Rally Cars tech stuff

[OldF]

Kiitos Gamle Finne..you know I manufacture suspension mainly gravel but in America every boy under 30 has compulive disorder which makes the feel they have to lower their car 100-120mm so their car is like this, so I have made things like that to correct the position of lower arm when using short strut.




Very hard to deal with silly boys who have mental disorders. Facts don't help, reasoning, drawings, nothing helps..

Sometimes to help understand I use teacher's aids like this:
First you point out the components or idea:


Then you impress on them how important the idea is...



with rally boys it usually takes a couple of times: (especially when they are "injur-near" and their name was originally "Håkansson" before it became "Hawkinson" and then I ''döpte om dom'' to Hoikansainalainen ---all rally drivers must have a Finnish name to channel to spirit)

That's me doing the technical instruction....over here i"m one of the "Old FARTs" (Flemish-American Rally Team)

Is that the motivational method or ”banging the information into the head ” method?

[gorganl2000]

Kiitos Gamle Finne..you know I manufacture suspension mainly gravel but in America every boy under 30 has compulive disorder which makes the feel they have to lower their car 100-120mm so their car is like this, so I have made things like that to correct the position of lower arm when using short strut.

Very hard to deal with silly boys who have mental disorders. Facts don't help, reasoning, drawings, nothing helps..

Sometimes to help understand I use teacher's aids like this:
First you point out the components or idea:


Then you impress on them how important the idea is...



with rally boys it usually takes a couple of times: (especially when they are "injur-near" and their name was originally "Håkansson" before it became "Hawkinson" and then I ''döpte om dom'' to Hoikansainalainen ---all rally drivers must have a Finnish name to channel to spirit)

That's me doing the technical instruction....over here i"m one of the "Old FARTs" (Flemish-American Rally Team)

i truly appreciate your approach to passing on knowledge...lol

[OldF]

In the beginning I was a little bit sceptical about the power, torque and bmep figures given in the article below. I found some equations using bmep so I decided to give it a try. I was little surprised how close the results are calculated with different equations. If the data in the article is not correct it’s at least consistent.


http://content.yudu.com/Library/A1wv...sources/19.htm

BMEP = break mean effective pressure
http://www.epi-eng.com/piston_engine..._yardstick.htm
“The definition of BMEP is: the average (mean) pressure which, if imposed on the pistons uniformly from the top to the bottom of each power stroke, would produce the measured (brake) power output.
Note that BMEP is purely theoretical and has nothing to do with actual cylinder pressures. It is simply a tool to evaluate the efficiency of a given engine at producing torque from a given displacement.”

The coefficient 0,0001424 I use in the calculations is derived from the equation Power = torque * omega.
Omega = 2 * pii * f (1/s)
Power = Watt
Torque = Nm

Omega -> rpm = 2*pii*rpm/60 = 2*pii/60 = 0,1047
Watt -> Power (PS) = Watt * 1,35962152 / 1000 = 0,001360

Coefficient = 0,1047 * 0,001360 = 0,0001424

The three equations I use are:
Power (PS) = Torque (Nm) * rpm * 0,0001424
BMEP (N/m²) = P (W) * nc / V (m³) * N (1/s) nc = 2 for a 4-stroke engine.
BMEP (N/m²) = 4 * π * T (Nm) / V (m³)

Ford Focus WRC

Data from the article:
348 bhp = 1,014 * 348 = 353 PS
353 PS @ 6500 rpm
680 Nm @ 3000 rpm
bmep @ peak power = 24 bar = 2,4 N/mm² = 2 400 000 N/ m²
Bore = 84,8 mm
Stroke = 88 mm

Cylinder / piston area = 5 647,83 mm²
Average radius of crank shaft turn = 0,02817 m

Torque at peak power

P (PS) = T (Nm) * rpm * 0,0001424 => T = P / rpm * 0,0001424 = 353 / 6500 * 0,0001424 = 381,4 Nm

