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Required exhaust back pressure


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11 replies to this topic

#1 mandalore4411

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Posted 01 September 2014 - 04:47 PM

Hey does anyone have experience with opening up the exhaust on an ea82t???
I have a 87 gl-10 auto turbo and I damaged the exhaust so it's gotta be redone.
Would a straight pipe work?
Or even just ditch the cat?

I haven't decided what I'm gunna do I wanted to hear from you guys. I was thinkin maybe cut out the cat and upgrade the muffler.

Thanks for your time, much much appreciated.

#2 Ibreakstuff

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Posted 01 September 2014 - 05:06 PM

In my humble opinion back pressure is a flawed definition/idea and it more applies to NA motors. It should be called flow velocity, where a smaller exhaust can be better at moving exhaust gases depending on the motor size. I can elaborate if you want a wall of rambling.

But turbo back, you want as little back pressure as possible. I think 2" from the heads (1.75" might be better for spooling) to the turbo and 3" turbo back would be about as big as you could ever want to go on an ea82t.



#3 john in KY

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Posted 01 September 2014 - 07:00 PM

I once ran a 90 turbo wagon. The only part of the stock system, starting at the turbo, was the flange that bolts to the turbo. Everything else was replaced with 2 1/4 inch pipe. Muffler was a straight through design. Not even close to being too loud. 



#4 86BRATMAN

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Posted 01 September 2014 - 09:48 PM

I get really tired of seeing people worry about back pressure in their 4 stroke engines. Back pressure has nothing to do with how your engine runs, unless you've slapped a 2 stroke racing bike engine in there. In which case, yeah you need to get that tuned right perfectly.

#5 skishop69

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Posted 01 September 2014 - 10:01 PM

+1 And it's actually scavaging effect you need to worry about, not flow velocity. Flow velocity is intake and head related though it can pertain to exhaust though it's rarely related to there. You want NO back pressure on a 4 stroke engine. You should never see more than 1 pound of pressure, and realistically, you should have a vacuum. Hence scavaging. Smaller pipe= more scavaging, Larger pipe=less. Of course, it's all related to displacement as Ibreakstuff mentioned. Turbo motors turbo back really has no effect going to larger pipe. NA motors suffer a loss of bottom end torque when you through too big an exhaust on.



#6 MilesFox

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Posted 01 September 2014 - 10:04 PM

my perfect combo is a glasspack just after the mitpipe flange and straight pipe out the bumper. 1-7/8 or 2 "

 

If you read my posts in searching i am always barking about 'backpressure' being confused with scavenging. 

 

Throw all that old man common convention out the window with these cars



#7 mandalore4411

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Posted 02 September 2014 - 03:21 AM

ok so you like running turbo-cat-glasspack-pipe.

isnt a glass pack like a cherrybomb?

#8 tweety

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Posted 02 September 2014 - 05:17 AM

86bratman, dont get tired of others asking basic questions. As soon as I saw the heading I thought what a great question and one I'd like answered.

 

We are not all knowledge guru's. chill out and let us low knowledged mortals ask the questions.



#9 MilesFox

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Posted 02 September 2014 - 11:04 AM

yes, glasspack = 'cherrybomb'. I would have used cherry bomb, but sometimes that is confusing if no one can make the correlation between a brand name vs type of muffler. I suppose brand names can be used to describe in general, just as kleenex means facial tissue, or u-haul means moving truck



#10 mandalore4411

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Posted 03 September 2014 - 03:30 AM

bump bump

and other experiences?? id love to hear from more people.

#11 bratman2

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Posted 03 September 2014 - 07:20 AM

I don't know how a turbo effects the exhaust myself. On my 87 Brat one of the very first things I did was add a 2" turbo muffler same length as the stock. To turn into my drive way you are exiting a fairly decent right hand curve on an incline taking a left hand turn up hill and cutting back slightly to enter. Originally my Brat did not like going into first gear unless you were practically stopped. Making that turn into my driveway in second would cause it to lug. After the muffler change it seemed to lug a lot less when making that same turn in second. That muffler rusted out at the inlet along with the mid-section of the original exhaust. I had it replaced from the Y-pipe back with 2" and added a Magnaflow SS muffler. Making that same turn now in second causes really no issues at all now, (though I have added a Webber and several other minor things)! I really like this combination as it has plenty of bottom end, is not obnoxiously loud and sounds pretty good to me. The original exhaust was 1 7/8" if my memory is correct with a 1 5/8" tailpipe. I think that design is for utter quietness rather than torque/bottom end performance.



#12 mandalore4411

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Posted 04 September 2014 - 02:12 PM

Bump




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