Rally Cars tech stuff

Suddenly remembered this post.

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Originally Posted by dimviii

We have to define when we say boost pressure whqat we mean.
Some people mean the overboost pressure,some other the ct boost pressure.
overboost is the turbo pressure we have at midrange rpm when turbo spools,ct boost pressure is when the rpms are at the higher band ie 5000-6000rpm etc. big overboost pressure help to create more torque,while big ct pressure will help to have bigger number at peak horsepower.

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Please explain more. I have always though that when you say overboost you mean the boost above atmospheric pressure or in other words the gauge pressure whatever the revs are. Ct is unknown term for me.

Sometimes people are discussing about same issue using different words, which can cause confusion. When I speak about boost I mean the pressure above atmospheric pressure.

In the book by Graham Bell (Forced induction performance tuning) he defines the pressures as follows.

Gauge pressure: “The pressure you read of a normal pressure gauge. This is the pressure above atmospheric pressure. Usually simply called the boost pressure when referring to the inlet manifold pressure in supercharged engines.”

Absolute pressure: “The pressure above perfect vacuum. Thus, at sea level, normal air pressure is 14,7 psi absolute. Adding supercharged boost of 5 psi would then give a reading of 19,7 psi absolute.”

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Originally Posted by dimviii

example grN evos can create about 2 bar overboost,but cant ''hold'' more than 1,5-1,6 bar at high revs with restrictor.All these are not rule,but depents to external temperatures a lot.

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I recall you once said that a gr N evo has 0,5 – 0,7 bar at 4500 rpm.

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Originally Posted by dimviii

At Finland-Sweden Norway or at mediterannean winter cold rallies you can,but at summer rallies with 30+ temp is difficult.

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I think it’s all about air density that changes with altitude, temperature and to some extent the humidity (100% relative humidity decreases the density by only 0,9% compared to dry air at sea level and 20 ^oC).

As known the wrc cars are said to loose 20-30% of the power in higher altitudes in Mexico. I compared the density at sea level with temperatures + 20 ^oC (1,204 kg/ m³) and - 20 ^oC (1,394 kg/ m³). The density is 15,8% higher with – 20 ^oC. Does this mean that the power also increases by 15,8%? Assuming a car having 330 PS at sea level at + 20 ^oC it would mean 382 PS at - 20 ^oC! Ups!

Air Density Calculations Impact of Altitude Temperature Humidity and Pressure.xlsx

Dimviii, if this is true you should come up north and run your Mitsu in the dyno. You would get good results. ;)

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Originally Posted by dimviii

Wrc cars now can have a 2,5 bar overboost(as the limit) and for sure can hold much more ct pressure from an N4-R4 due to less cc(1600 vs 2000) and different boost pressure hardware system.

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My opinion is still that it’s 2,5 bar absolute (atmospheric pressure + turbo pressure / gauge pressure).

Sorry for late reply.

yes its absolute pressure,thats the way everybody works at engines reffering.
About the density at low temps,yes it helps a lot cause the air density is higher,but no way if 20% more density will have 20% more power.As you drive the car yes you can feel the better response,the more power,but lets say that at a 350 bhp car feels like some 15-20bhp more.I am talking about temp difference from +30 celsious to 5 celsious.
Another point is with less temp you have less intake temps, due to colder air through the intercooler which helps to decrease the hot compressed air from turbocharger.

