Dyno runs

[SVXRide]

I just made an appointment for October 2nd at Altered Atmospheres in G'burg, MD to do some more dyno runs to baseline BillStock Level 4.0's performance. Drop me a PM if you're interested in joining the fun.
-Bill

[benebob]

I'll start the bidding here. 169 whp

[SVXRide]

Originally Posted by benebob

I'll start the bidding here. 169 whp

I'm hoping for something a bit higher
-Bill

[NeedForSpeed]

Bill,

You know that I'm interested!

Originally Posted by SVXRide

I just made an appointment for October 2nd at Altered Atmospheres in G'burg, MD to do some more dyno runs to baseline BillStock Level 4.0's performance. Drop me a PM if you're interested in joining the fun.
-Bill

[SVXRide]

Originally Posted by NeedForSpeed

Bill,

You know that I'm interested!

Ron,
So, get in your car and start driving now
-Bill
p.s. I think I'll need those parts from you in about 2 weeks...

[oab_au]

Originally Posted by NeedForSpeed

Bill,

You know that I'm interested!

Aren't we all.

Harvey.

[SVXRide]

Originally Posted by oab_au

Aren't we all.

Harvey.

Harvey,
FYI -- I'm still working with Scott on additional cam profiles -- he's getting more cores in to run through his new machine. We both believe the core he thought was a VQ core probably isn't, as the specs don't reflect what Mychailo and I dug up (independently).
-Bill

[benebob]

Originally Posted by SVXRide

I'm dreaming it'll be something a bit higher
-Bill

Cough... Fat fingers?

[SVXRide]

Originally Posted by benebob

Cough... Fat fingers?

probably just sore from getting the trans back in the car
-Bill

[longassname]

Glad to hear the trans is back in the car. I think the trans is the big variable as you know but put my guess down as 172.

[svxistentialist]

One of our UK guys, Mal, attended a rolling road shootout with a load of Imprezas.

The resulting graphs are in this month's [September] Japanese Performance magazine, in the Subaru supplement.

Now I don't know if the results as shown are flywheel hp or at the wheels, as it does not say. However, as the "expected" horsepower was quoted at 240hp, which is the engine output, then I would imagine flywheel is what they are quoting. The result was 173hp and 180 torque. See:
http://bbs.scoobynet.com/rolling-roa...t473891p7.html

This is a lot lower than many of us would expect, and also we think we drive a torque monster, but the figure here is way lower than most 2.0 litre WRXs.

The tester listed the car running at AFR 12:1, which is too rich, so maybe the tune was not optimal, I don't know.

One thing crosses my mind, and you experts may be able to give an opinion. The dyno measures the power at the wheels, and I understand a calculation is made to derive the hp at the flywheel, taking into account power losses at the drivetrain. As I see it, the power loss for a directly connected mechanical power train with a manual box will be pretty predictable. I'm not at all sure if the same would be the case for an automatic box, with fluid drive and a torque convertor between the engine and the wheels.

Just how reliable a calculation would be available for taking account of the auto box, and how much variability might there be from vehicle to vehicle?

Joe

[longassname]

Joe,

The numbers we are talking about are at the wheels. The factory quoted number is for the engine at the crank. The factory measures their numbers with an engine dyno which bolts directly to the the crankshaft. Chasis dynometers measure output at the wheels. Output measured at the wheels is lower because of the drivetrain loss. An SVX with an auto box in good condition seems to have about 30% drivetrain loss. Imprezas with manual transmissions seem to have about 25% drivetrain loss. As the condition of an auto box deteriorates the % of drivetrain loss increases and measured output decreases. The results you are giving for the UK svx are actually quite high, higher than I have ever seen for a stock SVX. I suspect the readings from that particular dyno are a bit optimistic.

[svxistentialist]

Originally Posted by longassname

Joe,

The numbers we are talking about are at the wheels. The factory quoted number is for the engine at the crank. The factory measures their numbers with an engine dyno which bolts directly to the the crankshaft. Chasis dynometers measure output at the wheels. Output measured at the wheels is lower because of the drivetrain loss. An SVX with an auto box in good condition seems to have about 30% drivetrain loss. Imprezas with manual transmissions seem to have about 25% drivetrain loss. As the condition of an auto box deteriorates the % of drivetrain loss increases and measured output decreases. The results you are giving for the UK svx are actually quite high, higher than I have ever seen for a stock SVX. I suspect the readings from that particular dyno are a bit optimistic.

Thanks Michael.

You are more or less confirming what I said above, and confirming that the gearbox fudge factor for the auto is 30% for a good auto, or maybe more for a worn auto.

That all sounds reasonable.

However, did you perhaps miss the point that I was making, that all the cars compared in the dyno run were given flywheel output figures? In this sense I am assuming the dyno people took the wheel hp, and extrapolated to give the flywheel hp figure. Probably because most owners like bragging rights with bigger numbers.

This being so, then Mal's car will only have produced 133 at the wheels, and then had the estimated 30% added to that to give the 173 quoted. If this is the case, then Mal is down 67 hp from the 240 he was expecting.
{a note in relation to this; I think Mal's car is UK spec. The factory quote something like 225 hp for UK spec cars. I think the state of tune of all engines is pretty similar, but the ECU for each market takes account of the available octane for the petrol in the region. In that respect, I think the only engines with a high expected output of 235 or so will be the JDM market, where they have 100 octane petrol available}

If, as you seem to suggest, Mal's car is doing 173 at the wheels, indicating 224.9 at the flywheel, then this is making exactly what I would expect for factory tune on the car, and Mal will be pleased.

Mal's car is a '96 Yellow SVX, and he keeps it immaculate. I would not be surprised if gearbox, engine, everything is in tip-top condition on that car.

I must ask him which hp was quoted.

Joe

[ItsPeteReally]

The first thing that I'd like to know is just how repeatable such rolling road dyno measurements are. What happens if you drive round the block and measure the power again, and again and again. Do it ten times. How repeatable are the figures?

Then put another 5 psi in the tyres, repeat it all again ten times. Then another 5 psi. And then another 5 psi.

Once you know how repeatable such measurements are, then you can start to trust the dyno measurements, and then have a degree of certainty that you've truly got another x bhp because you've done a demon tweak.

Trusting that x bhp on dyno A is the same as y bhp on dyno B is another matter entirely

There is little doubt that there is a considerable amount of power 'lost' in the transmission, most of it in the auto box. If there wasn't a power loss in the gearbox then nobody would worry about adding extra cooling and Subaru would not have added a gearbox temperature warning light.

[svxistentialist]

It's a good point you make Pete.

There is also the factor of wind resistance. Rolling roads are by definition static for the vehicle. Most of the shops blow a fan over the vehicle to keep the engine cooling system near to normal.

However, I would expect that "Normal" wind speed for an SVX or a WRX at 5000 rpm to be maybe 90 mph headwind. I doubt the cooler fan they put in place emulates this. Oh, and I do appreciate that the measurement at the wheels will still be correct, as the artificial "headwind" will not I think affect the drag at the wheels. The point I am making is that whatever hp figure you are given for 5000 rpm, or whatever you max figure may be, depending on your CD factor, a lot of this hp figure will be used just to push the car through the headwind, not just drag it down the road.

In other words you have less horsepower available to push you along than the bald dyno figures suggest.

These figures done oop north were on a brand new 4wd dyno. Some cars got a lot less than they expected. The preponderance got a few hp shy of what they were expecting. So I would not expect these to have been optimistic readings, I would expect them to be average or accurate, while taking Pete's reservations into account.

Joe