transmission/diff setups for 240z vintage race car

[chicago240z]

Hi, All I was hoping to get some ideas of what some others are using for

240z race cars in the trans diff dept. is a 4 speed better all around than a close ratio five speed and what diff gearing works the best, my friend bought a 240z gt2 car that runs a truck 5 speed and the 4.3 gearing in a r180, can I use the r200 lsd and cv joints?

[preith]

In regards to 4sp vs 5, based on my experience it's a bit of a toss up - strictly related to road racing, unless an actual Nissan comp unit (opt 2) is used, and good luck finding one relatively cheaply. The "close ratio" fs5w71b found in the 80-83 ZX's is really a wide ratio, hence the "w" in the part number, and there's no getting around that. The 1-4 ratios on both the 4 and 5 speeds are for practical purposes the same with 3rd and 4th identical. The problem with using such a numerically high final is you essential move up the "primarily used gears" from 2-4 to 3-5, and 5th IMO is the weak link of the trans.

Using the later zx trans as a baseline (1.858, 1.308, 1, 0.745), your final drive ratios with the 4.3 diff are:

3rd - 7.9894

4th - 4.3

5th - 3.2035

the same trans with 3.70's:

2nd - 6.8746

3rd - 4.8396

4th - 3.70

I've raced with a 3.70 final since day one (primarily at Blackhawk Farms) and for the most part I only use 2nd at race starts or when slowed by lapped traffic. Depending on the race start speed, which will most likely be the slowest you will go all session, rpm's in 3rd might already be a little too high with a 4.3 final, and depending on the track, a little too low at max speed.

You can use an R200, but there is a valid argument for the R180 based on weight savings alone as it is significant. Regarding the CV halfshafts, I would say if you stick by SVRA rules you will for the most part be allowed into all vintage clubs. With that said they list half shafts as "free"

Edited December 10, 2010 by preith

[DatsunDoc]

If you have a serious engine it's going to have a narrow power band so a close ratio 5-speed is always better than a 4 speed. If you go crazy on your engine and your not prepared to have a transmission to take advantage of it you will not go faster. You might be better off with a engine that is happier at a wider rpm range. Building a successful race car is about getting all the pieces working together really well. This is true of the engine and the entire car. A "trick" piece here or there doesn't do it. It's about maximizing the package.

Mike

[Carl Beck]

Just as a point of interest - someone running a 240Z at Sebring, Florida a couple years ago - was using a B/W World Class T-5. Any reason that can't be used in the Vintage racing scene?

Secondly - some of the race teams in the early 70's also ran 4 speeds in the enduro's because of the weak 5th in the 5spd.'s.

FWIW,

Carl B.

[preith]

If you have a serious engine it's going to have a narrow power band so a close ratio 5-speed is always better than a 4 speed.

Mike, define "close ratio 5 speed". Strictly related to Nissan transmissions, there's only the OEM stuff (which I delved on) or comp boxes - which are rarer than hen's teeth and replacement parts are even harder to come by.

Just as a point of interest - someone running a 240Z at Sebring, Florida a couple years ago - was using a B/W World Class T-5. Any reason that can't be used in the Vintage racing scene?

Carl, depending on the club you may be able to use it but per SVRA rules this is not allowed. Interestingly SVRA gr6 (big bore cars) are allowed alternate transmissions, including Jericos, with a weight penalty, but not gr8 (zcars). One of their many gr6-gr8 double standards.

Secondly - some of the race teams in the early 70's also ran 4 speeds in the enduro's because of the weak 5th in the 5spd.'s.

EDIT - one more thing I'd like to add, "5th" on the comp boxes is really 4th on an OEM trans as the "dog leg" 1st is used in place of 5th, or OD.

Edited December 10, 2010 by preith

[John Coffey]

If you can run the FS5W71C 5 speed (Austin sells adapters) OS Giken sells a closer ratio gearset: 2.596 1st, 1.765 2nd, 1.250 3rd, 1.00 4th, .833 5th. Comes with an upgraded mainshaft.

[jmortensen]

How much is the OS Giken gearset? $2000? ;-) That might be a very good option for the people struggling to find an option 2 box.

The later ZX trans is a lot better and has much closer ratios than the 4 speed or the earlier 5 speed. It's not that "close ratio" in objective terms, but comparing to the early ones I'd much rather have the close ratio due to the big gap between 2nd and 3rd on the wide ratio. The 4 and early 5 speeds are really bad if you have a cammed engine with a narrow power band. The T5 has about the same gear spacing as the early 5 speed. You can get a graphic representation of all of this using the Datsun trans calculator tool here: http://webspace.webring.com/people/cz/z_design_studio/

Coincidentally, I ran an 80 trans with a 3.70 like Phil and never got out of 4th on the track. I didn't do it to avoid 5th gear, but maybe that was a lucky side effect of having the "wrong" gearing. I know it was hurting me at autox though.

[rxsleeper]

Welcome Chicago,

I guess I will the the ogre for today. I have read this post and the other post(s) about head work on a race car and about I suggest you decide what sanctioning body(ies) you will be racing with and then located the rule set for that group. Sometimes what is legal for one body with regard to tranny's and head work, doesn't translate well to another sanctioning body.

Otherwise, all of the options listed above will work well. For what it is worth, I use 2 gears at Road Atlanta with a 3.90 rear gear. If I drive like I should(which doesn't happen very often ) then I rarely drop below 5700 or so and see ~7100 just prior to entry at 10a. At Barber, I use a 4.11 and try to only use 2 gears

Good luck with your quest and your racing. You have been given some very sound advice.

Paul

[DatsunDoc]

"Mike, define "close ratio 5 speed". Strictly related to Nissan transmissions, there's only the OEM stuff (which I delved on) or comp boxes - which are rarer than hen's teeth and replacement parts are even harder to come by."

I'm not talking about a specific transmission here. 5 closer ratios will always be better than 4 for a peaky engine. I have used the various Nissan transmissions in the past. I'm currently using a T5 based transmission because it's the best for my particular class, car, budget etc. My point is that the original question can't be answered without weighing the total goal of the effort. This will be governed by your sanctioning body rules, class rules, engine power band, your budget and the track where you race on a given weekend. The guy who considers how all these things work together will be the fast one. Sometimes it's easy to lose track of the total goal and that can affect the best choice for engine modifications, tranny and rear to use. Good luck. See you at the track.

Mike

[John Coffey]

How much is the OS Giken gearset? $2000? ;-) That might be a very good option for the people struggling to find an option 2 box.

Hah! Double Ha Ha! Remember, those are OS GIken parts. They best that (a lot) of money can buy.

[DatsunDoc]

"Carl, depending on the club you may be able to use it but per SVRA rules this is not allowed. Interestingly SVRA gr6 (big bore cars) are allowed alternate transmissions, including Jericos, with a weight penalty, but not gr8 (zcars). One of their many gr6-gr8 double standards."

This is incorrect, you can use an alternate production based transmission in group 8 SVRA (+75 lbs.)

[preith]

This is incorrect, you can use an alternate production based transmission in group 8 SVRA (+75 lbs.)

Thanks for the clarification Mike and sorry everyone for the misinformation.

In my defense the gr6 vs gr8 rules had me a little confused, revisited them for a refresher, gr6 lists "alternate racing transmissions" as acceptable whereas gr8, as you stated, lists "alternate production based". With that said if I interpret correctly, a Jerico for example is ok for gr6 but not gr8

Another peeve of mine is, like Jon mentions, is the OS Giken gearsets are around 2k, which is the going rate for a GOOD used Jerico, and IMO a better option, but it can't be used anyway.