Olds 403 Build

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88hurstolds

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Jun 24, 2008
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Some were curious on the 403 dyno results from Friday:
430hp @5500rpm and 471ft-lbs at 4100rpm, my guess was 430/475, not a bad guess
1f642.png


Specs: 410.6 ci, 9.789:1 final CR, includes top ring piston to cylinder wall gap otherwise it was 10.2:1 prior to final assembly
.030 cometic gaskets
#6 heads shaved to 57cc, .080 cut from Performer RPM intake to compensate...
fully ported, large valves flow 262/186 @.600, ported by Dick Stolpa of Rocket Racing, flow better than C heads
HS rockers, Smiths Bros push rods, modified Comp Cams guide plates for 7/16 studs
330 forged steel crank
Lunati Voodoo cam 219/227 .499/.510
Quick fuel 650
7 quart pan and HV Oil Pump

Unfortunately its not going into a G-body, I built this engine for a '77 Pontiac Can Am, 1 of 42 high altitude cars that was originally equipped with an Olds 403
I did build the driveline to with a G-body in mind: 3.73 posi, TH2004R, CK Performance billet HS converter
and cant forget the Lightning Rods...
One of the dyno runs to 5k rpm:
403.jpg

403a.jpg

35542690_10160535170755716_8962185643836833792_n.jpg

41406750_10160863535415716_8346687079081574400_n.jpg

403dynosheet.jpg
 
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Oct 14, 2008
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Just shows what good heads will do, even with a smallish cam for the compression and cubic inches. How was the torque curve? What length pushrods did you end up using? That should really move that heavy boat very well. My build will be very similar expect maybe a hair less compression and 14 more ci due to more stroke. My #6 heads also have filled crossovers, port and bowl work but only 2"/1.625" valves, Comp double springs, positive seals, 55cc chambers which I need polish to lower compression, intake face cut just enough to fit an intake with factory shim gaskets. I only have 91 non ethanol locally.
 

TURNA

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Jul 24, 2009
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Who built it?
 

JAMCAR223

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Jun 6, 2014
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Thanks for providing the specs. I will use this info on my 403 build, to help select a parts combo.
 
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Oct 14, 2008
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Me for assembly, finally finishing it this year, sending off the block to the machine shop once I get the studs and girdle, I have new Clevite cam bearings as well. The heads were picked up from a guy in Montreal, done by a well known porter, went 12.7's in his 73 Delta 88 with a 350, he went 455. I got the stroker 330 crank from Smitty, Ohio crank ground it. I picked up used the custom 550 gram Venolia 4.390" 21cc dish forged pistons with a .043" top ring, 1.5mm second and 3mm oil rings on 6" sbc Scat rods with the 2" rod journal. I am picking up a 5 main Halo as well. I also have Scorpion 1.72 SBF true roller rockers, studs and guide plates. I getting the longer main studs, cam(220/220 .504 with 1.6, .542 with my 1.72 to 1 rocker arms) main bearings, oil pump and pick up from Cutlassefi. I wish I could afford the $500 Canadian for the Canton oil pan, a baffled stock replacement will probably go on but can always change my mind. Since it has iron heads, just Felpro gaskets, including the head gaskets. I currently have a custom 800 cfm Everyday Performance Qjet with an easy adjustable APT, I may send it to Ken for a retune along with a notched divider Performer RPM intake. I am going with a 2025 rated stall, will probably actually flash much higher, TH350C with Trans Go shift kit and tractor hydraulic fluid, will see how long it lives and a 2.78 8.5" Type O rear either open or lunch box locker. I will either stay with Sanderson 1 5/8"shorties or go up to Hedman 1 3/4" shorties and my custom 2.5" compact X pipe dual exhaust with Aerochamber mufflers, I may switch to maximum flow mufflers. Going in my 70S Cutlass.
 
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88hurstolds

Royal Smart Person
Jun 24, 2008
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Just shows what good heads will do, even with a smallish cam for the compression and cubic inches. How was the torque curve? What length pushrods did you end up using? That should really move that heavy boat very well. My build will be very similar expect maybe a hair less compression and 14 more ci due to more stroke. My #6 heads also have filled crossovers, port and bowl work but only 2"/1.625" valves, Comp double springs, positive seals, 55cc chambers which I need polish to lower compression, intake face cut just enough to fit an intake with factory shim gaskets. I only have 91 non ethanol locally.
Torque curve is almost completely flat from 3000 to 5500
440 @ 3000
471 @ 4000
431 @ 5000
Crosses at 5100 @ 420
I went with that cam for drivability and to keep the low end torque and with 22inHg vacuum I can run power brakes and have good fuel economy for daily driving. I could have gone with a bigger roller cam but the gains are not much more and not worth losing torque.
Pushrods are Smiths Bros, not sure on the size, they came with the heads.
Flow is everything... anyone can copy this build but if the heads are heavily ported then you're not going to come close.
These heads are off a '70 Rallye 350 that was consistently running low 10's.
There's more in this engine but I would need to install a girdle and sacrifice drivability along with $3500 more in parts/labor. At that point I can build a 600hp 496...
47680599_10161200768460716_8993087856222142464_n.jpg

47679568_10161200766105716_4233940513713029120_n.jpg

47576822_10161200765625716_5050130298776322048_n.jpg

47573107_10161200763460716_2451393425036017664_n.jpg
 
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TURNA

Rocket Powered Basset Hound
Jul 24, 2009
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Flow is everything and it looks like whoever built it didn't port those heads much.

Just a quick clean up.

Those ports should look like mirrors.
 

88hurstolds

Royal Smart Person
Jun 24, 2008
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Flow is everything and it looks like whoever built it didn't port those heads much.

Just a quick clean up.

Those ports should look like mirrors.

:rolleyes:
You're not familiar with Olds heads I take it.
The roofs on those ports have been raised significantly to BBO size if you look at the water port an unported SBO runner will be even with that port, these require a BBO intake gasket...
Not to mention the flow numbers have increased to 262/186 @.600 from the stock 233/153 @ .600 and stock C's flow at 259/162 @.600,
Also they're used heads and they were ported for a max effort build by one of the best Oldsmobile porters in the nation Dick Stolpa (RIP) at Rocket Racing.
http://wildaboutcarsonline.com/cgi-...0382228543&action=viewad&itemid=9990405209377
403port.jpg

fel-ms99471_xl.jpg
 
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TURNA

Rocket Powered Basset Hound
Jul 24, 2009
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Heads are heads

gasket matching is fine

those valve guides should be almost non existent

not to mention all the ridges left inside the ports

See the difference in the walls




See the difference in the guides


 
Oct 14, 2008
8,806
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Melville,Saskatchewan
Stock #6 heads would be more like 190/160 for flow and around 210/165 with 2"/1.625" with a bowl hog under the valves, my other #6 heads have 2.05"/1.56" valves with the bowl hog opened up the bowls. Stock big valve BBO heads flow around 215/170, not impressive but better than the 1 through 5's 190/160 along with 8, J and 4A's 190/120 stock numbers. My #6's should be in the 220 range, ports are bigger than stock and guides hogged down. Filling the huge crossover's is supposed to help a lot as well,mine are filled. It does make cool weather running shitty from running them on my 350. My divider's aren't welded but the gap is very small compared to the awful later "#A" heads. I would believe the flow numbers from Rocket Racing especially considering Ralleye Bob's car really hauls *ss and those heads pushed it into the 10's.
 
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