Pump Fuel MCX Apex
- Thread starter Duke
- Start date
What do you mean "and 15-16 at Revy altitude would be tight i think"?
We drive between sea level and ~3000 feet, i know i know "flatlander"
, i live @ sealevel and here i set it ~15,9, not 16 or above, and @ 3000 feet i see ~17,6.As you all know by now it does not need any diffrent fuelmap, because it is the same Total Pressure @ both altitudes = 30,6 (14,7 + 15,9) @ sealevel, and 30,6 (13 + 17,6) @ 3000 feet, and same total pressure is the same power and the same need of fuel.
What do you mean "and 15-16 at Revy altitude would be tight i think"?
We drive between sea level and ~3000 feet, i know i know "flatlander"
As you all know by now it does not need any diffrent fuelmap, because it is the same Total Pressure @ both altitudes = 30,6 (14,7 + 15,9) @ sealevel, and 30,6 (13 + 17,6) @ 3000 feet, and same total pressure is the same power and the same need of fuel.
Yes , 18lbs at sea level is the same amount of air as 18lbs of air at 6000 feet , but there is less O2 in the air at 6000 feet , so you would have to cut fuel , or am i missing somthing
D
Duke
Well-known member
I wonder if this is done with a shimmed motor or can be done with low comp pistons?
N
NM
Well-known member
It's all about cylinder compression. Some companies say they can run pump gas at 17-18 lbs, and that is with 9-9.1:1 compression. That is the whole reason we lower compression for boosted applications. The only other way to run less octane fuel at higher boost would be to take timing out. It really is how much hp do you want to make. More compression and timing will make more power, but you have to have fuel to support it. Your setup would be good to about 12-13 lbs on pump, but would probably make as much power as a stock headshim motor at 17-18. Not sure why anyone would spend all the money on modding a motor and then not finish the job by running good fuel through it. I have been running 50/50 for 4 years without an issue...its just insurance.
Yes , 18lbs at sea level is the same amount of air as 18lbs of air at 6000 feet , but there is less O2 in the air at 6000 feet , so you would have to cut fuel , or am i missing somthing
I try again,
i wrote "As you all know by now it does not need any diffrent fuelmap, because it is the same Total Pressure @ both altitudes = 30,6 (14,7 + 15,9) @ sealevel, and 30,6 (13 + 17,6) @ 3000 feet, and same total pressure is the same power and the same need of fuel"
It's the "total pressure" that is constant on MCX!
an MCX kit adjusted to 15,9 lbs of boost @ sealevel is infact adjusted to 30,6 lbs total pressure,
and it keep the total pressure @ any altitude by adjusting boost, that means @ 3000 feet boost rised to 17,6 lbs as air pressure dropped from 14,7 to 13.
and because it's the total pressure the engine see it's same amount of fuel needed.
if you don't have altitude compensation (all other kit's) total pressure decreases @ higher altitude, as boost isn't adjusting and power drops, and less fuel is needed.
D
Duke
Well-known member
This is not for me, this is a shimmed MCX rearmount Apex, the owner is wondering what he can can get away with when running straight pump premium. One shop tells him he can run premium to 18#'s at altitude with rods and pistons. Sounds a little risky to me. I suggested taking to Vernon Motorsports to update the fuel mapping, etc.
N
NM
Well-known member
10-4. I guess there is only one way to find out!
What's the risk?
is there something complicated in my description about how MCX altitude adjustment works?
i can't explain it any simpler, sorry,
with an MCX290 that is mapped right, that is 15,9 lbs @ see level, you will see above 18 lbs of boost above ~ 3500 feet, and that as safe as @ sea level, because total pressure is the same, and it's the total pressure that the engine see, fundamental turbo knowledge!
is there something complicated in my description about how MCX altitude adjustment works?
i can't explain it any simpler, sorry,
with an MCX290 that is mapped right, that is 15,9 lbs @ see level, you will see above 18 lbs of boost above ~ 3500 feet, and that as safe as @ sea level, because total pressure is the same, and it's the total pressure that the engine see, fundamental turbo knowledge!
OK , sorry , i see now what you are saying , so if you want to run a lower total boost , you would have to run a different map , i would rather have a system that compensated for altitude by changing the main map no matter what boost level i am running .
Yes T-Birds theory is sound and this is how MCX explains the numbers as well. However what is safe on pump in Sweden may or may not be safe here in Canada/USA. I say this because the fuel is different from there to here.
I ran the 16T forever on pump at 12psi (6000-7000ft) i know a guy would be safe to 14psi for sure. Here in Canada when guys were running the 310 kit with the 16T they were running 17psi on straight Avgas. Can it be done on straight pump ?? I don't feel like being the test dummy. As NM said running a 50/50 mix is smart insurance but may or may not be for everyone cost or practical wise.
I understand the Nytro MCX 270 is set at 16 psi at sea level and then auto compensates at altitude. I know certain individuals can chime in and tell us they see 17-19 psi (auto comp) at the 6500-7000 foot mark all on pump premium. What these motors can take for max boost in all conditions on pump is a guessing game.
