Farid Posted February 3, 2017 Report Share Posted February 3, 2017 (edited) I see people spending thousands of dollars in either fitting an overdrive, or to opt for the so-called HVDA Conversion to their gearbox. Here is a naive question: Can one not put a taller gear on the 4th to resolve the high-RPM issue? Cheers, Farid Edited February 3, 2017 by Farid Quote Link to post Share on other sites
rhino_mac Posted February 3, 2017 Report Share Posted February 3, 2017 You could, but you'd have to rev the nuts off the car in third to stop the engine bogging down when you shift to fourth. Quote Link to post Share on other sites
Willie Felger Posted February 3, 2017 Report Share Posted February 3, 2017 Fitting a TR6 3.54 crown wheel and pinion set ( to an earlier car) from the standards 3.7 would make a bit of difference, but as cheap to buy a secondhand J type box with overdrive. Willie Quote Link to post Share on other sites
Lebro Posted February 3, 2017 Report Share Posted February 3, 2017 (edited) I see people spending thousands of dollars in either fitting an overdrive, or to opt for the so-called HVDA Conversion to their gearbox. Here is a naive question: Can one not put a taller gear on the 4th to resolve the high-RPM issue? Cheers, Zack Simple answer is NO. 4th gear isn't a gear at all, it simply connects the input shaft to the output shaft, so "gearing" is 1:1. There are no meshing gears that can be changed for 4th. To achieve what you suggest you would leave the gearbox alone, but fit a lower ratio back axle. Bob. Edited February 3, 2017 by Lebro Quote Link to post Share on other sites
stuart Posted February 3, 2017 Report Share Posted February 3, 2017 To achieve what you suggest you would leave the gearbox alone, but fit a lower ratio back axle. Bob. Higher ratio.- Lower number Stuart. Quote Link to post Share on other sites
Lebro Posted February 3, 2017 Report Share Posted February 3, 2017 Eh ? If 3.7:1 was standard then a lower ratio say for example 3.4:1 would make you go faster for a certain engine rpm Bob. Quote Link to post Share on other sites
Alec Pringle Posted February 3, 2017 Report Share Posted February 3, 2017 If 3.7 is standard, then 3.45 is a higher ratio for more mph per rpm relaxed cruising, whereas 4.1 is lower ratio for less mph per rpm but greater acceleration.Lower numerical final drive ratio equates to a higher gear . . . . . whereas higher numerical final drive ratio equates to a lower gear . . . . Cheers Alec Quote Link to post Share on other sites
Hamish Posted February 3, 2017 Report Share Posted February 3, 2017 I'm learning a lot on here -- I think ? ???? So a sprint / hill climb car would ideally want 4.1 And a long circuit race car 3.45 ?? So the standard for a 3a is somewhere in the happy medium 3.7 ?? (Depending on the gearbox / OD set up) ?? Quote Link to post Share on other sites
iain Posted February 3, 2017 Report Share Posted February 3, 2017 I'm learning a lot on here -- I think ? So a sprint / hill climb car would ideally want 4.1 And a long circuit race car 3.45 ?? So the standard for a 3a is somewhere in the happy medium 3.7 ?? (Depending on the gearbox / OD set up) ?? You and me both! But, yes is the answer to your assumptions. My Ex works car has always had a 4.1:1 axle.....Great acceleration but a bit peaky on the motorways! Iain Quote Link to post Share on other sites
Farid Posted February 3, 2017 Author Report Share Posted February 3, 2017 Thank you all for your input. I like to learn more about Bob's idea. Now the next equation would be, what be a compatible lower ratio back axle? Cheers, Farid PS. By the time I get a J-type gearbox with overdrive to this neck of the woods, it would cost me nearly $3000 Can (not a cost-effective option for yours truly!) Quote Link to post Share on other sites
Hamish Posted February 3, 2017 Report Share Posted February 3, 2017 Farid you are probably aware of Cheftush, he may be able to help out with sourcing Canadian parts. Though I understand Canada is not a small place. ???? https://m.youtube.com/user/cheftush Quote Link to post Share on other sites
Farid Posted February 3, 2017 Author Report Share Posted February 3, 2017 Thanks Hamish! Quote Link to post Share on other sites
Lebro Posted February 3, 2017 Report Share Posted February 3, 2017 I think we are attaching different definitions to the word "ratio" To my mind a ratio of 1 : 1 is a low ratio one side to the other, whereas a ratio of 10 : 1 is a higher ratio i.e. one side is 10 times larger than the other. Bob. Quote Link to post Share on other sites
Icarus60 Posted February 3, 2017 Report Share Posted February 3, 2017 No Bob It's not the definition word "Ratio" that's being debated it's the words high and low. Alec and Stuart are seldom wrong and blow me they are right again! Rog Quote Link to post Share on other sites
Lebro Posted February 4, 2017 Report Share Posted February 4, 2017 OK, (treading carefully here ) I am coming from a general engineering side so to me high = big etc. whereas in the more specific "motor trade" I guess high = higher road speed. So a "bigger" axle ratio of 4.2 : 1 will result in a "lower" road speed for a set RPM in top gear as compared with a "smaller" axle ratio of 3.7 : 1 which would result in a "higher" road speed for the same rpm in top gear. As Alec says: Lower numerical final drive ratio equates to a higher gear . . . . . whereas higher numerical final drive ratio equates to a lower gear . . . I'll get me coat Bob. Quote Link to post Share on other sites