About the ''overboost'' and ''ct''
lets say that you drive an Mitsubishi evo(or any turbo car with wastegate actuator) you are driving the car with 4th gear and 2000rpms,and you floor the gas pedal.Car will accelerate slowly at first(rpm range out of turbo at 2000rpms) and as the rpms climb to about 2700 turbo starts t build pressure.At about 3500rpms your absolute air pressure gauge reach its maximum pressure which is lets say 1,8 bar.At about 4500-5000rpms if you watch your boost gauge you will see that the boost pressure starts to drop slowly at 1,7-1,6-1,5bar.At 7000rpms your boost gauge will show 1,3 bar.This pressure is the ''ct''
The 1,8bar the maximum pressure your engine reach at 3500rpm is the ''overboost''
Why this happening?
We want more boost pressure at mid range rpms to help the car accelerate faster.As the rpms go up,we cant hold that pressure(1,8bar) for many reasons.Turbo not big enough,at grN cars just 33mm intake at turbo,turbo at continious 1,8bar will heat A LOT the air,and the oem intercooler will not succeed to low the intake temps etc.The reasons vary from car to car,so dont take it as a rule for all cars-engines.
At wrc cars we dont have overboost and ct.We have a steady boost pressure from mid range to high revs.At wrc we have big enough turbos,we have better efficient intercoolers,stronger engines that can cope with 2,5 bar all day(s) long,completely different boost pressure management and hardware.

Hope to helped with my s$ite English. :dozey:
if you didn t understant something dont hesitate to ask again.

By WRC cars do You mean 1.6T cars with lower boost compared to 2.0T? Because I have a turbo pressure curve from an early Fabia WRC Evo I engine and it looks like the one of Gr.N cars just has much higher values but the decrease is same (I think it must be similar with the restrictor).

It starts around 2700 rpm with something like 2 bars at 3000 rpm. It reaches maximum cca 3,3 bar at 3500 rpm but than it starts to decrease to 2,9 bar at 4000 rpm, 2,3 bar at 5000, 1,9 bar at 6000 rpm and finally some 1,4 bar at rpm limiter at 7500 rpm. Numbers are approximate, the grid is quite large.

The engine has max. torque at 3700 rpm and maximum power constant from 4000 to 5000 rpm.

Mirek the dynoplot i ve seen from escort wrc, was almost steady pressure to 6000 rpms and after that started to drop.From 3000 rpms had already 3 bars.Unfortunately haven t seen from later wrc cars,or the new 1,6 ones.
Of course restrictors doesn t help to keep high pressures at high rpms,but depents to turbo design,engine efficient,for how many rpms will manage to keep the boost.

ps the escort wrc i ve seen is with 38mm restrictor

How's the ALS affect all this, Mitsubishi's ones sound lot agressive to me, unlike Subaru's and WRC/RRC?

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Originally Posted by stefanvv

How's the ALS affect all this, Mitsubishi's ones sound lot agressive to me, unlike Subaru's and WRC/RRC?

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every als can adjust to aggresive or less agresive.Driver will choose how aggresive to his likes at every surface.

I saw a dyno from Subaru that had 2,9 from very low (think it was 2000 rpm) to almost 7000. I also ask PS if that was right, and he said yes. Think it was the 12B.

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Originally Posted by Coach 2

I saw a dyno from Subaru that had 2,9 from very low (think it was 2000 rpm) to almost 7000. I also ask PS if that was right, and he said yes. Think it was the 12B.

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yes its possible from so low revs with agressive antilag to build plenty of boost pressure.

Thanks, now I know the difference between overboost and ct but what does ct stands for?

The explanation you gave I assume is about an evo without a restrictor because otherwise I can’t understand 1,3 bar @ 7000 rpm.

Below is a dyno chart for a evo9 I got from a Finnish company that tunes cars with turbo (Google Translate.)

[img]MitsubishiEvo9Stage1_21_zpsc5d4ccdf.jpg%20photo%20 by%20OkdF%20|%20Photobucket[/img]

The lowest is a standard car. The next one is as they call it stage 1 with a power of 326 PS @ 1,5 bar. The most upper one have 355 PS @ 1,6 bar (Stage 2).

On an evo with restrictor I assume the pressure will decrease rapidly after torque peak because of the restrictor. On the chart below the torque decreases rapidly after peak torque -> pressure drop in the inlet manifold. As I said I recall you said about 0,5 – 0,7 bar at 4500 rpm.

