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#1 2.88 diff fitted

Posted: Thu Jan 10, 2019 5:59 pm
by jagwit
I have now fitted a 2.88 to my S3 (auto)

Its important to understand that my car was fitted with a 3.31 by some PO. If my car had the original 3.07, I would not have bothered. But running 3300rpm @ 120km/h (our speed limit) seemed so wasteful.

I removed the IRS (alone) in two hours - having done this before. Building the 2.88 into the IRS and installing the IRS back into the car took the rest of the day. Had to connect/bleed brakes (incl handbrake), connect propshaft, and install exhaust the following day.

There were no “showstoppers”. Calipers and discs went straight on, propshaft mounted fine.

Now she does 2850rpm (indicated tacho) at GPS 120km/h (115km/h on speedo). My car is fitted with 215/70/15 tyres. According to Ashcroft she should be doing 2686rpm at GPS 120km/h. Perhaps the tacho is not 100% accurate.

Very pleased with the end result. Standing start only slightly blunted but now she will do 100km/h in 1st. I will compare odo readings against GPS odo to be able to calculate exact fuel consumption (which is important to me regardless of what it comes out at).

#2 Re: 2.88 diff fitted

Posted: Thu Jan 10, 2019 7:39 pm
by JJC
Great results ! Put in a 5 speed next and you can do 80mph all day long and get over 20 mpg ! BTW, I'm using the same size tire....perfect for Series 3.

JJ

#3 Re: 2.88 diff fitted

Posted: Fri Jan 11, 2019 1:34 pm
by lowact
Phil I reckon yr tacho’s fine, 3300 rpm, multiplied by the ratio of the diff ratios, equals 2836 rpm?
My diff is 3.54. 3500 rpm at 120 kph. When I finally get around to fitting my 0.78 LdN overdrive it should be down to 2730 rpm. Won’t help the problem of having to snatch 2nd gear before the other side of the intersection. S’pose I don’t have to use 1st …
215’s also. Anything bigger doesn’t really fit in the spare wheel well.

#4 Re: 2.88 diff fitted

Posted: Fri Jan 11, 2019 3:29 pm
by jagwit
Drove the car again today....

Frikken bluddy marvellous!! Of course I'm being subjective, but I can't help feel that the car is happier now, MUCH happier. Now its a proper GT. With the 3.31 it was a misfit, not a GT and not a dragster either.

I would also say that it FEELS as if the car accelerates better in second now and acceleration in 3rd still leaves nothing on the table. Overtook several slower cars today, all in 3rd.

Find myself cursing the person who removed the 3.07 to fit the 3.31.

#5 Re: 2.88 diff fitted

Posted: Fri Jan 11, 2019 4:21 pm
by MLBS3V12
Thank you Philip,
A very interesting result I schould share when I will finish my own s3.
I do use a 2.88, a getrag 5 speed and 205 x 70 x 15 tires.
The speedo I have is a 6332/05 which is reputed to be used with a 3.07 diff. Dont know what all this will bring on the speed measure.....

A picture from the car with a few things to do :-)

Image

#6 Re: 2.88 diff fitted

Posted: Fri Jan 11, 2019 4:47 pm
by jagwit
MLBS3V12 wrote:
Fri Jan 11, 2019 4:21 pm
I do use a 2.88, a getrag 5 speed

A picture from the car with a few things to do :-)
What ratio is 5th on the Getrag?

Oi!! Just a FEW things....

I should add that my experience is with the car at 1400m (4500') AMSL - where normally aspirated engines lose 15-20% of the power they make at sea level. Acceleration 2nd is exhilarating now, at sea level it must be scary...

#7 Re: 2.88 diff fitted

Posted: Fri Jan 11, 2019 4:51 pm
by MLBS3V12
The getrag 5th has a 0.81 ratio.