Exhaust help

[Security guy]

I've got a couple questions for you guys. I've got a '71 short bed with a stock 402 and mid-length headers. Will 2 1/2" exhaust pipe be fine or do I need 3"? Whats the difference? Loudness or horsepower/torque? This will be used for cruising and a little towing but I want it to sound good also. One shop told me not to start it with the cold weather because having open headers, when you shut it off, the cold air coming back up the headers can warp the valves. Anyone heard of this? Also one shop quoted me around $400 for a full exhaust out the back with flowmasters and another shop quoted me about $250 with incenerator (flowmaster wannabe's) mufflers. Is it worth the $400 for flowmasters and does the price sound about right? Thanks for the help.

[texanidiot25]

2.5in exhaust will yield better low end torque, awhile the 3 would help high RPM breathing and HP. Bigger pipes will be a bit louder. Flows are stupid loud in the cab, so be prepared to hear it, all the time, no matter what, drumming at your ears. Besides that, only reason I don't like flows is because everyone has them. Ultimately, its up to you.

250 for a full system sounds purty good to me

[LuckyHenriksen]

I agree with everything texan said, but I don't mind flows =] try cherry bomb extremes they sound cool. 2.5 pipe will be fine with a stock motor

[Mike C]

2.5" will be fine with stock cam. When I had my '70 with the 402 I was planning on a dual 2.5" into a single 3" RV muffler. It had a crower 270 cam but still had stock manifolds. Killer flow and low sound level with the two into 1. If you go with two mufflers, I'm a big fan of the Walker Hemi Turbos.

[Sport/Truck]

Originally Posted by texanidiot25

only reason I don't like flows is because everyone has them.

s/t

[ProStreet68SB]

2 1/2 will be more than enough for a stock 402, if you dont mind a little raspiness in your exhaust, then i'd run dual 2 1/4" with an H pipe, would give that more some help with the bottom end torque that it already has.

[big_al_71]

I have a built 406 and I used 2 1/2 inch exhaust with dynomac mufflers and it cost me $425.00 from the collectors back to the rear bumper. It runs perfect no issue not annoyingly loud while cruising and it definetly barks when wide open throttle.

[10pointgmc]

I like the sound of just a regular old turbo muffler myself not a big fan of flows

[texanidiot25]

Can anyone back up what he said about the cold and open headers?

[chev-obsession]

unless you have more than 500 horsepower in that stock big block, then i would go with 2 1/2. i have 2 1/2 pipe and stock ramhorn manifolds and about 350 horsepower to the motor with flowmasters. i think the flowmastersdo just fine, not to loud but not quiet either.

[Mayo]

My truck has a single 3 inch pipe with an old flowmaster hooked up to a 292. it is loud and sounds awesome. The only problem is I can't go through drive thru's because the exhaust dumps out in front of the left rear tire so you can't hear a word anyone is saying over the intercom.

[bigguy69]

i think you will e fine with 2.5 also have heard of the same thing with open headers. i noticed you live in asheville could you tell me about the shops you found?

[Security guy]

Thanks for the replys everyone. I'm still not sure to go with the flowmasters or not. I like the sound of them but don't want to be annoyed by them either. I will have some good insulation in the cab though. Bigguy69 - I went to two shops. The first one is total performance on river road. They build lambo's out of pontiac fieros. They did an exhaust for me before for a '55 chevy and the incenerator mufflers. Sounded good for about $260 i believe. There welds didn't look all that good though. I checked on another shop on upper patton ave called affordable muffler and brakes. They quoted me ballpark around $400 for the flows. PM me if you want their numbers. Anyone heard of the cold air hitting the hot exhaust valves? I'd like to get this done next week. It may be above freezing by then, so it may not matter, but that sounds funny to me. Thanks guys!