3 1/2 inch x pipe and mufler

xj9140 · May 8th, 2011, 12:59 AM

I have a stock '86 GT. A local guy is selling a 3 1/2" x pipe with the two flowmasters for a great price. I was considering installing behind my stock headers and back into the stock tail pips. I think the tail pipes a 2 1/4 but not sure. What are your guys opinions? and what cam should I get to go with the new pipes?

FastStang91Lx · May 8th, 2011, 01:03 AM

Waste of time to have that big of exhaust only in the middle of the exhaust system with what I'm guessing is a relatively stock motor. And you don't buy cams to go with exhaust, you buy cams to go with motor combinations.

ryanw · May 8th, 2011, 01:09 AM

Originally Posted by FastStang91Lx

Waste of time to have that big of exhaust only in the middle of the exhaust system with what I'm guessing is a relatively stock motor. And you don't buy cams to go with exhaust, you buy cams to go with motor combinations.

Lol...I was just going to say that is the first time Ive heard of some one trying to match a cam to there exhaust

flyin ryan · May 8th, 2011, 01:54 AM

stock car you'll go slower with that setup

1FAST6 · May 8th, 2011, 08:40 AM

save your $$ and get a good 2 1/2 full exhaust.

orangestang42 · May 8th, 2011, 10:54 AM

yeah 3 1/2 is a bit overkill lol, ur gonna lose back pressure and hp with a stock car...

fogged306 · May 8th, 2011, 10:58 AM

Backpressure is a myth. It does nothing for your car.

You actually do want to match your cam to the exhaust. But it's the collector of the header, not the x pipe or anything else. A cam matched to a collector will maximize scavenging in it's application.

ryanw · May 8th, 2011, 11:30 AM

Originally Posted by fogged306

Backpressure is a myth. It does nothing for your car.

You actually do want to match your cam to the exhaust. But it's the collector of the header, not the x pipe or anything else. A cam matched to a collector will maximize scavenging in it's application.

I stand corrected then

xj9140 · May 8th, 2011, 04:47 PM

Originally Posted by FastStang91Lx

Waste of time to have that big of exhaust only in the middle of the exhaust system with what I'm guessing is a relatively stock motor. And you don't buy cams to go with exhaust, you buy cams to go with motor combinations.

I dont see how it would be a waste of time. I mean it would sound MEAN and that is what I am wanting, that a maybe a increase in fuel economy. I am already happy with the amount of power I get with my stock motor.

Originally Posted by ryanw

Lol...I was just going to say that is the first time Ive heard of some one trying to match a cam to there exhaust

Perhaps you haven't done much research on the subject.

Originally Posted by flyin ryan

stock car you'll go slower with that setup

I am having a hard time believing that. Maybe off the line, but it would open up the upper RPM performance. So your saying if I ran open headers it would hurt performance? hmmm even if I changed to the proper cam shaft?

Originally Posted by orangestang42

yeah 3 1/2 is a bit overkill lol, ur gonna lose back pressure and hp with a stock car...

Even if its feeding back into the tail pipes that are 2 1/4. I don't see anything wrong with over kill, as long as it don't hurt performance.

Originally Posted by 1FAST6

save your $$ and get a good 2 1/2 full exhaust.

The guy is selling the 3 1/2 in pipes from header to x pipe to two flow master 3 1/2 mufflers all for $150. the back of the mufflers have turn downs but I was considering plumbing them back into my tailpipes to add a little back presure. I can weld and install the pipes myself.

Originally Posted by fogged306

Backpressure is a myth. It does nothing for your car.

You actually do want to match your cam to the exhaust. But it's the collector of the header, not the x pipe or anything else. A cam matched to a collector will maximize scavenging in it's application.

I'm not to sure about that. I mean backpresure does help with torque. At least on my Jeep motor it did. I always thought with open headers you wanted a specific cam shaft.

fogged306 · May 8th, 2011, 05:06 PM

Originally Posted by xj9140

I'm not to sure about that. I mean backpresure does help with torque. .

Read

http://www.veryuseful.com/mustang/te...Scavenging.pdf

FastStang91Lx · May 8th, 2011, 05:28 PM

If you look at backpressure as a restriction, yes, it can have it's place depending on the motor setup. There must be a certain amount of resistance to create the scavanging effect. A stock motor with 1 7/8 primaries and full 3 1/2 inch exhaust will not perform as well under all circumstances as the same motor with 2 1/2 inch exhaust. But with the right combo, backpressure is a killer. My 900rr's exhaust is a 4 into 2 into 1 flowing through a straight though muffler. No backpressure there other than the size of the pipes and length of the tubes in the 2 into one section. That's how it can do 13,000 rpms, but off idle (1100rpm) to 3k, it's a turd. It's what the cam was designed for.

