Hi All,

Been a lurker, now getting into a new project - new exhaust after 20+ years.

69 442 convertible, automatic trans, 400 ci (correct block and heads) I had rebuilt in the late 80s when i bent a rod doing 0-60 times after a valve job; only current "upgrade" is an Edlebrock 600cfm carb i bolted on about 12 years ago when the fuel inlet cracked on the Q-jet (long story):

Tail pipes are rusted through but passed inspection last month, was going to wait another year, then yesterday the car backfired on start-up and blew apart a muffler (separate post). It runs much better now (seat of the pants) which leads to the next step in my thinking:

Time for an exhaust upgrade...

I've spent about 20 hours over the last day researching systems (didn't get much sleep) and now have too much information, and need some help...

Here is my analysis thus far:

assuming 325 HP stock 400 ci (automatic) requires 325 x 2.2 = 715 cfm exhaust flow to maximize power/torque based on accepted formula and research.

715/2 (dual exhaust) = 357.5 cfm per pipe

Right now it has a stock 2 1/8" exhaust (outside diameter), with 1 7/8" (od) at bends, through old standard turbo mufflers which probably gave me 200 cfm at best from that system.

To me, that says an overly restricted exhaust, based on the formula above, but obviously adequate as I've had a lot of fun over the past 20+ years.

In order to make sure I'm not restricted, but not go overkill and make it too free-flowing, I've decided to upgrade to a 2.5 exhaust from the stock manifolds back. I priced the torque tech and magnaflow and pypes and summit and american thunder.

I've read way too much about X pipes and would love to try for the extra HP but am scared off by reports of sounding too euro and high pitched (I love the deep 442 gurgle I have now).

For middle of the road price, I've settled on a 2.5" pypes stainless setup from manifold back and no x-pipe, a summit H-pipe to keep the tone deep and try to gain some low end power/torque and quiet the 2.5" exhaust, and dynomax super turbos (20") to keep it respectably quiet with a muscle car sound.

I've been tempted by the pypes race pros (18") for improved flow, as I'm getting contradictory cfm flow rates on the dynomax based on various sources, and some say the dynomax will rust through in a couple years, but am afraid the race pro might be too loud having never stood next to one in operation.

Can anyone add any feedback about the race pros vs dynomax?

It is a convertible and I like to be able to hear the radio and talk to people with the top down/up and without waking neighbors.

I could save some money by using a pypes downpipe and welding it to a summit header back system with summit turbo mufflers, but i've read the summit mufflers are junk (is this true?).

I've read all kinds of exhaust posts on here and I'm in a limbo phase with lots of doubt. Too much information.

I'm hoping some advice will balance out the information and cancel out any lag in my thinking ...

Thanks,
Aaron

 

P.S. What do you think about this as an alternative to bolt to the pypes downpipe?

http://www.jegs.com/i/Dynomax/289/89023/10002/-1

 

I can say that I'm using two Thrush glasspacks on my 71 98 and they sound great. I think if you buy that kit from Jegs you will be happy. Thrush is a reputable exhaust company. If you have the welding skills to install it yourself then go for it!

 

no welding skills, but a local shop could do it. noticed it's aluminumized instead of stainless, might go for the stainless mandrel bent pypes for the extra $100 and change... too many decisions...

 

That upgrade doesn't sound too bad for $100. Welcome to CO. I think 2.5 inch pipes are the correct size for a 350 and most commonly found on upgrades.

 

IF you are having a local shop do it just have them install their own pipes and mufflers. They will usually offer you a labor warranty and they can usually do it for a good price. I had the exhaust installed on my 71 98 for less than $300.

 

still on the fence, not sure which way i'll fall off, will report back what i do, and how it turns out, i really appreciate the feedback and taking the time to read my long thread.

 

Not sure what sound you are after but I have just been thru this process. If you have not read my thread in general discussion then you might want to take a look at it.
I went with the magna flow stainless system with the x pipe 2 1/2".
I think I had a very similar set up to yours before I started. Just wanted to beef up my sound a little. The outcome was a disaster (in my view), ended up with a loud drone and it sounded like a BMW the 442 chug was gone. My guy took the system back and I went with 2 1/2" that he made for my car no x no h and it sounds amazing. Nice rumble at idle and a little throaty went you hit it. It was exactly what I was looking for. Just used his knock off brand of turbo mufflers. I am just glad to have my car back.
Like you I did a ton of research and I can not believe I got that far off the sound I was looking for. Just want the same basic sound (low chug and rumble), taken up a notch or two. Just my .02 worth.

Good Luck.

 

thanks for feedback '71, yeah your thread and experience was extremely valuable and is what convinced me to avoid the x-pipe and not get a straight thru muffler like magnaflow or racepro.

i did finally just now hit the button on my order...

lots of good ideas and options, even considered just replacing the blown muffler and keeping my rusty old pipes and putting off the decision, but I finally chose the 2.5" mandrel bent stainless pypes system with downpipes, no x-pipe, and no mufflers. I ordered the dynomax 20" superturbos (17749), and the summit "h-pipe".

I'm just too curious about the idea of the crossovers, having read way too much info on them, and people seem to like the deep tone and rumbly exhaust the H-pipe retained, plus it might quiet it a bit.

I figure if I don't like the H-pipe, I can pull it, have some 2.5" welded in place (cut and splice) and have a stock style 2.5" dual system that should last me another 20 years. A $50 gamble.

I'll post feedback when it's finished, hopefully the pipes will arrive next week and my Dad can take it into the shop in the next two weeks; I won't be able to hear it in person for another month (I'm in Florida, I left the car in my parents garage in Massachusetts when I moved).

 

Keep us posted.

 

Good choice I believe you'll be happy with the sound

 

I used a Torque Tech 2.5" mandrel bent system with DynoMax 17749 long case mufflers.

This system went on in about 45 minutes. 2 cuts required.

The trumpets are perfect in the bumper.

Sounds great and adds power.

Highly recommended.

 

Update on the exhaust. Sounds great, but different with the H pipe. I got to drive the car for one day during my visit to my parents (where I store the car), and I had just gotten the transmission rebuilt, so I'm not sure what can be attributed to more power and what is simply a transmission that shifts right and doesn't slip anymore...

I didn't drive the car hard at all because the transmission shifts are so firm it squawks the tires under medium acceleration (1-2 shift) and even once on the 2-3 shift. Spun them pulling away from a light on a slight incline under medium pedal. I never floored it.

If I had to say, I'd say the car has more power, and the tranny is responding to it.

Only downside is that I do get a deep constant humming note (HMMMMMMM) when cruising around 30-40mph; perhaps that is the drone that people speak of with cross-pipes. Quiets down the faster I go.

I'm not sure what I think of it yet, between the tranny rebuild and the exhaust it's an entirely new car, but other than the loud note/drone, I like the new sounds.

I might take the H-pipe out, just not sure what kind of torque it's giving me, and I like the way the car is performing...

 

Add sound deadener under your carpet that may cure the hmmmmmm sound.

 

so drive really fast then DUH!!!!

 

That is the sound of the power you now have on tap!

 

good ideas... fast and sound deadener might just work as the noise seems to come from below, not around the car with the top down.