Yo!

I have been playing around with my powerband and tryng to find the ideal points to shift.

I've heard that MAX TORQUE = MAX ACCELERATION.
If that is the case, then you should be trying to hit MAX torque in the next gear you shift into.

However, my car can "safely" go up to 8000RPMs (redline). And MAX HP is at 7000 RPMs. Obviously it makes no sense to go beyond 7k.

SO if torque is what you want, then what's the point of HP? Perhaps the best is to comprimise a little HP and TORQUE. I was thinking that maybe this "magic point" would be where the 2 curves intersect on a dyno?

I am no expert, that's why I'm asking these (stupid) questions...



So what has been the best expirience with this? Anyone know the shift points the Mazda testers used to claim the 7.2 and 16.0 (0-60 and 1/4 mile) times they did for the RX-7 N/A's?



Here is a pic of a lightly BPU Series V FC3S.


---PS--- I DID search the forum numerous times but nothing on this subject turned up

 

 

Hey man, I've done some experiments too.
I find that when upshifting, hitting 5.5k in the next gear nets max acceleration.
So
1st - 2nd I shift at 8k
2nd - 3rd I shift at 7.5k
3rd - 4th I shift at 7.4k

 

Yeah, that's the way i used to shift.

But recently i LAID rubber on the shift from 1st to 2nd. It was the most AWESOME thing ever. I never thought that my little NA could chirp gears.

What was MORE shockin was that i made the shift at 5.5k. Landing me SQAURE at about 4k in 2nd gear . And that gave me enough UMPH to break loose in motion on a straight line. I have done this several times at those RPMs, but shifting near redline or at 7k could never do it. HHMMM....

Couldnt do it in 3rd though...

I found to land at 4k in the next gear you shift at:
1st 5.5k
2nd 6.2-6.5k
3rd = ??
4th = ??


Anyone care to share more info on how torque and HP work?

 

This dyno sheet looks SERIOUSLY wrong - it looks like the 6-ports aren't even opening!&nbsp The torque should be almost FLAT all the way almost to redline - it takes a DUMP after 5,000RPM, which is right where the 6-ports are supposed to open...



-Ted

 

Yeah, i dunno. I found it in an old thread and they said it was a stock S5. So i put it in as an example... gonna delete it now. The first one looks more accurate.

 

For a given GEAR, max torque will pull the hardest.

For a given SPEED, max HP will pull the hardest. That's because you'll be in a lower gear, so even though the engine makes less torque, you have more gear reduction.

So what to do? Plot out your HP curve vs. your gear ratios. What you want is for HP to be the same from your shift RPM to the new RPM the engine will be at in the next gear. If the two never match up, then shift just before the rev limiter. You'll probably be ending up that the engine is never down near peak torque - that's OK because you have gear reduction on your side.

 

hey is it still safe to shift above 7 if thats where ur read line if?

 

well then, it seems that if you shift @ 7500, you will land at 6000 (1st to 2nd) which looks like it makes about the same HP as at 7500... sound right?

Mazda put that redline in there for a reason. At 7k, your rotors are spinning at 2333 RPMs. I highly doubt that stock rotors can take more than 3000RPMs, let alone 2500 (7500 flywheel). Going over is pushing it and you are probably reducing engine life.

 

i lay rubber in 2nd shifting a little past 7k and chirp in third gear at 7k too.

 

Your tires bald?

No, seriously, what mods do you have? I haven't really heard of N/A chirping... ESPECIALLY in 3rd or higher...

 

happens evertime too, and my tires are not bald, they are toyo proxes w/ plenty of life on them. Thats why my next mod is 275-285's in the rear, that damn burning rubber slows me down so much. It burns rubber all the way though first too, droppin clutch @ 3k. That is how i get my best times, i have done almost everything there is to do, except port anything and a header ( cuz im going boost ) and it weighs 2500lbs. Oh yeah i haven't scrapped my OMP, probably not either just had my injectors clean not looking to clog them with premix. Ask Mazdaspeed i know he has to be able to chirp going into third gear too...

 

Close. The goal is to retain as much torque as possible in each gear. This is determined by the rpm at which the driveshaft torque at the top of one gear is most equal to that of the bottom of the next gear.

http://www.prestage.com/carmath/dynochart.asp

 

it's not THAT HARD to chirp in any gear

jeez

even my POS honda (90HP, 70tq, 2200lb, fwd) will chirp the tires in 3rd (and a little in 4th)
its easy
you're shifting at high RPM (7000 or 7500 or whatever), stick it in the next gear REALLY FAST, keep your foot on the throttle (just a bit, so you don't lose the revs, and then floor it and dump the clutch, and you'll chirp

spinning takes a bit of power though
and I haven't been in or even seen a car with enough power to get rubber in 3rd with posi.

 

It's harder to chirp gears in RWD cars cuz the weight is squatted on the back wheels

That's why anyones little civic or integra can chirp and do burnouts so easily.

I plugged the dyno into that site. These are the results:

Your best shift points are:
Best shift point for the 1-2 shift is 7000 with a LOSS of 105 Lb/Ft of torque.

Best shift point for the 2-3 shift is 7000 with a LOSS of 36 Lb/Ft of torque.

Best shift point for the 3-4 shift is 6600 with a LOSS of 21 Lb/Ft of torque.

Best shift point for the 4-5 shift is 7000 with a LOSS of 21 Lb/Ft of torque.

