It’s would be very hard to believe there’s anything to gain from 3.5 over 3” , but if that’s your preference so be it.
I think I can find that link to a tube supplier.
but I’ve never seen a supplied “ kit for a first gen Camaro in 3.5……doesn’t mean there’s not one.

 

It’s would be very hard to believe there’s anything to gain from 3.5 over 3” , but if that’s your preference so be it.
I think I can find that link to a tube supplier.
but I’ve never seen a supplied “ kit for a first gen Camaro in 3.5……doesn’t mean there’s not one.

It looks like the supported hp for 3" is around 680 and for 3.5" is 935 on dual exhaust.

 

Here’s a link to a supplier of oval 3” that I was going to use but couldn’t justify the expense over round.
I didn’t look to see if they had 3.5 but I bet they do.

Oval Exhaust

Large inventory of hand-crafted performance oval tubing products. Including oval tubing, oval mandrel bends, oval mufflers, oval slip joints, and custom oval x pipes.

www.stainlessheaders.com

 

If you want mandrel bends, buy them from Flowmaster (Summit, etc) and make up or have a muffler shop use them to make OTA's using the mandrel bends and straight 3 1/2"

With that said IDK if you going to get 3 1/2" to fit for OTA section

larger pipe kills low end TQ. Doing the 3 1/2 to transition into 3" after mufflers may be the solution for your build OP

 

My current thought is since the x-pipe make for better scavenging does that translate to better flow and then the 3" would work? The car will be 99% street driven.

 

My current thought is since the x-pipe make for better scavenging does that translate to better flow and then the 3" would work? The car will be 99% street driven.

than keep 3"...you will have more low end TQ

 

Agree with the above about IF it was a max power car...on the street, as a cruiser, and just HP bragging.. you should be fine with the 3"

 

I’ve never seen that. Giant pipe like that behind the tire would be cool.

or
Use a cut out for when you’re at 100% hp

I’d like to see 3.5” fit over the axle with any suspension other than leafs. Maybe the custom fuel setup that supports that hp allows more room.

 

I agree on the 3.5 over the axle being quite a challenge.
3” with leafs was about all I could imagine….. but I would like a shot at Franks setup with 3” over the axle.
Just because he said he couldn’t see a way to do it. 😄
It all depends on how much you have to work around …and when you go 3.5 the radius grows , unless your willing to go to an extreme on cutting, welding and utilizing something other than round, making rolling offsets etc…
At 60 I’m not to excited about spending hour after hour under the welding hood.

 

I've gotten parts from these guys
Ace Race Parts — V-Bands, Flex Bellows, Weld Els, Intercooler Cores
check their bent stuff and see if you can live with the radii.

 

What size are the collectors? I see people reduce the pipe right behind the collectors a lot, which isn’t ideal. I think a well thought out exhaust is more important than sheer size.

I’m probably 650 horse ish NA, my headers have 3.5” collectors, so I went 3.5” from collectors to a Dr Gas X that is 3.5” to 3” reduced at the X, then 3” to the axle. It’s actually not terribly loud really.

Back when I did my exhaust I discussed it with Boyd at Dr Gas (the founder) and he felt like that was enough to support all of my NA power and a blower (I planned to install one at one point).

No numbers to back it up, but some guys that know a lot more than I do approved of it. I’ve been very happy with it.

 

You could go 3.5" after the muffler and under the axle for looks, which could be cool.

Here's a table you might find interesting though. Notice the comment the pipe sizes are probably over estimated.
How To Calculate Muffler Size and Exhaust Pipe Diameter | Exhaust Videos

 

I'd be more concerned with the primary size of the headers. That's the bigger potential bottleneck. If it's the Beck Engine, peak torque would be at 4500rpm, which would dictate 2 1/8" primaries for a 555ci.

You could just run 3.5" from the collectors and through the mufflers, then keep the 3" after the mufflers, but really I think the 3" X-pipe and Ultra Flo setup is good for what you're doing.

 

When I ordered the headers for my car from Lemon's they were more concerned about collector size than primary size. So my engine is a 700HP+ smallblock when it was N/A. Now it has an F2 Procharger on it. Lemon's specified 2" primaries with 3-1/2" collectors for N/A and said to switch to 4" with the Procharger. If you don't take your car to the track, I doubt you will notice the difference between 3" and 3-1/2". For years I ran a 3" mandrel bent system with 50 series three chamber Flowmasters that exited behind the rear tire. It had an "H" pipe and was fairly quiet for a car that ran 10.40's through the mufflers.

 

For future searches...

 

For future searches...

View attachment 294689

important to mention.. these are only the loss free calculations.

Its not like you can build a 679 hp NA engine with 3" dual exhast and then slap a procharger on it and NOT expect power gain.

There is gonna be more power, just that the additional amount is affectec by some loss / deficiency.

The further you surpass the loss free limit, the higher the loss percentage of the surpassing amount of horses..

For a street car with low end torque emphasis this often might lead to the case that the owner doesnt change the whole exhaust for just like 15 more hp or so..

 

I can't imagine the gains would be worth it...get a cut-out system if you need to open it up. Unless I'm missing something...is the 555 a cummins and you're rolling coal? Sorry, couldn't resist.