john banks

Yes the damping is incorrect for the rolling road. On the road I was in two minds about actually reducing the maximum duty cycle as it was easily reaching boost target, but left it because RB5 Black lives nearby and if it overboosts in winter I can turn it down for him. But I am no way increasing the duty cycles after how it behaved on the road. I cannot map to give nice rolling road traces when the conditions are totally unrepresentative of the road. This is one reason why I am not too excited about mapping on a dyno. In the same way another car (still with cats) was hitting 17 PSI on the road (plenty IMHO given the cats) but on the rollers on the same day 1/2 hour later only just breached 15 PSI. If I map to reach target in hot conditions the cars do overboost. On a car in Greece on a hot day the boost control was great - just hitting target and holding really nicely in 3rd and 4th with a 1 PSI overshoot on changing to 5th. Then it goes north and only 10 C lower and raining and the boost is spiking a lot more. With the hardware on the car you have no alternative but to accept below targets in lower gears esp on hot days, unless you only want to run 15-16 PSI held and are happy with spikes to 17-18 PSI. I personally would rather allow the car to hold more not just peak more than 15-16 PSI as it will be quicker.

If this car hit 17 PSI on the dyno with this boost control method it would probably hit 19-20 PSI peaks on a cold day. Excessive boost spikes are a risk factor for detonation especially with the slug of charge temperature with a TMIC. You just need too much duty cycle to hit boost targets on this dyno.

[Edited by john banks - 10/2/2002 1:34:53 PM]

john banks

2 port solenoids on the late models are too puny to flow enough so need a restrictor. When the solenoid is at min duty cycle (=closed) then boost is related to the wastegate spring tension.

Different engine loads and environmental conditions create offsets in the equilibrium point that the boost reaches for a given wastegate spring and duty cycle.

[Edited by john banks - 10/2/2002 2:53:42 PM]

RB5-Black

I've just had the first rolling road session done with my car and had some funny results . I think the weather has played a bit of a part in this but just thought I'd post the graph to see what you all thought

Pavlo

can you point out the funny bits?

I suppose the torque is a little low, but not if standard, nice smooth torque curve.

Paul

RB5-Black

The problem is the torque

full decat + TEK the car seems lazy on the boost today so I think that's what's caused it.

Pavlo

It does seem that the boost is being throttled back at spool up. And it looks like the ecu is doing it deliberatly, otherwise I would expect the boost to level off more gradually.

you say it has a TEK ecu, but what TEK?

Was this the first run? Was the turbo already nice and hot?

Paul

RB5-Black

It's a TEK 2 The car had two runs so it wasn't the temperature of the air ? the boost seemed lazy coming up and then tailed off pretty quick. It's mapped for 1.2 bar but only got 1.1max before falling off. The car has felt lazy today (sunny, high pressure,been dry for days ) hope that's it. I normally get 17.5 psi but today only seeing around 15.

RB5-Black

I'll wait till the sun goes down and go for a blast that should tell me if it's car or weather !

ScoobyJawa

Thats very low torque for a TEK 2 car even on a hot day..........

RB5-Black

I think its about 20 lb/ft out but it's 2 psi + down

ustolemyname??stevieturbo

iTrader: (1)

Drag losses, due to the transmission also seem very low, at only 51bhp??

Pavlo

91 i think that must be, look at the graph.

ustolemyname??stevieturbo

iTrader: (1)

Oops, forgot to open my eyes.

ChrisG

The boost looks quite low at lower revs doesn't it?

Come on Dr Banks, what do you think?

[Edited by ChrisG - 9/25/2002 4:11:52 AM]

RB5-Black

Nightshift again chris ?

The weather had a big part in that !

I was only getting 15-16 psi held during the day after 8pm I went fr a spin and the boost came up strong and all the way to 17 psi+

cloudy today so I'll have another test.

Craig.

David_Wallis

p20spd had this problem... he solved it by adjusting the actuator slightly..

