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Discussion Starter #1
Running a bw s475 on a 4.8 LS. I have a 102mm throttle body, but I’m running 3” cold side before it.
If nothing else it just looks funny, but I’m wondering if there’s going to be any performance benefit from going 4” on the entirety of the cold side.
I also have nothing better to do...
 

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Appearance only. 3" is large enough for 6L+ IMO, 3.5" looks better than 4".

3" cold side 3.5" hotside on s475 408LS 99 trans am (what the customer wanted - long story)



 

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Discussion Starter #6
para I missed those pics before - that's great work! I suppose my next question is whats the move for an intercooler? I run a 3" ATA, and i'm thinking of just hacking the 3" in/out and modifying it to accept 4". It's fine china so I have no attachment to it if I fail miserably.
 

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Leave the 3"

You will not see any performance gain on that S475

I just went from a S484 to a S491 and will probably go from 3" to 3.5" but not until I run it on the 3" .

And probably not at all .
 

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para I missed those pics before - that's great work! I suppose my next question is whats the move for an intercooler? I run a 3" ATA, and i'm thinking of just hacking the 3" in/out and modifying it to accept 4". It's fine china so I have no attachment to it if I fail miserably.
Like I said, I prefer 3.5 instead of four. the bend radius is once you go to 4 inch start getting unwieldy and difficult to work with. And that your motor size and power level this is still all cosmetic.

If you make the swap there's two ways to go about it. You could just run a reducer coupler off the intercooler that will step the piping up to 4in using the 3in coupler already on the intercooler. Or you can cut off the end of the end tank and overlize a larger tube and weld it to the end tank
 

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Leave the 3"

You will not see any performance gain on that S475

I just went from a S484 to a S491 and will probably go from 3" to 3.5" but not until I run it on the 3" .

And probably not at all .
keep in mind you size intercooler piping to motor displacement and maximum rpm, not turbo size. If your new larger turbo combination still revs to the same maximum rpm is your old combination then there is no reason to change intercooler piping sizes.
 

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Pipe area size is directly proportional to amount of flow thru the pipe and velocity you wish to maintain. Pressure and temp of the air charge along with turbo mass flow determine the cfm thru the system and thus velocity can be calculated from the area

The question becomes how fast is too fast? I think keeping it below mach 0.3 is a good idea.

The motor only cares when its not in boost and has to breathe like a na motor.
 

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Discussion Starter #13
How about I wait until my local strip opens up. Last I ran this car it was consistent enough to get some sort of analysis from a change. I'll run it 3" and then make the change, been doing a lot of work on it since everything is shut down. Might be able to get it on a dyno even. This thing has never seen a dyno haha.

I'd be curious to see if it drops charge temp at all.
 

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Yes it does.. When the air expands into the larger tubing, it cools down some.. Now will that add power or just make your tune up safer, I don't know..
 

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The outlet of my S475 is 3 1/2", so I sized my frozen boost IC at 3 1/2". A simple 3 1/2"-4" 45* coupler gets me to the TB. Simple. My little 5.3 is making about 1060 (3400# @ 152 mph) on 23/5# and C16. I'm a fan of the KISS method.
 

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