The company Pypes makes some pretty nice exhaust systems. They have a 2.5 system that will fit convertibles, but to make it fit, you have to use an adapter kit for the special body brace unique to convertibles. Basically, it's a pair of solid aluminum blocks that look to be about 1" thick x 3" x 8". They lower the x-brace so that the pipes fit. This sure looks to me like it would lessen the effectiveness of the body brace by a substantial amount. Am I crazy, or does anyone else agree or have 1st hand experience with this?

Photo of installed adapter:
http://pypesexhaust.com/gallery39.html

Hotchkis has a better version of the lowered brace...

And there on sale>>>>> 156.00, I just put one on...Summit or direct from hotchkis. Looks nice and the steel was heavier gauge than I expected.

I'm not even sure the Pypes is better than nothing.

What is the normal price on Hotchkis?

From an engineering standpoint it likely is better than nothing, depends on how well the bolts are captured and resistant to movement (rocking) during flex.If the rails were welded to the bottom of the car it would perform near the same as stock.

Still tho they lower the height and are liable to bottoming out. I would prefer the ovals so the brace can remain where it is.

I've been told that "stock" brace works...but i have a hard time believing it.
Unless you have 400 hp with good traction.
But then you need frame connectors any way.

That's the ticket, sub-frame connectors.

Why do 2.5" when 2.25" fits with no problem? Does that extra 1/4 inch really make a dif?

With duals that is a combined 25% more cross-sectional area. Quite a bit actually. Whether the engine needs it depends on the rest of the engine specs.

yes.....

area of a pipe is PIxr squared, = 3.14 x 1.125 x 1.125 ( 2.25 pipe)=3.97
area of 2.5 pipe = 3.14 x 1.25 x 1.25 = 4.90

4.90-3.97 = 0.94 more than 3.97 = 25% more...

You guys are good...

Regarding those adapters, Those are just blocks of Al! Would be quite easy to make.

What would be more effective is sections of square tubing welded to the existing brace. Saw it done on another car.

That Hotchkis piece looks like it would work pretty well. In fact, today I ordered their f-body convertible kit that includes the body brace and a pretty slick set of subframe connectors. I'll let you guys know how well it handles. I've had some experience with different sized exhaust, and in my experience, on a big cube motor the 2.5" is a worthwhile upgrade from 2.25. I'm probably going to do the Pypes kit with long branch manifolds.

Thanks for the tip on the Hotchkis brace and all the feedback. -paul.

Ponchoshop, I'm pretty certain that brace is mostly for normal driving and prevention of "cowl flex" in convertibles, due to the lack of rigidity normally provided by a steel roof. I'm thinking the car would twist around like crazy without it in normal driving. These cars already move around alot (unibody, no roof). My Firebird convertible drives totally different than my 69 Chevelle coupe (full frame).

Agree.
1st 68 FB didnt have frm cntrs.
Both upper a-pillars cracked.
I swear you could feel the body twist on luanch.
And w/shield would crack 1/2" further.

Current 68 has frm cntrs.
BIG diff in launch, ride, and handling.

My 67 FB/400/4-spd will get them too even though it will be more of a stock appearing restore.

Forgot, all 3 are coupes, so convrt's must be really bad.

if you take your car to a muffler shop they can bend your system to go above the brace.and if you need a 3 inch system,than you really should not be driving that car on the street.keep it on the race track where it belongs with a roll cage and you will need to be pushing 600 hp to need that.in that case,open hedders is best.

BS

3" to big for the street?
As long as it's not to loud.
And a tuned exhaust will make more power then open hedders.

Whats wrong with having a cage for the street.
Have you ever been in an accident in a 1st gen?
I have. My brother has. Many other people i know have.
They should of came with them from the factory.

Here is a 2.5" (with a smaller "H" pipe installed) that goes under the stock X pan just for kicks:





I agree, a good muffler shop can do it up right.

Brett!

69firebirdman: Why shouldn't you drive something like that on the street? I have a feeling that you probably wouldn't have liked my daily driver that I had for 7 years: A big, green 68 BelAir with a 350, bowtie aluminum heads, huge cam, 10" converter, 3.73s and powertrax locker (clickity click, chunkity chunk), 3" pipes with 3 chamber flowmasters with dumps before the axle, and a Cheater NOS plate system. Oh yeah, no carpet. One time, humming down the highway spinning 3400 rpm on the way to a business meeting, a female coworker said "this car stinks, it's loud and don't you need to shift it into high gear since we're on the highway?" PERFECT! I have a feeling you would've shared her sentiment. It was my only transportation for 7 years. And, it spent a good deal of time wearing slicks -- unless they'd forecast rain : ) If I had a client meeting 60 miles away, I drove it. If it had the slicks on it, I stopped at a gas station and pumped em up to 25 or 30 psi for frictionless highway cruising. You can see a video clip of it (just barely) pulling the left front tire at the track via the link in my signature. It was the funnest all around car I've ever owned.

