18 replies to this topic

[Sphinx]

For those with 1.6L, at what RPM are you shifting?  I've got an AutoMeter shiftlight that was set at 6600 rpm by the prior owner, never messed with it.  Too high? Too low?

 

At what rpm are these engines at risk of mechanical overreving (say on a downshift)?

[svvs]

I have mine set to start flashing at 7100 rpm.

 

I have progessive lights.......first one lights up at about 6500 i think.

 

I guess it's whatever you get used to in terms of seeing a light and then when you shift.  I'm happy with mine, but I know that once it starts flashing I need to shift or I'm in the limiter.

 

As for the RPM at which motor damage occurs....I don't have a hard number.  I did screw a motor up though because of a few successive missed shits.  Went 3-2 instead of 3-4.....twice in about a second.  I have heard someone say 7800 is the number....but I never tested it and I don't even know how to take my motor apart.

 

-Vick

[pat slattery]

We shift at 7 to 7100.  Sometime 66 on a long track going into 5th gear

[Ron Alan]

Bench Racer will tell you that you are screwing yourself shifting at 6k...no torque at 4k!!!

 

What others said above...hitting the rev limiter is not the end of the world. I see many bounce off it for a short period rather than a short upshift then down shift. You're given up power not going close to the 7200rpm limiter in a 1.6. 1.8 cars have the added benefit of major torque at the lower rpms so short shifting is not as detrimental

[Sean - MiataCage]

7100 works good....... There is a really nice progressive shift light for under $200.00 on the market and the rumor on the AIM unit is that it will allow shift lights to be altered per gear, which might be nice.

 

Sean

[AW33COM]

Bench Racer will tell you that you are screwing yourself shifting at 6k...no torque at 4k!!!

 

 

He will be very correct.   Shifting at 6600 in a 1.6 car is lethal to your lap times.  You may as well buy the 99 at that point.   I was shifting at 6800, because I did not know better.  After some data gathering and power to weight ration comparison across different cars I realized it's OK to give up (maybe gain) some high end power by keeping my gear past 7000 RPMs in order to capitalize on the 1.6 power to weight ration advantage above 5600 RPMs. 

 

The most important rule in 1.6 car is to shift in such a way that you have 5550 RPMs or more after the up shift.  This becomes very important shifting into 5th gear (high speed mistakes are costly in terms of time) as any shift below 6900 is going to end up around 5100 RPMs and you're parking it at that point.  More, if you can't keep the engine above 5600 after the up shifts, try not to shift on some sections of the track if the 5th gear is only for a short distance.

                                         

Here is the data I have.  1.6 on the left side, 99 on the right side.

 

RPM     HP      Weight     Power/Weight Ratio

1.6                                                                   99
        5000    104    2300    22.11538462        5000    113    2400    21.23893805    
        5100    107    2300    21.4953271          5100    114    2400    21.05263158    
        5200    108    2300    21.2962963          5200    116    2400    20.68965517    
        5300    110    2300    20.90909091        5300    118    2400    20.33898305    
        5400    113    2300    20.3539823          5400    119    2400    20.16806723    
        5500    115    2300    20                         5500    121    2400    19.83471074    
        5600    118    2300    19.49152542        5600    122    2400    19.67213115    
        5700    119    2300    19.32773109        5700    123    2400    19.51219512    
        5800    119    2300    19.32773109        5800    125    2400    19.2    
        5900    120    2300    19.16666667        5900    126    2400    19.04761905    
        6000    121    2300    19.00826446        6000    126    2400    19.04761905    
        6100    122    2300    18.85245902        6100    127    2400    18.8976378    
        6200    123    2300    18.69918699        6200    128    2400    18.75    
        6300    124    2300    18.5483871          6300    128    2400    18.75    
        6400    125    2300    18.4                      6400    128    2400    18.75    
        6500    125    2300    18.4                      6500    127    2400    18.8976378    
        6600    125    2300    18.4                      6600    127    2400    18.8976378    
        6700    124    2300    18.5483871          6700    126    2400    19.04761905    
        6800    123    2300    18.69918699        6800    126    2400    19.04761905    
        6900    123    2300    18.69918699        6900    125    2400    19.2    
        7000    122    2300    18.85245902        7000    124    2400    19.35483871

 

By looking at the data above you can figure out when to shift.  Look at power ratios and figure out where you have the biggest advantage.

[Bench Racer]

Bench Racer will tell you

Ron, sometimes all I do is read, AW33COM fills in the blanks so nicely. 

[Sphinx]

He will be very correct.   Shifting at 6600 in a 1.6 car is lethal to your lap times.  You may as well buy the 99 at that point.   I was shifting at 6800, because I did not know better.  After some data gathering and power to weight ration comparison across different cars I realized it's OK to give up (maybe gain) some high end power by keeping my gear past 7000 RPMs in order to capitalize on the 1.6 power to weight ration advantage above 5600 RPMs. 

