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Old 03-25-2004, 01:16 PM
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olds 403?

Hey, Well I have another question on a oldsmobile motor. On a olds 403 do they have good power and how can you tell if its really a olds 403?

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Old 03-25-2004, 01:36 PM
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The only way I know to tell the differance is with the casting #s. as far as performance,in stock form nothing to get excited about, due mostly to its very low compression. You can coax some decent power out of it with bolt ons & a little bit of camshaft. If planning to rebuild it, deffinetly give it some compression. The 403 was a smog era V8 with decent torque & pretty decent potential as a mild performance street engine. John
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Old 03-25-2004, 01:55 PM
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It'll say "403" in big letters under each side of the exhaust manifolds on the block. To bump up the compression to 9.6:1 replace the heads with 5A heads from an 80's 307 non-roller.

The heads should also say "4A" on them on top of the front or back freeze plug port, right next to the exhaust runner.
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Old 03-25-2004, 01:55 PM
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Meka,
As John has said, this engine is not very impressive in stock form. But it has outstanding potential for a performance engine. It has basically the same bore/stroke ratio as the 302" Chevy and it has 6.0" rods, as I recall. Therefore it is a large bore, short stroke engine with a decent rod ratio. One of the other limiting factors of the engine, besides low compression, is restricted breathing. This engine can be a real screamer with good heads, cam, compression, etc. Just be prepared to spend much more for Olds parts than you would on comparable Chevrolet, Ford or Chrysler.
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Old 03-25-2004, 02:01 PM
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These engines do not suffer from "restricted breathing" The 4A(83cc) heads that came with the 403s were 2.000 intake valves and large intake and exhaust runners.

The 5A heads while reducing the intake valve size to 1.75, will still yield much more gain than loss. 5A(64cc) heads are also big intake exhaust runner heads like all other olds heads and intakes other than 6A and 7A of the 80s, and 10 and 2A for the 260.

Oh yeah.. if in your quest you happen to come across 10, or 2A heads these yield in the range of 10:1 on a 403. They are the same design of all other olds SB heads just material was added to the runners which can be removed and the valve seats have to be inlarged. Still looking for a set of these.

Last edited by 87442lover; 03-25-2004 at 02:12 PM.
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Old 08-30-2005, 10:04 PM
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Hey I Did The Same Thing With My 77 Olds It Is Hard To Find Info But To Build Power With A 403. Find A Machine Shop And Get Some C Cast Heads Fitted From Like A 425 Olds Which I Found In A U-wrench It For 30 $ A Mild Cam And Performer Intake I Could Turn Tires Till They Blew Up With A Solid Main Trans Am Motor
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Old 08-31-2005, 11:14 AM
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http://www.442.com/oldsfaq/oldsfaq.h...his%20Document


I don't think you need Edelbrock heads or anything too fancy to get 400hp out of a 403. Keith Black flat-top pistons and the original 4A heads with major exhaust port work would be a good starting point. Add a Performer RPM intake, 1.75" headers, and a cam with 220-225 intake duration and .500" lift, and you should be there.



I own a 77 Olds Cutlass, that in 95 I rebuilt the 403 back stock, bored .30 over, i wish i would of decked the block to get my quench down, and put #5 350 heads (butt did not do it, I rebuilt the 403 and stock heads plus a performance rebuilt tranny & PST front end kit and replaced all 4 coil springs, i had a life changing event so the the Olds has around 650mi onit, it's benn started every 2 weeks and a 2 to 4mi trip every month or sometimes every couple months, its been a garage queen for last yrs, PIC AT THE BOTTOM OF THIS)

My Plan now is a set of Olds 350 #5 heads milled some (i just picked these #5 Heads up ) and a ultradine cam some where around 220-225 intake duration and .500" lift

torq converter 2200 to 2600 RPM
crossover block
105 closed 280 to 300 open valve spring
800cmf edelbrock

http://www.442.com/oldsfaq/ofhed.htm...964%20-%201990

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

A stock 403 Olds engine has tons of torque. Carbs aren't the problem. The problem is the heads. Their combustion chambers are too large, around 83ccs. This results in a compression ratio around 8.0 to 1. Try to find a set of 350 heads from 1973 or before. This will raise compression enough to even think about HP. Before you think about a carb I would think about an intake manifold, if your's is stock.



http://www.442.com/oldsfaq/ofe403.ht...IDEngineDetail
The 403 responds well to a bit more camshaft and compression. I used earlier 350 heads ('68-'72 will do it, but the '72's are the best) to raise the compression, and an Edelbrock Performer-grind cam (these cams are available from other sources than Edelbrock, who I suspect purchases them from another supplier).


