dman0712

what rods and pistons would i need to build the 403 stroker? I have a 330 forged crank i want to use. do i have to have the crank welded and ground or can i use longer rods and a shorter piston?

cutlassefi

How much stroke are you looking for? Stock is 3.385.

dman0712

im not sure. what are my options? I just want to make more low end torque

marcar1993

First, with windowed main webs, a 403 stroker may not be the right way to go. The lack of strength + the extra strain of a longer throw may just prove to be disasterous.

Now the term stroker doesn't mean change the pistons and rods to make it a stroker. What you are doing is undercutting the rod journals offcenter to change the centerline of the journal.
So with a 2.5" stroke, you undercut the journal .25 OUTWARDS from the centerline, you now have a 3" stroke... It adds .25 to the top and bottom of the stroke. On the same note, if you cut .25 off inwards of the centerline, you have destroked to 2"... (for clarification, inwards being removing material from the side facing AWAY from the main journals, and outward being removing material from the side facing TOWARDS the main journals.)



So, what you need to do is make sure the journals are clean. Measure the diameter, then find a rod with the length and the journal diameter you need and cut the crank off the centerline down to the new rod size. Watch out because you CAN go to far and weaken the crank...
People with more experience than me can fill you in with specifics and correct me if I'm wrong.

dman0712

even with everything balance it would still put pressure on the mains?

cutlassefi

Horsepower/Torque will put pressure on the mains, not necessarily stroke if you keep the same rod/stroke ratio.

I'm having mine welded and then ground to a 2.00 rod journal size, stock is 2.123. It will be stroked to 3.75, 6.00in. rods and a piston with a compression distance of 1.425. I'm doing a 350 though, not a 403 so my pistons are off the shelf. Yours would probably have to be custom made.

dman0712

how much does that cost to have the crank welded?

507OLDS

CutlassEFI probably knows more about the SBO stuff than I do,but I think you can offset grind a 330/350 crank to 3.50" stroke,with a 2.00 SBC journal,no welding.Yes?
put the longest rod in there possible,& a short,lightweight piston.This will help take some stress off the mains,but is not a cure-all.What are your expectations with the car?

dman0712

a fun street car with close 500 ft/lbs of torque. Its going back into a 79 t/a. Ive seen an article where a guy stroked it and he got 505 ft/lbs of torque and ive seen articles where guys just use a stock cast or forged crank and make real close to 500 ft/lbs if not a little over 500 so i dont even know if its worth stroking. I wont be spinning it over 5500.

dman0712

and the problem is i cant find a short piston for this thing. The bore is huge, 4.375. will i have to have a custom piston made? i have the kb 0.24 Hypereutectic piston right now but i can return it.

507OLDS

You will need a custom piston for the 403 because of the bore size.If it were a 350 Olds,there are a few SBC pistons that will work with various rod/stroke combinations.

70 cutlass s

I have a little advice I know you like the Olds engine, but with 79 Transam you have a lot of engine options. The put Pontiac, Chevy and Olds engines in them. Their something like 10 different engines that came in it. So if you want to build a powerfull engine you have a few more options.

dman0712

yeah i know. i just already have alot of the olds engines parts so i want to use them. im just kinda at the pint in my build where it wouldnt hurt me very much to change engines so im looking at all my options. Another option would be the diesel block right?

70 cutlass s

You know you already have a lot of good parts. I say you can put to gather a very nice 403 with what you have. It will be a very strong engine. I think it will be a lot more engine than peoples giving it credit for. Just remember it doesn't matter how much power an engine make unless you can put it to the ground. So what's your plans for the rear suspension to get the power to the ground.

dman0712

i bought new stock leaf springs, new stock shocks, lakewood traction bars, beefier rear sway bar, and sub frame connectors. Its not a whole lot but im not to concerned. the car will just be for fun and burnouts are always fun

captjim

You won't make 500 ft/lbs with that 403, but you won't need it. My 355 makes 375 ft/lbs and will fry the tires at will. Don't over think it, you have the engine, you have the parts already, 409 cubes is plenty. Assemble it, tune it, have fun driving it.

dman0712

yeah i most likely will build the 403. the only problem is i would like to use lighter rods but i cant seem to find any that will work without a custom piston

BIGJERR

I wouldnt bother stroking a 403,There are so many more vaible ways to make the Olds SB run.........Just my .o2...........Jerr

dman0712

are the stock rods ok if they are polished and shot peened?

captjim

They are OK if you don't. You are making this way too complicated. All you want is a fun car to drive, right? Hit the cruises, a little stoplight fun, bust the tires loose on occasion? You don't need light rods or custom pistons for that.

507OLDS

403's came with a very nice rod.You can recondition them,& reuse them in your build,as long as you keep the crank as-is,& don't alter the journal sizes.
If you ever get to the point where you want to make some serious power,then yes,the diesel block is the way to go for a SBO.

cutlassefi

All excellent posts. A 403 will put out all you need. Couple that with a good rear gear and it'll be fun. Picking the right cam will be as important as alot of other things.

Again, Torque can be made without a big long stroke. Want to guess what the stroke is on a typical Nascar motor? 3.25, Bore is 4.185. They make plenty of torque down low to come off the corners and then spin em up to make hp on the top end. Shorter stroke means lower piston speeds as well. There are pros and cons to almost every scenario.

dman0712

yeah good point. im going to use the olds 330 forged crank though just because i have it. i have the early flexplate for it.