Running the auto compensate on the MCX say on the Apex 290 kit, hitting the 17-17.5 psi at altitude (6500) on pump may be pushing it in my opinion especially if your fuel is not top notch, which can supposedly happen. I'm no expert, just trying to come up with a good safe number to stay on pump premium. MCX says you need 200KPA total/absolute pressure for 290 pump. at 6500 feet you have 80KPA, you then need 120 KPA to make your 290 which is roughly 17.5 psi supposedly safe on pump. Who's pump ????
Air/Fuel may not necessarily tell you your in deto land. This is MCX head shim of course. Low compression pistons would change things especially if compression is lower than the head shim which i believe it is, but not 100%. Just some food for thought.
Some numbers for thought
Apex 16T 260 HP (180 KPA)
Sea 12 psi
6500 14.5 psi
Apex 19T 290 HP (200 KPA)
Sea 14.5 psi
6500 17.4 psi
Nytro 16T 180 HP (140 KPA)
Sea 6 psi
6500 8.7 psi
Nytro 16T 240 HP (190 KPA)
Sea 13 psi
6500 15.9 psi
Nytro 19T 270 HP (210 KPA)
Sea 15.9 psi
6500 18.9 psi
Keep in mind these are a little rounded and using 100KPA sea and 80KPA 6500.
I ran the 16T forever on pump at 12psi (6000-7000ft) i know a guy would be safe to 14psi for sure. Here in Canada when guys were running the 310 kit with the 16T they were running 17psi on straight Avgas. Can it be done on straight pump ?? I don't feel like being the test dummy. As NM said running a 50/50 mix is smart insurance but may or may not be for everyone cost or practical wise.
I understand the Nytro MCX 270 is set at 16 psi at sea level and then auto compensates at altitude. I know certain individuals can chime in and tell us they see 17-19 psi (auto comp) at the 6500-7000 foot mark all on pump premium. What these motors can take for max boost in all conditions on pump is a guessing game.
Running the auto compensate on the MCX say on the Apex 290 kit, hitting the 17-17.5 psi at altitude (6500) on pump may be pushing it in my opinion especially if your fuel is not top notch, which can supposedly happen. I'm no expert, just trying to come up with a good safe number to stay on pump premium. MCX says you need 200KPA total/absolute pressure for 290 pump. at 6500 feet you have 80KPA, you then need 120 KPA to make your 290 which is roughly 17.5 psi supposedly safe on pump. Who's pump ????
Air/Fuel may not necessarily tell you your in deto land. This is MCX head shim of course. Low compression pistons would change things especially if compression is lower than the head shim which i believe it is, but not 100%. Just some food for thought.
Some numbers for thought
Apex 16T 260 HP (180 KPA)
Sea 12 psi
6500 14.5 psi
Apex 19T 290 HP (200 KPA)
Sea 14.5 psi
6500 17.4 psi
Nytro 16T 180 HP (140 KPA)
Sea 6 psi
6500 8.7 psi
Nytro 16T 240 HP (190 KPA)
Sea 13 psi
6500 15.9 psi
Nytro 19T 270 HP (210 KPA)
Sea 15.9 psi
6500 18.9 psi
Keep in mind these are a little rounded and using 100KPA sea and 80KPA 6500.
Erik and Alf were in Canada last week. They felt thier premium is very similar to our 91-92 product.
I've got 10,000k on my nytro 270 19t pump fuel sled......I often see 19lbs at 6,000+ plus.
So yeah......I'd use the table below and run with it
RS
Apex 16T 260 HP (180 KPA)
Sea 12 psi
6500 14.5 psi
Apex 19T 290 HP (200 KPA)
Sea 14.5 psi
6500 17.4 psi
Nytro 16T 180 HP (140 KPA)
Sea 6 psi
6500 8.7 psi
Nytro 16T 240 HP (190 KPA)
Sea 13 psi
6500 15.9 psi
Nytro 19T 270 HP (210 KPA)
Sea 15.9 psi
6500 18.9 psi
Keep in mind these are a little rounded and using 100KPA sea and 80KPA 6500.
I've got 10,000k on my nytro 270 19t pump fuel sled......I often see 19lbs at 6,000+ plus.
So yeah......I'd use the table below and run with it
RS
Apex 16T 260 HP (180 KPA)
Sea 12 psi
6500 14.5 psi
Apex 19T 290 HP (200 KPA)
Sea 14.5 psi
6500 17.4 psi
Nytro 16T 180 HP (140 KPA)
Sea 6 psi
6500 8.7 psi
Nytro 16T 240 HP (190 KPA)
Sea 13 psi
6500 15.9 psi
Nytro 19T 270 HP (210 KPA)
Sea 15.9 psi
6500 18.9 psi
Keep in mind these are a little rounded and using 100KPA sea and 80KPA 6500.
