Is a different rear end all that?

[2wrench]

I have heard all the stories about four speeds and freeway
driving causing accelerated wear and tear on a 6's engine.

Two options to consider to alleviate this wear and tear
were:

1) Install an overdrive tranny; or

2) Change the rear end to a (please fill it in here)

which is geared differently resulting in a more relaxed
engine at freeway speeds.

Now, I've done one of the two choices. Leaves me to
consider the rear end as a further step in that direction.

Problems have seemed to be the calibrating of the speedo
(and this would be psychologically uncomfortable for me if
the speedo/actual speed are off).

Further, I have to wonder whether or not such a change
would ill affect power at either the low or high end. Seems
to make sense if the rear end is geared differently.

What are the particulars on this rear end I don't know
and what do you think of making this change?





about things like whether there would be loss of power

 

[TR3driver]

Well, the tallest gears that you can get for the Triumph case are 3.45; only about 7% taller than the stock (for US TR6) 3.70. (PI TR6 had 3.45 as standard.) I changed the Stag to 3.45 (from 3.70) a few months ago.

Coming off the line, there is a direct effect on acceleration. 7% taller gears mean 7% less torque available at the wheels means 7% slower acceleration. But it pretty much disappears once you get to your shift point in 1st gear; because with the taller diff you are going to stay in 1st gear longer.

At speed, the main effect is that I grab a gear (or two) more often to accelerate rapidly. Still lose about 7% for a given gear and road speed; but downshifting can more than make up for the loss, so it's more-or-less a wash.

One way to deal with the speedo problem is to get a "ratio adapter", which can be made up to any desired ratio. It's been a few years ago now, but a local speedo shop said they could build one for me for $100 or so. He also said the ratio could be changed later for $40.

In my case, my original plan was to use the 3.45 gears on the other Stag, which has shorter tires on it, making the ratios about a wash. After experiencing the effects on acceleration, I think I'll start looking for another 3.70.

 

[LastDeadLast]

Going from the factory 3.70:1 ration to a 3:45, you'll definitely feel it in "the seat of your pants". Off the line acceleration will suffer a little, but like Randall said, you'll gain it back after your up to speed.. and might even be a tad faster at highway speeds depending one what gear you're in.

The neat thing about an overdrive gearbox (or 5-speed) is that you get the best of both worlds; acceleration and top speed/highway economy. Plus an OD box will actually increase your cars value while adding a 3.45 gear would either net a zero increase or maybe decrease it's value.

Back before college and when I dabbled a little in street racing, I had a 1968 Z/28 Camaro that some yahoo had robbed the factory posi 3.73 gears and replaced it with an open axle 3.08. The engine was a modified 70 Corvette LT1 (360+hp) with a 4sp gearbox. That car stunk off the line, but we nearly unbeatable at 50+mph. I could take her down to 2nd gear at 55mph, putting it right in the best rev range... BAM! they never new what hit'em. I miss that car. I was stupid to sell it.

-Shannon

 

[TRMark]

There are several gear ratio, differential ratio, tire size calculators available. This is one from Buckeye Triumph site.

Calculator

 

[TR3driver]

Meant to add : I don't think you'll ever justify making the change in terms of either engine life or fuel mileage. You might pick up 1 mpg but I doubt it; the reduction in engine rpm is accompanied by a wider throttle opening to maintain speed, so the difference is nowhere near 7%.

Kind of the same thing happens to engine life; although it's turning slower it's also working harder (meaning more force against rings and bearings). And at this point, especially with modern lubricants, it's unlikely you'll wear out the engine anyway.

Hmm, did J-types ever come with taller ratios? I know the A-types did (eg some big Healeys used .78 instead of .82) and those gears can be installed in Triumphs ...

 

[Brosky]

<div class="ubbcode-block"><div class="ubbcode-header">Quote:]I miss that car. I was stupid to sell it.[/QUOTE]

How many times have I heard/said those words?

 

[angelfj1]

2wrench

This issue that you bring up has my attention. Notwithstanding the pleasures of overdrive, did you read some where that driving your TR-6 at freeway speeds was in some way detrimental? I have never heard this. Remember the USA was the primary market for the TR range and most of these cars were sold before the days of the 55mph era. So, TR engineers knew that 60 - 70mph would be common. Experience is that maybe 25 percent or less of the TR's sold in the USA were O/D. Now, if you are addressing long term engine wear and fuel economy, I would agree that O/D or a lower diff ratio might help.

 

[Trevor Triumph]

I believe that there is a speedo gear in the tranny that may have to be replaced to match the diff ratio.
Have you thought about replacing the four speed with the various five speed convertions? Some use late model Toyota truck tranmission.

 

[2wrench]

No real good, solid itinerary to quote on the subject. Just seemed to be
a common understanding that our cars are screaming down the freeway, at
least at 3,000 rpm and or higher, and that the constant rpm's in that
range or higher, can wear the ole motor.

I wonder if I'm the victim of overdrive marketing? I don't really know.
Seems to make sense, though, that there's less stress on an engine
running at lower rpm's.

 

[TR6BILL]

I think you will be an old man before you wear that engine out from overuse. If you don't want to shell out close to 3 grand for an overdrive, enjoy the car the way it is. You ain't gonna do any damage to it. Really, how many miles will you put on it in a year??

 

[BobbyD]

At 3000 RPM, I'm doing 67 mph with a Toyota 5 speed and a Nissan 4.08 diff. Seeing as the engine redlines at almost 6000 rpm, I don't think cruising at half that will do any harm. Your tire size also impacts rpm's so check out the Buckeye calculator that was previously posted.

