compression+boost?

[FreshFRS]

Originally Posted by ft_sjo

No, you've got it. The VVT is what makes or breaks this kind of turbo conversion.

yeah i kinda figured.

I personally Want to see an Eaton R1050 on Innovate's SC kit. more expensive? yes. but thermal efficiency in the 76% range (at 1.8 bar as the PR) is awesome and almost catching up with Centrifugal chargers. a well designed intercooler could bring AITs down close to ambient. A2W with a big enough heat-exchanger (with a fan or 2, and biggish coolant pump) could run at ambient in a car like this.

[ANTI_LAG]

While variable cam angle helps with spool, the reason why a higher CR motor will usually spool a turbo up quicker is simple. Most cases a higher cr motor will make more power na. More power= better spool up. We have ran motors all kinds of ways, on our Honda stuff we usually don't go lower than 11:1, this allows us to run a much bigger turbo to keep it spooling quickly. We have also ran 12:1 many times, this is where we run a class limited 72mm running around 44-47psi, helps to get us in the power band. Now take this for thought, go take a low cr boxer and see if you can put the large turbos we are running on these FRS and see if they spool the same, I'll tell you right now they won't. And I saw in a earlier post someone mentioned about the 2JZs couldn't make the power they do if they had high cr, most the big boys are not running that low of cr. I might add though camshaft plays an important role in this, we always run all motor camshafts in our turbo setups, no "turbo specific" camshafts. This might not work for everyone but has worked for us.

[ANTI_LAG]

I might add though that a lower cr will let you survive a lot more though :p

[Coheed]

Originally Posted by ANTI_LAG

While variable cam angle helps with spool, the reason why a higher CR motor will usually spool a turbo up quicker is simple. Most cases a higher cr motor will make more power na. More power= better spool up. We have ran motors all kinds of ways, on our Honda stuff we usually don't go lower than 11:1, this allows us to run a much bigger turbo to keep it spooling quickly. We have also ran 12:1 many times, this is where we run a class limited 72mm running around 44-47psi, helps to get us in the power band. Now take this for thought, go take a low cr boxer and see if you can put the large turbos we are running on these FRS and see if they spool the same, I'll tell you right now they won't. And I saw in a earlier post someone mentioned about the 2JZs couldn't make the power they do if they had high cr, most the big boys are not running that low of cr. I might add though camshaft plays an important role in this, we always run all motor camshafts in our turbo setups, no "turbo specific" camshafts. This might not work for everyone but has worked for us.

Cams and pressures! NA cams work amazingly well when the operating pressures of the engine are similar to NA environments. Get intake pressures and exhaust pressures to be similar to how an NA engine operates and you can get great scavenging and improve VE over 100% to a pretty large extent!

High compression also works well when VE is low. They intentionally lower VE on the Prius engine and run 13.5:1 compression for better mileage. The lower VE prevents detonation, even though 13.5:1 is way high for pump 85 octane.

This is a very deep subject and there are a lot of variables at play! But it is one of the things that fascinates me most about engines!

[arghx7]

Originally Posted by SkullWorks

also compression helps to spool a turbo,

Ehhh there's a lot that influences a turbo's spool. All things held equal, raising compression actually decreases exhaust enthalpy (exhaust potential energy) but when you change compression you tend to change other things at the same time. Usually the combustion phasing and gas exchange change at the same time.

I have read the articles about effective compression ratio...I disagree with the math because it tends to make people feel good about bad things...
a 75:1 motor wont ever exceed 100% VE but a turbo motor that is **:1 compression will achieve greater than 100% VE...that's why we all like Forced Induction more power same displacement.

I just want to let you guys know that dynamic or "effective" compression ratio is effectively a made-up term by car forum people who don't have access to combustion analysis tools. In real combustion engineering you look at the peak combustion chamber pressure and the amount of work done during the process (net/brake mean effective pressure).

I've never seen or heard any engine dyno technician or combustion engineer ever discuss "dynamic compression ratio" except in the context of Miller/Atkinson cycle processes.

