3.08 diff - again!
Discussion
The six speed box may well be the best solution, provided that the ratios are well chosen to suit the weight of car and power available.
My point is that the 5ltr cars ended up being substantially under geared.
As far as I can tell, TVR had no input into the gearing available in the T5 gearbox, but I'm happy to be corrected on this point. What they certainly could choose from, was the wide range of ratios available for the BTR M76 IRS differential. I have no doubt that the 3.45 ratio was a good choice for the 4ltr cars, bit not so for the 5ltr cars. 1st is hooelessly high and has to be got out of just as quickly as possible. 2nd is completely irrelevant. 3rd is a satisfactory 2nd. 4th is useful as a change down for roundabouts or a really fast overtake, but unnecessarily low for about town etc. 5th is the gear used most of the time and that is unnecessarily low for motorway or even A road cruising.
So as I see it, changing the final drive ratio is the perfect way to correct it. As to what the final ratio should be, that is the question. In practice it comes down to 3.23 :1 or 3.08 :1.
I think that 3.23 would certainly be an improvement and who knows, maybe the correct choice. To me, the figures still looked too close to the 3.45 :1, so I have chosen to try the 3.08 and time will tell. It's not a choice set in stone, if I don't like it next year, I'll change it again the following winter.
As I am doing all the work myself, the outlay is not great, so experimentation is viable.
Dougal.
My point is that the 5ltr cars ended up being substantially under geared.
As far as I can tell, TVR had no input into the gearing available in the T5 gearbox, but I'm happy to be corrected on this point. What they certainly could choose from, was the wide range of ratios available for the BTR M76 IRS differential. I have no doubt that the 3.45 ratio was a good choice for the 4ltr cars, bit not so for the 5ltr cars. 1st is hooelessly high and has to be got out of just as quickly as possible. 2nd is completely irrelevant. 3rd is a satisfactory 2nd. 4th is useful as a change down for roundabouts or a really fast overtake, but unnecessarily low for about town etc. 5th is the gear used most of the time and that is unnecessarily low for motorway or even A road cruising.
So as I see it, changing the final drive ratio is the perfect way to correct it. As to what the final ratio should be, that is the question. In practice it comes down to 3.23 :1 or 3.08 :1.
I think that 3.23 would certainly be an improvement and who knows, maybe the correct choice. To me, the figures still looked too close to the 3.45 :1, so I have chosen to try the 3.08 and time will tell. It's not a choice set in stone, if I don't like it next year, I'll change it again the following winter.
As I am doing all the work myself, the outlay is not great, so experimentation is viable.
Dougal.
Dougal9887 said:
The six speed box may well be the best solution, provided that the ratios are well chosen to suit the weight of car and power available.
My point is that the 5ltr cars ended up being substantially under geared.
As far as I can tell, TVR had no input into the gearing available in the T5 gearbox, but I'm happy to be corrected on this point. What they certainly could choose from, was the wide range of ratios available for the BTR M76 IRS differential. I have no doubt that the 3.45 ratio was a good choice for the 4ltr cars, bit not so for the 5ltr cars. 1st is hooelessly high and has to be got out of just as quickly as possible. 2nd is completely irrelevant. 3rd is a satisfactory 2nd. 4th is useful as a change down for roundabouts or a really fast overtake, but unnecessarily low for about town etc. 5th is the gear used most of the time and that is unnecessarily low for motorway or even A road cruising.
So as I see it, changing the final drive ratio is the perfect way to correct it. As to what the final ratio should be, that is the question. In practice it comes down to 3.23 :1 or 3.08 :1.
I think that 3.23 would certainly be an improvement and who knows, maybe the correct choice. To me, the figures still looked too close to the 3.45 :1, so I have chosen to try the 3.08 and time will tell. It's not a choice set in stone, if I don't like it next year, I'll change it again the following winter.
As I am doing all the work myself, the outlay is not great, so experimentation is viable.
Dougal.
Is’nt it great we have cars so powerful you only need use half the gears My point is that the 5ltr cars ended up being substantially under geared.
