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Discussion Starter #1
There was all this debate whether the 3.45 diff really gives you any advantage or not and i remember someone saying it cant given the same redline.. so my question is what happens if your redline is really 8000 rpm and have alot more power than stock.. ie my car! To be honest, im was never impressed with the 3.45 diff as it make you shifter faster without a clear advantage..

however im giving it second thoughts with my car and its new redline and high lift cams... the situation of car was that i never got to really see it past 7000 with boost only at 12 psi with another 6 psi and 1000 rpm in hand due to the SC belt slipping... make no mistake the car is a bullet and i have seen 320 km/h with the 4 on board with ease (with short shifting at 7000 in all gears) but i was thinking if the 3.45 diff will actually make it pull harder in the mid and top end range... i know im kind of jumping the gun and am eager to see how my car will perform with max boost at max rpm :M5rev:

so with the given info, do you think the 3.45 diff will be a good mod with an advatage all across is there is a pay off area where the 3.15 take the lead ? dont forget that my hp and torque are upward slopes all the way to redline mmmmmm
 

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I wouldnt have added it to mine if i didnt think that taking into consideration all variables, it was worth it.
 

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Black M5 said:
There was all this debate whether the 3.45 diff really gives you any advantage or not and i remember someone saying it cant given the same redline.. so my question is what happens if your redline is really 8000 rpm and have alot more power than stock.. ie my car! To be honest, im was never impressed with the 3.45 diff as it make you shifter faster without a clear advantage..

however im giving it second thoughts with my car and its new redline and high lift cams... the situation of car was that i never got to really see it past 7000 with boost only at 12 psi with another 6 psi and 1000 rpm in hand due to the SC belt slipping... make no mistake the car is a bullet and i have seen 320 km/h with the 4 on board with ease (with short shifting at 7000 in all gears) but i was thinking if the 3.45 diff will actually make it pull harder in the mid and top end range... i know im kind of jumping the gun and am eager to see how my car will perform with max boost at max rpm :M5rev:

so with the given info, do you think the 3.45 diff will be a good mod with an advatage all across is there is a pay off area where the 3.15 take the lead ? dont forget that my hp and torque are upward slopes all the way to redline mmmmmm
I got a Hartge M5 H 50 with 3:45 diff and love it. I my opinion this is how the M5 should have been from the factory. The resonse is incredible in every gear, however, down shifting from 6th to 4th going 140 km/h is a rush! The car responds immediately and goes like bullet! But of course everything is relative. It's not as fast as my F 40, but then again my F 40 doesn't have room for my kids and luggage! Tom:viking:
 

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Discussion Starter #4 (Edited)
Kelleners, im only considering it cuz i want the car to pull harder on the top speed especially after 280 km/h

ranumm5,
My car has more than 700bhp and is surely faster than my Diablo SE30.. but i dont want to add the shorter diff and loose any top speed or have to trade off at any given point.... yet it pulls good past 300 and easily eventhough im short shifting which is below my max hp and torque... still 1000 rpm to go and 6 psi on a set up that just pulls harder the faster the engine spins...

yet again, i think (not sure) the rpm was at 6900 when i saw 320 so i still have plenty of unneeded rpm in top gear

can anyone tell me if the stock diff will pull ahead in higher speeds ? ??????
 

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SC'dKellenersM5 said:
I wouldnt have added it to mine if i didnt think that taking into consideration all variables, it was worth it.
Rob Says it like it is!! I Second that Emotion!

I wouldn't have added it to my M5 If I didn't think it would help my "Off the Line" performance. It absolutely DOES Help my Off the Line Performance ! !

I wonder how many MORE times people are going to ask say question ... with the same response about the 3.45 diff compared to the stock 3.15.

Other than suspension ... It's the BEST performance mod for the $$$.
 

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Black M5 said:
Kelleners, im only considering it cuz i want the car to pull harder on the top speed especially after 280 km/h

ranumm5,
My car has more than 700bhp and is surely faster than my Diablo SE30.. but i dont want to add the shorter diff and loose any top speed or have to trade off at any given point.... yet it pulls good past 300 and easily eventhough im short shifting which is below my max hp and torque... still 1000 rpm to go and 6 psi on a set up that just pulls harder the faster the engine spins...

yet again, i think (not sure) the rpm was at 6900 when i saw 320 so i still have plenty of unneeded rpm in top gear

can anyone tell me if the stock diff will pull ahead in higher speeds ? ??????
Abdulla, honest man, who do you expect to take you with an M5? Have you lost your mind? Really...im being serious. You and Josh now own the most powerful ones on the planet..who else? No one. So no one with a M5 is going to take you even if they have a 3.15 or a 3.65

You are going to loose top end no doubt as thats the trade off with the higher diff but there are ways to figure out what the cars speed would be at redline with the 8K and a 3.45.
 

