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55 minutes ago, Don Del said:

For my off road needs the standard cam provides adequate performance. Where it lets me down is on the tarmac. As you can appreciate in the part of the world where I live you can spend a lot of time either going up or down hills with a change in elevation of 7,000 ft. in a 60 mile drive not being uncommon. The most common gradients I encounter at altitude just prevents being able to hold third gear at around 35-40 mph. This results in a lot of the time being spent thrashing the truck in second followed by a brief spell in third before having to change back to second. The cause of the problem is the drop off in power with altitude due to the reduction in the oxygen in the air, in La Paz there is only around 65% of the amount at sea level. For that reason I picked the 270 to, hopefully, get a bit more power in the 2,500-3,500 rpm range.

Del

If you had more torque lower down you wouldn't have to thrash it though?

Then again, as you've already got megajolt on there it's a small jump for upgrade to Megasquirt and EFI, with an optional 2nd MAP sensor to sense atmospheric pressure it can apply barometric correction for altitude automatically.

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42 minutes ago, FridgeFreezer said:

If you had more torque lower down you wouldn't have to thrash it though?

Then again, as you've already got megajolt on there it's a small jump for upgrade to Megasquirt and EFI, with an optional 2nd MAP sensor to sense atmospheric pressure it can apply barometric correction for altitude automatically.

The mid rev range of 2,500 to 3,500 rpm roughly equates to 30 to 40 mph in third which is where I am getting grief. The engine is on SUs and I have a lambda sensor and gauge installed which I use to reset the carbs when the elevation changes by around 3,500 feet

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On 1/19/2021 at 4:52 PM, Don Del said:

The mid rev range of 2,500 to 3,500 rpm roughly equates to 30 to 40 mph in third which is where I am getting grief. The engine is on SUs and I have a lambda sensor and gauge installed which I use to reset the carbs when the elevation changes by around 3,500 feet

Life just above sea level is much easier!

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59 minutes ago, FridgeFreezer said:

I don't see how more torque wouldn't help with this?

It would, but the problem is that the air is thinner (less pressure) at that height. So although the different cam may help slightly, you are still only relying on the outside air pressure to fill the cylinders. 

The real solution is a super/turbo charger. Or a bigger engine, or one that produces more torque in the first place. Like a diesel :ph34r:

The Torquemax or equivalent would be my choice BTW. Reasoning being that less revs will give the cylinders more time to fill, and give you enough to use a higher gear.

The carbs are always going to hobble you though. EFI would be a good choice. 

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On 1/21/2021 at 2:08 PM, smallfry said:

It would, but the problem is that the air is thinner (less pressure) at that height. So although the different cam may help slightly, you are still only relying on the outside air pressure to fill the cylinders. 

The real solution is a super/turbo charger. Or a bigger engine, or one that produces more torque in the first place. Like a diesel :ph34r:

The Torquemax or equivalent would be my choice BTW. Reasoning being that less revs will give the cylinders more time to fill, and give you enough to use a higher gear.

The carbs are always going to hobble you though. EFI would be a good choice. 

Even diesels require their fair share of oxygen and suffer from the same power reduction problem. I have ordered up a 270 and the various bits and pieces necessary to install it which should all be here by the end of next week. When I have got it installed and tried out I will report back, hopefully positively!

Cheers,

Del

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