Oldsragger

I friend of me talk about his engine,he have 403, and plan to install in a diesel crankshaft with the rods, i guess on the 403 pistons, he means that the engine will be on 8.0 liters then? Is that possible?

MDchanic

I'm no engine building expert, but I believe that it impossible, as the 403 has the smallblock 2½" main bearings, while the DX crank has the bigblock 3" bearings.

Unless you plan to turn down the crank journals from 3" to 2½"...

- Eric

Oldsragger

I think it was from a 350ci olds engine, i tought 350 diesel was a sb?

Yeah maybe its right thats its diffrents about crank. Lol

wr1970

The 350 d and dx diesel cranks have big block main journal size of 3 inch. The 350 diesel is a small block. Can it be made to work sure but the main journal will need machine work.

joe_padavano

Your friend is clueless. The 350 diesel has the same 3.385" stroke as all other Oldsmobile small blocks, including the 403. Assuming he turned down the main journals on the diesel crank and transplanted all of the parts into a 403 block, the resulting displacement would still be 403 cu in. Your friend is confusing the concept of using a diesel block (with it's BBO-sized mains) and dropping in the forged crank from a 425.

wr1970

Joe you may be correct about what his friend is thinking. But the OP stated it was a 403 trying to use a diesel crank. It would not be a 8.0 with a diesel crank without some machine shop work but possible i think. Correct me if i am wrong Joe because you know more about this than me i am sure.

Oldsragger

Yeah maybe he is confused or have misunderstand something, lol, Well im Just asking anyway, its interesting to read about what part to use or swap over, but i read some place the dieselblock is a good block to use for powerbuilds or overboreing.

joe_padavano

As I stated above, you can certainly put a diesel crank in a 403 if you machine down the main bearings. The result is still a 403, since the stroke is unchanged at 3.385".

Octania

damn lot of work to make a 403 that way
a better choice would be a 330 forged crank for a 403. Same stroke. Much less machine shop work.

Shanghai Smith

Offset grinding of the diesel crank to 2.5" journals would yield a longer stroke, would it not?

joe_padavano

It's the MAIN journals that are larger on a diesel crank. The rod journals are the same SBO size. You can offset grind any SBO crank (preferably the 330 forged crank) and use Chevy rods. This is how SBO strokers are built.

wr1970

Joe i stated that with Machine shop work it is possible is it not!! You are being stubborn!! Yes you can grind the mains of a diesel crank to fit then offset grind the rod journals to get more stroke which would be more than 403 ci correct? Now is it easier to do with 330 crank of course it is and cheaper. Can it be done with a 425 yes. We are still talking a 403 block which is the weakest block to turn into a stroker high performance olds. I would never do this with a diesel crank but it is possible!

olds 307 and 403

Using the 425 diesel crank in a small block supposedly causes issues with oil holes lining up when reducing the mains down to 2.5". Add in counter weight reduction and balancing and figuring out rod journals, no wonder no gas small block guys have done it to my knowledge. My 403 with a 3.5" stroke and 4.395" bore after final hone with still only be 425 ci. With a 3.6"
stroke a person could gain 10 more cubes. With a custom crank $$$, sure but on the flimsy 403 block, you would have to be nuts.

rustyroger

I suppose if you pour enough money into it you can create an 8 liter sbo. But surely a better approach is to start with a bbo, or better yet, get hold of a Cadillac 500ci engine and sink some money into getting reliable hp out of it if displacement floats your boat.

Roger.

wr1970

I am in total agreement i would never do it and stated it! But the op ask the question so i answered it yes but will cost mega bucks because of machine shop cost and still not have a very good foundation.

Oldsragger

Another thing my friend told about the 403, the Oil channels is not so good pruduced in these blocks and ppl use to customize the holes or something, maybe it was for the crank bearings, i dont remember,, something sounds familiar about that too? Im Just curious..

He told too that he damage the th350 cause of the tq from the 403, i think the engine was orginal, or maybe it was another carburetor and camshaft. Is that possible of a 403? I dont know how much tq the orginal 403 have, and it was 200hp?

rustyroger

A healthy th350 should have no trouble dealing with the output from a 403 unless it has been heavily modified. The cars left the factory with a 403/350 combination.

Roger.

joe_padavano

Sorry, but I have no idea what your problem is. Everything I've said is in complete agreement with what you are saying, yet you tell me I'm being stubborn.

Let's recap. Nearly all of my responses have been to the OP's original question about a friend who thinks that a diesel crank in a 403 block gives you something like an 8.0 liter engine. I respond TO HIM (not you) that once you got past the need to turn down the main journals (which I specifically said COULD be done), you still had the same 3.385" stroke as any other SBO crank, thus no additional displacement. I have no idea how to make that clearer.

I then responded to this post (again, not one of yours):

I pointed out that the diesel crank has the same size ROD journals as any other SBO crank (2.12"), so it's a little difficult to offset grind those UP to 2.5" diameter. I then pointed out that since (except for the added cost of turning down the main journals), any such offset grinding one could do on a diesel crank is exactly the same as what one could do on a lighter gas SBO crank, yielding exactly the same displacement. I further pointed out that if one were going to do all this machine work (including the offset grinding DOWN to 2.00", allowing the use of Chevy rods), it made a lot more sense to do it with a forged 330 crank.

