harvey

iTrader: (48)

Dave : An impressive spec and I don't doubt the great pleasure and sense of achievment the car gives you so please do not misinterpret my enquiring nature.

I note the car was run without "i" pickup. Some "experts" will tell you that is unreliable for a number of reasons. Any idea why it was not run with "i" pick-up which would have avoided any questions on that score. (according to the experts)
On standard cams, with vernier pulleys, I really am struggling to comprehend how max power is as low as 5,300 rpm. This has absolutely nothing to do with extrapolating 2 litre results. Perhaps an expert can elaborate?
Prior to the DD RR run(s) was the engine run on a dynomometer?

DaveBlueRA

harvey,
I have no idea what you are on about regarding "i" pickup, can you elaborate. The engine was built then put in the car, run in then mapped.

Tidgy

just predicted that you would come in to this thread saying its not right about 3 hours before you did, pmsl

harvey

iTrader: (48)

Cheers Dave : To provide reliable figures the rolling road needs to know accurately, the engine RPM. This can be calculated from gear ratio but that may be an unreliable method for a number of reasons. It can also be acertained from an accurate RPM source on the car such as injector pulse pick up.
When such a reliable and irrefutable method is used, the print out from the DD RR shows "i" mode on the bottom footnote along with other information.

I hope that clarifies the signifigance but perhaps a DD RR owner or operator would care to expand on this.

Tidgy :

Your clairvoyance, if indeed true, is quite remarkable. This is a technical thread. Do you have a worthwhile contribution or some knowledge on the subject in hand? Five people, including two, successful 2.5 owners and a top mapper with considerable 2.5 experience are interested to know why maximum power is at only 5,300 rpm and the explanation that this is with/because of cam timing could lead to further very interesting discussion. We may all learn something and move Subaru tuning on further.

Maddog

This might be a daft question but am i right in thinking that the turbo Dave uses is maxxed out at the moment, but to get more performance out the car, you've altered the cam timing so that the power it has achieved has been shifted along the rev band to get more torque? (if that makes sense..)

What i'm meaning is if the turbo is a 450bhp turbo (like the graph), will it still only achieve 450bhp if you alter the cam timing to produce the power higher up the rpm scale where power is "normally" seen?, so shifting the power band lower down isn't reeally changing what the turbo is capable of producing, but is giving a benefit in torque which is more suitable for road use?

Tidgy

so y not ask, how have you managed to get peak power lower down?
its never been in doubt the rr graph is a print out, so theres nothing unlikely about it

Maddog

Now now boys, I hope this thread isn't about to go downhill like so many others when it comes to power outputs.

Back on topic.

Can anyone tell me if i'm thinking along the wrong or right lines with my last question?

Tidgy

not sure

harvey

iTrader: (48)

Tidgy
Please refer to post #13. Do you understand the words. PLEASE EXPLAIN?


I am not sure what you are tring to say. Clearly the information presented is a rolling road print out and that is not in any doubt.
Do you understand the reasons why there will be differences with gear calculation figures and the use of "i" mode? Please explain what you mean.

Tidgy

hers a quote of post 13, read 'this seems very unlikey'

bob

Don't let this go downhill lads like so many other threads....
It seems to me Harvey is asking how the motor is producing its max power so low down the rev range when only using std cams. Not a hard question to answer for some of you boys.

Maddog

I agree and find it strange how none of the "experts" or "power junkie" regulars have came in on this one.
1200 views so far and the usual contributors aren't replying? I find it hard to believe they haven't read this thread...

DaveBlueRA

the turbo is no where near maxxed out. A GT30R maxes out at 3 Bar

Maddog

I didn't notice you run a GT30R Dave, so yes you haven't maxxed out that turbo judging by other 2.5 results i've seen with that unit.

Don't understand what you mean about a GT30R maxxes out at 3 bar. Maxxing out a turbo is more to do with the configuration and spec of an engine than just basic boost pressure.

I probably didn't explain things well enough in my earlier question but i was wondering if the cars spec was at its' limit (with the parts used) and so to make the car feel quicker on the road, the power band was shifted more towards the midrange than the top end.

karl h

raspflaspasspmsl

Maddog

wtfdtm?

