Traction Vs Boost and Clutch Set Up

[AAdavis]

I have a 2020 SRX and live in Jackson Hole Wy. I ride trails only and the amount of traction on offer can vary quite a bit depending on new snow and temp sequence. I also have to deal with elevation changes. I was working with a tuner on a custom tune and he kept saying I did not have the boost levels he was tuning for I must have leaks. At the time I was sure I did not have leaks. Well last year I did have leaks and got stuck at 5lbs of boost. Solved that problem over the summer. Now the first couple of rides this year did some data logging and on loose dry snow spinning the track at all times I was getting 14.5lbs of boost with the engine sitting at 8500rpm. This is on a off the shelf tune for Hi Altitude. I also have a MC Express intercooler and 3 inch exhaust and outside CAI and header. So I am thinking some clutch tunning is in order. So before I change anything I go for a ride not data logging and hit some very gripy snow hit the throttle and tag the revlimiter for the first time ever on the clutch set up. Anyone care to comment on changes in traction on boost levels and clutching? Also I am seeing only 20 degrees of intake air temps gain on boost. For you guys running 20lbs of boost on stock turbos what Intake temps are you seeing?

 

[Fords4life]

Need more details such as who's tune or tunes, clutch details you are running now, track lug hieght, reason i'm asking is i went threw this type thing 2 seasons ago, im also at elevation had header, big pump all the garbage that goes with it.

 

[KnappAttack]

The key for consistency from deep snow spinning and hardpack hookup is in the secondary helix angle and spring settings. If clutched correctly for the both, you should not see more than a few hundred RPM difference with temps and pressures being the same. We'll need to know what the setup is prior to making suggestions. Myself, I'd be using a 35 helix with a Dalton B/O set at 90 and Hi-Torque rollers for those type of conditions. Hardback you can get by with more helix like a 39-35 or a 41-37 type of deal, but spinning in snow requires a different less aggressive setup because of the track spinning.

14.5 lbs isn't much for boost and why intake temps are easily in check, and it should boost the same wether hardback or loose snow, should be no difference there. Should you not be up at 17 lbs or more in the mountains. 14.5 would be a pretty low HP number at altitude even with a header.

17.5-18 lbs at sea level is 300 HP with a header setup. You need more boost at altitude to compensate for the lack of air. As I recall 14.5 at sea level is only 240 HP with a header and intake never gets warm at that little bit of boost level.

 

[Doc Harley]

Ever consider 1.5" lug track? Possibly better suited to your varying conditions.

 

[fatchance]

The key for consistency from deep snow spinning and hardpack hookup is in the secondary helix angle and spring settings. If clutched correctly for the both, you should not see more than a few hundred RPM difference with temps and pressures being the same. We'll need to know what the setup is prior to making suggestions. Myself, I'd be using a 35 helix with a Dalton B/O set at 90 and Hi-Torque rollers for those type of conditions. Hardback you can get by with more helix like a 39-35 or a 41-37 type of deal, but spinning in snow requires a different less aggressive setup because of the track spinning.

14.5 lbs isn't much for boost and why intake temps are easily in check, and it should boost the same wether hardback or loose snow, should be no difference there. Should you not be up at 17 lbs or more in the mountains. 14.5 would be a pretty low HP number at altitude even with a header.

17.5-18 lbs at sea level is 300 HP with a header setup. You need more boost at altitude to compensate for the lack of air. As I recall 14.5 at sea level is only 240 HP with a header and intake never gets warm at that little bit of boost level.

Yeah, Mike sounds like a wonky tune for those altitudes and given it's only making 14.5 lbs of boost and turning 8500 revs with those components there's something way off here. You said you data log. Post one up and it will be easy to see what's going on

 

[NYTurbo]

Have you pressurized your system and check for boost leaks ?

 

[Doc Harley]

Have you pressurized your system and check for boost leaks ?

My first thought was those clamps on the backside of throttle bodies.

 

[earthling]

The key for consistency from deep snow spinning and hardpack hookup is in the secondary helix angle and spring settings. If clutched correctly for the both, you should not see more than a few hundred RPM difference with temps and pressures being the same. We'll need to know what the setup is prior to making suggestions. Myself, I'd be using a 35 helix with a Dalton B/O set at 90 and Hi-Torque rollers for those type of conditions. Hardback you can get by with more helix like a 39-35 or a 41-37 type of deal, but spinning in snow requires a different less aggressive setup because of the track spinning.

14.5 lbs isn't much for boost and why intake temps are easily in check, and it should boost the same wether hardback or loose snow, should be no difference there. Should you not be up at 17 lbs or more in the mountains. 14.5 would be a pretty low HP number at altitude even with a header.

17.5-18 lbs at sea level is 300 HP with a header setup. You need more boost at altitude to compensate for the lack of air. As I recall 14.5 at sea level is only 240 HP with a header and intake never gets warm at that little bit of boost level.

Engine is measuring absolute pressure, air density is lower at altitude, if boost is 14.5 lbs at altitude, it is the equivalent of a higher boost pressure at sea level. The other way to look at it is; If boost is set to 14.5lbs at sea level and air density drops with altitude, to maintain 14.5 lbs at altitude the turbo has to work harder but it only maintains the same absolute pressure as was set at sea level so HP stays the same. The turbo is the variable, air pressure and AFR are fixed targets.

