New Build for WTAC

Magpie · Postby **Magpie** » Tue Mar 06, 2018 8:17 pm

The plot is looking at a session in 2015 (red) and 2017 (blue), where the speed was over 120kmh. The acceleration was calculated by 'Accel G'*9.80665 to give m/sec² and then smoothed.

This helps identify if changes have helped. From this alone the 2017 acceleration has improved since 2015.

greenMachine is correct, improving acceleration between points will net a fair amount of time. To increase acceleration without changing power leaves on weight and drag to improve on. Yes there is the issue of grip, but this is about data analysis no5 trying to predict lap times etc.

Now some people have argued that the graph is not correct as the lines should start to converge as speed increases, however I am yet to do some statistical analysis and draw a least squared regression line. The software does not have this capability and I would have to export etc. To prove my point I may do this when home next...

greenMachine · Postby **greenMachine** » Tue Mar 06, 2018 9:35 pm

NitroDann wrote:What happens when you go extra tall and move the whole track back one gear and top out 5th on the straight?

If 3rd to 5th looks like a better set of rations than 4th to 6th?

Dann

Dann

Good question Dann! Short answer, dunno! Nothing to stop this, it would be dependent on an appropriate diff ratio(s). Note that 5th/diff ratio would need to be the same/similar to 6th/diff ratio. Closer ratios are generally held to be more desirable, but probably more desirable to be in the fat of the torque curve exiting important corners (eg T9, T12, maybe T7 (especially if you can take T8 flat)

The other issues would be identifying where 'high range' change points were compared to 'low range' and whether one or the other removed an awkward change/not change that cost time. The other would be whether the high range effective diff ratio was sufficiently different to the low range to be desirable in its own right, or vice versa.

Magpie wrote:[... some statistical analysis and draw a least squared regression line. The software does not have this capability and I would have to export etc. To prove my point I may do this when home next...

Ducks ... whoosh! I'm just the nut holding the steering wheel, I'll leave this to maths junkies!

:mrgreen:

madjak · Postby **madjak** » Wed Mar 07, 2018 1:41 pm

Setting gearing is really hard without knowing the aero and grip levels. Sometimes it's better to sacrifice a bit of kph at the end of the main straight to have a better gear out of a specific corner. That's all going to depend on how well the car is handling so it's basically impossible to predict now.

In order to be competitive the car will need to have excellent grip, so it would probably be cornering 10 to 20% faster than any MX5 has been around he track meaning the corner exit speed before the main straight will be higher and so top speed should also lift a little too. If you are building a turbo car with a big spread of torque it doesn't really matter what gearing you use. For me with my narrower powerband getting the gearing closer together is far more critical.

Postby **NitroDann** » Wed Mar 07, 2018 3:23 pm

Keeping the revs up higher in a shorter gear will help due to the linear nature of the torque i think.

Dann

madjak · Postby **madjak** » Wed Mar 07, 2018 6:58 pm

Torque means little to race car acceleration as it has to be multiplied by RPM to get a force... HP is a 1:1 mapping of the force that accelerates the car so you want to be running in the section of RPMs that makes the most HP. The HP curve is all you need to look at... forget torque. This whole thing about area under the curve is nonsense... you ideally want area under the curve but as high in the RPM range as possible. (which translates to: lots of HP up high in the revs)

If you compare two different examples you can quickly see the issue with torque:
20,000 rpm making 1000hp
2,000 rpm making 1000hp

Both engines make the same power but the 20,000rpm engine has 10 times less torque than the 2,000rpm engine. At the same total mass they both will accelerate at the exact same rate. HOWEVER the 2000rpm engine needs all it's rotating parts to be 10 times stronger to withstand the massive twisting force made by all that torque. So everything needs to be 10 times heavier to take the load and then heavier again to stop the larger forces from the heavier parts trying to break themselves. The end result like a massive rocket ship is that most of the power is lost in trying to accelerate all that extra mass in both rotation (moment of inertia) and in direction (car acceleration). If you haven't guessed the 20,000rpm example is an F1 and the 2,000rpm example is a truck.

So an ideal race car wants to have the least amount of torque possible to achieve the highest HP which means RPM is where it's at. If you are building a turbo MX5 for a track car you want the HP to peak at the highest RPM point you can without the engine throwing itself to bits. This is so you can run big power without having to run heavier gearboxes, diffs, axles etc. Of course with a turbo you have a big restriction in the exhaust that works against you pushing more air so you have to find that balance. But instead of 500whp at 4000rpm you want 500whp at 7000rpm so that the load on the gearbox and drivetrain is reduced massively. Actually you really want 550whp or 600whp at 7000 but I don't think you can do that without a larger turbo and introducing more lag. The guys on the US forums don't really understand this and tbh most are modifying stock engines for street use so it's a different need. To stop breaking gearboxes all they really need to do is to run larger cams to move the power higher in the rev range. It might not make much more power but it will make less torque which is better for the transmission.

Sorry for the long post but this whole torque vs HP thing drives me mad!

Postby **NitroDann** » Wed Mar 07, 2018 7:11 pm

madjak wrote:you want to be running in the section of RPMs that makes the most HP.

NitroDann wrote:Keeping the revs up higher in a shorter gear will help due to the linear nature of the torque i think.

We are agreeing with one another mate.

Dann

madjak · Postby **madjak** » Wed Mar 07, 2018 7:43 pm

I didn't mean to come across as arguing... I was agreeing too I suppose. It's just most people don't get that talking about torque is really meaningless and I was triggered by that word!

Yes, to what you said... keeping the revs higher is all you need regardless of gear in terms of gearing on the track. The problem comes when you have big drops in RPM due to the larger spacing between 3rd and 4th vrs 5th and 6th. I think it matters less on a turbo car than NA and supercharged though because the power band is so much larger.

Postby **NitroDann** » Wed Mar 07, 2018 8:49 pm

Everything you said I have parroted many times to confused onlookers. This is exactly why all of my dyno sheets look like this. I understand your frustration.

Magpie · Postby **Magpie** » Thu May 03, 2018 10:22 am

NitroDann wrote:A gentleman is entering this NA8 with VVT engine into the ClubSprint class at World time Attack Challenge this year.

Have you heard if he was offered a spot?

Postby **NitroDann** » Thu May 03, 2018 10:29 am

Ill text him. There are some new aero photos to share also.

Dann

chrons_rotary · Postby **chrons_rotary** » Thu May 03, 2018 5:10 pm

Unfortunately I was put on the reserve list.

Progress has been slow, but getting close to getting it on the track.
Also currently waiting on a fastback

madjak · Postby **madjak** » Thu May 03, 2018 6:41 pm

WTAC is getting faster and more serious every year so in order to get in competitors are going to need to prove that they can preform at a fairly competitive level. I think this means you need to have a fair bit of previous time attack history and be able to show class wins and lap times at the venue. Without that you're going to be put on the reserve list every year.