Tidgy

pat

In a rush at the moment so can't write a long reply, but in essence, yes, the turbo is maxed out in terms of turbine flow but not maxed out in terms of boost potential. We could run 3 bar and (if timing doesn't become an issue) get in the order of 740lb/ft, shortly followed by the bore liners splitting

Cheers,

Pat.

harvey

iTrader: (48)

As I said earlier, I don't want to take anything away from Dave and his achievment in having a powerful and torquey car. However, it is very, indeed extremely, unlikely the vehicle is producing maximum power at 5,300 rpm and that is what needs an explanation.
Had the car been run in "i" mode, then some of the variable would have been removed.


Also, this also may be of interest.

The ratio of road speed to engine speed is not constant. It changes with load.
The runs were done on gear ratios not an RPM pickup and any vehicle making sizeable tractive effort distorts the tyres significantly and the only way to get a proper torque readings is to use an RPM pickup, it cannot be done on gear ratios.

If the RPM seen by the dyno is less than that achieved by the engine that makes everything appear to happen earlier in the rev range.

Andy.F

Using an ignition pick up brings its own problems, the slightest slip on the rollers results in inflated power figures.

On a DD dyno running in 'shoot44' mode, simply pump the tyres up if you want more bhp on your graph either that or run it until the diff and gearbox oils are really hot, this has also shown considerable gains.

Andy

ps- nice result Dave, the area under the curve is what its all about, not peak figures or where they occur

pat

I was going to post a detailed reply but there was so much material to cover that it would have ended up half the size of the Encyclopedia Britannica, so given that the crux of the "problem" is that the graph is in doubt I would simply suggest that Dave pops his car up for another run with the ignition pickup installed (it was originally but was playing up that's why the graph isn't in iRPM)...

The way DD rollers measure power means that cannot happen, all that might happen is that the power will be displayed at the wrong RPM but the figure itself will still be correct. Of course the torque figure will be affected by the slip....

What you are describing might happen if the dyno applied the roller measured torque at the RPM pickup indicated RPM thus inflating the power figures. Other makes of roller may do this, Dyno Dynamics don't. Power is measured independantly of engine speed.

I've been saying that for years, nice to see someone agree with that for a change

Cheers,

Pat.

Andy.F

Thanks for the clarification Pat

Certainly that was the case at Well Lane, a wee bit slip and the power spiked up !

So on the DD rollers the bhp peak can shift in either pick up method, whether due to slip/tyre deformation or an error in mph calibration.

Andy

pat

Andy,

A bit of a leading question

If you have trye deformation because the car is pulling hard, then you might realistically expect the car to accelerate fairly rapidly on the road too, which would result in weight transfer, and therefore a reduction in the rolling circumference of the rear tyres... this is why it pays to wind off DCCD lock when you get into the higher gears on the drag strip. So it is true that even on the road the ratio of ground speed to engine speed is not constant.

If you run an ignition pickup on Dyno Dynamics it uses it to "tag" the entries in the SNAP file. From the point you let the dyno ramp up it records wheel power and tractive effort every 1MPH of roller speed (perhaps every 1km/h if running metric). For each entry it will either use a set ratio to get the engine speed, measure the engine speed directly or just not bother at all with engine speed.

You can plot wheel power against ground speed or time without having any ignition pickup or gear ratio defined. If you want engine speed data then you will need either of the two methods.

If you get wheelspin with ignition pickup then the power transmitted into the rollers tends to reduce due to the slip and the engine RPM will rise. It will therefore plot the power higher up the ENGINE RPM range, but still at the "correct" ROAD speed. You can plot road speed vs engine speed if you like If you are running on road speed rather than ignition pickup then you'de just see a glitch on the trace, road speed would continue to rise uniformly. That said, if a car is strapped right, it won't wheelspin

Cheers,

Pat.

Andy.F

Interesting that this one mapped by bob also made its peak bhp quite low, looks like 5600rpm and 5800rpm. So 5300 rpm seems quite realistic to me, especially as the cams were timed specifically for midrange.

scubbay

iTrader: (61)

Andy F been an gone an made mine go sideways all the time too. 98 RA STI goin mental

chrome

@ Post #1:
Nice graph there Dave.
I bet you're glad you hung on to it now eh?

PeterUK300

iTrader: (1)

Great figures Dave...

What a Good read this thread is. Even if half of it went over my head

DaveBlueRA

Erm ask me that when I have to shell out for 4 new tyres

chrome

surely that's water off a duck's back compared to what you've spent?