td3005

I haven't seen any info about chaning the rev limiter for a manual transmission. I hate having the thing cut out at 6700 rpm. Has any one done this for a manual transmission, is it crazy ?

Galo

gears, shifting at (first thre gears) or just below redline (last two gears) puts you smack in the middle of the HP/TQ curves of the higher gear u just shifted into, why would u wanna raise the rev limiter?

SteVTEC

00-01's are top-end beasts and need every bit of RPM they can get. You want to keep the revs centered around the peak power point for maximum performance. Since peak power doesn't occur until practically redline, it's imossible to get maximum potential out of the engine.

With a rev-ceiling of say 7200rpm, you'd be able to center your revs around the power peak much better and this would shave a good couple of tenths off of your 1/4 mile time.

IceY2K1

iTrader: (3)

Only 95-96 and people who swap ECUs into 97's have this capability.

Yes, it would make a WORLD of difference in the VQ30DE-K.

Don't hold your breath on this EVER happening though.

Galo

at your own dyno curves (way informative & cool, BTW) the 3-liter Max reaches peak HP at 6400-6500 rpms (we both agree there, it's a top-end screamer) but also, note the torque curve: almost flat from 3800 (peak) to about 5000 after which it begins to tail off somewhat.

To achieve maximum acceleration, the ideal shift point is at or near (could be a bit before, a bit after, no difference) of the HP peak in the gear you are shifting out of and where the shift 'lands' you within the 'fat' part of the torque curve in the gear you are shifting into.

With the Maxes drop-off in tq after 5000 rpms, shifting at 7k RPMs would slow u down because you have already revved way past your hp peak but more important, because after the shift you would be at an RPM where the tq curve begins to fall.

The 5-speeds have bigger gear spacing 1st to 2nd and 2nd to 3rd than 3rd to 4th and 4th to 5th so yes...one needs to wind tighter in the lower gears but there's still no need to go past 6600-6700 RPMs to drop into the fattest part of the TQ curve in the next gear

IceY2K1

iTrader: (3)

I'd suggest you go check out the JWT threads with MEVI manifolds in the General section.

There is MORE than enough evidence to show Steve is correct.

It's worth your time to read it, trust me.

IceY2K1

iTrader: (3)

MEVI + JWT ECU Dyno:
http://forums.maxima.org/showthread....5&pagenumber=1

CarTest of MEVI + 7200rpm JWT ECU:
http://forums.maxima.org/showthread....5&pagenumber=1

More info:
http://forums.maxima.org/showthread....5&pagenumber=1

There are a couple other recent ones you should read.

SteVTEC

Galo,

Using the dyno plot of stock 00-01 in CarTest2000 and giving the engine all the revs that it needs (with cartest extrapolating a bit), the calculated optimal shift points are as follows:

1-2: 7630rpm
2-3: 7080rpm
3-4: 6880rpm
4-5: 6590rpm


HP and TQ are mathematically related so they're really the same thing, but you get maximum acceleration when the revs are centered around the point of peak horsepower. When you punch it in a car with a CVT, the engine revs will rise to peak horsepower and then just stay there as the pulleys start to change ratios as you accelerate. This is why CVT's can give better acceleration than a traditional automatic or even a manual. When you have set ratios, you're always dancing around the peak power point and never quite there. A CVT can keep it there all the time and maximize acceleration and efficiency.

You'll get the maximum acceleration in each gear at the point of peak torque, but for highest overall acceleration, you need to keep the revs centered around the peak horsepower point. Remember, when you upshift to the next gear you have less torque multiplication so you want to hold the lower gears for as long as possible.

Galo

and still dunno if I agree -at least for a relatively stock 3-liter without ECU mods or Middle East Variable Intakes.

From one of the threads I read, shifting at 7000rpm we would be we'll be landing at:

1-2 ~4300 rpms, which is perfectly within the torque peak band
2-3 ~5100 rpms, which is just when TQ begins to fall off
3-4 ~5400 rpms, which is when TQ is in a good slide down

It's obvious from the many threads you pointed me to that a lot of work has been done by many folks on 'modeling' the Maxes HP/TQ relationships -but I'm not convinced that the data appears to show that Maxes 'work' differently from all other cars on the road...call me skeptical still

I guess the only way to be completely sure would be to be able to mod a 3-liter to shift at 7k & do comparative performance runs but...moot point since we dont have ECU mod that can take us there...

IceY2K1

iTrader: (3)

Yeah, it's mostly theory for now, but so far CarTest has shown to be very believeable compared to the track.

