I'm doing the 4-speed swap in my 82 Cutlass, with an Olds 350. I'm putting a set of Big Block C Heads on this engine as well. Now, since you can't run headers on these cars when using the factory 4-speed setup, I plan to run a set of dual exhaust manifolds, same ones used on the 70's 442's, as I heard they were good flowing manifolds, and there are reproductions being made of them now. I have found a place to get them from, but the one goofy thing is that they claim theres a difference between the small block manifolds and big block manifolds, and they sell a set to fit each application. So, being that I'm using Big Block Heads, wouldnt i want to use the Big Block manifolds, even though my engine is only a small block?
Exhaust Manifold Question
- Thread starter 82oldskid
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You'd want the small block set. It's not the heads that are the problem with the fitment but rather the difference in deck height between a SBO and BBO. They had to redesign the manifolds to fit a SBO because they are closer to the block and other pieces like the oil filter adapter.
Out of curiosity, why BBO heads on the 350?
Out of curiosity, why BBO heads on the 350?
ah, i see, thank you for this information.
and, as for your other question, theres a few reasons... firstly, i want to increase the power from this engine, plain and simple. secondly, i already bought the 350, so id rather just build it, than try to find a 455 for a good price. and thirdly, my motor is a 74, and from what i understand, the heads on it now are low compression heads. again, wanting to increase the power or this engine, so im getting rid of the emissions friendly heads, for something better. im not tryin to go balls-to-the-walls with power, but i definitely dont want it to feel like im running a healthy 307, and nothing more. that just defeats the purpose. not to mention, a decent 455 is not easy to come by in my area of the state. either that, or i just have bad luck, lol.
and, as for your other question, theres a few reasons... firstly, i want to increase the power from this engine, plain and simple. secondly, i already bought the 350, so id rather just build it, than try to find a 455 for a good price. and thirdly, my motor is a 74, and from what i understand, the heads on it now are low compression heads. again, wanting to increase the power or this engine, so im getting rid of the emissions friendly heads, for something better. im not tryin to go balls-to-the-walls with power, but i definitely dont want it to feel like im running a healthy 307, and nothing more. that just defeats the purpose. not to mention, a decent 455 is not easy to come by in my area of the state. either that, or i just have bad luck, lol.
82oldskid said:
I am not sure on what cc pistons came in that engine, but the 455 heads use larger chambers than the ones you have now. Pretty much, you will end up with a lower compression ratio and less power.
To be honest, you'd have to have one HEALTHY 350 to use big block heads on it. Most of the fast guys with 350's (in the 10's) are still using SBO heads.
If he has a '74 350, then the chambers on the #8 heads would be around 79-80cc's. The BBO heads have the same cc's so really he wouldn't be losing anything. However he's also not gaining anything either.
If it were me I'd try finding a set of 5,6,7 or 7a 350 heads to use on it. They'll help you up your compression ratio and would flow plenty for a 350. My brother has a set of the 7a heads on his 403 and it's got his '81 into the 13.1-13.2 range in the 1/4 mile unported or modified.
Also keep in mind that if you run the BBO heads you will need to run a Performer RPM intake on the 350 as it's the only one that has enough meat in the intake ports to port match to the BBO heads intake runners.
dan2286 said:
If he has a '74 350, then the chambers on the #8 heads would be around 79-80cc's. The BBO heads have the same cc's so really he wouldn't be losing anything. However he's also not gaining anything either.
If it were me I'd try finding a set of 5,6,7 or 7a 350 heads to use on it. They'll help you up your compression ratio and would flow plenty for a 350. My brother has a set of the 7a heads on his 403 and it's got his '81 into the 13.1-13.2 range in the 1/4 mile unported or modified.
Also keep in mind that if you run the BBO heads you will need to run a Performer RPM intake on the 350 as it's the only one that has enough meat in the intake ports to port match to the BBO heads intake runners.
Here are a few thoughts:
First, the aftermarket, alleged "W/Z" manifolds marketed for small blocks are NOT EVEN CLOSE to the real BBO W/Z manifolds. The BBO manifolds have individual runners cast into the manifold. The aftermarket SBO manifolds do not. There physically isn't room which is why the factory didn't do this on the W-31 motors. The aftermarket manifolds simply have a 1" deep divider between the two center exhaust ports. That's it. The rest of the manifold is identical to the factory SBO manifolds. The only other difference is that the aftermarket manifolds have the port for the single exhaust crossover pipe blanked off. The shape of the manifold isn't changed, the port is just not machined. You should closely compare these aftermarket parts to your stock manifolds and decide for yourself if they are worth $300+.
What part of the factory manual trans setup is causing you a problem with headers? If it's the clutch linkage, go to a hydraulic throwout bearing and the problem goes away.
As noted, the BBO heads have 80 CC chambers. If you want to run them, simply select the proper piston configuration to get the right compression. If you run the flattop 350 pistons, you'll probably be close to a reasonable CR, but again, you need to do the math for your particular combination.
You don't really need BBO or aftermarket heads to make 350-400 HP out of a 350 Olds. You do need to install the BBO valves in the SBO heads, just as the factory did on the W-31 motors. A little porting and you'll be amazed.
First, the aftermarket, alleged "W/Z" manifolds marketed for small blocks are NOT EVEN CLOSE to the real BBO W/Z manifolds. The BBO manifolds have individual runners cast into the manifold. The aftermarket SBO manifolds do not. There physically isn't room which is why the factory didn't do this on the W-31 motors. The aftermarket manifolds simply have a 1" deep divider between the two center exhaust ports. That's it. The rest of the manifold is identical to the factory SBO manifolds. The only other difference is that the aftermarket manifolds have the port for the single exhaust crossover pipe blanked off. The shape of the manifold isn't changed, the port is just not machined. You should closely compare these aftermarket parts to your stock manifolds and decide for yourself if they are worth $300+.
What part of the factory manual trans setup is causing you a problem with headers? If it's the clutch linkage, go to a hydraulic throwout bearing and the problem goes away.
As noted, the BBO heads have 80 CC chambers. If you want to run them, simply select the proper piston configuration to get the right compression. If you run the flattop 350 pistons, you'll probably be close to a reasonable CR, but again, you need to do the math for your particular combination.
You don't really need BBO or aftermarket heads to make 350-400 HP out of a 350 Olds. You do need to install the BBO valves in the SBO heads, just as the factory did on the W-31 motors. A little porting and you'll be amazed.
Sanderson makes a shorty header that fit very tight, should work. Get flat top pistons for your motor Speed Pro, Probe and CP? now makes pistons, gives you 9 to 1 or so compression. Your 8's are fine, just treat to a good valve job and maybe pocket porting under the valves. A mild cam is also a good idea, the factory is a .400 lift turd.
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