Tuning Is forced induction the best way ??

[garethedwards]

Originally Posted by Alsone

I'm sure it was used in Formula 1 under the name of turbo fan.

It was banned due to its success.

However, the only reference I can find these days to fans on the back of Formula 1 cars is of the Brabham cars that used fans to suck air from under the car as ground effect enhancers, these also got banned as they were too successful:

It maybe I was mis-remembering therefore but I'm sure there was some exhaust extraction benefit if that was the car.

The turbo fan car was actually used for "down force" it pulled air from under the car to create a vacuum.

[ash_rage]

Originally Posted by garethedwards

I was under the impression you actually require exhaust "back pressure" to aid the combustion process?

I cant see how inversion would ever be a good thing.

IMO particularly in a car that is forced induction. Not to mention on a K20 where there is a certain amount of exhaust cam overlap.


Relic - interesting idea, however as syx pointed out I dont think it would work as the exhuast valve would be closed half the time. Also if the air does get charged in the intake from the "pull" this system would generate it will still lead to it getting hot.

I imagine there was be some real nasty resonance created in the intake from the constant on off effect you would get. I also imagine throttle response would be pretty bizarre.

[Revs FN2]

The main problem with this is the lack of ability to go beyond a vacuum. With intake pressurising you can compress the air to whatever the engine can take.. 2.. 3 bar? If you're sucking the gasses out the best you can achieve is a vacuum... -1 bar, and the best you can expect with that is to make a little more room for the incoming AF mix.

I like your thinking though

If you can cool the exhaust gasses very quickly in the exhaust the shrinking air mass can have a suction effect, though. This does help a bit.

[ash_rage]

Originally Posted by Revs FN2

If you can cool the exhaust gasses very quickly in the exhaust the shrinking air mass can have a suction effect, though. This does help a bit.

Isn't cooler air more dense?

[Revs FN2]

Yesh! If you cool the exhaust gasses it shrinks, therefore reducing the backpressure.

In effect there would be more air volume going in than coming out the back. Same mass, but due to the increased density, less volume.

[Leepie]

Originally Posted by garethedwards

The turbo fan car was actually used for "down force" it pulled air from under the car to create a vacuum.

+1

[Syx]

Originally Posted by Leepie

+1

1 race, 1 win, 1 ban I think?

[Relic]

Originally Posted by Syx

I think it would be greater than double. You create the vacuum which is filled by incoming air, close the exhaust valve and the air flow reduces and immediately begins to return to equilibrium (piston downstroke would keep that equilibrium above atmospheric so here the eq. would be whatever the standard NA would draw) so as soon as you close that exhaust valve you're losing pressure.
But, like you, I don't know for sure. Fancy testing it out?

In essence I think the reason it's not done is because it's a lot simpler to force induction!

No it wouldnt ...only thing that matters is the Mass airflow going through the engine.
If its 23 lb min = roughly 230hp....46 = 460 when fueled right.
How you get that air mass flowing though the engine is the issue.

Thats the whole point of boost...to increase MAF not to raise pressure as such.
Although they are obviously linked with forced induction.

I see no reason why you couldnt increase MAF by forced extraction rather than forced induction.
But yes I see everyones point on the valve timing/overlap being the major factor.
A big overlap cam would respond much better than a low overlap cam.
As there is more time for extraction to work.

[Revs FN2]

But even if you extract every last atom of gas from the cylinder during the exhaust cycle, as the inlet valve opens for the inlet cycle and the piston is starting to drop, there is only a combustion chambers worth of vacuum to fill before the piston start to continue to suck air in as it drops. The amount of energy required to extract the gasses would far outweigh any increased performance from the slight increase in flow.

Another problem is that it would draw oil up the side of the piston and possibly down the exhaust valve stems.

[bxlyheathsupra]

ok might be a silly question but is my 2pence to the convo..

a turbo forces air into the engine which under pressure gets hot and needs and intercooler....

now if you are sucking air through the engine would you not need to suck it with enough force to in effect create the same effect as turbo boost pressure? which would mean air being pulled through the engine at such a rate it would appear as pressured air once in the chambers? which could then be in need of cooling still?

i get the theory you are applying, but what im gettin at is that air in the chambers = whatever is forced in or whatever is sucked through and so to get the effect of for example 1 bar of boost pressure you would need to suck through a certain amount of air to equal that pressure.... but then would the pressured air not still be subject to the outside factors of heat etc either way it gets into the chamber???

hope that makes sense?

[Syx]

Originally Posted by Relic

No it wouldnt ...only thing that matters is the Mass airflow going through the engine.
If its 23 lb min = roughly 230hp....46 = 460 when fueled right.
How you get that air mass flowing though the engine is the issue.

Thats the whole point of boost...to increase MAF not to raise pressure as such.
Although they are obviously linked with forced induction.

Exactly, and that's achieved by increasing the pressure via boost on FI as you're cramming more air into the same pipe to get better MAF.

The issue is that you can't do the same on forced extraction. The inertia of the moving gas being extracted is not great enough to draw in as much air as can be pushed in with FI, as once the exhaust valve is closed you lose much of that inertia/vacuum. You would need a significant amount of inertia to continue the airflow at the same rate once the exhaust valve was closed, which is why you would need greater than double. That's based on my own analysis of what's happening as to any actual fluid dynamics modelling though so I cannot really argue the point.

I understand what you're getting at and I agree that the fundamental issue is how you get enough airflow through the engine to maintain that inertia so the cylinder fills - but I don't think there's a solution with only forced extraction.
I'm not disagreeing with what you're saying, I just can't see a solution to the problem!