Calculating with bmep.
T (N/m) = BMEP (N/m2) * V (m3) / 4 * π = 2400000 * 0,001998 / 4 * 3,14 = 381,6 Nm

Calculating with bmep and cylinder / piston area
F = pressure (N/mm²) * area (mm²) = 2,4 * 5647,83 = 13 555 N
T = F * Average radius of crank shaft turn = 13555 * 0,02817 = 381,8 Nm

Bmep at peak torque
BMEP (N/m²) = 4 * π * T (Nm) / V (m³) = 4 * 3,14 * 680 / 0,001998 = 4 274 675 N/m² / 100 000 = 42,7 bar

Power at peak torque
P (W) = BMEP (N/m²) * V (m³) * N (1/s) / nc ( nc for a 4-stroke engine is 2)
P = 4274675 * 0,001998 * (3000/60) / 2 = 213 520 W / 1000 = 213,52 kW * 1,3596 = 290,3 PS

P (PS) = T (Nm) * rpm * 0,0001424 = 680 * 3000 * 0,0001424 = 290,5 PS

Ford Fiesta WRC

Data from the article:
Bmep @ peak power = 29,3 bar 2,93 N/mm² = 2 930 000 N/ m²
325 bhp @ 6250 rpm = 1,014 * 325 = 330 PS (329,6 with one decima)
Bore = 83 mm
Stroke = 73,9 mm

Cylinder / piston area = 5410,61 mm²
Average radius of crank shaft turn = 0,02365 m

Torque at peak power

T @ peak power = 330 / 6250 * 0,0001424 = 371 Nm (370,8 with one decimal)

Calculating with bmep.
T (N/m) = BMEP (N/m2) * V (m3) / 4 * π = 2930000 * 0,0016 / 4 * 3,14 = 373 Nm

Calculating with bmep and cylinder / piston area
F = pressure (N/mm²) * area (mm²) = 2,93 * 5410,61 = 15 853 N
T = F * Average radius of crank shaft turn = 15853 * 0,02365 = 375 Nm

Peak power

Using the torque calculated with bmep, 373 Nm
P (PS) = T (Nm) * rpm * 0,0001424 = 373 * 6250 * 0,0001424 = 332 PS

Calculating with bmep, 29,3 bar
P (W) = BMEP (N/m²) * V (m³) * N (1/s) / nc ( nc for a 4-stroke engine is 2)
P = 2 930 000 * 0,0016 * (6250/60) / 2 = 244 167 W / 1000 = 244,17 kW * 1,3596 = 332 PS

Another way to estimate the power of the Fiesta WRC

In the article is said that on a typical rally stage the fuel consumption for the Fiesta WRC is about 0,7 l/km.

On the Skoda’s web page (http://new.skoda-auto.com/en/motorsport/cars) the fuel consumption is 0,6 l/ SS km for the S2000.

The Fiesta consume 0,7 / 0,6 = 1,17 (17%) more fuel on a special stage. As I don’t know the power of the Skoda S2000 I have to make different estimates. What I’ve found out a turbo engine use a richer fuel to air ratio but as I don’t know the AF ratio I have to guess what it is. If a turbo engine use a AF of 12:1 and a NA engine 13:1, the NA engine need only about 92% of fuel compared to a turbo engine to produce the same power.
Skoda 300 PS => Fiesta = 0,92 * 1,17 * 300 = 323 PS
Skoda 305 PS => Fiesta = 0,92 * 1,17 * 305 = 328 PS
Skoda 310 PS => Fiesta = 0,92 * 1,17 *310 = 334 PS
Skoda 315 PS = > Fiesta 0,92 * 1,17 * 315 = 339 PS

By the previous calculations 328-334 PS seems to be closer to the “truth”.

[Mirek]

Sorry for uneducated answer (moreover I have no time now).

The torque values doesn't fit. Fiesta WRC definitely has much more torque than Fiesta R5 (cca 400 Nm). Old 2.0 litre WRC had huge torque. Even old Fabia WRC with really bad engine in terms of torque had 640 Nm. The latest cars had something between 800-900 Nm @ cca 2000 rpm in my opinion. I think that the problem is in turbo pressure.