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Discussion Starter #7
gra8fuldd ed said:
I wouldn't have added it to my M5 If I didn't think it would help my "Off the Line" performance. It absolutely DOES Help my Off the Line Performance ! !
remember the interest is in mid-range and top end and not acceleration

Rob,
There is no other SC M5 on the island so there is no worries there... i just want it pull harder on the top end... im flying back on monday and should go through the run-in period fairly quickly before i can post a video... i mean shifting at 7000 with 12psi which stays there for a second (in other words it more like 10 psi) still have 1000 rpm to go in each gear is still huge especially with the high lift cams... but i was curious what the opinions would... maybe it would be clearer with the video
 

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You guys are ill... :1:

Bill at D/A recommended a 3.45 for my car...after reading all the posts here on the board...I opted for the stock rear end ratio with modified guts...

I just got home from driving over 8000 foot passes...I started at 1800 feet...I bang through the first three gears so fast...I cannot imagine having "shorter" gears...especially if I was pushing 800 hp at the crank....at 5000 feet, I buried the tach in 5th on the way home on an up hill

My thoughts with the higher HP cars...stick with the stock ratio and get the rear end guts changed....after my rear end was modified...I almost have to make an effort to fry the rear tires...Now, it just hooks up....

Mark
 

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Discussion Starter #10 (Edited)
SC'dKellenersM5 said:
abdulla....

what duration cams are you running now?
ahhh i dunno know man... i am only the driver! ask the man who built it :cheers:

drallen,
hehehehe maybe we are ;) dont worry about the rear end cuz its all reinforced and has a rear subframe.. something Rob didnt install on his car. I knew it would be difficult to get any kind of traction out of the car in the first 2 gears... But now its really good. I only tried it once with an easy launch and nailed it... Suprisingly it went without any wheelspin till the top of first gear around 5500 where the wheels broke loose!

still thinking of the rear diff though... ahh maybe i should wait and see how the car turns out with the special built pullies "with teeth" then i can be sure it wont slip :thumbsup:

btw Rob, i recieved my double layered oil cooler and a tornado fan... tell you what, the mechanic who has kept my car idle for an hour said the temp was below half all the time :D bet that will make a big difference kinggf
 

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Would it not be better to ask the man that built your car what he thinks. But **** I guess it's just never enough right :1:
 

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Discussion Starter #13
Good idea Rob.. he for sure needs it and the man who built mine could easily help him out :cheers:

Jayson said:
Would it not be better to ask the man that built your car what he thinks. But **** I guess it's just never enough right :1:
ahh shesh.. you are making all blush now ;) hehehe just joking.. no honestly, with the highlift cams, shortshifting at 7000 rpm, 340 km/h dials which made the speedo go closer than it normally does... eventhough it was pulling nicely in the top end and 300 was no sweat... i just felt that maybe the diff will make it pull faster.... thats all hmmm

btw, since its a BMW... it realy drives extremely smoothly... not helping my butt meter either :crying:
 

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In my opinion I think you will see a decrease in real world performance...
With the kind of horsepower you are running traction is already an issue, and the new diff, would only magnify that. Being that the diff offers torque multiplication. Say for example with your existing 3.15 it takes "1" unit of HP to go "1" unit of distance in "1" second. With the new diff you'll see that "1" unit of distance in say ".8" seconds using maybe "1.2" units of HP. I hope that makes sense, I'm sure you know the basics of how the thing works, but my point is you've got enough HP to be able to use a "taller" gear ratio (3.15.) Using the 3.45 will give you the higher torque in turn making you accelerate faster at the low/mid end, but only up to a certain point. My theory is that for the mid/high range acceleration you're looking for, the solution is more HP, not just more torque.


-Audio
 

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Black M5 said:
Good idea Rob.. he for sure needs it and the man who built mine could easily help him out :cheers:



ahh shesh.. you are making all blush now ;) hehehe just joking.. no honestly, with the highlift cams, shortshifting at 7000 rpm, 340 km/h dials which made the speedo go closer than it normally does... eventhough it was pulling nicely in the top end and 300 was no sweat... i just felt that maybe the diff will make it pull faster.... thats all hmmm

btw, since its a BMW... it realy drives extremely smoothly... not helping my butt meter either :crying:

Maybe it's time to take the diablo and slap some twin turbos on it :) maybe 30 psi could get the butt meter happy :haha:
 

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Oh abdulla abdulla!

