john banks

Trout your reliability record so far surpasses the rebuilders! Interesting. Did you ever get to the bottom of the misfire issues? Thanks fivepint.

[Edited by john banks - 1/16/2003 11:47:13 AM]

P20SPD

iTrader: (1)

John, i think he did. When he did the Earthing mod, apparently seemed to cure it IIRC.

dowser

Isn't the design of the ring grooves in the piston quite important?

Richard

AlanG

David

Would it not be down to rate of expansion of particular type of pistons which govern recommended clearances?

Alan

Andy.F

What about torque figures ?? Nobody appears to run these 2.0 engines at anywhere near to their potential capabilities

Why is that ? A 2.0 cossie running 350bhp will normally be producing 340+ ft-lb. The 400 bhp cossie's are generally around 380lb-ft.
A 2.0 EVO on uprated internals will typically run 430bhp/400lb-ft

Apart from Davids and my own home brew engines where the torque holds close to the bhp figure, all the 350bhp+ scoobs seem to be way down around 300lb-ft ??

Surely some of these forged piston/ steel rod rebuilds should be up around the 400bhp/380lb-ft if not more

Andy

P20SPD

iTrader: (1)

My torque is close to my bhp Andy, although its not above 350, and its on standard internals.

I think i would be worried about it if i had more torque though!

john banks

Just my 2p, a few thoughts, and probably a few wrong assumptions but I'll throw them in anyway.... (never stopped me b4 )

Is it because a lot of people are scared to run a lot of midrange boost on a standard engine? Most with biggish turbos seem to run fairly flat boost curves. Because the turbo breathes better maybe 1000 RPM or more higher up the rev range than the one that the car came with, you get an offset between torque and power?

Most factory cars have a midrange plateau or peak of boost and torque. This seems most logically to fit in with OEM turbo choices which are normally on the small end of the scale to help driveability and the feeling of low down torque which "average" drivers like. It is that big capacity feel. Suppose even for the bigger turbos, they are usually more efficient in the midrange, and so could tolerate a higher boost pressure without excessive exhaust back pressure or charge temperature or risk of overspeed. If the turbo is really big then perhaps it wouldn't get into its efficiency band until well over 5000RPM, but arguably for a road car this could be a poor choice, and also might suffer surge issues?

People often state the boost they are running as whatever their midrange peak is, and forget that even a relatively trivial amount of boost at the top end can produce a lot of power. So a TD04 car which is making "270 BHP at 1.3 bar" sounds actually quite unimpressive (and is probably making 270 BHP at 1.0 bar), but the torque and power are close because of the midrange fullness.

Since the combustion pressures are way higher than boost presures then perhaps we should worry about those, but of course the combustion pressure is clearly related to the boost pressure! At peak torque the combustion pressures would be highest so that is where things might pop? OTOH as Andy has pointed out conrod (and presumably other rotating mass) strength requirement is perhaps as much related to engine speed.

Certainly on my car recently I have run between 1.3 and 1.5 bar midrange and between 1.1 and 1.35 bar at the very top. In some of these combinations there was a midrange that was up to 0.2 bar (?30lbft) over the top end, in others it was just flat. Oddly in the flat ones the top end feels relatively better because there is far more power than torque, and the top end can feel a bit flat in comparison to the midrange if you run a big midrange plateau. I still worry about the high revs high boost scenario in particular on a standard engine, so presently I am running 1.5 bar midrange, about 1.4 bar at peak power (at most) and 1.3 bar thereafter. it feels quite well rounded.

I gather Andy F's 369BHP and lbft (approx) was with 1.7 bar midrange, 1.5 bar at the top hence the similar power/torque figures?

[Edited by john banks - 1/16/2003 12:26:16 PM]

Andy.F

Perhaps some of the more recent 2.0 builds are running more midrange boost ? I don't know ?

We have ignition curves, fuel curves, torque curves, power curves and (most relative here) compressor curves. Yet some tuners hold the boost generally as a straight line but with a tail off at the top??

IMO It should also be a boost curve ALL the way. (works for me)

If a teensy turbo will max out at 270 bhp @ 6000 rpm chances are it could still make 270 at 5000 rpm and possibly even at 4500 rpm
depending on its maximum pressure ratio. This will result in a MUCH faster car than one with a flat line boost. It will also have no more requirement for fuel capacity.

