To the experienced blokes, what diff ratio would you recommend? Aim is to just hit 7000rpm at the end of the main straight, in 5th gear of course. And what genuine maximum speed have you got up to there?
What Wheel and tyre size is being used, and what is the ratio for top gear .. I have an XLS that will help calculate diff ratio. I have a 970kg 1972 sports car wth ~440hp at the flywheel and I'm pulling 7000rpm with 1:1 top gear (Holinger) and 3.08:1 diff on 290/625R16 slicks. Calculation is 166mph or 270kph. I hit the rev limiter about 70 metres just past the start/finish gantry. The Z32 has a bit more frontal area and therefore drag and is heavier, so unless you have a solid 350Kw+ atw, you might struggle to replicate that. The slot car does similar laps times to me so I'd anticipate similar Vmax given it will be a bit more draggy with the wing. If you are planning (plotting?) for Easter next year, I'd work on gearing for ~250-260kph on the assumption you have enough torque and revs to generate the power to overcome the drag. Let me know what sized rear tyres are fitted and 5th gear ratio and I can tell you the diff ratio required by return. RB
Assuming 285/30R18 rear tyre, @ 7000 rpm in Z32 5th (0.752:1 ratio), with OEM diff 3.692:1, speed is 186mph or ~300kph With 3.9 diff gears, is 176mph or 285 kph With 4.1 diff gears, is 167mph or 271 kph Suggestion is 4.1:1 diff gears are the way to go .... or maybe 3.9 as next step. Maybe check with John P as your garage indicates a "healthy" engine spec. Note that the limit for Vmax is usually entry speed onto the straight and that is all about levels of grip and speed carried thru the turn .... T12, T1 and T3 and T8 are all balls-out high-speed turns and are the key to a quick laptime. It is easy to lose a second in each of these corners (alternatively, it is the place to pick up time).
Rear tyres are 255/40 17, standard Z32 gearbox, present R200 diff ratio is 3.9:1. Top speed at Lakeside is 210+kph but of course L is a lot different to PI. I'm told that my (avatar) car should enter the PI straight flat out in 4th
Richard ... 255/40R17 with 3.9 equals 288kph at 7K rpm which will be overgeared. Flat in 4th will be 230kph which I suspect is just a touch optimistic ... more likely you'll be at 6000 rpm in 4th which is ~200-205kph. The gap between 4th and 5th is significant and I doubt that the torque will be sufficient to max out in 5th before you run out of straight at T1. 4.1:1 diff will give you max rpm exiting T12 onto the straight and then it 5th and pedla to metal for length of the straight. I still suspect that the car might struggle to pull 7000rpm as even with 4.1:1, this implies 275kph - but this matches my own race car experience - so I'dreckon this is the best option. Wykked and Tekkie have run PI a few times and can provide some empirical feedback. In my Z34 DD, admittedly with only 215Kw atw (NA not TT), I lap quicker by leaving the car in 5th and running to 7500rpm and not using 6th as the gearing is just too high for the engine to push it aginst the air-drag over 220-235kph. My data logging shows highest speed ever into T1 braking zone was 239kph .. now with more torque, you;ll improve on that, but not a lot over 275kph I;d have thought Rgds Robin Bailey
Thanks Robin, not too worried if the Z won't pull 7000 in 5th because the power curve is flat from 6 to 7 plus the engine develops good torque from under 4000 up. More concerned about over revving, it will be the first time at PI so the main aim is to have a fun day.
I changed from 4.375 to 4.1 (R200) diff for P I and was around 270k's top speed, maybe a bit more as over 7,000rpm, with about 380rwkw and standard gear box. 3.9 is to tall and even with big power and maybe hit rev limiter towards the end of the straight, it would be slower the rest of the track. Now I have a PPG straight cut gear set which has a shorter 5th gear and more power I should change to a 3.9. http://www.gtr.com.au/downloads/temp/PenFlyBy.wmv
I sold off my 4.11 gears. IMO the 3.9 diff is the way to go for Phillip island. Even my stock car with 3.9 gear set and only 250RWKW was reaching 245klm/hr. If you have upwards of 350+ RWKW you should reach 265 plus without throttling the tits off the car. Not everyone can or wants to rev to 7500 revs. Its not neccesary and way past the torque peak.
Thanks Tekky, that's good to know. My engine has been built to deliver a wide power band and good torque so gear ratios are not crucial, makes it a bit more friendly to drive too.
Hopefully when my car is finished ( before the nationals maybe) My power band is going to be not overly wide. 2860's R5's 2.5 inch pipes 1mm oversize valves ported heads big manifolds dual 3 inch system Should have 400+ RWKW @ 20 PSI Hopefully I am on full boost by 4200 The 3.9 diff will be all I need.
I've been told that even if my car is not done I have to get it in a state to enter at the Nationals so you should be able to as well.
Hey Tecky 3.9 is for cruisin. The last bit of the straight is less than 5% of the track, it is a trade off. 4.1 is ideal for the whole track. If you have really big power and good torque down low, then maybe 3.9.
Cruisin will do me But being the honest fellow that I am my Z should weight less than 1200kg with driver by the time NDN13 comes up, hehe.
The road car is gone, the only z32 I have now is the race car I bought partially built 4 years ago. I have been stock piling parts and are close to building it now. Somewhere deep down in the build forum I posted up the details, so if you are interested do a quick search in there.
Weight is the key isnt it. JP threw down the gauntlet 2 years ago I couldnt get close to 1000kg without driver. He reckons it cant be done. He shouldnt have done that cause he is gonna eat his words
yeah, but when I go past you after you have pegged out your engine revs. I want to be able to look back and poke my tongue out at you.
Love to see that. 1100kg with a cage is dreaming. With VG in mine I got down to 1230kg, still has heavy stock tailgate, so can get under 1200kg. With no fuel and with the VQ it is just under 1200kg.
Not 1100kg.................... 1000kg, You got a FAT ASS 2+2 Targa JP. Theres 100kg straight off. Most of the steel forward of the front axel in mine is gonna be gone. She will be a skinny biatch. Plastic windows. plastic doors and hatch Plastic guards Head lights removed radiator support panel and track rod supports removed, and mount points redone in alloy. Rear wheel well inside guards removed Rear light and hatch supports ripped out Double skin in front of fuel tank cut out Bonnet support frame removed and made one pce with nose cone attached. spare wheel well and boot floor cut out and replaced with alloy. manual steering (no pump) steering column replaced with one pce Fuel tank halved and rewelded. Alloy side mounts and pipes Driver and passenger floor cut out and replaced with alloy Exhaust exits on the sides (So short pipes) swiss cheesed to an inch of its life. PLASMA CUTTER IS GOING INTO OVERTIME. 1000KG man............