You should listen to me more often! Now do me a favor and order TWO!!!!
 

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Audioguy said:
In my opinion I think you will see a decrease in real world performance...
With the kind of horsepower you are running traction is already an issue, and the new diff, would only magnify that. Being that the diff offers torque multiplication. Say for example with your existing 3.15 it takes "1" unit of HP to go "1" unit of distance in "1" second. With the new diff you'll see that "1" unit of distance in say ".8" seconds using maybe "1.2" units of HP. I hope that makes sense, I'm sure you know the basics of how the thing works, but my point is you've got enough HP to be able to use a "taller" gear ratio (3.15.) Using the 3.45 will give you the higher torque in turn making you accelerate faster at the low/mid end, but only up to a certain point. My theory is that for the mid/high range acceleration you're looking for, the solution is more HP, not just more torque.


-Audio
BUT ... With the lower 3.45 Diff (instead of the stock 3.15) ... Abdullah's car will most definately get out of the hole much quicker ... so long as he can feather the clutch and prevent his tires from smokin' 'n burnin' up.

I feel strongly that by the time that having the lower diff (Higher numerical number) has a "Negative effect on his mid/high range acceleration" (as you call it) ... That RACE would be long over ! ! ! :M5launch:

PS ... I think that Vortech SC should give him ALL the HP he needs. AND ... If he still feel the need for more HP ... A little more boost & Fuel/Air or a shot of nitrous wouldn't hurt.
 

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gra8fuldd ed said:
BUT ... With the lower 3.45 Diff (instead of the stock 3.15) ... Abdullah's car will most definately get out of the hole much quicker ... so long as he can feather the clutch and prevent his tires from smokin' 'n burnin' up.

I feel strongly that by the time that having the lower diff (Higher numerical number) has a "Negative effect on his mid/high range acceleration" (as you call it) ... That RACE would be long over ! ! ! :M5launch:

PS ... I think that Vortech SC should give him ALL the HP he needs. AND ... If he still feel the need for more HP ... A little more boost & Fuel/Air or a shot of nitrous wouldn't hurt.
He's already got 800 plus hp.
 

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I don't think Abdulla is worried about shooting out of the hole. I think he's concerened about the pull over 280km's.

Abdulla, I've thought about changing back to a 3.15. I really like the longer gears. I also keep most of my races on the higher rpm's. I can't race it out of the hole. It's pretty much pointless. Also, the last time i did, and hooked, I broke the U-joint. (try to get the carbon fiber drive shaft. you don't want what happened to me, happen to you.....trust me.)

My car(belt) also slips from 10psi to 7psi above 6,800-7,000rpm's. So I short shift mine too. Its too bad you cant take a trip here to Michigan and test my car. Then you will be able to feel the differance your looking for. Even though, my gears are 3.64's. Other than that, car is great.

josh.
 

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gra8fuldd ed said:
BUT ... With the lower 3.45 Diff (instead of the stock 3.15) ... Abdullah's car will most definately get out of the hole much quicker ... so long as he can feather the clutch and prevent his tires from smokin' 'n burnin' up.

I feel strongly that by the time that having the lower diff (Higher numerical number) has a "Negative effect on his mid/high range acceleration" (as you call it) ... That RACE would be long over ! ! ! :M5launch:

PS ... I think that Vortech SC should give him ALL the HP he needs. AND ... If he still feel the need for more HP ... A little more boost & Fuel/Air or a shot of nitrous wouldn't hurt.


Well If it were 1/4 mile or street drags that he had emphasized, I'd be more inclined to agree with you, although even still in a real world scenario as i stated in my original post, the 3.45 would just be too hard to control with that kind of power.
But reading Black's post you'll see he is looking for mid high end power.. the 3.45 will give him the initial snap, but with the amount of torque his FI engine is making, increasing his torque multiplier wont serve the purpose in my opinion. As he sits he can run the gears for a decent amount of time. With the 3.45 he'll be shifting more often, and wont get that nice 3rd or 4th gear pull from 4-7k that the 3.15 provides. I think what he is looking for is enhancing that, and more HP is the answer in my book.
The general theory (as I know it) has always been to stick with the taller gears when running a FI motor.

-Audio
 
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