Apply this to a bigger turbo, typical of those fitted to the recent builds and you have every ingredient for decent torque

Andy.F

My point here is (on forged piston/rod built engines) you can run a safer combo by running more midrange boost and not using so many RPM.

Adam M

isnt the con rod ratio of the cosworth way under square? meaning that it has quite a large stroke, which might explain why ti would make torque more easily?

I wonder how much of our power figures is coming from the fact the fact that we are revving higher, and so if you limit our rpm to that of a cosworth the power delivery will be significantly lower and maybe more inline with the torque but just simply lower than that of the "equivalent" cosworth.

Andy.F

The cossie is 90 x 77 so not much difference there. The big difference is they are not scared to run decent midrange boost



[Edited by Andy.F - 1/16/2003 12:58:14 PM]

john banks

Andy,

I think the only one brave enough to run 1.7 bar on a TD04 was Dave Brown, as I remember indeed his power curve was remarkably flat from the midrange upwards, and he had over 300 lbft with 250 BHP IIRC.

Andy.F

If you check your compressor curve, chances are there will be a big zone of high efficiency which is not being utilised, this is where you go with midrange boost. Turbo is fine with it, fuel system is fine with it, conrods are happy with the lower rpm, remap the ignition and off you go minimum of 300lb-ft safely from ANY scoob.

Dave's car would also make more power on the road, he had the top mount on that day on the rollers with no cooling fan

[Edited by Andy.F - 1/16/2003 1:00:02 PM]

john banks

What about the combustion pressures?

This is what the TDi guys go on about as their limit to torque and their engines are rather more bombproof?

Makes a lot of sense otherwise though.

john banks

I know this 13g wheel might actually not be exatly the one in the MY99/00 Imprezas, might be more like the MY01, but yes it does seem to be reasonably efficient at moderate flow, high PR (alarmingly high).


[Edited by john banks - 1/16/2003 1:05:20 PM]

Andy.F

Agree that the BMEP can become the limiting factor......but not for a while yet !!!! Especially if you go for pistons and rods in a rebuild.
You are using similar components to the cossie/EVO and they will pump out 430lb-ft from a 2.0 all day !!!
I think the Norris car is over 500lb-ft now

Andy.F

Following a RPM curve may be a reasonable idea, that way you don't need the turbo rotor to accelerate mid pull which will absorb some power and create some lag

As an example on the above graph, follow 150k line

[Edited by Andy.F - 1/16/2003 1:10:39 PM]

Razor2001

LOL...I am lost

P20SPD

iTrader: (1)

Andy/John dont know wether this link would help, but it shows the boost curve of Norris' car, at the G Force rolling road.

I dont have the ability to convert the figures on the right to bar or psi, but they dont look that high in the mid range, may be wrong though. Holds boost well though.

john banks

About 2.0 bar relative dropping to 1.9 bar.

P20SPD

iTrader: (1)

Ahh! So it is quite a bit then!

Oh well, i shall keep quiet and continue to read

john banks

What is your boost curve like P20?

P20SPD

iTrader: (1)

Trying to think.....

RPM then Boost in 4th
2000 0.3bar
2500 0.8bar
3000 1.1bar
3200 1.35bar
still reads 1.35bar at 6000rpm IIRC

must take more notice of what is happening, afterall thats why i paid the moeny for the gauges.

Steven

john banks

At what RPM did you make peak power at Well Lane and what was the boost at the point?

P20SPD

iTrader: (1)

Not very clear i know, but best i can do



They had it recorded at 1.4bar, but i dont know how, as i was watching and it never went above 1.35bar!

[Edited by P20SPD - 1/16/2003 2:06:57 PM]

LG John

Was Dave Browns car running that boost on a standard TDO4 or was it a hybrid?

David_Wallis

my figure was with 22psi held to the limiter..

I'm sure my torque is down to the CR of the engine..

David

T-uk

forget it saxo,he melted it fairly quick

are there any graphs of VF based turbos with conventional torque curves.all the ones I have seen seem to look more like power graphs than torque.

steve McCulloch

Dave

22psi held to the limiter!

is that all

Mr Trouty

Boost is not everything, (or advance)

Once you get the clutch sorted it would be very interesting to compare your 1.7 bar to my 1.75 bar held all the way... see if its feels different.

Anyhow its only fair, you did try and scare me in your car at PE a while back!!

AlanG

JB

IIRC, Dave was running a VF23 that day, not a TD04, though stand to be corrected on this.

Alan