As far as I can tell, TVR had no input into the gearing available in the T5 gearbox, but I'm happy to be corrected on this point. What they certainly could choose from, was the wide range of ratios available for the BTR M76 IRS differential. I have no doubt that the 3.45 ratio was a good choice for the 4ltr cars, bit not so for the 5ltr cars. 1st is hooelessly high and has to be got out of just as quickly as possible. 2nd is completely irrelevant. 3rd is a satisfactory 2nd. 4th is useful as a change down for roundabouts or a really fast overtake, but unnecessarily low for about town etc. 5th is the gear used most of the time and that is unnecessarily low for motorway or even A road cruising.
So as I see it, changing the final drive ratio is the perfect way to correct it. As to what the final ratio should be, that is the question. In practice it comes down to 3.23 :1 or 3.08 :1.
I think that 3.23 would certainly be an improvement and who knows, maybe the correct choice. To me, the figures still looked too close to the 3.45 :1, so I have chosen to try the 3.08 and time will tell. It's not a choice set in stone, if I don't like it next year, I'll change it again the following winter.
As I am doing all the work myself, the outlay is not great, so experimentation is viable.
Dougal.
As the speed limit is 70mph The original gearing is what I’d expect from a car of that era which used parts from an even earlier era lol.
I agree broadly and yes experimentation is viable if you have the skills.
I think Daz 3.08 seems to work well so on the very powerful cars pushing 330 + a very good idea most likely.
Be good to hear your results.
I’ve been thinking of real life driving, town and roundabouts etc.
Most roundabouts can be negotiated in 3 rd gear if you have a decent set up and no shunting, down to as low as 1000 r3vs on some glorious cars, this is extremely low speed for 3rd gear, maybe as slow as 15/18 mph, the torque of the RV 8 easily pulls my car back upto 30 mph effortlessly, with the higher gearing these regular style roundabouts and local car slowing measures will require a gear change down to 2nd as shunt will be much more likely.
I think the gearing overall although feels low is not really. Over 110 mph you will be accelerating a lot slower unless like Daz you have 360 bhp which 99% of us do not have.
The only time I think the 3.08 will come into its own would be on long motorway runs, boring.
Or on a drag strip if you have huge power.
These cars are not that powerful once wind speed hits them. Even the 5.0l
That’s my take because I did think about this quite a bit when a few guys opted for it. I have driven over 40,000 miles in my TVR so it’s based on that experience.
Overall I’m happy with the gearing, it’s better through villages too, more revs = more noise
Most roundabouts can be negotiated in 3 rd gear if you have a decent set up and no shunting, down to as low as 1000 r3vs on some glorious cars, this is extremely low speed for 3rd gear, maybe as slow as 15/18 mph, the torque of the RV 8 easily pulls my car back upto 30 mph effortlessly, with the higher gearing these regular style roundabouts and local car slowing measures will require a gear change down to 2nd as shunt will be much more likely.
I think the gearing overall although feels low is not really. Over 110 mph you will be accelerating a lot slower unless like Daz you have 360 bhp which 99% of us do not have.
The only time I think the 3.08 will come into its own would be on long motorway runs, boring.
Or on a drag strip if you have huge power.
These cars are not that powerful once wind speed hits them. Even the 5.0l
That’s my take because I did think about this quite a bit when a few guys opted for it. I have driven over 40,000 miles in my TVR so it’s based on that experience.
Overall I’m happy with the gearing, it’s better through villages too, more revs = more noise
Classic Chim said:
Over 110 mph you will be accelerating a lot slower unless like Daz you have 360 bhp which 99% of us do not have.
I can't imagine why you think that. My rate of acceleration will depend where I am in my torque curve. In 5th gear:
With 3.08 at 110mph I will be at 3700rpm and well within the torque curve up to 4500 at 135mph.
With 3.45 at 110mph I will be at 4100rpm and shortly it will be in decline at 4500rpm at 120mph.
Obviously, if a lower speed was compared in 5th then 3.45 would look more favourable, but I would have the choice to change down and tip the balance in favour of the 3.08.
Thats what the gearbox is for.
Something to do with the higher ratios being slower at accelerating, each gear change revs drop right off as you now use a higher gear. At this point until you are back in the power band your pulling the same weight with the same power but with less acceleration.
