I just bought a 1984 6.9L diesel and as I was telling a friend about the truck he told me I should put 351 heads on the engine make a few other adjustments and just run gas through it since it has bigger pistons than a normal gas engine. I was just wondering if this was possible to do, as I have never heard of this being done before. thoughts/ opinions?

 

A 6.9 IDI has 17 head bolts per side; a 351 has 10 per side. Tell your friend to buy a 6.9 and try it himself.

There is nothing in common between these two engines other than being in between the frame rails of a Ford truck.

 

Welcome to FTE.

Even though it's not April 1st, this is hard to take seriously.

But just in case, your friend is full of beans. There is no relationship between the 6.9 and any 351 gas.

Trying to convert a 6.9 to gas would be beyond foolish, and probably outright impossible.

If you don't want a diesel truck, sell that '84 and go shopping.

You could do a powertrain swap, but it would make more sense to trade for a gas truck.

 

Running Gasoline through the Injection system would be short lived for sure...

Back in 1935 International Harvester came out with their first Diesel Tractor, for farm use.
This engine, model WD-40 started on Gasoline, and when warmed up would be shifted
over to Diesel.
I remember seeing an old International Road Grader with one of these engines. Row of
Spark Plugs down one side and Diesel fuel Injection down the other side.

Yeah there is no way to run a 6.9 on Gasoline unless you have some very deep pockets
for some serious redesigning.

You could try gas in it and let us know how it works out. People dump all kinds of other
crap in the tank and they keep on going.

Charlie

 

Or as the saying goes, with friends like that, who needs enemies?

 

Make sure that friend doesn't influence you on anything related to your truck, and maybe anything in general.

 

There were some boys back in iowa or something that custom cnc'd some heads for a 3208 and ran it on methenol... Either way the IDI doesnt even have interchangable parts with the gas engines they were "based off". I think your friend may have confused IDI for 5.7 idi and 351 for 350, but either way the pistons in a olds 350 are smaller than a standard chevy 350. Further more, the bore in a 6.9 is 4", the bore in a 302/351 is 4" so wrong again, the heads between 302 /351 are the same, so strike again, the heads on an idi already flow great, as good or better than stock windsor heads.

 

the military multi fuel engines would run on gas, but it was recommended to add at least 1 quart of motor oil for each gallon of gasoline for proper pump and injector lubrication. .

 

I'm convinced the Olds 5.7L IDI was a converted Olds 5.7L gasoline engine. This is contrary to what many believe in the Oldsmobile community. As you said, the Olds 350 and Chevy 350 were NOT the same engine. The coil and distributor cap were the only common parts. Here's the place to get info on the Olds 350 diesel.

https://classicoldsmobile.com/forums...sel-350-a.html

 

I think you are mostly correct. The basic design is the same, but the actual blocks were beefed up a bit iirc. It is possible to retrofit those blocks with gas heads, gas cam, manifolds etc, and make gas engine out if it.

Not so much--heck, not at all with the 6.9.

 

Yea, the 5.7 diesel is a 5.7 olds that was converted. They did use their own blocks, which were a bit heavier, but that was also one of the major failures of the olds diesel. The blocks were green and warped VERY badly. Ive heard stories in the drag racing circles that if you have a good 5.7 diesel block that they are desirable for hot rods because of the extra strength, and maybe something to do with how much they can be bored.

As for the 6.9/7.3, you could absolutely convert one im sure, with copious amounts of machining, throw a carb on there, distributorless ignition etc. but good luck getting it to run at 21:1 compression, even with race gas or methanol.

 

Not practical on the 6.9 really as it would require a set of custom pistons or a 0.110" over bore to fit MV446 pistons... Now the 7.3L on other hand would be a relatively easy swap. All that would be required is to swap the heads intake, pistons and cam lifters and push rods to those from a MV446 make provisions for an ignition system and block off the provisions to mount the Diesel IP. The issue is MV intake gaskets are very difficult to locate.

 

Actually I saw some recent research that said an engine using diesel injection ignition to burn gas also in the combustion chamber was more efficient than a gas or diesel engine, although I'm sure that would cost a fortune to play around with.

as for converting a diesel engine to gas, I guess in theory all it needs is less compression and spark plugs and bolt a carburetor and ignition system on. Oh wait that's quite a bit of stuff 😆

 

You need to find smarter friends.

 

Don't the guys on the alternative fuels forum use gasoline to cut WMO before running it through their truck?