Racing up Pike's Peak

[sperry]

So I've been talking over email w/ Mike Shields (of SPD Tuning) occationally since he helped me out with those Group-N rear brake rotors to get the 2-pots working on my WRX.

I was asking him about tuning and discussing my broken motor and the effects of high altitude, and he dropped some tech about how they tune their Group-N car for the Pike's Peak hillclimb. I thought some of you guys would be interested in what he had to say about racing a car up to 14,000 feet!

Originally Posted by Mike Sheilds

The problem with altitude is not really a problem until maybe 8-9000 feet with most modern turbo cars, although I would say from 6000 up the effects starting to show. The rally cars can also run JEMS or Pectel or other racing ecu that have provision for anti-lag and other racing tweaks not found on a road car. Yet it uses the same turbo, injectors, in short, a completely stock STI 2 liter engine with a 30mm intake restrictor. The Mass Flow sensor of the Subaru engine is pretty much going to give the same AFR at 15,000 feet that it will give in Death Valley. This is because it measures not the air flow, but the air mass flowing in. So it compensates for relative humidity, temperature and pressure at all times. Of course, how one programs an ECU to deal with that information is another subject!

The altitude issue concerns the very nature of turbocharging. The compressor has a map of flow/pressure ratio (note: not absolute boost, rather boost relative to 1 bar atmospheric) that shows the heat of compressing the air, that being known as inlet temperature in every day language. The ideal sizing of a turbocharger is related to the power expected (a mass flow issue) and the engine displacement. Each compressor has what is called the sweet spot, a largish , but skinny, 45 degree oval where the inlet temperature is as low as possible for the boost levels. We also have to size the compressor so as not to over speed the turbo, more on that in a minute. Anyway, an engine runs up and down the rev range in this lower inlet temperature area if sized properly . Put in technical language, the turbocharger is running at its maximum efficiency . Now you can imagine what just turning up the boost on a motor does. It moves the compressor load outside of the sweet spot and begins to (sometimes quickly) increase the air inlet temperature. A bigger intercooler is not quite the answer, although when running 20+ pounds of boost we need to go to large front mount (no where else to put it!). What is needed is a compressor housing that has its sweet spot better matched to the power, and in this case of a 2 liter displacement, the higher boost being needed to make that extra power for the given displacement. With 91-93 octane fuel and a proper timing and fuel curve we simply do not need a huge intercooler because we just do not take the boost level up that much. This is because we do not boost levels that will cause detonation, unless of course ,one backs the timing way off and dumps loads of fuel into it. That will give a nice reading on the dyno. The car has awful throttle response and tuning hard setup like that will kill a motor over time. For this reason, buying a re-flash based on maximum HP quoted is all to often a bit of a fool's paradise. What we want is a motor tuned for proper ignition and fuel with the boost curve where it comes out against the detonation sensor. This gives huge torque, excellent spool and throttle response, and what ever power number that the motor feels good making on a given day. This is how the Prodrive Stage 3 is setup. 10 years of rally car experience, 6000 units sold and no blow motors.

The problem with 14,000 feet is the air density is 50% that if sea level. The effect is to make the turbocharger work as if it was not making 14 psi, but as if it were trying to make 28 psi at sea level. Besides over speeding the turbine, this is will physically overheat the motor due to too high of an inlet temperature for which no intercooler will correct. So, we have to turn down the boost starting at ~8000 feet as we have reached the limit of the turbo speed and are already way outside the sweet spot. The driver also has to gradually lower the operating limit of the engine from 6000rpm down to 4500 from 8-9000 feet to 14,000 feet . By limiting engine speed, working as an air pump the compressor is now limited to pumping as much pressure RATIO from the thin air as it was pumping from thick air at sea level. We have to remap the engine for these extreme altitudes and very high full throttle duty cycle, only seen at Pike's Peak. The next highest rally is Mexico WRC run at 6000-7000 ft, but the real kicker at extreme altitude is the constant climb.

Pat' Richard (Rocket Rally/Easy Street) and Stieg Bloomqvist (Prodrive, David Sutton Cars, Ltd) were the only Group N (30mm restrictor) cars that had ANY power as they went past me at 13000 feet Saturday. The Rocket Rally crew worked on the ECU mapping Tuesday and even Wednesday during the first stages of the rally to get it right.. Andy, the Prodrive UK engineer for Bloomqvist worked even Friday night tweaking their setup. Andy joked it was the slowest rally car he had ever tuned!