That’s the science of it, I’m closer to my optimum power curve with less drag to get to those those revs, a higher ratio Dif it will take longer to get there in theory but if you are sure go for it. I’ve not heard any complaints so more than happy to be corrected.
It’s the slow speed stuff which really matters id suggest but that depends on how and where you use your car I’d have thought.
Don’t discount what I said about roundabouts, I no longer have to change down as I do not get shunt down to tickover since MBE, It’s a lazy drive and fantastic for it, it’s a right PITA changing down when there’s more than enough power in third but for shunt / gearing.
Just a thought really based on using my clutch by about 30% less than with a shunting car.
Real pleasure rather than slightly annoying but I am talking about lazy easy driving as speed matters little in the scheme of things if it’s a useable car. As so much driving is reduced speed now days this element is something of a holy grail to achieve in a TVR.
That’s the science of it, I’m closer to my optimum power curve with less drag to get to those those revs, a higher ratio Dif it will take longer to get there in theory but if you are sure go for it. I’ve not heard any complaints so more than happy to be corrected.
It’s the slow speed stuff which really matters id suggest but that depends on how and where you use your car I’d have thought.
Don’t discount what I said about roundabouts, I no longer have to change down as I do not get shunt down to tickover since MBE, It’s a lazy drive and fantastic for it, it’s a right PITA changing down when there’s more than enough power in third but for shunt / gearing.
Just a thought really based on using my clutch by about 30% less than with a shunting car.
Real pleasure rather than slightly annoying but I am talking about lazy easy driving as speed matters little in the scheme of things if it’s a useable car. As so much driving is reduced speed now days this element is something of a holy grail to achieve in a TVR.
Edited by Classic Chim on Wednesday 8th July 17:17
I went from a 3.73 to 3.08 and I wish i had done it years ago! Cruising is much more relaxed, and before I felt like i was changing out of first immediately after pulling away so it was pretty much a useless gear. Also on the 1/4 mile it was bouncing off the limiter in 4th gear over the line!
I do need a few more revs pulling away now (I also have a very light flywheel) but overall it has been a massive benefit to the car
I do need a few more revs pulling away now (I also have a very light flywheel) but overall it has been a massive benefit to the car
Classic Chim said:
Classic Chim said:
^^^^^^^ that’s good to know then. Most will be running the 3.45
ETA what power output are you pushing out
ETA what power output are you pushing out
My personal opinion (and it is just an opinion folks), is that the 3.45 diff is fine in a Chimaera that makes 250hp and 260ft/lbs like mine.
I'm also pretty sure my position would change if I ever hit or went north of 300
Dougal9887 said:
3.08 now fitted and I have a fully useable 5 speed gearbox! Very, very pleased with the result.
I have a trackday booked at Anglesey in a month so the 1000ml round trip and track outing will be a great all round test.
Hydratrak also fitted, but that's another story.
Dougal
Sounds like a good upgrade, I often find myself thinking mine could do with longer legs. And no matter how much we like to convince ourselves these cars are only for hooning round the twisties I suspect most of the miles racked up are actually on motorways, A roads and in boring traffic where it doesn't really matter. I have a trackday booked at Anglesey in a month so the 1000ml round trip and track outing will be a great all round test.
Hydratrak also fitted, but that's another story.
Dougal
indigochim said:
Sounds like a good upgrade, I often find myself thinking mine could do with longer legs. And no matter how much we like to convince ourselves these cars are only for hooning round the twisties I suspect most of the miles racked up are actually on motorways, A roads and in boring traffic where it doesn't really matter.
I think the more reliable you make them the more a mod like this might just come into its own because as you say depending on your driving choices the more reliable it is the more likely you will pull it out and do those longer journeys. I always has the same feeling but through France I found mine more economical at at steady 80 mph as opposed to a steady 70 mph, it just feels more balanced with then engine spinning slightly faster I think.
I’m hoping this will indeed be a great mod though so looking forward to a happy owner after some trials.
I wonder if the higher gearing will have any effect on your fuel and timing map?
Are the revs actually not that different, I’m sure I could find the answer but if it’s say less than 400 revs for any given speed mapping should still be in a good window surely?