[img]Mitsu_Evo9_grpN_Dyno-1_zps3780d166.jpg%20photo%20by%20OkdF%20|%20Photob ucket[/img]

Max rengas teho = max power from the wheels
Max moottori teho = max power from the engine
Max momentti = max torque
Max nopeus = max speed
Ilmapaine = atmospheric pressure
Lämpötila = temperature

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Originally Posted by stefanvv

How's the ALS affect all this, Mitsubishi's ones sound lot agressive to me, unlike Subaru's and WRC/RRC?

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I have always wondered how other Mitsubishi did their anti-lag as compared to the "rocket" system that Prodrive used. For that matter how do the modern systems from vw Citroen and ford work?

(really loving the technical discussion, is there any way to start another thread about it so we don't anger brother John and lose all this great info?)

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Originally Posted by OldF

Thanks, now I know the difference between overboost and ct but what does ct stands for?

The explanation you gave I assume is about an evo without a restrictor because otherwise I can’t understand 1,3 bar @ 7000 rpm.

Below is a dyno chart for a evo9 I got from a Finnish company that tunes cars with turbo (Google Translate.)

[img]MitsubishiEvo9Stage1_21_zpsc5d4ccdf.jpg%20photo%20 by%20OkdF%20|%20Photobucket[/img]

The lowest is a standard car. The next one is as they call it stage 1 with a power of 326 PS @ 1,5 bar. The most upper one have 355 PS @ 1,6 bar (Stage 2).

On an evo with restrictor I assume the pressure will decrease rapidly after torque peak because of the restrictor. On the chart below the torque decreases rapidly after peak torque -> pressure drop in the inlet manifold. As I said I recall you said about 0,5 – 0,7 bar at 4500 rpm.

[img]Mitsu_Evo9_grpN_Dyno-1_zps3780d166.jpg%20photo%20by%20OkdF%20|%20Photob ucket[/img]

Max rengas teho = max power from the wheels
Max moottori teho = max power from the engine
Max momentti = max torque
Max nopeus = max speed
Ilmapaine = atmospheric pressure
Lämpötila = temperature

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OldF
yes at the dynoplots you posted the boost pressure drops very quickly,this is not good if you want to gain significant power,and torque for enough rpms.Basically to make comments at a dynoplot we have to know some other things like,the afr ratio(air to fuel ratio) from 2000rpms to red line,the advance,and a diagramm with the boost curve to rpms.
These dynoplots are not so good for the ammount of boost pressure for an evo 9.Little power gains(360bhp) and little torque(460nm) for the first dynoplot.Here in Greece good mappers with 1,6 bar of boost(ct) can extract more than 400bhp and about 530-550nm.But again as i said we have to know all the engine parameters to comment safely.The boost is a lot for just 360 bhp.You can have 360 bhp with less boost,and thats only good.
Second dynoplot is strange because while this evo 9 has plenty of torque,has very little power gains.Something is wrong.

See here an evo 9 with Motec ecu+exhaust+cams 272 degrees.Watch how the maximum power curve goes after 6500rpms,and compare with yours dynoplots
Watch the torque line how drops slowly,with result to can keep maximum torque between 3500rpms to 5500rpms.To have this result you have to keep boost pressure as high as you can(not only boost,but other parameters too)
This evo the boost pressure is 1,8 bar overboost with 1,5 bar ct.

http://img823.imageshack.us/img823/1248/evo8komando.jpg

So for resume,we can t have conclusions when just pub talking and say that this car has 2 bar,but other car has 2,5 bar.Maybe the car with 2,5 bar is not faster even if they are same cars/engines.
Also we have to define which boost we mean,overboost at midrange rpms,or the ct boost pressure at upper rpms.

