Subaru Group N Rally car that keeps on breaking ringlands

[Martin]

Hi,

Im helping on a Subaru Group N Rally car (N12), 32mm restrictor. We continue to have a problem breaking ringlands. Does anybody have some experience on these cars?

We had the car on a Hubdyno with no DET problems, went testing, no Probs....till the rally where it broke ringlands. This is the 2nd Engine now. We used a Knock Box for detecting DET and we are running 102.6 Leaded Racefuel, timing is 23 Degs at 200KpaA

Lambda Tuned to this at 200KpaA (also runnig closed loop when at 150KpaA and higher)
2500 .86
3000 .85
3500 .85
4000 .85
4500 .85
5000 .84
5500 .84
6000 .84


Any suggestions?

Thanks
Martin

[John Reed]

With that kind of setup I suspect you are getting a very rapid rise in cylinder pressure at a relatively low rpm. What is your compression ratio?

Two suggestions I can make off the top. First is you may want to consider running it a little richer, especially at lower rpms. The extra fuel will help cool things off, and may not impact your power too much (not as much as a busted ring land ). The other thing would be take a look at your timing curve. Perhaps it is too much timing down low when it is hitting peak torque. The lower in the rpm range you hit peak torque, the more prone to excessive engine wear and/or detonation you are.

[Ben-S]

Do you have a log or cal file you can post? What are you doing for ALS? Dog box? If so what are you doing on shifts? I have some experience with rally setups and i have seen as many ringland failures due too a piston thats damn near melting (do you have a picture of the failure?)

From what i have done those lambda values are good but you leave a lot about your setup/calibration to the imagination

[Pascal]

Dear Martin,

I see it as it is a bit to much 23 on 200 kpa. Maybe i am wrong, but exactly this days i am doing STi and i cant run that much with turbo max 102. Maybe is just your fuel a bit better? Or maybe is to much 23. Mine is pinging and ponging like crazy on 23. I am on 180 on 22 and on 200 on 19. Check it well that maybe is knocking but nyou dont hear well or maybe some problem with your listening tool?

(To be honest i dont believe that this can be cause of breaking but if is damaged by melting your piston, i mean excedssive temp., then it mayt have some influence).

Cheers and good luck!
Please later keep us posted about results.

Pascal

[www.TDP.ie]

Hi, I am not sure that you are running rich enough for sustained periods. On the dyno the operator/tuner will be sympathetic to the engine in the rally the drive will not. Also in restricted GRPn the engine will be at peak torque all the time. This is very hard on the engine and epically the ring lands.

At what Rpm's dose the engine produce full boost. What timing do you have at it reaches full boost.

Also running closed loop fueling will only work well if the base map is spot on. Are you air temp compensations good.

Robbie

[Ben-S]

Thats a good point you could easily be leaner on the track i assumed those lambda values were from logs on track not just dyno numbers... As for the timing restricted cars run more timing than you would generally expect from a not restricted car. He's definitely at the limit but i wouldn't expect a failure based on those timing numbers and lambda values alone.

[Martin]

With that kind of setup I suspect you are getting a very rapid rise in cylinder pressure at a relatively low rpm. What is your compression ratio?

Two suggestions I can make off the top. First is you may want to consider running it a little richer, especially at lower rpms. The extra fuel will help cool things off, and may not impact your power too much (not as much as a busted ring land ). The other thing would be take a look at your timing curve. Perhaps it is too much timing down low when it is hitting peak torque. The lower in the rpm range you hit peak torque, the more prone to excessive engine wear and/or detonation you are.

Firstly thanks for all you guys helping me,

John,

the engine is standard for groupN 8.5to1 CR
And yes, since its restricted you try and use as much boost as possible when its available since we cannor rev it. What id also like to add is that the engine was mapped at 1450m Altitude....86 KpaA and the race was at sea level. These altitude changes are not uncommon for us in South Africa.

Do you have a log or cal file you can post? What are you doing for ALS? Dog box? If so what are you doing on shifts? I have some experience with rally setups and i have seen as many ringland failures due too a piston thats damn near melting (do you have a picture of the failure?)

