SRT10KLLR

iTrader: (11)

Guys I need some help here. I have read that you want to set the shifting to 200 rpm past peak hp but is this always true. I have a heavy(probably 4800lbs) 2003 Silverado and my tq is greater and flatter than my hp. So should I instead go by my tq numbers? Where should I set my shifting at based on the graph below.

Thanks for any advise.

SRT10KLLR

iTrader: (11)

Also, I have a 2600-2800 stall in it and it drops 1500-1600 rpm's in the 1-2 shift and 2K in the 2-3 shift. My stock tune was set at 5200 but I upped it to 6000 and right now I am at 5800. I will be going to the track on the 5th and can try different settings depending on how busy the track gets. Last time I only got 2 runs in with a best of 13.7.

WeathermanShawn

iTrader: (1)

I think the HP/TQ formula almost always favors shifting ~200-400 Rpms past HP peak. The main reason is that even though your rate of acceleration (TQ) is falling, you are covering more distance per unit of time (sec) at higher Rpm's.

I do not see anything wrong with your shift at ~5500 -5800 Rpm's. That way after your shift you are essentially back into the meat of your TQ curve and will quickly accelerate back into your peak HP area.

I am sure that are always caveats to the 'shift 300 Rpm's after peak HP', so keep an open mind. Perhaps someone has further insight from practical experience. Depending on your gearing and shift points near the 1/4 mile point, there could be a case of shifting slightly higher or lower than ~5500 Rpm's to maximize your final gear ratio.

Hope that helps. Good luck.

..WeathermanShawn..

SRT10KLLR

iTrader: (11)

Thanks for the input. The part I highlighted is what I was thinking too as far as getting back into the tq rather than hp.

If you disregard the tq and just focus on the hp then I don't see why I would want to shift at 200 past peak hp. My peak hp is at 52-5300 rpm so if I shifted at 5500(200 past peak) I would drop to 3900 rpm. I am only making about 235hp at that rpm but was making 290 at 5500. My hp was no longer going up at 5500 but it was still higher than at 3900.

So by just going by hp number would I not want to shift higher, say 6200. At 6200 I am still making about 270hp so when it drops to 4600 rpm I will still be at 270hp.

The problem I have with the last part was that it looks good from a hp perspective but not from tq as at 4600 rpm my tq is at 310 and past its peak. Whereas if I shifted at 5500 like the first part I would be right at about 320tq which is right in the tq's sweat spot.

I wish I could test it more at the track but with it open only about once a month it usually gets 400-500 people there plus a few breakdowns.

:e ek2:

WeathermanShawn

iTrader: (1)

The problem with shifting that far past peak HP is that from the time you hit peak HP ~5200 Rpm's until you hit that 6200 Rpm's shift point, you are rapidly losing acceleration (TQ). So your distance covered in that 5200-6200 range will be limited by ability to sustain HP in that Rpm range.

I guess in effect your first argument makes sense. Under ideal conditions shifting at peak HP (it is 200-300 Rpm's higher due to the normal lag in shifting) and then having your revs fall right into the meat of your TQ curve would be best. Then you would rapidly accelerate back into the 'meat' of your HP curve.

In the 3-4 track events I have had, just observing the Tach reinforces that conclusion. You would not want to hold a high rpm when the Tach is barely moving (peak HP). If your gearing is right and you picked the right combo of cam & valve events, you will normally fall right into the peak of your TQ curve after each shift.

I probably am not explaining it as well as some might. I know you can run some software using various shift points and find the 'sweet spot' with each gear. I would conclude that both HP and your TQ curve have to be considered to maximize your times.

Hey, good luck and let us know if theory meets reality!

..WeathermanShawn..

SRT10KLLR

iTrader: (11)

Thanks, your explanation right on. I picked up a bit going from 6000 to 5800 so do you think I should try 5500 since it's 200 above peak and it will go right to the heart tq curve after the shift?

BTW, what software are you referring too?



Anyone else care to chime in?

WeathermanShawn

iTrader: (1)

I think ~5500-5600 Rpm would do it for you.

On the software programs.. I have EFILive, so it is pretty easy to calculate RWHP and acceleration just by logging mph gain every second. I have a M6, so I tend to shift closer to my HP peak in 1-2 shift and 3rd gear I take to ~300 Rpm above peak HP. If I get to 4th I let it go to near redline (500 Rpm above peak HP.

If you 'Google' "Engine shifting Software", you can find tons of software..some free, some not. I am not sure if any of the sponsors have any suggestions, but that is always a good idea.

Perhaps some other members will share their experiences.

Good luck.

..WeathermanShawn..

SRT10KLLR

iTrader: (11)

I do have EFI Live that is how I make my shifting changes. I now enough to get me in trouble using it though, lol.

Here is a log of one of my latest runs with shift points set at 5800 for 1-2 and 2-3.

I will google "Engine shifting Software" to see what I get.

Again, thanks.