Anothervery important point is the air fuel ratio(afr) and the advance timing degrees.We can have same engine with ie 2,0 bar overboost and 1,6 ct.We programm the engine ecu at 11,4 afr and 13 advance degrees= ie 400 bhp and 500nm torque.
we reprogramm now the same engine with SAME boost but now with 12,2 afr and 16 degrees advance=440bhp and 570nm torque.
Thats why when you dont know all the parameters you can t have any conclusions for any engine/car output.We can comment,but not an conclusion.

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Originally Posted by TyPat107

I have always wondered how other Mitsubishi did their anti-lag as compared to the "rocket" system that Prodrive used. For that matter how do the modern systems from vw Citroen and ford work?

(really loving the technical discussion, is there any way to start another thread about it so we don't anger brother John and lose all this great info?)

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each wrc car has its own design antilag system.Maybe they seem to be same,but they have plenty of difference between them.
Its not safe to comment when we don t know how it works.The Subaru rocket system was a very different one created by prodrive.

Just few my comments to this very interesting discussion.
- about anti-lag in wrc cars - it's very complex thing, this Subaru/Prodrive "rocket" system was very unique, we once had S12 turbo but it was almost impossible to make it work good without Prodrive ECU and anit-lag mapping
- about power/torque differences - my experience shows that almost all rally cars from Finland (or Estonia) we were working with had smaller amounts of hp/Nm, at least on the paper comparing to the cars from Western/South Europe. Also at the same time almost all those cars were better balanced with better traction... so maybe it's some kind of different approach of the car builders, etc.

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Originally Posted by Brother John

Please go back to this thread. It's about the VW wrc car.

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Separate the posts regarding all the technical aspects into a new thread instead, so they could continue discussion over there.

I have a question to the engineers:

Can someone explain this two springs in the same shock?

IMG

Edit: Unfortunately I can´t post photos or links until I reach 15 posts.

In VW Motorsport official website, there´s a Polo R WRC photo gallery, taken in studio, and one of its photographs was taken from the front naked brake disk and shock/spring. I´m curious to know why in the same shock there are 2 different springs, the black one appearing to be stiffer than the top red one. Does ne1 has any clues on this suspension setup?

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Originally Posted by Brother John

Okay I start a new Thread with the name "Tech rallycar stuff". :idea:
I can still change the name later.

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Thanks.

Here is the thread for fans of technology, turbo boost and more of rally cars. Have fun.

Rally Cars tech stuff http://www.motorsportforums.com/imag...es/spanner.gif

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Originally Posted by worldrallynews

I have a question to the engineers:

Can someone explain this two springs in the same shock?

IMG

Edit: Unfortunately I can´t post photos or links until I reach 15 posts.

In VW Motorsport official website, there´s a Polo R WRC photo gallery, taken in studio, and one of its photographs was taken from the front naked brake disk and shock/spring. I´m curious to know why in the same shock there are 2 different springs, the black one appearing to be stiffer than the top red one. Does ne1 has any clues on this suspension setup?

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Tender Springs vs. Helper Springs

A helper spring is used to keep the main spring tight between the perches when the suspension is at full droop. It "helps" keep the main spring snug, if you will. A helper spring has a very soft rate, on the order of 10 lbs/in. It's just strong enough to push the main spring up against the upper spring perch, but that's about it.

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Originally Posted by dimviii

Second dynoplot is strange because while this evo 9 has plenty of torque,has very little power gains.Something is wrong.

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Did you notice that it’s a grp N (32 mm restrictor) dyno chart?

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Originally Posted by dimviii

we reprogramm now the same engine with SAME boost but now with 12,2 afr and 16 degrees advance=440bhp and 570nm torque.

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What is typical air to fuel ratio range for an evo9 grp N? Do you know the Brake Specific Fuel Consumption (BSFC) for an evo9 grp N?

Btw, the turbo used in WRC and WTCC is a Garrett GTR2560R. I asked them for some information about the turbo but the replay was:
- Sold only for cars homologated with that turbo.
- No information available.

