Forced Induction Intake Manifold Tuning, does it exist?

[NobleConcepts]

Greetings,
After completeing a search through the SAE docs and reference texts of Blair, Winterbone, Peterson, Horlock, Bell and the Wave Action simulators I am forced to ask the above question.

Forced Induction Intake Manifold Tuning, does it exist?

As the subject content implies I am in search for the knowledge to sort through a theoretically challenging dilemma. The design of a intake manifold (plenum vol, runner length @ fixed min runner area and taper) compromising design to yield MAX AUC for Trq and HP between 2500 and 7500 RPM.

Application:
I am preparing a car for the next One Lap of America event.

Engine Specs:
V6 182.3 cid
Bore 3.5in X Stroke 3.130in
Rod length 5.440in Rod ratio 1.738in Offset 0in
Cyl Heads DOHC 4 Valve, Pentroof, stock port.
Int valve Dia 1.380in Exhaust valve Dia 1.180in
Comp ratio 8.5:1
Comp space 65.8cc Cyl Vol 493.48cc
TB 605.4 cfm@1.5inHg
Present Intake specs:
Plenum Vol 2.6L
Runner length 14in(plenum junction to valve seat)
Beginning runner area 4.23sqin
Min port area 2.15sqin
Average Taper Angle 2.7deg
Forced Induction:
Twin Turbo GT28RS
Turbine:Inducer dia 53.85mm/Exducer dia 46.95mm,A/R.86,Trim 76
Compressor:Inducer dia 47.22mm/Exducer dia60mm,A/R.60,Trim 62
Press ratio 2.4/boost 20psi
IC liq/air at 75%eff
Turbo Manifold specs: Runner length 8.25in, Inlet dia 1.75in,Exit dia 2.0in
Taper angle 1.7deg
Exhaust port Min Area 2.15sqin
Camshaft specs:
Lift at valve Int 0.438in Ex 0.450in
Seat duration Int 260 Ex 280
Centerline angle Int 116 Ex 119 equals true centerline angle
Lobe centerline 117.5
Valve overlap 35.0
Valve events seat to seat:
IVO 14 IVC 66 EVO 79 EVC 21
Dur @.050 Int 205 Ext 225

I have reached a point that I am literally frozen in the prototype phase and can not commit to final dimensions.
I have approached as a NA system with Hemholtz eqn length 20in results in 2/3/4 resonance peaks in range of 3400-7100RPM. Plenum vols have ranged from 60%-200% cid.
Can you make reasonable predictions for a forced induction system?
Can I Max AUC for Trq/HP in the range 2500-7500RPM via Intake tuning with Forced Induction?
N/D-NOBLE

 

[MikeHalloran]

You're gonna lap the US @ 3400..7100 rpm?

Good luck with that.



Mike Halloran
Pembroke Pines, FL, USA

 

[NobleConcepts]

Mike,

The One Lap of America is a event sponsored by Tire Rack. The competition consist of multiple events including road courses, wet/dry skid pad and drag strip. The cars are driven on the road between event sites.

N/D-NOBLE

 

[MikeHalloran]

So, you need an engine that doesn't run like crap or overheat on the street, and doesn't frag itself in competition. Good luck with _that_. ;-)

To partially answer your question, you should be able to make a map of how the resonances move around with boost, by adjusting for changes in the speed of sound within the intake tract as the boost changes.







Mike Halloran
Pembroke Pines, FL, USA

 

[Fabrico]

First priority make it flow well for the widest RPM range. First compromise make it flow fairly evenly to each cylinder.

Spend the rest of whatever time you have left on reliability and setup of the engine and the rest of the car.

 

[NobleConcepts]

Mike,

"To partially answer your question, you should be able to make a map of how the resonances move around with boost, by adjusting for changes in the speed of sound within the intake tract as the boost changes."

The assumption would be that the Hemholtz resonance as applied to normally aspirated IC engines at WOT is subjected to atm press of 1bar. The relationship has been established as evidenced by the number of eqns and calculators available to the NA crowd. In the forced induction applications the additional 1 to 2 bar press applied to the flow in the tract I assume would potentially shift the resonance waves or alter their amplitudes. The question is if that relationship is established and can be derived with fair certainty, why is the relationship not widely discussed in the literature about the wave action analysis?
Point me in that direction and I will eagerly follow.

N/D-Noble

 

[MikeHalloran]

The equations you need are in here:

http://www.bently.com/prod/products/datasheets/GER-4273.pdf

The paper deals with minimizing the fluctuations that you are trying to maximise, or finding antinodes, but the science is there.

I assume that resonance in intake tracts in combination with supercharging is not widely treated in the literature because it makes the math a little harder, and because the primary challenge associated with supercharging is just finding room for all the plumbing. E.g., you may find it necessary to de-optimize your carefully tuned pipes just to squeeze the turbos into the available space.

You are, after all, trying to optimize an effect whose greatest possible influence will be swamped by 20 psi of boost.





Mike Halloran
Pembroke Pines, FL, USA

 

[patprimmer]

There are problems with tuned length in supercharged engines. These are:-

For positive displacement Belt driven blowers mounted directly on the manifold. The height, belt length and mounting strength required can severely influence the manifold design.

For blowers that are not positive displacement, boost varies greatly with speed, so the required lengths jump all over the place.

Also the greater the volume of air between the blower and the inlet valve, the slower the boost builds in the manifold. This delay can cause Turbo lag and this can negate any peak power gains over a narrow rev range.

This has been discussed at length in previous threads. Did you bother to do a site search before bothering us with a question.

Regards

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[GregLocock]

I think the latter point is the important one. The best figure for NA VE I can remember seeing is 115%, ie the equivalent of 2 psi of boost. How much extra friction loss in the runners can you accomodate before losing 2 psi?

The speed of sound is proprtional to the square root of the absolute temperature of the gas, therefore you need to retune an NA duct by that ratio, for the same speed.

Cheers

Greg Locock

Please see FAQ731-376 for tips on how to make the best use of Eng-Tips.

 

[MikeHalloran]

Another point occurred. If a turbo feeds a manifold that exhibits very strong resonances, that can't be very good for the compressor blades' fatigue life. It might be desirable to tune a turbo manifold so the individual pipe resonances don't occur at the same speeds, in the interest of compressor life. That's just conjecture on my part; I'm not aware of any published information on the subject. If I were a turbo manufacturer, that's the sort of thing I'd be disinclined to publish anyway.



Mike Halloran
Pembroke Pines, FL, USA

 

[mattsooty]

I wouldnt bother.

The greater deltas in intake temp & pressure render a tuned manifold a waste of time.

Regardless, if you want more charge in the cylinder - increase the boost.

MS

 

[patprimmer]

It's not so much the increase in intake charge temperature as the variability in charge temperature that makes it a futile exercise.

Regards

eng-tips, by professional engineers for professional engineers
Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.