Diff's

[sagaris22]

im lookign to alter my diff from standard to accelaration and ive bene told tvr or btr do a variety of crown wheels to increase acceleration although reducing top speed (which doesnt matter to me)

i dont have the close ratio box and just the standard gates and standard diff of 1.34 or 3.4 i think iv'e heard 3.7 or 1:37 will improove acceleration from 27/mph/1000 rpm to 23mph/1000 rpm

any one any exp or good knowledge of this theyre end as i cant afford to chage the gear box at moment and only the diff assumes the prices ive been told are correct or roughyl right

thanks in advance

rodger

[v8sag]

Probably doesn't help too much being on the other side of the globe,but you can get ratio's for that diff from around 2.7 to 4.1.
They are the same diffs as in the Holden commodores and HSV's(different casing)
Cost to change crown and freshen was approx 200 UKP.

[sagaris22]

thanks yes id heard firm was australian btr racing i think, im prob wrong

any more information would be good if poss and thanks
rodger

[v8sag]

I thought some of you guys were already changing ratios,I wouldn't know how to help you in the UK but if you run out of luck,pm me with the ratio you require and I can price one up.

[mongoose]

sagaris22 said:

im lookign to alter my diff from standard to accelaration and ive bene told tvr or btr do a variety of crown wheels to increase acceleration although reducing top speed (which doesnt matter to me) i dont have the close ratio box and just the standard gates and standard diff of 1.34 or 3.4 i think iv'e heard 3.7 or 1:37 will improove acceleration from 27/mph/1000 rpm to 23mph/1000 rpm any one any exp or good knowledge of this theyre end as i cant afford to chage the gear box at moment and only the diff assumes the prices ive been told are correct or roughyl right thanks in advance rodger

It might be possible that TVR put the wrong ratio diff in your car when built.I just heard about a sag that had only 330bhp as std and the diff ratio was completely the wrong type,it got blitzed by a mk1 Tuscan 's' and this is how the owner found out apparently.Might be worth finding out what yours is for certain,then taking it up with tvr if its not right?

>> Edited by mongoose on Tuesday 11th April 14:13

[sagaris22]

Now thats very helpful as i have constantly reffered to car as i drove a tuscan s and it would leave sagaris standing and thats what ive been trying to achieve from ratio and diff queries

[jellison]

More power and same CR is easiest way forward - maybe why not alot on here bother changing, my std 3.45 is perfect with 1.5+X the power, more top end and wider speed range in each (higher rev limit engine).

Try not to use TVR dealer for this you will get stiffed - ring thr BTR delaer in UK and go one higher CR - keep some top end but get more oomph / acceleration (I thought the Sag I had a go in lacked neck snapping acceleration - lack of torque not power).

All that changing diff CR S8 is planning on the Tuscan SBC is to my mine a total waste of time for the above reasons.

[sagaris22]

Yes i know where comign from but how do i get more power out it? i am lookign into supercharging it via tvr craft but otherwise cant see any other method at present?

rodger

[tvrolet]

Ah, maybe we want to swap diffs? The hydratrak that I guess is on your saggy is a BTR unit (made in Australia). I think it's now owned by hardy spicer, and if you find them on the 'net (I'm in an airport so not up to trawling) you'll find the site does list the ratios.

My Tuscan also has a hydratrak but I'm guessing the ratio will be too low for the slower reving chevy lump. I can show you my spreadsheets at the next Powmill meet and you can see the differences of the different ratio...

WB

[jellison]

tvrolet said:

Ah, maybe we want to swap diffs? The hydratrak that I guess is on your saggy is a BTR unit (made in Australia). I think it's now owned by hardy spicer, and if you find them on the 'net (I'm in an airport so not up to trawling) you'll find the site does list the ratios. My Tuscan also has a hydratrak but I'm guessing the ratio will be too low for the slower reving chevy lump. I can show you my spreadsheets at the next Powmill meet and you can see the differences of the different ratio... WB

Good idea.

Yesterday (19:58)
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Yes i know where comign from but how do i get more power out it? i am lookign into supercharging it via tvr craft but otherwise cant see any other method at present?

rodger

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But why not just go for one Crown wheel and pinion higher (larger number to one) - compromise but then life is!

Unless you want to do a straight swap?

