Modifications and Results... (archive)

The changes you've made *may* net you a maximum of 40-50hp and a bit less in torque based on the experiences of others with similar modifications, including myself. Given the stock 300hp and the lack of any intake manifold (extrude-hone) or exhaust manifold (headers) modifications, you *may* be at 340hp, but no more. The restrictions at the exhaust manifold and intake runners mean that the car cannot flow enough air/gas to create more than 340hp (without forded induction). Remember, its a "critical path," the weakest most restrictive flow point sets the maximum power output. Also, the K&N cones if not shielded from heat will actually lower horsepower. Get the car dynoed by a reputable shop to see what its actually making.

G-Tech's are great, I've played with them to see the results of improvements. But, they're 1/4 miles and 0-60mph times are known to be optimistic. People really only rely on them to set a base-line before changes and then modifying and then measuring any improvement. If you see an improvement of 0.5 seconds from a baseline measurement of say 8.0 seconds its safe to say you're running 0-60 in 6.7 seconds versus stock of 7.2. If you still think its better and want to back the claim go to a drag strip, track or other real timing facility to see what the car is really doing.

A 4.10 rear would likely be a good choice if you don't do much highway driving. Emir seems to have found a new swap from a 535ia with 4.10 diff? If so, this would be the first knowledge of anything but 540, M5 and 750 diff fitting. With the 4.10 ratio, if my memory servers me correctly you'd be turning over 3,000rpm, maybe 3,300 or even a bit higher in 4th gear at 80mph. A bit high for a V12 to be comfortable and avoid wear, but not terrible. Definitely run the calculations of rpm at mph before changing it to see what it would be like to live with.

The only performance advantage the 4spd has over the 6spd manual is faster shifting and fewer shifts because of two less gears. Manual shifts usually take the average person about 0.5 seconds each, autobox's make the same in about 0.3. That's a definite advantage. But that advantage is offset and then completely reversed by the missing two gears and lack of clutch control. Basically with 6 gears the gear spacing can be closer for faster accleration. What you describe, that is, puting a 4.10 gear set in both a 6spd and a 4spd autobox and then comparing results is a somewhat strange comparison. Effectively you'd be ruining the balance of the 6spds gearing by making 1st and maybe even second gear useless... it would in effect default to a 4spd. The 6 speed is very well balanced (maximum accleration and comfort) at about 2.93-3.15 given the gears contained in the getrag box. The 4spd Autobox appears to be very well balanced at about 3.91 or even a bit higher, again, given the internal ratios of its individual gears. You obviously cannot place the same ratio rear end in both of these cars and then make a fair comparison of performance to claim an advantage. Within the same chassis, final drive performance gearing is specific to the car's transmission ratios even with the same engine and weight.

Greg K

MY CAR HAS A VIRTUALLY STOCK 5.0 V12 IN IT. MODS INCLUDE:

*NO INTERNAL ENGINE OR TRANS MODS!
*TWIN K&N AIR PODS
*ACCEL 300+ RACE LEADS(CUSTOM MADE)WITH MOROSO HEAT SHIELD
*HAMANN CHIP WITH RELEASE OF 250KMH LIMITER
*ELECTRIC FANS
*DINAN TORQUE CONVERTER (RETAINS LOCK UP,STALLS TO 2500RPM)
*CUSTOM BENT TWIN 3" EXHAUST WITH FLOWMASTER MUFFLERS, RESONATORS(UNDER VEHICLE)NO CATS AND NO REAR RESONATORS(SOUNDS UNBELIEVABLE,AMAZING H.P INCREASE!)
*3.91 LSD DIFFERENTIAL
*LOWERED WITH HAMANN 3PCE WHEELS PIRELLI P-ZEROS
*FIBERGLASS BONNET(CUSTOM MADE)

I HAVE TIMED MY 850 USING THE G-TECH WITH PASSENGER:
*0-60 IN 4.97 SEC
*1/4 MILE IN 13.42 SEC
PRETTY QUICK DONT YOU THINK?

MY CAR IS DRIVEN ALMOST EVERY DAY,LOOKS STD FROM THE OUTSIDE(EXCEPT FOR THE WHEELS)IS FAIRLY QUIET UNDER PART THROTTLE, SOUNDS RADICAL UNDER FULL REVS (BUT NOT TOO LOUD)

WITH THESE MODS AND 3.91 GEARS THE CAR CAN STILL DO 140MPH!
I THINK IT CAN HANDLE 4.10 OR LOWER GEARS AND PROBABLY 1/4 MILE TIMES WILL DROP ANOTHER 0.15-0.30!

DOES ANYONE OUT THERE KNOW OF 4.10 DIFF GEARS (OR LOWER) BEING MADE FOR THE 8 SERIES? IF SO PLEASE REPLY?

MY CAR IS ALREADY 1 SEC QUICKER DOWN THE QUARTER MILE THAN A CSI WHICH HAS 380H.P. MY CAR IS MAKING AROUND THE SAME POWER. I BELIEVE THAT AN AUTO 850(WITH LOWER DIFF GEARS) HAS AN ADVANTAGE OVER A 6SPD. BECAUSE OF THE IST GEAR RATIO IN THE 6SPD BOX, 4.10 GEARS WOULD BE UNDRIVEABLE IN 1ST GEAR,SO WITH THE 6SPD,AND SAY, 3.15 GEARS, YOU LOSE OUT ON ACCELERATION WHEN DRIVING IN HIGHER GEARS THAN YOU WOULD WITH A 4SPD AUTO WITH 4.10 GEARS.GET IT? ANY THOUGHTS ON THIS?

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