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Originally Posted by OldF

Did you notice that it’s a grp N (32 mm restrictor) dyno chart?.

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No didn t noticed it :dozey: Thought that it was like the previous link with the road evo dynoplot.My bad.

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Originally Posted by OldF

What is typical air to fuel ratio range for an evo9 grp N? Do you know the Brake Specific Fuel Consumption (BSFC) for an evo9 grp N?

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No i dont know,but do we need it?

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Originally Posted by OldF

Btw, the turbo used in WRC and WTCC is a Garrett GTR2560R. I asked them for some information about the turbo but the replay was:
- Sold only for cars homologated with that turbo.
- No information available.

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yes they dont give outside information for motorsport products,specially when fresh launched at world motorsport scene.Garrett did the same also with TR30R used at 2,0 lit wrc cars,as the IHI RX 6 for Subaru wrc cars.

But you can try for info this company,maybe you are lucky.
Owen Developments - turbo, turbos, turbochargers, performance tuning and engineering

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Originally Posted by dimviii

A helper spring is used to keep the main spring tight between the perches when the suspension is at full droop. It "helps" keep the main spring snug, if you will. A helper spring has a very soft rate, on the order of 10 lbs/in. It's just strong enough to push the main spring up against the upper spring perch, but that's about it.

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Thank you!

Guys, It's a brilliant topic! I'm learning with every post. Keep up the good work, as I will not contribute here anything due to my lack of knowledge. But it is sure fun to read about it.

Polo's aerodynamics explained - Rally the World | Volkswagen and the Polo R WRC - rallytheworld.com

This excellent post by Zico deserves to be here. :up: It's from a thread ”two step launch” few years back.



Where are you Zico?


http://www.motorsportforums.com/wrc/...tml#post553319

Attachment 3093

Maybe more over-boost than ct-pressure dimviii?

Hello everyone, I hope my first post will be in the correct thread... I was wondering about manufacturers switching from mechanical to electric water (coolant) pumps, which seems to be the trend for the future (despite many problems with them in the past). From what I found so far they are used in Peugeot 207 S2000 and in Mini John Cooper Works WRC & S2000 1.6T. Do you know of other rallye cars using electric water pumps? And what is so fragile about them that they caused many drivers retire from events (e.g. Václav Pech in Barum Czech Rally 2012 lately)? I suspect that the manufacturers mostly use the pumps you can find in BMWs (in E90 etc.), which should be pretty reliable. By the way, are the homologation documents with detailed specifications available to the public? Thank you for any replies!

I think there are many reasons for electric water pumps. They do not use engine power (like auxiliary belt run water pumps do), smaller risk of them not working (when the belt broke), you can position the pump where you want (weight distribution, etc.), you can easier bleed the system (run the pump before the engine starts), let the pump work after turning off the engine, etc. In S2000 car it might be also problematic to use belt run pump because of very high engine revs?
At the beginning there were a lot of problems with electric water pumps, but now I think they are pretty reliable.
There is also electric water pump in Fiesta S2000 and it's also based on some BMW pump.

Thank you for the answer and tip on Fiesta S2000, I didn't know about that one. The advantages of electric pumps seem to be clear indeed, I think we will see more of them in the close future. What I would actually be interested in are details about how the temperature control is implemented etc., but such information is pretty secret, I can imagine. Or is there just a regular thermostat on the bypass hose of the radiator and the rpm of the pump is kept constant? That is probably not the way BMW does it...well if anyone has a tip where to look I will certainly appreciate it. :)

I don't know exactly how it is done, but I will find out, no problem! There sure is no such thing like thermostat. There is only Engine Coolant Temperature sensor which gives data to the ECU and it controls the pump.

for sure no thermostat,as the pump pulley is not working when engine is cold.

ECU controls the flow of the pump using coolant temperature sensor, engine load, revs, etc. So sometimes pump is not working at all, sometimes with very high revs. On WOT water pump stops, cooling fans stop, alternator also. It's quite complex thing in S2000 car.

