raising shift rpm in 4lo?

[mudygmc]

I want to raise my shift rpm in the 3-4 shift in 4lo for pulling. On Sunday I tried 4th and it shifted to soon. I was in 4th by 100ft. I only got 2800rpm down the track. I still placed 4th but I think there is alot more left in her if I get more rpms. When I change the shift rpms in the tune do I also have to change the shift speed? I have never messed with shift rpms only shift timing. Any ideas would be great.
Thanks
Adam

 

[racinmike77]

I use %. If I raise the shift rpm from 3200 to 3600 (about 10%) I raise the shift speed 10%. copy and paste the 3200 row in the TQ table for 3400 and 3600 and make sure your ECM tune has fuel to support the changes.

http://www.duramaxdiesels.com/forum/showthread.php?t=15194

 

[mudygmc]

My tune shows 3-4 wot shift speed at 46mph in 4lo. The shift speeds don't really make sense to me. They are all 43-46mph. That can't be right can it? I want my 3-4 shift at 3800rpm. I want to make sure that I have the power if it hits 4th. What should the shift speed be set to.

 

[racinmike77]

My tune shows 3-4 wot shift speed at 46mph in 4lo. The shift speeds don't really make sense to me. They are all 43-46mph. That can't be right can it? I want my 3-4 shift at 3800rpm. I want to make sure that I have the power if it hits 4th. What should the shift speed be set to.

Change it to 55mph

 

[RPM Motorsports]

Not sure whats done to your truck, but unless your pulling in sand, I would pull 4lo 3rd.

 

[racinmike77]

Not sure whats done to your truck, but unless your pulling in sand, I would pull 4lo 3rd.

You are probably right but shifting into 4th at 3800 compared to 3200 should make a big difference also. He may not even hit fourth with the raised shift point, so id just try the tune and see what happens.

 

[Dozerboy]

I changed my PT shift to match my WOT shifts and then blended the last few in the column. If you do that stock in 4Lo WOT shift are enabled at 70% throttle. I would change that to the IIRC 97% that is stock with 2WD. That way if you have to feather the throttle some your shift points ain't all out of whack.

 

[mudygmc]

Most of the tracks in the area are pretty solid. Just a few soft sandy ones. Usually when I pull 3rd I run down the track at 4-4100rpms. I would like to get a little more ground speed from 4th. Last time I pulled 4th I was in 4th by about 100ft. I never got up in the rpms. Stayed around 28-2900. If I raise the 3-4 shift to 3800 I think I will be able to carry 4th pretty good.

 

[radvans]

In regards to this topic, my question is does the tcm or ecm use one of the tables or the other for shifting. If I hit say 20 mph and my rpms are low in second it will shift to 3rd (not exactly but for purposes of my question it does) but if I am on it and the truck is past 20 it doesn't shift till the rpms hit a certain level. So to me the tch or ecm is looking at the speed table first ie..you get to a certain speed and as long as the rpms are not at a certain level at that speed it will shift. So does it really matter if you change the speed shift table...because if we are WOT we are past a set speed and the tcm or ecm will now look for our rpm level to shift. Does that make sense?

 

[mudygmc]

I don't understand the shift speed tables at all. I never sat down and did the math but my tune said 3-4 shift in 4lo was at 46mph. I don't think it is possible to go that fast in 4lo 3rd. I can't remeber for sure but I think like 4k in 3rd is like 30mph tire speed when I pulled. There is plenty of stuff in efilive that I don't understand.

 

[TNRGreene]

Leave it in 3rd & if you need 4th, click it up Sometimes the truck will blow the tires off & shift quick AND then hook up. You are screwed when that happens if in 4th

 

[ecc_33]

Yea, Manually shift it into 4th gear. Thats how I do mine everytime