Originally Posted by d1ck

\Note: Given two engines with everything equal except compression ratio they will have identical fuel consumption at a given rpm and MAP. The difference will be that the high compression engine will be producing more torque than the lower compression engine. Because fuel has a finite amount of energy which can be extracted through combustion, a higher compression engine will produce less waste heat (Coolant & Exhaust) and will actually result in an engine which takes slightly longer to spool a turbo. This is because you are getting the same volume of exhaust, but it is slightly cooler. A turbo relies on mass flow rate and heat to spool.
\

Yes, but I think you meant at a given rpm and Brake Mean Effective Pressure (BMEP). MAP, Manifold Absolute Pressure, might be related or it might not. With modern de-throttling strategies, MAP is not necessarily proportional to load like in the old days.

Originally Posted by Coheed

Cams and pressures! NA cams work amazingly well when the operating pressures of the engine are similar to NA environments. Get intake pressures and exhaust pressures to be similar to how an NA engine operates and you can get great scavenging and improve VE over 100% to a pretty large extent!

Yes, volumetric efficiency can be greater than 100% on an n/a engine using the right valve timing and resonance tuning. If you have high exhaust pressure inside the cylinder due to overlap, when the intake valve opens the air will actually rush backward and send a wave of compression to the next intake valve. If you have very low exhaust pressure inside the cylinder, the intake charge will help push out residual gases.

High compression also works well when VE is low. They intentionally lower VE on the Prius engine and run 13.5:1 compression for better mileage. The lower VE prevents detonation, even though 13.5:1 is way high for pump 85 octane.

The Prius uses late intake valve closing Atkinson cycle. It controls engine load using valve timing instead of a throttle valve. It also means that the compression ratio is lower than the expansion ratio.

They control knock with cooled EGR:



higher cooled EGR flow rates allow more advanced spark timing.

[Tansey86]

Cams help bleed off cylinder pressure so will help in terms of high compression high boost situations. Speaking of which, when will we see some aftermarket cams?

[ANTI_LAG]

Last time I checked turbos were powered by exhaust energy, thus a more efficient more powerful engine will spool faster due to the extra exhaust, but at the same time you will run into back pressure faster with the same turbo (where exhaust gases can't get out and back feed into the combustion chamber), this is why proper turbo selection comes into play, this what I was saying about you couldn't spool the turbos we run on the FRS worth a damn on a EJ20. Google all the graphs you want but race results prove it all.

As far as lowering cylinder compression on a turbo motor, you can simply do that with the exhaust cam angle, this is done for emissions already.

As for cams I'm sure they are working on them but I'm sure R&D sucks for that since you have to keep pulling cams in and out which would involve pulling the motor everytime, plus I'm sure while people are asking about them it's gonna be awhile before people actually start buying due to the install process, once more people are building engines I'm sure it will happen.

[Coheed]

Originally Posted by arghx7

The Prius uses late intake valve closing Atkinson cycle. It controls engine load using valve timing instead of a throttle valve. It also means that the compression ratio is lower than the expansion ratio.

Prius works just like a regular otto cycle. It just has late valve opening like you said. But it still has a throttle valve, as seen in this pic. As you can see, VE is also affected by its small size.


I don't consider this a real "atkinson cycle" because it is far from his designs, but the modern concept works almost identical, and is much simpler.

Its a beautiful thing. They close the intake valves late to push extra intake air back out of the cylinder. This limits the actual VE of the engine.

[arghx7]

One thing that's missing from this discussion about knock suppression is intake port design and head cooling. There is a trade off between charge motion (tumble, swirl) and port flow capability. The high charge motion ports found on most modern direct injection turbo engines (NOT this engine) like the Ford Ecoboost 3.5 improve knock suppression and combustion.

Cylinder head cooling has gotten a lot better over the years as well, due to better computer simulations of flow in cooling passageways. So there's more to it than just the nominal compression ratio.

Originally Posted by Coheed

Prius works just like a regular otto cycle. It just has late valve opening like you said. But it still has a throttle valve, as seen in this pic. As you can see, VE is also affected by its small size.


