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488ci V10 Power
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Discussion Starter #1
Right now i have a stock exhaust and im looking for a BPU replacement. I want an exhaust that i dont have to change out when i go single eventually.

Most likely i plan on going with a T-78 kit for my auto supra, or possibly a T51R KIA kit.

Is a 4" exhaust better? will i notice a difference if i got a 3.5" exhaust?

i need some input so i can place an order for one before spring settles in.
 

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boost is good
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any of the major brand will be fine, greddy, apexi, tanabe, hks, ect. 4" isnt gonna really make a big difference unless you are running a huge turbo and have 4" piping from the turbo back.
 

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488ci V10 Power
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Discussion Starter #3
Anyone else want to chime in on this???
 
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Whatever you do in terms of exhaust remember that the WHOLE exhaust must be a bigger diameter to make a difference. If you have a 3" downpipe and 4" exhaust won't do diddly.

Also, you can go too big. Bigger exhaust will have more surface area and cool the exhaust gasses quicker, which can actually cause a small amount of back pressure.

I think 4" is overkill on anything but a 1000HP+ car or maybe a turbo diesel truck.

3" should be fine in almost all cases. A full 3.5" might net some gain, but I wouldn't think it would be too much. 4" is just plain overkill.

Also if you have a external dump wastegate, you have less of a need for a big exhaust. Lot's of the exhaust gases when under full boost doesn't even need to go into the exhaust system at all.
 

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I agree...
If you're routing your wastegate into the exhaust system 4" inch from that union on might do nicely.
The exit from the back of the singles are around the 3" range so if your not routing the wastegate exhaust into main piping 4" probably won't help at all...
 

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Old School Socal Member
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T-78 or T-51 on an auto? You must be crazy or have a lot of money. I think that those turbos are a big overkill on the auto trans. I would suggest a six speed for those huge monsters. Just my $.02



ian
 

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fusion - T78 to big for an auto? Tell Henry Nguyen of Houston that, he's run multiple [email protected] with that setup on drag radials. I guess it's all up to the end user...
 

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488ci V10 Power
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Discussion Starter #10
fusion1 said:
T-78 or T-51 on an auto? You must be crazy or have a lot of money. I think that those turbos are a big overkill on the auto trans. I would suggest a six speed for those huge monsters. Just my $.02



ian
with a 4K stall, can you say..........6sp killer :D :D :D

so i guess a 4" really isnt neccesary then huh!
 

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AnArKey said:
Whatever you do in terms of exhaust remember that the WHOLE exhaust must be a bigger diameter to make a difference. If you have a 3" downpipe and 4" exhaust won't do diddly.

Also, you can go too big. Bigger exhaust will have more surface area and cool the exhaust gasses quicker, which can actually cause a small amount of back pressure.

I think 4" is overkill on anything but a 1000HP+ car or maybe a turbo diesel truck.

3" should be fine in almost all cases. A full 3.5" might net some gain, but I wouldn't think it would be too much. 4" is just plain overkill.

Also if you have a external dump wastegate, you have less of a need for a big exhaust. Lot's of the exhaust gases when under full boost doesn't even need to go into the exhaust system at all.
That is not entirely true.
a 3" DP and 4" Catback will flow better than all 3".
Having that extra volume before the muffler is a benefit.
It will most likely only be a few hp difference on a 5-600 hp car.
You will notice quicker spool up.
 
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