612 "golf tee" exhaust mod

Carlo- Motronic 7.3.2 612s (very early 612s have Motronic 7.1.1) have pneumatic exhaust bypass valves on the inside exhaust tailpipes that are spring loaded to the open position and closed by vacuum from the same accumulator that powers the brake booster. By removing the vacuum lines from the pneumatic valves and plugging them (bolts may be better than gold tees), the valves will stay open all the time. In this photo, you can see the pneumatic valves and where the vacuum hose fits. Make sure and tie the lines out of the way and plug the valve openings to prevent groad from getting inside.
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The Golf Tee mod is a BMW trick, been doing that to Bimmers for years...

 

Ferrari trick since at least the mid 90s, except on Maranellos the valves are fail closed so must be set up to have the vacuum hoses go directly to the pneumatic valve T.

 

I started to do this with my F430 at one point and was told there's a noticeable sacrifice in low end torque associated and decided it wasn't worth it. Any idea how noticeable it is on the 612, if at all? I love the sound of my 612 with tubi mufflers and wouldn't change it, not to mention I won't have it long, but still I'm curious.

 

Just don't stick a banana in there!

 

Bob- I doubt there is any torque reduction on an F430 or a 612. They are primarily there for noise reduction standards.

 

Googling old threads, seems a very common misconception that there's some loss of low end, people bringing it up as here say but nobody actually with any numbers or real proof. I've believed since my hotrodding days back in the 80's that you need some amount of back pressure for optimal results at low end, always thought a crossover pipe assisted, but doesn't seem so. Seems a crossover just evens pulses between banks. Huh. Anyway, I'd go tubi and leave the valves alone. Must be there for some reason

 

No loss of torque on the 599. Mine are always open and it's not that loud.

 

Bob- On a V12 any crossover or X-pipe will cost you hp and torque at all rpm levels with test data to prove it. On 90 degree crank V8s like those on US and German engines, a crossover or X-pipe will improve exhaust flow and hp and torque because of the way the exhaust pulses flow from what is essentially four V-twins on the same crank. Flat crank V8s are two inline fours on the same crank and the exhaust is self-extracting, like a V12.

 

What about the early models which have no bypass valves at all? Like my 2004 there is no vacuum pipe on the exhaust. Does that mean they are always completely open? Or is it a different exhaust? My Scag is very soft in sound and I wonder how I could get a little bit more out of it w/o changing the exhaust.

Any ideas?

Thanks, Stefan

 

I've got a couple of brand new 612 mufflers with the vacuum pipes if any interest. Wouldn't ask much for them.

 

Stefan- I have not seen anybody cut open a 612 muffler like we have for the Maranellos. I doubt if the mufflers are the same. You can check yourself by just putting your hand behind the pipes while she is idling. If you are getting the same flow from both pipes on one side, the mufflers are different from the later Motronic 7.3.2 mufflers. On those, if you plug the vacuum lines, nearly all the flow at all speeds will be coming out of the two inside pipes where the pneumatic valves are.

Unfortunately, I have only seen early 612 parts catalogs, so cannot confirm whether they are different or not. Even the HGTS/HGTC sports exhaust does not show on those early catalogs. Your local dealer can look it up on MODIS for you.

 

No worky on a 2007 the valves work opposite and require extensive plumbing to get more sound