MrDude_1

iTrader: (4)

you know, if you throw out enough variables, you can make any equation seem easy.




however, that doesn't make any conclusion drawn from that equation correct.. no matter how general you try to make the scope to compensate.

Big-DEN

We can make this easy.

I been on these forums boards for about 15 years now, seen and heard alot of configs, even saw things develop to work that was not supposed to work out.

With boost, you got the right idea, if you can double atmospheric pressure (14.7 at sea level) you should double your power output.

However its not that simple. In short terms it usually requires more than 14psi of boost to double an engines power but less than 20psi.

Things affecting it are:

1. Super or Turbo charger
2. Intercooled?
3. Elevation ( im going to throw this out, but diff between the flatlands and Denver makes a noticable difference
4. Impeller design ( getting in the way, making boost, or making heat )

Rules of thumb - supercharger relies on belt system to turn it, and at real levels of boost, are real levels of HP required to turned the supercharger.

Turbo charger costs a small exhaust restriction, the cost of which is less than a supercharger.

So yes in short it cost a little more than 15PSI to double your power output and less than 20PSI. Example may be 18PSI of non-intercool boost doubles the poweroutput vs 15PSI of intercooled boost.

Or 19PSI of supercharger boost required to double the poweroutput vs 17PSI of turbocharger boost ( supercharger required power to turn its belt )

Thing thats interesting to me today, is for example, a all N/A mid sized motor beating a S or T trim supercharger combination or mild turbo config.

Or also interesting - if you going to biuld for the strip alone, why not consider a big block? Why not a 600CI big block with two 101MM turbo's?

You know whats funny, is on a semi, you know they use like 5" or 6" exausht piping. Back in like 85 I assume its from such a big motor and the exhaust required those "big pipes". Nowadays theres cars putting out so much power, they require semi like exhaust piping.

As usual providing points to ponder.

XBR24

^^ did you even read my previous post?

intake manifold Air density is what you need to think of.. (cough.. mass flow.. cough) You double the mass flow you would be very close to doubling the indicated power (imep)

and as far as your turbo comment.. Why doesnt anybody belive it requires much energy to spin a turbo? have you logged data measuring exhaust manifold pressure? its a tad higher than you may think.. (hint.. figure out pmep)

topend

Thats where my idea for this question came from.I was reading about all these F1 motors (cosworth,toyota,renault) making peak power at 16-18k rpms. And was wondering in theory if a basic 350 spun to 12k rpm would it be double the power of a 350 making peak power at 6k rpm. The other way of doubling the power is to either make the 350" into a 700" or forced induction/N20(both increase torque).David Vizard stated in one of his books in order to increase engine power u must increase the rpm at which peak torque is achieved.

Big-DEN

The turbo/supercharger did not exactly double the power at 14.7psi because of losses thru:

1. Heating of intake charge thru compression
2. Exhaust restriction ( in case of turbo )
3. Power required to turn supercharger

In the case of high RPM N/A apps, it is possible for a vehicle for example to make over double what it makes at 4000 at 8000 rpm for correctly designed app. At higher air speeds the air has more momentum and piles into the cyllinder with more force.

mzoomora

iTrader: (36)

There will also be an increased exhuast restriction in any type of power increase. The more air you put through it, the more restrictive it will be. So you would also have to double(at least) the intake and exhaust capacities also.

Big-DEN

mzoomora.

I was giving a reasonable explanation for why 14.7PSI of manifold pressure never equals 2x the power level.

Its because there are losses in the system.

Quickin

From: Gayle Banks website

Twin-Turbo V8 Facts of Life

Few People Have Ever Experienced Really High Horsepower.

By C.J. Baker

Have you ever ridden in a vehicle powered by a properly engineered twin-turbo V8? No, a single-turbo V8, or heaven forbid, a single-turbo four cylinder is not the same thing, not even close.

We’ve all heard the wisdom that there’s no substitute for cubic inches, but cubic inches of what? Is it cubic inches of engine that count, or cubic inches of air in the combustion chamber? It’s obviously the latter. So consider this, 15 psi of boost effectively doubles the size of an engine. That means 15 psi of boost will make a 350-cubic-inch performance engine seem like a 700-cubic-inch performance engine!

