For years I have been bracket racing my Sunbird the same way, and never had a reason to change because it was consistent and very competitive. On the advice of my engine builder, I decided to test some lower shift points on the old engine before I swap in the race motor this summer.

I have always set my RPM Activated Module to throw the shift light at 5600 rpm. I would shift 1-2 and 2-3 at the light, and then short-shift 3-4 at 5000 to have some pull thru the traps. As the years have gone by, and the miles have added up (to nearly 152,000 now), I watched my ETs slip back from my record of 15.416 @ 86.54 in 1994 to 15.7- 15.8 range with an occasional high 15.6. I was used to the old shift points and did them nearly reflexively after over 900 1/4 mile passes. I'm not a big fan of change, but I'm glad I gave it a try yesterday.

We had decent weather at Great Lakes Dragaway yesterday, with temps in the upper 40s to lower 50s, humidity under 50%, barometric pressure of 29.2 all day, and density altitudes of under 500 feet. If only the track had been a little warmer and stickier, it would have been perfect. Traction was an issue for anyone on street tires, and I even had to lower my launch rpms on Drag Radials to avoid spinning. I started the day with my old shift points (5600/5600/5000), and managed a best run of 15.742 @ 85.79 mph (.024 RT, 2.134 60 ft, 9.998 @ 69.03 1/8, 13.097 1000 ft). This was consistent with past years, and I felt wasn't too bad for the tired old motor. Then I tried 5400/5400/5000, and dropped down to 15.657 @ 86.39 mph (.064 RT, 2.109 60 ft, 9.956 @ 69.22 1/8, 13.031 1000 ft). I figured since that worked so well I would drop down to 5200 across the board. My launches weren't as good, and the best I could manage was 15.759 @ 87.62 mph (.151 RT, 2.198 60 ft, 10.039 @ 69.27 1/8, 13.139 1000 ft), but I felt like if I had launched better, it would have improved more. I took a chance and dropped the shift points down to 5000 across the board, and boy am I glad i did! I managed to launch it just right, nail all of my shifts perfectly, and run a 15.471 @ 86.52 mph (.038 RT, 2.044 60 ft, 9.786 @ 69.53 1/8, 12.851 1000 ft). I would say that's not too bad for a tired old 3.1 MPFI 5-speed car!

I can't wait to get back once the track is a little warmer with more rubber on it, so I can launch at 3000 rpm like I prefer to. I made all of the above passes launching at only 2500 - 2600. I may just set a new PB with the old motor as it's "swan song."

What kind of shift points have you folks found successful?





'93 Sunbird SE 3.1 5-speed
'00 Grand Prix GTP Sedan
sunbird93racer@yahoo.com

On my 01 Z24 I shift right at the rev limiter.I do short shift 1-2 shift a little, but the rest all out.



FU Tuning

John,
There will be a bit of a difference between us since you have a 4-cylinder that has a higher powerband (winding a 3.1 that high makes no sense). My engine builder recommended that I set the shift light at or just past my peak power RPM. He said that no matter how fast the driver reacts to the light, they probably don't make the shift for another 200 RPM anyway. By shifting at that point, it puts you in the best position to make power in the next gear. I plan to dyno my car once I drop in the race engine. Not so much to found out the power it makes (althought I'll be curious), since almost all dynos will tell you something slightly different. I will want to know where that peak HP is made, and I will make my shifts accordingly. I am just amazed at how dramatic a difference this little change made for me, and it might for others too. Shifting higher isn't always better!


'93 Sunbird SE 3.1 5-speed
'00 Grand Prix GTP Sedan
sunbird93racer@yahoo.com

I agree our cars are different so my shift points are going to be different. I do not have a clue what the 3.1 redline is or rev limiter is. I do know that in a stock motor running factory ECU usually reving right up to the rev limiter is best. Why because when the RPMs drop for the next gear you will be in the peak HP. If you shift right at or even right after peak HP you are going to fall below and have to climb up into the peak power band. The 2.4 rev limiter is 6450 RPM, if I shifted at 5000RPMS I would fall so far out of the power band, it would kill me. Once you have a new (I assume built motor) getting it on a dyno and seeing where the power is and how high it can pull good power is a good thing. I have had my car on the dyno a few times (and my old 97 Z I use to have) they peak around 5700-5900 RPM and then rev limiter around 6400RPM.



FU Tuning

Your engine builder is right to a point, but it all depends on how sharply your power drops off after peak... For example, lets say your power peak is at 5600 rpm and you make 200 whp there. Now we'll just say for the point of example that your gearing makes the rpms drop 1500 rpm on the shift. Naturally, different gears have different amounts of RPM drop but this is just oversimplified to make my point.

Now, if you shift at 5600 rpm, your rpms will drop to 4100 rpm... you need to know how much power you're making at that point, and this is why... Lets say your redline is 6200, thats as far as you can rev safely. Now what if you make 180 whp at 6200, but only 160 at 4100 rpm? That means that by shifting at 5600 you are reducing your average hp through that gear, making yourself slower.

More likely, knowing the broad powerband of the 3.1, and sharp drop after peak, you make more hp at 4100 rpm than at 6200, so revving it to that point would make you slower than shifting at a lower point. This is why you really need to have a dynograph of your car to quickly and accurately determine your best shift points. Trial and error can work, but since so many factors are involved, it can take a long time to actually get your optimum shift point.

