Changing a 6 Speed over to a 5 Speed

[5isalive]

Hi all,

I hate my 6 speed box and have decided to put and older 5 speed in. I find the current gear ratios make the old girl perform like a slug.

My mate bought my previous '98 model NB, and when I drove it recently, compared to mine, it pulled like a train.

Anyhow, long story short...

Do I have to do anything besides changing one box over for the other? Any suggestions would be greatly appreciated.

Cheers, Wayne.

PS: I looked for answers in the "motor, gearbox and drivetrain" section, but every one of the discussions I opened, were gone.

[smy0003]

That's not how it works.
By putting in a box with larger spaces between the ratios in, you'll make it more sluggish.
You want to change the diff for a shorter one, the '98 NB has a 4.1:1 ratio diff, yours has a 3.6:1.

[Black_Penguin]

+1 for swapping in a shorter ratio diff over replacing a 6 speed with a 5 speed.
And if you still want to swap in a 5 speed I have one I'd be willing to trade your 6 speed for.

[greenMachine]

I have run 6-speeds in NB8As, and loved the extra grunt from the combination of 6-speed ratios and NB8A final drive ratio. The downside is the higher engine revs when cruising on the freeway.

I would have thought that the 8B would be a little punchier than the 8A, given the output was a little higher from the VVT, but would be surprised that it would be very noticeable. On the other hand, I would be amazed if the 8A was faster through the gears than an 8B (on a like-for-like comparison). If your old 8A feels faster than your 8B, I suspect something else is at play here, and it is not a like-for-like comparison.

Put a 5-speed in an otherwise stock 8B, and it will feel like a slug, due to the wider ratios and higher diff ratio. It will be a bit slower than a stock 8B even if you change to a 8A final drive, though a 4.3 would improve acceleration at the cost of high revs when cruising.

TL;DR - don't do the swap. If you want better acceleration, put a 4.3 in it.

[chrons_rotary]

+1 for diff swap. 3.9 or 4.1
You will have a 3.6 ratio diff in yours.
Even swapping to a 3.9 ratio diff will improve things a lot.
I am currently running a 6 speed and 3.9 in my NA8 turbo and I love it.

[lightyear]

Why don't you have a race with the NB8A. Then put a 5 speed in and have another race. You will be slower. Like the others have said, change to a 4.1, or 4.3 if you don't do too much hwy driving. Then put a turbo on.

[hks_kansei]

As all of the above, the late NB had a needlessly tall diff ratio.

The simplest option would be to have a shorter diff ratio fitted, the NB8A has a 4.1 vs the NB8B 3.6
That means the later one is roughly 12% taller in ratio, and would be roughly (very rough here) 12% slower.

The 6 speed however does have shorter ratios than the 5 speed (4th is 1:1 in the 5 speed, vs 5th in the 6 speed)
So in reality the difference is less (depending on gear)


Short story is that you're better off to either buy the diff from an 8A and install that (in whihc case it should end up a little quicker than an 8A since the 6 speed is shorter and the 8B has a little more power)

Alternatively, you can have a diff shop change the ratio of your existing diff, they'll just need to have the appropriate crown wheel and pinion.

[speed]

Some good advice from all the respondees there. Lower ratio diff.
Or forced induction or both :/

[Apu]

I put a 4.1 into my NB8C and loved it (had a lightened flywheel too) but once I turbocharged...it was crap. Well, 1st gear was useless. Went back to 3.6...I'm thinking it could do with a longer 1st gear.

In short, if you want to stay NA, do the 3.9 or 4.1 FD and a lightened flywheel. Very, very fun!

[5isalive]

Well, it seems the consensus is to change the diff ratio to either a 3:9 or 4:1, so I guess I'll go with one of those.

It does get quite a bit of highway work so I suppose the 3:9 would be the better trade off. Would you all agree?

Thanks again for all the advice. It's so good to have somewhere to go where the poeple are willing to pass on their valuable knowledge.

Very much appreciated guys.

Cheers, Wayne.

[hks_kansei]

The RPM at 100kph for each diff ratio (in 6th gear) are as follows:


3.6 ratio - 2725rpm (standard)
3.9 ratio - 2952rpm (+227rpm over standard)
4.1 ratio - 3103rpm (+378rpm over standard)


Of course real life figures won't be exact, as the above doesn't take into account tyre wear, tyre pressure, and general manufacturing tolerances, but i'd be confident they're within a few percent of what you'd be seeing.

Regardless, the differences between them are spot on, which is what you'll be looking at.

[hamx5ter]

I have a 6sp in my NB8a (4.1 diff), and the difference in revs is not really a big deal at all.
If you don't find the engine noise annoying at 2700rpm, you won't find it much worse at 3100rpm.

[greenMachine]

... It does get quite a bit of highway work so I suppose the 3:9 would be the better trade off. Would you all agree?

No, I would not. I am about to repeat the exercise on the new GM, slotting in a nice 6-speed I have acquired, and I will be retrieving the 4.1 torsen from the old GM to replace the open 4.1 I now have. So, I am pretty besotted with the combo. I did think about putting in the 4.3 I took out of the racecar, but that is now going back in the racecar, and anyway may be a step too far for the highway cruising that I do.

But, that is just me.

Go find an NB8A with a 6-speed, and have a drive - there must be a ton of them around. That is the gearing and revs that you will have putting the 4.1 in your 8B. Work it hard through the gears (especially 2/3/4), and see if that doesn't make your smile bigger. Then note the engine noise at cruising. Then decide.

Just my 2c.

[de Bounce]

Everyone quotes RPM in top gear as a comparison between a 5 and 6 speed.

For something different, I plotted the KPH @ 7000 rpm between a stock NB8A and stock NB8B in the first 3 gears where the acceleration actually happens.
NB8B with 3.636 diff at 7000rpm
1st 57km/hr
2nd 94.5km/hr
3rd 130.3km/hr

NB8A with 3.909 diff at 7000rpm
1st 59.1km/hr
2nd 98.2km/hr
3rd 139.4km/hr

Based on the above, a stock NB8A has taller gearing in the first 3 gears (all 5 gears actually) and should, theoretically be SLOWER to accelerate.

[greenMachine]

Maybe re-run that one with a 4.1 for the 8A ...