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Old 09-18-2002, 05:44 PM
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Post Olds power mods

3 years ago, a friend of mind bought a 79 Hurst/Olds from my brother. The car had a beefed up 403 Olds, Turbo 350 and 4.10 gears. It had a very wild Lunati Camshaft that liked to bend pushrodswasn't streetable. I replaced the Lunati with a Comp 280 Magnum, put on a Performer RPM intake with 750 Carter AFB, and went through the TH350 and put in a TCI street fighter converter. It was very nice to drive around with these mods, and at the trace ran mid 13s. This car runs very fast to 60 ft, but it runs out of breath around 5000 RPM. We would like to get down in the 12s, so should we just cam it up, or look elsewhere. Trap speeds are only around 92 MPH, so it really lays down on the big end, I would have to think the 403 should pull a little better than that up high, but I'm not and Olds man, so maybe the things don't like to twist.

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Old 09-18-2002, 08:46 PM
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OK; I'm not a heavy duty racer, I'm more of the shade tree type but here's what I know about 403s. The "claim to fame" of the 403 is it's cavernous cylinders (4.350")and long rod but short stroke. That thing will pull like the bejusus with the right cam and moderate head work. Use the largest valves you can stuff in there, 2.07" and 1.625" valves come to mind. Do the usual moderate bowl blend and port work on a set of the preferred 60s and early 70s heads. All you need is about 9.0 to 9.5 to one compression. Then install the cheap SSI 214/224 or the 224/234 cam. That 4.10 rear gear is too low in my view so lower it to no more than 3.73 or even 3.55 and you should keep the motor in the rpm realm where it shines. Run some 1 3/4" headers with 2 1/2 exhaust pipes and the Performer RPM manifold with a tweeked Q-Jet and I bet she'll tickle the 12s and do that for a long long time. Incidently, I've had a 81 Cutlass for 14 years and in it, I have run a Olds 350, 403 and now a 455. All motors ran solidly and dependably. My 455 is faster than the 403 but not as much as I thought it would be. Those 403s run well but you have to know a few secrets, using old heads is one of those secrets!
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Old 09-18-2002, 10:06 PM
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what about joe mondello racing engines, if anyone knows how to get you into the 12s. he does, i would contact him regarding some head work.

the other route is putting a centrifugal supercharger on it, which can add 35-65% power in about 10 hours, and you would still have your streetable car that ran like a stink when pushed
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Old 09-19-2002, 04:20 AM
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The one thing that is real restrictive on the Olds engines is the heads. Even with good porting, they don't seem to respond as well as they should (in my opinion). Edelbrock makes a real nice head for the Olds and should wake this engine up considerably. I agree with dallam, on paper the 403" looks like a real killer. With big bore, short stroke and long rods it shares very close bore/stroke and rod ratio (rod length to stroke) specifications with the 302" Chev engine. Limiting factor for the Olds is the aforementioned lack of breathing, large bearing surfaces (main & rod) and the clunky valve train. Breathing and valve train are fixable and coupled with a good carb/intake and header/exhaust system these engines can be made into real beasts. We used to build a lot of 425 and 455 Olds engines for flat bottom boats, both jet and v-drive. The Olds has tons of low end torque and could keep up with anything on the lakes.

[ September 19, 2002: Message edited by: engineguy ]</p>
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Old 09-19-2002, 07:05 AM
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Yes,the 403 shouldn't be thought of as a max effort race engine. The "winowed main" block simply won't allow sustained high rpm and the heads and valve train are a bit of a challange but the engine can be made to work. The heads are restrictive but even a minor port job will wake up this sleeping tiger. What this motor is, is a great street motor. If built with just of few of the modifications listed above, a bone stock looking 2nd generation Fire Bird etc. with STOCK exhaust manifolds can take on a new Z-28!And we're talking a 1500 dollar motor with a stock manifolds and a RV cam here! Think I'm full of malarkee? Well here's just one site that will help turn you into a believer...www.texastransams.com. Good luck

[ September 19, 2002: Message edited by: dallam1 ]</p>
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Old 09-19-2002, 07:39 AM
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the problem with the heads is the compression, around 83cc 8.2 to 1 or worse. get some older small block heads, some good ones will get u to 9.5:1 to 10:1 once you drill out the bolt holes the'll bolt right up.with a little intake work u can even go with big block heads.
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