HP per cubic inch question

RX-8...250 HP from 1.3 liters

 

I said that car earlier, but I think you mean to say 240 hp

 

clarified this misnomer before. it doesn't really displace 1.3 liters like a piston driven motor.

very well, but I think you are missing the point of technology developed in engines here. but again... no rules were specified. turbos themselves though - I've had them before, and while they are fun, there's nothing like raw power from an engine.

so there you have it, turbos are in, no more are the F20c, not even the F355, F360, not even the ITR in the lead. *rollseyes*

 

I see your point, there's nothing like a beefy n.a. engine under the loud pedal without turbo spool, complicated turbo or supercharger setups.

Unfortunately, you can't drive a Ferrari 20k miles a year without things going to hell on you. If anything, daily driveable might be a stretch to mean reliable. After all, most of us drive something that you turn the key and expect it to work, everytime, to get us to the office. If you have a critical meeting you simply have to get to, do you jump in the Ferrari or do you take the luxo barge or other beater? Some will take the Ferrari, but its rare.

If we add in reliability, suddenly, the exotics drop off the list.

I'm sure you could get 1000bhp out of 2 liters but how long would it last you? Thats another undercurrent of this thread, who can build engines that survive and do what they do.

Sunny

 

Ruf is not an aftermarket, his car's come with their own VINs, RUF IS A BRAND OF CAR, as is Saleen, I believe.

 

Damn! I wanted to say that!!!


Rick

 

It might come with its own vin but if Porsche didnt exist would RUF? Saleen the same thing if Ford didnt produce Mustangs...well... I dont care what the # says, its a Porsche.

 

If I understand what you are saying here, I think I have to disagree with your "raw power" statement... If you are talking about a big inch, high compression, high duration camshaft motor that makes lots of power, although fun to melt the tires with, they are a huge pain in the a$$ to drive on the street.

A 3 litre 500hp turbo motor is a lot more user friendly than a 6 litre n/a motor.

A turbo motor has a nice idle and can be driven mildly without any problem.

A high compression motor is stressed all the time. A turbo motor is only stressed when called upon.

I'm not sure if this really applies to this thread.......

RD

 

Wow, no way! So they are their own car like it was from a factory... what anout Brabus, RennTech, Alpine, Roush, Lingfelter (spelling?)? I would guess AMG etc would be an as new car with its own number, I had no idea about others though.
You learn something everyday, amazing thanks bostonmini.

 

My understanding is its all in how how you build your motor. A 3 liter motor is probably going to have no torque and the power is all from revs... fun but not great for drivavbility. That is until you hit the turbo. If your build your 6 liter N/A right... say a Maca F1, it will have incredible throttle response all the way from idle to red-line. You could no doubt build you 3-liter the same way, if you size the turbo's right etc. I dunno, maybe I'm way off, correct me by all means for no doubt I'm far off mark. Does gearing have much to do with it?... For around town, personally I'd take a massive motor with torque at 1500, then for the track, or empty country weekend road, I'll have the Ferrari long before I'd take a 'vette, viper, or muscle car.

I'd take any car right now(!) bloody tests and studying is a drag! I must get my F-car before I'm 25... anyone have some great buisness ideas they need a hard worker for to bring off the ground and get an IPO!

 

I believe all those other companies you mentioned are just "tuners". The only "manufacturer" tuners I am aware of are Ruf (Porsche), Saleen (mostly Ford Mustangs), Callaway (Corvette). AMG is a subdivision of Mercedes - sort of like SVT in Ford or PVO n Dodge.

 

Alpina was/is still a manufacter as well I think.

 

That 6 litre engine will last a lot longer than that turbo motor...

What's gonna run better at 70,000 miles, your F40 or a Viper?

 

"A 3 litre 500hp turbo motor is a lot more user friendly than a 6 litre n/a motor. "

Just the opposite. The torque curve of the naturally aspirated engine will be pretty flat, so the throttle response is linear. Torque is available from idle to redline. A turbo engine has a large step in the torque curve, so if you are accelerating though a turn and past though part of the rpm band when boost becomes available, it is extremely difficult to deal with. A lot of street turbo cars end up in guard rails for jus this reason. And forget accelerating if the engine is below 1/2 redline where boost is not available. Positive displacement superchargers make the power without the step or lag.

