Guys,

I recently moved from the DC area to Salt Lake City. My car is obviously running richer up here. My question is:

Does the fact that my car is running richer at altitude compensate for the 2 point reduction in octane in the fuel they sell out here?

Setup is in my sig. Thanks in advance for any help! (BTW SLC is @ about 4200ft)...

 

I would re-tune for max power and let the knock sensors deal with the lower octane gas.

 

It may be a good idea to take it to a dyno with a Wideband O2 sensor to make sure that it's ok. SLC should have 91 octane. I've been running 91 octane (or the highest available locally- possibly 89 in some places) since day one of my turbo setups. The difference is I initially tuned at high altitude with the lower octane gas.

Tim

 

Yeah, I'll get it retuned. Unfortunately, there's really not a tuner out here that has much experience with our platform. It doesn't matter too much, to be honest. So long as he knows the AEM EMS well, I can give him a quick run through of the characteristics of the car...

I just met a guy in my MBA class who was chief of two Dakar Rally racing teams. He's very familiar with Miller Motorsports Park and he said he will ask some buddies who they'd recommend. I should be in good shape. Until then, I'll just run a gallon of Toluene in each tank.

Thanks Tim and Snake!

Jorge

 

...altitude i'd think woudln't affect turbo cars as much as all others...even supercharged....


reason being is the turbo will compress the air to the same psi regardless of outside BAR. There should be little change under boost .....anyone????

This is why airplanes are so commonly turbocharged because at altitudes they INCREDIBLY big gains to be had.

 

 

You do NOT want to tune for max power and let the knock sensors take care of the rest. That may produce a marginally higher dyno number, but WILL result in the death of the engine. The AEM knock ability is not nearly as advanced as that of most stock ECU's. One big knock from stupid tuning and bad gas can toast you engine. Tune with whatever gas you will be using on the street. If done properly, there should be a safety margin between your tuning and the knock threshold of the engine. When bad gas is used, that threshold should narrow. If it disappears, that's why the knock sensors are there. They are NOT designed to retard timing every time you boost.

Tim

 

[QUOTE=CourageOO7,Aug 15 2007, 09:46 PM] Guys,

I recently moved from the DC area to Salt Lake City.

 

tim>

were only talkin an altitude change here. So tunning for the power increase to be had at sea level max is already the safe side. High altitude is just gonna richen the mixture so no worries. If he was turbo it'd stay the same as the turbo would just spool longer to create the same B.A.R. In his case he could just tune max hp. The knock sensore work is only going to be if he lets his car sit a long ass time till the octane rating in his tank falls....etc. situation like that. Seems plenty safe to me. ??????

 

Wow, thanks for all the responses guys.

Okay, so here's the deal. I picked up a 5 gallon pale of Toluene to tide me over until I can get to a dyno...A gallon should yield just about 93 octane and it's not my daily driver. That should last me a while cuz I bought a Honda CRV to put around in up here. 147hp and AWD FTW! Talk about slow! My S2000 felt like a rocket ship today. lol

Altitude affects all motors because effective compression goes down. So, let's say our car has 11:1 compression ratio at sea level. At 10,000 ft, the atmospheric pressure is so much lower that the motor may run as if it were a 9.5:1 compression ratio motor. Yes, boost will still be 5.5 psi or so for my setup...and yes, FI'd motors do MUCH better at altitude than NA motors for that very reason. However, if you're thinking I don't feel much of a power difference when I'm not boosting then you're crazy. At partial throttle the car feels quite a bit slower. The actual formula for effective compression ratio is:
FCR - [(altitude/1000) * .2]

I figure I drive between 5000 and 7000 ft out here, so let's use 6000
11 - [(6000/1000) * .2] = 9.8 ...and that's why my car feels significantly slower out here!

I'm at the U for my MBA and I live in Cottonwood Heights. Today, I went on a drive up to Brighton and Solitude and Snowbird/Alta. The canyons out here are great fun. Cheers to all!