Shifting for dummies

Chris Landi · **Joined:** Mon Mar 08, 2004 6:31 pm **Posts:** 579

Rich Anderson wrote:

...

Which is why you shift by HP, not torque. :word:

Ah, the real world answer I was looking for versus the suggested google link.

Thanks.

Rich Anderson · **Posted:** Tue Mar 21, 2006 4:16 pm

DanDurusky wrote:

i got the two extra credit questions right

that read killed my whole morning, doh

Different subject, but this one should take care of the afternoon. :twisted:

You'll laugh everytime you see a Wal-Mart greeter.

Richard Casto · **Posted:** Tue Mar 21, 2006 4:21 pm

Rich Anderson wrote:

Richard Casto wrote:

...which shows that if you care about wheel torque (or force), that this shows how a high RPM low torque engine can equal a low RPM high torque engine. This done via gearing. So RPM ( or HP

) is what does it.

Or, as importantly and perhaps more germaine to our discussion here, that high RPM in a lower gear at a high horsepower can result in superior acceleration to low RPM but high torque. Which is why you shift by HP, not torque. :word:

Well... In my calculations, I never directly look at HP. But I am looking at Wheel Torque at various RPMs. Which is as I hint above, it pretty much some type of HP type value (as we are mixing Torque and RPM). If I redo my chart and graph HP for each gear as specific speeds, I get the same results. I run out of RPM in 1st and have to shift into 2nd. Same for 2nd to 3rd. But my HP lines intersect between 3rd to 4th and 4th to 5th. Again, nearly at redline. Which is what the wheel torque values was saying as well. So maybe you, me and Mike are saying the same thing. Torque is the starting point for all of this, but we are not talking about engines with one gear and no RPM range.

Rich Anderson · **Posted:** Tue Mar 21, 2006 4:29 pm

I guess I am just lazy and don't want to multiply! If you have an engine where you can tune the power curve (like I can with adjustable cam gears) it is far simpler to calculate the effect on gearing by going by HP in my experience. You can easily determine when your shift point is 500 rpm past the limiter and it is time to bump the gears a degree or four. The extra step would confuse me and dyno time costing what it does means I would rather have a setup with fewer steps.

If it works for you, go with it.

Les Davis · **Joined:** Fri Aug 29, 2003 2:04 pm **Posts:** 2059

Rich, have you completely forgotten the LDSSPC (Les Davis Simplified Shifting Point Calculator)??? :-)

LDSSPC for any car properly designed from the factory equals redline or higher. As we modify our cars, we generally shift the hp peak even higher making higher rpm shifts even more important. Unless you have changed your gear ratios, or modified your engine output shifting the horsepower peak lower in the rpm range (very unlikely) there is virtually nothing to be gained in accleration form short shifting. Now, as Kevin mentioned earlier, there may be logistical reason when on course to short shift, but its not for the purpose of optimal acceleration.

Richard Casto · **Posted:** Tue Mar 21, 2006 6:19 pm

Thank you to whoever split this out into another thread. We had hijacked the other thread long enough.

Graham Jagger · **Joined:** Fri Aug 29, 2003 12:53 am **Posts:** 1718

Ok Rich since you're interested and want to calculate numbers here is one for you with specs and recent dyno. The specs below on HP/TQ are at the flywheel and advertised but not consist. The dyno is. The dyno numbers are taken in 4th gear roll on.

Car 2002 Corvette Z06
Engine 350V8-LS6
Horsepower 405hp/5000rpm
Torque 400ftlb/4000rpm
Redline 6500rpm
Trans Getrag 6sp
1st 2.97
2nd 2.07
3rd 1.4
4th 1
5th 0.84
6th 0.56
Rear End Ratio 3.42
Tire Diameter 26.1
Tire Size 295/35-18

Use the Blue Line/Numbers in the JPG as that is after adjustments and what it is running at now.

Dyno Chart

I have all the speeds and rpms for each gear in a spreadsheet. I know where I shift. Let's see where you think I should. Especially 3rd-4th.

Graham

Rich Anderson · **Posted:** Tue Mar 21, 2006 7:05 pm

Graham, can you please get the data file from Jeff at CAM. It will make it so I don't have to do a bunch of data entry.

Chris Landi · **Joined:** Mon Mar 08, 2004 6:31 pm **Posts:** 579

Rich Anderson wrote:

OK, so I spent 15 minutes making a spreadsheet. Someone who can host it post your email and I will get it to you.

I'd like to see what it spits out (hopefully I can find my 4th gear pull dyno sheet)... clandi@cisco.com

Thanks, Chris

Rich Anderson · **Posted:** Tue Mar 21, 2006 8:19 pm

Chris Landi wrote:

Rich Anderson wrote:

OK, so I spent 15 minutes making a spreadsheet. Someone who can host it post your email and I will get it to you.

I'd like to see what it spits out (hopefully I can find my 4th gear pull dyno sheet)... clandi@cisco.com

Thanks, Chris

It is on my work computer so I will send it to you in the am. Anyone else who wants one is free to have a copy. Hopefully it is intuitively obvious.

Graham Jagger · **Joined:** Fri Aug 29, 2003 12:53 am **Posts:** 1718

Rich Anderson wrote:

Graham, can you please get the data file from Jeff at CAM. It will make it so I don't have to do a bunch of data entry.

I'll send him an email and ask him. I just scanned the printout he gave me. I hadn't planned on getting this deep into shift points. I kinda like Les' theory. It's easier for me to remember :wink:

Rich Anderson · **Posted:** Wed Mar 22, 2006 9:00 am

Graham Jagger wrote:

6th 0.56
Graham

Bugger. My sheet is only setup for five gears. Hmmm, guess I'll have to come up with v1.1!

Rich Anderson · **Posted:** Wed Mar 22, 2006 9:29 am

Les Davis wrote:

Rich, have you completely forgotten the LDSSPC (Les Davis Simplified Shifting Point Calculator)??? :-)

Actually, look at the first post. :twisted:

Rich Anderson · **Posted:** Wed Mar 22, 2006 10:58 am

Damn, I am a post whore on this one.
http://www.v8mongrel.com/index.php?p=howto
OK, my version is available online now. All the numbers are for my Focus, btw, and you need to input your own. I have included both rear axle torque (Whitney method as best I can figure it) and the HP method I use. The graph is for the HP method, but anyone with beginning Excel skills can use the other numbers with a couple of changes. Basically, the thing to do is look for a straight line for the shifts.

If you use it, please give me feedback. As of now, I plan the following changes.
v1.1 will accomodate six speeds (I might go to seven, JIC). v2.0 will accomodate variable RPM shift points per gear. v2.1 will extrapolate information to allow for shifts not in increments of 100. v3.0 will do the work in reverse where you can modify the graph and have it read out the RPM you need instead of trying to get the line straight.

Any comments welcome.

Les Davis · **Joined:** Fri Aug 29, 2003 2:04 pm **Posts:** 2059

Graham Jagger wrote:

I kinda like Les' theory. It's easier for me to remember :wink:

Definitely the best feature of the theory. :-)

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