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Larger wheel diameter - slower acceleration

Skylarking

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... If you watch any youtube videos about dyno tuning you will note that the ones that know there **** will mention the effect of rotating mass of the rear wheel effect on power output.
Yes its a high moment of inertia issue. Heavy clutch, rims and tyres with much of the weight away from the rotational axis will impact how quick things can spin up. But, although a high moment of inertia will impact the transient power delivery, it does not change steady state (or instantaneous) power delivery.

One example of an engine in which insane levels of design and build effort went into reducing parasitic loss, rotational mass (moment of inertia) and other power robbing issues that slow the engines transient responce was the Lexas LFA. It can spin up from idle to 9000 rpm in less than 1/2 second according to this megafactory video, see the 26:24 minute mark. I think that it's this engines ability to deliver such a high transient responce, when coupled with a light vehicle, that would make for a very responsive pedal on the road. It's a full on quick machine around the NB track.

What does this mean for our commodores? Well, buy a set of Aussie Carbon Revolution wheels (19"x8.5" at 7.8 kgs each) and a set of brembo light alloy hat floating disc brakes (at ? kgs each) can't hurt anything but the wallet :p F1 styled clutch, even more so :eek:
 

rognvald261

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@Skylarking Brembos expensive, not Australian and on several points not as worthy as the Disc Brake Australia 5000 Series.
 

Skylarking

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@Skylarking Brembos expensive, not Australian and on several points not as worthy as the Disc Brake Australia 5000 Series.
@rognvald261 I know Brembos are Italian, so should have made that clear rather than being slopping in my wording.

Interesting bit from Carbon Revolutions web page is:

"ACCELERATION & BRAKING — Less weight means less work, with lightweight wheels reducing the rotational inertia of the drivetrain components. A simple swap to Carbon Revolution wheels will reduce unsprung weight, while generating better acceleration and deceleration. The improvements in lap times seen on the racetrack from fitting lightweight wheels would require significant engine upgrades in order to achieve the same results.

DYNAMICS — Lightweight Carbon Revolution wheels will enhance the suspension’s ability to maintain contact with the road surface, improving traction and driver control. Through a significant reduction in wheel inertia, the steering feel and chassis response is also quicker and sharper, making the car more predictable and controllable."
 

Anthony121

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Following on from this. I now have all 3 types of the VF Redline 19" staggered rims

Their are subtle differences between the forged MY15 and cast MY16/MY17 Redline rims like, weight, spokes are thinner and slightly narrower and the paint finish on the back of the spokes (which you can't see when on the car).

The MY14 VF1 forged are slightly lighter around 500g then the MY15 forged. The MY16/MY17 are around 2.5kg each more heavier. According to my dodgy home scales.


MY14 VF1 19" Redline, Alcoa USA, forged:
View attachment 203177
View attachment 203178

MY15 VF1 19" Redline, Alcoa USA, Forged:
View attachment 203179
View attachment 203180

MY16/MY17 VF2 19" Redline, Cast, made in Thailand:
View attachment 203181
View attachment 203182

They are the same as I have. The Forged wheels are a tiny bit different than the cast. On the car you wouldn't know.
 

rognvald261

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@Skylarking still trying to get my head around the Yamaha / Toyota V10 F1 engine going 950 -> 9000 in 0.6 secs, when I came across this
Thing is our car can do that, just against GM’s controls for engine protection. Specifically there is a little-known calibration under engine protection called Rev Limiter Accel Modifier, which is a proven rate of engine acceleration for the stock build, presumably safe enough to satisfy warranty expectations.
Needless to say I zeroed that out :)
 

Skylarking

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^ Yeah, seen that before and it's way cool though it always reminded me of the buzzer on old Motorola 8080 computer being controlled to simulate music. Redbull must have had some old hats around :p

As for the Toyota/Yamaha V10, it wouldn't surprise me that it also has some version of Rev Limit Accel Modifier within it's ECU. Thing is this engine can accelerate from idle to redline in 0.6 seconds without issue and safely protect its warranty status while repetedly doing such ;) That's because the engine was designed with low parasitic loss (low friction seals and bearings) and low moment of inertia (itsibitsi flywheel and clutch and probably small torsional damper) with strong internals. Thus the V10 is miles from the LS3 design (as it should be considering cost). The LS3, which without the Rev Limit Accel Modifier, would almost certainly not be as quick to sping up as the V10, and the warranty would be unsafe while repetedly doing such.

As a counter thought, could Rev Limit Accel Modifier also have some pollution control aspects to stop too quick an engine deceleration which may cause a spike in NOX?

I'd love to learn more but ECU programing and all the parameters one can play with but where to start is the problem, any pointers?
 

Immortality

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I think the problem is with anything LS onwards it's not cheap to just get the software to learn about tuning, not only that but to actually tune a car you also need a license and with the latest models you need a license for the PCM and another for the TCM.... it really is a money making scam from certain tuning companies.

Having said that, the boys at the PCM Hacking website are working on a free software option that's looking real promising.
 

rognvald261

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@Skylarking I think the combustion and emissions would be fine given the design and compression ratio, snap decel blip is likely answered with clever valve control.
Worth pointing out that the SS V8 with GM mild performance cam (even Walkinshaw or Harrop) all make same warranted power at 2/3 the RPM. But the real stinger is of course comparing torque, LS delivers up to 50% more with mild cam.
Regarding tuning, easiest way is to buy a handheld for $1200 (comes with two VIN licences), and install a wideband controller $500. Yeah not cheap but easy to find second hand for our car with wideband and a VIN slot available ~ $750.
From there basically explore the stock tune, compare it to model and drivetrain variants. First mod might be as simple as upping the idle or lifting the stationary RPM limit a bit.
There are dozens of manuals and guides and forums and videos and interactive tutorial workshops to guide you through specific areas.
Is pretty much as easy as learning spreadsheets and macros for first time.
 
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