93hatch · May 8th, 2011, 05:31 PM

my car picked up 3mph pullin mufflers and runnin skinnys

do the math

FastStang91Lx · May 8th, 2011, 05:42 PM

Originally Posted by 93hatch

my car picked up 3mph pullin mufflers and runnin skinnys

do the math

That's why I said under all circumstances... if that was directed at me.

93hatch · May 8th, 2011, 05:50 PM

na wasnt specifically just my personal experience as a pro race car driver

FastStang91Lx · May 8th, 2011, 06:27 PM

and pro engine builder, lol

May 8th, 2011, 12:59 AM	#1
xj9140 Newbie Join Date: May 2011 Posts: 4 iTrader: 0 reviews	3 1/2 inch x pipe and mufler I have a stock '86 GT. A local guy is selling a 3 1/2" x pipe with the two flowmasters for a great price. I was considering installing behind my stock headers and back into the stock tail pips. I think the tail pipes a 2 1/4 but not sure. What are your guys opinions? and what cam should I get to go with the new pipes?

May 8th, 2011, 01:03 AM	#2
FastStang91Lx I Post Entirely Way Too Much 1991 Mustang LX 5.0 Join Date: Jan 2010 Location: Minnesota Posts: 5,572 iTrader: 2 reviews	Waste of time to have that big of exhaust only in the middle of the exhaust system with what I'm guessing is a relatively stock motor. And you don't buy cams to go with exhaust, you buy cams to go with motor combinations. __________________ Point made in less than a few hours with minimal response. http://www.moddedmustangs.com/forums...ml#post4465184

May 8th, 2011, 08:40 AM	#5
1FAST6 Regular 1989 LX hatch 15 and change Join Date: Jan 2011 Location: FL Posts: 95 iTrader: 0 reviews	save your $$ and get a good 2 1/2 full exhaust. __________________ 1987 Buick Grand National 1989 Mustang LX 5.0 Both BLACK

May 8th, 2011, 10:54 AM	#6
orangestang42 Enthusiast 1995 Mustang GT Join Date: May 2010 Location: Port Charlotte, Florida Posts: 816 iTrader: 0 reviews	yeah 3 1/2 is a bit overkill lol, ur gonna lose back pressure and hp with a stock car... __________________ "my wheel bolts require more torque than your honda makes"

May 8th, 2011, 05:28 PM	#11
FastStang91Lx I Post Entirely Way Too Much 1991 Mustang LX 5.0 Join Date: Jan 2010 Location: Minnesota Posts: 5,572 iTrader: 2 reviews	If you look at backpressure as a restriction, yes, it can have it's place depending on the motor setup. There must be a certain amount of resistance to create the scavanging effect. A stock motor with 1 7/8 primaries and full 3 1/2 inch exhaust will not perform as well under all circumstances as the same motor with 2 1/2 inch exhaust. But with the right combo, backpressure is a killer. My 900rr's exhaust is a 4 into 2 into 1 flowing through a straight though muffler. No backpressure there other than the size of the pipes and length of the tubes in the 2 into one section. That's how it can do 13,000 rpms, but off idle (1100rpm) to 3k, it's a turd. It's what the cam was designed for. __________________ Point made in less than a few hours with minimal response. http://www.moddedmustangs.com/forums...ml#post4465184

May 8th, 2011, 01:54 AM	#4
flyin ryan Banned Join Date: Jun 2008 Posts: 3,387 iTrader: 0 reviews	stock car you'll go slower with that setup

May 8th, 2011, 10:58 AM	#7
fogged306 MM Fanatic 89 GT Join Date: Apr 2007 Location: NY Posts: 4,875 iTrader: 2 reviews	Backpressure is a myth. It does nothing for your car. You actually do want to match your cam to the exhaust. But it's the collector of the header, not the x pipe or anything else. A cam matched to a collector will maximize scavenging in it's application.

May 8th, 2011, 05:31 PM	#12
93hatch Banned 1992 Lx 11.39@119.24 Join Date: Jan 2008 Location: Az Posts: 11,644 iTrader: 0 reviews	my car picked up 3mph pullin mufflers and runnin skinnys do the math __________________ [QUOTE=93mustank;2577445]We speed tested my right arm for quickness in shifts... So he could design the cam for proper shift recovery.[/QUOTE]

May 8th, 2011, 05:50 PM	#14
93hatch Banned 1992 Lx 11.39@119.24 Join Date: Jan 2008 Location: Az Posts: 11,644 iTrader: 0 reviews	na wasnt specifically just my personal experience as a pro race car driver __________________ [QUOTE=93mustank;2577445]We speed tested my right arm for quickness in shifts... So he could design the cam for proper shift recovery.[/QUOTE]

May 8th, 2011, 06:27 PM	#15
FastStang91Lx I Post Entirely Way Too Much 1991 Mustang LX 5.0 Join Date: Jan 2010 Location: Minnesota Posts: 5,572 iTrader: 2 reviews	and pro engine builder, lol __________________ Point made in less than a few hours with minimal response. http://www.moddedmustangs.com/forums...ml#post4465184

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