Ba Xr6 Modded Dyno Figures - Is This Normal?

[Never had any say Panda]

I didn't think diff gears affected dyno's..

[Henz]

I never used to, till I saw mate lose 40kw after changing from 2.9 to 3.7.

His car made 123kw stock. 185 tuned

Pretty sure he runs 10.1 comp now.

Edited 25/07/13 08:35 AM by Henz

[Pazzo]

It would as I have seen different Dyno figures on the same car from using a 17" wheels to 20" wheels.

[ratter]

power should be the same but torque would be different

[arronm]

152 is about right with no tune. With no increase in comp dont bother with e85

[Bazza96]

BRK - Man, I thought a underdrive would get it to a good solid 158-160 itself? And a tune atleast 170rwkw? Or am I dreaming? Ive seen lots of those figures, even on BA's, not just BF's.

[BRK]

The underdrive system reduces the power losses from driving the water pump, the alternator, the power steering (and air con - but ignore that for this debate). The designers of these factory engine accessory things are in the same game as us - good design to minimize power usage and reduce fuel usage. On the dyno, the alternator and the water pump are the two big contributors to these power losses. An underdrive generally promises around 20% reduction in the rotational speed of engine accessories so it basically saves 20% of the power usage.

We want to gain around 8 KWKW - so about 10KW at the engine. Now, think about what 10Kwatt at the engine really means - and do that by having a look at what a standard 240 volt electric engine looks like - big suckers - and 10KW can do a lot of things especially if it is being used to pump water. Lets get rid of the alternator - At full output power, a 120 Amp alternator @ 12 volts will need around 1.8KW ( 120x12x 1.2) to drive it; I allowed a very generous factor of 0.2 or 288 watts for friction losses. That leaves us 8.2KW to drive the water pump. That is a lot and well below what the stock pump needs at an engine speed of 5500 RPM but let's use it. So, we say the underdrive saves us 20% - the maths therefore tells us that to gain a steady 10KW at the flywheel - being 8 KW at the wheels - we have to be using 50KW to drive the engine accessories at the outset. That power usage to drive these things is not feasible in a car engine. The underdrive systems do assist in reducing inertial power losses in that they accelerate the engine accessories at a a slower rate so there is no doubt they are useful in that area.

So, yes, you will gain some power with underdrives. You will get a lot more from the tune but I understand the VCT system in the early BA is not as sophisticated as that in the later models and so the comparative power is down a bit. Maybe do the 98 octane tune first and see precisely what it delivers then think about the underdrives. If 170RWKW is being reported and you get that then I am more than happy to be proven wrong - my estimate of 165 was based on first hand observation of a retune done on a BA series 2 with air and exhaust mods but no underdrives. They were fitted later. The general info above on underdrives comes from the results of a real experiment on an earlier model Ford 6 engine.

BTW - 166 at the wheels is what I recorded out of a 5 litre VP C/dore with exhaust / cam / cold air /91 Octane tune. It ran a best of 14.9 with a 4 speed auto and 3.45 gears at around 151/152 Km/hr.

[Bazza96]

Well the guy at Forced Performance and Tuning said that 98 octane can make about a 3rwkw difference, so. Lets say, 155rwkw, and a tune of a minimum 10rwkw. that's 165rwkw? Say we only got 5rwkw from the underdrive pulley, that's still 170rwkw? And the tunes increase was way under estimated.

I think 170 is defiantly achievable..

[BRK]

By all means try and like I said I am more than happy to be proved wrong. On the forum, there are some interesting entries on results from underdrives with varying information. The entry and opinions above comes from data obtained by a mate who did a Masters Degree in Mechanical engineering with a research paper on pumps and blade design. There was a lot of work in this but to summarise in a few sentences, they used an EF Falcon 6 connected to an engine dyno. They ran a series of tests on this engine gradually eliminating the power drag caused by all the accessories. His main focus was on impellor / blade design in all pumps and part of the work was done on engine water pumps. They looked at ideal rotational speed for water output, power usage on a few blade designs, cavitation and so forth. On the EF, the factory water pump used close to 4 KW at 4000 engine RPM - that was its best pumping performance in terms of water delivery and power usage. He also advised that accelerating pumps too quickly can cause cavitation and spikes in power usage ( beyond the scope of what we are talking about).

Anyway - IMO, do the tune first because there is NO doubt that lower exhaust restriction coupled with correct ignition timing and fuel delivery rate matched to 98 octane fuel will see a real and repeatable power gain and three back to back runs will prove that. I hope that alone will put you >165RwKW and then you can decide if the underdrives are worth the investment. Maybe talk to Brad at Atomic performance and get an opinion from him and Pitlane (site sponsor). Pitlane got good results from underdrives on a 5.4 V8 - dyno sheet is on the forum.

[ratter]

This is a before and after comparison on my car, the car was strapped to the dyno, several runs made to get a base reading, the car was left on the dyno so no changes were made to the strapping, the underdrives were fitted and then run up again. No changes made to tune, not resetting ECU, as close to back to back as possible.

I was actually surprised that they showed a gain on the dyno