RogerH Posted February 4, 2017 Report Share Posted February 4, 2017 (edited) It is probably more difficult than one thinks. The words high/low/ratio have been distorted over the years 10:1 is a high ratio. The relationship of the 10 to the 1 high (or big) 2:1 is a low ratio. The relationship of the 2 to the 1 is low (or small) However if you look at gearboxes - 10:1 gives 10 turns in and 1 turn out - so the effect on the output is a low gear ratio 2:1 gives 2 turns in and 1 turn out - so the effect on the output is a high high ratio. So in my mind Stuart is correct for a gearbox etc. Bob is correct for general things Roger PS - that is strange; something odd is happening to the forum structure.. Before I posted my post above I did not get the pop up to tell me Bob had just posted before me. i have noticed that when I get a PM the content of that PM is displayed in a small box Also I am not receiving email notifications of PM's arriving Edited February 4, 2017 by RogerH Quote Link to post Share on other sites
stuart Posted February 4, 2017 Report Share Posted February 4, 2017 PS - that is strange; something odd is happening to the forum structure.. Before I posted my post above I did not get the pop up to tell me Bob had just posted before me. i have noticed that when I get a PM the content of that PM is displayed in a small box Also I am not receiving email notifications of PM's arriving Roger I havent been able to get Email notifications of PM`s for months despite having the box ticked in settings. I did ask Wayne about it and he had a fiddle but it still isnt happening. Its been like this since the Cyber attack and we can no longer sign in anonymously Stuart. Quote Link to post Share on other sites
peejay4A Posted February 4, 2017 Report Share Posted February 4, 2017 Just to confuse things further don't the F1 boys use longer and shorter when referring to final drive ratios? Quote Link to post Share on other sites
stuart Posted February 4, 2017 Report Share Posted February 4, 2017 Just to confuse things further don't the F1 boys use longer and shorter when referring to final drive ratios? Probably, short being low (like a 4.1) and long being high. (Like a 3,45) FWIW Years ago I bought a series 1 XJ6 that was originally a 2.8 but converted it to a 4.2. The original 4.28/1 diff meant it went like stink to about 90 and ran out of revs. I replaced it with a 3.08/1 diff and it then had a theoretical top of 168 though I never tried it! But it also made a world of difference to the economy Stuart. Quote Link to post Share on other sites
SuzanneH Posted February 4, 2017 Report Share Posted February 4, 2017 Roger I havent been able to get Email notifications of PM`s for months despite having the box ticked in settings. I did ask Wayne about it and he had a fiddle but it still isnt happening. Its been like this since the Cyber attack and we can no longer sign in anonymously Stuart. I'm still getting e- mail notifications, see below. Very odd......... Quote Link to post Share on other sites
classic225 Posted February 4, 2017 Report Share Posted February 4, 2017 Farid, Check Kijiji Ontario, I've seen overdrive boxes there for 1500$. Yves Quote Link to post Share on other sites
M. Pied Lourd Posted February 5, 2017 Report Share Posted February 5, 2017 Farid, As mentioned, kijjji is a good option but also look at your local ( or kinda local ) Clubs Classified Ads sections. The Toronto Triumph Club website about 2 months ago had an OD for sale actually located in Nova Scotia! I'm always searching Clubs like the Ottawa Valley Triumph Club, Victoria British Car Club, Boots and Bonnet Club, Georgian Bay British Sportscar Club, Headwaters and Hamilton Sportscar Club etc etc... Also, try calling some of the British Specific Vendors that might be local to you...you might try calling Fred at British Auto Sport or give Obsolete Automotive a call...they deal in used parts as well and may be aware of something that will work for you. I know these are Ontario Vendors but I'm sure that they would be willing to Ship. Cheers Tush aka Cheftush Quote Link to post Share on other sites
Hamish Posted February 5, 2017 Report Share Posted February 5, 2017 Hi Tush Love the you tube Chanel. The car work and the weather updates. Keep up the good work. H Quote Link to post Share on other sites
M. Pied Lourd Posted February 6, 2017 Report Share Posted February 6, 2017 Thanks Hamish! I appreciate the kind words. Cheers Tush Quote Link to post Share on other sites
Farid Posted February 10, 2017 Author Report Share Posted February 10, 2017 (edited) Folks: I have been waiting over a week for someone to suggest a compatible rear axle swap option! The whole discussion got diverted by gear-ratio! I have seen TR6 swapping real axle with Ford 8"; I have been told that by changing the rear axle, one could lower the RPM for a given speed, and also get a better ride. Apparently, this alternative is even less expensive than the J-type gearbox alternative. What do you guys think? I would appreciate your comments (hopefully directed to my query!) Cheers, Farid Edited February 10, 2017 by Farid Quote Link to post Share on other sites
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