3-inch exhaust
3-inch exhaust
Senior User
Joined: Dec 2005
Posts: 350
Likes: 0
I would say that if your engine isnt pushing about 500hp then a 3in is going to hurt you. A smaller pipe will give the exhaust gases more velocity and create the scavenging affect to actually suck the gases out of the cylinder, without being restrictive. For the size I would stick with nothing bigger then 2 1/2 in pipe. I run 2 1/2 on my stock 390 and it performs pretty well.
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New User
Joined: Mar 2007
Posts: 24
Likes: 0
390 engine slightly warm, nothing to fancey. I guess I just would liek the deep rumble. As it is now there are a couple of kids in the begining of my neighbor hood that have car alarms.
I put it in low gear and lightly tap the throttle as I go by and next thing I know there are sirens and lights going of from their cars.
Mike O.
I put it in low gear and lightly tap the throttle as I go by and next thing I know there are sirens and lights going of from their cars.
Mike O.
Freshman User
Joined: Sep 2006
Posts: 25
Likes: 0
From: Perth Western Australia
When I had my previous 78 F100 4x4 4 speed 3.5-1 diffs with a mild 351c in it I went from std manifolds and single 2" system to a dual 2 1/4'' system and extractors and the acceleration at higher revs improved but lost a bit at low revs particularly in 3rd gear as you take off in second third is quite wide.It did allow the engine to rev more and went from ~90kmh in 3rd flat out to ~100kmh flat out and seemed to pull harder up top as well and economy improved markedly. I then went to a 2 1/2'' single system and turbo muffler with the extractors and the top end became even stronger and would rev out to ~110kmh in 3rd and I gained about an extra 20 kmh top speed from stock but did lose some more at the bottom end. This for me was not much of a problem as the truck was used mainly on the road, in fact it was quite nice having the extra go when driving on the street. I would probably not want that big a system on if I were 4WDing a lot as I felt that I lost too much torque down low.
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Senior User
Joined: Dec 2006
Posts: 408
Likes: 0
From: Emmett, ID
I actually was going to run 3" in as well but it cost an arm and a leg to do it so i decided to stay straight headers....if anyone has any good ideas on how to get it cheaper let me know.... thanks
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Posting Legend
Joined: Sep 2001
Posts: 30,255
Likes: 37
From my files...
SUGGESTED EXHAUST PIPE SIZES:
Engine HP; SINGLE/DUAL
=============================
200-300; 3.0"/2.25"
300-375; 3.5/2.5
375-450; 4.0/3.0
450-550; 4.5/3.5
550-650; 5.0/3.5
650-800; ---/4.0
800-1000; ---/4.5
1000+++: ---/5.0
STRICTLY DAILY DRIVER- GO DOWN ONE SIZE
BIG NITROUS- USE ONE SIZE BIGGER
SUGGESTED EXHAUST PIPE SIZES:
Engine HP; SINGLE/DUAL
=============================
200-300; 3.0"/2.25"
300-375; 3.5/2.5
375-450; 4.0/3.0
450-550; 4.5/3.5
550-650; 5.0/3.5
650-800; ---/4.0
800-1000; ---/4.5
1000+++: ---/5.0
STRICTLY DAILY DRIVER- GO DOWN ONE SIZE
BIG NITROUS- USE ONE SIZE BIGGER
Elder User
Joined: May 2006
Posts: 636
Likes: 1
yeah tell me about it i didnt do the exhaust it was like it when i bought it. they fabbed the pipes out of a roll bar just cut and welded em to fit so i have 3" duals that are almost a 1/4 inch thick walled some hills i gotta go into 3rd just to pull em after i wind it out on a start.
but soon that will be a thing of the past when i build the motor up
but soon that will be a thing of the past when i build the motor up
Senior User
Joined: Jun 2005
Posts: 169
Likes: 0
From: Kissimmee
I wondered the same for my 73. So I called Flowmaster and one of their techs told me to use stock 2 1/2 in exhaust into 1 flowmaster(40 series). He also said to throw away my radio because I wouldn't be able to hear it. I acquired two sets of flowmasters, one is 2 1/2 in and out and the other being the 3in. Now its a neighborhood alarmclock!