And I'll sell you engine and and lob in an LS7

[sagaris22]

yes one higher crwon and stuff but whats an ls7?

sorry im stpuid this end hence why i posted

rodger

[tvrolet]

OK Roger - here's the link to Dana, aka Spicer, aka BTR. www.spiceraxle.com.au/products.htm

The M80IRS is what I think is in the saggy. You'll see the ratios of 3.07, 3.23, 3.46, 3.73, 3.91 are available. I can't confirm what the ratio is in your car, and I'm not sure I'd trust what the manual/spec says either However, it WILL be marked on the diff itself. Not on the actual unit, but there's an oil level plug on the diff, and it should be screwed through an aluminium 'tag'. This 'tag' will have the ratio marked on it. On my Tuscan, I've 3.73 unit, which arguably is better for acceleration, but not wanting to rev my Chevy motor much past 5500rpm, it'll give a pants top speed so I'm on the lookout for...well a 3.07 sounds good to me!

Chaging the diff rations cannot gove you more power - power is a funtion of the engine. All it can to is lift or lower the overall gearing. However, as a funtion of lifting or raising the gearing the ratios themselves will become wider (or closer). So, assuming you are on a 3.46, if you went to a 3.73 (like mine ) then all the gears would deliver 0.88 if their current maximum speed. So, if 1st currently gets you say 49mph and 2nd gives you 74, then on a 3.73 ratio 1sy would deliver 45 and 2nd would max out at 69. But, the difference in speeds between 1st and second would go from 25mph to.....24mph. But then if your top gear pulls 170, then the same revs on a 3.72 will max out at 158.

So, if you have to slip the clutch like crazy to pull away at full tilt, then a different diff ratio might gain you a few thousanths. Likewise, of you are coming out of the powerband between shifts a different ratio might help (but of course a CR box would be a better alternative). Or of top is acting like an overdrive and you simply can't pull peak revs, a different ratio might let you max out.

However, all in all, there are more effective ways of getting more performance than just changing the diff - especially if it's a road car and you're not trying to extract every last ounce of performance.

WB

[sagaris22]

Thanks for that and i do appreciate it, i was aware of the diff ratios etc etc and obv the reduction in speed/gear etc.

i just cant get head round how i get the saggy accelarting like the tuscans i drove as its was ballistic to 100mph and would leave saggy in the dust i feel

if not diff then not lot else i can think off
this end

rodger

[tvrolet]

sagaris22 said:

i just cant get head round how i get the saggy accelarting like the tuscans i drove as its was ballistic to 100mph and would leave saggy in the dust i feel

There are obviously good'uns and bad'uns out there, and all points inbetween as all rolling road reasults show. Yours may still have a tight motor and/or the tuscan could have been real loose. Lots of cars are run in wrongly (too gently) and don't make the power of thrashed (when hot) cars. Car might just be a wee bit off tune too. Plus any of the more low-tech options, like is the throttle really opening fully. On loads of cars what seems full throttle in the cabin is actually limited by carpet/pedal stops etc. So for a start, with the engine off, press the throttle hard down and make sure the thottle bodies on the engine are opening up 100%. Other that that - make sure it's setup 100% and give it the thrashing of its life for 5000 miles (once warmed up!) and see how it goes. Or, and of more practical benefit, just carry 10-15 mpg more into the corners than the 'fast' tuscan, and you'll have a head start of 15-20mph on the next straight Straights only just mess up the roads between the corners anyway.

[sagaris22]

many thanks for response and detail in them

i had car out wee while ago and its 27mph/1000 rpm which i think is the 3.1 diff not sure


but many thanks also

appreciated
rodger

[jellison]

not wanting to rev my Chevy motor much past 5500rpm!!!!!!!!!!!!!!!!?

[Arnoldgroves]

Seeking some advise... I have a mate in the UK with a 4.5ltr 1999/2000 Cerb. It has the BTR rear diff and I want to get hold of a service kit (seals and the aluminium centering screws driveshaft into diff) is this something that is readily available in the UK? If so from where ?

Are the parts readily available in Australia (Holden) if so any idea on part numbers ? I'm in Sydney at the moment and could purchase here if possible and take back to the UK when I go on 10th October.

Thanks all in advance

[teamHOLDENracing]

Ring John Read at Grantura Engineering. 07799 117211

They rebuild BTR diffs, we use them in the race TVRs