Yeah that is the case. Luckily with higher compression you get better spool and transient response. This is why you can run larger turbochargers than you otherwise would be able to (given the same spool).

I’m sure inertia of the turbine is a factor, but I believe more of a factor is the housing diameter. In flow dynamics, the radius of the cross section is the most important factor, and it is why pressure increases and water/air shoots out faster when someone reduces the diameter of the tip of a hose. Similarly, it takes a lot of air to raise enough pressure in a big turbine to force air to move rapidly through the turbine. And like our example with the water hose, the small turbine reduces the diameter, which means it takes less air from the pump (engine) to accelerate air through the turbine.

I guess my point is that if you actually measure the weight of the turbines, you might find that they aren’t too different in weight. In fact, I bet you could improve transient response with some exotic, lightweight titanium turbine that weighed as much as a small turbine, and maybe you would shift the spool time slightly lower, but I bet the large turbine would still struggle to spool as fast as a small turbo.

But you are correct, that such a problem is one of the reasons why compression is dropped and a smaller turbo is used. Goingnowherefast is correct that a higher compression motor will spool the turbo sooner and provide enough low end torque on its own, but this is not as desirable in the industry from the factory. Look at sports cars like the Supra that have a small turbo for immediate torque, but that gases out up top, which gives high torque, but low, relative horsepower.

Top Gear did a comparison of the Evo vs Lamborghini to show how capable the Evo was, but to our topic of interest, they did a demonstration of the turbo lag. Actually, it was more a demonstration of boost threshold, but the point was that the Evo they were testing was a 400hp model with a large turbo and really low compression, so the delay was terrible. They recommended getting one of the less powerful models. See part 2:

https://youtu.be/Ees2aZcDUn8
https://youtu.be/VVt1IjIdLxY

The ideal thing is to use an electronic motor to torque fill down low along with a bigger turbo. Some have used an electronic motor to spool the turbo to help with boost threshold and turbo lag when a larger turbo is utilized in lieu of a supercharger and compound boosting.

The Muppets will prevail!

So if I can do 10lbs on the FA20 I should be able to do 20 on the 24 since it is larger.

Can't afford the turbo an the tune at the same time but I should be OK to run a little boost until I can tune.

There is no need for premium gas it is a scam!

I read on Facebook that the higher the compression ratio the better it takes boost so I am cranking it to 20.

My 1999 Civic need all sort of things so this car will as well.

I also thought of this. I think in order to stay cheap they just put the same cylinder heads from the old fa20 and this resulted in the compression this high:clap:

If they did that then my Harrop kit would fit on the FA24 swap or second gen car.

For what it's worth supposedly the FA24 has hit 500+ on a stock long block with ARP head studs. I think anything over 300 on a 2800lb car is already plenty quick.

https://forums.nasioc.com/forums/sho....php?t=2907007

I bet a bag of donuts it doesn't match the MPH or trap that a 500hp car of that weight should do

Copies of dyno runs to prove power gains is lame

Excuses as to why they cannot do a run are usually many, and lame

Are you saying they are lying about the power? I see no reason why they would lie or why the motor couldn’t hit that power level.

I am not a tuner, so I can't say this for certain, but if E85 can protect the car then there may be more gains at the same psi for power because compression is higher. I have been told by a tuner, and I have read tuners write here that lowering compression is not necessary on E85 at 12.5:1 when people were asking if they should lower compression when they build their motor.


Obviously compression should be lowered if all someone has access to is pump gas, so they can maximize their potential. The lower the compression the more power the car can theoretically make, but there is obviously a trade off with low-end/off-boost power, especially as compression drops and as the turbo compressor gets larger to accommodate more boost.


For perspective though, the FA24F in the Ascent makes 277tq. The FA20D makes 150tq, so the Ascent makes almost double. The rods on the FA20D hold to around double the output, so 250-275wtq. I wouldn't be surprised for the torque to be close to double too, so around 500tq.

To be clear that is the FA24F they are talking about. Just because it is the same base engine code does not mean it is the SAME engine. Who knows what they changed for internals.
The FA24F has a compression ratio of 10.6:1. That is a huge difference that can not be ignored.
We will know what they can do eventually but saying they did this that or the other thing to the F is almost meaningless.

Ah I didn't realize it was different. My point was just that even if that dyno run was exaggerated, it seems reasonable that the engine could be hitting 3-400HP on E85, which in my mind would be enough. I guess we'll just have to wait like 2 years to find out

The FA24F is a low compression, direct injection only, turbo engine. It brings it torque and power on way down low in the rev range and is for all intents and purposes a truck engine.

The FA24? is a high compression, direct and port injection NA engine. It brings it's torque and power in at high revs and should be a very nice sports car engine.

The FA24? should work really well on E85 but looking for 300-400HP out of it with a tune and some bolt on's is very optimistic.

What they can do to the one doesn't mean much when compared to the other.

OH and they were running 22PSI on that heavily modified FA24F to get that 500HP. Try doing that on an engine with a 13.5:1 compression ratio and you will be finding parts of the block and rods for several blocks around you!

Yeah you're right. I didn't think that the engine would have such a different compression ratio. Although I guess that means I won't be as tempted to drop big money on a supercharger so yay?

some engine pics from Motortrend

https://www.motortrend.com/uploads/s...aru-BRZ-45.jpg
https://www.motortrend.com/uploads/s...aru-BRZ-46.jpg
https://www.motortrend.com/uploads/s...aru-BRZ-47.jpg
https://www.motortrend.com/uploads/s...aru-BRZ-48.jpg
https://www.motortrend.com/uploads/s...aru-BRZ-49.jpg