350zQ45a

Brilliant

Diesel350

iTrader: (6)

Makes sense.

Nano

iTrader: (1)

yeah, nice... unfortunately, doesn't quite work that way. You are forgetting about the gearing...

even though your power may start to decline after redline, you are still putting down more torque at the wheel in 2nd gear redline than in 3rd gear engine peak power. so you NEED to shift at redline(6600) to get the best acceleration possible. At some point, the engine power will drop so much the higher gear will put down more torque.. but this comes well after 6600rpm(with some bolt-ons, I say easily after 7200rpm). Nissan Engineers did their homework... If there was only loss in performance and loss in engine life above 6400, they would have placed it at 6400.

In case some of you haven't noticed... the car accelerates faster in 1st gear at 1000rpm than in 5th gear at 6200rpm.


BTW... what is this secret mod? Have stormed through 14 pages and I am still puzzled. I seem to understand that it's some modified 287hp part adapted to the 300hp engine???

DaveO

No, I didn't forget about the gears.

Feel free to rev your engine as high as you'd like.

I'm quite sure that most of us have noticed there is a difference in acceleration in the various gears at the same rpm.

And yes we did complete independent tests of the Motordyne Engineering MREV mod on two Rev-up engines.

GEE PASTA

[QUOTE=Nano]yeah, nice...
In case some of you haven't noticed... the car accelerates faster in 1st gear at 1000rpm than in 5th gear at 6200rpm


You got that right! My friend

Nano

iTrader: (1)

From what I understood from your post, you said you where shifting at 6400 rpm because there was no point in going above that...

I thought that was missleading. To get maximum acceleration(and performance) out of the car, you need to shift at redline whenever possible. Anyone is free to shift at whatever RPM he prefers, but claiming it's irrelevant to shift above peak engine power because the engine is not producing anymore power above 6200rpm is just wrong.

DaveO

Please re-read my original post. Nowhere will you find "shifting at 6400 rpm because there was no point in going above that... " or where I claimed "it's irrelevant to shift above peak engine power because the engine is not producing anymore power above 6200rpm... " What you will find is the words -- Here's what I'm doing.

As for my shifting method being "just wrong" we'll just have to agree to disagree on this matter.

You're welcome to rev your engine as high as you'd like... and I won't use words like "irrelevant" or "just wrong" as I believe you have the right to your opinion even if it is different than mine.

turbo-maxima

I guess it does not really matter where you shift in the Z because it has a pretty flat torque curve. If you didn't have a flat torque curve shifting at a higher rpm in lower gears would help you shift into a higher rpm in lets say 3rd or 4th gear where you could then take advantage of the torque curve, lets say if you had a linear torque curve. Sorry thats a really badly written sentence.

Nano

iTrader: (1)

Proper shifting technique has nothing to do with opinion or mood. IF you want maximum acceleration and performance you shift at redline. You want to shift at 6400 rpm for whatever mystical reason you believe in... fine. but saying:

"Even though I could rev my engine to the factory 6600 rpm or even the TS 7100 rpm redline I don't because above 6200 rpm the power is decreasing and the inertial loads are increasing expedientially. If my engine was still increasing power at a higher rpm, say 6800 rpm, I'd increase my shift point ("redline") to take advantage the additional power.

doesn't make any sense.... and sorry, to me it reads that there is no point in shifting above 6400rpm because the engine is not producing power anymore. Otherwise, WHY do you shift at 6400rpm? Unless the situation calls for short shifting, I don't see why anyone would shift at 6400rpm.

racin

iTrader: (1)

Nano, I'm sorry, but I will disagree with you. In reality, you want to shift into the next gear so that when you get into that gear, you are near the torque peak of the engine, assuming that you have reached the HP peak in the gear you are switching from,already. There is NO reason to shift a 287 HP engine above the HP peak. I shift the race car at 6300 rpm. With our new engine strategy, which includes our cams and the other parts and pieces that will allow the engine to make power to something just north of 7100 rpm, I will probably be shifting at something close to or just beyond that. It will depend on the track situation.

Shifting at redline for no reason other than to wind the engine out at peak stress is useless, and as was stated above, inertial loads are increasing exponentially (diminished returns), you are just wasting time.

The same holds true for the rev up engine, except that you will want to shift at or above the HP peak of that engine, to a point as close to it's torque peak rpm in the next gear....

Try it at the drag strip, and you'll see that shifting at a lower point (as stated above) will equate to lower times.

Xeinth

Nano is right. Its so obvious (outside special situtations), for straight line acceleration you need gearing, the torque gained from downshift by the engine is far less than the loss in gearing. Does anyone have the gear ratios and a torque vs rpm plot (in excel)? I'll make up a quick model showing torque at the wheels for each gear across the powerband.

You can use that to see the ideal shift points (i.e. all the crosspoints).

X

Nano

iTrader: (1)

I'm sorry you don't agree...but facts are facts.

Shifting so you will be at engine torque peak in the NEXT gear, does not equate to faster time and is totally meaningless. You want to maximize torque at the wheels, not at the crankshaft! As I said, 6600 rpm in 1st gear produces more torque at the wheel than 2nd gear at 4800rpm... how hard is this to understand???

I have more than 200 dragstrip runs.. shifting at redline (or very close to 6600 rpm) will yield the best times. I ran 13.9@101 bonestock and 13.5@105mph with few bolt-ons on street tires. I also track the car frequently on road courses.

