hfm

iTrader: (1)

Finally got my UR pulley installed. Butt dyno, definite gain in torque and probable gain in hp. I will have to redyno to confirm the gains.

Besides the obvious gain in power, there is a clear loss in engine braking. If you're used to downshifting to slow your car down, and you have a lightweight flywheel, you will notice a substantial loss in engine braking. Add the UR lightweight pully and it's compounded. I notice very little engine braking when downshifting.

This may or may not be a good thing at the track or on the twisties but I really did like engine braking to slow the car down to save my brake pads. That's pretty much is tossed after these two mods.

Whatever the case maybe, there are significant gains with the UR Pulley. The fact that I can feel the difference suggests a 10 hp/5-10 ft/lb gain in hp/tq. But, bear in mind the trade off loss in engine braking if that is something you like.

I'll post a dyno sheet whenever I can get back to the dyno shop.

jreiter

iTrader: (6)

I've heard a number of people say this about the lightened flywheels so far, and I seem to be having some trouble wrapping my mind around it. My logic keeps telling me engine braking should be improved when removing rotational inertia, not diminished. I would think that when you have a heavy flywheel spinning along when you take your foot off the gas, the rotational interia of that flywheel would try and keep the engine rpms from falling, and would thus diminish the engine's ability to engine brake.

But when you greatly lessen that rotational intertia, it would seem that the engine braking would be much less hindered, and would thus be improved. Didn't Raceboy make a post a long time ago saying exactly this after putting in his lightened flywheel?

Not saying I don't believe you. I'm just trying to understand the physics going on. It's not making sense to me. Can I ask you a question? When you say engine braking, do you actually mean the braking that happens when you downshift then let out the clutch without rev matching?

infidsg35

iTrader: (2)

Umm this info about the Light Flywheel is WRONG!! I got the JUN lightweight Flywheel and when you downshift the RPM go down much quicker. When you have the stock Flywheel it has more weight and will hold rev better because of force. When you lighten it it doesnt have as much force and you will loose RPMS faster. Im sure the UR Pully does the same thing but I can say yes or no for that as i dont have one...

hfm

iTrader: (1)

When I say engine braking, I mean if you're in 3rd gear and downshift into 2nd the car will slow down as the revs will jump up from say 3,000 rpm to 4,500 rpm. I'm talking about the slowing down of the vehicle by shifting from a higher gear to a lower gear.

Infidsg35 is correct that the rpms will go down quickly but the car does not slow down quicker as a result.

The way I see it is this lack of engine braking is the opposite effect of acceleration. With reduced rotational mass and rotational inertia of the lightweight flywheel and pulley, accelleration and throttle response is increased because there is less resistance to the change in speed of rotation of the driveshaft.

With a stock flywheel/pulley, the revs drop slower giving the car time to slow down due to the effects of the engine load. With a lightweight flywheel/pulley, revs drop faster and less time for the engine to slow down the car takes place.

Here is a site that discusses the acceleration but not the effects of engine braking. http://www.nissanperformancemag.com/march03/ask_sarah/

I wish D'oh! or some other engineering types could explain this better.

Regardless, this is the effect that I'm reporting.

FLY BY Z

HFM, my findings coincide with yours.

https://my350z.com/forum/showthread....ywheel+braking

https://my350z.com/forum/showthread....g&pagenumber=2

https://my350z.com/forum/showthread....ywheel+braking

hfm

iTrader: (1)

Wow Fly! Zzzya and your experiences are consistant with mine. I was reading that last thread and the discussion got a little heated. My experience concurs with yours.

Here was my first impression. Note how I originally thought the car was slowing down quicker. I subsequently changed my mind after more time driving and found that engine braking was 30% to 40% less than stock.

https://my350z.com/forum/showthread....204#post473204

Add a lightweight pulley to that lightweight flywheel and the percentage is even higher. I would say engine braking is now 70% to 80% less than stock.

What is amazing is how many people don't understand this experience.

It is clear to me is that by reducing the rotational mass of these drivetrain components, acceleration is improved but engine braking is reduced. Your experience does coincide with mine. Thanks for your post.

FLY BY Z

The way the revs move now, I can be cruising along, fast or slow, take my foot completely off throttle, put in the clutch quickly, and the revs will jump or keep rising about 500 RPMs just from being released from the drivetrain! It just wants to go up now!

NismoKid

How much easier does the engine rev with both the lightweight flywheel and crank pulley?

hfm

iTrader: (1)

It revs up to redline quite a bit quicker and the car goes slightly faster. Acceleration is definitely improved.

350ed

iTrader: (17)

So to clear things up for my simple mind:
1. Cruising or end of accelerating, foot off throttle, foot on clutch, revs don't drop? Not too good for rev matching your upshifts.

2. In gear, around 5k or so rpm, let off. Does it take much longer to come back down?

3. When dropping the clutch or not rev matching now, is it less violent due to the less mass?

Thanks!

FLY BY Z

Foot on clutch, meaning clutch pedal in, revs drop nicely. If you have the clutch out (engaged) and coast, that's when the drivetrain has an easier time propelling the car forward and there is less actual car braking due to the engine compared to a heavier flywheel. If the clutch is in, the engine drops easier.

Jason@Performance

iTrader: (11)

hehe.. i remember going back and forth on this with fly by...

if i take my foot off the gas with my flwheel and clutch set up it is like hitting the brake...

oh wel..

FLY BY Z

I had forgotten about that last post. Kind of embarrasing that we would get into arguments like that. I'm sorry.