Pat had ten seconds on Stieg as of Saturday morning with the full climb ahead of them. Stieg was his usual smooth as glass self, but Pat's car broke a rear drive axle putting the power down on the very last of the lower tarmac section.

So the problem became that Pat had to try to keep our position by abusing the motor with too high of RPM, using 6200rpm all the way up and outside of any hope for a reasonable inlet temperature. This caused the turbo compressor to pump heat into the engine, which was being taken out through the cylinder walls . Just at the 14,000 foot finish we stuck the pistons as they continued to expand right past their normal racing clearance. Stieg was able to gain 10.5 seconds and just pull off the win. They do say you make your own luck in racing. In this case, Stieg's 30 years of experience got him to the top without breaking anything on the final run after three days of abuse. So much for altitude stories at Pike's Peak.

Regards,
==m==
Mike Shields
SPD Tuning Service
www.spdusa.com

There's some good tech in there about why running the most boost possible isn't usually a good idea, as well as the difference between a dyno queen and a useful racecar.

And, yes that's right, Pat Richards finished the last 7 miles of the climb spinning the center diff to power only the front wheels! Somehow the motor lasted to just *after* the top... for a P2 finish, .5s behind the leader. If only the car had broken just a few seconds later!

BTW: Mike Shields is one of the original Subaru gurus... he runs SPD and was the original Prodrive importer to the US! Check out more tech over at http://www.spdusa.com/

[Nick Koan]

Man, that is some good info there. I think I grasped most of it.

[sybir]

Good stuff.
Scott's current motor issue aside, this is why we've never been about cranking max boost on the cars we're tuning; Scott's car's sweet spot in terms of the turbo was right around 16 PSI, as opposed to the 22 PSI peak that would have made more power, but put the car at higher risk during hard driving at higher elevations and different conditions.

That's great info from Mike, he's an incredible guy to talk to, besides his opinion many years back that I should never have touched the suspension on my car

[JC]

Ya Mike's the man even if he did lose.

[Libila]

Now I understand why so many guys with DSMs have trouble (aside from poorly made parts). Whenever you ask a DSM guy a question like, "How can I squeeze more power out of my stock motor?" Their first responce is, "Buy a boost controller."

There is some really good information in there. I now understand to some extent why so much work goes into setting up a motor for more boost.

[doubleurx]

Nice info. Hmmmmm I'm running 22 psi at 6500 feet? Of course I am not racing it at this altitude. Scott, what actually happened to your motor? I haven't made the last couple meets so I don't know the low down. Sorry in advance if it is toast.

[sperry]

The short version of the motor story:

52,000+ miles +
16psi +
repeated pulls to 7200rpm in anger +
hard lateral G's (potentially reducing oil pressure, although Mr. Shields disagrees) +
known lean condition on cylinder #3 due to stock fuel rails
=
probable detonation on #3 which damaged the bearing and left me w/ rod-knock

Since the cost of inspecting and repairing whatever's wrong w/ the EJ20 is probably more than just replacing the short-block, I'm not going to even bother to crack the motor. The guys at the shop are just going to install an EJ257 long block on the car. Afterall, if it breaks, and you don't make it better, it's just gonna break again.

So... once they're done (probably late next week) I should have a 2.5L STi motor w/ the GT30-10. We're also probably going to do the TGV deletes, and I'm leaning towards a small front mount, since the GT30-10 spools so fast on that block I can get away with some increased lag.

[MattR]

Or the Short-Short version.....Scott was trying to keep up with Mike K and Me all day at Solo trials, and blew his shit up....


( I know Scott is going to blow my doors off when the motor is done, so I have to get my shots in now.)

On a side note...Lets make sure everyone is at the meet Thursday night, so we can catch up on stories, parts, racin, etc..(I've been absent a lot lately)...I'm feeling sentimental.

[MattR]

BTW, great read there Scott, thanks for posting that up...Make sure you share more of the stuff you get from Mike...

[doubleurx]

Originally Posted by MattR

Or the Short-Short version.....Scott was trying to keep up with Mike K and Me all day at Solo trials, and blew his shit up....


