C heads fit on a 403 olds?

[DROLDS84]

I have a 403, .60 over, J heads, and RPM intake(milled and port matched to fit BBO heads). Ran 11.89 in the 1/4 with full weight '87 442 with 373 gears, 28" tires, and Edelbrock 750.


The idles nice and lumpy at the lights....cruises like a dream...and
stays cool on long trips. I love Olds motors!

With the C heads, and added breathing the motor will have, you'll be pushing the higher rpm bandwidth further out... I'd highly suggest strengthening/lightening your crank assembly! Get a girdle, and lighten and re-balance your rotating mass. Those windowed main webs in the 403 will always be haunting you!

Thats pretty damn good...what are your cam specs.Also were you running slicks?

 

[olds307 and 403]

He already has a Performer RPM intake. A rev limiter is a good idea, keep it below 5500 rpm for sure.

 

[Gozer442]

It's a Comp cam, 500 lift... but the 1.7 crane aluminum rockers and the degreed cam install make it a little more nasty sounding. The guy I bought the motor from (and who hand built it as well) had it in his "test" car which only saw some track time. He was the one that showed me the time slips for the motor. I'm pretty sure it was a TH2004r, with a 8.5" and stock suspension...not sure if it was slicks or not...but I'm leaning towards that it was on slicks.

 

[High Roller]

Hope you ain't going to just get, and bolt on? Besides having them machined for 1/2" Head bolts $50, have a reputable Olds builder go through them, like Knowlton Thunderheads. Install bronze guides, Teflon valve seals (DO NOT USE CHEVY ONES), get a competition valve job, blend bowls, port/polish the ports and combustion chambers, mill heads 0.030", Fill heat riser passages with zink alloy ZA12, Braze the center divider on the Exhaust Port, and surface milled. Purchase new 2.120"/1.710" stainless valves, and get them undercut, and new springs/retainers for your cam, and use .027" cometics head gaskets, also run BB intake gaskets

Get them C heads to flow.
226/128 (stock) to 265/175 at .500 lift

 

[fleming442]

...still need a cam to take advantage of the increased flow.

 

[High Roller]

He has the RPM Cam In it, 224/234 496/.520

 

[fleming442]

Exactly. My BTR cam in my 468 is only .491/.510 w/ 236/242 on a 110, and it's awesome.

 

[olds307 and 403]

Those 243 cfm stock intake numbers are about 30 cfm high according to other C heads tested. They are still much better than J heads.

 

[pontiacgp]

I have a chance to buy C heads to replace my j heads.But will they fit on a 403 with a edelbrock rpm intake? I know they can fit big block and small blocks but just wondering if it needs anything extra to fit the 403

I don't know much about Olds engines so I was hoping to find the answer the thread but I'm still confused. The way I read the op is that the C head can fit a big block and a small block. What am I missing?.....😵

 

[Gozer442]

The only difference with big block, and small block Oldsmobile V8 motors, is deck height.... with BBO having a higher deck. Almost all the parts are interchangeable bolt-ons, with some of the parts requiring some modifications to fit like cranks and heads. All Olds heads are interchangeable...260ci up to 455ci. Many mistakenly call the 403 a big block, and the 350 "Rocket", or 350 "Gold Block", a big block... all small blocks. The 403 uses 1/2" head bolts, and the big block have 7/16" head bolts, so the BBO heads need to be drilled out to 1/2" to be bolted to the newer blocks... along with the port-matching on the intake. So, because the deck height is higher on a big block Olds, the BBO intake is wider, so it won't fit a SBO. Everything else is pretty much interchangeable!