Fact or fiction - final drives

[newkid]

Was back up at Crail today with the bb1 with @vanzep

Now the car has the a8 engine converted to obd1, type-s/a8 intake, fujitusbo mani/downpipe, greddy evo 2, rob spoon chip, lightened flywheel, 4.64 final drive, think that's it for performance related items re power.

Now based on my tyre size of 205/50/16 and the fact the 4.64 final drive is in a m2f5 this is the figures mfactory give re speeds per gear @7500

1st 3.307 35mph
2nd 1.95 59mph
3rd 1.36 85mph
4th 1.071 108mph
5th 0.87 133mph

Now same info on our own calculator gives these figures

1st 3.307 32.3mph
2nd 1.95 54.7
3rd 1.36 78.5
4th 1.071 99.6
5th 0.87 122.6

As you can see there's a huge difference between what ours says and what mfactory claim, mfactory claimed numbers are actually that of a 4.266 final drive

Now based on today's runs I believe comparing my times an speeds that our calculator is the accurate one, this means even tho the gears are the same length as these haven't changed that a lower speed is achieved even tho you accelerate at the same rate in a like for like car. Basically what I'm saying is by the time both cars reach the 1/4 mile the car with the 4.266 will have achieved a higher max speed v the car with the 4.64.

This leads me to believe that the information giving is fiction but

on the other hand both cars are @ 50mph and in the same gear, the car with the shorter final drive will accelerate quicker than that of the larger final drive as its 400rpm up the rev range so higher up the power band.

Thoughts and info would be appreciated as I'm starting to think fitting a final drive on a road car wasn't the right move.

[RattyMcClelland]

The shorter final drive will get to it's top speed quicker than the longer fd. However the shorter fd will have a lower top speed.
Final drives have no effect on gear ratios. They are always the same however the speed at certain ratios is now changed on the shorter drive.

The revs counter are very inaccurate and same as the Speedo so comparing to mfactorys ratios can be difficult.



What this video at 4.30 secs.


[youtube]es1RKcW_tSA[/youtube]

[newkid]

Ok here is some calculations, I've used another calculator which is working the speeds out the same as the mfactory one

Car 1 (vanzep)

h22a, a8 cams, a8/type-s air box, spoon chipped ecu, plm mani, 2.5 catback 4.266 running 205/55/15

@7500 vtec stay in vtec

38 25
64 43 no
92 61 yes
117 78 yes
159 106 yes

@7200 vtec stay in vtec

36 25
61 43 no
88 61 just
112 78 yes
152 106 yes

Car 2 (mine)

h22a8, a8/type-s air box, spoon chipped ecu, fujitsubo mani, 2.36 catback, 4.64 running 205/50/16

@ 7500 vtec stay in vtec

35 23
59 40 no
85 57 yes
108 72 yes
133 89 yes

@7200 vtec stay in vtec

34 23
57 40 no
82 57 just
104 72 yes
128 89 yes

1/4 mile bests on the day

Car 1 14.8 @ 98.3
Car 2 15.1 @ 92.4

Now going by what everyone says with the final drive I should be reaching my top speeds quicker, yet as you can clearly see the longer final drive is reaching far higher speeds, this was the same no matter what times were achieved.

So going by this its either

1 my a8 is producing really crap numbers
2 a bb1 weighs alot more than a bb4
3 something is holding my car back
4 mfactory talk a load of rubbish

My research does show the greddy is meant to have a bottleneck where it joins to the cat as that join is meant to be 2" but surely that cant make me lose that much speed/time.

Ratty haven't dismissed the video you put up but it does say they lightened the nsx-r by 120Kg so thats going to make a huge difference come power to weight.

[wurlycorner]

There will be quite a weight difference between your bb1 and vanzeps bb4. The standard cars are 1240kg (bb4) and 1315kg (bb1) nb: those are unofficial figures from carfolio, because I don't have access to the service manual right now....
Plus, vanzep has lightened the car a fair bit with carbon bonnet (and air-con removal etc iirc?)
So there's quite a difference there.
The PLM Mani is meant to be the best and he has a bigger exhaust, so, I'm not too surprised his was faster on the quarter mile?
If you were to go up against a standard bb1, yours would be faster I'm sure.

I wonder how well an a8 runs under a spoon chipped 4th gen ECU?
Would be interesting to see yours against vanzeps on the same dyno?

[Drax]

i'd say weigh both cars at the same place, and get them dyno'd at the same rolling road, then go from there - it would be good research

[newkid]

Ok I'll put it another way.

Say both cars are 200bhp and both weigh 1000kg. Infact everything is the same except the final drive. Now this means the gears are the exact same length as the final drive doesn't effect the ratios.

Surely that means both cars will accelerate at the same rate from a standing start?

If that's correct then the car with the longer final drive will reach a higher speed per gear?

[4thgenphil]

Your gears will be shorter mate, the ratios the same but due to the final drive they'll be shorter.
What gear did you both go over the line in? My guess is newkid was 4th and vanz was 3rd

[newkid]

Both in 4th.

Surely if both cars are identical in everyway except the final drive then from stationary they accelerate at the same rate. Both reach 4000rpm, 6000rpm etc. If this is right then the longer final drive is reaching a higher speed in every gear.

The only advantage I can see is if both cars approached a corner at the same speed and had to drop a gear. The shorter final drive will then put you 400rpm up the powerband giving you the advantage.

[mercutio]

you pretty much have it on a track the car with the shorter final drive will win but will be buzzing up and down the box in a drag race the longer final drive will be better as less gearchanges/hold the gear for longer well thats how i understand it

[vanzep]

i'd say weigh both cars at the same place, and get them dyno'd at the same rolling road, then go from there - it would be good research

im happy to do this if your paying

there are a few other things to consider - some already mentioned by wurly etc
a)you have a larger spoiler - creating a bit more drag
b)your engine has just had a manual tensioner conversion done so belts will be very tight and creating a bit of drag
c)fujitsubo manifold with 2.375 piping vs plm with 2.5" piping
d)your car may be marginally heavier with sunroof/16" wheels/300mm front brakes

I wouldnt expect the H22A8 engine to offer much more power vs H22A1

I dont think there is anything to be disappointed about as i think all the money/time spent on building your gearbox will pay dividends out on track or on twisty B roads