I know its been a topic of the past about how the RB motors affect the handing and balance of a 240sx. The common answers ive seen has aways been "i cant tell the difference" or "it hardly changes the hadling." The fact of the matter is that putting an RB in a 240 (S13 chassis discussed here) does have a significant effect on the handlin and balance of the car and even more so, the feel of the car. There are significant changes in both grip and drift dynamics vs a SR or KA powered car. I am an an active track drifter and i engage in grip driving every now an then on the street. Ive done both things with KA, SR and RB powered cars but feel free to give input on the topic.
The mechanics:
There are two key differences between a KA/SR powered S13 and an RB powered S13. One factor being weight, the second and most critical, where that weight is located. SR/KA motors allow the placement of the motor to be almost entirely behind or just inline with axis of the front wheels. In newer performance FR cars its all about "Front Midship" which places the motor behind the front wheel axis of the car, hence the term "midship." found on cars like the 350z, G35 etc.. Front/Rear weight distribution greatly affects the nature of a cars handling. 50/50 arguably the best. This is where the RB comes in. No matter what mount kit you have for the RB, the position of the motor in terms of its longitudinal position, is limited by the firewall. Most kits aim to place the motor as far back as possiblem which is good, but 6cylinders not only means more pistons, but more length. The lengths of RB motors is roughly 50% longer than KA.SR motors. This length results in weight in position in front of the front wheel axis. Of course, in combination, with the added weight of the RB motors (RB25's are estimated 180lbs heavier than a KA, motor and tranny combined according to SCC). So instead of a, say 52/48 split, now we have a 55/45 split. Yes some of the weight does come from the beefy transmissoin of the RB25's but id say RB transmisssoins(NOT GTR) are hardly more than 40lbs greater than KA/SR/RB20 transmiossions. Overall more weight, and more of that weight over the front wheel axis, results in more initial load on the front tires of the car.
The dynamics:
So what does all this mean? So what if we're a little front heavy? I was running a stock KA in my car for quite some time and did a fair amount of track drifting at Drift Day events. I swapped in an R34 NEO RB25 not too long ago and have been to the same tracks with the new motor and the same suspension setup, a world of difference. Jumping to grip driving for a second, you can FEEL the front weight driving. steering response is slightly hindered, also the car is slower to turn in. A Down hill clover leaf results in increased understeer at the limit (expected). Up hill clover leaves however offered a noticable increase in cornering stability.
The real changes come while drifting. You have to muscle the car around the track, really man handle the car to get it to do what you want. In comparison with the KA or SR powered cars, they are more balanced and easier to manuver. The car felt slightly less predictable in switch backs. Perhaps the most annoying thing was the car's tendancy to dive into the apex early, even with the extra power and speed, "pushing" towrds the apex in abnormal way.
The solution:
Suspesion Tuning. Wheel/tire selection, spring preloads, camber and toe angle. everything. To compesate for the extra weight, a slightly stiffer spring rate up front may be advisable, also running a smaller stagger for tire size. ie 235/245 insdead of a 225/245. You may want to play around with front tire sizes and compunds to find the setup that works for you. I was planning to modify the firewall and move the motor back 6-7 inches but formula D rules do not allow firewall modification so that plan is scrapped. In all, by no means do RB's make 240's handle bad, but they do offere a significand change in handling charactersitics. Maybe some of you who have drivin EVO's and STi's can better relate to what i mean.
I havent posted on the forms for a while so just thought id give a more clear contribution to the subject of RB's and handling in S13 chasiss, input and feedback are always welcome. This is just my personal experience having drivin a number of KA/SR/RB 240's.
The mechanics:
There are two key differences between a KA/SR powered S13 and an RB powered S13. One factor being weight, the second and most critical, where that weight is located. SR/KA motors allow the placement of the motor to be almost entirely behind or just inline with axis of the front wheels. In newer performance FR cars its all about "Front Midship" which places the motor behind the front wheel axis of the car, hence the term "midship." found on cars like the 350z, G35 etc.. Front/Rear weight distribution greatly affects the nature of a cars handling. 50/50 arguably the best. This is where the RB comes in. No matter what mount kit you have for the RB, the position of the motor in terms of its longitudinal position, is limited by the firewall. Most kits aim to place the motor as far back as possiblem which is good, but 6cylinders not only means more pistons, but more length. The lengths of RB motors is roughly 50% longer than KA.SR motors. This length results in weight in position in front of the front wheel axis. Of course, in combination, with the added weight of the RB motors (RB25's are estimated 180lbs heavier than a KA, motor and tranny combined according to SCC). So instead of a, say 52/48 split, now we have a 55/45 split. Yes some of the weight does come from the beefy transmissoin of the RB25's but id say RB transmisssoins(NOT GTR) are hardly more than 40lbs greater than KA/SR/RB20 transmiossions. Overall more weight, and more of that weight over the front wheel axis, results in more initial load on the front tires of the car.
The dynamics:
So what does all this mean? So what if we're a little front heavy? I was running a stock KA in my car for quite some time and did a fair amount of track drifting at Drift Day events. I swapped in an R34 NEO RB25 not too long ago and have been to the same tracks with the new motor and the same suspension setup, a world of difference. Jumping to grip driving for a second, you can FEEL the front weight driving. steering response is slightly hindered, also the car is slower to turn in. A Down hill clover leaf results in increased understeer at the limit (expected). Up hill clover leaves however offered a noticable increase in cornering stability.
The real changes come while drifting. You have to muscle the car around the track, really man handle the car to get it to do what you want. In comparison with the KA or SR powered cars, they are more balanced and easier to manuver. The car felt slightly less predictable in switch backs. Perhaps the most annoying thing was the car's tendancy to dive into the apex early, even with the extra power and speed, "pushing" towrds the apex in abnormal way.
The solution:
Suspesion Tuning. Wheel/tire selection, spring preloads, camber and toe angle. everything. To compesate for the extra weight, a slightly stiffer spring rate up front may be advisable, also running a smaller stagger for tire size. ie 235/245 insdead of a 225/245. You may want to play around with front tire sizes and compunds to find the setup that works for you. I was planning to modify the firewall and move the motor back 6-7 inches but formula D rules do not allow firewall modification so that plan is scrapped. In all, by no means do RB's make 240's handle bad, but they do offere a significand change in handling charactersitics. Maybe some of you who have drivin EVO's and STi's can better relate to what i mean.
I havent posted on the forms for a while so just thought id give a more clear contribution to the subject of RB's and handling in S13 chasiss, input and feedback are always welcome. This is just my personal experience having drivin a number of KA/SR/RB 240's.
