52 replies to this topic

[Blatherskite]

Glad its going the right way! by the way, you are unlikely to be able to out-drag the Viper, but will win in the bends!

[A-Cell]

Glad it's better. Trust me will be even better with 10 degrees advance at your altitude. Be you are glad you didn't listen to the retard it for low octane/ethanol sea level brigade!
Try to get a15psi rad cap and sounds like you will be sorted.
Glad my experience at the Denver mile high Emissions Lab with British Leyland cars has come in useful again after 40 odd years!

[jaydee]

4 deg static timing is really not enough for a 1275 at altitude, as A-Cell pointed out, you definately need 10 degs and a leaner needle

[sdjones121]

I'd started with +4 since it was about 15 degrees off from where it was and wanted to make small changes at a time (learned that the hard way...several times). I'll pop it up to 10 later this weekend and report back.

 

One thing I just realized as I was watching the footy was that I forgot to reattach the vacuum advance tube before I set out. And idea how this might have affected my results during the test drive?

[A-Cell]

Without it connected the timing will not advance more at idle. The idle will be better, more stable, with the vacuum advance connected. It will have no effect above idle on the timing. It will mean an air leak though, effectively weakening the mixture throughout the rev range. Better to have it connected for a stable idle.
Run it for a bit then check plug colour before deciding whether to install a weaker needle is what I would do.

[Captain Mainwaring]

Glad it's better. Trust me will be even better with 10 degrees advance at your altitude. Be you are glad you didn't listen to the retard it for low octane/ethanol sea level brigade!
Try to get a15psi rad cap and sounds like you will be sorted.
Glad my experience at the Denver mile high Emissions Lab with British Leyland cars has come in useful again after 40 odd years!

 

The cap won't make much difference. A quick way to tell is to wet your hand and shake water over the rad header tank after a hard run and see if the water droplets start to boil.

Remember this is a spring biased cap with a fairly small surface area - it will boil at pretty much the same temperature whether at sea level or at 5250'.

It may appear that the opening pressure will be relative to atmospheric, but the reality is that within limits it will be constant. The air pressure at 5250' ASl is 12.2 psi and the 2.5 psi difference won't make much difference. In anycase if the gauge gets to the red now, it will get up there with a 15 psi cap which will stop the water boiling until it reaches 121C.

 

Remember...the thin air making mixture rich is the same thin air making cooling difficult. Your low RH is also making things difficult for the cooling system.

[A-Cell]

Think you need to re visit the laws of physics. Water boils at 94 C at a mile high, pressurising the rad with a 15psi cap will raise this to about 102. The concern here is is avoiding vapour (steam) pockets in the cylinder head.

To cook boiled potatoes at this height requires a pressure cooker!

[Captain Mainwaring]

Think you need to re visit the laws of physics. Water boils at 94 C at a mile high, pressurising the rad with a 15psi cap will raise this to about 102. The concern here is is avoiding vapour (steam) pockets in the cylinder head.

To cook boiled potatoes at this height requires a pressure cooker!

I'm a thermal engineer. Please re-read my post. 

The 15 psi cap will probably give pretty much the same pressure in the system at altitude as it will at sea level. The 15 psi may open a tad early compared to normal operating conditions. 

Please understand that it's 15 psi in addition to atmosphere. At sea level we have 14.7 psi atmospheric, at 5250' we have 12.2 atmospheric, not 0 psi, therefore the difference between the two is 2.5 psi . 

The OP's cooling system will boil at 118C. There is a difference between gauge and absolute pressures.

Nah.... the specific enthalpy of the steam at that altitude will be different, but we don't care about that - if it boils, we've lost the game.

Please note that the OP doesn't seem to have complained about boiling over and loss of coolant - therefore his existing cap may be doing the job. Raising the temp across the radiator by 4-5C won't effect the heat balance very much - however changing the airflow across the radiator - ideally bringing it back to seal level mass air volumes will help.

Edited by Captain Mainwaring, 26 May 2013 - 01:38 PM.

[A-Cell]

Re read my quote

Glad it's better. Trust me will be even better with 10 degrees advance at your altitude. Be you are glad you didn't listen to the retard it for low octane/ethanol sea level brigade!
Try to get a15psi rad cap and sounds like you will be sorted.
Glad my experience at the Denver mile high Emissions Lab with British Leyland cars has come in useful again after 40 odd years!

You wanted the OP to retard his ignition.....

[Captain Mainwaring]

Assuming that refers to me, I'm not sure where I said he should retard his ignition - I said I tend to run slightly less advance than standard to prevent pinking with pool petrol - same applies to the Mini and the Bonnie - but I can't see where I told the OP to run retarded - i just posted my own boring observations.

 

My observations regarding the rad cap remain unchanged.

[sdjones121]

Well, this escalated quick!

For the record, I just checked my current rad cap, and the only non-asian writing on it says 1.1. I would assume that is a bar measurement, which would mean I have a 16 psi cap currently. I'm going to put the timing up to 10 degrees a bit later today and will then report back what I find. But, the weather has really cooled off, so It's likely my results won't be typical of this area.

 

Thanks again for your help...even if you disagree. :)

[A-Cell]

Glad you are getting it sorted. Hope you personally "modulated" to the higher altitude!

[sdjones121]

My lungs aren't happy. Still getting used to trying to run at this altitude without looking like a 4 pack a day smoker.

[sdjones121]

Just got back from a good long test drive after having upped the timing to 10 degrees. I drove for about 20 miles, varying from 50-70 mph, with the grille back in, and the advance tube connected. It's 81f/27c, so still a bit cooler than it has been normally. I don't think the extra six degrees of advance had any impact on the running temps, but it did seem to run/sound just a touch better than before. One thing I forgot to do was to check the plugs, I'll do that after my next freeway blast. I was running very hot for quite a bit of the drive, not as bad as before my changes suggested by you all, but still not anywhere near where I'd be comfortable with.

 

I think the engine is running quite well now, so I'm a bit less worried about having to buy a part now, knowing I won't simply be masking an underlying mechanical issue. With that in mind, what is the consensus as to the best part to buy first? After a bit of research, I'm pretty sure I have the Mini Spares 2-core alloy radiator, which as far as I can tell should give pretty good performance. Upon further examination of my fan, it seems a fair number of the blades are relatively flattened out compared to the pics of a new 11-bade plastic. When I was topping up the radiator and bleeding any air, I gave the engine a little rev and a torrent of water rushed into, and out of, the radiator, which leads me to believe the water pump is reasonably strong.

 

With all those variables, I am leaning toward biting the bullet and getting the tropical fan. I think it's quite likely, as has been suggested, that at this point I'm just not moving enough of the thin air up here to get the best out of my radiator. I've even considered adding an auxiliary electric fan on the other side in a push-pull setup, but that would require a modification to the inner wing which is something I'm loathe to do unless absolutely required. Also, wonder if it might just create a bunch of turbulence anyways and not have a big positive impact.

 

A US distributor has the fan on offer right now (though still much more than it would have been in the UK), so I may be able to convince the boss to let me pull the trigger.

[A-Cell]

Before you do this, check the thermostat you are running. There are 74 and 82 ones available, this and a gasket will be a lot cheaper than a new fan, and also a lot less noisy!