3 Inch Exhaust Question
Thread Starter
Instructor
Joined: Apr 2006
Posts: 114
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From: Spring Texas
3 Inch Exhaust Question
I have a 71 Vert with 350SB & std trans. The trans cross member in this car has holes provided for the exhaust pipes to pass through on there way back to the mufflers mounted rear of the differential.
I was thinking about 3 Inch pipes back and marring them up to my headers that have 3 inch collectors. I was planning on using an 8 inch long stainless braided flex section from the headers to the exhaust pipe to reduce any engine vibration that would be transmitted through the exhaust pipe and bank into the Trans cross member. I found the stainless braided flex section similar to what is used in front wheel drive cars and they do come in 3 inch diameters.
Has anyone done this and what should I be aware of (maybe to avoid)?
I was thinking about 3 Inch pipes back and marring them up to my headers that have 3 inch collectors. I was planning on using an 8 inch long stainless braided flex section from the headers to the exhaust pipe to reduce any engine vibration that would be transmitted through the exhaust pipe and bank into the Trans cross member. I found the stainless braided flex section similar to what is used in front wheel drive cars and they do come in 3 inch diameters.
Has anyone done this and what should I be aware of (maybe to avoid)?
Instructor
Joined: Dec 2006
Posts: 105
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From: biloxi mississippi
I changed to 3" two years ago. didn't use any flex stuff. once the pipes were thru the crossmember and centered i placed hanger brackets to keep the pipe centered. I have had no problems - i like the sound better -but i seem to have lost some bottomend power going to 3" exhaust.
CF JASOC Member
Joined: Feb 2006
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From: Downtown Annapolis, MD. The Future is where we all have to live. Let's not screw it up.
St. Jude Donor '08-'09-'10-'11
That should come as no surprise, as you really need back-pressure at lower rpm band. 3 " pipes will definitely reduce back-pressure. Great at top end though. It's a trade off.
Burning Brakes
Joined: Jul 2006
Posts: 830
Likes: 1
dyno didn't lie
I had my car on a Mustang Dyno with the Stans TriY headers & 2" exhaust and I had it on later with the 3" exhaust....Guess what...
Absolutely NOTHING! There was NO marked difference between 2" and 3" exhaust on my mildly tuned 350. It has dual (free flow) cats & 3".
The only difference is that is sounds a bit cooler now.
I wish I could post that either way had superior numbers on HP or Torque but...Nope. On my own personal car, no difference between 2 and 3 inch exhaust.
Absolutely NOTHING! There was NO marked difference between 2" and 3" exhaust on my mildly tuned 350. It has dual (free flow) cats & 3".
The only difference is that is sounds a bit cooler now.
I wish I could post that either way had superior numbers on HP or Torque but...Nope. On my own personal car, no difference between 2 and 3 inch exhaust.
Team Owner
Joined: Apr 1999
Posts: 21,953
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From: Reno Nevada
2024 C3 of the Year Finalist- Modified
I used 7 inch pipe to add to my cross member. It doesn't need to be that big. My exhaust is 3 inch and I didn't need to cut so much out of the CM. Because the floor is now lower that the upper part of the arch.
You are better off with a custom cross member. The stock exhaust holes are too close to the tranny and heat is the enemy. It also makes for complicated exhaust pipe bends. My system is a straight shot back from the headers.
You are better off with a custom cross member. The stock exhaust holes are too close to the tranny and heat is the enemy. It also makes for complicated exhaust pipe bends. My system is a straight shot back from the headers.
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Drifting
Joined: Jul 2002
Posts: 1,943
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From: Rosemount MN
Yes, I did exactly as you're saying, 3" with the flex (8" look like braided steel hose). Similiar to these.
http://store.summitracing.com/partde...5&autoview=sku
I attached the pipes directly to the back of transmission crossmember and solidly from there back. No rattles.
http://store.summitracing.com/partde...5&autoview=sku
I attached the pipes directly to the back of transmission crossmember and solidly from there back. No rattles.
Instructor
Joined: Sep 2007
Posts: 197
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From: Norton MA
I had my car on a Mustang Dyno with the Stans TriY headers & 2" exhaust and I had it on later with the 3" exhaust....Guess what...
Absolutely NOTHING! There was NO marked difference between 2" and 3" exhaust on my mildly tuned 350. It has dual (free flow) cats & 3".
The only difference is that is sounds a bit cooler now.
I wish I could post that either way had superior numbers on HP or Torque but...Nope. On my own personal car, no difference between 2 and 3 inch exhaust.
Absolutely NOTHING! There was NO marked difference between 2" and 3" exhaust on my mildly tuned 350. It has dual (free flow) cats & 3".
The only difference is that is sounds a bit cooler now.
I wish I could post that either way had superior numbers on HP or Torque but...Nope. On my own personal car, no difference between 2 and 3 inch exhaust.
Melting Slicks
Joined: Dec 1999
Posts: 2,116
Likes: 156
From: Mid West
Cruise-In III Veteran
I did something similar, but I used some stainless bellows instead of the flex pipe. I put them in the system just in front of the tranny x-member. No rattles, sounds better, and even has more ground clearance than my old pre-bent 2 1/2" pipes I bought from one of the major vendors.
I don't have any before & after HP numbers to compare the difference. No complaints though .... I've got 300 ft-lbs @ 2k rpm at the rear wheels, and I get 1.9 sec 60' times on street tires so it isn't too soft on the bottom end.
I don't have any before & after HP numbers to compare the difference. No complaints though .... I've got 300 ft-lbs @ 2k rpm at the rear wheels, and I get 1.9 sec 60' times on street tires so it isn't too soft on the bottom end.
Race Director
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From: Tampa, Florida
Tech Contributor
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From: I tend to be leery of any guy who doesn't own a chainsaw or a handgun.
No, no, no. Backpressure is never a good thing. Engines make horsepower by pumping air. Restricting the output (exhaust) decreases the input (volumetric efficiency), and thereby, reduces horsepower.
Melting Slicks
Joined: Dec 1999
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From: Mid West
Cruise-In III Veteran
Tech Contributor
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From: I tend to be leery of any guy who doesn't own a chainsaw or a handgun.
Jason: (My apologies to the OP, as I'm not trying to hijack this thread.) What driveshaft are you running in that picture? Size, weight?
Racer
Joined: Nov 2007
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From: Forrest City Ar
I am not trying to argue but Visard says sometimes you can get too big, and I just talked to Jerry Stahl today and he told me I should run 1 5\8 Primarys not 1 3\4" for better streetablity but my engine guy said 1 3\4 so who knows?
Tech Contributor
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From: I tend to be leery of any guy who doesn't own a chainsaw or a handgun.
Le Mans Master
Joined: Sep 2001
Posts: 7,739
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From: Unreconstructed, South Carolina
Bet dollars to donuts stahl's had more hands-on with more real motors ... and stahl's in the "optimal performance via exhaust" business. If both your wrench & stahl are given exactly same parameters ... I'd go w/ stahl's advice.