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Discussion Starter #1
Looking at a doing a vitara with GT35 vband .63 housing build.

Should I be using 1.25" runners or 1.5"? I am probably going for 1.25" to promote spooling, however, I see a lot of setups running 1.5".
 

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Well since youre running a GT35, Im going to assume youre going for 550-600 hp. In which case I would suggest you go with the 1.5" primaries.

The design of the manifold also plays into this. If youre building some long tube design that has a lot of volume, then you may want to keep the primaries small. While on a compact design the 1.5" primaries would make sense even on lower power setups.

I would also take into consideration which size pipe matches up to the exhaust ports when you crush the pipe down to an oval.
 

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Discussion Starter #4
Well since youre running a GT35, Im going to assume youre going for 550-600 hp. In which case I would suggest you go with the 1.5" primaries.

The design of the manifold also plays into this. If youre building some long tube design that has a lot of volume, then you may want to keep the primaries small. While on a compact design the 1.5" primaries would make sense even on lower power setups.

I would also take into consideration which size pipe matches up to the exhaust ports when you crush the pipe down to an oval.
Exactly my thoughts, however, I'm looking at doing long primaries which may have an effect on response if I choose to go 1.5"? I have seen Evo's make huge power on 1.25", totally different make and model I know - But seeing as it's a SOHC 1.6l, 1.25" should be OK?

Just can't find any dyno plots comparing the 2
 

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Well since youre running a GT35, Im going to assume youre going for 550-600 hp. In which case I would suggest you go with the 1.5" primaries.

The design of the manifold also plays into this. If youre building some long tube design that has a lot of volume, then you may want to keep the primaries small. While on a compact design the 1.5" primaries would make sense even on lower power setups.

I would also take into consideration which size pipe matches up to the exhaust ports when you crush the pipe down to an oval.
Exactly my thoughts, however, I'm looking at doing long primaries which may have an effect on response if I choose to go 1.5"? I have seen Evo's make huge power on 1.25", totally different make and model I know - But seeing as it's a SOHC 1.6l, 1.25" should be OK?

Just can't find any dyno plots comparing the 2
Never thought about this but, wouldn't this have the same effect as a large vs small turbine housing? If so, youu are getting a 35r to make power, not spool fast. Go 1.5
 
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