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Thread: Bigger Exhaust ? for 550+ whp

  1. #1
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    Bigger Exhaust ? for 550+ whp

    I ve searched alot through the internet , but I cant find a solid answer
    I ve an e30 M50b30 (m54b30 internals ) with top mount Holset 6764 exh16 , I m shooting for 550-650 whp (I hope )on 95 octane + water Methanol

    my turbine flange is 2.5", and I used an adapter 2.5 to 3" down pipe , to a whole 3" exhaust with Mitsubishi evo 3" resonator to an HKS hi power muffler replica , I only have 4 90 degree bends from the turbo to the end of the exhaust

    20272201_10159099344690363_868885174_n.jpg

    20885149_10159099346180363_2141922492_n.jpg

    would this exhaust cause any restriction ?
    would bigger down pipe (only) increase spool ? ( was planning to upgrade to 4" but my tuner tells me that I ll lose some torque and suggest 3.5")

    If I go bigger ( do I need ? plan is to have power available on lowest boost , 18 -19 psi Max ) ,
    I hear two theories ,
    1- Bigger downpipe is better into smaller exhaust as of 4" downpipe to 3.5 exhaust ( based on that, for a turbo engine better exhaust is no exhaust , and gases slow down at the end of the exhaust )
    or
    2- 3.5 " downpipe to a bigger 4" exhaust ?

    I ve been searching for 3 days and only getting mixed reviews

    N.B :in my country the 3.5 pipes are rare and though more expensive

  2. #2
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    Why would your tuner tell you that there would be a TQ loss ?
    Turbos need to flow. Its not a SCer.

    For 600 whp or even 750 3.5" is more then sufficient. Probably no gains from 3.5 to 4. But certainly a gain from 3 - 3.5.

    Go 3.5 for clearance. I ran a full 4" for a few years, sucked for clearance. Recently tigged up a 3.5 and couldn't be happier with it. No more scrapping
    1996 332IS
    Built 3.2
    CES/Steed TS Precision 6466, spraying a "$π!℅" load of meth.
    Technique Tuning 80# tune.
    1/4 mile 10.84 @ 136.72
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  3. #3
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    Bigger Exhaust ? for 550+ whp

    You should leave whatever tuner that is... yesterday.




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    1998 Turbo: PTE6870 | 1.15 ar | Hp Cover, Custom Divided T4 bottom-mount, 3.5" SS exhaust, Dual Turbosmart Compgates, Turbosmart Raceport BOV, 3.5" Treadstone Intercooler, 3.5" Vibrant resonator and muffler, Arp 2k Headstuds | Arp 2k Main studs | 87mm Je pistons | Eagle rods | 9.2:1 static compression, Ces 87mm cutring, Custom solid rear subframe bushings, Akg 85d diff bushings, 4 clutch 3.15 diff, , Poly engine mounts, UUC trans mounts W/ enforcers, 22RPD OBD2 Stock ECU id1700 E85 tune, 22RPD Big power Transmission swap w/ GS6-53

  4. #4
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    Another note, its more important to have a larger exhaust than downpipe.
    Or equal.
    3" downpipe into 3.5 exhaust is better than 3.5 downpipe into 3" exhaust.
    Reasons velocity, and as the exhaust cools it expands. Kinda like how its kosher to have 2.5 hot side then 3" cold.
    For 600 HP I would do either 3" downpipe and 3.5 exhaust or 3.5 the whole way.
    1996 332IS
    Built 3.2
    CES/Steed TS Precision 6466, spraying a "$π!℅" load of meth.
    Technique Tuning 80# tune.
    1/4 mile 10.84 @ 136.72
    Your 1 and only stop for all your BMW performance needs
    WWW.CESMOTORSPORT.COM

  5. #5
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    Quote Originally Posted by Butters Stoch View Post
    Another note, its more important to have a larger exhaust than downpipe.
    Or equal.
    3" downpipe into 3.5 exhaust is better than 3.5 downpipe into 3" exhaust.
    Reasons velocity, and as the exhaust cools it expands. Kinda like how its kosher to have 2.5 hot side then 3" cold.
    For 600 HP I would do either 3" downpipe and 3.5 exhaust or 3.5 the whole way.
    It's the other way around really... Larger DP is more important... hot gases expand

  6. #6
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    Quote Originally Posted by NOTORIOUS VR View Post

    It's the other way around really... Larger DP is more important... hot gases expand
    Not sure about that.
    Iirc tests have shown how I wrote it. Maybe I'm wrong but velocity will push and then expand as it cools. Like charge piping.
    1996 332IS
    Built 3.2
    CES/Steed TS Precision 6466, spraying a "$π!℅" load of meth.
    Technique Tuning 80# tune.
    1/4 mile 10.84 @ 136.72
    Your 1 and only stop for all your BMW performance needs
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  7. #7
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    Gas expands as it heats up. There could be other forces at play in a turbo exhaust that make it work with a big DP and small rear, but I would go big on both. The Super Street article on the turbo showed a 3.5 rear added power at the 500+ rwhp level over a 3.0 exhaust on a Toyota Supra. They then added a 3.5 DP and picked up more power. They never tested the 3.5 DP with the 3.0 rear so we don't know how that combination would have fared.

    http://www.superstreetonline.com/how...ust-test-tech/

    Charge piping might be different. The added velocity of the air in the smaller hotside pipe might be helping get the air through the intercooler.
    Last edited by pbonsalb; 08-16-2017 at 01:47 PM.