NismoKid

Jason, do you have the Tilton setup or is that Jeff? If not, what clutch and flywheel combination are you using?

D'oh

Here are my thoughts, but I don't have any of those mods so I can't say for sure what will happen.

First, lets talk about gains.

When you reduce rotating inertia, you are not actually making the engine stronger, but you are reducing the amount of force required to spin up the drivetrain. This means that you will free up some horsepower, and the amount you gain will depend on how fast you are spinning up the components. So, in first gear you will see a much larger gain than you will in 6th, since in 6th gear you are accelerating the drivetrain much more slowly. Now, since most perfromance driving takes place in 2nd and 3rd gear (AutoX, track, strip) with a bit of fourth, these mods should certainly help improve the acceleration. If you were going for top speed however, adding these mods wouldn't help nearly as much since now you need the power to overcome air resistance at an essentially constant speed.

OK, now my take on engine braking/rev matching. First, since the inertia of the system has been lowered, I would definitely expect the throttle response and revability to be improved. It sounds like pretty much everyone agrees on this. Should make it easier to rev match since you don't have as much of a delay.

For engine braking, I can see that their might be two methods that could have different results.

Method 1 is to go from a higher gear to a lower one (4--->3) and letting out the clutch without matching revs. In this case, the lighter flywheel should REDUCE engine braking because when you increase the RPM quickly when letting off the clutch, you are no longer spinning up as much inertia and therefore the engine can reach the new, higher RPM more easily.

Method 2 is either to go from a higher gear to a lower one WITH a rev match, or to just let off the gas while staying in gear. In this case, you are using the engine braking to slow the mass of the car, but you are not changing the rotational speed of the engine at a great rate (at least not like you would be in method 1). In this situation, the lighter flywheel will again reduce the inertia that needs to be slowed by the engine and should therefore INCREASE engine braking. However, engine braking typically occurs at a relatively slow rate, and just as in the case of accelerating in higher gears, the change in inertia won't have as much as an effect.

I can therefore see how many might not notice the slight (theoretical) increase in engine braking in method 2, especially when using a higher gear, but would notice the more significant change in method 1, while others may have expected the slight increase in braking, and have been rev matching, and therefore noticed something different.

Anyhow, maybe my theory is complete crap (hey, it's been known to happen) but maybe that is one explanation for the two different opinions.

Later,
D'oh!

350ed

iTrader: (17)

Yeah, it's weird how the different setups perform. You would just expect the Tilton to amplify the JWT/Nismo fly effect. I heard that with F1 cars when they let off the throttle, the engine braking effect is worth 1.1g! Thats better than a normal car can brake
Course their flywheels are under 4" versus ~7" for the Tilton, and double the rpms.

jreiter

iTrader: (6)

This is exactly what physics would dictate and what seems totally logical to me. I think what some of the disagreements might be are simply in terminology. Here's my take on it:

When I think of engine braking, I think *only* of when you let off the gas. Engine braking has nothing to do with the clutch.

When you downshift without rev matching, though, letting out the clutch does definitely slow you down quickly. But this is not engine braking. I suppose you could call it flywheel braking. (For lack of a better term?) The heavier your flywheel, the more braking it provides as you are letting out the clutch. Conversely, the lighter the flywheel the less of this braking effect is felt.

Given all the above explanations, this is why I would consider a lighter flywheel to increase increase the engine braking effect (even if just slightly). Of course, there could certainly be more to it that I'm not considering, but I just can't think of any other factors in this particular situation.

jreiter

iTrader: (6)

I wonder if that might partially be due to the extreme downforce that all their bodywork provides. Sort of like in my old pickup, which had really bad aerodynamics. If I was doing down the freeway at 80 and pushed in the clutch, it really slowed down quickly. In my Z, if I do the same thing it doesn't slow down very quickly at all. I'm guessing this is largely due to the fact that the Z has much, much better aerodynamics than my pickup had. (Which is why my Z can also have a bigger engine and more power than my truck had, but still get better gas mileage.)

hfm

iTrader: (1)

Grr. I'm breaking a rule, I'm posting after drinking. :P

First, I have no doubt that Jason has a different experience that Fly and I. If he says he lets go of the gas on the Tilton and drops from 4 to 3 and gets a brake response. I believe it.

On the other hand, I have no doubt with the Jim Wolf LWFW that if we let go of the gas and drop from 4 to 3, there is very little engine braking. I know it.

Thank you D'oh! for making your response. I will have to read it again tommorrow because I don't understand method 2. Ah, nevermind, I re-read. Yes, this is correct. Method 1 is the standard downshift. Method 2 is a quirky rev match downshift that I would never do. My experience is just to downshift without rev matching. So, from 4 to 3 which would take 3,000 rpm for example and bump it up to 3,500+ when the downshift is made. Very little engine braking takes place with the lightweight mods.

Thank you D'oh for posting.

jreiter

iTrader: (6)

Once again, I really don't feel that downshifting without rev matching then letting out the clutch constitutes engine braking. You're absolutely right that if you have a lightweight flywheel then downshifting without rev matching won't slow you down nearly as much as it would with a heavy flywheel.

Engine braking is when you simply take your foot off the gas pedal. Ignore the clutch pedal, leave it engaged, don't shift. Just take your foot off the gas. Does your car slow down more or less with the lightweight flywheel? I believe what Jason@Performance is saying up above is that, in this situation, his car slows down like hitting the brake. This makes perfect sense.

Ugh, I give up. I think we all agree on the simple physics of it. We're really just having a terminology debate.