Top speeds...G/boxes

Matatak · Post by **Matatak** » Wed Dec 26, 2007 12:33 am

is there a way to work out the theoretical top speed of G/boxes knowing the ratios and that stuff...

or ne actually no?

eg. wts the top speed i culd acheive with my car and its current 4 speed 3.7 Box? (running in High obviously lol)
say compared to a 5 speed 3.7?

tyres obviously matter to coz i can notice changes in the revs to the speeds i do with different tyres on. so if any1 knows how to work it out for me then presume 27" tyres.

Cam · Post by **Cam** » Wed Dec 26, 2007 1:17 am

yeah get the speed at x revs and then use the ratio to work out what it'd do at redline.

Or if you know the ratio's of each gear, work the engine revs through first box ie 0.9 then diffs 3.7 then using this calculated revs at the axle work out the distance traveled each revolution of the tyre, (circumference) ie 2 metres and multiply them.

Pretty sure that didn't make sense but someone else may be able to explain better

My old My 4 speed did around 150-160 max but that was behind a worn out ea82...

Matatak · Post by **Matatak** » Wed Dec 26, 2007 1:28 am

so if my car, in 4th High with the 4speed box does.
3000 at 100km/hr
4000 at 140km/hr
then can i presume around 5000rpm is like 180km/hr
which wuld mean i culd get to virtually 220km/hr doind 6000 before it gets onto actual Rev limiter of the EJ22

i recently went down tyre sizes by a little bit but i used to get 4000rpm at 150Km/hr. which possilby means 250km/hr...kinda unbelievable for my car

brumbyrunner · Post by **brumbyrunner** » Wed Dec 26, 2007 6:23 am

have a look here http://www.4lo.com/calc/gearratio.htm
Fill in your diff ratio, tyre height & rpm and each gear. Make transfer case 1:1

PeeJay · Post by **PeeJay** » Wed Dec 26, 2007 9:15 am

Put car on jack stands, take wheels off.

When I had my MY wagon in RWD I managed 195 in a Kmart carpark!

Phizinza · Post by **Phizinza** » Wed Dec 26, 2007 9:54 am

With the low power from the Subie engine its wind resistance thats going to stop you going fast. Gearing won't help there.
Its simple, 0RPM on the engine is 0kph. Just say 2000RPM in top is 60kph, then 4000RPM will be 120kph. 6000RPM is then 180kph.

dfoyl · Post by **dfoyl** » Wed Dec 26, 2007 10:01 am

>>With the low power from the Subie engine its wind resistance thats going to stop you going fast

Absolutely correct. I know a few of the USMB guys could get to higher speeds in 4th than in 5th, simply because the engine couldn't push the car along in 5th gear at 160kph+. This was with EA81 and EA82Ts, with the extra power of the EJ22 you might be ok...

Dean.

Post by **Alex** » Wed Dec 26, 2007 10:28 am

bahaha matatak...i know exactly what got you thinking about this..was it when we where pushing 190km/hr the other day?? l-series 5speed box FTW

alex

Matatak · Post by **Matatak** » Wed Dec 26, 2007 12:38 pm

Alex wrote:bahaha matatak...i know exactly what got you thinking about this..was it when we where pushing 190km/hr the other day?? l-series 5speed box FTW

alex

yes that it was

lets find that commonwhore again:twisted:

Phiz - im pretty sure i culd make it there. i still had plenty of power left to accelarate with the 22 pushing me along....just need the time to get there
and wt i said before is wt my car actually does at RPM to Speeds..so i wuld be right in thinking i culd get 220km/hr...

so if my car, in 4th High with the 4speed box does.
3000 at 100km/hr
4000 at 140km/hr
then can i presume around 5000rpm is like 180km/hr
which wuld mean i culd get to virtually 220km/hr doind 6000 before it gets onto actual Rev limiter of the EJ22

i recently went down tyre sizes by a little bit but i used to get 4000rpm at 150Km/hr. which possilby means 250km/hr...kinda unbelievable for my car

Peejay - i did actually try that once....didnt actually work aswell as driving on the road wuld.

the revs to speeds im qouting are form my speedo and tacho. not from a GPS.

Phizinza · Post by **Phizinza** » Wed Dec 26, 2007 4:57 pm

Matatak wrote:3000 at 100km/hr
4000 at 140km/hr

4000 should be 133.3kph if 3000 is 100kph. Think about it. 0RPM is always 0kph. There for 1000rpm on top of 3000rpm should be third of the speed you were doing extra. As 1000rpm extra is a third of 3000rpm.
I got my brumby to 160kph with standard OD tyre size and the EA81dc. I don't think she'd do much more then that now with the 2.2. I'm doing 2750rpm at 100kph. She just doesn't want to push through the air happily over 140kph.
But she gets to 140kph pretty quick.

PeeJay · Post by **PeeJay** » Wed Dec 26, 2007 5:03 pm

I didn't have a rev counter, and the speedo went off the end of the dial!

Matatak · Post by **Matatak** » Wed Dec 26, 2007 5:16 pm

i dont have a dial

and i have a tacho which may or may not get to 9999 if the engine culd

wts the end of ur dial ??

PeeJay · Post by **PeeJay** » Thu Dec 27, 2007 8:19 am

180

.....

90brumby · Post by **90brumby** » Fri Dec 28, 2007 6:07 pm

the 5sp box and 4sp box top gear is the same 4th gear in the 4sp is od and 5th in the 5spd is the same ratio

u basicly get a 3 1/ gear so tp speak like theres an extra gear in the 5spd its between 3rd and 4th

if that makes sence

inflames83 · Post by **inflames83** » Wed Aug 06, 2008 2:06 pm

I have a 4 speed 1984 wagon and have done 160+, not sure of revs though. Around 5000 I think.

YouTube · Post by **El_Freddo** » Wed Aug 06, 2008 2:52 pm

I've heard this about the 4 and 5 speed's top gearing being the same but I'm not so sure about that now - The brumby has 3.7 diff ratio, as does my L, yet at 100km/h the brumby is at about 2750RPM and the L is 3100RPM. If that's the case, how is it possible that the final gear in each box is the same ratio?

We're both running 13 inch rims with 175/70 tyres from memory.

Cheers

Bennie

discopotato03 · Post by **discopotato03** » Wed Aug 06, 2008 3:24 pm

I wouldn't want to be you in a Brumby if you came unstuck at 140 -160 . Your not going to walk away from that - you know that don't you ?

Just to be on topic most auto people think in terms of MPH or Km/h per thousand revs in the highest ratio .
An RX L series (std ratios/wheel size) is around 3000/100 or 33.3/1000 RPM .
Mine has the L carby ratios with the ~ 11% shorter 5th so ~ 3000/90 or
30/1000 rpm .

205/50/16's will get it a bit closer to std later .

A .

Suby Roo · Post by **Suby Roo** » Wed Aug 06, 2008 3:39 pm

I managed to get my old L series Up to 180kph on 195/65's.
Ea82 FTW!!!