It starts out at 0.5mm - if you increase it to 1.5mm then it is like having a small bleed after the Dawes as discussed before with benefits on driveability and more sensible but still sharp part throttle response. Saves you bothering with a separate bleed valve and extra plumbing. I think 2mm would probably be OK as well but have stopped at 1.5mm - certainly 2mm drill bits are easier to source and the bleed would still only be 3 or 4 PSI I reckon which is just right.

If you do this you will have to unscrew the Dawes a bit to reset your boost. Another benefit is that it is much less likely to clog the bleed hole.

BTW have not posted in the Muppet thread featured below in Drivetrain

This is the last I do to this Dawes I promise! My bonnet is closed until the next service now

 

Thanks for all your input regarding the dawes device John - it's nice to have a 'Guinea pig' who tries out these things before the more cautious people, like myself, follow suit.

I was about to post 'what bleedhole??', but I've just found it

Rich

 

John,

After seeing your 3D graph showing the acceleration results at different pressures, I was wondering if you have a figure for the acceleration tests at Standard PSI Vs Dawes fitted set at standard PSI, rather than 16/17 etc..etc...just to see where the difference lies.

 

I don't but when we are comparing pressures we are all talking about the best held boost figure we get in 4th or 5th gear in between 3000 and 4000rpm. If you take a standard car as being 13 or 14 PSI and set a Dawes to the same it will be a quicker car for three reasons:

1. Your spool up will be earlier
2. Your spool up will be quicker
3. Your boost will hold as long as your turbo can make it - ie you will probably still see 13.5 PSI at 6500rpm which is a massive increase on standard.

If you run a PPP'd car you will see 17-17.5 PSI in the midrange. But with a MBC the car will be quicker still at the bottom and top, with no real gain in the midrange. The PPP in the midrange takes it as far as is sensible already, but there is more to be had at the top end even from the tiddly little TD04L.

 

John
Now that sounds interesting. I've yet to fit mine,What with getting married yesterday etc...!!!!
I will fit mine in a vertical position and try drilling out to 1.5mm.

Would still need the assistance of someone local with a "Spare boost valve " to help me set it up. I dont want one fixed in the car.

Have you contacted Darren Dawes about this drilling mod ?? He might find it interesting

 

CONGRATULATIONS. Hope you are enjoying married bliss.

I would try it as it is first before you drill it out and see what you think. I think 2mm would actually be ideal checking orifice sizes off the datasheet of my bleed valve as it has a 3mm orifice and was half open (plus the 0.5mm to start with).

"Have you contacted Darren Dawes about this drilling mod ?? He might find it interesting" - no only did it today. His current solution is to use a pressure switch to directly connect to the wastegate until you reach say 8 PSI and then switch to the Dawes. But this requires a solenoid and wiring and to be honest I think it would be too slow to spool up.

 

Luke,

Congratulations!

You'll probably find that you don't need to do it on your car as it has a big turbo.

Try it first before drilling (as John suggests)...

Thanks

Gavin

 

Good point Gavin. The bigger turbo is probably a bit slower to spool up hence it isn't quite so manic, but if it is too much for you it can be calmed down.

 

Just to add some substance to what John is saying about top and bottom end performance increases from his Dawes set up, I did some more re-runs for a direct comparison.

My car is mechanically identical to John's, without the Dawes. See the post below "John Banks hasn't done anything to his car for 48hrs etc.." for the full story.

Anyway, I can match John's accelleration times very closely, except in two key areas. The first is 53-73mph in 5th gear which, despite perfect conditions (temp zero deg, clear sky, no wind) I could not improve on 6.7 secs, whereas John claims 5.5 secs. That's a big difference and shows how much earlier and stronger his car comes on boost. My car hits peak boost about 2,700rpm and I think John said his now peaked at 2,200rpm (but that was several days ago, it may have changed since )

The other key measure was 65-105mph in 3rd and 4th gears, changing up at 6,500rpm. My times were very consistent and averaged 8.4 secs against John's 7.8 secs. Not such a big difference, but proof again that the Dawes holds on to high boost longer.

Cheers,

Richard.

 

It hits 18PSI at 2500rpm now Hoppy - by using no bleed I could get 53-73 in 5th in 5 seconds dead. I use the bleed to make it more driveable at the expense of slightly slower and therefore later spool up. I think my midrange times will have improved slightly by running an extra pound of boost. I deliberately set the thing to 18PSI peak/held to run on the Select monitor for a worst case scenario for ignition advance - I will not and cannot safely go higher since fuel cut is reputed to be 19.3PSI.

