I am very interested in buying your 4.56 FD. I have heard from many people on this forum that it makes a pretty signficant difference in terms of acceleration (as compared to a stock S2K). What I am interesting in know is what this actually translates to on the track. I have heard several members state that you could shave about .5 seconds of the 1/4 time. All I am looking for is some slips which substantiate that type of statement.

It is customary for companies that produce turbocharger / supercharger kits to provide dyno graphs which substantiate the gains made from their products. Has your company done any testing on the track to determine the performance gains of your 4.56 FD?

BTW...I am not trying to put your company on the spot.

 

Let me try to anwser these questions..

Is this a fairly common and easy thing to do correctly? No, it is not that easy. Mainly becasue the skill needed to properly install a ring and pinion is a lost art. Honda dealers can't do the job becuase this is their only rear wheel drive car. It is becoming a dying art in an age when they swap major assemblies. You need to find a place that build rear end for Jeeps. It is common to install gears in Jeep.

How do I go about finding a good shop? Post a thread in your regional forum would be where I would start. They know where the trusted tech is locationed in your area. But you can use the yellow pages too. I have found a few this way. The shop I use have been building diffs for the past twenty years. I watched him do one, completly without gauges. he got the gauges out to check it and he was spot on.

Is it better to get the gears installed by a pro mail to me and do a pumpkin swap Or is it better to just get the ring and have a local mechanic have a shot at it? That depends on if you can find a tech. This is the reason that we offer a Bolt and Go setup. We install the gears in a diff and ship it to you. You can install the diff and return your diff. Takes about 4 hours with the right hand tools. But is it better, that is your call.

Is the yellowbox hard to do? No, not really. Cut one wire under the dash, add in the yellow box. Connect it to power and ground. Flip a few switches and you are done. It took me five minutes to do mine, and I put it off for 6 months. I was kicking my self for not doing it sooner.

All I am looking for is some slips which substantiate that type of statement. YOu are not going to find any. This is a well know fact that is you change the gearing of the car, it will move slower or faster. It is in the math.

Has your company done any testing on the track to determine the performance gains of your 4.56 FD? Again it is in the math. With a turbo you are changing the amount of power that is put out. That you can measure. But changing the gearing from say 4.10 to 4.57, the dyno will show exactly the same plot. That is how a dyno is designed. To show RWHP.

Think of it this way. You have a sea-saw that is 4' on one side, and 4' on the other side. (this is a 1:1 ratio) If you apply 200lbs to one side you can move 200lbs with the other. Now if the sea-saw was 40' on one side and 4' on the other (10:1 ratio). If you apply the same 200lbs on the 40' side, you can now lift 2000lbs. That is all you are doing, changing the lever.

You see you are not gaining performance, you are changing how the performance you have is being used. Stock gearing is 4.10, that means you have to turn the pinion 4.10 times to make the ring gear turn once. With the 4.57 gears, you have to turn the pinion 4.57 times to turn the ring gear once. This is the same with the sea-saw example. You had to move the long end more to get the short end up. It was not harder to move, but easier.

Does that help?

 

I understand that changing a FD doesn't add any power to a car and therefore cannot be measured on a dyno. However, if changing the FD makes the car accelerate quicker, it would seem to me that the difference in performance could be measure in the 1/4 mile. Am I wrong?

Thanks for all your help. I look forward to buying your products and having them installed on my '06 S2K.

 

a few people have given times. One guy claimed a 13.6 on his first run with gears.

 

IMO 1/4 mile times (while valid) are not important (to me). I've never been to a drag strip, I've never done a 6000-rpm clutch drop etc..

More important (I think) is what happens in every day driving. If you're anywhere in the rev range and you want to accelerate, what FD will give you less resistance or feel as if it's easier to accelerate?

For example, I'm driving around my neighborhood in 3rd gear at 37 mph. I have to make a left turn for which I'll coast down to 30 mph. Now at this point, I may need to shift into 2nd gear if I want some pick-up. But with 4.56 gears my engine will be a few hundred rpms higher so it may have enough pick-up without shifting.

Now in my example, it's not like the stock gears won't work b/c I could just leave it in 2nd and be a thousand rpms higher.


Next example, I am slowing to a stoplight that turns green before I stop fully. I may be in low rpms 2nd gear or low rpms 1st gear but without a clutch drop or high rev launch. Which FD will allow me to accelerate quicker? It seems quite obvious the 4.56 will be better than 4.44 and those better than 4.1 etc..

I'm not saying the 1/4 mile is meaningless, but more important (to me) is every day driving which you can't put a number on.