[garethedwards]

I would think that if this would improve performance in anyway we would already be seeing it in at least one form of motorsport already.

I stand my original statement that at least some (even if it is very low) backpreasure is actually needed in order for the engine to work. As engines are designed around this element being present.

[Relic]

Originally Posted by bxlyheathsupra

ok might be a silly question but is my 2pence to the convo..

a turbo forces air into the engine which under pressure gets hot and needs and intercooler....

now if you are sucking air through the engine would you not need to suck it with enough force to in effect create the same effect as turbo boost pressure? which would mean air being pulled through the engine at such a rate it would appear as pressured air once in the chambers? which could then be in need of cooling still?

i get the theory you are applying, but what im gettin at is that air in the chambers = whatever is forced in or whatever is sucked through and so to get the effect of for example 1 bar of boost pressure you would need to suck through a certain amount of air to equal that pressure.... but then would the pressured air not still be subject to the outside factors of heat etc either way it gets into the chamber???

hope that makes sense?

Air temperature depends on pressure.
A vacuum is a drop in pressure

I am using 2.45 bar to get 200hp.
That pressure makes it 160c at least before the intercooler.
The intercooler loses 110c of that.

A 200hp NA engine does not have 160c Inlet air temps and will be 1bar or less.
It relies on piston suction and cam timing only.

2.0 NA engines produce anything from 100 to 300hp+ depending purely on camshaft.
thats anywhere from 10lb per minute to 30lb minute without any boost whatsoever.
Cylinder ramming only and nothing else.

A good point was raised earlier that you could never get anymore tham 0bar absolute...which would be 2bar MAP or 1 bar Boost.
So yes thinking on it you could never achieve the same pressures as forced induction without working with cam design too like the NA enignes.
But I repeat... NA race engines... dont make their power figures from boost

[J. Derek Riddell]

Well, I once read about a WW2-era aircraft engine, which was supercharged, but would have a power drop when violently maneouvering (dogfighting etc.) - not good if you have an enemy fighter up your arse !

The solution was to fit chunky electrically-driven compressors to the ends of both manifolds - and as a bonus, it was discovered that BHP increase some

But, forced extraction without forced induction ? - ah hae ma doots, laddie !

[ghost_bhp]

how about fitting a turbo well away from the engine bay into the exhaust?

Rear Mount Turbocharging - STS Turbo Systems, Vertpower 205GTi Turbo System

[Jon_G]

Isn't exhaust scavenging (but not the type used on two-stroke engines) a well-established method of forced extraction?... Exhaust manifold - Wikipedia, the free encyclopedia

[Relic]

Originally Posted by Jon_G

Isn't exhaust scavenging (but not the type used on two-stroke engines) a well-established method of forced extraction?... Exhaust manifold - Wikipedia, the free encyclopedia

..... the threads about if the effect can be amplified.

[delta0]

I think with forced extraction you will only assist with the removal of gases from the cylinder. Even for the minute time that the exhaust and intake are open you are not going help the engine because it will still pull the gases through to the exhaust. There will be no compression of air into the cylinder prior to the compression by the piston.Also the exhaust valve opens just before it reaches the bottom of the stroke which means the extraction system will work against the motion of the engine periodically.

[Relic]

OK, so overlap, or at least too much of it, is not good for a street-driven engine. But let's not overlook that the actual amount of overlap is not the sole issue toward killing vacuum. If we replace the open plenum intake with a two-plane (180 degree) intake, in one fell swoop, we space out the induction pulses seen in each half of the manifold to 180 degrees instead of 90. This means there is no time when the one cylinder's intake can draw through the exhaust of another. As a result, the intake vacuum goes up by something in the order of 50 percent.

Read more: Engine Camshaft Basics - Popular Hot Rodding Magazine
Engine Camshaft Basics - Popular Hot Rodding Magazine

What dictates the cam's success in the quest for maximum area under the output curve along with highest peak torque and horsepower is not (as is so often assumed) the duration involved. The most important factor is actually the overlap and the Lobe Centerline Angle, often referred to as the LCA. I realize this may fly in the face of everything you have been told or have read before, but it's not that hard to see it must be so.

Read more: http://www.popularhotrodding.com/tec...#ixzz21FffqidC

Now that we have covered the effect overlap has on street manners, it is time to look at its effect on power output. Let's make one thing clear here: Big (but not excessive) overlap is a prime key to big power numbers, but only if your exhaust system sucks. Literally. If you have ever heard that an engine needs a little backpressure, you might want to ask yourself why an engine would want an exhaust system that literally pushes exhaust back into the combustion chamber rather than sucking it out. The simple answer is, it doesn't. If a big-overlap, big-cammed engine has an exhaust system with any measurable backpressure, the price paid is a big drop in output.

Read more: http://www.popularhotrodding.com/tec...#ixzz21FgQS6yE

[Relic]

Originally Posted by delta0

I think with forced extraction you will only assist with the removal of gases from the cylinder.

Even for the minute time that the exhaust and intake are open you are not going help the engine because it will still pull the gases through to the exhaust.

No...the extractor is pulling in fresh air and the piston is aiding the process. The whole point is to prevent the piston sucking exhaust.

There will be no compression of air into the cylinder prior to the compression by the piston.

If the MAF is making the numbers via adjacent cylinders it doesnt matter.
It behaves just like a car with a bigger engine with more suck.

Also the exhaust valve opens just before it reaches the bottom of the stroke which means the extraction system will work against the motion of the engine periodically.

Unless the gases are still expanding after combustion

..