High Altitude, heat, tuning and intake/exhaust

BlackZeda

I have read a lot about the Z's heat issues in this forum and I definitely have something going on in the summer. Whenever the outside temperature is 83F or above, or the oil temperature approaches 230F the engine performance degrades quickly (never limp mode though). Specifically from a stop my Zeda will as best as I can describe it "bogs down" to the point where I think the engine has completely stopped. After a few seconds the engine regains its composure, but I still don't feel I am getting acceptable power from it from then on.

Because I live at high altitude it makes me wonder if this is both a heat and air (oxygen concentration) issue.

I had a great, long conversation with Bill at MAC Autosport in Parker, CO and am arranging an oil cooler install in the near future. We also delved into intake/exhaust and tuning options as well, which would seem to make sense in resolving the issue and enhancing the performance.

Has anyone experienced my issue at altitude and/or how have modifications short of FI affected your Z?

Thanks in advance for any insights (and referrals to other threads that I have missed)!

_ace_

I'm in Salt Lake City. At an HPDE at Miller Motorsports Park (4400 ft altitude), my car would hit limp mode at about minute 3-4 of each session if I drove hard. The car was stock on stock tires. Most reports from low altitude tracks were saying I would probably hit limp mode towards the end of the run if I kept on it, so I assume the altutude makes it considerably harder on the car to manage heat well.

That said, I've never hit limp mode on the street.

It looks like you're at 5400 ft altitude, so it's a little worse but similar to what I see here. You're also only making ~80-85% of the power you would make at sea level.

BlackZeda

Heh, tell me about it. I had a supercharged Tacoma before my Z and when I traveled down to sea-level I would almost tear the tires off the first time I started from a stop being used to the lesser power at altitude. It is pretty dramatic. I am also suprised how well my Zeda does when going over mountain passes where I know most cars will hit a wall.

I have a sneaking suspicion that FI cars have a huge advantage at altitude, maybe even overcoming a large majority of the power-loss, but I would have to look into that.

It looks like (like me) your first mod will be an oil cooler, which I assume is an attempt to tackle the heat issues. What is your feeling about CAI and CBE? Do you think those will help the Z breath better?

I have had one tuner tell me that the Z will "adjust itself" to the altitude, but conversely the service manager at the dealership and another tuner said that a tune would help significantly. What is your opinion?

Thanks for the reply! And by all means, I will let you know what effect my mods will have regarding these issues.

dal1307

Bill and the guys at MAC will take care of you. Adam (Skip) is an awesome mechanic and Nick their tuner can work magic. I don't trust my car to anyone else. FI definitely adds a lot but you will only get 80% of sea level boost at our altitude. My Stillen supercharger with the 9 PSI pulley only makes around 7.2 PSI. Here is a link to my review if you are interested. I have also had suspension and brake parts installed at MAC.

Review: MAC Autosport Stillen SC Install on G37s

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2008 G37s 5AT, Stillen SC, Stillen CBE, Stillen tranny cooler, DBA 5000 front/4000 rear, Stillen sways, Tein SS-P coilovers, SPC front & rear control arms, Goodridge lines

_ace_

Yeah, the oil cooler is my first performance mod, just for that reason. I did bolt-ons and a tune in my S2000 (previous car), and yes it helped. I was still making ~85% of the power I would make at sea level, but with the bolt-ons and tune, I just would have made noticeably more power at sea level, so I enjoyed the improvement.

Sorry if all or some of this is old news to you, but just in case it's not, here goes. And maybe somebody doing a google search down the road will benefit from it.
The reason you're only making 80-85% of the power is because that's about how much air pressure/density you have compared to sea level. Any NA engine (NA = naturally aspirated = no turbo/supercharger) just takes air at atmospheric pressure and density and adds enough fuel to hit its target AFR, say 12:1 (12 parts air mixed with one part fuel) or 14.7:1 for gas. If you have less air, you add less fuel. The more fuel and air, the more power you get. At altitude, atmospheric pressure, which is what pushes air into your NA motor, is something like 11.5 psi compared to 14.5 psi in most areas close to sea level. You therefore have about 11.5/14.5 = ~80% as much air going through your motor, and you make about ~80% of rated power.There are a lot of higher order effects like efficiency ranges, but that's the driving force behind the problem.