"A turbo motor has a nice idle and can be driven mildly without any problem."

The same is true for a naturally aspirated engine.


"A high compression motor is stressed all the time. A turbo motor is only stressed when called upon."

Mostly not true. The load on the engine is just a factor of how much power it is delivering and what rpm it's running at, not the compression ratio. A high compression engine is more efficient than a lower compression engine. A high compression engine will also tolerate more valve overlap, which often also means more lift. Big lift cams beat up valve guides, so they are under more stress all the time.

 

I would go for the 6 litre NA motor for both TQ and power and longevity.

It is true the the 6 litre motor may have a flat TQ curve, but throttle response does not necessarily follow. Consider putting on a 200mm throttle body instead of the 70 mm
factory original. Throttle response would go to heck.

A turbo can be sized and tuned to develop power just above idle, its just they are mostly tuned to deliver the top end kick. I will notice in passing that Porsche, over the TT years, has been moving the point of turbo boost down the RPM band to mask/elimiate turbo lag.

Correct, a high stressed motor is only operating at high stress levels when the throttle is open more than 75%! under this amount of throttle, the cylinder pressures are just as low as any other engine at moderate loads.

Lets be careful about efficiency, different people use different definitions of efficiency. A high compression engine is more efficient at turning the same amount of fuel and air into power than a lower compression engine of exactly the same engine architecture. However, a moderate compression SCIB engine (old american V8) will be more efficient at converting a given amount of fuel into distance than a high compression DOHC engine in a vehicle with the same transmission, and at the same rolling weight.

High compression is better at self scagengine the burnt mixture because the piston to cylinder clearance is tighter, thereby forcing more burned mixture out of the chamber. High compression is better at utilizing the pressure waves setup by the header and collector during valve overlap for similar reasons.

But in general, high compression tollerates more overlap because high compression has more TQ down low in the RPM band. This TQ can be sacrificed down to the level of the lower compression engine by adding more overlap. In effect, moving the TQ curve up the RPM band.

A BIG cam operating a valve that is safe at 9,000 RPMs has virtually no wear at 5000 RPMs and below because the forces involved are so small that the oil film can carry the loads. This is not necessarily the case with pushrods and some of the rocker assemblies used in SCIB engines. In general, the sideways induced CAM loads in a DOHC engine are absorbed by the inverted buckets and not by the valve guides. Rocker based valves do not have a component that absorbes the sideways forces.

 

I think you contridicted yourself here and helped make my point.... Not only will a high compression engine tolerate long duration and high lift cams, it requires it to survive. Yes big lift lift cams beat up valve guides, are hard on valve springs and cause rough idle. A high compression motor has "high compression all the time". If you don't believe it, try running it on regular fuel. A turbo with low compression only has high compression (or maybe the term cylinder presure is better) when it is in boost.
Do you need 500hp to cruise down the road at 60mph or to start from a stop light? No, you don't. With a turbo it is there only once it goes into boost. With a N/A motor it is there as soon as you open the throttle. With a N/A motor it is how much you open the throttle with a turbo it is How lond you keep it open.

Make sense?

Variable valve timing sort of gives you the best of both worlds.



Rick

 

I think that is your example, the responce would/could still be linear for about the first 25 or 30 degrees of throttle rotation, then tfurther opening the throttle would have no effect. To point I was trying to make about turbos is the engine behaves very differently on the turbo vs off. If the throtle is configured to produce a linear responce at low rpm, it will be very non linear at high rpm and also the other way around because at low rpm there is only the engine the consider. At higher rpms, the turbo will begin to spool making the engine more sensitive, matching one condition means mismatching the other.

Well...maybe..a little. If the turbine is small enough to make boost off idle, it will not flow enough to work at redline. The best stuff I've seen makes 4 or 5 psi at about 1/3 redline, but nothing at 1/4 redline. The big change I've notice in the turbo cars is that they are using less boost and more compression to make hp. The higher compression gives them more torque below the boost line and less boost make the step in the torque smaller and less noticeable. It also means smaller turbos that spool faster reducing the lag.

Yes, I was thinking pushrod when I wrote that. Yes on the efficiency point as well.

 

maybe the best answer is the MB one: a 6 litre Turbo'd v12! sooooo much torque and no noticeable lag! and tons of HP too, torque pulls like a locomotive!