T25 Diesel / Baywindow gearbox ratio question

Bugsy_malone 666

Someone mentioned on another thread somewhere else that the gear ratios of a T25 diesel are worse than a 1600 bay lawn mower box!

I was wondering is this true? at 60mph if you have a diesel how many RPM are you doing?

THe reason I ask is im doing a conversion to my 72 bay soon and i got a complete engine and gearbox out of the T25 diesel as one unit(thinking this would be the best solution), I understand that the T25 diesel bell housing fits straight onto a bay gearbox, if the ratios are better on my 1600 box it would make more sense to keep that and save problems with the gear linkage etc.

can any shed some light on this?
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Second Gear All The Way Baby!

Doing Thing Differently.

illzlee · Posted: Thu Apr 10, 2008 11:48 am Post subject:

http://www.partsemporium.co.uk/t25_gearbox_codes.htm

check out this link for a load of ratio's - you will probably have to put some big tyres on the back to up the gearing.

most peoples buses i have seen have had to do this unless they have a rebuilt box with better ratios
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'79 Bay running citroen 1.9td and phat tyres!

bajabaybutcher · Initiate Jedi Joined: 09 Apr 2008 Posts: 40

t25 5 speed is kack with the diesel. with td it drives much better, plus you can tweek the boost pressure;) if done right a 1.6td is pretty dam pokey

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slide in, life is short.

Bugsy_malone 666 · Posted: Thu Apr 10, 2008 8:35 pm Post subject:

This is shocking, according to parts emporiums list there, I have found my gearbox a `DY` code, final drive is the lowest final drive out of all gearboxes!

The DY diff is a 5.86, the stock petrol 1600 air cooled is 5.375!

this means with the current 185/80(maybe 85+ no actual hieght on the side?) 4500 rpm which is the governor on the diesel (from what i understand) will be 70mph! the stock 1600 petrol gearbox with the same tyres would do around 77-80mph, while a 2litre would do around 84-86mph.

I know slow is where its at with a bay, but not that bloody slow! I have had the stock petrol 1600 (mild tweek to the inlet ports) round to the VDO bit of the dial (the problem with running 185/60s up front) but that is still 85-90mph(scary!)

I'm guessing at the moment the best option would be to put my diesel bellhousing on my 1600 box as it would give me 10mph more top end (thus lower cruising rpm) and get rid of all the problems with the front mount/gear change assosiated with using a t25 box in a bay.

Question is other than swapping the bellhousing over are there any other mods I should know about like input shafts?

then I'm thinking some nice 16" merc wheels and some tall tyres like maybe 225/70s!
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Second Gear All The Way Baby!

Doing Thing Differently.

beetleseb · Posted: Thu Apr 10, 2008 9:06 pm Post subject:

Dont forget its not just the ring and pinion

(RPM X TYRE HEIGHT)/(GEAR RATIO X RING & PINION X 336)=MPH

Tyre height in inches!

Truth is for a good mpg and speed its custom box time! I have 225 55 17's a 2 ltr box and am still not happy.

A 2.0 16valve gti engine would go in there and could give 40mpg with 150bhp

Am I giving away my next plan Grin

or do 'i just miss my scooby

Seb
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Everybody is someone else's weirdo

Bugsy_malone 666 · Posted: Thu Apr 10, 2008 9:23 pm Post subject:

ElusiveStranger · Posted: Thu Apr 10, 2008 10:29 pm Post subject:

caddy · Padawan Joined: 13 Feb 2006 Posts: 71 Location: Armagh

my bay started out with a 1.6d fitted to a 1600 t2 box , from memory the engine pulled through the gears well and topped out at about 75mph .

driving over hills like shap on the m6 we had to go to third gear , and struggled to get over 50mph on steep climbs.

crusing was ok at 65mph.and we got over 50mpg average on a run Grin

.

engine noise was the biggest problem thats why we change eventually to a t25 box and shifter.
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1969 bay with vw 1.6td

sven · Jedi Guardian Joined: 27 Dec 2006 Posts: 814

Guys,
If you want to play around with different gearboxes to lower the engine RPM you can try out my Excel sheet that can be downloaded here.
I used to play around with tire size and my gearbox to find a suitable configuration. If you like to try it out with miles instead of km, there's a another version found at the Ratwell page.

Regards,
Sven

beetleseb · Posted: Fri Apr 11, 2008 8:58 am Post subject:

illzlee · Posted: Fri Apr 11, 2008 2:47 pm Post subject:

phat tyres are the way forward guys.

i've got 205/75/15's on the back and i'm going larger!

also on the lookout for an AAZ box as this offers the best ratios for a stock box. fetch good money though........
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'79 Bay running citroen 1.9td and phat tyres!

sven · Jedi Guardian Joined: 27 Dec 2006 Posts: 814