( I know Scott is going to blow my doors off when the motor is done, so I have to get my shots in now.)

On a side note...Lets make sure everyone is at the meet Thursday night, so we can catch up on stories, parts, racin, etc..(I've been absent a lot lately)...I'm feeling sentimental.

I haven't been in the last 2-3 weeks as well. I'll try my best to get down there Thursday.

Scott your car will rock! Thank god those STI blocks are "fairly" reasonable.

[bruspeed]

Wow, man I had no idea 14,000 ft the air is half as dense than sea level. That means that were around 75% of sea level density.

[ScottyS]

Wow, I even got a little out of that tech post --- that was pretty clear information.

Scott, so that's what happened, eh? Harshness. 7500rpm in anger? Send the next Expedition-driving-bimbo the bill. The new setup sounds like it will be really sweet.

Originally Posted by bruspeed

Wow, man I had no idea 14,000 ft the air is half as dense than sea level. That means that were around 75% of sea level density.

Hmm, pressure really isn't linear, but I don't personally know the exact values for, say, 0-30,000'. Either way, I can tell you that the air at 18,600' is very thin ;-)

Here's table I found online here: http://www.auf.asn.au/meteorology/section1a.html, but I don't know if it's exactly accurate, but doing the calculations using formulas found at the JPL's website could confirm it.....plus, the curve rate varies dependant on latitude.

[bruspeed]

Originally Posted by ScottyS

Here's table I found online here: http://www.auf.asn.au/meteorology/section1a.html, but I don't know if it's exactly accurate, but doing the calculations using formulas found at the JPL's website could confirm it.....plus, the curve rate varies dependant on latitude.

I was right. looks like close to 75 percent to me, At least gardnerville is like 6,000 feet, or something like that.

[JC]

Originally Posted by MattR

On a side note...Lets make sure everyone is at the meet Thursday night, so we can catch up on stories, parts, racin, etc..(I've been absent a lot lately)...I'm feeling sentimental.

Bah I'll be in Atlanta. Just say "rice" and "bugeyes suck" occasionally and it will be just like I'm there.

Ugh, no more tables, I'm having college flashbacks.

[sperry]

IIRC, air pressure decreases logarithmically with altitude... but that isn't quite what I'm seeing in that chart... is there anyone that's been out of college less time than me that might remember? I haven't used PV=nRT, and the rest of that ideal-gas stuff in like 9 years!

[bruspeed]

[QUOTE=sperry]
hard lateral G's (potentially reducing oil pressure, although Mr. Shields disagrees) +


So are there any internally bafled, or trap door style oil pans for Subarus?

[sperry]

[QUOTE=bruspeed]

Originally Posted by sperry

hard lateral G's (potentially reducing oil pressure, although Mr. Shields disagrees) +


So are there any internally bafled, or trap door style oil pans for Subarus?

I did a little looking, but I haven't found anything.

'Course my EJ20 did have a pretty banged up oil pan... it's hit some significant rocks, and once the car slipped off the jack and landed on the oil pan, so it wasn't exactly the shape it was supposed to be, which might have exaserbated the situation.

A baffled pan might not be necessary. And as Mike Shields told me, he's never seen oiling issues on any of their rally cars, and they're drivin quite hard.

So the oil think might have contributed, but there's no reason not to suspect the simple age of the motor and the hard load I was putting on it as the primary culprits.

[sti deede]

Originally Posted by MattR

On a side note...Lets make sure everyone is at the meet Thursday night, so we can catch up on stories, parts, racin, etc..(I've been absent a lot lately)...I'm feeling sentimental.

Yes please. This will be my last regular meet. Course I won't be gone forever.

(sorry for the additional off-topic)

BTW I found the information especially interesting, thanks Scott.

[Dean]

Originally Posted by sperry

...as Mike Shields told me, he's never seen oiling issues on any of their rally cars, and they're drivin quite hard.

So the oil think might have contributed, but there's no reason not to suspect the simple age of the motor and the hard load I was putting on it as the primary culprits.

Did you ask Mike about the weight oil you were running? I think you said 10-50... As far as I know, you are the only one I know running anything near that heavy an oil. I know it is under the heavy use section in the manual, but [0,5]-30 & 10-40 are much more common. It would be interesting to get his take on it.