Wheres the best place to measure boost pressure?
#1
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fitting up my boost pressure gauge on my zetroinix afr/boost gauge and was wondering where you guys think the best place is to take the accurate readings from???..
what bout pipe going between the inlet manifold and the ez69 unit?
what bout pipe going between the inlet manifold and the ez69 unit?
#3
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Should be accurate pretty much anywhere, so long as the diameter of the pipe is adequate.
Below the throttle plate will register vacuum but no boost spikes, before the throttle plate won't show vacuum but boost spikes will register.
Below the throttle plate will register vacuum but no boost spikes, before the throttle plate won't show vacuum but boost spikes will register.
#4
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what do you mean by boost "spikes"?
Taking a vacuum reading below the throttle plate would give the same reading as anywhere on the intake manifold, accept that there could be some venturi effect skewing the vacuum reading if it's taken from a vacuum port right next to the butterfly while it was in a part throttle positon making extreme turbulance next to that vacuum port.
The brake booster vacuum hose is from the drivers side of the intake manifold.
T into into it down under the dash where it comes out of the center tunnel and crosses over above the pedals. Or right at the brake booster hose fitting.
You will see high vacuum on deceleration, moderate vacuum at idle or steady speed, and pressure when on boost from that hose.
The inline check valve for keeping some vacuum in the brake booster is right at the brake booster port.
Taking a vacuum reading below the throttle plate would give the same reading as anywhere on the intake manifold, accept that there could be some venturi effect skewing the vacuum reading if it's taken from a vacuum port right next to the butterfly while it was in a part throttle positon making extreme turbulance next to that vacuum port.
The brake booster vacuum hose is from the drivers side of the intake manifold.
T into into it down under the dash where it comes out of the center tunnel and crosses over above the pedals. Or right at the brake booster hose fitting.
You will see high vacuum on deceleration, moderate vacuum at idle or steady speed, and pressure when on boost from that hose.
The inline check valve for keeping some vacuum in the brake booster is right at the brake booster port.
#7
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Originally Posted by JFairman
what do you mean by boost "spikes"?
This seems to be well-understood in the import tuning market, from a random VW forum:
http://forums.vwvortex.com/zerothrea...ostid=40377025
Quote, originally posted by Arin »
So why would that cause the boost pressure to increase after letting off the throttle?
So why would that cause the boost pressure to increase after letting off the throttle?
Even if the recirculation valve has vacuum, it's a mechanical assembly with mass and inertia and spring pressure to overcome - it cannot react instantaneously.
And all the while, the turbo hasn't stopped spinning. What is that, 100,000 RPM?
So boost will temporarily go higher on the turbo side of the closed throttle plate than it is on the motor side (where pressure will drop into vacuum).
Boost spike.
The factory puts both the overboost switch and the boost sensor before the throttle plate. Coincidence?
If your recirculation valve is sluggish to react or stuck, you'll have a bigger/longer spike than if it's working correctly.
Also, find Jim2's video of his EFI 930 on YouTube; he has a dual absolute pressure gauge from an twin-engine WWII bomber, one gauge plumbed before, the other after, the throttle plate. Watch them do completely different things when he shifts, it's rather neat.
The motor itself never sees the spike, except possibly if you can get straight back on power after slamming the throttle shut, but before it's been bled off.
It can be significant because it can indicate issues with your recirculation valve (although leaking boost is probably a different failure mode), and also because some people posit that any overpressure getting forced back through the compressor blades (some racers don't run a recirc or BOV, saying response after the shift is better without) can damage them (that twittering sound is apparently the blade tips stalling in the charge air stream).
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#8
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Thanks for the explanation, that makes sense.
The "twittering" sound... do you mean the chirping like sound that blow off valves that vent to atmosphere make when closing the throttle(s) at high revs?
Like that sound a 962 used to make while off throttle and braking into a fast corner?
Are you saying it's the sound of the turbo impeller tips stalling or cavitating to some degree when closing the throttle(s) and you are hearing it in the air thats escaping from the pop off valve?
I always thought it was a high frequency reed like sound the pop off valve made as it opened releasing the air pressure build up when closing the throttle butterfly(s) at high revs and boost.
The "twittering" sound... do you mean the chirping like sound that blow off valves that vent to atmosphere make when closing the throttle(s) at high revs?
Like that sound a 962 used to make while off throttle and braking into a fast corner?
Are you saying it's the sound of the turbo impeller tips stalling or cavitating to some degree when closing the throttle(s) and you are hearing it in the air thats escaping from the pop off valve?
I always thought it was a high frequency reed like sound the pop off valve made as it opened releasing the air pressure build up when closing the throttle butterfly(s) at high revs and boost.
#9
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Originally Posted by JFairman
Thanks for the explanation, that makes sense.
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The "twittering" sound... do you mean the chirping like sound that blow off valves that vent to atmosphere make when closing the throttle(s) at high revs?
Like that sound a 962 used to make while off throttle and braking into a fast corner?
Like that sound a 962 used to make while off throttle and braking into a fast corner?
Are you saying it's the sound of the turbo impeller tips stalling or cavitating to some degree when closing the throttle(s) and you are hearing it in the air thats escaping from the pop off valve?
As to whether 962's make the noise - the links I found on YouTube sound more like a BOV venting when they shift to me, but they don't just go "whoosh", there's a on/off modulated thing going on there - I dunno what that's about...
Here's the thread on PP on the topic of running wthout one:
http://forums.pelicanparts.com/showthread.php?t=327438:
Originally Posted by 930Turbolader
I know I'm coming in a little late in this thread but here is my own experience with no BOV. I ran with out one for 2 years. Hammered the throttle many a times and heard my turbo stall and chatter occasionally (the sound was just like the 935's I watched at the IMSA races years ago). Never had any issues. I'm not advocating for anyone else to do it, I took the chance on my own. I chose to leave it off for a couple of reasons....1. I got a LOT better throttle response without it. 2. The race cars back in the day (935's) didnt run them. Yeah, I know they rebuilt the turbo's or whatever after every race but from a performance standpoint they were not needed. 3. If I damaged my turbo from not running one then I would buy another turbo AND reconnect the BOV and never do it again! But as it turned out.....nothing happened."