help with shift points

ciara · 09-10-2002, 06:34 PM

I used one of those shift point calculators on the net and it says optimum shift point is at 7000 rpm. Only problem is that the max rpm according the my cam card is 6000 rpm. The engine makes peak torque at 4500 rpm and peak hp at 5500 rpm. Any tips on how to get a close guess so when I go to the track tomorrow I don't blow up something up.

Mustang_289 · 09-11-2002, 06:28 AM

I was asking this very question in a previous post, pretty much everyone said shift points should be set between 5000-5200 rpm. This would put you pretty much right between your peak torque and hp rpms.

Jeff Chambers · 09-11-2002, 06:44 AM

I've got an illustrated discussion on my website. Follow the URL in my sig and check under the Tech Articles section. Believe it or not, but there is some science to choosing the optimum shift points. Science aside though, the best way to find the optimum shift points is with some consistent test & tune. The science part will point you in the right direction though.

302 LX Eric · 09-11-2002, 07:18 AM

I take it you have a dyno sheet on your car?

I did with my old 302 setup and found my 'optimum' shift points by doing something rather straight-forward...

I entered my dyno results into Excel by 100 rpm increments with torque in one column and HP in another. Then, I calculated percentage of torque and percentage of HP based off of peak. This provided me with a gauge. From here I shaded the torque column from all points were torque was at or above 90% and did the same thing with HP. Then, I overlapped the shaded areas to visually 'see' where the most power was being made (both torque and HP).

To better illustrate, I was making at least 90% of peak HP from 4400 - 6000 and at least 90% of peak torque from 3600 - 5300. So, from 4400 - 5300, I was making at least 90% of peak HP and TQ. No conincidence that this is where I seem to feel that the car pulls hardest. (The butt dyno never lies!

)

From here I decided to go ahead and try shifting a tad higher than 5300 in order to keep the power up b/t shifts. That way when you go from say 2nd to 3rd, your not too far down the power band and have to 'wait' for the rpms and power to climb back up. I ended up with my best runs shifting right around 5600.

Sorry this was so long and boring, but I really enjoy analyzing this kind of stuff.

E

gofastmercury · 09-14-2002, 12:19 AM

If you really want to crunch numbers and have dyno sheets and your trans gear ratios, you can do it mathematically. You multiply the rear gear by 1st gear, times that by the torque at whatever rpm you want to check. do the same for second. When the value for second becomes greater than the value for first, that’s the shift point. Pretty simple, but we don’t race calculators, and the real thing is always a little different.

09-10-2002, 06:34 PM	#1
ciara Registered Member Join Date: Jan 2002 Posts: 100	help with shift points I used one of those shift point calculators on the net and it says optimum shift point is at 7000 rpm. Only problem is that the max rpm according the my cam card is 6000 rpm. The engine makes peak torque at 4500 rpm and peak hp at 5500 rpm. Any tips on how to get a close guess so when I go to the track tomorrow I don't blow up something up.

09-11-2002, 06:44 AM	#3
Jeff Chambers Moderator Join Date: Aug 2000 Location: Milan, OH Posts: 2,699	I've got an illustrated discussion on my website. Follow the URL in my sig and check under the Tech Articles section. Believe it or not, but there is some science to choosing the optimum shift points. Science aside though, the best way to find the optimum shift points is with some consistent test & tune. The science part will point you in the right direction though. __________________ Jeff Chambers 1990 Mustang GT 10.032 Seconds / 137.5 MPH 14-time Street Warrior World Record Setter CRT Performance 2001 Tropic Green Mustang GT - 12.181 / 113.2 MPH 2002 Ford F-250 Crew Cab 7.3l Power Stroke - 17.41@77.2 "There's nothing boring about a small block automatic shifting gears at 9400 rpm!"

09-11-2002, 07:18 AM	#4
302 LX Eric or '331 LX Eric' Join Date: Jan 1999 Location: Columbus, Ohio Posts: 2,142	I take it you have a dyno sheet on your car? I did with my old 302 setup and found my 'optimum' shift points by doing something rather straight-forward... I entered my dyno results into Excel by 100 rpm increments with torque in one column and HP in another. Then, I calculated percentage of torque and percentage of HP based off of peak. This provided me with a gauge. From here I shaded the torque column from all points were torque was at or above 90% and did the same thing with HP. Then, I overlapped the shaded areas to visually 'see' where the most power was being made (both torque and HP). To better illustrate, I was making at least 90% of peak HP from 4400 - 6000 and at least 90% of peak torque from 3600 - 5300. So, from 4400 - 5300, I was making at least 90% of peak HP and TQ. No conincidence that this is where I seem to feel that the car pulls hardest. (The butt dyno never lies! ) From here I decided to go ahead and try shifting a tad higher than 5300 in order to keep the power up b/t shifts. That way when you go from say 2nd to 3rd, your not too far down the power band and have to 'wait' for the rpms and power to climb back up. I ended up with my best runs shifting right around 5600. Sorry this was so long and boring, but I really enjoy analyzing this kind of stuff. E __________________ 1991 5.0 LX Coupe - 40,750 miles 331 cu. in. / Tremec 3550 / BFG Drag Radials 12.22 @ 114.31 mph - w/1.89 60'

09-14-2002, 12:19 AM	#5
gofastmercury Registered Member Join Date: May 2001 Location: calgary alberta canada Posts: 366	If you really want to crunch numbers and have dyno sheets and your trans gear ratios, you can do it mathematically. You multiply the rear gear by 1st gear, times that by the torque at whatever rpm you want to check. do the same for second. When the value for second becomes greater than the value for first, that’s the shift point. Pretty simple, but we don’t race calculators, and the real thing is always a little different. __________________ 93LXcopcarSOLD14.3@96 @ 4500ft 2.02 60ft on street tires. my 67 ranchero NOT A 390 ANY MORE! 460! 3.70's cast manifolds, comp cams 262H, performer, 750DP 100K out of 79 F250 NEW(oct20/02)14.58@95mph 2.3 60 ft corrects to:13.86@100 66 merc comet351w, isky roller 600 lift 268/260@.050, vic jr. 700DP, 5000stall, 4.56's c-4, 3400lbs with driver 12.3@110 @ 4000ft 1.69 60 ft corrects to:11.69@115

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09-11-2002, 06:28 AM	#2
Mustang_289 Registered Member Join Date: Sep 2001 Posts: 512	I was asking this very question in a previous post, pretty much everyone said shift points should be set between 5000-5200 rpm. This would put you pretty much right between your peak torque and hp rpms.