Jussi

When I did my engine rebuildning, I took pictures of original 993TT intake manifold to wonder why that all are needed..
See picture what I mean:

Why are there so many chambers in turbo intake??
I would understand that, if the engine would be NA model because they get advantage of "some kind of resonation systems"..

But for efficient turbo engine, where lot of air will be pushed through intake by force, I would choose much simple model like smooth Y- tube after the throttle body without any chambers continueing (and of course dividing) to cylinders' intake with as little restriction as possible..
I have had that in my mind because by doing that kind of own "better" (or worse) intake manifold, I would get much more room for bigger IC also..

But now when I saw the new intake of the GT2 model, that idea came to my mind again. So without further speaking is that kind of model also better to old 993TT? (see picture below)

911/Q45

Unless you are on boost, the intake needs to work the same as the NA engines.

ACEparts_com

Perhaps you're visualising it all wrong? Maybe you're thinking that the compressed air is more like a liquid as opposed to just air under higher pressure - so therefore the same principles that apply to NA engines apply to turbos.

Jussi

I admit that I can be also wrong in this idea..
but this "short and restrictionless" intake idea came also from formula 1 world. I have seen the engine of Ferrari which won year 2000. That was V10, 3 liter, and produced 770 horses. In that engine, intake (and exhaust) was very very short. In those machines, the breathing must be very efficient.

So I would say that this helps when you are in boost area or in full throttle..

Maybe only cruising (driving slowly without boost and steady throttle) might suffer little from that chamberless and non-resonance intake?
or what do you think?

Jussi

Yes, I can visualise that also wrong. But in that topic there are two different cases: 1) when cruising, 2) in boost or full throttle.

But think that situation also from another side:
when (my) 993TT engine revs 7000 rpm and still produces 1.1 bar at that rpm, this means 459 L/s flow in 3.8 L (3.75/102mm) engine
which is also 79 lb/min (those GT2871Rs' max flow with good VE..)
and that means over 100 metres per second flow at 75mm throttle body !
That is a Fast speed for air! So if there are many chambers and angles etc. that causes air's warmening.. and it can't be good for efficiency..
But hey, I can be wrong and these are just my thoughts, so I like to hear also other opinions..

jt993ttchicago

I think I can help shed some light on this topic.

To Understand these desins we must first understand the needs of these 2 very different engines. to start with:

Formula 1 engines are made to work at a much different RPM range (always close to redline, a redline over twice that of sophisticated road cars). Formular 1 cars dont have to worry about mid range torque, off throttle response, emissions, sound, etc. Therefore through requirements you get results and with 2 very different requirements you have to very different results (designs).

Short intake tracks feed air very fast to the cyclinders, you're right but that is only efficent at high RPM's, if you want a nice broad spread of torque for road use you want nice long intake tracks so the air can compress and give a "supercharging effect" so when the valves are only opening for a short amount of time down low in the rev range as much of a "charge" can come out ot that track, ruch into the combustion chamber and enhance combustion at those lower RPM's.

So yes under WOT, full boost conditons your short intake track design would be a dream, but around town you would be upset at the "lack" of mid rpm engine response.

Hope this helps!

Red rooster

Nice picture of the new GT2 . A quick look at the 993 Varioram inlet will highlight how intake length and cylinder volumetric efficiency are related .
Most Turbo motors use brute force to get the end result .
Its interesting to see a company that gives this a little more thought moving in the correct direction .
The current Boxster has a very clever inlet system that I am tempted to copy on my GMC Envoy , to raise low rpm torque !

Sorry for using a G** word on this forum !!!

Geoff
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KS400200,the oldest 964 on Rennlist,unless you know differently !

Jean

What is that relationship? Is there a specific formula that calculates the resulting gas velocity when going through the longer intake runners and their impact on VE?

tar6day

I think ViperBob touch on this topic with this thread:
https://rennlist.com/forums/showthre...ferrerid=19929

Red rooster

Jean ,

Maybe the easiest thing to do is take a look at the factory 993 technical information ? Torque variation enhancement is well explained .The runner length is to do with VE at certain rpm/path lengths .

It helps a turbo motor to achieve desired boost levels at lower motor speed
to run longer inlet runners . The GT2 is running enhanced plenium chambers
to help the top end as well !

Maybe a look at other turbo motors , V6/V8 Audi , BMW etc would show that ideas in this area are always being altered to give the desired end result .

