6 speed conversion on an NA

Hi all.

Took my SZ-R to the track on friday and I am totally hooked!

Going to do as many as I can before the end of the year.

The only gripe I have is that Mondello is a fairly technical track and while I posted some decent times (1:06, about 3 secs off average clubman TA times) in a lardy NA with a 5 speed on stock suspension I was just coming into the "power":innocent: in fourth on the main straight before I had to rein it all back in for the Honda hairpin.

If that all sounds like fun believe me, it was!

My question is would it be worth my while converting the car to a 6 speed gearbox while retaining the original 5 speed lsd diff to give me the shortest gearing possible?

And my other questions are:

Am I even right in thinking that this arrangement is the shortest gearing possible?

Would the extra weight of the 6 speed and extra gearchange cancel any gains to be seen from the NA lump?

Which 6 speed would be better for the job, v160 or v161?

Is there any differences between a NA 6 speed box and a similarly labelled one found in a turbo?

Is mating a 6 speed 'box to a 5 speed lsd diff even possible and if so what extra parts would I require to complete the job?

If anyone says a turbo I'll put a hex on you! Anyway I'd still need a 6 speed box should the idea of a turbo ever become attractive.

I realise weight and suspension set-up are crucial to lap times also, I just can't seem to shake the idea that a 6 speed box will help.

Opinions welcome folks, thanks for taking the time to read this tripe!

Regards,

Damien.

p.s. as a reward for getting this far here is a link to the trackday pics, I'm in the Supra, if you couldn't guess!

http://s34.photobucket.com/albums/d125/touge_drift/

I think the 6 speed helped me post some good times at Llandow but i'm not sure it would be worth all the hassle/cost to do it to yours..........as with most conversions the selling what you have and buying what you want (NA 6 speed) will be the easiest/cheapest way........

Personly if i was driving an NA on the street id go for the 5 speed. I drove a 6 and was just changing gear all the time it was annoying. On the track i dont think it would make much difference to be honnest. The 161 and 160 are almost identicle. the ratios were changed a little but not very much. you wouldnt notice the difference. The best way to get a better time out of an NA on a track is similar to the answer for "how do i get more power from my NA?"

I doubt you'd notice much difference if you went 5sp->6sp, you'd mostly be getting an extra gear (i.e. for high speeds above 5th gear) and not really benefitting from a closer ratio which is what you sound like you'd really want.

ermm correct me if im wrong but didnt all sz-r's come with 6 speeds or were they facelift only?

The best way to get a better time out of an NA on a track is similar to the answer for "how do i get more power from my NA?"

nitrous

ermm correct me if im wrong but didnt all sz-r's come with 6 speeds or were they facelift only?

 

nitrous

Facelifts came with the 6 speed as standard on one model (i think) and an option on others. My NA facelift had all the fancy bits like LSD but had the 5 speed box. It was a great box. i loved it. Compared to a 6 speed i drove for a day it was great. the 6 speed was very annoying maybe i wasnt used to having 6 gears but it was just wierd.

6th gear is just for motorway cruising then not for the track

6th gear is just for motorway cruising then not for the track

Depends how fast the track is.

dont give the fuel for the fire steve!

Surely the money you'll pay to convert your car to a 6-speed will be about the same money as a TT conversion! Wouldnt it be better doing that?

I accept the "Hex" in advance!

I doubt you'd notice much difference if you went 5sp->6sp, you'd mostly be getting an extra gear (i.e. for high speeds above 5th gear) and not really benefitting from a closer ratio which is what you sound like you'd really want.

My recollection of my first 5 speed NA is that 5th cannot be maxed out.........my recollection of my 6 speed NA is that max speed is very close to max rpm in 6th. IMO its likely the first ones were geared for low noise better economy for the motorway in top gear ie the sort of normal considerations for any production car. The later 6 speeds seem to have their gearing adjusted to get the max from the NA's lowly power.

Ok its only 1 gear extra but combined with the fact that 6th actually can near redline means the gears are alot closer ratio than the 5 speed. There's always a 'correct' gear to extract the max torque/bhp from, so no bogging down on a particular corner ie the twisty bits of Llandow or Druids at Brands etc......

hmmmm thats a good point!

