CR box and diff ratios
Discussion
TVRMs said:
Easy tiger, assumption based on a shortage of information will lead to misinformation.
Standard 3.6 and 4.0 are over geared with a 3.46 diff so could have higher top speed with 3.9.
The combinations and their ability to work well or less well very much depends on engine power and torque characteristics, so our well known dealer, unless he qualified his statement, is talking out of his backside.
3.46 will give you higher top speed Standard 3.6 and 4.0 are over geared with a 3.46 diff so could have higher top speed with 3.9.
The combinations and their ability to work well or less well very much depends on engine power and torque characteristics, so our well known dealer, unless he qualified his statement, is talking out of his backside.
3.9 will give you better acceleration
the 3.9 would be to short for my cup of tea. 3.7 seems to be a good compromise...
Interesting thread from a few years ago, there is a chart for the different gearbox and diff MPH permutations also.
See page 2 for the final figures.
http://www.pistonheads.com/gassing/topic.asp?h=0&a...
See page 2 for the final figures.
http://www.pistonheads.com/gassing/topic.asp?h=0&a...
K
3.9 will give you better acceleration
the 3.9 would be to short for my cup of tea. 3.7 seems to be a good compromise...Based on experience? And if so, of what??
gacksen said:
TVRMs said:
Easy tiger, assumption based on a shortage of information will lead to misinformation.
Standard 3.6 and 4.0 are over geared with a 3.46 diff so could have higher top speed with 3.9.
The combinations and their ability to work well or less well very much depends on engine power and torque characteristics, so our well known dealer, unless he qualified his statement, is talking out of his backside.
3.46 will give you higher top speed Standard 3.6 and 4.0 are over geared with a 3.46 diff so could have higher top speed with 3.9.
The combinations and their ability to work well or less well very much depends on engine power and torque characteristics, so our well known dealer, unless he qualified his statement, is talking out of his backside.
3.9 will give you better acceleration
the 3.9 would be to short for my cup of tea. 3.7 seems to be a good compromise...
Edited by anonymous-user on Wednesday 29th April 17:01
TVRMs said:
Based on experience? And if so, of what??
you dont need experience for that. use any gearboxcalculator Edited by TVRMs on Wednesday 29th April 17:01
with the gear ratios available. it will do the math with the tyres for you.
let me say it like this. the shorter is not evertime the better as you then experience different problems like traction. you can overcome a bit of that with wider or softer tyres like semi slicks but only to a certain point. for sure a 3.9 makes fun but what will happen e.g. 10 year old toyos on the back unexperienced driver and full throttle out of the corner..... hopefully nothing
as for real life experience have the standard box with a 3.73 in the T350. Had before the 3.43. As i dont drive the car max speed on the motorway i dont care about top speed so 3.73 went in. It just pulls a little bit harder. nothing else.
in the chim have the 3.73. and the CR box as the old one needed a rebuilt. on the roads i drive i seldom use 2nd and 4th gear. Mainly switching between 3rd and 4th on the straights. 5th is modded with longer gearing for motorway cruise but rarely dont need that.
Both cars have that much torque that a CR is not needed. CR makes sense with low torque high rev engine....
Edited by gacksen on Wednesday 29th April 17:19
gacksen said:
TVRMs said:
Based on experience? And if so, of what??
you dont need experience for that. use any gearboxcalculator Edited by anonymous-user on Wednesday 29th April 17:01
with the gear ratios available. it will do the math with the tyres for you.
as for real life experience have the standard box with a 3.73 in the T350. Had before the 3.43. As i dont drive the car max speed on the motorway i dont care about top speed so 3.73 went in. It just pulls a little bit harder. nothing else.
in the chim have the 3.73. and the CR box as the old one needed a rebuilt. on the roads i drive i seldom use 2nd and 4th gear. Mainly switching between 3rd and 4th on the straights. 5th is modded with longer gearing for motorway cruise but rarely dont need that.
Both cars have that much torque that a CR is not needed. CR makes sense with low torque high rev engine....
Standard `box and 3.91 diff gives the shortest first 3 ratios.
The shorter the ratios the (on paper) quicker the acceleration.
However we are talking TVR speed 6, which IMO, is driver dependant to get the best acceleration.
For me the capability to hit 60 in first and 100 in second would be the most appealing.
The shorter the ratios the (on paper) quicker the acceleration.
However we are talking TVR speed 6, which IMO, is driver dependant to get the best acceleration.
For me the capability to hit 60 in first and 100 in second would be the most appealing.
Lotus E300S said:
TVRMs said:
Interesting school of thought, not sure I agree though.
Would love your thoughts before I fork out for a 3.9 diff Before I give advice, need to know...
What model
Which engine (and state of tune)
What will it be used for
O
Standard Sagaris, normal road driving and a few track days a year, bigger circuits like Silverstone, Spa.Close ratio and 3.73.
If you were doing more track days on shorter circuits or sprinting, I would have said CR and 3.9.
Lotus E300S said:
TVRMs said:
Happy to provide baSed on what I've had.
Before I give advice, need to know...
What model
Which engine (and state of tune)
What will it be used for
ThanksBefore I give advice, need to know...
What model
Which engine (and state of tune)
What will it be used for
Standard Sagaris, normal road driving and a few track days a year, bigger circuits like Silverstone, Spa.
If you were doing more track days on shorter circuits or sprinting, I would have said CR and 3.9.
TVRMs said:
The close ratio box keeps the engine on the boil. If you gents don't understand the benefits don't bother. You asked me what I would do., I advised what I would do and what I have done in the past.
I know I'm a mechanical numpty, but, as I understand it, it's all about optimising the gearing (combination of 'box and final drive) to ensure that gear changes allow the engine to stay comfortably in its power band?Or, not wanting to experience the ire of Uncle John
, stay in the torque band (one of those will be wrong so I've covered both bases TVRMs said:
The close ratio box keeps the engine on the boil. If you gents don't understand the benefits don't bother. You asked me what I would do., I advised what I would do and what I have done in the past.
i get your point don´t know what a bog standard 4.0 puts out on horses but would gestimate around 370@7250 285lb/ft@5400 plus minus.... brings us to a usable power band of around 1850 rpm on paper. 
left box is with the standard and right with the CR box. take a closer look at the rev drop
if you shift at 7250rpm. with the cr box revs are dropping around 1450rpm in 2/3/4th gear.
with the standard box 2250/1840/1450 in 4th to 5th.
in what situations you max out gear ? means every gear ?
let´s say you want to keep your engine in a mainly safe region and you do shifting around
5-6000rpm. CR box drops revs at around 1000rpm. standard box 2nd to 3rd of 1550 3rd to 4th 1200
and 4th to 5th 1000. Means the lower the shift point the smaller the differences between the
boxes. what you have with a cr box is a little bit longer 1nd and 2nd gear. difference in 3rd is
minimal.
left box is standard and right with CR box.
brings me to the conclusion if you rev your car to the max most of the time and need a longer
first and second gear you will be fine with the CR box. in case your box is fine and it´s
just about a little more punch a shorter diff like the 3.73 or 3.9 will do the trick
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