LocostBuilders - powered by XMB

Transmission Ratios

DarrenW - 16/4/08 at 09:36 AM

Never fully understood transmission ratios etc, or spent time to find out what potential effects they can have.

Following on from John's thread ive just downloaded gearcalc from the BGH site for a bit play. Bloody hell. No need to bother modding engine any more then eh!

Just sussed that a 3.62 diff would be a good budget mod and allow 60 to be had in 2nd. Then a change to an E3 box should in theory transform the car (not so budget mod).

Never been inside a gearbox before - cant be that hard to rebuild can they if you take time and are methodical. Dont have any pocket money at the mo but sounds like a decent future project.

mcerd1 - 16/4/08 at 10:23 AM

the only real gain you'll get from t9 boxes with a long 1st gear (like the BGH E2) is 1st should become a usable gear, not just for parking

after that your basically aiming to get the best use of the torque (& power) that your engine can produce over its rev range in each gear

assuming you've got a 3.92 diff just now - if you change to a 3.62, then all you've done is make all the gears 8% higher, so the engine will be running at lower rev's for the same road speed

that'll be good for the motorway, but your engine will be working harder to accelerate (and since you don't have a V8 with masses of spare torque you'll probably notice this)

if you make the gearing too high you might end up with a 5th gear that's so high you can only use it for motorway speeds at low rpm (your engines only got so much power)

ask yourself how you really drive it, on the road I doubt you'll take it all the way to the rev limit in 2nd gear - so working with the revs at max. power (or rev at a normal gear change) will give you a more realistic idea of the differences

but the real question is:
when your driving the car - do you wish the gears where closer together ? higher ? lower ?

then run you current setup through a gear calc and see if you can spot the bits you don't like when driving it - then you just need to try and work out if any of the other ratio sets would actually correct this

[Edited on 16/4/08 by mcerd1]

DarrenW - 16/4/08 at 10:54 AM

Good points. car is mainly used on the road. What ive noticed more is that 1st is almost waste of time, 2nd and 3rd dont seem too bad but when i change down to do a quick overtaking move i could do with a bit better pick up. Drop to 2nd and there isnt enough left to get passed before changing to 3rd. Drop to 3rd and thee isnt enough oomph to accelerate how id like. Does that make sense? Dont get me wrong - car is rapid, a lot faster sincer changing to bike carbs. Problem is ive got more confidence to overtake now so thinking about how to fine tune that part of the driving pleasure. It never stops does it?

Is it also true that changing to 3.62 diff may allow me to get to 60 with one gear change but car will likely take longer to get there? Mind you at this time of year anything other than bone dry just means the wheels spin up off the line anyway. The 3.62 also seems to give a slightly higher theoretical top end, so im guessing when cruising ill be doing a few less revs and maybe better mpg.

So is it also true that changing to 4.1 or 4.44 ratios = faster acceleration in each gear, lower top end and higher revs at cruising speed.

What ive learnt so far is that there isnt any right answers to this. Shame we cant have a diff with 2 or 3 selectable ratios, kind of like high and low ratio on a land rover but not as far apart.

I should say that other than poss the diff i probs wont change the gearing of the car - just interested in the reasearch of it to understand what ive got now better.

[Edited on 16/4/08 by DarrenW]

mcerd1 - 16/4/08 at 11:23 AM

quote:
Originally posted by DarrenW
So is it also true that changing to 4.1 or 4.44 ratios = faster acceleration in each gear, lower top end and higher revs at cruising speed.

well sort of .....

I'm not really up to speed my self on this - but as I understand it:

if your overall gearing is too high, the car will bogg down and struggle to pull away (just like if you try and pull away in 2nd or 3rd) - obviously this is slower off the line but higher top speeds are theoreticaly possible (if your engine has the power)

if your gearing is too low, you'll have to change gears alot more often (slowing you a little), and you'll run out of gears and rev's before you've run out of power

so your just tring to find the best compomise of these to suit your driving style (and fuel econnomy if your worried about that)

if your building the car for a single purpose (say drag racing, or 1 particular track) then you can test all the options and pick the one thats fastest

if your just driving it on the road, I'd say your best bet will be to try it and see if you like it - but it does sound like one of the long 1st gear kits would be good for you (especially if you try a 3.62 diff)
or better yet, compair it to someone elses car that already has the ratio your thinking about using

one thing I've been checking is the engine rpm at different speeds in different gears - but everything I've done so far is a guess

I'm building my engine for higher revs, so I've gone for a 3.92 diff just now, lowish compaied to some cars but not too low for the road (but later a 4.44 might be better for the track)

I've got 245/45 R16 tyres and 2.66 1st/ 1.75 2nd/ 1.26 3rd/ 1.0 4th/ 0.86 5th
but the main resons for the BGH box were 1st gear and the HD bearings

[Edited on 16/4/08 by mcerd1]

britishtrident - 16/4/08 at 11:42 AM

best single mod is to get the 1st and 2nd ratios close to either the old semi-close ratio "2000e" or for 2litre engines the "Bullet" ratios.

oldtimer - 16/4/08 at 06:11 PM

I think you are getting some useful advice. I am having the same issues. We all want to get it right first time instead of having to re gear after its all up. I am suprised you were thinking of a 3.62 if you are already wanting more ooompph whilst overtaking though. Surely most of us want a car for a quick blat, the odd track day, and only occasional motorways??.. My thoughts were for a BGH high first HD box with 4.4 diff. OK so motorways won't be that relaxing but thats not where I'll be spending my time or having my fun. There are no 4.4 ratios to be had as the moment but I think that would cure your bogging down issues and the tall first still is useable. Drag makes high top speed irrelevant. Good luck!

