Author Topic: Longer 4th and 5th gear & strengthening ATV gearbox  (Read 8347 times)

Offline physicsfool

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Re: Longer 4th and 5th gear & strengthening ATV gearbox
« Reply #15 on: September 17, 2013, 05:38:48 pm »
Do you know the ratio of your 5th gear? Are all the others standard. And who built the box. Keen to speak to a gearbox guru on the matter

Offline dan1300r

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Re: Longer 4th and 5th gear & strengthening ATV gearbox
« Reply #16 on: September 17, 2013, 07:01:04 pm »
In my gearbox it is believed to have a longer 5th and supposed to be at 2750rpm at 70 but I haven't tested it because I haven't had the gearbox fitted to my car yet haha!
Was yours the one that was on here for sale a few months ago with the gripper LSD? I fancied that one but didn't fancy the gripper... I should have bought it and sold the diff. Ended up buying an ATB now so should be good if I get the 8p 5th. Let's know how big a gap you got from 4-5th, if you get your box in before I do. Hope it's not like 4th-6th  ???

Offline Nick_S

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Re: Longer 4th and 5th gear & strengthening ATV gearbox
« Reply #17 on: September 17, 2013, 07:42:26 pm »
Gap is like 4th to sixth, no good for performance only cruising.

Offline z3i

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Re: Longer 4th and 5th gear & strengthening ATV gearbox
« Reply #18 on: September 17, 2013, 08:53:46 pm »
Gap is like 4th to sixth, no good for performance only cruising.

ah dam, that sucks. i would rather put up with slightly higher revs

Offline physicsfool

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Re: Longer 4th and 5th gear & strengthening ATV gearbox
« Reply #19 on: September 17, 2013, 09:49:32 pm »
I need a proper cruising gear. Will get it done and follow up

Offline vee-dub90

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Re: Longer 4th and 5th gear & strengthening ATV gearbox
« Reply #20 on: September 17, 2013, 09:51:21 pm »
Yeah mine has a gripper fitted, still haven't fitted it and Im not sure on who built it but it will be having a rebuild before its on the car

Offline physicsfool

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Re: Longer 4th and 5th gear & strengthening ATV gearbox
« Reply #21 on: September 17, 2013, 10:00:43 pm »
Well when you do, would you post the ratio/part number of the 5th. Cheers pal

Offline dan1300r

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Re: Longer 4th and 5th gear & strengthening ATV gearbox
« Reply #22 on: September 17, 2013, 10:04:52 pm »
Somebody just come up with a 6 speed box mod and make us all happy! When I win the lotto I will spend a lotto getting a 6 speed box in there somehow  8)

Offline dan1300r

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Re: Longer 4th and 5th gear & strengthening ATV gearbox
« Reply #23 on: September 17, 2013, 10:06:32 pm »
I need a proper cruising gear. Will get it done and follow up
This will be good

Offline dan1300r

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Re: Longer 4th and 5th gear & strengthening ATV gearbox
« Reply #24 on: September 17, 2013, 10:11:11 pm »
Gap is like 4th to sixth, no good for performance only cruising.
I wonder if when I put my forged rods in and take my RPM to 8k (head flow/inlet temps pending) if (I don't like quoting my current dyno result - 2??hp due to scepticism) would make a low revving 5th gear pull?? - Like mine eats 5th almost as fast as 4th right now so I may benefit... Decisions.. decisions..

Offline RyanC

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Re: Longer 4th and 5th gear & strengthening ATV gearbox
« Reply #25 on: September 17, 2013, 10:43:38 pm »
what 5 gear are u thinking off? a 8p box gear? so ur saying u will get ur g over 150 mph?
150 is plenty for me in a polo lol
im thinking of getting my casing machined out and fitting bigger bearings to the diff.

Offline physicsfool

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Re: Longer 4th and 5th gear & strengthening ATV gearbox
« Reply #26 on: September 17, 2013, 11:15:54 pm »
Worth having a quick read through this thread.

My problem is that I am running a GT box so I spend 30 miles a day running 60mph @3200rpm!

http://www.polog40.co.uk/forum/index.php?topic=4733.15

Offline dan1300r

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Re: Longer 4th and 5th gear & strengthening ATV gearbox
« Reply #27 on: September 18, 2013, 12:11:37 am »
what 5 gear are u thinking off? a 8p box gear? so ur saying u will get ur g over 150 mph?
150 is plenty for me in a polo lol
im thinking of getting my casing machined out and fitting bigger bearings to the diff.
I have had it to 150mph and it was pretty damn close to limiting and was almost at 7000rpm on 13" wheels, it does have a lot of blowby on no3 cylinder which could have been caused by the duff injector making it run lean and as such I was terrified having it in the red as long as I did as I have forged pistons which I didn't want to burn before I do the rebuild with new rods so I backed off. Thing is the two times I've took it this far it has gotten there with stupid ease and if a 6th gear was there, it would pull it. I used http://www.endtuning.com/gearratios.html to work out the road speed if using the ratios on the earlier posted chart, obviously speedo error will need to be taken into account. Not using the 8p gearbox no, using the ATV with the the 5th gear from an 8p, if you use the chart to fill out the gear ratio conversion you will get a road speed figure.. Don't know where to stop! Bigger bearings, metal casings, shot peened gears, ££££'s, I think I may just stick the diff and the 8p 5th into the ATV and hope for the best from the rest of my gubbins.

Offline dan1300r

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Re: Longer 4th and 5th gear & strengthening ATV gearbox
« Reply #28 on: September 18, 2013, 12:28:57 am »
Do you know the ratio of your 5th gear? Are all the others standard. And who built the box. Keen to speak to a gearbox guru on the matter
Sounds like the 0.740 ratio 5th from the 8P box.  If you use http://www.endtuning.com/gearratios.html and fit your car with 175/60/13 standard wheels/tyres and stick the 0.740 ratio 8P 5th into an ATV box with a 3.333 final drive ratio the engine will be doing 2728RPM at 70 mph. I'd say 2728rpm will look pretty damn close to 2750rpm when looking at a G40 rev counter hence I think it's this gear. Go to 14" wheels with the same sidewall and your revs will drop to 2606RPM at 70mph and so forth.

Offline RyanC

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Re: Longer 4th and 5th gear & strengthening ATV gearbox
« Reply #29 on: September 18, 2013, 06:45:40 pm »
When u hit 150 what were u running turbo or a charger? Will be interesting to see what the 8p 5gear will do