Reminder: Cold Weather Changes Air Fuel Ratios!
10-29-2002, 11:40 PM
#1
Senior Member
Thread Starter
Join Date: Jul 2002
Posts: 253
its getting cold in the northeast. we have had sleet and hail tonight and the temperature is about 28 degrees right now here in eastern pennsylvania. i want to remind everyone that winter brings cold air and that means denser air, which will lean out your air fuel ratios and increase both power... and the chance of detonation!
the reason for this may be apparent to everyone, so i apologize to those who already know all about it for wasting bandwidth. but i suspect that many who are newer to rx7 and rotary ownership may not know how this can effect modified cars. denser air means that for a given amount of time, more air is taken in than when the temperatures are higher (warmer) and the air is less dense. many of you may have already felt the effects of this, since your car will pull better and have noticeably more pwoer in the winter months. however, the reason for this is that the air fuel ratio has changed. it has "leaned out" and you are now running a much leaner A/F than you tuned your car to in the summer months.
if you can get access to a wideband lambda meter, get your car hooked up and adjust the air fuel ratio back to where you want it to be. you'll see on your first check that its leaner than you thought. just bump up your injector duty cycles or, if you don;t have an aftermarket computer, and have a rising rate fuel pressure regulator, increase the gain a little bit. bith will richen up your air fuel ratios and you'll be safe for the winter. then, readjust it in the sp[ring. -gordon
the reason for this may be apparent to everyone, so i apologize to those who already know all about it for wasting bandwidth. but i suspect that many who are newer to rx7 and rotary ownership may not know how this can effect modified cars. denser air means that for a given amount of time, more air is taken in than when the temperatures are higher (warmer) and the air is less dense. many of you may have already felt the effects of this, since your car will pull better and have noticeably more pwoer in the winter months. however, the reason for this is that the air fuel ratio has changed. it has "leaned out" and you are now running a much leaner A/F than you tuned your car to in the summer months.
if you can get access to a wideband lambda meter, get your car hooked up and adjust the air fuel ratio back to where you want it to be. you'll see on your first check that its leaner than you thought. just bump up your injector duty cycles or, if you don;t have an aftermarket computer, and have a rising rate fuel pressure regulator, increase the gain a little bit. bith will richen up your air fuel ratios and you'll be safe for the winter. then, readjust it in the sp[ring. -gordon
10-31-2002, 12:20 PM
#7
Member
Join Date: Oct 2002
Posts: 95
The base modmap air temp correction map is way off for moded cars (actually none of the maps we've tested provide enough correction for colder temps to maintain a close ARF if tuned during warmer weather).
We've seen cars which were turned to 11.2 during 70 degree
days get as lean as 13.5 on 40 degree days.
I'll try to get some "ballpark" correction factors posted in the next week so those datalogit users can "check" their correction #'s.
k
We've seen cars which were turned to 11.2 during 70 degree
days get as lean as 13.5 on 40 degree days.
I'll try to get some "ballpark" correction factors posted in the next week so those datalogit users can "check" their correction #'s.
k
11-01-2002, 12:38 AM
#8
Senior Member
Join Date: Dec 2001
Posts: 147
I don't really trust the stock air temp sensor. It's located on the bottom of the UIM and it seems like it's very prone to heatsoaking, and slow to react to temp differences. It seems that the problem is that once it heatsoaks, it's reads high temps. So then when you start moving and getting some cool air through the intercooler, your charge temps could be around 30C, but the sensor is still reading around 50C.
11-13-2002, 04:53 PM
#9
Senior Member
Join Date: Nov 2001
Location: Jersey
Posts: 194
well that's one of the things i noticed when i first got my FD almost 2 years ago. in the winter the car would blow the tires off through the first 2 gears and spin a little bit going into 3rd and pull harder than ever. i wonder what times i could get if run it in this cool weather vs. the 95+ degree heat day august 01' when i ran my best time ever ?
11-13-2002, 09:49 PM
#10
Senior Member
Join Date: Sep 2002
Posts: 247
Originally Posted by neevosh' date='Oct 31 2002, 10:38 PM
I don't really trust the stock air temp sensor. It's located on the bottom of the UIM and it seems like it's very prone to heatsoaking, and slow to react to temp differences. It seems that the problem is that once it heatsoaks, it's reads high temps. So then when you start moving and getting some cool air through the intercooler, your charge temps could be around 30C, but the sensor is still reading around 50C.