Actually, this picture isn’t accurate. If you understand engines, you’ll immediately realize that 15-psi boost more than doubles the performance an engine. It does this for two reasons: first, the internal friction of the engine remains largely the same regardless of boost, so the extra power from turbocharging is almost totally available to power the vehicle; and second, the 15 psi of boost in the induction system actually helps push the pistons down on the intake stroke whereas the intake stroke created a pumping loss (negative torque) when the engine was normally aspirated.

Now you may be thinking that the turbochargers create exhaust backpressure that increases the pumping loss on the exhaust stroke, but let’s go back to the first sentence of this discussion — we’re talking about a “properly engineered” system. That means the exhaust restriction created by the dual turbos will be minor, and that boost pressure will always exceed exhaust system backpressure. Simply translated, in terms of performance, a good twin-turbo 350 V8 will turn your inside out!

Okay, just for fun, let’s compare our 350 twin-turbo V8 at 15-psi boost to a 120-cubic-inch compact four cylinder running 30 psi of boost — twice that of the V8. By our rule of thumb, the little four-banger will now be flowing air equivalent to a 360-cubic-inch normally aspirated engine. That’s impressive for a small engine, but it will still have only half the power potential of our twin-turbo V8 running at half the boost. If you push the V8 to 30-psi boost, you’ll have the equivalent of 1050 cubic inches and over 1500 hp, if it is done correctly.

By now you get the point. Bigger engines add power, but turbocharging bigger engines really gets the job done. Happily, there’s more good news associated with turbocharging the small-block Chevy V8, and almost all of it comes down to durability. To begin, the performance industry offers a variety of high-strength cylinder blocks in both iron and aluminum. Thicker main webs and four-bolt main caps are just what a turbocharged engine needs. Next, the small-block Chevy uses five head bolts or studs surrounding each cylinder to help secure head gaskets. And of course, the aftermarket has a variety of premium head gaskets too. Then there are other heavy-duty parts readily available, such as forged crankshafts, forged connecting rods, forged pistons, special piston pins, and premium rings and bearings.

Finding all of these things is difficult for other engines, especially for four-cylinder engines.

Of course, the small-block Chevy V8 also benefits from a wide variety of high-performance cylinder heads, intake manifolds, and valvetrain pieces. Simply stated, nearly everything that improves airflow on a normally aspirated engine will also improve total flow on a turbocharged engine.

The next good news is that extreme duty drivetrain parts are readily available for rear-wheel-drive vehicles with V8 engines. This includes clutches, transmissions, u-joints, differentials and axles. Most of this was developed for drag racing or circle track racing. Such strength and durability is important when dealing with real power. For example, a 350-cubic-inch V8 running at 20-psi boost is capable of roughly 900 lb-ft of torque! You don’t feed that through a front-wheel drive transaxle to high-traction tires — at least not more than once.

Turbocharging is fun. It’s addictive. How much power can you make?

There are always big-block engines to consider, and in fact, Banks is developing a drag car with a 526-cubic-inch engine with four turbochargers. Admittedly, such an engine stretches the bounds of credibility. It would seem like that is the ultimate, but there’s another entire chapter to turbocharging that’s just being opened. Can you say diesels at 150-psi boost? Don’t blink. They’re not coming … they’re already here!

Genesis_26317

iTrader: (2)

People quit posting unless you read the entire thread. Instead of everyone constantly bringing up "you gotta add this variable" read the five other posts that say the same exact thing.

If the guy is just asking a question saying no you don't understand and then mentioning five different "variables" isn't going to due a damn thing.

Just direct the guy to a post that explains everything or just answer the specific question.

"On a forced induction motor, 14.7 psi of boost is considered x2 the engine NA output.
So if a given 350ci engine made 400 hp NA at 6000 rpms. Would the same engine size make 800 hp at 12000 ( with a better flowing induction and exhaust system of course). Would this be right???"

That's a pretty specific thing.

In a perfect world, if there was not any restriction, no 2 atmospheres will not provide double the hp because of the air would heat up when compressed.

That wasn't his question!!!

He just wants to know if double RPM's would that double hp.

"So if a given 350ci engine made 400 hp NA at 6000 rpms. Would the same engine size make 800 hp at 12000"

300bhp/ton

If you doubled the airflow by increasing the rpms then providing the fuel was their to match it then yes I think double the power potential would exist - in theory.

