455 using 307 exhaust?

[cjldevildog]

hello everyone and happy thanksgiving!
i have an 86 cutlass that had a 307 in it and is now in the process of getting a 455. i am wondering if i will need to get new exhaust manifolds or if i can use the ones off of the 307. they look like they will bolt right up however i am curious as to weather or not it will hurt performance. i have looked into headers and also some manifolds off of an older cutlass with the 455 but they all are more than i feel like spending right now. any input is appreciated. thanks alot!
Chris

 

[historyg]

yes it will hurt performance, as far as i know, and i am still learning, the 307 exhaust is restrictive, as i have one and its a single manifold that goes from both ends back to one single exhaust. its like a human using one lung, your vo2 would just not be the same with only one working lung. Try to source another one, maybe from a older rocket, but i could be wrong on this one. ANyways Happy Turkey day enjoy hope that 455 roars.

 

[joe_padavano]

Would you spend the effort to swap a 455 into your car and then run a one barrel carb on it? Of course not. Same issue with the 307 exhaust manifolds. The tubular welded steel manifolds used on the roller cam 307s are especially restrictive and have smaller ports than even the cast iron manifolds used on the early 307. Neither one is a good choice for a 455. Spend the money, get the 69-72 W/Z manifolds.

 

[madmaxstyle]

stock 307 exhaust piping is atleast 1/2' smaller diameter than the stock 455 you would think

 

[cjldevildog]

Thanks for all of the good info. I am going to buy some 455 manifolds for 250 off of eBay. Is that reasonable? They are new. I ended up buying a 72 gmc 2500 so that I can do the cuttlass up right and I don't have to drive I through the winter.
Thanks,
Chris

 

[foxtrot]

Theese are good:
http://thorntonmusclecars.com/products/ ... -manifolds

 

[FE3X CLONE]

Are they W/Z reproduction manifolds? If so, $250 is about right. But you'll have to factor in a whole new dual exhaust system as well.

I can tell you that a 307 exhaust sytem is definitely not enough to allow a 455 to breath properly. When I swapped my 455 into my '87 back in college I used the stock 455 single exhaust manifolds and hooked them up to my stock 307 442 cat-back dual exhaust.

I kept blowing out the exhaust donut gasket and manifold gaskets because there was so much backpressure in the system. I removed the catalytic converter but that didn't help any.
I had it at the drag strip one day and through the 307 exhaust, it ran a 14.7. The very next run it blew apart the connection where the stock Y-pipe connected to the "test pipe" and it ran a 14.2.
When I swapped to the W/Z manifolds and 3" exhaust with H-pipe it dropped to a 13.9.

You have to let that 455 breath!

 

[88hurstolds]

Your only other option is Hooker Super Comps. or Dick Miller Racing aside from the W/Z setup.
The only downside is that cast Iron is prone to cracking due to heat cycling and has poor heat dissapation.
I ran stock 455 manifolds with the stock crossover on a stock motor with stock exhaust and still had problems with the gaskets as well.
I'm not positive but I think the 455 manifolds are the same as the 350 manifolds and 80-84 307 manifolds but the outlet is .25" smaller??? I'd have to pull them out of storage to compare...
Don't use the 86-90 tubular manifolds, much smaller and restrictive.
I could be wrong but I don't see any difference in between the two stock setups, you can run it if you are not looking to hit the track but what fun is that

 

[FE3X CLONE]

For a mostly street car, W/Z manifolds and true duals with an H or X pipe would be plenty.

 

[cjldevildog]

thanks guys,
Im going to buy some reproduction w/z manifolds off ebay because the last thing that i want to do is reduce the output of this 455. does anyone have any ideas what im looking at as far as 1/4 mile times? im going to use the manifolds, stock qjet carb and it is a smog motor with a turbo 350 and 2. something rear end. i should have it running by this time next week, as long as it gets a little warmer her in indy and the manifolds come in soon. the 19 degree high temps have been slightly discouraging since im working on it in a non heated garage.
thanks,
Chris