Big Bore Butterflies

[99 svt]

The SHO shop used to sell 37mm butterflies, stock SHO size, for an upgrade for the SVT. It sells 40mm ones for the SHO. Now that the SHO shop is no longer a vender I was trying to think how to do this upgrade. I e-mailed the SHO Brothers who still do the 40mm mod for the SHO and asked what they did with the old butterflies once they performed an upgrade. I also asked wheather the 40mm could be used on the SVT with some more machine work. This is an intrest thread. If enough people are interested I might be able to get the SHO Brothers to work something out. Also, does anyone know any other possible places to get the SHO butterflies besides a junked SHO engine?

 

[beyondloadedSE]

The largest bore on the svt uim is no bigger than 35 mm maximum! DemonSVT is running the largest bore uim with his triple extrude honed uim and his secondary ports measure 34.3 mm in diameter and thats honestly as much as you can get. The stock UIM measures 33 mm primary ports and 34.3 mm secondary ports. Making the LIM 3 mm larger than the uim would do nothing but slow intake velocity down. Of course, afterwards it meets the heads that cant be honed to 37 mm either since the LIM diameter tapers down anyways. Youll have a nice restriction when it hits the heads. 40 mm is out of the question. I dont think youll have any LIM left after that LOL.

Imagine making these ports 3mm larger?

Youll basically just end up with a oval port head thats been ported to fit the split port manifolds. You might as well just buy yourself some oval port heads if you want an intake that flows more cfm.

 

[SVTJON87]

yea sorry man but hes right it will do nothing more than slow intake velocity. bigger is not always better.

 

[99 svt]

I assumed since the SHO shop sold 37mm modded secondaries they could be made to work. Also at the higher RPMs it would make a difference, if only for us forces induction guys. Wish there was some way to flow test it to see the improvements or lack there of.

 

[morbid]

I don't think the 37mm butterflies imply they fit in 37mm ports, rather the ovular butterflies were 37mm long, and probably ~35mm wide. Our butterflies sit at an angle, not completely horizontal.

 

[beyondloadedSE]

I assumed since the SHO shop sold 37mm modded secondaries they could be made to work. Also at the higher RPMs it would make a difference, if only for us forces induction guys. Wish there was some way to flow test it to see the improvements or lack there of.

I believe SHO SHOP only did this to the secondary ports, but still, making the LIM 37 mm and not being able to compensate with the UIM is a waste.

 

[Pole120]

I've got two sets of SHO butterflies i acquired back when i was thinking of trying this. I was not surprised to find they will not bolt up to the contour LIM secondary shafts, the mounting holes are different distances apart. Also, the SVT and standard contour plates are nearly round whereas the SHO butterflies are very ovular.

I'll take some side-by side pics when i get out to my garage next.

You've got your work cut out for you if you decide to try this.

My intention is to do something a little different to go with my max honed UIM.

~Josh