70 or 75 TB?
TECH SAVANT
Joined: Dec 2006
Posts: 10,937
From: Saint Augustine, FL
It true--although a toilet's operating cycle is manually initiated, the remainder of the cycle is handled by a fully automated, hydraulically powered, negative feedback closed loop flow control system--and of course gravity...
There's nothing like that in a lousy throttle body--at least not in ours, those fly-by-wire things are kind of scary looking...
There's nothing like that in a lousy throttle body--at least not in ours, those fly-by-wire things are kind of scary looking...
Underboss
Joined: Jan 2006
Posts: 20,272
From: Helaware
4th Gear Member
Joined: Apr 2008
Posts: 1,306
From: New York
anything over 70mm will be a waste. Once you have a plenum and a 70mm that section wont be the bottle neck of your intake system and you will be at WOT earlier then your flooring it. You will be moving as much air as the engine can suck in even with the TB at say 3/4 open so the rest of the range will be wasted in a way. One way to look at it is that under normal driving you will need very little pedal movement to get going.
If you dont want to S/C it you should get a 70mm, the velocity charge of the air (momentum basically of the air) will be lost with a large TB. Think about a massive TB with the same volumetric flow rate you will have slower moving air.
With your exhaust work, you could see some gains with a tb and plenum, make sure to tune it though. A wideband & tuner will be huge, more so then a TB and plenum. I mean i trap at near 105 with only a 70mm accufab TB on my intake side beside a drop in K&N filter.
EDIT:
i didn't see you posted this, basically the same thing you said haha
Good luck on your build!
If you dont want to S/C it you should get a 70mm, the velocity charge of the air (momentum basically of the air) will be lost with a large TB. Think about a massive TB with the same volumetric flow rate you will have slower moving air.
With your exhaust work, you could see some gains with a tb and plenum, make sure to tune it though. A wideband & tuner will be huge, more so then a TB and plenum. I mean i trap at near 105 with only a 70mm accufab TB on my intake side beside a drop in K&N filter.
EDIT:
When running naturally aspirated, with our 46L 2V engines, a 70mm TB (coupled with an after market upper plenum) provides an optimal combination of air flow and charge velocity.
A 75mm TB will not flow any additional air, as the plenum is the limiting factor--it won't hurt anything so much as to be noticeable (a very slight decrease in charge velocity), but it won't help either--again this is when running n/a.
BBKs 78mm TB/plenum combo is gross overkill if running n/a and would likely cause a large enough decrease in charge velocity, at WOT and lower/mid rpms, to be quite noticeable.
Here's some good info from Accufab, introduced and annotated by your's truly...
A 75mm TB will not flow any additional air, as the plenum is the limiting factor--it won't hurt anything so much as to be noticeable (a very slight decrease in charge velocity), but it won't help either--again this is when running n/a.
BBKs 78mm TB/plenum combo is gross overkill if running n/a and would likely cause a large enough decrease in charge velocity, at WOT and lower/mid rpms, to be quite noticeable.
Here's some good info from Accufab, introduced and annotated by your's truly...
Good luck on your build!
Last edited by stangalator; Jul 1, 2010 at 09:00 AM.