David

Pavlo

Looking at it, it looks like the duty cycle is topping out. I know there have been problems, and that JB has been supplying restrictors/valves etc.

Essentially the problem is the boost map, it's in 2 parts, the pressure target, and the max duty cycle. The max duty cycle won't be exceeded, even if the boost is below target, and this is what's happening here.

Adjusting the actuator or fitting a different restrictor are both valid fixes, as they effective change the boost for a give duty cycle.

Paul

P20SPD

iTrader: (1)

yep agree with david. really bugged me, but adjusting the actuator solved the problem. It just would not hold the boost and felt lazy, i think cause the wastgate was opening too early. Adjusted and better spool up came back and held boost better.

SCOSaltire

i think JB is on holiday isnt he?

P20SPD

iTrader: (1)

Looking at the map, it looks like it was hitting 0.8 bar at about 2800rpm. This is what mine was doing. Adjusting the actuator only half a turn brought it back to about 2500 and full boost 1.15bar at 2700-2800rpm. Made all the difference to me.

john banks

Sorry guys missed this thread.

The map is virtually identical to the Tek 2.5 doing the rounds.

Note this rolling road is a bit conservative, but agree the boost is low initially, explaining the low torque. However on these rollers 260 BHP with that temperature correction is expected.

As pointed out there are two main boost maps - boost achieve and maximum duty cycle. The maximum duty cycle on this map is clearly inadeqaute on this car on these rollers in these conditions to reach target boost of 1.2 bar. But if I used a higher duty cycle then it would overboost on the road and that is where it is driven, not the rollers, and clearly it is hitting good boost on the road from the post. On the road when setup this car hit about 1.25 bar in top gear when given some stick, and this was on a summer day. It is a limitation of JECS boost control with a 2 port solenoid - you simply can't hit target boost on the rollers or in hot weather in low gears and then not overboost on the road. It will closed loop control the boost, but you have to limit boost spikes and possible cold weather fluctuations by being careful with the duty cycle.

A car that hits boost target by having plenty of duty cycle is very nice to drive, until it goes too far and the boost fluctuates. A little bit too little boost in harsh conditions is better than a car that overboosts with a TMIC risking detonation.

Dawes with a Knocklink (to add some safety) will give fewer boost offsets on the rollers compared with the road, and in different conditions, which is why I use it personally.

I would rather gauge improvements by something like an AP22 performance meter or similar personally - as g force is what matters in the end and actual acceleration figures with realistic airflows. There are too many counfounders and uncontrolled variables on most rolling roads. Sometimes they work to your advantage and make for good pub figures and other times you are disappointed. Just my 2p, but I have no concerns over your car's on road performance.

john banks

Sorry another thought - the reason the boost curve is increasing late is that it is following maximum duty cycle which I can do at higher revs as it doesn't tend to overboost - I increase it in the upper midrange to compensate for the natural drop you would get. 1.0 bar at 6000 RPM is the result which is about as good as a TD04L gets.

Pavlo

Still looks over damped to me, especially given how long the Star runs are, which is a lot longer than most from what Andy has said.

Paul

Turbo_Steve

Sorry to sound dense (like a nice cold charge! lol) but could someone please explain the relationship between Actuator Spring Strength/tension and Wastegate Solenoid Duty?

As I understand it..if the solenoid is at maximum duty cycle (i.e. open open open?) then wategate control is completely dependant on the vacuum overcoming the spring tension. But the solenoid means that the spring just has to be strong enough to overcome the pressure of boost in the turbo, and the solenoid controls when the wastegate opens?

So how do you get boost spikes and all these other artifacts?
Is it just because the solenoid is too slow?

And why do I overboost on cold days with NO restrictor? (the pipe broke) Surely having no restrictor makes the solenoids control MORE accurate?

Turbo_Steve

Scooby engines have rendered me an idiot.

Thanks for your answer john...I THINK I understand this thread now.