TR4/4A High Altitude Adjustments

[HarryL]

Just shifted the car from sea level to 6500ft.
What's the thoughts on timing(adv. or retard).
Running SU's. Perhaps a needle change or leave the carbs alone
til I do a plug check.
Harry

 

[NutmegCT]

Harry - is this a permanent move to 6500' ?

I'll let the experts comment on the timing. But if the carbs were tuned at sea level, and you're now at 6500', then thinner air is entering the engine, so the mixture is probably rich.

Tom

 

[Hot Wings]

In general, at our altitude the idle needs to be leaned up considerably. Depending on the performance level, and driving habits, this might need to be extended to the upper ranges as well. Also due to the lower effective compression ratio the timing can/should be bumped up a bit. I've found it better to increase the advance rather than the initial timing.

Also keep in mind that our thinner air doesn't cool as well due to the lower density. The ratio of power lost per unit of cooling lost doesn't seem to be linear. A higher radiator cap pressure helps to keep the liquid stuff doing it's job by maintaining sea level PSIA. The higher PSIG means that any marginal hoses tend to present themselves at this point.

 

[TR3driver]

Usually, they can tolerate a bit more timing at higher altitudes as well. But not much, and it doesn't seem to make all that much difference. ISTR I added about 4 degrees at about 10000 ft (VTR at Breckenridge, CO) and one or two flats leaner on the carbs. But it will still never make as much power as it did at sea level.

 

[charleyf]

Usually, they can tolerate a bit more timing at higher altitudes as well. But not much, and it doesn't seem to make all that much difference. ISTR I added about 4 degrees at about 10000 ft (VTR at Breckenridge, CO) and one or two flats leaner on the carbs. But it will still never make as much power as it did at sea level.

The lower power produced comment is right on. I grew up in Colorado and moved to California with my TR3, which I had been driving for a number of years. A short time after the move my first gear went out. I realized that starting off in second gear in California felt the same as starting off in first gear in Colorado. Then three years ago following the VTR in Breckenridge a friend and I drove around in Colorado for about a thousand miles. Upon returing to California at my first stop light off of the freeway with a left hand turn I almost put the car over the curb because I was going way to heavy on the gas.
Charley

 

[HarryL]

Thanks Guys,
What rad cap pressure would you recommend. Believe I have the 18-21 on it now.
Guess go up to the next higher one
Looks like it may be up here(Steamboat) permanently.
So advancing the timing is the way to go.
Will do that first ,run it a bit before messing with the carbs.
Harry

 

[TRMark]

I wouldn't worry much about the SU's, the beauty of the design is it self adjusts to altitude. My TR lives at 3300', it regularly (well, in the summer) goes to the cabin at 6200' over the Beartooth pass at 11,900' and into Yellowstone park mostly around 7000'. It has been to Victoria BC at sea level and toured the Michigan UP. Never a problem. Had some DCOE's on it for awhile, made my life miserable.

 

[HarryL]

Rad cap is straight 15# Will go to the 18-21.
Harry

 

[TR4nut]

Harry- If you have a heater in that car I'd stay with a stock cap - 7 psi I believe. Don't tell me you moved that car out of the area without me getting to see it!

Randy

 

[HarryL]

Have a heater completley rebuilt. I'll leave the present cap(15) on for the moment.
Have a Macy's fan; so it was running midway on the gauge down south.
More than likely will end up bringing it and the Super 7 south for the winter.
I really need to take some pics and post it here. Found a 12yr old that will help me !
Can you believe it ! As soon as you retire you become helpless Ha
Harry

 

[Hot Wings]

Rad cap is straight 15# Will go to the 18-21.
Harry

Don't change it if you don't have problems. I was in Weber mode when I mentioned the mid and high range. With the SU's setting the idle leaner pretty much takes care of the rest.

Sea level is 14.7 psi. 6500 at normal laps rate is 11.5 psi. So a cap 3 psi higher cap compensates for the change. Keep the caution about weak hoses, and as another mentioned heater cores, in mind. The extra pressure can cause failure if the components are weak.

 

[glemon]

Thinner air, only one real solution, supercharger