Advice Needed! Diff Gears & Stall Converter

[smitchy]

Hi there,

I am looking at getting some modifications done soon and gearing up for some research advice.

If i was to get the VCM11 cam (suitable for my application and what im chasing) in an auto VCM recommend to upgrade the Stall Converter and Diff gears.

Primarily VCM (the horses mouth) said 3.46 yo 3.7 diff gears and 3000rpm stall converter.

I went back to my workshop (not naming) they said its not necessary and they have plenty of other cars much higher output with stock stall and stock diff gears.

So i have this conflicting information now, VCM said it is not ESSENTIAL but recommended and that it comes down to the tuner?

They also said regardless, upgrading those will make the car drive better.

I would like some clarification on the above please.

Thanks guys.

 

[monstar]

Most “tuners” are actually installers who follow basic instructions, mostly crap really. To tune the idle and low speed air pressure requires skill (understanding and experience), as does the interplay of tuning the stall (TCC) apply and release speed (kph) and load (torque).
Because near zero installer will do this correctly, the easy install is to bypass steady idle and low speed air altogether with a manual stall and short diff gears.
Changing those components is a waste of time and money in my experience, definitely if you plan to have steady idle smooth rise to torque plateau from around 2k (95% of Street use), your car will not drive better with shorter gears and stall, only WOT in a straight line for first 60’.
I tuned my heavy wagon with big VVT cam and 2.92 gears to do 0-100 in ~4s, 0-200 in ~12s. Plus it putts around town with tuned TCC slip most days.

 

[_R_J_K_]

Ask the shop for some dynographs from existing these cars they have done and decide if those results are what you're after (pay particular attention to the torque curve). I doubt that having a 3k stall converter would make the thing more streetable though, and you probably wouldn't get torque converter lockup on the highway.

Diff gears might be worth a look depending on what you're after, but they don't have to be tuned for.

 

[GMVPSS]

Smitchy,

I cant comment on the VCM cam you're looking at as I have a large Harrop cam in my wagon.

I can tell you that my car is awesome to drive with a converter and 3.7 gears. I was told that they had installed the same cam in cars with standard converter, but I didn't want to risk the car pushing forward at the lights so I went for the converter to be safe.

If you have the diff out, it is only a few more bolts to pull the transmission back to change my converter and while the exhaust was out it was best to do it all at the same time for me.

RJK is wrong, the torque converter can be tuned to lock up at any speed you want. (It is controlled electronically the same way the engine is.) The Harrop tune in mine has it locking up in 4th at 58km at light throttle and in second in sport mode at medium throttle.

The higher stall means you're using much more pedal to get the car moving, meaning fuel economy drops if you do a lot of stop start city driving. on the freeway once the converter is locked fuel economy is almost back to normal.

Going from 3.27 to 3.7 is 200rpm at 100kmh but it makes it fun around town!

Cheers and good luck.

 

[Mike Litherous]

I’ve never owned a performance automatic so I can’t comment. On the diff gears though it’s not a straightforward answer. As the power levels go up, low diff gears can be counter productive

If u carry weight, tow, or car power is still modest (say under 300rwkw), or u like making effortless wheelspin then lower diff can be your thing (as it is mine) but as monstar said it may be counter productive especially when the power levels start to climb.

 

[OzTurtle]

I went down this path with my VF2 Redline, started with the W375 from new but wanted the sweet lumpy sound and extra shove so went a Harrop H02 cam (224/232 114) and was told it wouldn't need a stall upgrade. It definitely did, I ended up getting a smallish 2830 convertor and 3:70 gears. The stall has really smoothed out low speed surge and made daily duties much better, the 3:70 gears is great around town and has gone to around 1950RPM at 100k/ph. Negatives as stated before is fuel use does increase, and requires more pedal to get moving from a standstill, and 1st gear is very short. Also expect your dyno reading to drop 15-20RWKW from a stall upgrade, you haven't lost the power it's just how dyno's read things.
All up I'd recommend the upgrades, and she really moves from 3000RPM on, and if you stall up at the lights it flies on take-off.

 

[Tryg]

I went down this path with my VF2 Redline, started with the W375 from new but wanted the sweet lumpy sound and extra shove so went a Harrop H02 cam (224/232 114) and was told it wouldn't need a stall upgrade. It definitely did, I ended up getting a smallish 2830 convertor and 3:70 gears. The stall has really smoothed out low speed surge and made daily duties much better, the 3:70 gears is great around town and has gone to around 1950RPM at 100k/ph. Negatives as stated before is fuel use does increase, and requires more pedal to get moving from a standstill, and 1st gear is very short. Also expect your dyno reading to drop 15-20RWKW from a stall upgrade, you haven't lost the power it's just how dyno's read things.
All up I'd recommend the upgrades, and she really moves from 3000RPM on, and if you stall up at the lights it flies on take-off.

My cam must be a tad shyer than yours as it doesn’t need the stall converter. I’m wondering if the diff gears alone might work as it’s a tad more doughy off the mark, but explodes after 3,000rpm

 

[Tryg]

I went down this path with my VF2 Redline, started with the W375 from new but wanted the sweet lumpy sound and extra shove so went a Harrop H02 cam (224/232 114) and was told it wouldn't need a stall upgrade. It definitely did, I ended up getting a smallish 2830 convertor and 3:70 gears. The stall has really smoothed out low speed surge and made daily duties much better, the 3:70 gears is great around town and has gone to around 1950RPM at 100k/ph. Negatives as stated before is fuel use does increase, and requires more pedal to get moving from a standstill, and 1st gear is very short. Also expect your dyno reading to drop 15-20RWKW from a stall upgrade, you haven't lost the power it's just how dyno's read things.
All up I'd recommend the upgrades, and she really moves from 3000RPM on, and if you stall up at the lights it flies on take-off.

My cam must be a tad shyer than yours as it doesn’t need the stall converter. I’m wondering if the diff gears alone might work as it’s a tad more doughy off the mark, but explodes after 3,000rpm

 

[OzTurtle]

My cam must be a tad shyer than yours as it doesn’t need the stall converter. I’m wondering if the diff gears alone might work as it’s a tad more doughy off the mark, but explodes after 3,000rpm

A lot of cams sacrifice low down torque for power in the cam shafts optimal range, so changing gear ratio's help with that 'off the mark' flat spot.

 

[Tryg]

A lot of cams sacrifice low down torque for power in the cam shafts optimal range, so changing gear ratio's help with that 'off the mark' flat spot.

True, but I am also guessing the 'step out' on hard acceleration into second and also into third, will also be amplified....It's a tricky balancing act.

 

[SS Flo Rida]

A vcm 11 with a 112.5 lsa is a grind more suited to m6 not an auto. If you put this cam into your a6 you will definitely want a hi stall converter or it will be a pig down low and not a pleasant experience in traffic / around town