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Triumph TR6 - 5800 RPM Redline

A buddy at work got a new Honda S2000 that I got to check out yesterday. Nice modern car that lives at high RPM. It apparently switches cam profiles at 6000 rpm and redlines at 8000 rpm. The bore is bigger which is why the redline's not 9100 rpm like the 2003 model.

This made me wonder what the stock TR6 redline of 5800 rpm is based on. If it's valve float, wouldn't stiffer springs and roller rockers help there? Any of you racers know the parts that limit rpm and the increment it can be increased with each improvement?

Brent
Brent B

Let's see.

Rotating mass. That is, the crank, the rods/pistons combinations.

Just about any of the pieces that go up and down and their mass would be a limiting factor. Overhead cam, of course, sure makes a difference since there's less 'stuff' moving to open the valves.

How close is the valve/piston crown clearance? That's gotta be a factor in high performance, high stress, high heat situations.

An example of a high revving engine is my 1982 Honda CBX inline 6 cylinder motorcycle. Redline is 9500 RPM. The thing starts to come on the cams at around 4k and then it starts to pull. In first gear redline is good for 55 mph.

Cruising down the road in 5th (top gear) at about 60 it won't come alive unless you drop two gears.

This is interesting since it's a "sport tourer" much like our TRs. It equates to a comfortable, fun scooter just as our TRs equate to a comfortable, fun car. I get the same enjoyment from the bike as I do the car.

Did I get off topic? Yep.

Jim (just likes 6 cylinder engines that are all in a row)
Jim Deatsch

I think the single biggest limiting factor is the valve gear on a pushrod engine, even way back in the 60's a standard Lotus twin overhead cam engine would rev quite happily to 7000+
[or at least mine would]
Modern engines are also built to much higher standards of balance and clearance which probably helps as well
Ron
R. Algie

Back about 80 years ago, the British Motor Vehicle Office developed a way of taxing the motor-car. The old cars were called 7 HP as in an Austin 7, Standard 8 or Riley 10. This so-called HP was called "taxable HP". It was calculated mathematically based on the bore and the stroke. Nothing to do with real HP or torque at the wheels.

So to reduce the amount of tax that a new owner would have to pay (for his annusl registration fee - I believe), British automotive engineers developed engines where the "taxable HP" would be low, therefore they would sell mote cars if the tax was less.

The way they did this was to have tiny bore diameters and very long engine strokes. The Tax Man calculated the low tax after he knew the bore and stroke.

In addition to lowering the Tax to be paid, it resulted in bad engine design. Since then, British engines rev fast and get you nowhere fast. The high revving resulted in short engine life. The Japanese changed all this with short-stroke engines that permit high RPM, all the while improving engine life, combustion efficiency, etc.

That is why the TR6 and other British engines have relatively low "redlines".

And now you know the rest of the story . . .
Thus endeth the first lesson.

Don Elliott, Original Owner, 1958 TR3A
Don Elliott

Don? Don? Was that 'typo' intentional?

snicker.

J
Jim Deatsch

On the new Honda S2000 it is not the bore than increased, it is the stroke that increased. Therefore at any given engine speed the piston velocity is increased. This is the primary driver for the lowered redline. (From a portion of shop conversation on the S2000 Thursday night with a friend that works for Honda)

While valve train is an important factor, piston speed is a major contributor. The TR6 motor is rather "undersquare," i.e. the bore is considereably smaller (2.94") than the stroke (3.74") so one can expect a relatively lower redline due to the higher piston speed. This ties right in with Don's "annusl registration" above on caluclated HP

Piston speed in feet/second can be calculated by converting the stroke to feet, then multiplying by 2 and then multiplying again by the engine speed. At 5800 rpm, the TR6 engine has a piston speed of 3625 feet/second. For normal factory components (cast crank and rods) of the era, it was generally thought that the maximum sustainable piston speed was on the order of about 3500 feet/second. From that, the 5800 rpm redline is reasonable. Using the Spitfire motors as an example, the 1300s are generally considered better motors to build up since the 1500 is nothing more than a stroked version of the 1300.