 

The most important rule in 1.6 car is to shift in such a way that you have 5550 RPMs or more after the up shift.  This becomes very important shifting into 5th gear (high speed mistakes are costly in terms of time) as any shift below 6900 is going to end up around 5100 RPMs and you're parking it at that point.  More, if you can't keep the engine above 5600 after the up shifts, try not to shift on some sections of the track if the 5th gear is only for a short distance.

                                         

Here is the data I have.  1.6 on the left side, 99 on the right side.

 

RPM     HP      Weight     Power/Weight Ratio

1.6                                                                   99
        5000    104    2300    22.11538462        5000    113    2400    21.23893805    
        5100    107    2300    21.4953271          5100    114    2400    21.05263158    
        5200    108    2300    21.2962963          5200    116    2400    20.68965517    
        5300    110    2300    20.90909091        5300    118    2400    20.33898305    
        5400    113    2300    20.3539823          5400    119    2400    20.16806723    
        5500    115    2300    20                         5500    121    2400    19.83471074    
        5600    118    2300    19.49152542        5600    122    2400    19.67213115    
        5700    119    2300    19.32773109        5700    123    2400    19.51219512    
        5800    119    2300    19.32773109        5800    125    2400    19.2    
        5900    120    2300    19.16666667        5900    126    2400    19.04761905    
        6000    121    2300    19.00826446        6000    126    2400    19.04761905    
        6100    122    2300    18.85245902        6100    127    2400    18.8976378    
        6200    123    2300    18.69918699        6200    128    2400    18.75    
        6300    124    2300    18.5483871          6300    128    2400    18.75    
        6400    125    2300    18.4                      6400    128    2400    18.75    
        6500    125    2300    18.4                      6500    127    2400    18.8976378    
        6600    125    2300    18.4                      6600    127    2400    18.8976378    
        6700    124    2300    18.5483871          6700    126    2400    19.04761905    
        6800    123    2300    18.69918699        6800    126    2400    19.04761905    
        6900    123    2300    18.69918699        6900    125    2400    19.2    
        7000    122    2300    18.85245902        7000    124    2400    19.35483871

 

By looking at the data above you can figure out when to shift.  Look at power ratios and figure out where you have the biggest advantage.

 

 

So, you're saying shift much higher than 6600, right?  When does the fuel cut-off on the 1.6L?  Thanks for the info.  Going to review my data closely when I get home.

[svvs]

I think the rev limiter on the 1.6L is 7200 rpm.

[Roger Caddell]

When I studied this very deeply (disclaimer...from a 1991 1.6 way back in 2006!) it was not even close... shift as close to the rev limiter in each gear, maybe not the 1 to 2 shift but we did not race there.

 

When you do the math comparing 'rear wheel torque' in each gear based on our actual rear wheel hp/tq numbers the car always had less rear wheel torque in the next higher gear, and again it was never even close.

 

When you study actual acceleration rates, the data also always showed less acceleration after every shift. Again it was not even close.

 

The drivers instructions were to shift the car at each and every shift, as close to the rev limiter as possible without ever hitting it.  There was always a noticeable reduction in acceleration when the rev limiter was hit.

 

Of course the cars are more prepped that we knew how to do back then but I would be surprised if this was not still true.

[davew]

When you do a gear chart for a Miata, you find a slightly over 1800 rpm drop during the 3-4 upshift. And I am only going to address the 3-4 shift as it is the most common.

 

Using the numbers given above, shifting at 6600 (peak hp) puts you down to 4800 rpm after the shift which is somewhere below 104 hp

 

Shifting at 7200 (rev limiter is usually a tick over 7200 in a 1.6) gives you 5400 rpm after the shift or 113 hp.

 

Comparing a 6600 shift vs a 7200 shift will cost you 2 horses at the top end, but will gain you at least 9 horsepower. Not to mention the torque increase. I'll make that trade any day.

 

The second item to look at is the accuracy of your tach and checking your rev-limiter. Rev limiters are very accurate unless they have been messed with. At some point in time put the car on the rev-limiter in second gear, while watching the tach. Most factory tachs are 200-500 rpm  off. Do a little math to find what YOUR tach reads at the true 7200 rpm rev limiter. Compare your shift light to the tach, I would bet on the shift light over the tach.

 

Shift at a true 7100 without hitting the 7200 rev limit.

 

If you are over-reving on a downshift, work VERY HARD on your shifting technique. It will save your engine, trans, clutch, tires, wallet, marriage etc.

 

Dave

[Sphinx]

Is Vicktor's number of 7800 a consensus number for an overrev?

[CruzanTom]

 

 

If you are over-reving on a downshift, work VERY HARD on your shifting technique. It will save your engine, trans, clutch, tires, wallet, marriage etc.

 

Dave

 

Great advice! Ask me how I know (but I am still married)!

