24 replies to this topic

[mr5000]

trying to decide what gears for the 9 inch will be the v8 up front and aussie 4 speed behind it wheels will be 14 inch for now just wanna run some good quarter times before i build up the 355 but dont want it to top out to early was thinking maybe 3.55 ratio would work?

Edited by mr5000, 16 December 2009 - 05:23 PM.

[Heath]

Got lotsa options, I know they have 3.55 in 9" but is that actually a common ratio? I think 3.5s are very easy to come by.

I would probably go 3.25 or 3.5, or something in between like a 3.33 if you can find it. May as well put one on that you can use with both motors, and that can just hack the highways without being stupidly unpleasant

[ls2lxhatch]

You can check out the different rations using Gearcalc. Tyre size and profile can have a significant effect.

I think the M21 ratios are.

2.54
1.83
1.38
1.00

[TerrA LX]

get all your peak HP and peak torque figures then work out tyre roll out then gear ratio.

Im listening, so what is the secret?

[MRLXSS]

You'll want a 3.5 or 3.7 ask around at most carshows what people have in their torries, and most will tell you either of those.

If you are running an Over-Drive (5/6 Speed or 4-5 speed auto), Go 3.9 or 4.11!

[Heath]

do yourself a favour when you build your 355. Run it on the dyno ,get all your peak HP and peak torque figures then work out tyre roll out then gear ratio. Just takes the guess work out of everything.

I disagree, it all depends on your driving style and what you want from the car.

Unless it is set up for a certain race track or a drag strip, I don't believe there is one "right" ratio.

[rodomo]

But....but.....but.....
Ryan IS talking about 1/4 times.
I think what scottya! is getting at is calculating the mph over the 1/4 through the tyre/wheel size and ratios keeping the engine in it best power range.

[Heath]

Sorry I thought Ryan was gonna re-register it. If you are just gonna race it again and then swap the gears then go shorter and work it out that way

[ls2lxhatch]

The M21 will have a very short life expectancy behind a 355 on the strip.

[mr5000]

i am re registering it and m20 will no be going behind the 355 not that silly and i am re registering it and i wanna run as quick as i can with out it being un driveable on the roads

[wot179]

Buy a Moroso speed calculator. http://performancepa...oroso_89650.jpg

If you have already raced the car it will set you straight.

[Heath]

Dont worry about trying to save on weight in the car. Because at the end of the day, every 50kg you remove from your car, that equates to 1 tenth of a second gain over the 1/4 mile(not really worth the trouble)

[TerrA LX]

So a 1500kg car with 300hp will only gain 1sec over the quarter if i take 1000kg out of it?

[ls2lxhatch]

According to the calculator on this site a 1500 kg (3300 lb) 300 hp will run a 12.86 and a 500 kg (1100 lb) 300 hp will run a 8.919 which makes 1000 kg worth 3.941 seconds or 600 hp.

Taking 50 kg off a 1500 kg car with 300 hp is worth around 1/10th of a second. However the effect of weight reduction on 1/4 mile times increases as the vehicle gets lighter.

Kg Pounds Time Diff
1500 3300 12.86 ----
1450 3190 12.72 0.14
1400 3080 12.56 0.16
1350 2970 12.41 0.15
1300 2860 12.26 0.15
1250 2750 12.10 0.16
1200 2640 11.94 0.16
1150 2530 11.77 0.17
1100 2420 11.59 0.18
1050 2310 11.42 0.17
1000 2200 11.24 0.18

[wot179]

So a 1500kg car with 300hp will only gain 1sec over the quarter if i take 1000kg out of it?

2 seconds,mate.

50kg =1/10. Ive always known it as 100lbs=1/10th

It only a ballpark calculation.

as is "if you can pick up 1/10th to the 60,its worth 2/10s in the top end."

Its not gospel,but its pretty close .

[Heath]

He said it was a GAIN of 1/10th of a sec, I just realised how I misinterpreted that

[ozyozyozy]

i agree with MRLXSS, if street driving 3.5 or 3.7, depending on tyre size may want 3.25, depends on how much you want the engine to rev when sitting on 100kmh roads. m21 with 355 uuummm ok. maybe look at other gearbox options.