NS Dev - 16/4/08 at 07:40 PM

I have a std 2.0 type 9 sierra gearset and 3.62 diff on my XE engine and I actually find it great on the road.

First IS useable, in "modern" road environment where everybody is so slow, and 2nd is EASILY good for more than 60 (though I have 7800rpm available)

Only gear that is a bit pointless is 5th, only really use that for over 100mph and that isn't a comfortable proposition for any length of time!!

mcerd1 - 16/4/08 at 09:03 PM

I don't know what size tyres your all running but, tyre size could be a big factor here

the differnce between a set of 185/60 13's and my 245/45 16's is more than the difference between a 3.92 and a 3.62 diff !

btw if you can use a 7.5" diff (with 100mm flanges) the ugly scorpio 2.0's had some low ratios (8v = 4.09 and 16v = 4.27 )

DarrenW - 17/4/08 at 08:09 AM

quote:
Originally posted by oldtimer
My thoughts were for a BGH high first HD box with 4.4 diff. OK so motorways won't be that relaxing but thats not where I'll be spending my time or having my fun. There are no 4.4 ratios to be had as the moment but I think that would cure your bogging down issues and the tall first still is useable. Drag makes high top speed irrelevant. Good luck!

This company do the 4.4 ratio sierra diffs.
http://www.kamdiffs.com/sierra.htm
Not sure what other diff options they do - sems to be loads listed.

2nd reason for this post was to capture some common sense etc for other people to read. Looks like its achieving that.

Mcerd1 - im running the bog std regulation 195/50 x 15's. Toyo T1s's at the mo - good budget tyre but not the stickiest and they are a factor this time of year. Trying to do standing 0 - 60's and they just spin up - need to assess affect of bike carbs when its dry.

Ive no intention to go silly with mods. In the order of things cam timing, megajolt fine tune and suspension set up are higher in the order anyway. Right now im loving the bike carb conversion - what is interesting is that as you do one mod another rears its ugly head. Trick is knowing when to stop!! Im probs only after a bit more 40 - 70 ish mph acceleration so i can get past one more car - maybe thats asking for bother! A year ago i would have sat back and enjoyed the scenery more.

Drier months always yield a different driving experience than this time of year anyway so i guess ill have to stop being mechanically sympathetic and work the revs more.

[Edited on 17/4/08 by DarrenW]

mcerd1 - 17/4/08 at 12:54 PM

quote:
Originally posted by DarrenW
Ive no intention to go silly with mods. In the order of things cam timing, megajolt fine tune and suspension set up are higher in the order anyway. Right now im loving the bike carb conversion - what is interesting is that as you do one mod another rears its ugly head. Trick is knowing when to stop!!

you said it - pity I've not mastered that trick yet....

mine isn't even nearly on the road, but I've upgraded/ mod'd nearly everything that I've looked at

my engine was going to be a bogg standard ford EFI pinto, but I couldn't be bothered with all the wires - so bike carbs got added to the list (thanks to PPC mag and this forum)

then I got the 'upgrading' bug - and as a result I've got: 285 cam, crank, conrods, flywheel, megajolt, BGH box, LSD........... and thats before I've done any real head work (never mind powdercoating)

but for all that, is my car really going to be that much quicker ???

[Edited on 17/4/08 by mcerd1]

NS Dev - 18/4/08 at 01:45 PM

quote:
Originally posted by DarrenW

quote:
Originally posted by oldtimer
My thoughts were for a BGH high first HD box with 4.4 diff. OK so motorways won't be that relaxing but thats not where I'll be spending my time or having my fun. There are no 4.4 ratios to be had as the moment but I think that would cure your bogging down issues and the tall first still is useable. Drag makes high top speed irrelevant. Good luck!

This company do the 4.4 ratio sierra diffs.
http://www.kamdiffs.com/sierra.htm
Not sure what other diff options they do - sems to be loads listed.

2nd reason for this post was to capture some common sense etc for other people to read. Looks like its achieving that.

Mcerd1 - im running the bog std regulation 195/50 x 15's. Toyo T1s's at the mo - good budget tyre but not the stickiest and they are a factor this time of year. Trying to do standing 0 - 60's and they just spin up - need to assess affect of bike carbs when its dry.

Ive no intention to go silly with mods. In the order of things cam timing, megajolt fine tune and suspension set up are higher in the order anyway. Right now im loving the bike carb conversion - what is interesting is that as you do one mod another rears its ugly head. Trick is knowing when to stop!! Im probs only after a bit more 40 - 70 ish mph acceleration so i can get past one more car - maybe thats asking for bother! A year ago i would have sat back and enjoyed the scenery more.

Drier months always yield a different driving experience than this time of year anyway so i guess ill have to stop being mechanically sympathetic and work the revs more.

[Edited on 17/4/08 by DarrenW]

tyres make a HUGE difference.

I had driven a few sevens on the road (various makes and suspension setups) and one thing they all shared (even a std westfield with 100hp bog std pinto) was a total lack of full throttle traction.

On my locost, running medium compound yokohama A048R's, I can give it full throttle from 25mph in first gear, through each gear, in a straight line and on a dry road, and it chirps on the gear changes and squirms a bit but the revs never flutter or soar.

Traction just isn't an issue, and that's with 200hp and 540kg split almost exactly 50-50.

I also run soft (140lb) rear springs, which also helps.

DarrenW - 18/4/08 at 08:16 PM

I reckon thats my biggest issue at the moment Nat. Good corner weight set up and some sticky rubber would probs transform the car and inspire more confidence.