  8. #8
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    Quote Originally Posted by pbonsalb View Post
    Gas expands as it heats up. There could be other forces at play in a turbo exhaust that make it work with a big DP and small rear, but I would go big on both. The Super Street article on the turbo showed a 3.5 rear added power at the 500+ rwhp level over a 3.0 exhaust on a Toyota Supra. They then added a 3.5 DP and picked up more power. They never tested the 3.5 DP with the 3.0 rear so we don't know how that combination would have fared.

    http://www.superstreetonline.com/how...ust-test-tech/

    Charge piping might be different. The added velocity of the air in the smaller hotside pipe might be helping get the air through the intercooler.
    At the end of the day, on a turbo car you're working with a pressure differential to drive the turbine... a bigger pipe after the turbine is always going to be better for a turbo car.

  9. #9
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    This is what I have been through for past days 😂😂😂 Mixed reviews
    I came across the superstreet article
    They picked up to 100 whp from going full 3.5 exhaust

    Another trusted tuner from sweden showed me 4" dp into 3" exhaust on holset hx40 making 685 whp on m52 with e85
    I m. Really confused

  10. #10
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    Quote Originally Posted by JOMARO View Post
    This is what I have been through for past days  Mixed reviews
    I came across the superstreet article
    They picked up to 100 whp from going full 3.5 exhaust

    Another trusted tuner from sweden showed me 4" dp into 3" exhaust on holset hx40 making 685 whp on m52 with e85
    I m. Really confused
    There isn't much to be confused about.

    Can you make 600+ on a 3", sure... Will you gain power by going bigger? Most likely.

    What it is all worth to you, only you can answer that.

  11. #11
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    I m settled on upgrading my exhaust , just cant choose wither a full 3.5" (DP+ Exh)
    or 4" DP with 3.5 "exhaust

  12. #12
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    do whichever fits better.


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  13. #13
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  14. #14
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    Quote Originally Posted by JOMARO View Post
    I m settled on upgrading my exhaust , just cant choose wither a full 3.5" (DP+ Exh)
    or 4" DP with 3.5 "exhaust
    option two would by my choice if you have the room and the $$... option one is going to be more than sufficient for your power goals though.

  15. #15
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    Step one: Calculate the amount of Air flow is required through an engine to obtain said hp.
    Step 1.5: calculate density of hot gas
    Step Two: Given density and flow rate, you can calculate velocity of the gas through each diameter of pipe.
    Step three: Calculate the pressure drop from each diameter.
    Step Four: Choose the diameter that gives you the lowest respectable pressure drop. (at some point it will be minimal difference)
    Step five: Confirm diameter will fit.
    Step 5.5: Don't forget to confirm that your waste gate will be able to control your low boost levels. (larger exhaust now means more flow through it and less through waste gate meaning harder to control boost levels at lower levels)
    Step Six: Drink beer that was a lot of math
    Step seven: Ask euro to find his excel sheet for this bs
    Capital Driving Club Car # 102
    How to turbo your car:
    Step one. Install ecu and learn to tune and or have it tuned.
    Step two. Install injectors and retune.
    Step three. Install turbo parts and bits. get it running with out leaks. DO NOT DRIVE IT. Idling should be ok
    Step four. Retune car
    Step five enjoy

  16. #16
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    Step 1: put the biggest mfer exhaust pipe you can fit on that hoe.
    Step 2: brapppppppp
    Step 3: stututututu
    Step 4: thank me

  17. #17
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    5' of 3'' exhaust $180.
    hoorry shiitt!



  18. #18
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  19. #19
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    I went 3.5" for the downpipe and exhaust (just a straight pipe ,no mufflers no resonators ) will hit the dyno on Monday , and will see what numbers can we get

  20. #20
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    Quote Originally Posted by JOMARO View Post
    will hit the dyno on Monday ,
    Results ?
    1996 332IS
    Built 3.2
    CES/Steed TS Precision 6466, spraying a "$π!℅" load of meth.
    Technique Tuning 80# tune.
    1/4 mile 10.84 @ 136.72
    Your 1 and only stop for all your BMW performance needs
    WWW.CESMOTORSPORT.COM

  21. #21
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    650 whp -577 lb/ft on 1.5 bar 93 octane + water methanol

    I m more than satisfied :-) , will post dyno sheets soon

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