This is why cam selection and bottom end build is such a factor with the TR6 motors. What is the point in having a cam that doesn't really "come on" until say 4000 rpm and makes max power at 7000 rpm in a TR6 that hasn't been beefed up to some degree on the bottom end? You can bump up the maximum sustainable pistion speed through careful build and use of better components. Bottom line is that valve train components and bottom end build need to work hand in hand if you are looking to build a really hot motor.
SteveP

D'oh!

While out running errands, I went back in my mind to when I was figuring out which cam grind, springs and rockers to select for my own TR6 motor build when it suddenly occured to me that I had been thinking minutes and writing seconds in posting. While the principle stands, the units must be corrected. The piston speeds as presented above should be stated as feet per minute.
SteveP

Assuming the pistons can tolerate higher speeds, the limiting factor becomes a long and quite "whippy" crankshaft supported by four bearings originally sixed for much smaller capacity versions of the engine; i.e. inadequately supported.
The situation can be improved at great expense, for race applications, by use of a forged chromemoly crank, but the real solution is a shorter block (as when the bores are in a V), deeper block skirts extending further down past the crankshaft bearings, and bigger bearings with good strong bearing caps.

For road use 6000rpm should be enough, I would think!
Simon.
Simon Rasmussen

Oh yeah - quite enough. I was just dumdfounded by the 50% higher redline of my friends Honda and what was done to get enable it.
Brent B

Brent,
As appealing as 240 HP and a 9000 RPM redline is, (and it is fun to drive) I was told by one owner that the car is murder on long trips, as the usable RPM is in the higher range, constant shifting and running the car at that RPM just beat him to death. He honestly said he never bought into Brit cars much, but confessed a TR6 would be a lot more comfortable on the road. Got to drive an S2000 awhile back, and life begins at 6000 RPM in that car!!! That in itself was pretty impressive. But the Acura NSX pulls 80 in 2nd gear at 8000 RPM. WHHHEEEEEEE!!!! I'll still take the TR6, and some people can't understand that, but they just don't get it, do they?

Rod
Rod Nichols

While we're on the subject of long verses short strokes, I would like to register my preference for long strokes!!!......and while I'm in an inquisitive kinda mood.....could somebody please explain why the sound made by a long stroke is deep, resonant and 'growly', opposed to the beeps and tweets that are made by short strokes....
Roger H

The answer is one of each!

I was recently relocated from the East Coast to Calif. and bought an S2000 rather than ship the TR6 (frankly, I didn't trust shipping my '6 and the coporate apartment prohibits any auto maintenance in the garage).

I recommend driving them back to back if you can for no other reason than to see what 25 yrs. of technological development does. The S2K is not that bad to drive around town, actually at normal revs it drives like an economy car, but it is a bit difficult to get a smooth start in first and I still wince revving a car that high....fun though. The worst part is the ride and the oscillation that can develop over expansion joints on certain roads.

Rod, I was the opposite of your friend Brit toys and never into Japanese cars, however this may make me a convert...TR6 still gets the prize garage spot though.

I'm told that valve float and rather generous factory limits on the balancing of rotating components are the limiting factors on the TR engine.



Happy driving, W


W

It's a personal thing, but relatively low revving torquey engines are just more comfortable for me. High revvers seem to accelerate my metabolism to where I'm out of sync and definately NOT comfortable.And yes, there is truth in the British HP tax, the Brits have always been the Taxmeisters. I'm a Brit and have not lived there most of my life as I don't like being taxed to death, but I love their cars. Peter G
Peter Gooch

One major drawback of revving a 6 to 6000 revs is it tends to attract the boys in blue like a magnet!!
Peter, our government tells us we are one of the lowest taxed countries in W Europe, and politicians don't lie-----------do they!
Ron
R. Algie

Hi. A funny question...

Why the need for a high RPM. The jap's car rev. quite high but are not torquey at all. Have you ever see a dragster with a non-torquey engine. It is just a matter of engine conception.
You could get some extra engine RPM by balancing, blueprinting, modifying crank and valvetrain,etc., but for a daily driver does the cost has some rentability.
You must also have in mind that too much modifications to get performance at high RPM yield to a bad behaviour at low RPM.
JGC.
Jean G. Catford

This thread was discussed between 24/01/2004 and 28/01/2004

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