Brainteaser of the day
Discussion
Good mapping session with Trevor yesterday after an engine re-build.
Power, however, down 26bhp on same map with same spec (only upgraded clutch + gearbox). Due, we think, to the unusual boost curve you can see below.
Thoughts on what could be causing the "heartbeat" at c.6.2k rpm. Fluctuation is about 4lbs from peak to trough. Happens at the same RPM, irrespective of the boost level/map being run.
Don't think it's a turbo/wastegate issue as they're making the boost. Resonance in the exhaust? Although the exhuast and intake are identical to prior to the re-build, where there was no issue.
Frustrating.
Power, however, down 26bhp on same map with same spec (only upgraded clutch + gearbox). Due, we think, to the unusual boost curve you can see below.
Thoughts on what could be causing the "heartbeat" at c.6.2k rpm. Fluctuation is about 4lbs from peak to trough. Happens at the same RPM, irrespective of the boost level/map being run.
Don't think it's a turbo/wastegate issue as they're making the boost. Resonance in the exhaust? Although the exhuast and intake are identical to prior to the re-build, where there was no issue.
Frustrating.
If its at the same rpm that's normally something like spark plugs or coil issues but can't see why that would affect boost without an obvious misfire.
Im not sure but would I be right in saying regardless of boost level required, the volume of exhaust gases created increases with the revs. So perhaps the higher flow of exhaust gas at that 6200rpm is something the wastegate can't control as easily as it can at low revs because of a weak spring and no need to dump excess gas into the exhaust as the turbo is using it all? As the revs increase and the wastegate detects there is too much gas it try's to open to prevent over boost and then you see a sudden drop in pressure because of a weak spring.
Maybe not I'm just guessing and trying to make sense of this in my head.
Im not sure but would I be right in saying regardless of boost level required, the volume of exhaust gases created increases with the revs. So perhaps the higher flow of exhaust gas at that 6200rpm is something the wastegate can't control as easily as it can at low revs because of a weak spring and no need to dump excess gas into the exhaust as the turbo is using it all? As the revs increase and the wastegate detects there is too much gas it try's to open to prevent over boost and then you see a sudden drop in pressure because of a weak spring.
Maybe not I'm just guessing and trying to make sense of this in my head.
April day vs September day conditions between this map and the prior.
Ambient conditions consistent across yesterday's runs. Fan running over engine air temp sensor to try to regulate temps.
The hiccup happened on all runs over the evening, at the same RPM, at different power and boost levels.
Bruntingthorpe runway + laptop sounds like the solution....
Ambient conditions consistent across yesterday's runs. Fan running over engine air temp sensor to try to regulate temps.
The hiccup happened on all runs over the evening, at the same RPM, at different power and boost levels.
Bruntingthorpe runway + laptop sounds like the solution....
markrichards said:
Thanks.
Surprised if it's actuators as happens at various boost levels, but consistently the same RPM...
Well actuaries don't fluctuate, as the ecu bleeds air away from then so they still see the same pressure from the inlet manifold regardless of boost level.Surprised if it's actuators as happens at various boost levels, but consistently the same RPM...
But the pressure on the hot side of the waste gate itself trying to push the actuator open will vary as power rises so still find it strange.
I had boost spikes like this.... My turbo bearings had gone and blades were hitting the housing causing the spike as it slalled then recovered.... It wasn't in exactly the same place each time so don't think yours is this as well.
Id check coil packs and sensors but I'm also scratching my head lol
You were obviously at track and road, so if the two Steves and Trevor can't put their finger on the problem then I'm guessing valve surge /float, were the up-rated springs fitted during re-build?
I have seen similar graphs where this was found to be the problem.
Ets is the base of the "heart beat" closer together in the lower gears?
I have seen similar graphs where this was found to be the problem.
Ets is the base of the "heart beat" closer together in the lower gears?
Edited by F.C. on Monday 24th September 22:48
Yet to try to diagnose. The car is with Jetstream.
Updated valve springs will have gone back in after re-build. Making c.510bhp / 480lb/ft, which I expect it could only do with the uprated springs.
Manifolds aren't blowing as you'd hear this.
While the spike etc happens at the same RPM, it is less pronounced at lower boost levels.
Will disconnect the boost controller and see if it repeats. Also checking exhaust I expect.
Updated valve springs will have gone back in after re-build. Making c.510bhp / 480lb/ft, which I expect it could only do with the uprated springs.
Manifolds aren't blowing as you'd hear this.
While the spike etc happens at the same RPM, it is less pronounced at lower boost levels.
Will disconnect the boost controller and see if it repeats. Also checking exhaust I expect.
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