Toymods Car Club Inc: Tech & Conversions => BOV. is it needed??

Toymods Car Club
www.toymods.org.au

F.A.Q.

Home

Members

Toymods » Tech & Conversions » BOV. is it needed?? Show: Today's Posts :: Show Polls Email to friend

Author

Topic

JustenGT4
Forums Junkie

Location:
Canberra
Registered:
June 2003

Re: BOV. is it needed??	Tue, 12 April 2005 02:00

OMG how much ill informed info is out there on BOV's 1st up, no ST185 ever came with a factory BOV. Manufacturers who use BOV's do so for only one reason...to reduce noise. All factory BOV are recirculating, they are there to prevent reversion of the intake charge back thru the turbo which makes that lovely fluttering noise. Some may like it but manufacturers do not. Actually i tell a little lie there, for homologated models like the 205 the BOV was also there to feed the antilag system...sneaky buggers. In very high boost applications this intake reversion (or more accurately the pressure wave reflected off the closing butterfly)can supposedly 'shock' the compressor wheel and cause a shaft failure. I have never seen this happen (and i have run some pretty decent boost levels) but have heard 3rd hand of it happening on a big boost circuit car. Sounds possible but it is obviously very rare. The other reason is as Norbie states that the pressure spike can pop hoses...of course Norbie could just shell out for decent clamps and it wouldn't be an issue Now, i have done with and without BOV testing and can confidently state that the preformance gain or loss is so small as to be of no consequence. I actually had a very small drop in performance as the intake piping had to refill after every BOV vent. The turbo does this very fast so you couldn't feel any difference but by the clock i dropped a 0.1-0.2 secs off 0-100 kph (Haltec data log). As for the pressure build up slowing the compressor, bollocks. The loss of exhaust gas energy on closed throttle is many orders of magnitude greater than any energy the reflected pulse might impart to the compressor wheel. The wheel does slow on closed throttle but just because you have taken away the energy that drives it. What most people don't understand about turbos is that they are NOT a pump, they are a turbine. All turbines do is speed up air. You create the pressure differential by that fast moving air hitting the diffuser and slowing down again...basically more fast air runs up the arse of the slowed air in front of it thereby creating a pressure increase. You can run a turbo flat out with your hand over the outlet and once you overcome the energy from the moving air boost pressure will stabilise and NOT continue to build...it'll just stop moving air. It's not like a positive displacement pump (roots blower) that will keep trying to force more air in. Here's a classic test for the doubtful. Grab an electric fan (the turbine) block the outlet and see what happens.....you'll hear the fan actually speed up, NOT slow down. Hope that clears up some of the misinformation. [Report message to a moderator]

[Message index]

-=] Back to Top [=-

Current Time: Tue Jul 29 23:32:30 UTC 2025

Total time taken to generate the page: 0.0043890476226807 seconds

.:: Contact :: Home ::.