ZGlide

today on the highway i repeatedly tested the shift from redlining 3rd (with that beep going off) to fourth, then i get this dip in power before it starts pulling again while in fourth. I tested a few time from 2nd to 3rd but dont get that same dip. Anyone else has the same experience? Could this be a clutch issue?

93rdcurrent

It could have something to do with the synchros or gear ratio from 3rd to 4th. I haven't noticed it for myself but I do know what the rev limiter feels like. Is it similar or is it more subtle? I will have to try it out for myself.

ZGlide

this dip occurs after the shift, and I just got the car!! only 1200 miles

93rdcurrent

That is unusual and I know that I'm not experiencing any dip after a shift for sure. I would take a tech out and show it to them. That way they can give you a good idea what it could be.

D MENAC 7

What were you topping out at in speed redlining in 3rd gear? 2nd gear redline is about 65-66 MPH.

ZGlide

i forgot but I will try it again tomorrow

Psylence

I know what you're talking about ZGlide. My '8 does the same thing. At first I put it off as a bad shift.. but I've been driving stick all my life and I'm not so bad that it should happen as often as it does.

It feels like the clutch slips then grabs.. but the revs don't jump up like the clutch was slipping.

RX8_Buckeye

Redlining in 3rd gear would put you at about 95 mph. Think about road load and aerodynamic drag at that speed. Just before shifting, you are still near the torque and power peak of the engine, which gives sufficient tractive force at the tires to feel significant pull. After shifting to 4th gear, not only does your engine drop to an operating point where it has less power, but your torque multiplication due to gearing decreases because of the higher transmission gear. Combined, these factors might cause the vehicle to feel like it has no "pull" until the engine is able to approach its torque/power peak again.

I'm not sure if this is what you're feeling, but what I've explained happens with every vehicle. If you were to install a driveshaft torque meter, or read tractive force from a chassis roll dynamometer, you would see that the net force at the tires (total tractive force - road load & aero drag) decreases with increasing vehicle speed. As a result, acceleration decreases with increasing vehicle speed, and there are unavoidable dips in acceleration whenever you shift to a higher gear. These may feel more pronounced at higher vehicle speeds because of the high road load and drag forces.

I have never redlined in 3rd gear with this car, unfortunately, so I'm not sure exactly what you're feeling. You may very well have a synchro problem or something if it feels extremely severe. I find it unlikely that it would be a clutch problem, because clutch engagement operation is independent of the transmission gear that is engaged. If you had a clutch engagement problem, it would be most noticeable at launch from a standstill when the torque across the clutch is maximum.

guy321

I did not have this problem..

However, Some 8's have sychro problems, it is known by mazda.. My problem was grinding when shifting over 6k rpms in 3rd gear..

HollywoodHall

Does anyones 8 feel like it doesnt have 238 hp??!?!?!.. Sometimes I feel like the old' accord has more ***** then my 8.

Jailbreak'74

oh geesh, never man. I'm sorry to hear you have that feeling. BTW, 3rd to 4th really takes off, i never beep it, 7500-8000 is good and i'm gone....no dip and I've done this several times entering a highway.

f1michel

please Hollywood, we have had that conversation over and over here, enough with the groundhog day ! :-)

MyRxBad

iTrader: (1)

When you are doing the shift into 4th, is your traction control light flashing?!?

Last time I made a 3 to 4 shift hard, the traction light came on and the car slowed down to gain grip. (probably because of a dirty road.)

Turn your traction control off and try that run again, see if you get the same results... If not, then the computer is the culpret. If it doesn't change the results then the problem is somewhere else.

BasenjiGuy

Most likely you're experiencing aerodynamic drag vs. the power curve of the engine affecting how hard the car seems to pull. Also, as you run up thru the gears, the ratios may widen between gears, creating greater gaps as you shift up. If the engine drops to a lower rev with a successive shift, given the car's softness down low in the powerband, you'll get less pull as the engine is at less rpms than at the beginning of the previous shift. Factor this with increasing the aforementioned aero drag vs. torque at higher speeds and you'll be feeling less pull in the higher gears than you do in 1,2, and 3.