Compared with a PPP car running over 17PSI which yours does and mine did I think there would be no improvement in the midrange - both cars have similar boost. Even 50-70 (53-73) in 3rd is still midrange and a non Dawes PPP car will be just as quick. But stray below 2500rpm or above 5000rpm and that is where you get the difference. On a standard car there is more to be had all over the rev range (30-90 in 3rd on a std ECU to show the whole rev range including some off boost on std car knocks about 10% (one second) off the time in the same conditions whilst only running 1-2 extra PSI measured in the midrange), on a PPP car the midrange is very sorted to start with.

[Edited by john banks - 12/30/2001 9:09:50 PM]

 

Hoppy / John,

Another comparison: I did some runs in my car today, all times where averages of 4 runs. MY00, SS D/P, ITG Filter, 15PSI held on guage (16 PSI corrected), 0-1 deg C, 1/2 tank of Optimax. Autocar P1 times in [].

5th 55-75 6.2 [50-70 6.8]
4th 55-75 3.8 [50-70 3.9]

5th 75-95 5.3 [70-90 6.1]
4th 70-90 4.1 [70-90 4.4]

5th 65-105 12.0

3rd 35-75 5.0
2nd/3rd 30-70 5.0 [4.8]

I was hoping for a little faster 30-70 times but was impressed that holding 3rd gear for 35-75 produced the same time......


Harry

 

A few more pounds of boost would improve your midrange only I reckon - given that you will probably be running about 13.5PSI at 6500rpm your top end is probably as good as it gets.

 

John,
What AFR were you reading during all these runs, and did it change at all with the different PSI settings.

I have my AFR fitted now and it is currently calibrated to run from 720mV to 900mV. One thing I have notice tho', when revving at standstill approx 5 or so LED's come on at a time, of which scroll from lean (720mV) to rich (900mV) and back to lean as the revs rise and fall.

When I boot it a similar number or maybe more light up yet it seems to go right up to 900mv, although I have get to check it fully at full boost and full revs.

Would you expect so many LED's to light or do you only see 1 at a time.

Bench tests only light 1 or 2 at a time, maybe it's something to do with the sample rate.... ?

 

It stays at or over 7% CO on full boost whatever you run. I haven't checked to see how much over as my last light on my three led setup is about 7% CO. If I see this on full boost I am happy.

Scrolling behaviour is normal by giving it some revs at idle. Also normal is the wide number of LEDs lit. If pin 9 is not connected the LM3914N is in dot mode, but even so several lights go on. It depends on how fast acting your LEDs are and also 20mV is the best resolution the LM3914N is supposed to be able to do. As you say on the bench you can sometimes just get two adjacent lights to come on over a 1-2mV transition range. I think the lambda signal is clearly quite dynamic - you get a higher voltage off our display than you do off a 3Hz monitoring DVM - the DVM just doesn't see the peaks. I work off the top light that is lit even if flickering as long as it is fairly bright. Slower acting LEDs will just glow of different intensities - I pick the brightest one. Most bargraph LEDs seem pretty quick for response. My 3mm LEDs were only 1 or 2 lit. On my current display with 5mm LEDs all three LEDs are often lit on full boost even though it is in dot mode - but you can easily spot that the top (green) one being the brightest. Easier to read in the dark.

The LM3914N is just a string of op amps with a resistor chain in 10% linear steps between the reference points. It is pretty fast acting. We get lots of lights on because of a dynamic signal and slowish LEDs, and also because we are using 20mV resolution which is much better than most AFR meters.

All it does is give you an idea, but you get a feel for reading it after a while. Just pick the brightest most evenly lit LED.

 

Great, seems all is working well then....
may post a piccie if I can get hold of a camera in the week....

 

Thanks to John banks, I tried the Dawes as is with the 0.5mm bleed hole on my Standard MY99, with boost adjusted to 1.05 bar it was very agressive and not very driveable in daily use.
I then tried to enlarge the bleed hole to 1 mm and it was now more smoot and easier to drive. I have not done any test yet, but it is spooling up quicker and earlier and deliver more power 3000 to 5000 rev.
I stay with the 1mm bleed hole and 1.05 bar for a while until my AFR is installed.

To measure max boost without getting into trouble, I use the process Volvo used on their early Turbo cars. 3 gear WOT and left foot on the brake to keep the load up and the speed down.

 

Excuse my thickness, but what is WOT

 

Wide Open Throttle.

P.