My recollection of my first 5 speed NA is that 5th cannot be maxed out.........my recollection of my 6 speed NA is that max speed is very close to max rpm in 6th. IMO its likely the first ones were geared for low noise better economy for the motorway in top gear ie the sort of normal considerations for any production car. The later 6 speeds seem to have their gearing adjusted to get the max from the NA's lowly power.

I didn't realise that, I thought the NA's 6 speed was the same ratios as the TT's 6 speed (either the 160 or the 161).

i think im gonna have to try out a 6speed NA and compare it to the old 5 speed even though it was such a long time ago

Surely though if(?) the NA is making good power from 4,500rpm, there are enough gears in the 5 speed box to keep it between that number and the redline? AlexM's track car is an 5-sp NA and I was quite impressed with that when I went out in it at the start of the year.

I didn't realise that, I thought the NA's 6 speed was the same ratios as the TT's 6 speed (either the 160 or the 161).

gearbox the same afaik, diff is different..........

i think im gonna have to try out a 6speed NA and compare it to the old 5 speed even though it was such a long time ago

If you want a go in a 6-speed SZ-R youre welcome to have a drive of mine. Whether or not its worth the trip north of the border is up to you!

I test drove a 5-speed NA at McKay Trading afew years ago, and it seemed fine to me. The 6-speed box feels far meatier, and the gearshift a fair bit shorter than the 5-speed.

Mine is a V161 in a 97 facelift. Im currently trying to work out whether to 2JZ-GTE or 1UZ my car, but thats a whole other story...

My recollection of my first 5 speed NA is that 5th cannot be maxed out.........my recollection of my 6 speed NA is that max speed is very close to max rpm in 6th. IMO its likely the first ones were geared for low noise better economy for the motorway in top gear ie the sort of normal considerations for any production car. The later 6 speeds seem to have their gearing adjusted to get the max from the NA's lowly power.

Wrong and right Scott in terms of the original question, I'll try to explain, despite the hour!

The NA 6spd has he V161 with the "small" NA diff, the 6spd TT prefacelift has the V160 with the "big" diff, the 6spd TT facelift the V161 with the "small" TT diff.

Without taking in to account the variations of these it's not really comparible. The diff, tyre size, gearbox need to be taken into account as any variation in either makes a VERY dramatic difference in the in-gear acceleration and in-gear max speeds.

Easiest way to check out the differences is to use Homer's gear/diff ratio calculator (which I'm surprised he didn't link himself ).

If you change into fourth just before hitting the rev limiter in third, you should be at about 5,300 rpm, which is well 'in the power' for the non-turbo.

I often think a 6th gear might save a bit of fuel on the old M62...

Hi chaps thanks for the input.

I did use homer's calculator before I posted the original question. It appears to me that the ideal gearbox would be the v161 as it has a better ratio spread, especially between fourth and fifth compared to the v160 where the drop in revs would be too hard to recover from on Mondello's main straight where incidently this car will see most of it's use.

I left the ring/pinion value as it was on the calculator, (4.083) as I assumed this was the value given to the NA 5 speed diff, please correct me if I am wrong.

I am also running the standard 17" wheel size so thats one less variable to worry about.

Its worth noting that when comparing a 5 speed box to either of the 6 speed models the input to output ratio of fourth gear in a 5 speed is the same ratio as fifth gear in a 6 speed which, in essence, would make the 6 speed box a closer ratio box than the 5 speed.

As for redlining the engine I didn't see the point of it on friday, I usually changed up around 6.5k as I assume the max torque of the engine can be found considerably lower down the rev range.

Where I really noticed a lack of get up and go though was when I felt it was necessary to short shift up to third for a couple of sweeping corners, had I held onto second I would have be grabbing third mid corner which I believe to be bad driving!

Also selling my car and buying a 6 speed NA is a non-runner as I have invested far to much time, money and material in the rolling shell of mine already with the addition of the custom built roll cage. The idea is to use this car as a starting point for a half decent track car.