3.5" vs 4" downpipe.. - Diesel Truck Forum - TheDieselGarage.com
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post #1 of 13 (permalink) Old 05-03-2006, 12:34 AM Thread Starter
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3.5" vs 4" downpipe..

not sure what to use? will going to 4" make that much of a difference on just a chipped truck? i kinda want to go with a 3.5" one just so i can keep my stock cat back (see sig). what do u guys think?

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post #2 of 13 (permalink) Old 05-03-2006, 01:42 AM
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You already killed the kitty, why not just do the 4 inch all the way??


Just my 2 cents.

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post #3 of 13 (permalink) Old 05-03-2006, 03:29 AM
 
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Quote:
Originally Posted by Diesel Dog
You already killed the kitty, why not just do the 4 inch all the way??


Just my 2 cents.
because IMHO, a 3.5" DP is superior to a 4" downpipe until you start dealing with larger frame turbos that have outlet's significantly larger than 2.8" :

Dave, did my 3.5" downpipe look like it was at some sort of disadvantage at the track the other day? :umno:

Hammer
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post #4 of 13 (permalink) Old 05-03-2006, 03:56 AM
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Quote:
Originally Posted by TheHammer69
because IMHO, a 3.5" DP is superior to a 4" downpipe until you start dealing with larger frame turbos that have outlet's significantly larger than 2.8" :

Dave, did my 3.5" downpipe look like it was at some sort of disadvantage at the track the other day? :umno:

Hammer
Just preparing for future mods : :

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post #5 of 13 (permalink) Old 05-03-2006, 04:05 AM
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The 3.5" vs 4" debate will live forever I fear. Some swear by it, others have even gone so far as to build custom 4" downpipes for H2E style turbos only to switch back to 3.5".

My standard answer is this...if the truck spends a SIGNIFICANT amount of time at low RPM (in town), particularly towing (work truck in rush hour traffic for example)...stay with the 3.5" downpipe. If bottom end grunt is a MUST, stay with the 3.5" downpipe. If the truck is running stock or close to stock power levels, stay with the 3.5" downpipe.

If top end charge, higher RPM driving, etc...is the primary concern...go with the 4". If max highway towing EGT reduction is the primary concern, go with the 4". If you're building a race truck, go with the 4" downpipe.

That's my take on it...FWIW.

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post #6 of 13 (permalink) Old 05-03-2006, 05:09 AM
 
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Quote:
Originally Posted by Diesel Dog
Just preparing for future mods : :
The cool thing is...if you ever are in the situation that you need a 4" downpipe (i.e. large frame turbo) you will be using a different downpipe to go to the outlet of that turbo because it is not in the OEm location. In other words, whether you buy a 3.5" or 4" now...you would have to replace either one later anyway. That is hwy I say 3.5

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post #7 of 13 (permalink) Old 05-03-2006, 06:01 AM
 
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If there is no price difference go for the 4".If not stay with 3.5 DP.

I had a 4" on my BB turbo never could compare to see but for future upgrades like Hammer said the H2E and QSSB come with a 3.5 in the kit and it mts in a completely different location.

I gave away my 4"DP along with mostly all my other turbo parts.

Mike
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post #8 of 13 (permalink) Old 05-03-2006, 11:23 AM
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Quote:
Originally Posted by ITPDiesel
The 3.5" vs 4" debate will live forever I fear. Some swear by it, others have even gone so far as to build custom 4" downpipes for H2E style turbos only to switch back to 3.5".

My standard answer is this...if the truck spends a SIGNIFICANT amount of time at low RPM (in town), particularly towing (work truck in rush hour traffic for example)...stay with the 3.5" downpipe. If bottom end grunt is a MUST, stay with the 3.5" downpipe. If the truck is running stock or close to stock power levels, stay with the 3.5" downpipe.

If top end charge, higher RPM driving, etc...is the primary concern...go with the 4". If max highway towing EGT reduction is the primary concern, go with the 4". If you're building a race truck, go with the 4" downpipe.

That's my take on it...FWIW.
:agreed: I've been told by many different people their looks on the turbo pipes. All of which has made sense to me. Just like now. All I can suggest is to do what you want. I know people with 4" turbo pipes, and love it, I also know people with 3.5". Like mention above, it all depends on what you do with your truck,and what application will work best. My opinion is to go with a 4" dp, the quicker spool up, and lower egt's are worth it, IMO. Whatever you decide good luck!!:Thumbup:


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post #9 of 13 (permalink) Old 05-05-2006, 11:31 PM
 
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I have heard that a 4" down will lose some bottom end. A guy technically (sp) explaned it on another site. Stay with a 3 1/2"
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post #10 of 13 (permalink) Old 05-06-2006, 12:13 AM
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Quote:
Originally Posted by ITPDiesel
The 3.5" vs 4" debate will live forever I fear. Some swear by it, others have even gone so far as to build custom 4" downpipes for H2E style turbos only to switch back to 3.5".

My standard answer is this...if the truck spends a SIGNIFICANT amount of time at low RPM (in town), particularly towing (work truck in rush hour traffic for example)...stay with the 3.5" downpipe. If bottom end grunt is a MUST, stay with the 3.5" downpipe. If the truck is running stock or close to stock power levels, stay with the 3.5" downpipe.

If top end charge, higher RPM driving, etc...is the primary concern...go with the 4". If max highway towing EGT reduction is the primary concern, go with the 4". If you're building a race truck, go with the 4" downpipe.

That's my take on it...FWIW.

Yep. :Thumbup:

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