[Healeys] Speed to RPM ratio?

[banjojohn]

Jim, you are right.  I have used GPS and my speedo is not accurate, but close enough for me.  My point was that the speedo is mechanically linked, from the tranny, to the engine, and my tach gets its signal from the coil, which also is directly linked to engine speed through the distributor.  Regardless of my actual speed, my speedo and tach should maintain a direct relationship in any given gear.Thanks again for all the opinions and various charts and facts provided by the list members.JohnSent from my T-Mobile 4G LTE Device
-------- Original message --------From: Jim Ryan <ryan at jimryan.com> Date: 6/13/21  4:17 PM  (GMT-06:00) To: i erbs <eyera3000 at gmail.com> Cc: banjojohn <banjojohn at cox.net>, Ahealey help <healeys at autox.team.net> Subject: Re: [Healeys] Speed to RPM ratio? Am I missing something?  I just check accuracy with the GPS on my phone.On Sun, Jun 13, 2021, 3:25 PM i erbs via Healeys <healeys at autox.team.net> wrote:My tach is driven by my distributor gearSpeedo comes off my transmission.  Not sure about the relationship to accuracy. Ira Erbs1959 AH 100-61967 MGBMilwaukie, OROn Sun, Jun 13, 2021, 11:50 AM banjojohn <banjojohn at cox.net> wrote:Thanks.I am actually just comparing the tach with the speedometer indicated speed, which, I believe reads a little high due to tire size.  But the relationship between the indicated speed and the tach should be consistant since they are both driven by actual engine or output shaft speed.JohnSent from my T-Mobile 4G LTE Device-------- Original message --------From: Bob Spidell via Healeys <healeys at autox.team.net> Date: 6/12/21  12:25 PM  (GMT-06:00) To: Bob Haskell <rchaskell at earthlink.net>, healeys at autox.team.net Subject: Re: [Healeys] Speed to RPM ratio? That's it!On 6/11/2021 4:31 PM, Bob Haskell wrote:> http://longstonetyres.co.uk>> Cheers,>> Bob Haskell> Austin Healey 3000 BN7/BT7 registrar>> On 6/11/21 7:01 PM, Bob Spidell wrote:>> Note there is a not insignificant difference in diameters of tires >> with the same nominal size (e.g. '165/80-15'). The English tire >> site--can't think of the name offhand--has (had?) a table comparing >> the diameters of different brands/models of the same size tires, and >> IIRC they could differ by as much as half an inch. I'd say to measure >> the actual diameter of your tires, but it's kinda hard when moving; >> the 'flat spot' goes away--partially, at least--and the tires 'grow' >> some from centrifugal force (anyone seen film of top fuel dragsters >> launching; the rear tires must expand a few inches or more?).>>>>>> On 6/11/2021 3:36 PM, John OBrien wrote:>>> Thanks to all who replied.  These will give me something to work with.>>>>>> John>>>>>> On 6/11/2021 4:26 PM, John OBrien wrote:>>>> Hi Guys and Gals>>>>>>>> I am trying to calibrate my tach.  I installed a Spiyda RVI - RVC >>>> conversion board, because my tach was acting wierd. Anyway, I am >>>> still trying to get this setup to read correctly.  My question is, >>>> on my BJ8 with standard 3.9:1 diff. what should my RPMs be in >>>> fourth gear going 50 MPH , without overdrive engaged.  I'm running >>>> 165/80R15 tires. I'm just looking for a reference point to compare >>>> what should be, and what I am reading.>>>>>>>> Any help is appreciated.>>>>>>>> Thanks>>>>>>>> John>>>>>>_______________________________________________Support Team.Net http://www.team.net/donate.htmlSuggested annual donation  $12.75Archive: http://www.team.net/pipermail/healeys http://autox.team.net/archiveHealeys@autox.team.nethttp://autox.team.net/mailman/listinfo/healeysUnsubscribe/Manage: http://autox.team.net/mailman/options/healeys/banjojohn@cox.net_______________________________________________
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