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Thread: 4 inch exhaust?

  1. #21
    turbo addict
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    Re: 4 inch exhaust?

    The melting point of aluminum is 1218 degrees Fahrenheit do you think egts get that high? The head is aluminum and doesn't melt.

  2. #22
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    Re: 4 inch exhaust?

    Pistons are aluminum as well. The alloy probably plays a big part too.

  3. #23
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    Re: 4 inch exhaust?

    I just did a quick google search. Didn't list many of the alloys and such

  4. #24
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    Re: 4 inch exhaust?

    The material for engine heads vary from aluminum alloys to cast iron. Cast iron heads are of the SAE G2500 grade gray iron. In the case of aluminum heads a thermal resistive alloy is used, usually 356-T6 or A390 heat treatable alloys. It is important to choose a thermal resistive alloy to prevent the condition known as warped heads. Warped heads are caused from uneven thermal expansion and contraction.

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    For some reason it won't let me post the link to where I found that from. Keep getting 403 forbidden.

  5. #25
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    Re: 4 inch exhaust?

    I don't think the exhaust would melt but that's just my guess/opinion

  6. #26
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    Re: 4 inch exhaust?

    I don't think the exhaust would melt but that's just my guess/opinion

  7. #27
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    Re: 4 inch exhaust?

    the combustion chambers and exhaust ports are surrounded by coolant also... egts can be as high as 1800 in extreme conditions, but 1500 can be "normal"...

  8. #28
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    Re: 4 inch exhaust?

    Pistons aren't though. Unless splash oil and the bores being cooled by coolant is enough.

  9. #29
    Super Moderator Turbo Mopar Staff contraption22's Avatar
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    Re: 4 inch exhaust?

    Pistons are not constantly exposed to those temps. They are alternately exposed to cool air fuel mixture. Plus much the piston's heat is absorbed by the engine oil and cylinder bores.
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  10. #30
    turbo addict Turbo Mopar Contributor
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    Re: 4 inch exhaust?

    Does a Super 50 stage 3 turbine need a 4" exhaust? No.

    You might gain a little spool but probably zero top end. That means if your exhaust is heavier, its not going to help.
    Brent GREAT DEPRESSION RACING 1992 Duster 3.0T The Junkyard - MS II, OEM 10:1 -[I] Old - 11.5@125 22psi $90 [U]Stock[/U] 3.0 Junk Motor - 1 bar MAP [/I] 1994 Spirit 3.0T - 11.5@120 20 psi - Daily :eyebrows: Holset He351 -FT600 - 393whp 457ft/lb @18psi 1994 Spirit 3.0T a670 - He341, stock fuel, BEGI. Wife's into kid's project. 1990 Lebaron Coupe 2.2 TI/II non IC, a413 1990 Spirit 3.0 E.S. 41TE -- 1993 Spirit 3.0 E.S. 41TE -- 1994 Duster 3.0 A543 1981 Starlet KP61 Potential driver -- 1981 Starlet KP61 Parts -- 1983 Starlet KP61 Drag 2005 Durango Hemi Limited -- 1998 Dodge 12v 47re. AFC mods, No plate, Mack plug, Boost elbow -- 2011 Dodge 6.7 G56

  11. #31
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    Re: 4 inch exhaust?

    I found a few things while searching around. People that do use aluminum downpipes use 11 gauge and then 16 gauge for the rest of it. Some have said they can crack if you have a tight bend right off the turbo. Some said if it backfires you can have problems.

  12. #32
    Garrett booster
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    Re: 4 inch exhaust?

    Quote Originally Posted by glhs875 View Post
    I ran a 4" exhaust on my 87 GLHS. I don't see myself running anything smaller than 4" in the future.

    Quote Originally Posted by Lotashelbys View Post
    I have 4" exhaust on my 89 CSX and love the sound. It makes me want to run it on every car I own. The only way to run it full length on a Shadow is to run 2.5" rear spring/coil-over setup.
    Are both of you running an internal wastegate?

  13. #33
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    Re: 4 inch exhaust?

    Quote Originally Posted by cdavis View Post
    Are both of you running an internal wastegate?
    I had an internal wastegate. Although with uncontrollable boost creep starting at 5500rpm. So my next 4" exhaust will have an external wastegate set up.

  14. #34
    Garrett booster
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    Re: 4 inch exhaust?

