Overall Gear Ratio for boosted car
 

Hi guys

I've been lucky enough to get a second-hand Holinger sequential six-speed for a good price. With the internal 1.3:1 drop gears the overall gearbox ratios are as follows:

1st - 3.157
2nd - 2.294
3rd - 1.755
4th - 1.357
5th - 1.144
6th - 0.963

So it basically a little taller 1st gear (vs 3.626) and a shorted 6th gear (vs 0.767) gives me a close-ratio gearbox.

With a stock 4.1 diff that gives a top speed of 210km/h @7000rpm.

I have an opportunity to change either the internal drop gears or the diff ratio to change the overall drive ratio, but swapping gearset in the transmission is not cost effective.

The car is turbo'd with 240kW at the wheels. The car is dual-duty track car and daily driver. The aim is to try and get to full revs (or close) in 6th gear.

What sort of top speeds can a 240kW car get to? Is 210km/h @7000rpm (225km/h @7500rpm) too short an overall ratio? Views and opinions please.

It depends on the track. Have you considered maximizing 5th instead?

The longest track I'd likely run it on is Phillip Island in Melbourne Australia. You enter a 900m straight at about 145-150km/h. It's slightly downhill and a stock 98 can get to maybe 210km/h which is about max RPM on 5th. I haven't drive this track yet and it would be infrequent only.

The longest track I'd run routinely would be Sandown in Melbourne also. Top speed of a stock 86 is maybe 185-190km/h which is maybe 6500rpm in 5th.

The stock engine is out of puff in both cases here.

What I don't have a feel for is the extra top speed of 240kW ATW. Will be a while before I can get another track day in after the turbo install but the gearbox will be available in a week or so. Just hypothesising if I should change the drop-gears whilst its being installed and or the diff ratio (I'm doing an LSD install at the same time). I definitely don't want to change diff ratios once the LSD is installed but changing the drop gears in the transmission is only 20 minutes (once the gearbox is out).

you will be hitting 260 easily at Phillip island. my box is going to run out at 250 with my gearset on the 4.1 rear gears. you can get 3:71:1 for 1500 here.


https://neatgearboxes.wordpress.com/...561-and-3-731/

So what power does you car have to support a 250+km/h top speed? Just want make sure we're comparing apples here.

Looks like my gearing will be short (for Phillip Island at least) but probably OK for other tracks and street. Problem is that if I put in a taller diff or drop gears then getting off the line in my taller-than-standard 1st gear will get even harder.

Gonna try and do Sandown this weekend (first time on track since turbo) with the stock gearbox and diff and will know more from there.

mine has 331 kw at the wheels. a bit more i know but phillip island is 900m after 150kph, and you have a shorter ratio box.

i havent run at phillip island, bit it will do 210 past the kink at wakefield park and thats much shorter..

my gears
http://www.ft86club.com/forums/pictu...ictureid=10575


i think you will need to do something cos 210 is not good enough for most aussie tracks at high power.

in an NA 86 i enter turn 1 at 185kph at eastern creek.

you could always raise the rev limit for 6th to 8500, that could help you.

8500? Oiling ..

I assume Surok is being ironic

Actually I wasn’t aware that these cars are so fragile.
I run mine to stock RPM redline, but on most other engines with different valve springs 8500rpm is quite easily attainable.. that said, they were inline 4s.

It should t matter once a lap for 2 seconds

Stock rpms are already not exactly lowest from among modern engines, so i'd rather say that lot of capabilities are already used out-of-box. While many regard twins engine as not powerful enough, it actually is very good one, getting NA 100hp/lr AND still under modern smog standards, which is no small feat, so imho it can be lined up among other best 4-bangers of past, which may have produced more power but also being stringed by less harsh eco standards. One thing is mod shit out of some deforced engine, and another to get more from already close to limits one. I have seen slightly rised redline in many tunes, by 100-200rpm, but >+1000 seems certainly out of reasonable rise bounds, even on built engine. Oil pressure is what will limit it most. For safe prolonged very high rpm use one needs it to be completely reworked. No clue if it's possible on these.

240 kw to the rear wheels should redline 6th on a stock car with room to spare. When I get back to my laptop on Monday I can offer theoretical estimates as I have a spreadsheet for top speed > hp required > rolling resistance > aero resistance.

What other engines can you extend the rev limit by 1000rpm with everything else being stock and it be beneficial for performance?

the response above explained it, seems we have some limitations with oil flow due to the oil pump.