factory boost operation - from earlier discussion
08-18-2008, 07:49 AM
#1
Drifting
Thread Starter
factory boost operation - from earlier discussion
Unfortunately I can't find the recent thread where we (John from Vitesse, Richard Bennett, etc.) were discussing the factory boost control spike and resulting fall-off.
I had a track event this past weekend and shot and compiled some footage of the boost gauge while on-track. The video is here:
http://members.rennlist.com/jwelte/boost_operation.wmv
Car is '89 951. The video shows 3rd and 4th gear pulls. Shift points were right around 6k rpm.
Near the end of the video I deliberately lift then reapply the accelerator while in 4th. You can see the boost climbs again up to 13psi then falls back to 10.
Cycling valve and wastegate are factory, as are chips. No cat and 3" exhaust. I forgot to check, but I think the hose from the CV to the WG is the factory rubber type.
So, normal operation? The factory service manual doesn't indicate a spike, just max of .75 bar (~11 psi) +/- 10%.
Ignore the engine miss. I'll describe in another post as I'm still chasing this problem.
I had a track event this past weekend and shot and compiled some footage of the boost gauge while on-track. The video is here:
http://members.rennlist.com/jwelte/boost_operation.wmv
Car is '89 951. The video shows 3rd and 4th gear pulls. Shift points were right around 6k rpm.
Near the end of the video I deliberately lift then reapply the accelerator while in 4th. You can see the boost climbs again up to 13psi then falls back to 10.
Cycling valve and wastegate are factory, as are chips. No cat and 3" exhaust. I forgot to check, but I think the hose from the CV to the WG is the factory rubber type.
So, normal operation? The factory service manual doesn't indicate a spike, just max of .75 bar (~11 psi) +/- 10%.
Ignore the engine miss. I'll describe in another post as I'm still chasing this problem.
08-18-2008, 01:13 PM
#2
Drifting
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I was just looking at the '89 model year service manual yesterday and remember the "normal operation" boost curve did not have a spike, but there was a few psi between the normal curve and the top of the safety curve. Do you have a wideband on the car?
I think the +/- 10% is to cover for possible spikes if the cycling vavle/KLR do not react quick enough when you start making modifications that can potentially increase the spool rate of the turbo (no cat and 3 inch exhaust)
I think the +/- 10% is to cover for possible spikes if the cycling vavle/KLR do not react quick enough when you start making modifications that can potentially increase the spool rate of the turbo (no cat and 3 inch exhaust)
08-18-2008, 04:52 PM
#3
Drifting
Thread Starter
I was just looking at the '89 model year service manual yesterday and remember the "normal operation" boost curve did not have a spike, but there was a few psi between the normal curve and the top of the safety curve. Do you have a wideband on the car?
I think the +/- 10% is to cover for possible spikes if the cycling vavle/KLR do not react quick enough when you start making modifications that can potentially increase the spool rate of the turbo (no cat and 3 inch exhaust)
I think the +/- 10% is to cover for possible spikes if the cycling vavle/KLR do not react quick enough when you start making modifications that can potentially increase the spool rate of the turbo (no cat and 3 inch exhaust)
I remember reading that in the factory workshop manual as well. Though it doesn't specify a spike, it wouldn't be the first time a subtle thing isn't mentioned.
I conferred w/ my mechanic today (very experienced w/ 951s) and he said what I'm seeing is normal operation.