Hayabusa mated to T1 transaxle questions

[frankysfree]

So i have a stock bodied beetle and im in the process of having an adapter plate machined to mate a hayabusa engine to the T1 IRS transaxle. I am not certain about the gear ratio i need to run and i have looked at Masterfabr build and would like to do a similar thing(run the vw transaxle in a fixed gear and shift the busa engine) but want to make sure i get the gearing correct.

Keep in mind this will be a street ONLY driven beetle weighing in about 1800lbs so i dont need super low gearing. Once i figure out what i want to do i will be pulling the transaxle to put a super diff, Welded 3rd, etc to beef it up and also eliminate the uneeded gears inside.

I am getting my gear ratios off of this online calculator:
http://woodsware.aciwebs.com/gears/gears.asp
It has a first generation hayabusa listed and gives all the ratios from crank, for each gear, primary, and final. It also lists what speed in what gear, rpm, etc. I can input my own figures to compare and it gives me a comparison of speeds/rpms as well.

From my research(might or might not be correct...) my transaxle has a 4.125 R+P in it, but i am unsure on what ratios are inside the transaxle as im still trying to find those. One source says they are as follows:
1st: 3.80
2nd: 2.06
3rd: 1.32
4th: 0.89
REV: 3.69

[fabr]

Welcome to the site. First off we will need to know for sure the gear ratios (you're likely correct tho) and how tall your rear tires will be. What is your target top end and more importantly what MPH do you wish to cruise at down the highway?

[frankysfree]

Thanks. Cool site here.

Being as i own a motorcycle shop and do some out of the box things this was really the next part of the evolutionary ladder for me.

Ill check when i get home and see if the Bentley manual lists the gear ratios.

I will also have to double check my tire sizes but they are stock rims so unless i decide to change rims they would still be the stock height and rim size. Ive just been plugging in the stock tire size on my calculations.

I would like a top speed in the(theoretical) 130mph range.  Cruising speed on the hwy is not all that important. This wont be a daily driver but a pure weekend warrior/play toy so as long as the rpms are in a usable range im fine.

I do plan on turbocharging the engine once ive got a running, driving car. Dont want to do it beforehand as i am pooling resources to get the bug in driveable condition including fixing areas that need attention and to get the engine to bolt to the transaxle and move under its own power. I simply dont want a drawn out(expensive) project that build time is measured in years instead of days and months. 

[frankysfree]

How exactly would i calculate final drive ratio from the motorcycle, through the vw transaxle, to the wheels? Like if i have the busa in 1st gear which is a 1.596 ratio how do i calculate what the ratio is through, say 3rd gear in the vw assuming its 1.32 with a 4.12 R+P? Math was never my strong subject...

[fabr]

I'll post up the math formula if you like but here is a good example of what you can expect with a gear ratio that works pretty well in the sand. For high speed highway/track (130 mph) use the r&p gear would need to be at least 1/3 higher.

OK ,this is what I've come up with using Albin R&P(5.43:1) and Albin 3rd(1.4:1) and 4th(1.0:1). Assuming the busa is capable of turning 10500 in each gear which makes countershaft =6862 RPM with busa in (1.043:1)6thgear. Use 31" tires.Assume no tire slip in sand.
1st-3.80:1=30.66 MPH
2nd-2.06:1=56.58 MPH
3rd-1.40:1=83.25 MPH
4th-1.0:1=116.54MPH


There is some good discussion about this for the first several pages of this topic-
http://www.dtsfab.com/index/index.php?topic=206.msg1331#msg1331

[frankysfree]

Thanks. I would actually like to use the busa transmission and keep the vw transaxle in one gear except to go in reverse. I was just using the gear choices in busa and vw as examples. I did read your thread and i will have to go back and take another look at it but i seem to remember you using the 3rd gear in the bus transaxle and shifting the busa as the primary transmission.

[fabr]

I do use the busa trans as the primary trans with the vw being used as the "overdrive/underdrive" secondary trans. The mph numbers are nonetheless the same for top speeds based on my 091 custom ratios. It's getting too late for me to look up the actual formula tonite but if you wish I'll post it up tomorrow for you.

[frankysfree]

3.8 first
2.06 second
1.26 third
0.89 fourth
4.125 R&P

Checked the transaxle code and according to that(and some very helpful vw guys at STF) these are the ratios.

[frankysfree]

Yes, id be very interested in getting the formula for that. The last thing i want to do is get the car all together and find out the gearing is unusable. It would be better to know now when i go into the transaxle to upgrade the internals if i need to change anything.

Thanks for all the help btw.

[fabr]

(rpm x tire diameter) divided by (differential ratio x transmission ratio x 336) = mph 

                                                                    OR

you can use one of the many online calculators such as these.
 http://www.bgsoflex.com/rpmmph.html
http://www.wallaceracing.com/gear-speed.php
http://www.richmondgear.com

There are many,many online calculators . You can either do all the math from the formula or ,as I do,use the easy way with the calculator programs..

[fabr]

REMEMBER to adjust your engine rpm BEFORE doing any of the calculations. The busa has a primary ,internal before the trans ,reduction of 1.596:1  . What that means  is that,for example,  10,500 busa rpm redline/1.596 = 6578 rpm at the vw trans input shaft. Using that example you would use 6578 as the engine rpm in the formula or with any of the calculators available for free online.

[fabr]

I'd also consider at what engine rpm I wish to cruise comfortably at also.Say 70 mph at around 5000 engine rpm would only be 3132 input shaft rpm.
 Using the richmond gear calculator above that has a neat alternative calculator to figure rear gear needed ,you will find that a cruising rpm of 3132 will give you 70 mph with a 31" tall tire needing a rear gear of 4.13:1 . Pretty close to what,IMO,you need. 

[fabr]

Here's another good calculator I found also.
http://www.tremec.com/performance/gear-calculators.html

[frankysfree]

Thanks. I havent had a chance to do any calculations yet as i spent all day yesterday at the drag races.

Ill see if i can do some figuring today.

[frankysfree]

Math is really not my strong point.

So check it and let me know if this is right.

If i use the calculator that i linked to at first all i have to do is punch in the final drive numbers and tire size and it gives me the stock compared to the updated results. If my 3rd gear is 1.26 and R+P is 4.12 that would give me an axle ratio of 5.19 correct?? If i stick that number in the calculator along with new tire size(185/80-15) it comes out to a top speed at redline of 36.6 mph and a theoretical top speed in 6th of 91.8 mph. If the VW was in 4th that would give me 51.9 mph in first and top speed in 6th of 115.3 mph.

Does this sound right or am i doing it wrong. I figured the easiest way was to just use the final drive on the calculator (its assuming chain + sprockets) for the Vw final drive instead of doing all the calculations seperate. It also gives me a good idea of what the stock busa ran at certain rpm with stock gearing for a good comparison.