    Quote Originally Posted by Ondonti View Post
    Does a Super 50 stage 3 turbine need a 4" exhaust? No.

    You might gain a little spool but probably zero top end. That means if your exhaust is heavier, its not going to help.
    I would think that if it gained a little spool time that would mean I have reduced the backpressure after the turbine wheel. With that in mind, it should make a difference across the entire rpm band, along with a wider powerband from earlier spool time. Either way, I don't see a down side to going to 4 inch. I think I'm going to leave the 3 inch for now and get it running and tuned, then build a 4 inch downpipe about half way back and see what it does.

  15. #35
    Moderator Turbo Mopar Staff Vigo's Avatar
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    Re: 4 inch exhaust?

    I just saw a data point for the new supercharged Z06 that said that the exhaust had cooled to 600f by the time it entered the mufflers.

    Our EGTs might be 1600f as measured in the exhaust manifold, but that temp will drop sharply as the gas moves from a high pressure area in the manifold to the low pressure area after the turbine.

    I would guess that an aluminum exhaust it perfectly safe once you get past the downpipe and the bigger the exhaust, the safer the temp due to the pressure/temperature correlation.

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  16. #36
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    Re: 4 inch exhaust?

    I would think that if it gained a little spool time that would mean I have reduced the backpressure after the turbine wheel. With that in mind, it should make a difference across the entire rpm band, along with a wider powerband from earlier spool time. Either way, I don't see a down side to going to 4 inch.
    this... except weight, but thats why we are talking aluminum... or very thin stainless...

    and we prob wouldnt need full 4" to the back, once exhaust temps cool, the gases would condence and fit in 3-3.5" tubing...

  17. #37
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    Re: 4 inch exhaust?

    Hmmmm, going back to my side pipe setup, with a small bullet muffler, and mulling staying 3" or going to 4".
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  18. #38
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    Re: 4 inch exhaust?

    I think once I upgrade my turbo I will go to 4" aluminum exhaust out the side.

  19. #39
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    Re: 4 inch exhaust?

    Quote Originally Posted by cdavis View Post
    I would think that if it gained a little spool time that would mean I have reduced the backpressure after the turbine wheel. With that in mind, it should make a difference across the entire rpm band, along with a wider powerband from earlier spool time. Either way, I don't see a down side to going to 4 inch. I think I'm going to leave the 3 inch for now and get it running and tuned, then build a 4 inch downpipe about half way back and see what it does.
    How about I just say it won't do anything for that baby turbo. In my experience, spooling the turbo is not the same function of exhaust as top end HP when the wastegate is open. This is especially true if you have an open dump wastegate. I give less consideration to bandaiding subpar setups with exhaust that is way too big. Just because you minutely drop exhaust backpressure doesn't mean you will have measurable gains. People in more well refined platforms usually step to 3.5" when they get in the 700-800whp club. 3.5" pipe is more expensive so that is one reason to skip it.
    Brent GREAT DEPRESSION RACING 1992 Duster 3.0T The Junkyard - MS II, OEM 10:1 -[I] Old - 11.5@125 22psi $90 [U]Stock[/U] 3.0 Junk Motor - 1 bar MAP [/I] 1994 Spirit 3.0T - 11.5@120 20 psi - Daily :eyebrows: Holset He351 -FT600 - 393whp 457ft/lb @18psi 1994 Spirit 3.0T a670 - He341, stock fuel, BEGI. Wife's into kid's project. 1990 Lebaron Coupe 2.2 TI/II non IC, a413 1990 Spirit 3.0 E.S. 41TE -- 1993 Spirit 3.0 E.S. 41TE -- 1994 Duster 3.0 A543 1981 Starlet KP61 Potential driver -- 1981 Starlet KP61 Parts -- 1983 Starlet KP61 Drag 2005 Durango Hemi Limited -- 1998 Dodge 12v 47re. AFC mods, No plate, Mack plug, Boost elbow -- 2011 Dodge 6.7 G56

  20. #40
    Supporting Member Turbo Mopar Contributor rx2mazda's Avatar
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    Re: 4 inch exhaust?

    I have a full aluminum exhaust and muffler after about 12-15 inches of SS Dp. It cracked at the same weld point twice during the first 2 months or so. Both times it cracked was during acceleration with wheel hop being the culprit. Once I got the engine and wheels to play nice during accel it hasn't been a problem. Mine is full 3inch.

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