How is this being difficult? It's all fact.

Oldsragger

Ok i see.

wr1970

Took you long enough to finally make the statement when Smith and i were already on that page and stated that the diesel crank would work on the get go and you could get more than 403 ci.Not a smart ideal but possible with $$$$$.You seem to be stuck on correctness not what can be!!When i comes to correctness Joe you are most the time like 99% spot on. Smile Joe!!See my post number two machine shop work would include mains and offset grind to rod journals to get more than 403 ci. I didn't state it but the intent was there!Now go look at your post #2 then tell me you were thinking stroking the rod journals.Eh what say you now?The op first question was to use the diesel crank to get more than 403 ci was it possible i said yes i thought.On a side note you never said no!

joe_padavano

That would have been post no. five above...

In any case, you are still apparently missing the point. The issue was never about fitting a diesel crank into a 403 block. The question asked by the OP was: does a diesel crank in a 403 provide about 8.0 liters displacement? This has NOTHING to do with the ability to machine the main journals or not, but the fact that the diesel crank has the same stroke as the stock 403 crank. Displacement will be the same. There was never any mention by the OP about offset grinding, simply dropping it in, and the fact still remains that both cranks have the same capacity to be offset ground - which will yield considerably less than the displacement suggested in the first post:

My original response from post no. 5 remains: It is NOT possible to get that displacement from a diesel crank in a 403 block.

For the metrically challenged, 8.0 liters is 500 cu in. If you could magically stuff a 455 crank into a 403 block, you would get 505 cu in, which is likely what the OP's friend is thinking about. It isn't physically possible to offset grind an SBO crank to get a 4.25" stroke.

M-14

If you used diesel crank & rods you'd have to use custom pistons because the diesel rods are so short.

wr1970

There you have it buy your last response you are still stuck on correctness!! The op doesn't know if the diesel crank works or not if even possible! So he wouldn't know about what to do to get this crank to work!! My point was yes it would! I wasn't thinking you could get to 8.0 liter Joe. With custom rods and custom pistons and offset ground even to small block chevy rod journal size this engine would scream! The simple point is the cost to do this with such a bad foundation block makes it not worth it. Think what you want but you were slow to throw out this would need custom parts. A ton of machine shop work to get this thing to perform and out perform the 403 in stock from.

Octania

Grinding the main journals has no effect on the stroke to the best of my knowledge.

Grinding the 2.125 inch rod journals *up* to 2.500- a trick I would pay to see- would make for interesting big end rod fitment. Mathematics says, assuming you keep the inner edge of the rod journal for maximizing the stroke, you could in so doing move the rod journal out 0.1875" for a stroke of 3.5725 and a new displacement with stock size pistons of 425 cubic inches.

The rods, now with big ends on the order of 3.5" wide, would hit the block and the engine would not turn. The rods may be so short that the pistons have to be drawn into the crankshaft at BDC... [have not drawn it up to see...] but that was not the question, right? Can't let practical factors get in the way of what might be possible.

Actually, if you are grinding larger, you are adding material, so there is no need to be limited by the location of the original rod journal, so you could have any stroke at all. Just move the block out of the way where it hits.

Which reminds me of my clever engine design that turns both directions.... I wonder if it would work?

wr1970

Chris i am thinking offset grind for a reason longer stroke means more ci faster rapping motor Bigger bore.Hmm a win win three rod journal choices to go longer rods, bigger bore.They do this all the time with big blocks and diesels.The problem is the 403 is a weak block. The cost of a diesel crank to modify not worth it when other cranks are better suited at much lower cost. Possible yeah good ideal no no no!!!Better to switch to a diesel block and go from there!

joe_padavano

Actually, I was stuck on answering the real question, which was about getting over 500 cu in from a 403 block.

cutlassefi

As I see it Joe answered the question. Most of the rest of you changed the rules. Joe stuck to the original scenario.

Jmo.

wr1970

Mark you missed that post. I was the first that stated the crank would work but needed machine work. Not that he could acceve 8.0 The rules what rules!!I just didn't think he could get 8.0. But modifying mains, rod journals and getting custom rods and pistons would get more than 403 and by boring it. That is why i said Joe was being stubborn and didn't want to get off the 403 using 403 rods, pistons stock bore. I didn't change the rules i was throwing out what might get done to make the engine have more hp with that diesel crank.I also thought that the cost wasn't worth it.The op didn't have a clue! I agree other cranks were better options with less cash still not going to get to 8.0.

tomskydog

Has anybody ever heard of a 403 having lower end problems due to main webs? I hear warnings about it, but never heard of any problems. I put one in a '86 442. It shifts at 5200-5500 with 3,70 gears. To me it's quick.. It has a a Lunati voodoo cam. The motor cost me $800 plus cam and intake. Beats the heck out of the wimpy roller cam 307 with swirl port technology woo hoo!

olds 307 and 403

Some have died in a disastrous way but most will spin bearings like the 455. Heavy pistons, rods and a weak crank in a flimsy block means trouble. I spun the bearings at 5500 in my 403 but the crank was not balanced properly. Old enough thread to drag up. With custom pistons and the 4" stroker crank, 480ci is possible.