 

Dude you didn't think N/A's could chirp gears. I can break the back end of my car lose and it even starts to go sideways in 1st to 2nd and if I shift at the right point from 2nd to 3rd I can chirp also. Just depends on when you shift and how you drive it. I think it also depends on the car's shifter to. I got a 90 GTU and the guy that i bought it from said that the GTU came with the short throw shifter. Correct me if I'm wrong.



kleach

 

HERE is the ONLY wat to do it !

Put your power curve into something like excel so you can do average power over a selected RPM range.

Now you need to calculate out your rev drops for all gears based on a few different situations say shifting at 6750rpm, 7000rpm, 7250rpm and 7500rpm (looking at your graph)

Then with the average rev drops ie. looking at second to third.

shifting at 6750 will give 4659rpm (2091rpm drop)
shifting at 7000 will give 4832rpm (2168rpm drop)
shifting at 7250 will give 5004rpm (2496rpm drop)

NOW through excel or other method find what the AVERAGE POWER IS for the above rpm ranges ie 6750rpm to 4659rpm (for the 6750 shift) or for the higher shift 7250 to 5004rpm (for the 7250rpm shift)

THE RANGE WITH THE HIGHEST AVERAGE POWER will be the one to choose ! The highest average power through a gear ratio will give the the HIGHEST acceleration....PERIOD.

This is the method I use.

If you do this for ALL gear changes 1st to2nd, 2nd to 3rd (the one I just did for you), 3rd to 4th and so on you will find that due to the lower rpm drop between shifts it may be the case that you do not reve the car as high in the higher gears so as to stay in the higher average power range of that gear ratio.

POWER is what accelerates the car, so find where the engine will make it's HIGHEST AVERAGE POWER for the gear ratios...simple as that, it will take you a long time but it is worth the effort

 

Just doing a quick analysis of your power curves, I would suggest 7800rpm shift points for 1st to 2nd, 7800rpm for 2nd to 3rd, 7600rpm for 3rd to 4th and around 7500 to 7400 rpm shift from 4th to 5th.

These points will yield the HIGHEST average power through all your gear ratios and will give you MAXIMUM acceleration.

 

Ahhh that dyno sheet he posted above is of me and kahren....

Anyway once again, this is a dyno sheet of my car at 82K, all stock
http://www.geocities.com/tmak26b/90dyno1.jpg

at 93K, all stock, except a K&N filter and 10K old plugs
http://www.geocities.com/tmak26b/90dyno2.jpg

This is the latest at 160K, mods are bonez cat, RB muffler, custom cut stock airbox
http://www.geocities.com/tmak26b/90dyno3b.jpg

The graph that you saw was a comparsion between my run and Kahren's FC run (he has the same mod except he has a RB straight pipe replacing my cats, and he has an electric fan) His car is obviously not running right since he is making hte same hp as me. he determined that his 6 ports were stuck OPEN, thats why you see the low end is so bad, and his VDI is like half stuck. It opens very slowly. He is in the process of cleaning it. Anyway, I've learned a good way to check out to see if a NA FC is running normal from the dyno sheet is watch for when the 6 port kicks in and the VDI kicks in. As you see, torque drops after it hits peak at 4500-4700. It would drop until 5200 where it stayed flat until like 6500 rpm. That's what the VDI can do for you. On Kahren's car, his torque dropped until 6200 rpm. Then his VDI kicked in and its torque stopped dropping until 7K.

Btw dont be surprise if you cant just click and see the picture. YOU HAVE TO COPY AND PASTE IT SINCE GEOCITIES DONT ALLOW REMOTE LINKING

 

Yeah I konw. I found it in an old thread and thought it'd be pretty representitive of a lightly modded S5 --which it is.

 

right on man.

 

exactly as he sais but sometimes u still have to rev all the way up to the redline. the only real way is to go to a strip and do it there. there are too many factors that can go into this and is almost impossible to calculate this. there is wind resistance which u will rather have hp then tq to beat. then there is the drive train loss, and all sorts of friction coefficients...liek i said go to a track and try diffrent runs...u will see that shifting at red line is the fastest way.
by the way that dyno is of mine and tmak26s cars. my 76 ports are stuck open and i have about 3lbs of carbon boulildup in the lower intake manifold. my low end sucks cause i have too much air goign to the motor...my mid is good cause teh 6 ports are stuck open and i have some carbon buildup and my top end is not as good as toms because i have carbon buildup and cant obtain full velocity and volume of the air. tom has a healthy NA go by his graph which is blue on that sheet. he also has a cat and i dont. after i get my car running righ ti am going to the strip i am expecting very low 15's or a high 14 if i am lucky.

oh and one other thing there is no such thing as HP its calculated from TQ HP=(rpm x tq)/5252
where 5252 is a constant. and this is true for any engine

 

Ok ok, seeems like the ideal shift point IS after max HP is made...

How safe is it to go all the way up there often? I know i know, everyone says "rotaries can rev to redline all day and not care." Is there any truth to this? I've already lost one engine.... don't wanna make it 2

 

its actually good to go there, u wont give teh carbon a cahnce to pile up on there...dont go past 8 and u shoudl be fine...a litte over 8 is ok too but then u get all sorts of missfires and stupid fuel maps...so tehre is really no point to go past redline...unless u wanna break things faster...rotary dont put much stresss on the bearings but if your motor is not modded there is no gain to go up higher.

 

I can chirp gears in my stock n/a