2" or 2 1/2" straight pipe?

I'm gonna run straight pipe on my 58 Caddy 2 door. It has a 454 that's stock with a Demon carburetor. I don't plan on doing anything with the motor other than an EFI system a little later down the road. I was wondering what would be better for the dual exhaust, 2 inch or 2 1/2 inch. I know the 2 inch will add a little more back pressure and that may help with some torque. Any input would be appreciated. Thank You.

Lou

 

2 inch seems fine to me......

 

Stock , my 454 in a gmc 1-ton has 2 1/2".

dave

 

2.5". You have a lot of displacement.

 

http://www.jalopyjournal.com/forum/showthread.php?t=737874&highlight=really+good+exhaust+info

All tests via an independent lab
All tests @ 15” wc

2 “ Straight Pipe 283 CFM
2 ¼ “ Straight Pipe 365 CFM
2 ½ “ Straight Pipe 521 CFM

2 ¼” Typical Bent tailpipe 268 CFM
2 ½” Typical Bent Tailpipe 417 CFM

This is a exhaust pipe situation is where bigger isn't always better. Bigger will loose exhaust velocity in the pipe and kill your performance. Especially critical on no muffler straight pipes.


Match your pipe size to your engines ideal range and you'll be happy.
If you match it to WOT on a street car that may see WOT 2-3% of time you'll be not happy.

 

So it sounds like the 2 inch will be better.

 

Wow. Just read another one of those links. There's alot if info there that I don't understand. I did notice there's a big difference in CFM's between the 2 and 2.5 inch stuff. Anyone running dual 2 inch straight pipe on a big block that wants to chime in before I make my decision. I'm leaning towards the "2 inch because bigger isn't always better" approach.

 

what about 2-1/4" ? that's probably what i'd use

 

This. Science is not a guessing-game.

 

With a stock motor I would lean towards the 2" as well.

 

It's gonna stay stock. I'm gonna throw an Edelbrock E-street EFI system on it and that's it. I have displacement on my side and besides, it's a Cadillac and I want to just cruise and have a little bit of torque when I want it. Thank you everybody for your input I really appreciate it.

Lou

 

I am running 2" out to the back of the car no mufflers. The motor is a 241" Dodge Hemi and it sounds just fine. Not too loud not too quiet. Yes, my motor is tiny but no mufflers on dual 2" you outta do just fine.

 

do the dos...

 

Will do...

 

heavy vehicles will benefit with a smaller pipe....I say do the two

 

I say do the 2 two.......

 

How did it turn out ?

 

Went with the 2. Turned out great. Sounds really good. I'm really happy with it. Once again, thank you everyone for your input.

 

What size in a twin setup would work best on my Cadillac flathead 346 cubic inches with mufflers, relatively low compression and small rev range upto about 4,000 rpm max and lots of torque???
It has only 3 exhaust ports each side out of the block similar to a Ford flathead...