From what i have done those lambda values are good but you leave a lot about your setup/calibration to the imagination

Ben,

Logging is prohibited in GroupN Racing here, but I think there might be some logging. The config i have, ill attach it. In the config you will be able to see the ALS settings. Yes its a 5speed Dog Box. Regarding the shifts ill try and get you some nice data where shifts are visible. Pictures, ill get you some and attach it aswell. It may only be in 2 days time since im not at the car but i will have somebody take them. Unfortunately ill be away over the weekend but i will try and get as much info as possible.

Dear Martin,

......Check it well that maybe is knocking but nyou dont hear well or maybe some problem with your listening tool?


Pascal

Pascal,

We have used the "Knock Box" for listening to Knock. Does anybody have suggestions?

Hi, I am not sure that you are running rich enough for sustained periods. On the dyno the operator/tuner will be sympathetic to the engine in the rally the drive will not. Also in restricted GRPn the engine will be at peak torque all the time. This is very hard on the engine and epically the ring lands.

At what Rpm's dose the engine produce full boost. What timing do you have at it reaches full boost.

Also running closed loop fueling will only work well if the base map is spot on. Are you air temp compensations good.

Robbie

Robbie,
I Understand that rally will have the engine run at WOT for longer periods, there is a ET comp for Lambda aim though, but not a Full TP comp. Maybe worth looking at. About the boost, it makes Max boost at about 3500 Rpm, Ill have to double check on logging and the amount of boost. I guess it should be about 270KpaA at sealevel but drops a bit at 1450M altitude.


Thanks again for everybody`s input

Regards
Martin

[Ben-S]

Your problem is most likely the tuning, you need to do some real world testing at those sea levels. Just because you can't log in the actual event doesnt mean you can't test and log prior to an event. That is a huge difference in air density, who knows what your actual lambda is while your running the event. Have you accurately tuned the BAP comp? I see your boost control is extremely basic. Boost control on a restricted motor is one of the most important aspects of tuning, you need to make sure you are opening the wastegate fully when the restricter chokes to minimize back pressure (granted this is most likely not the cause of your problem but will cause excessive heat and power loss)

Also probably unrelated to your problem the gear change cut seems odd to me why bother with a cut if your going to lift on the throttle anyway? I've always wondered why that option was even there, to shift a dog box a simple lift is plenty to throw the next gear the advantage of the retard then cut strategy instead is keeping power on between shifts and reducing shift time. There is no reason to do a 100% cut either and you could definitely benefit from some ign retard there as well.

[Martin]

To be honest with you i didnt tune the car myself, nor was i at the event. I know the base map came from AUTOTEK in the UK, and it was built from that. Im not too familiar with restricted turbo cars but i would appreciate a few tips from you about the do`s and donts. What would you consider a good way to do boost control on a restricted car? If you have a GrpN Map that you are willing to share i would really appreciate it.

Also, there is no gear change ignition cut at the moment, those are just setttings that are in the map but its swithed off. That would be the next thing we would like to set up, we just need to get it to last. DO you have any suggestion on that?

Other that than the boost control, whats your impression of the map otherwise?

[Ben-S]

The map honestly looks like a base map like you said that really hasn't been modified much at all. The fuel an ign map look reasonable. If i had a group N map that i thought would help i would be happy to share, but i don't really have anything useful for you. My restricted turbo experience is limited to much smaller engines but the concept remains the same. What i would do to tune your boost maps is to do a pull on the dyno at the highest boost level you can run (without using extremely high duty cycles where you know it wont boost anyway) then back the duty cycle off a few points at a time starting with the highest RPM and working your way back until you have the min duty cycle for peak power (of course its safer but slower to work your way up instead of down). I would use as much feedback as possible to maintain that relationship including BAP, EGT, EMAP, MAP, etc. Granted theres only so much time and money but the more the better. With a car like that if you can't test at your race location or at least in race conditions your going to have a really hard time getting anywhere so i would work on that as well. As for the gear change ign cut i can't give you specific values as thats gearbox dependent but i would use some retard then cut based on a strain gauge on your shifter and try to slowly lower shift times by shortening the cut values until your at the mechanical limit of the box, if done right it should not effect longevity of the box. I also just noticed your ign has no BAP comp which it probably should. Again all of this is going to need to be tested at race altitudes... maybe you can find a dyno at that level? You could even try pulling a vacuum in your dyno room if your desperate (restrict incoming air). Ideally you would have logging of a test session in the same area as your next race.

As for your knock detection i use a knock box and it works great, some engines are to noisy to hear unless you use the pro analysis though.