With fuel consumption it doesn't make sense because turbo cars have anti-lag (pure waste of fuel). 70 l/100 km seems to be really low figure but maybe with direct injection it is possible. On the other hand there is no direct injection in Fabia S2000 so even without ALS it's not comparable. I'm no expert at all.

[br21]

now engines both in r5 or wrc, so with direct injection, are using much less fuel than previous rally turbo engines, like in 2.0l WRC cars or GpN cars.
for example fiesta s2000 was using some 70l/100km ss, and R5 uses around 60l/100km ss, but it also depends on stage characteristics, etc.

[OldF]

I'm no expert at all.

Me neither, I just put numbers into the equations and see what happens.

Sorry for uneducated answer

What do you mean by this?



AS I said, if the data in the article is not correct it’s at least consistent. 680 Nm seems low in my opinion also if a N4 evo has above 600 Nm with a lot lower boost and 1 mm smaller restrictor.

Mirek, I think you was in hurry when you read the post.

Here’s a summary of the results.

Focus
Torque at peak power 381 Nm
Power at peak torque 290 PS
Bmep at peak torque 42,7 bar

Fiesta
Torque at peak power 371 Nm
Peak power 332 PS

There was not enough data in the article to calculate the peak torque of the Fiesta WRC. It has 6% bigger restrictor and probably a turbo more adapted to the restrictor.

If someone would like to have a different results concerning the torque for the Focus, you could try these equations.

http://www.turbobygarrett.com/turbob...Tech%20103.pdf

If using bar, Celsius, cubic centimetre:

Wa _kg/min= MAP_req(bar) * VE * N * Vd _cm³ / 2 * R * (273 + Tm C^o)

PS = 60 * Wa _kg/min / BSFC _kg/hr*PS * A/F

MAP = 4,3 bar
Vd = 1998
VE = volumetric efficiency
N = rpm
R = 2871
Tm = manifold air temperature

I can ensure you that you will have a better result.

[br21]

Unfortunately Anthony looks to be busy and in thread about his blog somebody asked about geometry settings in WRC cars. It might be still interesting for some, so for example MSport recommends toe: 0 in front and in 1mm (total) in rear both on tarmac and gravel. Camber -0,75deg front, -1,0deg rear on gravel and -1,5deg front, -2,0deg rear on tarmac, but that really depends on tires you're using. Caster around 12/13.

Also in free time this might be interesting to watch:
https://www.youtube.com/watch?v=FYbMk50awO0
nothing extra special there, but always worth watching I think.

[N.O.T]

You have a nice face Jan, a rally face... for your age i expected you to be a lot whiter and uglier... you gained a point in my book... still below threshold but a point is a point...

[OldF]

I found a page with a formula for calculation of the choked flow true a restrictor. There’s also a Java Applet calculator lower on the page by which the mass flow can be calculated.
http://www.grc.nasa.gov/WWW/k-12/airplane/mflchk.html This is rocket science.

A wikipedia formula looks different but gives the same result with C_d = 1. http://en.wikipedia.org/wiki/Choked_flow

Calculating with 1 bar and +25 ^oC the choked flow for a 33 mm restrictor is 0,200 kg/s. The volume is 0,200 / 1,168 (density) = 0,171 m³ or 171 litre. In the video (In br21’s post) the guy said the airflow is 70 litres per second. Dividing 171 / 70 = 2,44. Close to the 2,5 bar boost limit.

In this article (page 31) http://content.yudu.com/Library/A1wv...sources/19.htm
is said that airflow for the Focus is/was 748 kg/h and for the Fiesta 720 kg/h. Calculated value for a 34 mm restrictor is 765 kg/h, 765 / 748 = 1,0227. In the case of the Fiesta the result is 720,7 / 720 = 1,001. I don’t know how correct the values are in the article but quite close to theoretical.