Hi all,

just a general question.. how is an engine's redline determined?

I'm guessing a plain cam swap without changing anything else won't allow you to rev higher?

Also, is it bad to occasionally or regularly stray past the redline?

My car makes so much noise (especially the cooling fan) even before the redline that I never go up there. It doesn't seem to pull as much up there also..

hg.

Depends on the motor

most people dont come close to what the motor is capable of mainly due to it being noisy they think they are revving too hard, a good thing i guess

Cheers
Aaron

_________________

My Cooper S has a 1330 motor, 45mm weber, 266 cam & some slight headwork, it topped out at 7,800rpm in a motorkhana last weekend.

Doogie

_________________
I won Hay once, here's the pic to prove it..


Hay, it's not about the car, it's not about the venue, it's about the people that come here. Peter Dwyer, Mayor of Hay NSW.

My fresh 1360 with 45 Dellorto, S crank & rods, headwork, RE282 cam & 1.5 rockers will run past 8000 easy, but these days I don't let it go over 7000-7500. I want it to last a while...

_________________
DrMini- 1970 wasaMatic 1360, Mk1S crank, 86.6HP (ATW) =~125 @ crank, 45 Dellorto (38 chokes), RE282 sprint cam, 1.5 rockers, 11.0:1 C/R.

I guess a simple explanation is that a redline is usually a red line thats drawn on the tacho
No but seriously now, it's put there by the manufacturers as a conservative limit as to what the motor should stay under so that nothing breaks.
And you are very right an unmodified motor will run out of puff well before red line so there is no point in reving it that hard, just change gears...



Not really, changing the cam to a 'lumpier' cam will allow better performance at higher rev's, but you should really do an overhaul if you want to spin high revs as a worn motor won't last long if thrashed.
The question that this leads to is why do you want to rev higher?

You need to rember it that horse power is simply torque multiplied by rpm and so working backwards an efficient engine is one that produces loads of torque at low rpm, a bit like a truck And why motorbike power figure sound great

Example:
250cc honda bike
45 hp (33.6 kW) @ 15000 rpm = 21.392 Nm

John Deer 2.9L Diesel
PowerTech 2.9L Engine 58 hp (43 kW) @ 2500 rpm = 164.26 Nm

Now thats not really comparing apples with apples but at the end of the day it's the torque that moves you...

The redline on the Smiths tacho fitted to MK II S's in NSW Police was specified to be put at 6,000 rpm.

Have to ask a dumb question here ... what's the difference between S rods and normal 1275 rods?

Basically there are 3 families of 1275 rods you can find in Oz-
1. Cooper S/early Morris 1100S (1.625" crankpins)
There are also 1275 Midget rods, identical to Cooper S except steel spec slightly lower.

2. Later Morris 1100S/Clubby 1275LS (1.750" crankpins)- with HEAVY lumps on caps

3. A+ rods (1.750" crankpins), used in last of the 1275 Moke/Rover Mini/Metro etc.

S rods are strongest, they are also used when building a stroker motor by offset grinding big journal crankpins down to 1.625" dia.

There are also aftermaket rods like Carillo, if you have the do$h.

_________________
DrMini- 1970 wasaMatic 1360, Mk1S crank, 86.6HP (ATW) =~125 @ crank, 45 Dellorto (38 chokes), RE282 sprint cam, 1.5 rockers, 11.0:1 C/R.

Cheers Doc. Are the different rods numbered in any way? I'd assume yes.

Yep most S ones have a number AEG521 in the forging (there were earlier ones too, different number).
Midget ones are marked AEG625.

big J 1100S ones 12G1506 (I think)

A+ rods, I'm not sure of the number- my books don't go that far..
A+ rods are a bit lighter than all the others but are fine for a road motor.

_________________
DrMini- 1970 wasaMatic 1360, Mk1S crank, 86.6HP (ATW) =~125 @ crank, 45 Dellorto (38 chokes), RE282 sprint cam, 1.5 rockers, 11.0:1 C/R.

thanks doc

My 1100S large journal rods have 12G1507/8A1

My A+ rods have 12G4114/5 on them.

KB

_________________

KB, re the part numbers, the cast or forged numbers are often 1 digit away from actual p/no in the books.
So, your 1507 rods are 1506 in the MK book.

another example- 648/649 cams.

_________________
DrMini- 1970 wasaMatic 1360, Mk1S crank, 86.6HP (ATW) =~125 @ crank, 45 Dellorto (38 chokes), RE282 sprint cam, 1.5 rockers, 11.0:1 C/R.

red line - whats that. Just rev it until the power starts to drop off and then it all again.

Always a good idea to check that your tacho is reading correctly! I thought I had some lazy valve springs as it was bouncing at high revs...turned out the tacho was under reading in a big way (only at the big number end!).