RPM

[Winston Teague]

Whatever it is Simon, it definitely wont stand 4000 on the motorway! W

PS What is it?

[Kneeslider]

I've been musing about this for a while too. 3.5-4k RPM seems to be the sweet spot for my car too, which nicely equates to 75-80mph cruising on UK motorways which is all fine, as most other people seem to be doing that speed too, and higher cruising speeds are fairly tough to sustain on the busy parts of the motorway network.

This also means that oil temps seem to stick around 100°C, and I have rarely seen anything higher, even in France with outside air temps in the low 30°Cs. I think that the main limitation to cruising speed isn't RPM, but oil temps, so I tend to drive at high speed with an eye on the temp gauge, and sometimes on the aftermarket oil pressure gauge I have installed also.

The main limitation seems to be the engine, transmission and wind noise, and the driver's willingness to tolerate more of it, the radio gets lost in all the racket at higher speeds, so that looks to be the comfortable cruising speed.

It is interesting that the racers report using additional oil coolers, and that keeps the temps down when they are using many more revs than I ever would, so the basic bits of the engines are able to tolerate higher engine speeds when everything is in good shape.

Now, my engine is an odd one, because I think that I have super 75 heads, with manifolds matched to Solex Pii-40s, and a SC cam, so if I were after more power, the way to go would be to open the heads out and fit bigger valves. The problme with this would be that all the extra power would come at higher RPM, which I don't use anyway. The only time I ever really run the engine past 4k is the odd burst up to 5k ish before changing up. The gains from the 1720cc big bore kit have given a nice torque boost in the midrange, and the engine has plenty of power, and can run up to 90+mph easily, so if you are after more cruising speed, then a higher 4th gear might be the way to go.

P.S. Come on Simon, what have you bought? Do tell!

[POR68]

My car is pretty much original in almost all respects. I do some big trips and the last was over 1400kms. I travel at 3000 rpm or a bit over most of the time (60mph). Only car I have with an accurate speedo. Keeps the rozzers and me happy. Runs cool and not too much stress on the crank and rods. If I want to go faster, that's what the Boxster 987.2 is for

[S.J.Szabo]

The Trusty Coupe has seen more than its share of open road work, and most often at 3.5K rpm/70 mph and its always been happy as a clam. Even in adverse conditions (Nevada, Death Valley, Monument Valley, etc.) in season, its hummed along nicely, abiet with 220-230 deg oil and 60lb of pressure.

To put this in context tho, I should note that I have long eschewed high revving a motor just to hear 'em scream. Every time I hear some hot shoe boast of such floggings because "it loves to rev", I want to tie 'em to a stake with a long rope and make 'em run real hard in circles for an hour or so.

But speaking of distance work, I wonder what other such aficionados choose to roll up those miles on.

I have long been a fan of 185/70R15s as they are over 25" (my personal minimum dia. requirement) for good leg, have a good contact patch compromise with aero resistance, and don't weigh a ton. Unfortunately, a 70 a.r. can only be found in boutique tires (at hefty prices) anymore, so I have evolved into a 195/65R15 user. A little shorter, a little heavier, but a good contact patch still. And, of course, its a size still relatively easy to find among cheap tires.

So, what do the road warriors amongst you like to run, if one may inquire?

[Winston Teague]

I'm on 185/70 15 Avon CR6ZZ. Got them second hand ex TR4 racecar. They are pricey new but they seem to last indefinitely! W

[oldtimer]

Hi S J , I use Michelin XZX 165SR15 on my 356C ( previous owner bought those) , and Pirelli Cinturato CA67 165HR15 on my 356 Outlaw '55 Continental which runs on C wheels . Both seem to work well , there's not enough power to break grip at the rear and there's not enough tread width to make steering heavy at the front.

Your preferred tyres are a lot fatter !!

Have just returned from a pre A meeting where everyone had the proper 16 inch wheels with proper skinny tyres , they managed the hairpins in the mountains OK !

[Lightweight_911]

.
I used 175/70 x 15 Avon CR6ZZ's on 5.5 & 5.75 in steel/alloys on my GT-inspired C.

[Burma-Shave]

Here you go, happy as Larry, and you can still hear Radio Scotland!

https://vimeo.com/296211259