smeehere
06-11-2011, 01:21 PM
Hi , having read many many build diaries and searched for info on final drives and found alot of threads with talk of 3.4 diffs etc and seeing a few times people saying this thread has been covered many times etc, Well maybe its just me , or i cant dedicate enough time to search but i cant find answers to my questions .
Here goes , i am bulding a 72 mini with a B18C4 from an aerodeck . I have been trying to decide on a fd , or whether to keep the honda one...
The problem is i see many people saying get the 3.4 , but when i do a gear calculation , with rpm set for 9000 (jun racing ecu) it works like this in 5th gear
1. standard gearing with 195/50/15 , 4.2 fd (standard) @4000 rpm = 73 mph ,@9000 rpm =167mph
2. same but with 185/60/13 @4000 rpm= 71 mph, @9000rpm =149mph
3. with a 3.4 fd that becomes @4000 rpm 88 mph @9000 =201 mph
4. with a 3.7 fd that is @4000 rpm =82mph @9000 = 185 mph
5.with a 4.05 its @4000 rpm =75 mph @9000 rpm =169 mph
It would seem to me to be the 4.05 that i need , im never going to need more than 169 mph (aerodynamics may help stop that) lol
this is very close to the original gearing , and it went quite well in the honda shell...
Im worried that the 3.4 will be over geared and the problem is that whereas with no change of fd first gear becomes short , does the3.4/3.7 become to long in 5th ?
I have seen the 3.4 recommended quite a few times , and a couple of people saying they will be letting people know once its done , this would be what i need to hear , the way the engine pulls the higher gearing and how much acceleration is lost and what will the car pull to if the power output is near standard ?
From the online calculators i think the 3.4 is too high , the reality may be very different , im at the stage where if im going to do this i need to order up the right fd , im using allspeed frame , shafts and bottom arms , i have 175/50/13's at present but figure on using 185/60/13 .
Has anyone got real life figures of the difference at say 70 mph in top and how useful 1st gear is , i calculate the 15" wheels does 49 mph @9000 rpm and the 13" wheels 42 mph with the 4.2
with a 4.05 it does 44 mph in 1st @9000
with a 3.7 its 48 mph
with a 3.4 its 53 mph
I realise its all personal preference , but i dont want it so high as to upset the acceleration greatly , but also dont fancy revving its nuts off on a run , has anyone got a 4.05 fitted ? cheers
Here goes , i am bulding a 72 mini with a B18C4 from an aerodeck . I have been trying to decide on a fd , or whether to keep the honda one...
The problem is i see many people saying get the 3.4 , but when i do a gear calculation , with rpm set for 9000 (jun racing ecu) it works like this in 5th gear
1. standard gearing with 195/50/15 , 4.2 fd (standard) @4000 rpm = 73 mph ,@9000 rpm =167mph
2. same but with 185/60/13 @4000 rpm= 71 mph, @9000rpm =149mph
3. with a 3.4 fd that becomes @4000 rpm 88 mph @9000 =201 mph
4. with a 3.7 fd that is @4000 rpm =82mph @9000 = 185 mph
5.with a 4.05 its @4000 rpm =75 mph @9000 rpm =169 mph
It would seem to me to be the 4.05 that i need , im never going to need more than 169 mph (aerodynamics may help stop that) lol
this is very close to the original gearing , and it went quite well in the honda shell...
Im worried that the 3.4 will be over geared and the problem is that whereas with no change of fd first gear becomes short , does the3.4/3.7 become to long in 5th ?
I have seen the 3.4 recommended quite a few times , and a couple of people saying they will be letting people know once its done , this would be what i need to hear , the way the engine pulls the higher gearing and how much acceleration is lost and what will the car pull to if the power output is near standard ?
From the online calculators i think the 3.4 is too high , the reality may be very different , im at the stage where if im going to do this i need to order up the right fd , im using allspeed frame , shafts and bottom arms , i have 175/50/13's at present but figure on using 185/60/13 .
Has anyone got real life figures of the difference at say 70 mph in top and how useful 1st gear is , i calculate the 15" wheels does 49 mph @9000 rpm and the 13" wheels 42 mph with the 4.2
with a 4.05 it does 44 mph in 1st @9000
with a 3.7 its 48 mph
with a 3.4 its 53 mph
I realise its all personal preference , but i dont want it so high as to upset the acceleration greatly , but also dont fancy revving its nuts off on a run , has anyone got a 4.05 fitted ? cheers