33 replies to this topic

[JRMGingerMan]

Matt, 3rd gear is usually a gear for the turns and slowing the car down, the steeper 3rd blows past the powerband very fast and do not allow the engine to produce output efficiently, if you are tuning to mid 12 : 1 in 3rd , the efficiency in 4th will be different and probably run leaner.

[ECOBRAP]

Matt, 3rd gear is usually a gear for the turns and slowing the car down, the steeper 3rd blows past the powerband very fast and do not allow the engine to produce output efficiently, if you are tuning to mid 12 : 1 in 3rd , the efficiency in 4th will be different and probably run leaner.

 

Thanks for the explanation, makes sense, although I have not seen that difference on track (maybe 0.2 leaner if anything).

[Steve Scheifler]

0.2 is not nothing. On the 1.6 in particular we do see a difference when we slow the pull down. The door probably "bounces" less, and with a longer sweep the ECU and O2 sensor can keep up with the changes better. Whatever the reasons we get a much smoother AFR curve with a longer pull. On the track of course it is probably bouncing around a lot more given how low we have the tension and we use 2nd - 5th, but we can't reproduce all that so best I think to tune in 4th with a longer pull. Then we can simulate a 2nd gear pull to see how different it is.

[ECOBRAP]

Fully understand that, but what you see with a slow fourth gear pull on a dyno, you will never see on the track because the flapper doesn't have as much time to stabilize as a 3-7k smooth dyno pull, my aggressive 3rd gear data worked fantastically for me and I will stick with it unless I tune it on a smaller roller. Either way, 3rd vs 4th gear is nowhere near as important as the other things mentioned in my post, so I just deleted it so we don't hijack the post any further

[Steve Scheifler]

Have you looked at how slowly they actually accelerate in 4th? We can set not only the load start RPM and ramp rate but also a pause of any length at the start RPM or any value below that. So to simulate 4500 - 7000 I can have it pause at say 4200 for 2 seconds before starting and then record starting at 4500 up to 7000 over whatever period of time we want to simulate.

BTW, besides the slight difference in gear efficiency, a faster pull in a lower gear will read less power because you are compressing the time allowed for spinning up all the rotating mass, which is significant. But, if it better correlates to your track data and is done consistently then that really does trump the rest.

[Csingletary01]

Chris I sent you a PM.

[Jesse Prather]

It's the drag in the transmission pushing the power through the countershaft and then back up to 3rd gear that makes it show less power.  I've proven this many times with many different cars.  4th gear is straight through the transmission thus less drag.  NASA requires a 1:1 pull for their dyno classification because of this.  I have a dynojet 224 as well and like the slower pull in 4th anyway to gather more data.  

[Jim Drago]

Try dynoing a VVT in third and 4th.. completely different afr

[Steve Scheifler]

Interesting. So you tune them based on the time spent in each gear at a given track?

I'll start a new topic at some point, but if anyone has specific testing they want to do and is will to bring their car here or send parts to try on cars already in the area, I'll provide free dyno time throughout the winter.

[Jim Drago]

Interesting. So you tune them based on the time spent in each gear at a given track?

In typical MB Fashion...
Yes

[cam]

Try dynoing a VVT in third and 4th.. completely different afr

 

Sorry for going off -topic, but can someone explain this better?  I'm having a really hard time understanding why and engine using the same RPMs with similar load, conditions, and full throttle would have different AFR.   In my mind, the AFR should be the same but the test results show different!

 

TIA

[davew]

As the ECU's have gotten smarter, they can calculate gear ratios. If I am going this fast at that RPM then I must be in 3rd gear. Then some engineer type programs the ECU to different values in 3rd  versus 4th. VVT cars run like crap without the speed sensor hooked up, HUMMMMM

 

Dave

[Ron Alan]

As the ECU's have gotten smarter, they can calculate gear ratios. If I am going this fast at that RPM then I must be in 3rd gear. Then some engineer type programs the ECU to different values in 3rd  versus 4th. VVT cars run like crap without the speed sensor hooked up, HUMMMMM

 

Dave

Speedometer? 

[Jim Drago]

As the ECU's have gotten smarter, they can calculate gear ratios. If I am going this fast at that RPM then I must be in 3rd gear. Then some engineer type programs the ECU to different values in 3rd  versus 4th. VVT cars run like crap without the speed sensor hooked up, HUMMMMM
 
Dave

I don't find this to be accurate ? Someone may have tried this to see if he could tune he car to rpm and not gear/speed

No change in afr ratio plugged or unplugged ... No difference in performance?
I have not investigated further