Buckeye3d

I have redlined 3rd but have always eased off when I shifted into 4th b/c of how fast I was already going. :D There was no noticable lack of power but again I was not pushing it in 4th.

RX8_Buckeye

Just curious, did you read the entire thread? :p

MTLbroker

I'm jealous......I'm still in midst of engine break-in and haven't made a run to readline yet :-(
But I did read somewhere on this board that at <3500 rpm, the engine runs with 2 injectors, at <6500 rpm, 4 injectors and >6500 rpm 6 injectors. Is that true (I'm not technical so it could be BS and I'd still beleive it)? Could it be that by upshifting, the revs drop and 2 injectors shut off before you get over 6500 rpm again? Just a thought.

John Corbitt

I noticed that on the track. It is a slight drop. It feels more like a maping issue. It will take Mazda a few tries or an aftermarket company so solve that issue. The loss in lap times I felt were minimal. It feels like a softer version of the stumble the FDs had at 3200 rpm.

John

RX8_Buckeye

If it's simply a mapping issue, why is he only noticing this after a 2-3 upshift at redline? The engine mapping isn't vehicle-speed or gear dependent, so if there is a problem with the mapping in a certain RPM range, you would feel a "drop" anytime an upshift put you into that range.

Gord96BRG

Actually, it IS gear dependent - with the M flash at least, it seems that Mazda has different maps for gears 1-2-3 and 4-5-6. I've seen that mentioned a couple of times around here, and it's caused Canzoomer some problems with coming up with an appropriate map for his piggyback units.

Regards,
Gordon

RX8_Buckeye

Really? If that's the case, it surprises me. I'll ask around and see if this is common in other vehicles.

I don't see many advantages to making the engine mapping gear-dependent, except that it could help PREVENT the very scenario that we're discussing--lack of tractive effort at WOT upshifts. Drivers of MT vehicles expect the engine to behave the same throughout the powerband regardless of what gear is engaged, so I wouldn't expect that the mapping would vary too much from gear to gear.

Can you think of any other advantages of a gear-dependent engine mapping?

guy321

I don't know much about cars at all, and I'm horrible at math.

However, I think gear dependent mapping could be useful to increase MPG.

This is why I think so. Theoretically, if fuel mappings were the same across all gears, it would be beneficial for you to cruise around town constantly at 65mph. This would be at 3k RPM's in 6th gear.. If you're in third gear then you're consuming the same amount of gas but going half the distance.

So, by having gear dependent mapping you could program some gears to run leaner at certain RPM ranges to squeeze out extra fuel efficiency.

Psylence

I know it's not a clutch issue.. but that's the feeling that it has. It's not a traction control issue either, since I always disable it and I'm just not that violent with the clutch so as to break it free at such a high speed.

Fuel mapping? Could be.. it's just a momentary stumble.. not like an entire part of the rev range that it has to labored through.

RX8_Buckeye

Well you're not taking throttle position into account. The fuel flow rate depends on throttle position as well as engine speed. Let's say, for example, that the throttle position is at 40% to hold 65 mph / 3000 RPM in 6th gear. Now in the city, you might drive at 30 mph / 3000 RPM in 3rd gear. True, you're only covering half the distance in the same amount of time, but it requires much less throttle, say 20%, to hold that speed. The point is that 3000 RPM in 3rd gear might be almost as efficient as 3000 RPM in 6th gear from a MPG standpoint.

As far as I know, the engine is calibrated to make a certain amount of torque at a given pedal position, regardless of transmission gear. When you start making the calibration gear-dependent, it could feel very funny to the driver. However, this might explain why the 2-3 WOT shift feels funny.

guy321

I thought that if the engine is spinning at 3k RPM's then the throttle position is the same, because the gearing does not dictate what RPM the engine is spinning at.. It should spin the same and use the same fuel when in neutral and at 3k RPM also.. is that incorrect?