, it may have pinging issues. Also a gas 4 bbl intake is needed, either an Olds 330, 350 or 80 to 84 Olds 307 intake, avoid the 260 and 85 up Olds 307, both tiny ports, heads are no good either. The starter and flexplate are unique on the diesel due to the massive starter to crank over 22.5 to 1. The diesel timing chain is unique and like a bicycle chain, if the injection pump boss is ground down, a regular gas timing set can be used. Also a fuel pump eccentric must be added to the cam gear if running a mechanical pump, I believe there is a spot in the block.
thank you it seems very simple to do.

did you know if the crank is too heavy ? i've heard the build can't revup too high.
 

Olds 307 and 403

Active member
Oct 4, 2018
597
212
43
Melville, Saskatchewan
Yeah, a heavy cast crank with 3" mains, not a rpm machine.
 

crazymathlefou

New member
Mar 23, 2020
5
3
3
sorry for the late,

did you have an idea of the max rpm - horsepower for these build ? ( it's for a street application ).

Best regards
 

Olds 307 and 403

Active member
Oct 4, 2018
597
212
43
Melville, Saskatchewan
I would keep it under 5000 rpm, will probably run out of steam by 4500 rpm anyways. Most factory transmissions shift just over 4000 rpm, about perfect.
 

SupremeSpeed

Member
Oct 13, 2018
31
18
8
Northwest Ga
Hello everybody,

i'm curious about olds 350 diesel conversion. we have many engines here in europe but nobody really dives into how their works what are their weakness.

So the idea could be to do a gas conversion for a barn find. But i don't really find any guidelines, only some talks about it.

Someone had done it by past ?

best regards
I have one but I bought it built. From what I hear they are really good for big torque.