Also, as far as the MEVI is concerned, our "-K" engines NVIS is FAR SUPERIOR to the MEVI. So, we could benefit even more. The MEVI just sustains power from 6000rpms to 6800ish, where as our NVIS keeps climbing. I believe the MEVI uses a tuned resonance chamber/runners for the long/short path switchover, whereas our NVIS actually has separate runners.

Yep, no fun for us.

Galo

real value of the Cattman camshafts...would they be worth the moolah if we cant twist our engines into an RPM range where the added lift and duration would REALLY be noticeable...

Hmmnnnnn.......

IceY2K1

iTrader: (3)

Until I see dynos, I'm a skeptic also.

SteVTEC

But in all of those cases, the TQ may be falling, but the HP is still increasing

I know why you're getting confused, and it's sorta hard to explain. I'll use a 4G as an example. TQ drops off like mad after 5000rpm, and peak power is from 5000-5600rpm. After that the engine starts wheezing, yet you still have to keep the revs above 6000rpm on the first two gears before shifting.

1-2 shift @ 6600rpm (130 whp) lands you at 3700rpm in 2nd (130 whp)
2-3 shift @ 6300rpm (140 whp) lands you at 4300rpm in 3rd (140 whp)

The optimal shift point always occurs when the power you have at the wheels in your current gear crosses over and you have more power available if you shifted to the next gear.

What would happen if you shifted before those points in the 4G Maxima? You would land at a lower rpm where you have LESS power at the wheels than if you had just stayed in the previous gear. This results in less overall acceleration.


You get the best acceleration at any single point in a given gear at the point of peak torque.

But you will ALWAYS get the best overall acceleration up through the gears by keeping the revs centered around the point of peak power.


Here is is from the torque perspective...

1st gear is 3.29:1, 2nd is 1.85:1, and 3rd is 1.27:1


I'll use the 2-3 shift as an example.

At 6300rpm in 2nd you have a pathetic 114 lb-ft of torque at the wheels. But the 2nd gear multiplier is 1.85:1, which is much higher than 3rd.

114 lb-ft x 1.85 = 210.9 lb-ft (this is very simplified)

Now when you shift to 3rd and land at 4300rpm you have a HELLuva lot more torque (171 wtq), but there is less multiplication now.

114 lb-ft x 1.85 = 210.9 lb-ft
171 lb-ft x 1.27 = 217 lb-ft (not exact, but close enough)


Even though you were WELL BEYOND where the torque curve started to drop off when you shifted, the shorter gear ratio was multiplying the torque enough that it still wasn't optimal to shift to the next gear until all the way up at 6300rpm.


Lets say you shifted at 5600rpm instead:

2nd: 151 lb-ft (@ 5600rpm) x 1.85 = 279 lb-ft, but this lands you at...
3rd: 175 lb-ft (@ 3800rpm) x 1.27 = 222 lb-ft


As you can see, this is too early to shift, and you had more torque at the wheels if you had just stayed in the previous gear, even though the torque curve of the engine at that point was still falling rapidly. Even though the engine itself has more torque by shifting earlier to 3rd, you still have more torque at the wheels due to gearing by staying in the lower gear for longer.

SteVTEC

Not theory! CarTest2000 is based directly on real world "F=ma" physics.

Real world physics are not a theory. They are proven facts!

Here are some screen shots of what this program does...

http://mywebpages.comcast.net/stevte...Test2000_1.jpg
http://mywebpages.comcast.net/stevte...Test2000_2.jpg
http://mywebpages.comcast.net/stevte...Test2000_3.jpg
http://mywebpages.comcast.net/stevte...Test2000_4.jpg
http://mywebpages.comcast.net/stevte...Test2000_5.jpg
http://mywebpages.comcast.net/stevte...Test2000_6.jpg
http://mywebpages.comcast.net/stevte...Test2000_7.jpg
http://mywebpages.comcast.net/stevte...Test2000_8.jpg
http://mywebpages.comcast.net/stevte...Test2000_9.jpg

Galo

completely forgotten about the torque multiplication aspects of the gearing...now it makes MUCH MORE sense & I can see why it's the crossover point that's key...thanks

I feel like 'duhhhhh....'

SteVTEC

Also, here's a stock 4G dyno just so you know what I'm talking about...


http://www.boostaholic.com/maxima/dyno/dyno.gif

IceY2K1

iTrader: (3)

JoO are my HERO!

BTW, OT but can you explain/model the effects(1/4, 20-XXXmph, etc.) of a lightened flywheel compared to OEM. Do you have any dynos of this mod?

I've read that OEM is better for 1/4-mile due to the inertia for the next gear, yet the lighter flywheel is better for throttle response, ie RPMs climb faster.

I'm unclear how the inertia into the next gear outweighs the RPMs climbing faster for the 1/4-mile. Which is better on the street from a roll?

