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-   -   how far can u bore a 403 olds engine (http://www.hotrodders.com/forum/how-far-can-u-bore-403-olds-engine-62581.html)

403pontiac 05-11-2005 06:07 PM

how far can u bore a 403 olds engine
 
Hey my name is carl i need to know how far can i bore a 403 over with out overheating.if u got any info on how i can set this motor to high performance and what i will need to buy plase let me know.I atleast want to run a low 10 or 9. please tell me everything including what i need to do to the gear in the axle :confused: :sweat:

firechicken383 05-11-2005 06:21 PM

Sorry dude, I dont see it happening on that block- windowed main webs are a problem with that much power.

mj_lover 05-11-2005 06:23 PM

what type of car is it? do you intend to keep it purely strip, or are you going to drive it on the street as well? 403 is pretty big, if you don't need to over bore, i personally wouldn't overbore. (keep cylinder walls as thick as possible, but thats just me) i would look into forged parts, bigger cam, forced induction, proper tolerances, valve job, higher flow heads, etc. for gears, 4.11 or 4.56 if your only out for strip. they are not very good for mileage.
hope it made sense, post more info, and we will be able to help better. good luck on your project.

machine shop tom 05-12-2005 07:19 AM

383 is right, the block is a weak spot in highly stressing the 403. If your heads are not cracked, your best bet would be to bore it no more that .020", install a torque cam and perform some bowl clean-up.

tom

403pontiac 05-12-2005 10:42 AM

so this motor 403 u really can't do anything with it
 
the motor is in a 81 pontiac bonneville is is mostly going to be used for street.Can u tell me which is the best brand to use if am looking for good performance,such as piston,headers,carb,intake,and cam.I also have another problem my 400 trans keep shooting fluid back through the filler tube

bracketeer 05-12-2005 11:21 AM

my choices for economy
 
SCAT rods
SRP pistons
Edelbrock heads (AFR are better but more money)
Edelbrock intake
Holley carb
Crane cam (Comp has a crappy lube and cam failures seem to be occurring more frequently)
MSD ignition (more money but worth it)
Hooker headers
Cloyes true roller chain

firechicken383 05-12-2005 07:53 PM

Oh well if its going to be mostly street in your bonneville, then that 403 could make an excellent choice, just depends on what your after. I've had a few in street cars and they are alright. Alot of T/A's came with them and thats what I'm into so thats where my experience with them is.

When you said you wanted it to run a low 10 or high 9, I was thinking drag strip only. That was 9's in a 1/4 or 1/8 mile? If its a 1/4, you might as well forget it with that 403 and street car. But if you meant 1/8, then you shouldn't have too much promblem running 9's with a 403.

They can be great if your looking for a 400h.p. engine or less. They can definately be made to produce more though, but I wouldn't try to push much over 400-450 h.p. with one due to the main webs. I mean, I dont know exactly what you want from this car, but a 403 can be pretty stout for the street.

Because it is an olds engine, parts availability isn't near what it is for chevy (or price either). But ****uming you don't go with high $ aftermarket heads, you could run the new KB pistons with your current heads or run flattops with a set of earlier 350 heads. ( I would choose the second route if your rebuilding this thing) The earlier 350 olds heads (4,5,6,7,and 7a) flow approximately the same on the intake and about 20 cfm more on the exhaust. (the earlier heads would need a little modification to run on the 403 block, but nothing to bad) As far as cam, listen to tom, a "torquey" cam is what you need. (Somethin less than 220* @.050) A edelbrock performer rpm and any of the small tube hedders should work fine. I like a quadrajet for mild applications of less than 325 h.p. For over 350 I would go with whatever brand you prefer (edelbrock, holley, demon, etc) Everyone will have their opinion on what carb is best. BTW, I listed them in order I would use them.

Also be aware that you will likely have to convert the valvetrain over to an adjustable setup. This stuff will add up quick and you will likely spend plently of hard earned money on it but with the earlier olds heads and around 9.5 compression, and a cam in the 216-222 range, you should around 300-375 REALISTIC horsepower and some pretty good torque to go with it. (In other words if a magazine did an article on the same build, it would make over 400 horsepower) Just add a 2500-3000 stall convertor and 3.42-3.73 gears and you should have a great street runner.

BTW, I agree with tom, I'd try not to bore it more than .020 if possible. I'd also have the block decked too. Add ARP rod bolts to the rods and resize them. If Its like most olds blocks, it'll have very little wear, they seem to wear good IMO.

Good luck with it and ask if you have any more questions. :thumbup:

4speed 03-22-2009 10:01 PM

I agree don't go over .20 that motor already runs hot.

curtis73 03-23-2009 01:22 AM

I don't share the apocalyptic views of the 403 like many others do. Windowed mains does not mean weak mains. Mondello used to run 500+ hp in a 403 without a main girdle, so street/strip power is just fine if you ask me. He also did it with the block filled with cement up to about 1" from the deck, so overheating isn't a big issue according to Mondello.

But... most of the 403s I've built are street-only so my experience with really hi-po olds is limited. I had a 403 in an 87 Caddy making about 390-400 hp on a 30-overbore and I never had a single overheating issue idling in traffic in the Florida summer with the AC blasting... and that was using the stock 307 radiator.

I personally like the 403 and have found no particular weakness with them for street and street/strip use.

cobalt327 03-23-2009 07:45 AM

A list of Joe Mondello’s (aka “Dr. Oldsmobile”) articles, including two on just the 403 are located HERE.


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