AbeFM

iTrader: (3)

In the quest for cheap horsepower, it seems to me a little less torque at a higher speed can be a winning battle.

I've got biggie valves, headwork, H-beam rods on my 2000 FM-II. I have stock, 97 pistons, 2000 cams.

I'd like to put in biggie springs. Get some more revs. Is this reasonable? I've never really heard where the limits are on anything. Also, can I just pressuize the cyl, and pull the springs out from the top, or do I need to pull the head? I don't mind pulling it, but I've always wanted to try it that way.

Anyway, curious what people think the limits on things are, and what the payoff is.

UrbanSoot

iTrader: (24)

you can get about 7k rpm out of stock engine.

Stealth97

iTrader: (5)

I talked to FM about their valve springs... they told me unless I had big cams I would not need them.. I turn 8k on occasion and I have not had any float.

AbeFM

iTrader: (3)

Christ, all this time Mazda had the factory rev limit set at 7200? Someone should tell them they can't go that high!

I've got my rev limit set to 7500, and my knock sensor triggers ~7k, which is my real limiting factor.

I am a bit worried about not making any power there, but just staying in the gear longer would be nice sometimes. In the lower gears (bigger spacing) it makes more sense to stay in it longer. Cams I've never gotten any good info on, but I have a feeling maybe I'd have to look at some of the 300hp cars on here to see what their intakes look like.

UrbanSoot

iTrader: (24)

sorry, i meant to say 7400
thats what i had mine set to at last track day and didnt have anything weird happen. i did have some really bad valve knocking at 7600 though...

AbeFM

iTrader: (3)

How did you know it was valve knock?

Did it still feel alive? I.E. Would more rev limit made you happy, or were you feeling overdue for a shift anyway?

cjernigan

iTrader: (13)

I highly doubt you'll make any power out there without custom cams. Above the stock rev limit i would be worried about minimal gains while sacrificing reliability of the stock oil pump.

UrbanSoot

iTrader: (24)

well, it sure did sound like valves and once i lowered my rev limit it stopped. also there was no power there anyways. it was peaking at about 7200 and i shifter around there. on my current car im keeping it at 7200.

AbeFM

iTrader: (3)

Makes sense.

Then again, if you're "peaking" right before valve float, that means you DID have more in it, and you just stopped closing the valves, hence power dropped off.

Not trying to argue, but it stands to reason no?

UrbanSoot

iTrader: (24)

i was peaking around 7200 and my valves float was at 7600. see the 400 rpm difference?

UrbanSoot

iTrader: (24)

anyways, when you wot, 400rpm is just too little to notice.
again, everything depends on what kind of driving you do and what you care about more - torque or hp. if you care about torque more then hp then you **** at around 5-6k because thats where most of our engines peak in torque.

then again, here is a situation i had to deal with on track:

going wot on straight line in 5th gear at around 6000rpm, then some heavy braking and into a 3rd i go with around 4000rpm, go through turn, floor it for a second in 3rd, then some braking and again - 4000rpm or so into a turn, then redline on 3rd, shift to 4th, floor it, brake and into 3rd gear at 4000rpm i go again.

see? everything depends on track you run.

AbeFM

iTrader: (3)

Jesus, you didn't have to call me a ****. :-)

Here it gets interesting again. So, let's do a little thought experiment (as Einstein was so fond of).
Anyway
Shifting at 7k from 4th to 5th gets you torque at the wheels which is higher because you're in your torque peak, but lower because you've now divided the torque by 23%. So, if you're making 150 ft-lbs at some RPM in 4th, when you shift you'd better be ending up at 185 ft-lbs or you'll accelerate even slower than before.

In first gear, this is especially obvious. There's a 66% loss in torque (hence resistance to wheelspin in the real world) when you shift out of first. 42% from second to third.

Here you're one up on me, never done track time, only autocross.

In that example, the floor-it-in-4th, if you're in it for several seconds, is entirely worth it. But, if you're only in 4th for a second and a half, even reduced power of reving to 8500 would save you time on the shift. That translates to a smaller amount of power delivered for a longer time, and overall, you win.

Anyway... I guess that was my point - that your ideal shift point gets earlier and earlier in the higher gears, but being able to stay in it longer, even at a power loss, helps. Certainly it would be something loggable - what's the acceleration in each gear?

UrbanSoot

iTrader: (24)

just to clarify, im not a track expert. i did 2 track days and i was spinning like a ************ on my first event. second event was much much better then first because i wasnt as nervous as first time.

most of my observation comes from 1 track day (about 25-30 laps overall) and extensive canyon driving which i do occasionally for few years now.

i find that if i shift between 5000 and 5500 rpm from 3rd to 4th i have more torque then if i would shift 6k+

also, i jam-shift. that means that it takes me almost no time to go one gear up.

AbeFM

iTrader: (3)

That's interesting.... To me, 3rd is where my car seems to have it's biggest strength. It just seems to go forever in that gear. 1,2 is getting you up to speed, and 4,5 are just for getting to the higher top speeds. Generally I find the problem with third is it's too touchy for real turning. But it depends on this weeks tuning tables, IC piping, etc. :-)

Anyway, a data log of a pull in 3rd and a pull in 4th would answer those questions really fast.

JasonC SBB

LOL my ex beater stock Honda Civic takes longer than your car's forever in 3rd. Does that mean it's better than your car?

UrbanSoot

iTrader: (24)

forgot to add: there is no problem being in 4th gear for only 2 seconds or so because i gain another 5-10mph during that time and then i down shift while im braking.

one more thing - i ran both drift event and second track event without turbo

patsmx5

iTrader: (16)

I've got datalogs of my stock 99 motor at 7950. It wasn't floating. It wasn't pulling much either though. Still it wasn't valve float holding it back. I've had motors float valves at high RPMs. You know it when it happens. Motor will buck and backfire and basically hit a wall. It will refuse to go any faster.

Nothing on the motor supports making power in that RPM range. You can put Power-Card-Valve-Springs that don't float to 11ty Billion RPMs, but many aspects of the head, cams, intake manifold, and undersquare engine design will hold you back from making high RPM power. If you want more power, turn up the boost and bring DOWN the rev limit. IMO that's the road to reliable HP. A lot goes wrong at high RPMs. VE is downhill, friction is up, crank flex is multiplying, etc. For example if the motor would turn 9K it wouldn't make any measurable HP because the losses would be so high. You can fight them or you can work around them.

UrbanSoot

iTrader: (24)

maybe because 99+ motors have solid lifters?

MX_Eva

I actually have a new intake manifold and I'd be curious to see how much farther up my peek is. It definitely pulls a lot stronger after 4,500. this may be because the loss in low end torque makes the ramp up much more noticeable. However, my engine rather likes climbing up the RPMs much more now. You look away and next you know you are nearing 7k. I think with some head work she'd love to sing at 8k and up.

Gonna have to hit a dyno soon.

UrbanSoot

iTrader: (24)

its not really problem with intake mani but with overall engine design in my opinion