Shifting Gears: Where? - Competition Diesel.Com

BC847 · 12-07-2009, 07:42 AM

So where's the best point to shift gears: at torque peak? At horsepower peak? Somewhere in between?

Thanks.

*Big Blue24* · 12-07-2009, 11:25 PM

I would look at your gear ratios between gears and try to get the next gear to start just a few RPM before the the sharpest rise "greatest slope" in the torque curve.

inline6359 · 12-07-2009, 11:52 PM

Where either the valves float or the pump wont go any further....

Jff24Gordn · 12-08-2009, 04:29 AM

Quote:

Originally Posted by inline6359

Where either the valves float or the pump wont go any further....

duallyspeed · 12-08-2009, 07:08 AM

You should shift at 2500.My guess it would fun a faster time than if you shifted at 3500.My thinking, everything is still at the point of 2500 "working together".It would be nice to see what your truck is doing as far as fuel at each point.

BC847 · 12-08-2009, 08:53 AM

Quote:

Originally Posted by duallyspeed

You should shift at 2500.My guess it would fun a faster time than if you shifted at 3500.My thinking, everything is still at the point of 2500 "working together".It would be nice to see what your truck is doing as far as fuel at each point.

That's what I'm begining to think. Over the last 20 or so passes, I've been trying different shift points between 3K and 4K. The ET slows with the higher RPMS (rate of acceleration dropping off).

Good reading: Competition Diesel.Com - Bringing The BEST Together

How do you mean as far as fueling?

Thanks.

kscummins · 12-08-2009, 09:01 AM

I know that when racing a gasser the key is to stay above peak torque so maybe shift so that your rpm's drop to around 2400 rpm after the shift. Just my .02.

paulb · 12-08-2009, 09:34 AM

Quote:

Originally Posted by kscummins

I know that when racing a gasser the key is to stay above peak torque so maybe shift so that your rpm's drop to around 2400 rpm after the shift. Just my .02.

That in my experience what works best. If you drop much below the peak torque, you can often bark the turbo, or on a manual not spool right back up. I typically like to have the transmission (automatic), setup so that it will drop to a couple of hundred rpm above peak torque after the shift. Ideally you would setup the fueling so that peak hp happens just before the shift.

Paul

Hurley · 12-08-2009, 10:57 AM

shift after the torque curve, somewhere in the 2800rpm range, making sure the resulting rpm post-shift isnt much below the torque peak

JTaylor · 12-08-2009, 11:45 AM

Your graph seems to be pretty flat. I "personally" would shift around 3200 rpm for every shift other than the 1st-2nd shift... I "personally" would make my 1st-2nd around 3500 rpm. I don't think that you will benefit by running much higher than 3500 rpm...

BC847 · 12-08-2009, 10:10 PM

Thanks for the suggestions folks. I appreciate it.

*JQmile* · 12-09-2009, 12:15 AM

On a side note, that's still a VE right? Those are some pretty good numbers, and RPM out of one of those pumps.....I should know

.

BC847 · 12-09-2009, 07:21 AM

Quote:

Originally Posted by JQmile

On a side note, that's still a VE right? Those are some pretty good numbers, and RPM out of one of those pumps.....I should know

.

Yup, 12mm, no correction / fuel only.

Scooter's Roofing · 12-09-2009, 08:36 AM

you'll want to shift as early as possible while still allowing the turbo to come on instantly on the next gear... while your turbo may be smacking around 1700-1800 when rolling from 1400rpm, it may lag a bit of you just mash it at that RPM... whereas if you mash it at 2,000, it lights instantly

BC847 · 12-09-2009, 09:52 AM

I need to say I'm running the factory/OEM non-lockup A518 transmission (modded some).

Scooter's Roofing · 12-09-2009, 10:20 AM

ahh, shift early and often then!

*JQmile* · 12-10-2009, 09:04 AM

I'd shift at about 3500, right in the middle of the power curve seems to work best for most. If you get enough runs in at the track next time, I'd try a bunch of different shift points and see how fast you run.

DMcpherson · 12-20-2009, 04:04 PM

I have always said that you want to shift just past peak Torque (hp in gas) so that when the rpm drops your pulling up the curve to peak again

Scooter's Roofing · 12-20-2009, 06:32 PM

I have always looked at the RPM drop on every gear change and looked at the power curve to give me the most average horsepower going down the track

12-07-2009, 07:42 AM	#1
BC847 Name: BC847 Title: Too Much Time Status: Not Here Join Date: May 2006 Member`s Gallery Posts: 851	Shifting Gears: Where? So where's the best point to shift gears: at torque peak? At horsepower peak? Somewhere in between? Thanks. __________________ Original owner of a VE fueled 1993 W250 ClubCab. Silencer ring MIA, str8 pipe with 10" exhaust tip, 250psi boost gauge, ghost-lights 'n truck-nutz. K&N air filter next (if my grades are good enoufh).

12-07-2009, 11:25 PM	#2
Big Blue24 Name: Big Blue24 Title: Comp Diesel Sponsor Status: Not Here Join Date: Jan 2008 Location: Cedar City, UT Member`s Gallery Posts: 6,310	I would look at your gear ratios between gears and try to get the next gear to start just a few RPM before the the sharpest rise "greatest slope" in the torque curve. __________________ 95' 2wd Junker Drag Truck 1502 HP Fuel-Only 12mm P7100 Pump SXE 472 over GTX55 116mm OEM 12v Block

12-07-2009, 11:52 PM	#3
inline6359 Name: inline6359 Title: Microwaving cats since 01 Status: Not Here Join Date: Aug 2006 Location: Western PA Member`s Gallery Posts: 2,043	Where either the valves float or the pump wont go any further.... __________________ "If at first, the idea is not absurd, then there is no hope for it"-Einstein

12-08-2009, 07:08 AM	#5
duallyspeed Name: duallyspeed Title: New Speedway Boogie Status: Not Here Join Date: Jan 2009 Member`s Gallery Posts: 1,558	You should shift at 2500.My guess it would fun a faster time than if you shifted at 3500.My thinking, everything is still at the point of 2500 "working together".It would be nice to see what your truck is doing as far as fuel at each point. __________________ 01 dually 4x4 Last edited by duallyspeed; 12-08-2009 at 07:14 AM.