If you add 72 or earlier 350 cylinder heads, your compression will be abound 9.5:1-10:1. It will increase your HP considerably, though you'll probably want to add a cam that can take advantage of that high compression. If matched with an Edelbrock intake, I'm guessing around 300 hp, though that's a really rought estimate and depends on the parts that you use. Most 350 heads will boost compression, not much boost from the common #8 heads.

Yeah, what he said. My calculations say that unmachined 64 cc heads such as '68 to '72 350 heads would boost the stock 403 to 9.50:1 compression. Mill the heads 0.030" and you have just over 10:1 CRatio. This assumes 0.040" head gasket, and a few other assumptions.

Get '72 350 heads [hard xst seats], install the 403's bigger 2.000 valves or even larger W30 2.072" valves, and limit your expenses. That motor will kick *** w/ the appropriate cam, intake, exhaust. As for those who doubt the ability of the 403 to handle power with its open main webs, you might call a racer who uses one.

Any 350 head will raise compression a little to a lot. Depends on combustion chamber size.
A set of 1968 to 1972 heads will raise compression, and allow the engine to make more power.
Use the 2.00" intakes from the 403.
Ream the head bolt holes for the 403's " head bolts. You'll have to use premium gas, and perhaps recurve the distributor.

Any head from the #5's to the #7a's (basically, from 1969-1972) will have the smaller combustion chambers, and will give you decent compression, and flow well too. The 7a heads from the 1972 350's have the advantage of factory hardened exhaust seats, if that is a concern to you.



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Old 08-31-2005, 11:16 AM
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these guys can answer Any Olds Question, http://www.realoldspower.com Mr. Olds Knows his Stuff
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Old 09-01-2005, 09:42 PM
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wish my ols looked like that one mine is still in the restoration process but my motor just blew up i was to hard on the 200000 mile motor and it has no compression left. and were can i find flat to pistons i called everywere and they all said the only place to get them is mondello. they want a fortune for them
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Old 09-06-2005, 10:58 AM
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K B makes a nice Olds 403 Piston





http://www.kb-silvolite.com/index2.php



i've heard a lot of horror stores bout mondello, at one time he was top notch, but i heard management has changed.

Mustangsaly
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Old 09-10-2005, 05:15 PM
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[QUOTE=engineguy]Meka,

It has basically the same bore/stroke ratio as the 302" Chevy and it has 6.0" rods, as I recall. Therefore it is a large bore, short stroke engine with a decent rod ratio. QUOTE]

Then it would be only 302 cubes wouldn't it????
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Old 09-10-2005, 05:23 PM
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Quote:
Originally Posted by Mustangsaly
K B makes a nice Olds 403 Piston





http://www.kb-silvolite.com/index2.php



i've heard a lot of horror stores bout mondello, at one time he was top notch, but i heard management has changed.

Mustangsaly
That is 7.9 comp ratio..... still have to change to 350 heads
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Old 09-10-2005, 07:30 PM
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Quote:
That is 7.9 comp ratio..... still have to change to 350 heads
the KB pistons were designed to give 9:1 (or close to that) with the factory 4A heads (83cc). With a 350 head (70cc) the compression would be well over 10.5:1.

Correct me if I am wrong, this is what I was told when I inquired about these.

BTW, I would still rather use a bigger dish pistons with the early 350 heads that flow more with a smaller valve than the KB's with the smog 403 heads.
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Old 09-10-2005, 08:42 PM
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I Wish I Would of Decked my block and went with some KB Pistons, With a plan of Shooting For around the 9.5.1 CR Range, and Run the Stock Olds 403 83 cc Heads (Maybe milled them a little) Them 403s Will Eat Some Big Cam

Just My Opinion I Guess
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Old 09-10-2005, 10:15 PM
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[QUOTE=xntrik]
Quote:
Originally Posted by engineguy
Meka,

It has basically the same bore/stroke ratio as the 302" Chevy and it has 6.0" rods, as I recall. Therefore it is a large bore, short stroke engine with a decent rod ratio. QUOTE]

Then it would be only 302 cubes wouldn't it????
N o, he said same ratio...not sizes
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