Thoughts chaps
Edited by Classic Chim on Monday 10th August 10:41
My road test showed I was now running leaner, so about a 12% on average EGO correction. After a few miles I switched on autotune to start correcting this.
Regrettably the clunk from the rear was still present.
Back on the lift it was obvious that the unwanted backlash was in the spider gears.
On hindsight, I should have checked this out before dismantling the hydratrak diff, which was new to me. It is difficult to determine side gear backlash once dismantled.
Anyway, diff back out again, 2 hrs flat this time now that I know all the short cuts!
So now a bit of delay while I source suitable shims for the side gears.
One very interesting side benefit to this unexpected disassembly, I was able to view the actual tooth pattern after a 20 mile drive as some reassurance that my gear paste adjustments were good. It was spot on, so very pleased. (This was possible only because the new gears start with a matt black heat treated finish which is polished shiny in use)
Dougal.
Regrettably the clunk from the rear was still present.
Back on the lift it was obvious that the unwanted backlash was in the spider gears.
On hindsight, I should have checked this out before dismantling the hydratrak diff, which was new to me. It is difficult to determine side gear backlash once dismantled.
Anyway, diff back out again, 2 hrs flat this time now that I know all the short cuts!
So now a bit of delay while I source suitable shims for the side gears.
One very interesting side benefit to this unexpected disassembly, I was able to view the actual tooth pattern after a 20 mile drive as some reassurance that my gear paste adjustments were good. It was spot on, so very pleased. (This was possible only because the new gears start with a matt black heat treated finish which is polished shiny in use)
Dougal.
Dougal9887 said:
3.08 now fitted and I have a fully useable 5 speed gearbox! Very, very pleased with the result.
I have a trackday booked at Anglesey in a month so the 1000ml round trip and track outing will be a great all round test.
Hydratrak also fitted, but that's another story.
Dougal
Hi DougalI have a trackday booked at Anglesey in a month so the 1000ml round trip and track outing will be a great all round test.
Hydratrak also fitted, but that's another story.
Dougal
can i ask where you purchased the 3.08 gear set from and if it is the 7.75" dia version?
Also be interested in where you got your hydratrak diff please.
I took my whining diff to John Reid for another rebuild last week. It will only be back in the car temporary to see my through the end of this year as while i was there i had a nice chat with John and agreed to have a M80 built for 2022 with a 3.07:1 gear set and will also be fitting the superior Quaife LSD.
Not cheap but I think the way forward for my car. Next will be a gearbox upgrade. How my T5 is still in 1 piece is beyond me. Maybe its my smooth mechanically sympathetic gear change technique
Something else i am wanting to try soon is flat shift. A micro switch on the clutch pedal wired to the Megasquirt ECU. Keep my foot buried on the throttle maintaining boost and when stabbing the clutch on gear changes the ECU temporarily sets a specified rev limit. Whats the worst can happen?
Not cheap but I think the way forward for my car. Next will be a gearbox upgrade. How my T5 is still in 1 piece is beyond me. Maybe its my smooth mechanically sympathetic gear change technique
Something else i am wanting to try soon is flat shift. A micro switch on the clutch pedal wired to the Megasquirt ECU. Keep my foot buried on the throttle maintaining boost and when stabbing the clutch on gear changes the ECU temporarily sets a specified rev limit. Whats the worst can happen?
DangerousDerek said:
I took my whining diff to John Reid for another rebuild last week. It will only be back in the car temporary to see my through the end of this year as while i was there i had a nice chat with John and agreed to have a M80 built for 2022 with a 3.07:1 gear set and will also be fitting the superior Quaife LSD.
Not cheap but I think the way forward for my car. Next will be a gearbox upgrade. How my T5 is still in 1 piece is beyond me. Maybe its my smooth mechanically sympathetic gear change technique
Something else i am wanting to try soon is flat shift. A micro switch on the clutch pedal wired to the Megasquirt ECU. Keep my foot buried on the throttle maintaining boost and when stabbing the clutch on gear changes the ECU temporarily sets a specified rev limit. Whats the worst can happen?
