I have 3 5.7 diesels and I believe 1 is a dx. I was wondering if it would be a good candidate for a peppy gas conversion rebuild? mild cam, headers, intake, 4bbl, etc. I have a set of 69 #5 heads just stock valves and springs to match a cam. looking for good street manners with a mild idle. It would go in a 69 cutlass s with th350 trans and stock stall. just a driver car. So my question is would I get a more reliable engine out of the diesel or rebuild a gas 350 block?

 

For that type of build I would stick with a gas block. Doing a gas conversion on a diesel block is more for the hard core type of build because of the strength of the block.

 

Yes just use a gas block. IMO

 

Thank you. I guess I will have to find a complete 350 sbo, to rebuild.

 

Where are you located? I may be interested in one of your diesel blocks.

 

south central MI.

 

Oh well thanks anyway!!

 

Back in the day, Mondello used to sell a conversion kit for diesel motors. If your diesel had blown the head gasket, simply change the cam, heads, intake, and add a distributor for a minimum impact conversion. Of course, that assumed the engine was already in a car. In your case, I agree that it's overkill for a street driver.

 

Sorry Joe but there is more to it than that. No matter what Mondello said.

 

ok, thanks this is a short block that I have. My dad did a simple rings and bearing rebuild. I am trying to figure out what pistons are in it. it is a 395558 block with a big 2. the piston dish measures 2.5 x .200 deep are these the low comp pistons?

IMG_20130819_102439.jpg
He has his mind set on no cam. It will probably get a set of redone stock #5 heads a edelborck performer intake and a 600 carb with headers and 2.5 exhaust. would this make a pretty decent driver?

Thanks

 

I'm shocked, SHOCKED I tell you...

Seriously, I'm aware that my response was a simplification. They did use the existing diesel pistons in the conversion, however.

 

Unless you change the pistons the engine wont last long at high rpm.
Diesel pistons are much heavier than gas ones, they have to be very robustly constructed to deal with the 22;1 compression and shock load of diesel ignition, rather like constant very bad pinging to put it simply. That's why diesels have their characteristic rattle.
The main bearing and rod journals are the same size as the BBO, so the rods will need to be changed and suitable pistons installed, I don't think the diesel cam is suitable for gas use either.
Unless you want to make a monster power engine for the strip or similar I agree with most other posts that a gas block in good shape would be a simpler and cheaper option.

Roger.

 

I understand that the diesel block is for performance builds now. The short block I posted is a gas block, I was told early 70's. Can anybody confirm if the pistons are 14cc dish? Is this a decent short block for 250-300 hp with intake carb and headers/stock cam?

 

Keep in mind that the engines converted using the Mondello kit were typically in grandma-car 88s and 98s. Not everyone drives around at 5,000 RPM all the time.

 

Incorrect, only the main journals are BB size, the rod journals are SB size.

The Diesel rod is 5.885 long and has the large pin. You could change out that combo to regular small block stuff if you wanted and rebalance.

Red97, yes those are 14cc dish pistons. Yes you can get 250-300hp fairly easily with decent heads, intake and the right cam.

 

We are both right (and wrong) In 1981 the rod journal size increased from 2.124" (same as the 350 gas engine) to 2.500" (BBO size).
Maybe the later ones are the DX engine?.
It seems the later engines were a big improvement over the earlier ones, too late to stop the engines reputation going down the pan.

But the earlier crank should withstand any load a road use gas conversion will give. Plus it makes finding suitable rods and pistons much easier.

Roger.

 

Hmmm that could be a misprint. Until someone can show me a 5.885 inch Oldsmobile rod with the 2.500 big end journal size I'll stick with my original info.

Thanks.