 

Tom

[Roger Caddell]

To bring back a topic from a few weeks ago, I found some dyno sheets for 4 different years of SM cars, most off this site; 1991, 1994, 1999, and a 2002 and I wanted to check my prior conclusion I did back in 2006 on our 1991 1.6 SM where I found that the driver should run the car to max revs in each gear before shifting to the next gear for maximum acceleration.

 

I suppose the data could be different with the current prep levels so I did the calculations on all 4 of these years of SM's based on the dyno sheets I found.

 

Attached are 4 images of the results based on the different dyno sheets I found/used.  The lines are representing the 'Rear Wheel Torque' in each gear. If the lines do not cross, the prior gear has more 'Rear Wheel Torque' than the next gear and would suggest that taking the car to the max revs is better than shifting early. If the lines cross, that is the point where the 'Rear Wheel Torque' is higher in the next gear.

 

What is shown in the images from the data I found is:

 

With a 1991, shift at max rpm (+/-7200) for each shift except 4 to 5 where optimum would be 7100.

With a 1994, shift at max rpm (+/-6900) for each shift.

With a 1999, shift at max rpm (+/-7000) for each shift except 4 to 5 where optimum would be 6900.

 

Clearly the above 3 years of SM's get very close to saying "max revs in each gear" as even the 2 years that show a 100 rpm early shift into 5th are so close that the difference could go either way with your engine or dyno values.

.

And here is the exception, With a 2002, shift at max rpm (+/-7000) for each shift except 3 to 4 where optimum would be 6800 and 4 to 5 where optimum would be 6600.

 

Disclaimer: I pulled this data off of printed dyno sheet graphs, extrapolating 100 rpm increment torque values. While I think the trends are correct, your numbers could vary. :-)

 

[AW33COM]

^ This is the almost exact same shift points I came to with my calculations, but I personally call them static shift points.  Those are the shift points when you're trying to go as fast as possible on a race track and you're not passing.  When you want to make a pass or have an edge on a specific car model you should shift differently.  For example, with the 99 I would shift at 6700 or 6600 in order to get a run on a 1.6, but I would shift as late as 7000 or 7100 against a 2002 car.  Same thing can be said in reverse as well. 

 

When it comes to shifting you can get creative per racetrack, racetrack section, competition, and etc. 

[Adax]

 

 If the lines cross, that is the point where the 'Rear Wheel Torque' is higher in the next gear.

 

Thanks for posting this data Roger. Now that I'm driving a torque advantaged '01, I've been interested in this data and thinking about it a lot. The flaw in the statement above is that it assumes shifting to the higer gear (and higer wheel torque curve) puts you at that RPM again (where the lines cross). If fact, shifting drops you somewhere further down the RPM curve where torque is no longer equal. So your statement is correct if you add "at that RPM" to the end.

 

There are several shift point simulators available where you input your torque curve and gear ratios. I've done this with two of them and both show that shifting a '01 at redline is fastest (actually they say shift at 6980).

[mdavis]

Thanks for posting this data Roger. Now that I'm driving a torque advantaged '01, I've been interested in this data and thinking about it a lot. The flaw in the statement above is that it assumes shifting to the higer gear (and higer wheel torque curve) puts you at that RPM again (where the lines cross). If fact, shifting drops you somewhere further down the RPM curve where torque is no longer equal. So your statement is correct if you add "at that RPM" to the end.

 

There are several shift point simulators available where you input your torque curve and gear ratios. I've done this with two of them and both show that shifting a '01 at redline is fastest (actually they say shift at 6980).

I'd be interested on what simulator you were using.  The torque on the 01+ is really, really low in the RPM band.

[Roger Caddell]

Thanks for posting this data Roger. Now that I'm driving a torque advantaged '01, I've been interested in this data and thinking about it a lot. The flaw in the statement above is that it assumes shifting to the higer gear (and higer wheel torque curve) puts you at that RPM again (where the lines cross). If fact, shifting drops you somewhere further down the RPM curve where torque is no longer equal. So your statement is correct if you add "at that RPM" to the end.

 

There are several shift point simulators available where you input your torque curve and gear ratios. I've done this with two of them and both show that shifting a '01 at redline is fastest (actually they say shift at 6980).

 

I may not fully understand what you are saying Alan but my calculations assume the same mph after a shift and assume the resulting decrease in rpm based on several factors (tire circumference, rear gear ratio, and of course gear ratios). So "at that speed" is accurate with this method as the rpm certainly changes with the change in gears.

[Adax]

Sorry Roger, I think I misread your post. I didn't realize you had MPH on the X-axis. What you are saying makes sense, it's just not what I found. I guess I need to think about it some more. Hope you are right though.

 

http://vlsicad.ucsd....i/perf_est.html

 

http://www.bgsoflex.com/shifter.html

 

The first takes more data into account, but I can't get it to run at the moment.