Anyway... 3" isn't too big for the street and open headers aren't always best. It depends on the combo. I have firsthand experience with that with my chevy projects over the years. I have a buddy who's played with a lot of Pontiacs and has found that the Pontiac motors (particularly 455's) also respond well to 3" pipes.

I will say this... 3" pipes are LOUD regardless of the type of muffler, so if you don't like loud, don't do 3".

The wife's Firebird will get 2.5" cause she likes her stereo and cell phone. If it were my car, i would put 3" on it and a radio delete plate, but hey, everybody's different. Hopefully she won't bottom out that nifty expensive Hotchkis brace I just ordered.

And, I here ya on the good muffler shop -- they're hard to find, though.

-paul.

This guy has only been on the forum for 3 days and I like him already...

several HALFers have 3" pipes (at least 2 or 3 do)...I stick with my 2.5" , since they work well with my combo.....

but Drew and Blake both drive coupes with 450 and 550 hp using 3" pipes

Paul, 69firebirdman, Terry, is one of our best preservationists. He likes em stock, and is also a great contact for parts as he sells original parts from cars he's parting out etc... He is great at keeping us all in check... and we like to tease him a bit now and then with wild tales of extreme modification we plan to do to all of our birds...

Welcome to the boards!

Brett - 67 Drop Top 455!

As a matter of fact, we are currently taking donations to purchase the 8th remaining Trans Am 'Vert. The plan is to tub it, install a 4-link, and drop in a BB Chevy. It won't go to Terry, however. Instead it will be given to a former member Chevybird on the promise he will drive it to Terry's house and smoke the tires until they pop all the while singing "Free Bird."

I think I'm going to name my recently purchased (and soon to be highly modified) 450HP 4 speed vert 'Terry'. It's going to be a 100 point car. 1 point for each modification. Thanks again Terry for helping me with the shipping! You da man!(with the plan)

Let me know when it gets home...

And I surely couldn't have pulled this off without the keen eye of 'Ron the Great'!(aka maxepr) It's all packed and ready for the truck which will snatch it up on Tuesday.

Here's some pic's for Terry.
This will make him pull his hair out, and give him nightmares

Be sure to check page 2.
Click on pic to enlarge

http://s207.photobucket.com/albums/bb72/ponchoshop/

Not much stock left on the 68(black car), but it was beat up non original plain jane car when i got it.

My 67(buried in garage) will be as original as possible with out spending a fortune.
In fact it is except intake, carb, dist, exhaust, stereo, and wheels.
Already gone before i bought it.

Thanks for the welcome. I'm going to forgo outwardly teasing Terry because I'm new AND because I'll be needing advice from him before too long when I need to know how something on my Pontiac was done from the factory. But, Terry would REALLY hate what I'm doing to my 69 Chevelle. I'm a preservationist too, but my interest is in what a street / strip kind of guy would do with one of these cars back in the day. Kind of a vintag drag racing thing. It's all bolt on stuff and I won't cut up the car, but it's got a tunnel ram, a Grump Lump (hand fabbed sheet aluminum scoop), vintage Cragar Super Trick front runers and Cragar SS on the back. I may even through on some vintage racing decals for fun. I'm going to hide the MSD in the glove box and stuff like that so that when you walk up to the car and look it over, it looks like 1971. The car is a nicely restored original and won lot's of show trophies. I've had the car for 14 years and just got bored with driving my bone stock looking red Chevelle to cruises along with 15 other red Chevelles that look the same. (I know, bet a Pontiac). So, I've done the original thing for years.

The Firebird will stay stock. My wife likes them original and it's her car. I put in a Custom AUtosound stereo because she loves music and she's not even thrilled with that because it looks added on.

Oh my God. LOL. THAT is hilarious. And "Free Bird" would be the best song. Or, maybe some Foghat. My dad and uncle built a 31 chevy pickup street rod in 1961 and drove it to high school. My uncle still has it. When I was a kid, my dad would get it out and use it as his daily driver all summer. I can remember old timers balling my dad out at stoplights. "Why would anyone ruin a perfectly good Model A like that?" The irony was, that they all thought it was a Ford because there weren't too many 31 Chevys running around. Oh, and that they thought somebody would actually want to drive a stock Model A with other cars buzzing around.