oldsmobile 403 : Personally, I test-drove a couple of 403 T/As. They had a nice initialsurge, then....not much. Passing kickdown pretty much sucked. One ofthem had headers and true duals, so it wasn't an exhaust restrictionslowing it down.It was my observation that the converters on 403 cars seemed pretty loose.Thanks for the input Ed. Appreciate any other info folks out there mighthave about this. I got one response which basicly said the heads are junk(said they are 2 barrel 350 chevy heads) and combined with the camsituation you described makes for a dog of a motor. So I'm wondering;what would be a good set of heads to replace them with or should I suggestmy friend to spend the bucks to rework the stock heads? I hear there issome possiblitiy that 455 heads will work. As for the exhaust situtationit's amazing the aftermarket hasn't jumped on the dual cat/H pipebandwagon for these cars! I fully expected someone to refer me to a dualcat/H pipe mfgr. If anyone has experience in determining which intakemanifolds will work and produce good power that would be much appreciatedalso. Thanks again!
oldsmobile 403 : -> A good friend of mine just purchased a builder 79 TA. After buying-> it he found out it had an Oldsmobile 403 in it. Does anyone know-> what types of mods can be made to the olds motor to make it pump out-> some ponies and still remain emissions legal? The goal is to get max-> HP while still staying emission legal The Olds 403 is a *good* motor. It's wildly oversquare - 4.35 bore x3.39 stroke - and revs up real nice. As supplied in the TA it's pretty choked up. You need to swap the camfor something around 225 degrees @ .050, 108 or 110 degree lobe center.The valvetrain is nonadjustable. Some cam grinders make their cams tothe standard Olds base circle so they'll work without changing the restof the valvetrain; others expect you to buy their adjustable rockerkits. Check before buying! Buy the complete kit, cam, lifters,springs. A pair of 2.5" inlet catalytic convertors, a crossover tube,2.5" pipes, and some free-flow mufflers will also help. Offenhauser andEdelbrock make some decent intakes. You should have 4A heads with the2.00/1.50 valves, which aren't bad. You could bump compression with aset of 350 heads if you wanted, but it probably wouldn't be worth thecost and effort unless you had a bad head to start with.
oldsmobile 403 : Get an Accel HEI Super Coil and an HEI advance curve kit. The stockdistributor gives very little advance, and the Olds likes advance. Mr.Gasket, Moroso, and others make advance kits for under $10. When the engine wears out you can fit in a 425 Olds crank with a littlefiddling and wind up with about 490 cubic inches.What kind of lift would you suggest? Do you know if 455 heads will work?Seems like the exhaust valves are a little bit small at 1.5 for a 400 cimotor. Are the intake runner volume and exhaust runner volumes capable ofdecent flow without a lot of head work? Are you suggesting a custom groundcam or off the shelf unit?How much fiddling is a little fiddling? Does it require different rods orcustom pistons? How prevelent are the 425 cranks and where might I findone?-> have about this. I got one response which basicly said the heads are-> junk (said they are 2 barrel 350 chevy heads) I'm surprised someone didn't pop up and claim they were InternationalHarvester heads.
oldsmobile 403 : There's nothing wrong with the 403 heads. You can raise the CR byusing certain of the 350 heads, but you'd be getting 1.875 intake valvesinstead of the 403's 2.00s.-> my friend to spend the bucks to rework the stock heads? Don't mess with them unless something's wrong. You can put the moneyto better use in other places.Nope. The International Harvester heads show up on American Motors V8's, 304to 401. Trust me. Lift isn't that important. The duration and lobe centers will havemuch more effect on your mildly-modified motor. Don't worry, be happy. They'll bolt on, but you'll lose power unless you want to invest innew pistons. Not a worthwhile swap unless you're going to tear theengine down.-> Seems like the exhaust valves are a little bit small at 1.5 for-> a 400 ci motor.-> Are the intake runner volume and exhaust runner volumes capable of-> decent flow without a lot of head work? Runner volume is a practically meaningless piece of information, on thelevel of "this head is painted blue, whereas this other one is paintedred." You see runner volume figures because runner volume requiresabout $2 worth of equipment to measure, while you need a flow bench togive meaningful figures, like In general larger runners flowmore air, but there's much more to it than that.
oldsmobile 403 : -> Are you suggesting a custom ground cam or off the shelf unit?Engine tear down is a distinct possibility......... Why is it that the455 heads require different pistons, compression ratio?-> Seems like the exhaust valves are a little bit small at 1.5 for-> a 400 ci motor.So, you think the 1.5s won't hold it back given a good cam, intake andexhaust?By the way, what power level are you talking? What kind of HP/Torque canbeexpected from making these kinds of mods with the Olds 403? If we'retalking 300HP or better then we are on the right track, otherwise it's time toswitch to some other strategy. I'm after some decent HP for my effortsand it needs to be able to pass the sniff test. -> Are the intake runner volume and exhaust runner volumes capable of-> decent flow without a lot of head work?I was just wondering, comparison wise, how good these heads are comparedto other possibilities for this engine. Different heads or mods to theexisting heads aren't out of the question. Not afraid to tear it down,all the way if neccessary. Just like to know what I'm getting into,compatability wise, before the machining and assembly stages take place. Don't like surprises!
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