aluminator with a supercharger

[bluebeastsrt]

9.5/1 compression, 1100 rwhp on e85:



I know I know....but Predator....however as far as I know, physics, thermodynamics, and kinematic works the same across different engines, especially if it’s the same architecture.

Cliff notes homie. What part of the video does my dude talk about physics, thermodynamics and kinematic? I Tried to watch but after about 5 minutes I got bored. My take away is different pullies sizes make different power from this video. That and maybe stangmode should have watched this video before he went for 1100 wheel.

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[robmustang201528]

Cliff notes homie. What part of the video does my dude talk about physics, thermodynamics and kinematic? I Tried to watch but after about 5 minutes I got bored. My take away is different pullies sizes make different power from this video. That and maybe stangmode should have watched this video before he went for 1100 wheel.

 

[IamCDNJosh]

Yea it’s definitely not the popular opinion of this board, but the FACTs don’t lie.

This is fact, both from theoretical and practical standpoints:

For any given power or torque level, lower compression ratio will reduce peak stresses on the engine reciprocating parts. This is indisputable.

The Predator is 9.5/1 and yet performs extremely well even on E85, and the 2018 Cobra Jet is 9.7/1 even though it specifically designed by Ford for C16 fuel. Ford also specifies the 9.5/1 aluminator for supercharged applications and 11/1 for NA. Meh....what do they know...probably just a bunch of “google engineers” right? More food for thought is the 660 hp 3.5 liter Ford GT supercar is 9.0/1 compression. Ford’s engineers are probably just stuck in “old school” thinking right?

It is also true that for the same boost and spark values, a drop in compression will lose power and torque, 3-5% per compression number. This means that you will have to raise boost about 2 psi to break even when dropping from 11/1 to 9.5/1. Resulting engine stresses will be lower. Also keep in mind it will likely require some tuning. The torque and speed density models will undoubtedly need recalibration.

So what you're saying is that FP engineers have no idea what they're doing?

 

[SolarFlare]

Cliff notes homie. What part of the video does my dude talk about physics, thermodynamics and kinematic? I Tried to watch but after about 5 minutes I got bored. My take away is different pullies sizes make different power from this video. That and maybe stangmode should have watched this video before he went for 1100 wheel.

Cliff notes.....

great tuner fine tunes his 100k car to make 1070ish whp at 23-24 psi....runs 9.30s with further fine tuning

little peasant me gets cookie cutter email tune with 14psi and 800 and change whp and runs 9.30s at same track with 11:1 compression and E85 on 45k mile 6 year old $40k coyote.

 

[bluebeastsrt]

Cliff notes.....

great tuner fine tunes his 100k car to make 1070ish whp at 23-24 psi....runs 9.30s with further fine tuning

little peasant me gets cookie cutter email tune with 14psi and 800 and change whp and runs 9.30s at same track with 11:1 compression and E85 on 45k mile 6 year old $40k coyote.

Did you use physics, thermodynamics and kinematic? If you didn’t I’m gonna need you to pipe down.

 

[SolarFlare]

Did you use physics, thermodynamics and kinematic? If you didn’t I’m gonna need you to pipe down.

I am afraid I did not.

 

[engineermike]

For those who don’t know the history, some like to argue that any information regarding the Predator is not relevant to the coyote.....as if the governing principles aren’t transferable.

 

[engineermike]

... the lower compression the safer you'll be. More life out of the motor....I'll have to run more boost with a lower compression but I'll be safer...

One way or the other, this is the OP’s reasoning for wanting to lower compression and it is absolutely correct.

 

[engineermike]

Instead of looking a static compression, look at dynamic compression. With the high tuneability of the cams you don't need to hamper yourself with a low SCR motor just to be safe.

I’ve understood what DCR is and how to calculate it for a long time, but I’ve learned a lot more in the last 2 weeks. I’ve been tuning the borderline knock tables on my Whipple 2018 gt. I first locked the cams at maximum wot overlap (mapped point 25) and found I could run quite a bit of timing without knock. Then I locked them at minimum overlap (mapped point 15), which pushed the intake cam back 50 degrees (!). This should have lowered the DCR quite a bit. However, I ran into knock a full 5 deg of spark timing lower than the prior cam timing.

As a sanity check, I pulled the Predator cal and it showed the exact same thing. So, lowering DCR doesn’t actually help us. Interestingly, at max overlap also has the lowest MBT, so it definitely lets you close in on optimum spark from both sides of the equation.

“Someone smarter than me” suggested that more overlap is helping purge exhaust gas, which would move me away from knock even though DCR is higher. I can’t refute that theory.

So now I’ve learned the running max overlap might have higher DCR but it also allows me to run more spark timing before knock. This presents another problem. Advancing the intake cam the far hurts top end power in spite of being able to run more spark.

 

[GuardEcoBeast]

I’ve understood what DCR is and how to calculate it for a long time, but I’ve learned a lot more in the last 2 weeks. I’ve been tuning the borderline knock tables on my Whipple 2018 gt. I first locked the cams at maximum wot overlap (mapped point 25) and found I could run quite a bit of timing without knock. Then I locked them at minimum overlap (mapped point 15), which pushed the intake cam back 50 degrees (!). This should have lowered the DCR quite a bit. However, I ran into knock a full 5 deg of spark timing lower than the prior cam timing.

As a sanity check, I pulled the Predator cal and it showed the exact same thing. So, lowering DCR doesn’t actually help us. Interestingly, at max overlap also has the lowest MBT, so it definitely lets you close in on optimum spark from both sides of the equation.

“Someone smarter than me” suggested that more overlap is helping purge exhaust gas, which would move me away from knock even though DCR is higher. I can’t refute that theory.

So now I’ve learned the running max overlap might have higher DCR but it also allows me to run more spark timing before knock. This presents another problem. Advancing the intake cam the far hurts top end power in spite of being able to run more spark.

Tuning for one extreme hurts the other extreme.

 

[WildHorse]

I was told the lower compression the safer you'll be.

You were told wrongly.

 

[engineermike]

Correct. But 9:1 @ 25 psi is around the same power level 11:1 @ 15 psi. With the lower psi, there is less chance of blowby, oil leaks, air leaks, etc., etc.

First of all, it OBVIOUSLY doesn’t take 10 psi to overcome 2 numbers of compression. More like 3-4 psi. So if we’re talking 9/1 at 18 psi vs 11/1 at 15 psi, they will make roughly the same power but the 9/1 18 psi combination will have lower chance of detonation, lower peak cylinder pressure (Pmax), and lower peak stresses on the components. Ring leakage will be similar because average cylinder pressure is unchanged.

 

[IamCDNJosh]

Correct. But 9:1 @ 25 psi is around the same power level 11:1 @ 15 psi. With the lower psi, there is less chance of blowby, oil leaks, air leaks, etc., etc.

You're negating the cylinder pressures at TDC. In you're scenario those pressures (assuming static compression, ATM @ 14.7psi and no loss) are going to be within ~10%.

 

[turnswrench]

 

[bluebeastsrt]

Barbie says.

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