9krpmrx8

iTrader: (46)

In another thread there is some discussion about the angle of the ends of the eccentric shaft on the bearings at high RPM. It got me thinking, is shift all the way up to red line really needed?

I would like to confirm on a dyno/strip/whatever, if shifting that high is needed for both power and for keeping the revs up when banging through the gears. I know there are other variables but just thought it would make an interesting discussion.

MazdaManiac

iTrader: (3)

I generally shift around 8200, but my power curve is not typical.

I have found myself on the Auto-X course, bouncing off the rev limiter to avoid shifting in and out of gears excessively.

Since the typical RX-8 sorta runs out of puff around 8500, that is probably high enough.
I don't know if the high RPM benefits outweigh the potential detriments, but I think the typical driver is not going to see any damage from just letting her rip from time to time.
Its the racers that keep her at 8000+ for loooooong periods of time that have something to think about.

kersh4w

iTrader: (3)

the real reason to shift at 9300rpm (especially when drag racing) is not staying higher up there for a longer period of time... but when you shift, you shift at a higher horsepower point.

PhillipM

When our engine first went on a dyno the peak power (with a stock map) was about 8.4krpm and dropped off rapidly thereafter, I don't know what it's like on the stock gearing but with our short ratio 'box then changing at ~8.8k would have been best.

As it is, we've more power up top now, but the engines' not stock.

olddragger

iTrader: (3)

needed for what?
It all depends, but personally since i am not in a competitive race and dont plan on being in one with my DD--i limit myself to no higher than 8K. A lot of times I shift at 7.5. But we all know our tachs are off?
I dont think in my case that the benefits outweigh extra strain on the drivetrain.
Sure sounds good though!
OD

TeamRX8

iTrader: (25)

If you ever get your car on a real dyno instead of your booty dyno you can calculate all that out

Snrub

kersh4w is on the right track. You want to use the maximum amount of power under the HP curve. Usually at 9k the engine makes more power than it would than at say 6k. If you were planning on using 6-8.5k vs. 6.5-9k, the later would mean more power under the curve. Simple math. In most dynos I've seen power drops off a bit at 9k as compared to 8.5k, but not massively so.

9krpmrx8

iTrader: (46)

Really?

TeamRX8

iTrader: (25)

http://www.datsuns.com/Tech/whentoshift.htm

9krpmrx8

iTrader: (46)

Sweet. I'll have to figure that out.

TeamRX8

iTrader: (25)

You'll have to get a real dyno test first ....

alan23

I normally shift at 9-9.2k rpm on the track.

If I shift at 8k rpm, my timing will be slower by about 2sec.
The most obvious being the straights when the speed differential is about 5kph slower at 190+kph region

However, if shifting at such a high rpm is so damaging to the renesis, I seriously should consider shifting early to preserve the engine.

my 2 cents

9krpmrx8

iTrader: (46)

Yeah if the weather clears up I may get it done tomorrow.

olddragger

iTrader: (3)

i like a flat torque curve
OD

Snrub

...You're the one who asked.

BTW: I don't think it makes sense to dyno a virtually stock car to find out that you have 5-10hp more than stock due to a mid-pipe. There will be far more varience in the type of dyno, procedure, etc. than there will be with your car compared to others. Your power curve won't be significantly different either. If there is a difference it's due to a problem with the car or dyno varience.

Nubo

Watch and learn.

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DAC17

Nice... Of course, remember that the speedo is reading in KPH.

olddragger

iTrader: (3)

Also remember its not his car--trans was taking a beating there and I would be afraid of his engine temps after about 3 laps. Obviously a oem car.
Sorry but it looks to me that he really had some sloppy moments. Too much steering wheel input and did you notice some speed rate change in the higher band?
OD

9krpmrx8

iTrader: (46)

Yes but you have to get a baseline. I just wanna see if my new motor is up to spec.

Snrub

Losing an engine clearly causes one distress (been there, done that with my old FC). However, it's pretty hard for a Mazda manufactured short block to not be up to spec unless it's something very obvious. Compression is a metric by which this is judged. There's no reason for compression to not be up to par unless the engine has undergone significant wear. Performance due to a semi-newish short block and the OEM ECU are more or less static. The long block with the VDI functionality, etc. are more likely to be potential issues.

As for the baseline, what are you hoping to acheive? Unless you're planning on converting the car to a race car, you've done the modifications that make sense. The car does not respond well to modifications. Some half decent power gains can with a tuned exhaust and by sacrificing the volume of the exhaust, but most people don't really want to do this on the street. The mid-pipe is the biggest bang and the best bang for the buck mod you can do and you've already done it.

I guess what I'm trying to say is just enjoy your car and drive it.

Nubo

Maybe he had TCS on? Lol. The car will shrug off briefly excessive steering inputs and just scrub some speed, in my narrow experience. But mostly I was referring to the shift points. Holding until just before fuel cutoff puts you close to 7000 rpm after the shift and the engine set for max power, which is better than landing at 6500, imho.

kersh4w

iTrader: (3)

^ yep.

teamrx8 posted a nice link if you go turbocharged and dramatically change the power curve.