What tuning should I do before going to dyno?
03-29-2016, 11:22 AM
#1
Drifting
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What tuning should I do before going to dyno?
Sorry im actually a c4 guy but there is pretty low traffic in the c4 scan and tune section. I'm about done with my install of my megasquirt 3 and hopefully if everything works I will start getting my base tune. Engine is 383 stroker with pretty large cam. This car is 98% track duty TT and HPDE instruction car.
My main concern isn't wot Afr buy the in-between. My past tunes were using a Holley commander which had no autotune function and I would aim for 12.3-12.5 afr but I'm is what people are shooting for at lower throttle for a car that occasionally sees the street? Maybe 13.5:1 for anything below 50% throttle? Or should it stay at 12.5 the whole time? Should timing be brought up to the edge of knock or should I be backing off 3-4 degrees?
Then, what can the dyno do that I can't on very vacant back roads? Is it just getting it from 12.5 +/- .1 to exactly 12.5 through the whole power band? Or is it more a timing thing and smoothing a few isolated spots that might be hard to get to on roads?
My main concern isn't wot Afr buy the in-between. My past tunes were using a Holley commander which had no autotune function and I would aim for 12.3-12.5 afr but I'm is what people are shooting for at lower throttle for a car that occasionally sees the street? Maybe 13.5:1 for anything below 50% throttle? Or should it stay at 12.5 the whole time? Should timing be brought up to the edge of knock or should I be backing off 3-4 degrees?
Then, what can the dyno do that I can't on very vacant back roads? Is it just getting it from 12.5 +/- .1 to exactly 12.5 through the whole power band? Or is it more a timing thing and smoothing a few isolated spots that might be hard to get to on roads?
04-04-2016, 11:34 PM
#2
Le Mans Master
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St. Jude Donor '13-'14-'15
If your car is using the stock ECM programming utilizing the open loop /closed loop system and the front 02's then that system is centered around all P/T fueling being corrected to a 14.68 AFR---Anything lower would be too rich---
ALL N/A engines should run at 1 4.68 AFR during P/T or when not in power enrichment---
If you are data logging your P/T fuel with a wideband and are seeing 12.5 to 13.5 it is very rich
The most often cause for rich P/T fueling is from LT headers---because of the further aft front 02 bungs they read incorrectly---Fixes are tough---Either re scale your 02 switching points or trick your ECM by commanding a leaner AFR in order to achieve the 14.68
At WOT with a rich condition as yours the PE fueling will remain as commanded
However a lean condition at P/T would make the PE fueling richer than commanded
PE is commanded by a couple triggers --One is Throttle position and the other is MAP
With a large cam where the idle MAP is much higher than stock you must alter the MAP trigger in your tune otherwise PE will false trigger
Stock engines idle around 15-20 KPA with a PE trigger of about 55 KPA--However with a large cam the engine may idle as high as 60 KPA so you would have to raise the trigger to like 70 KPA to prevent false triggering
ALL N/A engines should run at 1 4.68 AFR during P/T or when not in power enrichment---
If you are data logging your P/T fuel with a wideband and are seeing 12.5 to 13.5 it is very rich
The most often cause for rich P/T fueling is from LT headers---because of the further aft front 02 bungs they read incorrectly---Fixes are tough---Either re scale your 02 switching points or trick your ECM by commanding a leaner AFR in order to achieve the 14.68
At WOT with a rich condition as yours the PE fueling will remain as commanded
However a lean condition at P/T would make the PE fueling richer than commanded
PE is commanded by a couple triggers --One is Throttle position and the other is MAP
With a large cam where the idle MAP is much higher than stock you must alter the MAP trigger in your tune otherwise PE will false trigger
Stock engines idle around 15-20 KPA with a PE trigger of about 55 KPA--However with a large cam the engine may idle as high as 60 KPA so you would have to raise the trigger to like 70 KPA to prevent false triggering
04-05-2016, 04:52 PM
#3
As tblu92 notes, the AFRs you mention are rich - you don't need to be as rich as say in the 12s at less than 90% throttle. At easy cruise you should be in the upper 14s. When decelerating your AFRs can even go much higher than that.
I've done most of my tuning on roads. It's not as time efficient as the dyno, but certainly less expensive. Dialing in spark advance will be much easier on a dyno but you can certainly get the car to drive nicely without dyno tuning.
You don't mention compression or fuel that you anticipate using. With that info it would be hard for me to say how close to knocking would be best - without that info it is impossible.
I've done most of my tuning on roads. It's not as time efficient as the dyno, but certainly less expensive. Dialing in spark advance will be much easier on a dyno but you can certainly get the car to drive nicely without dyno tuning.
You don't mention compression or fuel that you anticipate using. With that info it would be hard for me to say how close to knocking would be best - without that info it is impossible.