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Old 11-25-2007, 12:32 PM
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Should I build an Olds 403?

I was starting to work on a Chevy 350 I was given, but have recently put the breaks on it. I've been given a 1977 Olds 98 with a 403. I don't plan on keeping the car itself (I'm not into the body style and would rather not mess with smogging the car), but am considering pulling the 403 and rebuilding it to stick into a pre 73 GM car. For some reason I keep coming across engines and haven't found the right cars yet.

I've done a little research and found that this engine has some of the same faults (overheating and blowing head gaskets due to the siamesed cylinders) as the 400 (now a 406) in the El Camino my dad and I have, but it also has a larger bore (some websites claim it's actually the larger that a 454's) and a longer stroke. Apparently switching the heads, intake, and cam can turn this into a decent enginewith a load of torque.

I wanted to get opinions on whether this engine is worth building, if it's really comprable to the 400, and if anyone knows if parts are available? What are the obstacles of removing emissions equipment from an engine like this (other than legal), and what small block chevy items (i.e. heads) may be compatable? Last question, since this is basically a GM small-block,, will it mount up to most GM vehicles with stock motor mounts?

Thanks for any help you can provide,
Josh

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Old 11-25-2007, 12:53 PM
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First, this is not "a GM small block". Olds motors have nothing in common with Chevy motors. Motor mounts are different, bellhousing bolt pattern is different, accessory brackets are different - it has as much in common with a Chevy as a Ford motor.

Having said that, I think the 403 is a very underrated motor. As you pointed out, huge bore, great bore/stroke ratio, a lot of potential. The big drawback is the windowed main webs. The 403 was designed in the dark days of the late 1970s and every trick was tried to save weight. The block casting is very light (especially as compared to an Olds 455, for example) but high HP motors have a tendency to spit out the crank. Dick Miller sells a full girdle that fixes this problem.

The 403 shares most parts with all other Olds small blocks and except for deck height, is very similar to Olds big blocks. My dream 403 starts with a forged crank from a 64-67 Olds 330 (same stroke as the 403) and big block Olds heads. These heads were fine on the Olds 400 big block, so the 403 small block should also be able to flow enough air to use them. You'll need to use a Performer RPM and port match it to the larger big block ports. Engle dual pattern cams work best in an Olds.

Any GM with an optional Olds motor can accommodate the 403. For example, to put the Olds in an ElCo, you need the equivalent year Cutlass motor mounts and frame mounts. The frame will already be drilled for the Olds mounts. You'll need a BOP or dual pattern trans. Good luck.
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Old 11-25-2007, 05:31 PM
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I don't share the same fear of the windowed mains. just because they're windowed doesn't mean their weak.

Joe Mondello used to spin 403s to 7000 rpm without a girdle, and even offered them as a crate motor.
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Old 11-25-2007, 05:56 PM
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i'm pretty sure the first year of the olds 403 didn't have the windows above the main webbing. i think they are solid, i think the first year was the 77 so you might be in luck.

i like the 403 olds motor. i had one i put in a 80 cutlass & it would fry the tires in first gear at 35 mph with an airplane gear.

i always wondered if the 455 olds crank could be made to fit the 403 block. the 403 has a bigger bore from what i remember & with the longer stroke 455 crank, for an olds stroker. it would be a beast but i wouldn't want to spin it over 5 grand.
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Old 11-25-2007, 07:52 PM
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455 crank has larger mains which could be turned down, but then you'll have a pretty weak crank. The 455 is also an incredibly long stroke; more than the deck height of the 403 will accomodate.

Many guys find a forged 425 crank and turn down the counterweights to fit the "small" block olds. That's about the limit of stroke in a 403.
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Old 11-26-2007, 12:55 PM
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Quote:
Originally Posted by 406 ss monte
i'm pretty sure the first year of the olds 403 didn't have the windows above the main webbing. i think they are solid, i think the first year was the 77 so you might be in luck.
The solid main web 403 is an urban myth, despite what Mondello may say. There have been many offers of cash for proof. No one has collected yet. I have two 403 blocks in the shop, one from a 77 and one from a 79. Both have windows.

I will recommend a thorough deburring to remove potential cracks and stress points before building one.
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Old 11-26-2007, 03:15 PM
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I have a 403 in a 77 Olds Cutlass Supreme 2DR. that I rebuilt. I put #5 350 Olds Heads on mine to raise CR. watch out the 403 re-builder pistons are .20 shorter that original pistons. Mr. Olds knows a KB piston to cure that problem. my 403 has never got Hot B4 or after boring .30 the bottom end is a lot stronger than people say. theres a KB piston that can get the CR up with the bigger 403 heads. the 403 has a bigger bore than a BBC does.


As Was Said, The solid main web 403 is an urban myth




heres some Olds Info

http://www.442.com/oldsfaq/ofe403.ht...IDEngineDetail

head info
http://www.442.com/oldsfaq/ofhed.htm#Heads


http://www.442.com/oldsfaq/oldsfaq.htm





good Olds Info Here, do a search on the 403 and read whats posted and ask questions there.
http://www.realoldspower.com/phpBB2/index.php

mondello was the Olds man, but now the mondello business is a joke.


this guy builds and races the 403s he is a 100% Olds Nut ! he goes by Mr. Olds on realoldspower.com Mr. Olds build a 425 or 450HP 403 street engine. you can call FCR Performance and talk to Terry a.k.a Mr. Olds hes a nice guy and can answer any Olds 403 question you have. he knows more about the 403 than mondello
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Old 11-26-2007, 04:17 PM
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Would the main web hold up to 450 - 500 hp and lbs.-ft and a 5500 rpm limit? If I plan I trying to go this high, would I need a girdle?
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Old 11-26-2007, 04:44 PM
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Quote:
Originally Posted by El Co 406
Would the main web hold up to 450 - 500 hp and lbs.-ft and a 5500 rpm limit? If I plan I trying to go this high, would I need a girdle?

yup again I can't stress enough to call terry at FCR Performance. toll free #
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Old 11-26-2007, 04:54 PM
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Quote:
Originally Posted by El Co 406
Would the main web hold up to 450 - 500 hp and lbs.-ft and a 5500 rpm limit? If I plan I trying to go this high, would I need a girdle?
on www.realoldspower.com look at the engine builds & combos section.

look at this

403 Olds 9.70 compression 491 hp 489 tq

http://www.realoldspower.com/phpBB2/...ic.php?t=21960


http://www.realoldspower.com/phpBB2/...ic.php?t=24363
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Old 11-27-2007, 08:38 AM
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Thanks for all the help, looks like this might be an engine to keep for a project after all.
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