Thanks!

SteVTEC

No problem

Y2KevSE

iTrader: (13)

A lightened flywheel makes you feel like you can't drive stick. Not from personal experience of course.

SteVTEC

I haven't read any of these threads, but by "inertia for the next gear" they probably mean that...

...with the heavier flywheel, more of the engine's momentum is conserved off-throttle and between shifts when engaging the next gear so that when you engage the gear you're bleeding off a lot more energy into the next gear which can help you get some wheelspin, which is helpful.


But like I said, I haven't read any of those threads so I dunno.

jjs

But the info provided in this thread has been very helpful and extremely well explained! Just wish we could put it into practice.

IceY2K1

iTrader: (3)

As far as CarTest is concerned, couldn't you just use an UDP dyno and multply the gains by say a factor of 3, since it's basically the same?

Have you done CarTest on an UDP alone?

SteVTEC

One thing it would do is change the free-running engine deceleration rate (would increase the deceleration rate) so it would definitely take some getting used to when shifting gears if you were used to the OEM flywheel before.

Bucking a bit are we Kev? hehe

SteVTEC

There's a parameter in CarTest2000 called "Engine Free-run Deceleration Rate" (mentioned above) and this is the parameter that the flywheel would affect. It doesn't really increase power directly. It's set by default to 2000. I changed it to 4000 and the 4G Maxima I have modeled went from 15.01 @ 92.80 to 14.98 @ 92.97 mph.

Hardly any gain on ET, but it did seem to give a little more acceleration in each gear from the 0.2 mph faster trap. This is one of the little things you can do that when combined with a bunch of other little things will finally add up and give you a noticeable and measurable improvement.

0.03s and 0.17 mph is within run to run variability


And plus I'm just purely guessing on that parameter. I don't know how the flywheel would measure stock and lightened.

IceY2K1

iTrader: (3)

So by increasing the "Engine Free-run Deceleration Rate" from 2000 to 4000, the 1/4 was faster?

I would think it would be the other way around. Hmmmn.

SteVTEC

You're not understanding completely what the flywheel does.


With a lightened flywheel the engine is able to accelerate faster (good). But it also decelerates faster (bad). So when you're accelerating you gain something. But when you're between gears and shifting, the engine is decelerating faster, so you have less inertia/momentum conserved in the engine when dumping it into the next gear - you lose something.

At least in the simulated case, the car was still faster with the lightened flywheel, but I have no idea how accurately that test applies to the actual cars. From what I understand, there isn't much to "lighten" on the existing flywheel.

Other side-effects of a lightened flywheel is that it's harder to go up hills. The engine doesn't conserve its momentum as well so you have to feed it more gas. Same thing with cruising. But these same things also allow you to acclerate faster. On cars with extremely lightened flywheels it would be noticeable, but probably not on the Maxima.

SteVTEC

Okay I have a good analogy for the flywheel



Imagine a pinwheel. It accelerates VERY easily but you can stick your finger in it and it will stop instantly.

Now imagine a solid "ROCK wheel" the same size as the pinwheel. That heavy **** is tougher to acclerate, but once it gets spinning fast, you have a HELLUVA lot more energy built up to slam into the next gear with. And if you put your finger on the outer edge as hard as you can to stop it like you did with the pinwheel, you're gonna need a bandaid


If you slam your "pinwheel" into gear, not much is gonna happen because it doesn't posess very much inertial energy. The pinwheel is pretty much gonna stop.


Now slam your SOLID "ROCK wheel" the same size as the pinwheel into gear. You have a TON more inertial energy built up and you'll actually move (lurch!) when going into the next gear.



Does this make more sense?


So with the OE flywheel you'll get slightly less acceleration in the gear, but more LURCH when slamming into the next one.

With a lightened flywheel you'll get a little more acceleration in the gear, but less LURCH when going into the next one.


I'm pretty sure I'm explaining this right....

Y2KevSE

iTrader: (13)

http://forums.maxima.org/showthread....light=flywheel

SteVTEC

IceY2K1

iTrader: (3)

I just didn't understand that the "Engine Free-run Deceleration Rate" included the benefit of lower inertia on the acceleration component. It just sounded like a RATE of change for once the clutch disengages NOT change for decreased inertia under acceleration.

Also, if an UDP frees say 3-5hp throughout the curve by dropping 3-6lbs., then a flywheel that drops 12-13lbs. is going to make a NICE difference.

Threads for your enjoyment:
http://forums.maxima.org/showthread....lywheel+pounds

http://forums.maxima.org/showthread....light=flywheel

P.S: I don't feel like regurgetating what they said so I'm going to take the lazy way out and just let you read their thoughts on the matter.