So the same effect as a partial lift of the throttle but not actually shutting off. Not cheap but I think the way forward for my car. Next will be a gearbox upgrade. How my T5 is still in 1 piece is beyond me. Maybe its my smooth mechanically sympathetic gear change technique
Something else i am wanting to try soon is flat shift. A micro switch on the clutch pedal wired to the Megasquirt ECU. Keep my foot buried on the throttle maintaining boost and when stabbing the clutch on gear changes the ECU temporarily sets a specified rev limit. Whats the worst can happen?
Gearbox cart drivers using two stroke screaming engines do that and simultaneously pull it up the box. Crash gearbox but it won’t do it without the slight throttle lift. It’s all instant changes with no real loss of acceleration and a massive kick up the arse so it works.
The difference is the flywheel weight on a big engine wouldn’t allow it to react quick enough so yeah a good idea to use some tech
DangerousDerek said:
I took my whining diff to John Reid for another rebuild last week. It will only be back in the car temporary to see my through the end of this year as while i was there i had a nice chat with John and agreed to have a M80 built for 2022 with a 3.07:1 gear set and will also be fitting the superior Quaife LSD.
Not cheap but I think the way forward for my car. Next will be a gearbox upgrade. How my T5 is still in 1 piece is beyond me. Maybe its my smooth mechanically sympathetic gear change technique
Something else i am wanting to try soon is flat shift. A micro switch on the clutch pedal wired to the Megasquirt ECU. Keep my foot buried on the throttle maintaining boost and when stabbing the clutch on gear changes the ECU temporarily sets a specified rev limit. Whats the worst can happen?
Sounds good Derek I have the wiring in place for flat shift but thats all I got Not cheap but I think the way forward for my car. Next will be a gearbox upgrade. How my T5 is still in 1 piece is beyond me. Maybe its my smooth mechanically sympathetic gear change technique
Something else i am wanting to try soon is flat shift. A micro switch on the clutch pedal wired to the Megasquirt ECU. Keep my foot buried on the throttle maintaining boost and when stabbing the clutch on gear changes the ECU temporarily sets a specified rev limit. Whats the worst can happen?
set-up flat shift would def work well for your use too the uprated M80 diff sounds good with spares and options in abundance the T5 certainly takes a bashing seems to be the yanks opinion too well the ones avoiding brutality (constant power shifts etc) but that will bust a standard trans anyway ....eventually 
Derek, probably a bit late for a reply! I haven't been on the forum for a while.
Yes, it's a correct 7.75" set and I got it from Australia. However it was a NOS Holden part, so quite cheap compared to the current Dana price. Still had the cost of transport and import tax however. The shop I bought it from had bought up a job lot of Holden stuff and at the time had 5 of these. It sounds like you are sorted now but I can let you have the contact details if your interested.
The Hydratrak was from a Cerbera diff. As it allegedly had a low mileage, I rebuilt the differential without dismantling the differential gears. Then found I had the dreaded clonk. I took it all apart again and found the play to be in the Hydratrak differential spider gears. Their backlash is set with special conical cast iron shims which, when they wear thin enough, break in half. They are completely unavailable here or in Australia so far as I could find. So that was an end to the Hydratrak experiment and I went back to the shimmed up cone diff. I could of course have chosen the very good Quaife lsd, but decided, for me, it wasn't worth the expense. (However I am fitting one to my Honda Elise track car)
Dougal.
Yes, it's a correct 7.75" set and I got it from Australia. However it was a NOS Holden part, so quite cheap compared to the current Dana price. Still had the cost of transport and import tax however. The shop I bought it from had bought up a job lot of Holden stuff and at the time had 5 of these. It sounds like you are sorted now but I can let you have the contact details if your interested.
The Hydratrak was from a Cerbera diff. As it allegedly had a low mileage, I rebuilt the differential without dismantling the differential gears. Then found I had the dreaded clonk. I took it all apart again and found the play to be in the Hydratrak differential spider gears. Their backlash is set with special conical cast iron shims which, when they wear thin enough, break in half. They are completely unavailable here or in Australia so far as I could find. So that was an end to the Hydratrak experiment and I went back to the shimmed up cone diff. I could of course have chosen the very good Quaife lsd, but decided, for me, it wasn't worth the expense. (However I am fitting one to my Honda Elise track car)
Dougal.
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