I don't consider this a real "atkinson cycle" because it is far from his designs, but the modern concept works almost identical, and is much simpler.

Its a beautiful thing. They close the intake valves late to push extra intake air back out of the cylinder. This limits the actual VE of the engine.

A "real" Atkinson/Miller cycle engine uses the physical geometry of the engine to have a greater expansion stroke than compression stroke. Today's Atkinson/Miller processes on passenger car engines use valve timing tricks.

Of course the Prius engines have throttle valves. So do BMW Valvetronic and Toyota Valvematic engines. De-throttling is a bit of a catch-all term for reducing pumping loss from the throttle valve. Two primary means of de-throttling are from changes in valve timing/lift and load-point shifting.

Valve timing tricks for de-throttling come in various implementations. The most expensive are continuously variable valve lift systems like BMW's Valvetronic, which they use on basically every engine now. Some use cam-phasing, like the Prius engines. Others use a cam profile change, like on the Honda Civic R18 engines which also use Miller Cycle. You can control engine torque output with more than just a throttle valve. The throttle valve is there as a failsafe and as a way to create some vacuum in order to drive the evaporative emission purge system.

Cylinder deactivation is a type of de-throttling. It's load-point shifting--on an 8 cylinder engine, run 4 cylinders at a higher load (BMEP) to get into a more efficient operating condition. This is now being implemented in 4 & 6 cylinder engines.

[Coheed]

^^^^ This guy knows what's up!

Cylinder head cooling, and the open deck design are important designs that will impact how well the engine can absorb the heat of combustion. A larger cooling pocket over the combustion chamber can absorb more heat.

The open deck design is very good at keeping an even cooling effect on the cylinders, much better than most closed-decks. And I would imagine the head is designed to absorb a lot as well. Of course, I don't have a spare head to saw in half to determine if that's the case.

[subatoy]

Is there a simple way to calculate torque for this car based on compression ratio?
my goal with adding FI is Torque, I can't stand torqueless cars.
In a perfect world, if this car runs 5-6 PSI you get 250whp and 210 lb torque (estimate) with current high compression ratio.
if you were to achieve the same 250 whp with 9.5:1 compression ratio (example) is it possible to calculate/estimate torque?

[Tansey86]

Every point of compression added or lost takes away about 4% power. So say a turbo kit with aftermarket pistons at 10.5:1 will make about 8% less power at the same psi as the stock motor given everything else is equal.

[serialk11r]

Originally Posted by FreshFRS

good point about fuels. tuning window becomes very small at high compression + higher boost levels when using pump gas . i only use 94 from chevron up here seems to be the most consistent fuel i can find with no ethanol. i'm planning hopefully to run 12psi on pump gas on a Twin-screw supercharger and i think i will be okay from what i've seen.

Whoa whoa whoa, you have ethanol free 94? Blend it up to 10% (or even 20%) ethanol and get some ~96!

And @subatoy no there is no way of calculating torque, even if you knew exactly how much air was going through. You could attempt to get in the ballpark by going off the amount of air going through the engine, but once you increase the amount of air fed to the engine by any significant amount you're changing a lot of things.

@Tansey86 it's not that simple. Going from 8 to 9 is a lot bigger than going from 12 to 13, and higher compression ratio increases friction and cooling loss as well. It also depends on the temperature of the intake air, which can vary a lot (summer vs. winter, that's 10% absolute temperature already, and in a hot heatsoaked engine bay, even more).

[FreshFRS]

Originally Posted by subatoy

Is there a simple way to calculate torque for this car based on compression ratio?
my goal with adding FI is Torque, I can't stand torqueless cars.
In a perfect world, if this car runs 5-6 PSI you get 250whp and 210 lb torque (estimate) with current high compression ratio.
if you were to achieve the same 250 whp with 9.5:1 compression ratio (example) is it possible to calculate/estimate torque?

you would need more boost at 9.5:1 to build the power. torque would probably be roughly the same but that is only speculation.