| Author |
Message |
Robert Faber (F129b)
New member
Username: F129b
Post Number: 21
Registered: 8-2003
| | Posted on Wednesday, September 03, 2003 - 8:26 pm: | |
The previous owner of my 355 put a toggle switch behind the seat which actuates a valve/chamber(?) in the TUBI. I can open it and have a beautiful loud(3,000 +RPM) sound at idle and <3,000 rpm. Is THAT a bad thing to do? Seems to have no effect on engine performance or health. |
Stewart Chung (Navygakman)
Junior Member
Username: Navygakman
Post Number: 122
Registered: 2-2002
| | Posted on Tuesday, September 02, 2003 - 11:29 am: | |
Good point Steve. When I think "back pressure", I am thinking of the "popping" my car makes during downshifts and deceleration (but not "back fire" which sounds like a loud firecracker). After the motor was rebuilt by Nick and Kermit, it is consistently popping while downshift and deceleration. They (and others when race cars) say that modified motors always pop and they call it "back pressure". I noticed it is less noticible with the Tubi than the "Kermit" (a custom made exhaust). It does not bother me much but I just want to know that this is normal and not harmful to the motor in the long run. |
Steve Magnusson (91tr)
Intermediate Member
Username: 91tr
Post Number: 2079
Registered: 1-2001
| | Posted on Tuesday, September 02, 2003 - 8:38 am: | |
Jp -- IME you'll get both answers to this question because the definition of "back pressure" gets misused/abused/confused/misapplied -- e.g.,
a small diameter, long exhaust tube will be characterized as "high back pressure" when, in fact, it actually has a lower effective back pressure than a larger diameter, short exhaust tube at low RPM due to resonance effects in a pulsed flow and how their timing inteacts with the valve openings/closings.
Bottom line is that you want to match your intake/valve/stroke/exhaust systems in a reasonable way for the running characteristics that you are trying to achieve. Personally, I wouldn't trade a few top end HP if it means dropping the mid-band torque. What's the motivation for your post -- someone trying to sell you something? |
John M.Pisacane (Chazferrari)
New member
Username: Chazferrari
Post Number: 24
Registered: 8-2003
| | Posted on Monday, September 01, 2003 - 5:48 pm: | |
Jp |