RS/RSR High/low Butterfly Throttle Body Assemblies

[RIX 911RS]

Why was there two different styles? Did one make more power at higher RPM? What size where the RS/RSR Throttle Bodies?

[BReyes]

RSR more R than RS. But yes mods include bigger, for purpose of greater horsepower output. And can't help but think of the bling factor when you open the lid.

Regards,

[lateapex911]

Ah...but thats not "bling"......... those are old school..."bling" to me is showy flashy stuff that serves no real purpose. Like most wings on Honda Accord LXs. Or the "Blue" headlights.....kinda look like HIDs, but less light than a standard halogen, and more annoying to everyone else..

But these...they are the real deal. When originally installed they were part of the ultimate HP package for that particular engine/cam/compression/fuel injection, etc combo.

[prebordao]

Discovered this old thread and i wonder what answer is. Can anyone chime in ?
Why high or low ?

[RWebb]

my guess would be either torque at lower rpm, or avoiding reversion

a [prolonged]search might be illuminating...

[boba]

The HB were for racing and the low butterfly were for street daily driver. The race motor was optimized to run wide open at high RPM. This include larger ports, valves, exhaust primary tubes, head flow, higher compression. The HB matched the larger ports (high RPM power) and higher velocity flow. The low butterfly was more flexible throughout the power band. Smaller ports pull the power band lower in the RPM range and make it wider. In other words, more drivable. The race engine was peaky with its power band at the top of the RPM range. Not comfortable driving around town in traffic.

The 2.8 RSR was 43mm and the 2.5 ST was 41mm. I think the 2.7 RS was 38mm.

[prebordao]

I've found another thread where the reason for HB was to avoid intake reversion probably due to more agressive / overlapped cams.

[Flieger]

They were less prone to sticking than slide valves were.

[Steve@Rennsport]

Originally Posted by prebordao

I've found another thread where the reason for HB was to avoid intake reversion probably due to more agressive / overlapped cams.

That is correct.