 

[TR3driver]

Not the same engine, but I've driven my TR3 motor for extended periods of time at over 4500 rpm. Doesn't seem to bother it at all. I've been into it a few times, but always for other reasons, nothing I would attribute to sustained high rpm operation. And I take the factory 5K redline as more of a suggestion than a rule

 

[poolboy]

In my 74 TR6, 4 speed, if you can believe the gauges, at 3k I'm doing 64 as near as I can tell. Tires are 205/70/15.
At 3k, I've got good torque for passing quickly.

 

[TR6oldtimer]

I know the O/D guys like them, but in my opinion, for every day driving they are just another thing to break, add more weight to the car, and when engaged, use more power. In the long run, you will blow your transmission and or O/D before you wear out a properly maintained engine. Neither my TR4 or TR6 had an overdrive. The only work I had to do on the engines was the head, and for the heck of it, rods and main bearings, and rings.

That said, if someone gave me one, or I found one dirt cheap, and I mean dirt cheap, I would probably install it, otherwise if I had the money for an O/D, I would instead buy leather seats and a wool interior, which the wife would like better.

Just my two bits worth.

 

[Trick6]

As always, it depends on what you want to accomplish. But I feel that if you have the stock O/D tranny and 3.70's, what is the issue? I to have the Toyota 5 speed and the 4.08 Nissan rear. I love it. The car is very happy in stop and go traffic. It likes the CT back roads, downshifts and power curves and is very comfortable on the highway at about 3200 rpm and 70-75 mph, to Montreal and back. All around driving is enjoyable. Gas mileage is pretty good in the city, very good on the highway (about 28 mpg with tri Z's). But I put maybe 4-5000 spirited miles a year on the car. That is not a lot.

IMHO, I feel that you are in a good all around happy range with your setup.

 

[Andrew Mace]

...Just seemed to be
a common understanding that our cars are screaming down the freeway, at least at 3,000 rpm and or higher, and that the constant rpm's in that range or higher, can wear the ole motor.

"Screaming" might be a bit of an exaggeration! :smirk:

Now try a stock Herald 1200 at freeway speeds: over 4000 rpm...which I've done all day in mine. It's quite happy to do so, and in the 30,000 or so miles I've put on the car since I got it in '02, there's been no noticeable degradation of engine performance or overall condition. No doubt OD or other different gearing would benefit the old MPGs at highway speeds, but even at this past summer's high gas prices, it would take a long, long time to amortize the cost. (Actually, it's physically almost impossible to put an OD gearbox in an earlier Herald due to the design of the chassis...but I digress!)

I wonder if I'm the victim of overdrive marketing? I don't really know. Seems to make sense, though, that there's less stress on an engine running at lower rpm's.

To a point, absolutely correct! Admittedly, I don't know where the power band is on a stock TR6, but I'd not be surprised to find that one can accelerate rather more quickly in 4th than in OD 4th in said TR6.

Tradeoffs....

 

[vagt6]

It's very important to consider exactly what kind of driving you'll be doing in this car before you go changing gearboxes, diffs, etc.

I did this once with a GT6 and after all was said and done, I didn't really need it in the first place. I avoid Interstate highways like the plague, and usually travelled relatively short distances at 60+ MPH. Most of my highway driving was on trips of less than a couple of hours or so. Everyone's driving styles are different, but most of us don't drive these cars like you would in a modern car, anyway, on long Interstate trips, etc.

I installed a J-type in a GT6, however, I didn't really drive on Interstate highways, or above about 65 mph for any long periods of time. I had a 3.89 diff, which rendered about 4,000 RPM at roughly 65 mph. 60 mph was about 3,700 if I remember correctly.

The J-type came from a Volvo donor and had a 27% reduction in gearing, but at a cost! Purchased from Quantumechanics, the final cost installed was over $2,300. Heck, the GT6 was only worth about $10,000, so that's a considerable sum to change gearing in a relatively inexpensive car. Really not worth it, and you won't recoup such a cost when you sell the car.

The GT6 engine love revs. Also a well-sorted 2500 Triumph six will also endure 4,000 RPMs or so all day long with absolutely no problemo. In fact, I think they love it!

So, unless you're commuting at 60+MPH daily, or driving at sustained higher speeds regularly, forget about changing the gearing. Spend the $1,500-$2,500 on a new paint job, a leather interior or some new wire wheels! These engines were <span style="font-style: italic">made</span> to run at 3-4K RPMs all day. I can't see any significant benefit from changing gearing unless do a lot of highway driving. It's not really worth the additional cost.

However, if you live on Jupiter and your portfolio isn't affected by the current recession, go for it!!! Buy, buy, buy!!!

IMHO/YMMV.

Let us know . . .

 

[billspohn]

1 - you aren't going to wear out your engine in the time you will own it by running it at 3000 - 4000 RPM - unless you use it to commute by highway every day.

2 - having a longer gear ratio can be nice as it allows more relaxed crusing

3 - just swapping in a lower ratio diff reduces performance and possibly value, as indicated by others above

4 - the best way to accomplish what you want is to simply install an OD trans - fool proof and it does exactly what you want without losing anything (except a little money)

5 - if you are performance minded, and even better thing to do is put in a higher numerical diff (4.1) and the OD trans. You'll get better acceleration than stock but still have a good relaxed top end.

6 - the very best way to go iis to install a significantly higher diff ratio, OD trans, and close ratio transmission gears. Hard to do in a TR I believe as close ratio gear sets, although homologated for SCCA, are hard to find and expensive, but I stand to be corrected by those more in tune with TR matters.

My MG race car uses a CR gearbox with OD and a 4.55 diff giving about 1200 RPM drops between gears at 6000 RPM or so - a really nice set up for racing (wouldn't bother for the street)