12-08-2009, 09:01 AM	#7
kscummins Name: kscummins Title: Diesel Enthusiast Status: Not Here Join Date: Aug 2009 Location: Central Ks Member`s Gallery Posts: 149	I know that when racing a gasser the key is to stay above peak torque so maybe shift so that your rpm's drop to around 2400 rpm after the shift. Just my .02. __________________ 98 12 valve QC LB Auto. slow and ugly

12-08-2009, 10:57 AM	#9
Hurley Name: Hurley Title: BLAKLUNG Status: Not Here Join Date: Apr 2008 Location: Statesville, NC Member`s Gallery Posts: 3,698	shift after the torque curve, somewhere in the 2800rpm range, making sure the resulting rpm post-shift isnt much below the torque peak __________________ THIS IS COMPD. 95 2500 RCSB 2wd back-halfed and 4-linked 5x14/7mm +100cc/4k/11-blade billet 63/68/.91 T4 539/989 03 RCLB 4x4, SSR

12-08-2009, 11:45 AM	#10
JTaylor Name: JTaylor Title: Too Much Time Status: Not Here Join Date: Jul 2007 Location: Washington State Member`s Gallery Posts: 668	Your graph seems to be pretty flat. I "personally" would shift around 3200 rpm for every shift other than the 1st-2nd shift... I "personally" would make my 1st-2nd around 3500 rpm. I don't think that you will benefit by running much higher than 3500 rpm... __________________ 1992 Dodge D250 CTD. 2005 Dodge Ram 2500 2WD. Some old Buses also.

12-08-2009, 10:10 PM	#11
BC847 Name: BC847 Title: Too Much Time Status: Not Here Join Date: May 2006 Member`s Gallery Posts: 851	Thanks for the suggestions folks. I appreciate it. __________________ Original owner of a VE fueled 1993 W250 ClubCab. Silencer ring MIA, str8 pipe with 10" exhaust tip, 250psi boost gauge, ghost-lights 'n truck-nutz. K&N air filter next (if my grades are good enoufh).

12-09-2009, 12:15 AM	#12
JQmile Name: JQmile Title: Comp Diesel Sponsor Status: Not Here Join Date: Nov 2006 Member`s Gallery Posts: 6,976	On a side note, that's still a VE right? Those are some pretty good numbers, and RPM out of one of those pumps.....I should know . __________________ 89 Dodge 972rwhp on the hose, still a VE!

12-09-2009, 08:36 AM	#14
Scooter's Roofing Name: Scooter's Roofing Title: Too Much Time Status: Not Here Join Date: Oct 2006 Member`s Gallery Posts: 17,007	you'll want to shift as early as possible while still allowing the turbo to come on instantly on the next gear... while your turbo may be smacking around 1700-1800 when rolling from 1400rpm, it may lag a bit of you just mash it at that RPM... whereas if you mash it at 2,000, it lights instantly __________________ that's pretty much all of it

12-09-2009, 09:52 AM	#15
BC847 Name: BC847 Title: Too Much Time Status: Not Here Join Date: May 2006 Member`s Gallery Posts: 851	I need to say I'm running the factory/OEM non-lockup A518 transmission (modded some). __________________ Original owner of a VE fueled 1993 W250 ClubCab. Silencer ring MIA, str8 pipe with 10" exhaust tip, 250psi boost gauge, ghost-lights 'n truck-nutz. K&N air filter next (if my grades are good enoufh).

12-09-2009, 10:20 AM	#16
Scooter's Roofing Name: Scooter's Roofing Title: Too Much Time Status: Not Here Join Date: Oct 2006 Member`s Gallery Posts: 17,007	ahh, shift early and often then! __________________ that's pretty much all of it

12-10-2009, 09:04 AM	#17
JQmile Name: JQmile Title: Comp Diesel Sponsor Status: Not Here Join Date: Nov 2006 Member`s Gallery Posts: 6,976	I'd shift at about 3500, right in the middle of the power curve seems to work best for most. If you get enough runs in at the track next time, I'd try a bunch of different shift points and see how fast you run. __________________ 89 Dodge 972rwhp on the hose, still a VE!

12-20-2009, 04:04 PM	#18
DMcpherson Name: DMcpherson Title: COAL SLAYER Status: Not Here Join Date: Aug 2006 Location: middletown ct Member`s Gallery Posts: 210	I have always said that you want to shift just past peak Torque (hp in gas) so that when the rpm drops your pulling up the curve to peak again __________________ 02 2500 loaded, 5" stack, adrenaline, injectorparts 200's. he351 over s465, 47re with some billet stuff

12-20-2009, 06:32 PM	#19
Scooter's Roofing Name: Scooter's Roofing Title: Too Much Time Status: Not Here Join Date: Oct 2006 Member`s Gallery Posts: 17,007	I have always looked at the RPM drop on every gear change and looked at the power curve to give me the most average horsepower going down the track __________________ that's pretty much all of it