CAI and exhaust improve things, but they do it by reducing restriction on the airflow exiting the engine. You have reduced exhaust pressure, which essentially pulls air through the motor faster. That increases the flow rate of air through the engine, so in the end more air moves through your motor, matched by fuel, and you get more power. I did I/E to my S2000 because I liked the sound better, and after also adding a HFC and tune to fix AFRs and change cam engagement/redline I felt a significant performance improvement over stock. I haven't done anything to the Z because we just bought a house (I feel broke) and I'm kind of enjoying having a quiet car for a while.

Turbos were actually invented to fix this altitude issue for airplanes flying high up in the sky. They can be set up to make up for altitude or at least to let you lose less of your power if you choose. If you set the turbo to boost up to a predetermined wastegate pressure, it will essentially add XX psi to your intake pressure, so at altitude you'll have atmospheric plus that boost pressure to match with fuel and make power. Say 11.5 psi atmospheric + 10 psi boost, or 21.5 psi driving air into your motor at whatever density and flow rate. At low altitude, you'll instead have about 14.5 psi atmospheric + 10 psi boost. So at high altitude vs low with a 10 psi turbo, you end up with 21.5/24.5 = 88% of the power you have close to sea level--better than the 80% for an NA car. If you boost higher, you lose a smaller percentage of your power.
You can just set the boost +3psi higher than you would at sea level and hit a given power target that way. Sometimes you're already pushing the turbo to its rated RPM limits, so in that case you can't spin it any faster and you won't be able to compensate at all.
Centrifugal superchargers are geared to an RPM and will give you what they give you. Like dal said, you can lose the same percentage of power on your boost pressure and end up hitting that same 80% number, but it's 80% of a far a bigger number. Like the turbo, you could compensate by increasing the boost (smaller pulley) until you hit your original goal, so long as you don't approach the RPM limits of the charger.

And of course with boost, you'll burn more fuel at a time and will have that much extra heat to shed. Like we're finding, it's harder for the car do deal with it up here. So at the end of the day you'll get back to square one, cooling, except the car will be a lot more powerful.

_ace_

And dal, I just read your thread and see you did the same thing--you wanted about +7 psi so you picked the bigger pulley to take the air pressure into account. Nice review thread. Do they use a MAP sensor to tune? If so I would guess your tuner could have just guessed rich on the higher (low altitude) manifold pressure ranges and you would be good to go.

The interesting thing to me about the altitude issue is that, while it slows the cars down at low speeds, at high speed power to drag starts to dominate instead of power to weight. Since drag is also reduced by the altitude--a little more than power actually--the car gets some of its speed back.

BlackZeda

That is a lot of great information and helps me understand what to expect when I start adding mods. My takeaway is that more than anything the oil cooler and the tune may be the most valuable things I can do to help my Zeda perform better at altitude.

I am sure someone else will appreciate the information in the future.

Thanks a bunch and I will let you know how things turn out.

BlackZeda

Actually your thread prompted me to pay him a visit! I am going to wait till my car is paid off before I even contemplate going FI, but I am glad to know you had a good experience and MAC is only less than 5 miles away from my house.

For right now I will be doing the more mild modifications.

Is the Stillen "Dual Exhaust System" (as indicated on their website) the same as the Cat-back Exhaust that everyone mentions in posts?

dal1307

Oh man, if I was that close to MAC I would probably be getting a divorce from spending too much time and money at their shop!

My Stillen Dual Exhaust system is the Stillen Cat-back Exhaust that is on their website and the one that everyone references here.

Have fun with your mods and start saving now for the FI LOL!

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2008 G37s 5AT, Stillen SC, Stillen CBE, Stillen tranny cooler, DBA 5000 front/4000 rear, Stillen sways, Tein SS-P coilovers, SPC front & rear control arms, Goodridge lines

BlackZeda

Just between you and me (and everyone that reads this) I would be a scared with all that power. I think I might invest in some HPDE sessions and the mild mods before getting that power-hungry!

I do know what you mean about MAC; Bill definitely inspires a Z owner to add more goodies than planned. The other day I stopped by my dealer to see what the warranty implications were regarding a tune...they said it was a gray area. Looks like I will be doing that in the near future.