I think that probably this is the best topic to post this doubt I have regarding homologations.

How do they work? For example, for a certain car there's a certain brand of dampers homologated? Or any damper with the dimensions and characteristics can be used?

And what all those variant mean (VO, VK, etc...)?

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Originally Posted by dimviii

for sure no thermostat,as the pump pulley is not working when engine is cold.

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you sure.....

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Originally Posted by bubbaontour

you sure.....

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haven t see such a system,but as the ecu controls the pump speed,can t find a reason for working pump at cold engine.
except if it turns the pulley slowly just to prevent from extreme heating near cylinder head? and after a point of degrees ie 70 c turns faster?

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Originally Posted by bubbaontour

you sure.....

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yes, I'm 100% sure. there are moments when pump is not working at all, for example after engine start in cold conditions, then as dimviii says it starts to work really slowly and then "normally". also on WOT it stops for short periods of time.

All we will ask for is 400k :)

How to build a World Rally Championship car | Pole Position - YouTube

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Originally Posted by Co-driven

I think that probably this is the best topic to post this doubt I have regarding homologations.

How do they work? For example, for a certain car there's a certain brand of dampers homologated? Or any damper with the dimensions and characteristics can be used?

And what all those variant mean (VO, VK, etc...)?

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A car has a basic group A homlogation where the cars dimensions, weight and all those parts which must be original in group A (e.g. intake manifold, exhaust manifold etc.) are described. By a VO (Variant Option) a manufacturer homologate the parts that are allowed to be homologated in the groups A and N and modified parts in the other groups (R, S2000 & WRC). VO is also used when a modified part replaces the previous one. VK is a kit which includes all the parts homologated for use in rallying. ER (erratum) is used when there is an error in previous homologation. ER is also used when homologating modifications to the engine. Little easier to homologate only the modification and not the whole engine for every modification.


Parts that must be homologated varies in different groups. For example dampers are free in groups A and N but but must be homologated in the other groups.


Everything begins with a group A homologation. In group N there is a complementary homologation form where are all the parts that must be original in group N but didin't had to be original in group A. All the other parts allowed to be homologated in group N (brakes, clutch etc.) are homologated with a VO.


In the other groups (R, S2000 & WRC) the basic rallying parts are homologated in a VK and all the modifications with a VO or ER.


The explanations for the other ones you can find here


Homologations you can find here


R1A/B = VR1A/B, R2B/C = VR2B/C, R3C = VR3C, R3T = VR3T, R3D = VR3D, S2000 = KSR (VK-S2000 rallyes or SUPER 2000 1.6 turbo), WR = WRC parts (bigger rear wing, fly wheel etc.)


Here you can find homologation forms for different Mitsubishi evolutions. Citroen used to have the homologation forms for the C2 R2 on their web site but they're not there anymore.


Hope this help and hope I got it all right. :)

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Originally Posted by br21

ECU controls the flow of the pump using coolant temperature sensor, engine load, revs, etc. So sometimes pump is not working at all, sometimes with very high revs. On WOT water pump stops, cooling fans stop, alternator also. It's quite complex thing in S2000 car.

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What is WOT?
Alternator stops, why?

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Originally Posted by dimviii

haven t see such a system,but as the ecu controls the pump speed,can t find a reason for working pump at cold engine.
except if it turns the pulley slowly just to prevent from extreme heating near cylinder head? and after a point of degrees ie 70 c turns faster?

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I think that is the idea to have few more horsepowers. The pump is operating only when necessary.

Quote:

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Originally Posted by br21

yes, I'm 100% sure. there are moments when pump is not working at all, for example after engine start in cold conditions, then as dimviii says it starts to work really slowly and then "normally". also on WOT it stops for short periods of time.

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If I remember correctly bubba is a mechanic for the mini wrc, so now I am really intrigued why he asked that.