Bob,
With a 4.3 rear end, and a healthy engine, I cruise very
comfortably at about 3800-4000 rpm. This is in the vicinity of 65-68
mph with the 165-15 SP20's. The engine is a bit peppier than standard
primarily due to having had Lawrie Alexander do his magic on the head
with TF valving, polished ports and a compression ratio of about 9:1.
The bores are also running .040" over pistons from Skip Kelsey. I
experience no lagging problems on hills when traveling with other MG
folks. The 4.3 conversion was something that I would certainly do
again. No regrets whatsoever.
Bud Krueger
52TD (53 engine)
Bob D. wrote:
>Andrew:
>
> If you can buy/borrow a portable GPS, you'll be able to measure your
>speed to an accuracy of 1/10th mph. You can also use it as an odometer, and
>of course it will show you where you are any where in the world. (It's like
>magic!)
>
> The rear ends of the T series are really short, even for the period in
>my opinion. I have a TD with the stock 5.125 rear end. It takes 4500 rpm to
>go 60 mph. Does anyone know of any other car manufactured in the '50s with
>gearing that short? But, I have cruised many thousands of miles at that rpm,
>and the engine keeps coming back for more. I never cruise beyond 60 mph,
>because that exceeds some rule of thumb about not sustaining a piston
>velocity above 2500 ft. per min. Has anyone else heard of this piston
>velocity rule?
>
> I'm really curious about how fast other T owners cruise. Please reply.
>
>Bob Donahue (Still stuck in the '50s)
>Email - bobmgtd@insightbb.com
>52 MGTD - NEMGTR #11470
>71 MGB - NAMGBR #7-3336
>
>----- Original Message -----
>From: "Andrew Comrie-Picard" <musketeerracing@yahoo.com>
>To: <mg-t@autox.team.net>
>Sent: Tuesday, August 26, 2003 6:44 AM
>Subject: TF rear axle ratios
>
>
>
>
>>Hello - new to the list here - first post.
>>
>>I have a rear axle ratio question on my TF - I read
>>the archives and in 1999 a similar question came up
>>but I'm hoping I might be able to dig a bit deeper
>>now.
>>
>>I have a 54 TF 1250 - very original. I've always
>>thought all the ratios very numerically high (high rpm
>>at relatively modest road speed, and a first that is
>>almost useless on flat starts) but it was not until
>>this past weekend that I thought the ratio might be
>>even higher than usual.
>>
>>I ran a bit of a road rally this weekend and we found
>>our odo fully 10% fast from the organizer's very
>>accurate distances. That suggests to me that the tires
>>are smaller and/or the rear axle is numerically higher
>>than the odo anticipates. The tires are 155R15 which
>>at a presumed 82% aspect ratio I put at 25 inches in
>>diameter. Stock was of course 5.50-15 which at a
>>presumed 92% aspect ratio I put at 25.12 inches. That
>>is a difference of only about 0.48% in circumference
>>which can't in itself account for the odometer error.
>>
>>On the axle ratios, I understand that my TF should
>>have 4.875, and that the TD had 5.125. That in itself
>>is a 5% difference.
>>
>>So then, should I presume that I have a TD rear axle
>>in this car? But then how to account for the
>>ADDITIONAL 4.5% error? Is it possible that I have an
>>odo calibrated for an optional 4.55 ratio and also
>>have a 5.125 rear end? That's about 11% (which is
>>actually a little too much?). When you got an optional
>>rear end did you get a different odo calibration?
>>Thoughts?
>>
>>My understanding of how the odo works (as opposed to
>>the speedo) is that there is no room for error - it is
>>direct drive all through that system.
>>
>>The only reasons I really care are:
>>
>>1. I've always thought the ratios ABSURDLY fast and
>>many people have said "oh, that's just the old MGs!"
>>but I am not foreign to old foreign cars.
>>
>>2. I'd like to go to a more leisurely ratio but don't
>>know what I'm at right now!
>>
>>2. I am quite a serious rallyist (see
>>www.musketeerracing.com) and we're quite serious about
>>distances - I am likely to put a Halda or Aifab or
>>Langwell in this car for vintage TSD rallies and
>>calibrate it to a rolling distance, but I'd sure like
>>to figure out if there's something in the drive ratio
>>affecting the standard odo.
>>
>>Thanks in advance for your help.
>>
>>Andrew Comrie-Picard
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