You need to know the RPM drop after each shift, 1-2, 2-3, and 3-4 (4-5 if your car is REALLY fast, but you know what i mean), and what power you make at the shift point compared to how much you're making at the point the RPM's will drop to. If your rpms will drop to less hp than you're making when you shift, you should shift higher (as long as it is safe to do so). If your rpms will drop to more hp than you're making at the shift, you can be faster by shifting lower.

So yes, shifting higher isn't always better! But its not always worse either! Anyone who races needs to know what their powerband and rev drop is. This is why you see a lot of the 4 cylinder guys who are accustomed to V6's and V8's running really slowly, because experience teaches them to shift lower than they should with the motor they have.




Arrival Blue 04 LS Sport
Eco
Turbo
Megasquirt
'Nuff said

What if your engine makes 240 @ redline and from idle all the way up it NEVER drops, not even sorta drops, lol!



ASE Master Certified Automotive Technician

i know back in the day with my 94 (befor i ported the 3.1's to emulate 3400 Exhaust side) it woldent pull past 5grand, so i shifted right at 5, but after i ported them it wanted to go past 5 grand, so i let it go to 5500 or so, and i droped 1/2 a sec off my ET's.... to 15.5.

lol and it got better milage.

building a motor now are ya?, what top end?

Chris


'02 Z-24 Supercharged
13.7 @102.45 MPH Third Place, 2007 GMSC Bash SOLD AS OF 01MAR08

Chris,
Yes, I already have the built shortblock on a stand in my basement (details in my profile). I am going against conventional wisdom and trying to get the most I possibly can out of an MPFI intake and heads. I will be sending them off to Ben from 60degreeV6store soon to get them worked over. He, along with everyone else, has warned me that they have distinct limitations, and he can only get so much out of them (especially the intakes). I accept this in order to maintain the original appearance of the engine compartment of the car. The headers and TB will be the only thing that will appear non-original. Based on my present performance with a tired old engine, compared to the combination that I am putting in, I am convinced that the car will run close to 14.25 in the 1/4 mile at about 95 mph. If I can do that, I think that will be mighty impressive for an NA MPFI set-up, and will turn some heads. I have built up the bottom end solidly enough to handle a top-end swap later if I decide to do it. The headers will only need modified slightly with a new flange to handle that. Don't bother to try to convince me to do the hybrid now, I've already made up my mind. I'm doing this under the premise that people gave up on the MPFI set-up too soon, since the 3X00 heads and intakes were so much better in stock form. If I dropped into the low 14s (maybe even high 13s with the right weather and traction) with a hybrid engine, that's no big deal. Lots of other folks have done it. If I do the same thing (or close to it) with the older more restrictive MPFI set-up, that will be something that very few people have done. I like to take the path less traveled sometimes !


'93 Sunbird SE 3.1 5-speed
'00 Grand Prix GTP Sedan
sunbird93racer@yahoo.com

... well like i said, all i did was make my 3.1 heads LOOK like 3x00 exhaust style and i droped 1/2 sec, you should run that time.

but when you do come around to better intake...(lol) let me know, i have a extra set of 3.1 heads and 3400 heads laying around, as well as 3100 GM pistions (.40) and rods too.

Chris


'02 Z-24 Supercharged
13.7 @102.45 MPH Third Place, 2007 GMSC Bash SOLD AS OF 01MAR08

Cant wait to see you down at GLD this year Joe! Have fun with that new engine.

I shift my car at 7 on the tach, which is about 7300 on my HPT scanner.

Drop about 2k rpm between gear changes, puts me right before the HP peak on the graph....... works pretty good so far.




SPD RCR Z - '02 Z24 420whp
SLO GOAT - '04 GTO 305whp
W41 BOI - '78 Buick Opel Isuzu W41 Swap

Bryan,
I'll be there on Sunday for Import Wars. Hope to see you there!


'93 Sunbird SE 3.1 5-speed
'00 Grand Prix GTP Sedan
sunbird93racer@yahoo.com

somebody needs to teach SRZ how to rotate images




Arrival Blue 04 LS Sport
Eco
Turbo
Megasquirt
'Nuff said

Joe Morgan wrote:Bryan,
I'll be there on Sunday for Import Wars. Hope to see you there!

Not sure if I'll make it down....... I'll have to try and talk my wife into it. I wont be racing, thats for sure.

Scarab (Jersey Jay 1.8T) wrote:somebody needs to teach SRZ how to rotate images

lol, I had it rotated..... but when I went to find it to post it up just now, it wasn't rotated....... I think its saved correctly in my CarDomain page.




SPD RCR Z - '02 Z24 420whp
SLO GOAT - '04 GTO 305whp
W41 BOI - '78 Buick Opel Isuzu W41 Swap

Quote:

If your rpms will drop to less hp than you're making when you shift, you should shift higher (as long as it is safe to do so). If your rpms will drop to more hp than you're making at the shift, you can be faster by shifting lower.

cant wait to test this!

Using my power graph and translating this onto another graph that shows vehicle speed against (torque x gearing) I get the following. Took 0.7 off my best time on the 1/4 mile this way. The gear change points are different in each gear due to the way the gear overlaps are not consistent between each gear. It feels wierd shifting at these points, low down seems too high revs and up high seems too low but it works really well

Power graph



Gear change points