Olds 403 Head Upgrade

[foxtrot]

I rebuilt my Olds 403 afew years ago -- a basic rebuild with stock ported/polished(cheap job) heads, cam upgrade (Edlebrock performer) and flat top pistons. My question is with regards to the Edelbrock SBO aluminum heads. I have the opportunity to acquire a set of SBO Edelbrock heads on the cheap ($700). Has any here installed a set of these on a 403? What compression would I obtain with the upgrade? Do the heads flow better than the stock ported / polished (cheap job) heads? Is the upgrade worth the time for a back yard mechanic / weekend warrior?

Thanks in advance for the advice.

 

[kornball426]

From what I have ever read, and a guy I know with a worked 455 with Edlebrock he said the heads made a HUGE improvement in power over stock. And I think it was Car Craft, or Hot Rod did a build up shoot out between all the GM big inch motors and the olds guys said the Edlebrock head made a huge improvement in flow. All the engines used the Edlebrock heads except the Buick 455 which used T/A performance heads because Edlebrock didn't make heads for Buicks (I think they might now).

But with the 403's huge bore... I dunno, never did it, don't know anyone that has I'm sure someone here does though.

All I know is that flow wise, they're a big improvement over stock.

 

[foxtrot]

Thank you for your input.

I'm planning on possibly doing this upgrade after the winter once it warms up. 🙂 Just want to make sure that I'm not wasting my time even tho it always fun when I'm turning the wrench -- just hard to steal the time. ;-)

 

[FE3X CLONE]

Edelbrock doesn't make a small block head for the Olds engine.

The heads they offer are designed for the BBO engine. Bigger runners/ports, larger combustion chambers (77cc) etc.

Now this isn't really an issue for the 403 considering it's bore size is larger than any of the big block engines. In fact I believe it's the largest bore size of any production GM block.

The issues your going to run into:

1) You'll need a Performer RPM intake to port match it the heads. It's the only intake with enough material at the roof of the port to port it out to the BBO port size.

2) You'll probably want to mill the heads to get the CC's down in the 65-67cc range depending on your piston choice.

3) You'll need to convert to an electric fuel pump as the stock mechanical fuel pumps won't fit with the Edelbrock heads.


You may want to check and be sure they are really Olds heads first and not someone selling Chevy heads and figuring they'll fit an Olds engine (because it's all GM )

If they are truly Olds heads, then you'll want to find out what was done to them to make them "small block" heads. My hunch is they milled the crap out of them to get the CC's down.

 

[foxtrot]

Thanks for the info!

 

[joe_padavano]

Also be aware that due to the shorter deck height of the SBO, a mechanical fuel pump will not clear the E-brock heads. You'll need to run an electric pump. The chamber size of the heads is not an issue if you select pistons to match and thus get the correct CR. Frankly I'd rather do that than mill a bunch off the heads. Also, the Performer RPM is only one of several SBO intakes with sufficient meat to be port-matched to these heads.

 

[G-Body_Vet]

From what I've heard over the years, your best bang for the buck is the '71 "7" or '72 "7A" heads from a 350. Don't get them confused with 85-90. 307 "7A" heads. You will have to ream out the bolt holes for the 403's 1/2" bolts and add the steam holes. 403's came with 83cc heads and 8.0 to 1 compression. According to what I've read, stepping up to 64cc heads will put you around 9.5 to 1. That compression bump would really wake that engine up, especially with a cam.

This page has been around for years but it has some good info.
http://www.442.com/oldsfaq/ofe403.htm#E403 403CIDEngineDetail

 

[79loserbluebu]

I've never heard anything about steam holes, but you'll also need to drill the locating pin holes on the heads slightly larger for the pins on the 403. You'll also need the valve covers with the correct number of bolts.

 

[G-Body_Vet]

I've never heard anything about steam holes, but you'll also need to drill the locating pin holes on the heads slightly larger for the pins on the 403. You'll also need the valve covers with the correct number of bolts.

I could be wrong, but I thought the 403 heads had the steam holes similar to the Chevy 400 because they're both siamesed cylinder blocks. I don't want to give out the wrong info, so feel free to chime in.

 

[joe_padavano]

You'll also need the valve covers with the correct number of bolts.

Not really. The five bolt covers fit the ten bolt heads and vice versa. The gaskets are the same.