Beside, what you are saying only makes some sense in higher gears. Shifting at redline(6600) in 1st gear will put you at 4000rpm in 2nd gear, still well bellow the engine torque peak. redline in 2nd gear puts you at 4600rpm in 3rd gear, still bellow peak engine torque. Shifting in 3rd gear and 4th gear will put you at 5000rpm in 4th and 5th gear. Gear torque multiplication benefits do fade off in higher gears as the ratio fade off. IN anycase engine peak torque and power are not the sole figures you want to consider when shifting for maximum acceleration... you want to maximize torque at the wheel.

= Engine torque X Gear multiplier X final drive) / Wheel radius

GEE PASTA

ExceptionsThere are no exceptions; a car running at its (net) power peak can accelerate no harder at that same vehicle speed. There is no better gear to choose, even if another gear would place the engine closer to its torque peak. You'll find that a car running at peak power at a given vehicle speed is delivering the maximum possible torque to the tires (although the engine may not be spinning at its torque peak). This derives immediately from first principles in physics.

However, note the following: - Transmission losses are not shown on engine power curves. The net power curve (power delivered to the ground) may have a different shape or even a different peak RPM as a result. This would result in different shift point. Best results are obtained from a power curve measured by a chassis dynamometer. - The discussion above assumes negligible tire slip. If you exceed the maximum traction available from the tires, then additional power doesn't help. That's why it's sometimes no loss at all to shift early when the tires break loose, and in fact it can be a benefit.

To the PointTorque and power are (almost) flip sides of the same coin. Increasing the torque of an engine at a particular RPM is the same as increasing the power output at the same RPM.

Power is just as useful and relevant in determining vehicle performance as is torque. In some situations it's more useful, because you may not have to play with gear ratios and a calculator to understand what's going on.

A car accelerates hardest with gearing selected to stay as close as possible to the engine *power* peak, subject to the traction capability of the tires.

Not all cars should be shifted at the redline for maximum performance. But it's true for many cars. You can determine optimal shift points by graphing horsepower vs. velocity or transmission torque vs. RPM. Engine torque alone will not determine shift points.

racin

iTrader: (1)

Well put, Gee... A better explanation than I provided.

Xeinth

Anyone without a degree in Physics or Engineering, please step away from the keyboard.

The fact that you make this statement,

You'll find that a car running at peak power at a given vehicle speed is delivering the maximum possible torque to the tires (although the engine may not be spinning at its torque peak).

as aboslute without considering gearing is quite telling. If you are talking about peak power to the engine, then your arguement is gearing doesnt matter, if you are talking about peak power to the wheels, then your not making a connection to engine power, thus your not arguing the benefit (either way) of pushing to the redline.

x

GEE PASTA

Quote:

Originally Posted by Xeinth

Anyone without a degree in Physics or Engineering, please step away from the keyboard.

as aboslute without considering gearing is quite telling. If you are talking about peak power to the engine, then your arguement is gearing doesnt matter, if you are talking about peak power to the wheels, then your not making a connection to engine power, thus your not arguing the benefit (either way) of pushing to the redline

Quote:

Originally Posted by Xeinth

.

x

Maximum Acceleration vs Torque
I'd like to think that torque is an intuitively easier concept to understand. If that were true, though, then more people would understand the relationship between torque, horsepower, and vehicle acceleration. In reality, none of it is intuitive. If it were, Newton wouldn't be considered the Really Great Guy that he is.

The classic mistake is to conclude that the fastest way down, let's say, a 1/4 mile drag strip is to keep the engine RPM at the torque peak (or as close as possible). The technique is usually stated as "shift just after the torque peak", or "shift N RPM above the torque peak so you are N RPM below the torque peak in the next gear when you finish the shift".

Unfortunately, *engine* torque does not tell you the full story. What matters is the torque *delivered to the tires, including the effects of the transmission. We all know a car does not accelerate as hard in second gear at peak torque RPM as it does in first gear. The transmission amplifies or multiplies the torque coming from the engine by a factor equal to the gear ratio. So to determine how much the car is accelerating at a particular instant, you have to know both the torque output of the engine as well as the gear ratio.

To figure out your shift points knowing only torque, generate tables of transmission output torque vs. RPM for each gear. To get transmission output torque, multiply the engine torque by the gear ratio. You are simply comparing gear to gear, so the final drive ratio can be ignored. You may also need to know the relationship between RPM in one gear and RPM in another gear (which is RPM * (gear2ratio/gear1ratio) at any particular vehicle speed.) Then it's easy to see what shift points to choose to maximize your transmission output torque at all times. PS I slept, at a "Holiday inn last night.

Xeinth

I agree with this 100%.... Does anyone have a Dyno plot, stock in excel format?

X

Glex25

iTrader: (11)

Here are my Dyno runs as promised.
They were done on the same Dyno on the same day.

My car is stock(no K&N Filter, no Ztube, No Exhaust) 100% stock



Baseline:




MREV Mod Installed with Throttle Heater Valve Closed:



Overlay of best of both Runs

dovla

I don’t understand. On same dyno today I made 242 HP with 234 torque. And I have 2004 G35 MT.

Glex25

iTrader: (11)

Maybe cause you have 1/2 spacer where i have 5/16 spacer.
Maybe Z-Tube and K&N filter add HP also.
Maybe 19" Wheels take away HP on my end.