Big drop on map at high RPM

[dazjb]

Just found my dyno map which found its way folded up into a random folder since last Friday when my car was tuned. I remember seeing the drop off when I was there but didn't realise how bad it was, around 5500rpm it tumbles. Here's how my dyno run looks ...

75840

75839


First chart shows bhp against torque and second one shows bhp against boost.

I know the guy tuning it mentioned he was hearing knock which is why the boost was dropped down.

Any ideas what could be the cause of this big drop off?

[swinks]

Just found my dyno map which found its way folded up into a random folder since last Friday when my car was tuned. I remember seeing the drop off when I was there but didn't realise how bad it was, around 5500rpm it tumbles. Here's how my dyno run looks ...

75840

75839


First chart shows bhp against torque and second one shows bhp against boost.

I know the guy tuning it mentioned he was hearing knock which is why the boost was dropped down.

Any ideas what could be the cause of this big drop off?
Have you got afr vs. boost plot? It will help with answer, but if tuner mentioned knock then it's very likely that ecu pulls boost down due to knock event occuring whilst running lean.

[dazjb]

We didn't activate knock control on the ECU so it won't be that interfering.

I'll give him a call and see if he can send me the the AFR v boost plot

[dazjb]

He's just text me back. On holiday this week so he's going to call me up on Monday.

I remember we definitely didn't activate knock control .. it wasn't accurate enough, picking up all sorts of noise and throwing up CEL's even when idling.

[Davezj]

firstly the prints are not o-max they are about 100 to max so the drop looks as big as the clim but it is not in reality. it is a zoomed in section of the graph so the drops look bigger than it normally would do.

secondly the run goes to 7200rpm normally the runs stop at about 6500-6700 as there is no point going higher as all you get is drop off with a standard VR4 engine and small turbos.

thirdly the pictures you have taken are at a funny angle and makes the scaling very difficult to read, and put an odd perspective on the graphs. picture of printout are better off taken straight on to the print.
can you take some better pics and it will make things much clearer.

are these graphs wheel HP or guesstimate engine HP.
you have 200hp+ from 3600 to 6750 roughly. which is slightly late coming on but seems about the right ball park to me. torque peaks at 4000 prm which again is a little higher than normal and then drops off to the redline which is normal for the vr4 engine. at 7150 rpm you still have more than 150ft/lb of turque. i dont see anything wrong with it for a first pass tune, you still have a lot to do with the car in relation to idle setup and sorting out why you are registering so much knock at idle, boost sability, etc.

you are only running 11psi of boost at 5500 rpm to the redline so this is not going to help your cause at the top end of the rpm range.

if you are running standard turbos they should be able to run 14psi boost right up to the redline from about 2500-2700 rpm. and you should be able to get it nice and flat line for the boost control. so you need to sort that out as well.

2 diagnostic tools that will help you sort this out are a reliable boost gauge and a wideband sensor/gauge.
as far as i ab concerned you need to setup the desired boost level first and tune the fuel and timing to that boost level. start low and stable with the boost, maybe aim for 12psi and get it rock steady then tune the fuel and timing then raise the boost to 14psi get it rock steady and retune the fuel and timing for that.

[dazjb]

Cheers for that Dave, some good info there.

He asked me what safe running boost is for VR4 turbos and I said around 1 bar, based upon what others have on here so that's the pressure he tried to run them at. Got some knock so the boost was lowered, I'm using an Apexi AVCR.

My tuning was done on a hub dyno so these figures are actual hub figures, not flywheel.

Re the knock at idle, I think that's something to do with the knock sensor settings. It's picking up some noise and thinks it's knock when it isn't.

I have a brand new Innovate MTX-L Wideband fitted and have an Autometer boost gauge which seems to read accurately.

I'll ask for the graphs to be emailed over to me next Monday and pop them up on here.

[Davezj]

It sound like you are setup to make this conversion work.
You have access to the standard knock setup via Kenneth's 1.03 rom so you should be able to get close with those settings.



Sent from my space-aged gizmo

[Confused]

Does your ECU not support boost control?

I'd have thought that, if it did, it would be better to do so from there - it should then have the ability to raise or lower based on other aspects, such as AFR, knock, TPS etc? The AVCR will target a pressure with no respect to anything else.

[dazjb]

Yeah the ecu does have boost control. It has gear based boost + you can scale the boost against vehicle speed, IAT or EGT.

I already had an AVCR installed + had the display cut into my sun visor so decided to use that. The AVCR has gear based boost as well which I thought would be the most important thing with my car being FWD.