 

[KnappAttack]

Engine is measuring absolute pressure, air density is lower at altitude, if boost is 14.5 lbs at altitude, it is the equivalent of a higher boost pressure at sea level. The other way to look at it is; If boost is set to 14.5lbs at sea level and air density drops with altitude, to maintain 14.5 lbs at altitude the turbo has to work harder but it only maintains the same absolute pressure as was set at sea level so HP stays the same. The turbo is the variable, air pressure and AFR are fixed targets.

Boost has to be higher at altitude to compensate for less density, hence at altitude it would need to increase in pressure to make up for it. Boost should read higher than at sea level for same given HP. The turbo is going to work harder yes.

The ECU compensates for barometric pressure, allowing for more boost as you go up in elevation to keep HP levels. The boost is not fixed and it’s gonna be different every day based on barometric pressure differences, with the ECU compensating for it.

 

[earthling]

Boost has to be higher at altitude to compensate for less density, hence at altitude it would need to increase in pressure to make up for it. Boost should read higher than at sea level for same given HP. The turbo is going to work harder yes.

The ECU compensates for barometric pressure, allowing for more boost as you go up in elevation to keep HP levels. The boost is not fixed and it’s gonna be different every day based on barometric pressure differences, with the ECU compensating for it.

My understanding is that the boost number shown on the cluster is a derived number (intake pressure - barometric), not an actual 'boost gauge' number but I could be wrong about that. If it is an actual boost number as measured at the turbo then yes, I would expect it to be higher and everything you said is absolutely correct.

Boost is higher (as measured at turbo) but manifold actual pressure is the same because atmospheric pressure is lower. Boost pressure goes up relative to ambient pressure going down, because the engine is operating off of actual pressure (total air mass of boost plus atmospheric) as measured by the map sensors. Since the wastegate actuation is controlled by this, the turbo is forced to work harder to build more boost in compensation for that thinner atmosphere. The engine only cares about the total actual air mass so HP stays the same. In reality there are limits due to pumping losses in the turbo and actual HP will start to drop as intercooler efficiency drops and the turbo heats the air to higher temperatures.

 

[KnappAttack]

My understanding is that the boost number shown on the cluster is a derived number (intake pressure - barometric), not an actual 'boost gauge' number but I could be wrong about that. If it is an actual boost number as measured at the turbo then yes, I would expect it to be higher and everything you said is absolutely correct.

Boost is higher (as measured at turbo) but manifold actual pressure is the same because atmospheric pressure is lower. Boost pressure goes up relative to ambient pressure going down, because the engine is operating off of actual pressure (total air mass of boost plus atmospheric) as measured by the map sensors. Since the wastegate actuation is controlled by this, the turbo is forced to work harder to build more boost in compensation for that thinner atmosphere. The engine only cares about the total actual air mass so HP stays the same. In reality there are limits due to pumping losses in the turbo and actual HP will start to drop as intercooler efficiency drops and the turbo heats the air to higher temperatures.

Not sure what's on the dash as I never look at it anyway, it should be intake manifold boost, but on the logs, boost is actual boost in the manifold taken there, and the ECU compensates for going up in altitude, or a decrease in barometric pressure, as its taking in to consideration the barometric pressure and compensating to keep the HP in close proximity to what the power level is supposed to be. What's in front of the throttle bodies for pressure should also be what's behind the throttle bodies for pressure at wide open. Boost measured at anypoint in the intake tract should measure the same no matter where you pull it from, with the exception of measuring behind the throttle bodies if not in a wide open state.

The issue is the boost (MAP) sensor psi, which is the pressure behind the throttle bodies, is only using the stock map sensor and it ends up being tapped out at that 16-17 lbs. even if you are boosting upwards at say 20 psi at the intake manifold. So if the air density gets worse as you climb, or a low pressure day, the boost is supposed to increase. Now if the tuners change these parameters in the ECU, then all bets are off on that, but in essence more altitude is going to need more boost to make the same power at sea level, so yes, the turbo is going to be working harder and be less efficient in doing its job. I doubt 300 HP is attainable when you get to a certain point on the stock turbo like we can achieve at sea level, my guess is 270 HP at best may be maxing it out for these guys at mile high and above.

All I know is NA sleds get real anemic and slow at altitude, and thats why everyone boosts them up there to help them get thru the snow.

No matter what, 14.5 lbs of boost as he states he had, would barley be making much for power. I'd guess about 240 with a header tune depending on altitude, and that little bit of boost level certainly isn't taxing the intercooler much at all. It seems like it should be boosting higher than that by a wide margin. I'd only be guessing you need 17-18 lbs of boost on the logs to get 270 at altitude, vs getting 300 at sea level. Like I said thats only a guess, but 14.5 lbs isn't much at altitude and its not the spinning the track and soft snow causing it. They still boost up even spinning the track.

 

[earthling]

One of the map sensors is only used at idle and low throttle. There is a note in the tech bulletins about that.

 

[Fords4life]

As i recall working with Dave from hurricane a few seasons ago dialing in my 240,270,300 header tunes out here @ 6500 feet of elevation 300hp was alittle over 20psi, 270 was making around 18psi and 240 as close as we could get her tamed down was 16-17 psi.

 

[KnappAttack]

As i recall working with Dave from hurricane a few seasons ago dialing in my 240,270,300 header tunes out here @ 6500 feet of elevation 300hp was alittle over 20psi, 270 was making around 18psi and 240 as close as we could get her tamed down was 16-17 psi.

That would sound about right to me. Thats why the OP's boost of 14.5 sounds pretty low at that.

 

[1nc 2000]

Stock they were designed to up to 14 psi at 15,000 or 19,000 ft and make 180 horsepower.
That is where the stock advertised hp number came from.