ryoung

I use <A HREF="http://www.performancetrends.com/">Performance Trends</a> "Engine Analyzer Pro" software to tune our race motor. Better late than never, I finally got around to modeling the S8 motor.

First pass - 357 hp @ 7000 rpm

Considering how many guesses I made, this is ridiculously close to Audi's 360 hp. Some of the many assumptions I used in the model:

1. Cam timing is shown in the Bentley, but not cam lift. I used 0.4" for both intake &amp; exhaust.

2. Bearing sizes (which determines friction losses)

3. Intake manifold runner length. I assume 7" in "short" mode with no taper.

4. 80 mm throttle body

5. Head port dimension:
..... a. Intake - 3" length, 2" diameter
..... b. Exhaust - 3" length, 1.7" diameter

6. Intake manifold plenum volume" 600 in³

7. Free flowing air cleaner (since I can hear induction noise) and restrictive exhaust (since I can't hear it).

9. etc, etc, and etc

I'm sure many of the assumptions are in error, but most must be canceling each other out. Anyway, since I do seem to have a reasonable model, what's possible?

A few Tweeks:

1. A dry sump results in partial crankcase vacuum, reduces windage losses, and allows very low tension piston oil rings: + 17 hp

2. Replace clutch driven cooling fan with electric: + 5 hp

3. Replace belt driven water pump with electric (which isn't over-revved at high rpm): +8 hp

4. Install a more free-flowing sporty exhaust: + 35hp (an open exhaust adds 42 hp)

All "runs" @ 77 oF and 29.6" Hg

Many more little things could be done, but with just 1 thru 4 together, 357 hp goes to 428 hp @ 7000 rpm,

A total gain 71 hp!

KaMaKaZieP -ALUMIN8-

how accurate do you think they are? i am already switching to an electric fan... 16 inch on ebay for 59 bucks... had it on my A6 for 2 years no temp problems at all...

skiwi

i've got the software, and would love to play with the model!

Maxster4.2

How much do you estimate that all these Mods would cost to achieve the end result of 428 hp?

chucklane

I can agree with the exhaust. Cargrphic exhaust give +28 to hp

ryoung

Just guessing, for parts:

1. Replacement electric fan: &lt;$150
2. Electric water pump, such as the Davies Craig: $400 (plus hoses, fittings)
3. Exhaust: anywhere from $500-$1500
4. Dry sump system (multistage oil pump, custom oil sump, oil tank, plumbing): $3000 ?

Labor costs shouldn't be too bad for the first three, but a dry sump system requires major customization and replumbing, including just finding a place to locate a 3+ gallon oil tank.

And one caveat: The gains from electic fan, electric water pump, and the dry sump system should be very achievable, but this is my first pass with the model. My main concern is the large gain, perhaps too large, available from an improved exhaust. Certainly the S8 motor is very sensitive to exhaust system back pressure, but the stock system may be better than I assumed (which means perhaps that the intake system is not as good as I assume). I'd like to spend a little more time refining and validating the model before anyone spends big $$$ on mods.<ul><li><a href="http://www.daviescraig.com.au/newproduct.asp">Davies Craig electric water pump</a></li></ul>

ryoung

Garbage in, garbage out ... which is why I'd like get some hard numbers for more of the inputs.

Still, this Performance Trends software has been amazing good at finding useful tuning mods for our 2L OHC racing motor, and the gains were confirmed on both track and dyno. With this motor, though, I had the opporturnity to measure the dimensions of <b>everything</b> during a rebuild ... no garbage in. The huge advantage of the software, once you have a good model, is that you can make the changes on paper and see how they work, a lot less expensive than modifying actual parts and then finding out whether or not you wasted time and money.

ryoung

the software is installed on an ancient 386 PC that I use primarily as a fax machine, and the floppy drive on that PC died years ago.

I've been meaning to fix this machine, at least well enough to get some files off of it, and migrate everything to my laptop. Now I've got a reason to get off my butt, and when done, I'll email a copy of the model to you.

KjellA

And do you really believe that just the exhaust will get you so much gain, with nothing else done? I find it hard to believe, as not even the most optimistic tuners will promise you that much with an exhaust/chip combo.

I suspect the stock exhaust is highly effective, and not as restricitve as you should think judging from the sound.

ryoung

I made each change individually to see the effect of that change only, and they total 65 hp. When I made all the changes at once, the gain was even higher, 71 hp!

I think the rather surprising result is because of the dry sump system. The 17 hp gain for the dry sump is all the result of friction reduction (the stock motor has 84 hp of friction losses). Even though cooling system loads are reduced, this would have no secondary benefit for the stock fan or stock water pump. With an electric fan and cooling water pump, the dry sump reduces waste heat dumped into the cooling system allows the energy used to run the pump and fan to be reduced from "stock".

I don't know what to say about the exhaust system, except that if I'm overly pessimestic with the stock system, I'm overly optimistic somewhere else.