ipse dixit

Perhaps a better way to think about this is not that FI engines cannot be high revving engines; rather, they do not need to be. This, in part, has to do with the engineering aspects and setup of the FI v. NA engines.

In an NA engine, air is pumped by the pistons. To pump more air, the pistons need to move faster. In a FI engine, air is pumped by the turbocharger. How fast the pistons are moving is not as important.

As we all know, engines need air and fuel to make power. Faster flow of air + fuel into the engine, greater power output.

In an NA engine, air enters the engine by being sucked in as the piston goes downwards. The appropriate amount of fuel is added. To make more power, you need to make sure air can enter the engine unhindered. This may mean modifications like better air filters, higher valve lift, longer lift duration, etc. However, the absolute upper limit of how much air enters the engine per stroke is already determined by the size of the engine and atmospheric pressure. To make more power in an NA engine of limited/fixed displacement, you need to suck in air more often, which means higher revs. Therefore, high-end modifications to NA engines are focused on allowing the engine to rev faster without breaking anything.

In a FI engine, the way to make big power is still to ingest copious amounts of air. However, in the presence of a turbocharger, air intake per stroke can be made much higher by the fact that the air is made denser (which means more oxygen in the same volume, so can allow more fuel to burn). To make lots of power, the focus is on ensuring that air density is kept as high as possible. This means that pressure must be kept high and air temperature kept low.

In other words, the airflow is increased with a forced induction system by pressurizing the intake system; in a naturally aspirated engine, the airflow is increased by raising rpm.

Drifting

Completely agree with ipse and he provides a nice technical description of the engineering facts.

Again I never said a random turbo engine couldn't have a high redline, I simply said that on average turbos have a lower redline compared with NA engines. That is a fact, because as ipse described, turbos don't need a high redline to produce their power.

sticky

You made an incorrect blanket statement about forced induction motors and now were forced to backtrack.

As covered, this is incorrect. A turbo engine can have a much higher RPM than an NA engine. The McLaren turbo V8 redline is but one example and just happens to be higher than any other NA V8 on the market.

Also, you will notice turbo engines in the aftermarket tend to seek revs as well especially as turbocharger size increases. Pretty common in the Nissan GT-R and Porsche world. Weird, eh?

Needsdecaf

The problem is lag and the size of the turbo.

To have a turbo that can still push enough air to accomplish higher RPM,(and meaningful power at higher RPM, after all you can let a turbo car run up in revs but there is little point if you've overworked the turbo) , the turbo size required will typically give you more lag than is acceptable to your average consumer.

I don't think McLaren / Ricardo has big turbos on that engine so not sure how they are achieving their witchcraft.

The 488 redlines at 8k RPM, IIRC.

Drifting

I didn't backtrack at all, you are simply wrong and can't admit it.
I've been taking about turbo models as a whole this entire time, not just one brand, yet you still perseverate on Mclaren.

BTW, you're even wrong about Mclaren, when you said their turbo redline was higher than any V8 redline. How about a Ferrari 458?, 458 speciale? Which both redline at 9,000?

Amazing how many times you can be wrong in a row.

GrantG

I think McLaren just lowered the redline to 8,000 rpm in their latest version (720S).

https://www.autoevolution.com/news/f...0s-115811.html

sticky

I haven't really looked into the new 4.0 liter yet. Doesn't have direct injection though. Something else people should consider when talking about redlines.

sticky

How about the Ferrari 458? How about that it isn't for sale? Ever heard of the 488 GTB? What I wrote was NA V8 on the market. The closest you will get is the Voodoo V8. Literally the highest revving production V8 is turbocharged flying in the face of your entire argument.

Are you going to bring up the S2000 redline now too? Maybe the E92 M3?

I have no idea how I'm wrong when literally every fact written by everyone contradicts you. Your backtracking from turbo motors having to have a lower redline proves it.

What are VR38DETT's revving to these days btw? What are Huracans being dialed down to with turbos? Yeah... that's what I thought.

DY369

7500 RPM's what more do you need or want? Shift already. How is 7500 a lot less than a NA engine?

jimbo1111

It's less than its predecessor. I know I use too rev my gts to 8000 rpms every day. It really sings a glorious song at peak. Im sure the 991.2 is a great car but surely the sound is subdued a few notches.

Drifting

Sticky I'm done discussing this with you as I'm worried I'm debating this with a teenager or mental patient.

But my final point since you brought up the 488 is that the 488 has a 8,000 redline compared to the 9,000 for the 458, thus proving my main original point again that when a car company switches a particular model to turbo that was previously NA, that new turbo engine almost always has lower redline!

mike drop

sticky

Well I'm not surprised you lose debates to teenagers or mental patients for that matter.

The redline is determined by the engine design and not aspiration alone. As previously mentioned, to get more power in NA form you need to rev. Horsepower is torque x rpm / 5252 isn't it?

Your original statement claimed a turbo engine will have a lower max rpm. That is false. Just because an engine is turbocharged does not mean the rpm has to go down. If displacement continues to decrease you will likely see turbo motors with an rpm increase.

Aspiration is just one part of a larger picture. What about the bore x stroke? The new Mclaren 720S increases its stroke yet dials back the redline to 8200 rpm. Why? Do you think piston speeds might be a factor?

Tuned Nissan GTRs go for more rpm with bigger turbos. Why? I thought being turbo meant reducing the redline?

The point is your blanket statement is basic, false, and does not take into account the numerous factors in engine design.

Don't hurt yourself picking that mic back up.

911boy

Current 1.6 liter turbocharged Formula one engine spin up to 15,000.

Dewinator

You guys are ridiculous, I think the main difference between your arguments is semantic. Of course there are additional engineering challenges associated with a higher redline when you add turbos... you have more exhaust gasses to expunge with a now impeded exhaust path, and you have more heat to dissipate just to begin with. Those challenges can of course be overcome, but you may not necessarily want to since you don't need as high of a redline on the turbo'd engine. Throwing anecdotal examples around where the engineers may have overcome the challenges in order to have a redline as high as an NA motor, or just accepted a lower redline because it's all their design goals required doesn't prove anything. In fact the redline itself doesn't prove anything, because that's just a number chosen by the engineers.