However being able to achieve double the airflow via rpms will still result in restrictions and losses, so in the real world I doubt it would see double. But this would depend on the rpms being used. I mean 3000 to 6000rpm might be the same percentage as 6000 to 12000rpm, but in reality its a much bigger jump.

Case being the 350ci SBC. It has 2 valves per cylinder, which means curtain area will be largly dictated by the size of the valves. But the higher the rpms the more curtain area you would require. Beyond a certain point 2 valves really aren't going to cut it.

Multivalve is the only answer, this is why Ferrari's tend to use 5 valves per cylinder. And this is where generally the DOHC design shows its benefits. It can produce a higher specific output (bhp/litre) by generally running a comparitivly more agressive cam for high rpm use.

With the SBC you would also have issues with the rest of the drivetrain, OHV push rod engines just aren't designed for that level of rpm. Multivalve OHV's do exist but they only have part of the potential of a DOHC unit.

Big-DEN

Say a 5.0L V8 was terribly efficient at 6000RPM and put out 450HP there.

Say the same 5.0L V8 can be terribly efficient at 12000RPM, would it put out 900HP?

No, it should put out more. It should put out more because higher RPM efficiency == greater VE.

Or simpler, the momentum of the air is much greater at 12,000 RPM than it is at 6,000 RPM.

hammertime

iTrader: (1)

with regard to the original question, this would seem to be the best answer so far. If you have everything properly setup to produce peak power at twice the rpm as the example, then why not? Since it is a discussion of theory, I think everyone is having trouble getting around the 12,000 rpm required in the example.

To make is easier, lets say that the 350ci engine made 300hp at 4000 rpm. I'm sure we can all agree that 600hp at 8000 rpm is possible, especially given that a Stock Car can develop in excess of 750hp from 358ci.

There are vast differences between theory and reality, but for sake of theoretical discussion, 2x the rpm should net 2x the power.
:flame suit on:

Big-DEN

One more time.

14.7PSI on boosted app is never double the power, because to get the 14.7PSI was not free it cost something.

Case in point, say your S-trim is putting out 14.7PSI on the car, to get that 14.7PSI or lets say stock 302 might have cost 75HP. Also the air temp at 14.7PSI is higher than at 7PSI so you lost power potential there too.

ProdriveMS

Doubling the rpm will not double the power because friction increases as the square of rpm. So if you double your rpm, you get four times the friction. Triple your rpm, you get 9 times the friction, and so on. Vibration also increases as the square of rpm, which isn't a huge factor on a V8 with a dual plane crank, but it is on a V8 with a flat plane crank such as in F1.

Al

Big-DEN

ProdriveMS - you can't say that.

It depends on the shape of the TQ curve!. Case in point.

Say you put down 350rwtq @ 2500 RPM or 170rwhp

And you put down 425rwtq @ 5000 rpm or 404rwhp

These are very normal situations.

Or f1 where you where quoting, say thing thing put out 20% more TQ at 12,000 RPM than it does at 6,000 RPM. ITs very possible!

However heating of intake charge as I put it, and belt losses to turning a supercharger are very normal phenomina.

P Mack

iTrader: (6)

Doubling the rpms will double the power if you can maintain the same torque. You would have more friction but also the potential for higher ve.

Richiec77

iTrader: (3)

Ben. This guy know's more then most people on this site. Yes he can say that. Cause he KNOWS.

Thanks for the info Al. I didnt know how the math worked on those exact issues.

Big-DEN

I can pull 100's of dyno's to prove my point.

I didn't say double of max rpm i said double of rpm.

mzoomora

iTrader: (36)

But that 350rwtq engine probably makes its peak HP at closer to 4500 rpm. Very few engine have their torque and HP peaks within even a few hundred rpm's (maybe some diesels and moderate revving engines). If the peak torque rpm is greatly increased than the peak hp should also be greatly increased, there is no doubt about that.

Big-DEN

Statement was made into the allusion that double the RPM greater than doubles the frictional losses so that you cant just assume double the rpm == double the hp.

I gave example where starting point, is somewhat before the TQ peak to pretty much knock it out the box.

I think you see what I was saying.