307 Exhaust manifold upgrades?

[81X11]

After climbing under my 88 Cutlass I have to say the stock exhaust is about the most restrictive thing I've seen....the drivers side pipe is rounted INTO the passenger side manifold?? And then a single pipe comes out of the rear of the passenger manifold to the actual exhaust. No wonder the poor car can't breathe!

So anyone have a suggestion for replacement manfolds? I want to dual the car out shortly, but don't want to attack it until I replace the manifolds...and I don't want to use headers, prefer stock manifolds. Will older Olds 350-403 manifolds bolt on....or do they have this "wrap-around" design too?

I can't imagine I'm the first person that has tackled this issue. Advice is welcome!

-Mike

 

[shotgun]

Troy Thorton started making these and eliminated the cross over.

http://thorntonmusclecars.com/

 

[xitabl442]

I had a mechanic tell me "Just make a blockoff plate for the right side and route the left down like normal. These motors are low compression and don't require large high flow exhaust systems."
Plus it's cheap!

 

[dan2286]

Pretty much all Olds engines had that design. You have the worst one of them all with the tubular log style manifolds and crappy small port heads. Older manifolds may help, but not by much.

 

[foxtrot]

Swapping out the intake manifold, valve train along with heads from a vin 9 motor would also help. Also if you're going to rebuild the engine, flat-top pistons would help. These mods along with the Thorton manifolds would really wake up the 307.

 

[foxtrot]

http://thorntonmusclecars.com/products/ ... -manifolds

 

[foxtrot]

I'm thinking that you should have the vin9 heads rebuilt/ported before you install them.

And

Here's the Napa part number for the Flat-top pistons:
Part Number: SEP W534NP

 

[joe_padavano]

The Thornton manifolds are virtually the same internally as the cast iron factory manifolds. Look closely and you'll see that the only significant difference is that the Thorton passenger side manifold is flat where the stocker has the crossover outlet. Even the factory W-31 motors used a cap over that hole. Your call if the appearance of duals is worth $300 vs. virtually free for a cap. Frankly, I'd just get the 1981-84 307 cast iron manifolds, which retain the O2 sensor if you need it.

 

[81X11]

The Thornton manifolds are virtually the same internally as the cast iron factory manifolds. Look closely and you'll see that the only significant difference is that the Thorton passenger side manifold is flat where the stocker has the crossover outlet. Even the factory W-31 motors used a cap over that hole. Your call if the appearance of duals is worth $300 vs. virtually free for a cap. Frankly, I'd just get the 1981-84 307 cast iron manifolds, which retain the O2 sensor if you need it.

I think I'll just look for an Olds 350-403. ; )

For now I'm going to install an new cat converter and 442 cat-back dual exhaust. At least it'll sound better, and I bet the cat is a little clogged anyway.

-Mike