Geoff
----------------------------------------------------------------
KS400200,the oldest 964 on Rennlist,unless you know differently !

Jean

I was hoping I would get a straightforward answer.

If you take an intake from the new 997 GT2 and use it on your 993TT you might end up with a dead mule, just as if you use the 993 N/A intake for the 993TT you might also end up with sub-optimal performance.

The intake characteristics has to be closely matched to the tuning, namely timing and what are the torque targets (at what RPM) and engine usage.

Starting from a stock setup, if you use:

• Longer and narrow runners => Better torque at lower RPM, air has more acceleration as a result of the smaller diameter and longer distance while accelerating, but will flow less air amount.

• Short and wider runners => Torque at higher RPMs, air flow is slower, but will flow more amount of air.

Choosing the right length and diameter of the intake runners is a trade off between high and low RPM performance.

Plenum has a critical role, it creates energy through the air resonation (is it resonance?), as it builds up from bouncing back and forth between valve openings, once the air is finally released from the plenum, it will create an important ram effect (around speed of sound) and maximize cylinder filling… The chambers are there to improve that resonation and energy buildup, they do not create resistence, they are very carefully designed to optimize that resonance and energy buildup. Cylinder filling is directly proportional to VE, which is directly related to Torque. Max Torque occurs at max VE point, so better cylinder filling => better VE=> better torque

Turbo engines prefer larger plenums than N/A, so when you use a N/A intake, you should make sure they are appropriate. A Varioram intake is very difficult to tune properly to a turbo engine, since you need to carefully monitor and match valve intake opening with air flow release from the plenum at different RPm levels..

Finally, throttle Body… to know if your throttle body is too small for your plenum, you need to determine what the intake manifold absolute pressure (MAP) sensor is reading in the plenum when you are at WOT, while the car is accelerating using a datalogger for both measuring performance and MAP readings. The MAP readings from the plenum should be close to the absolute pressure reading while at lower RPMs under full boost. If it isn't, or there is a MAP drop at WOT, then your TB is too small.

All of this applies differently to a race car if HP at high RPMs is your only target, i.e. ITB setups with straight/short runners.

Red rooster

Jean,

Dont lets fall out ! The point I was trying to make is that at different rpm/VE points the intake manifold requirements , even for a turbo , are different .

The results that motor designers come up with can be quite different . I have always taken an interest in these solutions .
No way would the poor , Varioram inlet find its way to a turbo ! but it showed that on a N/A some of the air consumption rules were obeyed .
Interesting that the new , simpler , non turbo inlet system for the Boxster is more effective than Varioram !

My rule is to keep an open mind and my eyes open to find a better solution .
Too many times people think in simple terms that more boost equals more bhp. That can easily be a scale showing poor VE !Back to the inlet !

This is all a facinating subject !

All the best

Geoff

Jussi

same here. I also want to talk about different choices..

How about fitting that new GT2 intake manifold to 993TT and then dynoadjust and -optimize ECU for that?

I did some experiment to my earlier car (non-porsche, non-turbo) many years ago which had modern variable length intake manifold. So, I took it away and installed new simple "powerbox" to it. The engine were dynoadjusted and result was that mid torque dropped about 10% but top horsepower level raised about 10%..
So something similar reaction could happed also if fitting that new GT2 style manifold to 993TT..
For example if you have 700Nm/650hp car:
middle RPM range will be dropped to 630Nm (-10%)
but respectively upper horsepower will be raised to 715hp (+10%)
So which one you want to choose?

edpurplett

I have a NA intake and throttle body, IMO they work much better at mid and high lRPM evels than the turbo intake..and give more room for the intercooler (btw a non-VR from a '95 I believe.)

I didn't get chance to read all the posts, but I'm sure some posted that higher flow velocities are generally better for driveability and fuel atomization until you reach a point of diminishing returns and potential warming issues...

and if memory serves inlet tract pulsing/mid torque will be better with longer runners...

If anyone really cares I can get Todd K to elaborate I think...



Ed

Jussi

Your experience from that NA intake is same that what I feel it should be in real life: more power to mid and high revs because there are much less restriction..
and that plenum and complex turbo system is just for low and mid rpms and also fuel economy - which nobody cares in these cars
WOT rules

btw. Can somebody calculate or estimate that "RPM point of diminishing returns and potential warming issues"

I'm also interested in what Todd K says !