1330cc Engine spec help - Gearbox
Turbo Mini Forums

Hey Guys, I'm fairly new to this site, and mini's in general although I'm very keen to learn.

I'm currently building (very slowly) a 1330cc engine to a spec of around 100BHP. And after a little look at some turbo mini's and also being talked into it I'm very interested in building a turbo engine.

I've already got the block - metro turbo block, the crank conrods etc... And i also got given a loada turbo bits with the block.

I've also gone and bought a 1275gt close ratio block, pre A+ but with the layshaft conversion with a 3.44 diff. Will this gearbox be okay to use for a turbo?

well welcome, yes the box will be fine .but i would would go up on diff ratio to a 3.1 final drive.

and fit a minispares x pin diff.
if the box is helical you will need SC drop gears .........i would get reading on the forum as many subjects have been discused before......... welcome on board

I'm assuming I have a helical box..
The box is a 1275 gt rod change type. (22G1832)

Yes you will have a helical box, the gears themselves are actually stronger than a straight cut gear due to more surface area, but a straight cut gear puts less sideload on the bearings.

You need to provide us with a little more info, a completely standard but good condition helical box, I would not like to put more than 120bhp though it, what sort of power are you looking at and we can advise you on where to go next.

Audi s4 b5 - 470bhp & 486ft lbs

On 30th Apr, 2012 Brett said:
yeah stick the bit in and give it a wobble

Have a look inside, are the gears all diagonal or all straight? Diagonal is helical, straight is straight cut

I'll be getting some pictures up at some point soon. I'm not to sure what power to look for really as I'm not sure as to how much power to expect if you know what i mean?
I've been thinking about 140-160? Or is that a bit silly?

We ran 150ish in the metro van on a helical box with straight cut drops. We where on borrowed time as the input bearing collapsed.

I would personally go straight cut, as what ever you build it to is never enough!

140-160 is fine, for that you could use a helical box but replace al the bearings and use some straight cut drops, or go for a straight cut gearset with helical drops or straight cut box with straight cut drops.

I think he would know if he had bought a straight cut box tbh.

Audi s4 b5 - 470bhp & 486ft lbs

On 30th Apr, 2012 Brett said:
yeah stick the bit in and give it a wobble

Trust me, this is not s straight cut box! I got it off ebay for £20 Everything spins okay but i'll be using a guide in order to rebuild it at some point.

Ill post a pic up tonight of what happens when you put that sort of power through a standard diff, took about 300miles as it was about to shit its self lol

Audi s4 b5 - 470bhp & 486ft lbs

On 30th Apr, 2012 Brett said:
yeah stick the bit in and give it a wobble

I was gunna use that diff before i decided turbo, although the turbo-mini website reccomemends a 3.44? And I was told 3.1 earlier up the thread.

The fd doesn't not matter its all to preference, just make sure its a 4 pin diff. ( x pin diff)

Audi s4 b5 - 470bhp & 486ft lbs

On 30th Apr, 2012 Brett said:
yeah stick the bit in and give it a wobble

Ah i see, I'll be getting that.

As above, helical gears have more surfs e area so are naturally stronger, however the materials used in a straight cut (quality) gear are stronger than the oem helical fitted.

Helical gears naturally push in a side direction because of the cut angle.

Straight cut gears don't. You'll also benifit from smaller transmission losses by virtueof a smaller contact (friction) area.

The drop gears (transfer) are the same - factory are helical.

Some people use helical drops with sc gearbox gears as the drops can be very intrusive (read fucking loud).

I believe someoneon here was running (Robert?) 200bhp through helical drops.

You pays your money and takes your choice.

Would anybody recommend helical drops then? Or Just go for straight cut drops?

I have a sc box with helical drops, as above, robert uses them at 200-250bhp.

Audi s4 b5 - 470bhp & 486ft lbs

On 30th Apr, 2012 Brett said:
yeah stick the bit in and give it a wobble

Oh I get it i think.. If you have a helical gearbox, you can fit straight cut drop gears for the power increase and less load on the side load bearings.

And if you have a straight cut box you can fit helical drops as they're stronger?

you got it slightly wrong, sc gearset and sc drop gears are stronger, but there fooking noisy, some argue there is no need for sc drops with sc gearset, some swear by them. the combinations people use are

helical gearset + straight cut drop gears
straight cut gearset + straight cut drop gears
straight cut gearset + helical drop gears,

i chose to use helical drops as its a lot quieter.

heres the very worn diff pin of mine.

Edited by bennyy on 11th Aug, 2011.

Audi s4 b5 - 470bhp & 486ft lbs

On 30th Apr, 2012 Brett said:
yeah stick the bit in and give it a wobble

Ah I see! I was close :) People on here explain things so much better than the mini forum! They just say "Use the search engine" or "read a book".

This explains a lot, I'll get a picture up tommorow as I'm off work.

Audi s4 b5 - 470bhp & 486ft lbs

On 30th Apr, 2012 Brett said:
yeah stick the bit in and give it a wobble

ah they do try though,

the thing that really pisses me off about TMF is the search is absolute wank!

Yeah the seach is pony, but all they do is tell you to use it!

The search function on TMF seems to bring up every single thread on the forum...

Audi s4 b5 - 470bhp & 486ft lbs

On 30th Apr, 2012 Brett said:
yeah stick the bit in and give it a wobble

I've just been having a think..
If I'm using a close ratio gearbox, and a 3.44 final drive, will the engine just go through the gears really quickly? Will I need to get a better final drive?

have a look on guess work's web site. there's a ratio calculator, which will show you how it will rev in each gear with each gearset/final drive combination.