cylinder head porting theories... and such

[flubyux2]

soo, i was in the FAQ and looked at Allans flow bench results for unported and ported 7M heads.

stock lift is about 0.311". IIRC, the intake side flows 178cfm at that lift, and exhaust side flows 124cfm at that lift.

the exhaust side is significantly imbalanced from the intake side. i feel that the exhaust side might benefit from being balanced and having flow numbers closer to intake flow numbers. or balancing the flow rates.

ideally, i would like to have at LEAST 200cfm of airflow per cylinder. 220 would be awesome!

now, i know that everyone thinks we should keep exhaust gas velocity high so that it can spool turbos better and what not. but, the exhaust ports are ridiculously small. i mean, velocity is good and all... but at what point does reduced cross sectional area begin to be detrimental to overall flow rate? like, when do we start sacrificing the importance of volume in favor of velocity?

lets hear some thoughts, aight?

 

[cjennings]

I hear that theory alot about keeping the exhaust side smaller for faster velocities, but when you are under boost and cramming in as much air as we can on big turbos that seems to be counter intuative. I think you would be best to focus on smothing out the outflow to reduce turbulance while opening it up alittle.

But, i have no flow data and know little about heads to be qualify my above statement. The hair dryer at the side of the car seems to overcome other defiencies by just increasing the pressure and fuel. If I was a NA car, i am sure then it would be all that more important/

 

[souprat]

i may just be a noob but....
we all know that you want big or no exaust after the turbo. low pressure after the turbo and high pressure before it = low spool time and high boost. duh

but if you increase the diameter of the exaust ports and the manifold giving them more volume, you would have to flow much more gas through them to to get the high velocity, high pressure gas that can spool your turbo. porting the exaust side to a huge diameter would give you lots of top end power. but your turbo would never spool untill you were at high rpm. in other words you dont want it to be easy for the engine to pump out the exaust cuz thats what drives the turbo.

just my.02

 

[Boostedstr8six]

The turbine housing a/r is the restriction that determines exhaust manifold pressure and exhaust velocities onto the turbine. I think opening the exhaust ports would be greatly beneficial. You'd have to be conservative enough to maintain functional reversion dams though.

 

[chevyeater]

Ever wonder why the ehaust valve is smaller than the intake valve?

When the exhaust valve opens after the combustion stroke, the pressure inside the cylinder is much greater than that in the exhaust manifold. This naturally expidites exhaust flow out of the cylinder. The port needs to be smaller to maintain any velocity as flow begins to slow to extract the most exhaust possible. With a turbocharged engine, reversion will become a serious factor towards the end of the exhaust stroke, even without any valve overlap. If your exhaust ports flowed as much as the intake, your turbocharged engine would run like shit, IMO.

 

[limequat]

Ever wonder why the ehaust valve is smaller than the intake valve?

When the exhaust valve opens after the combustion stroke, the pressure inside the cylinder is much greater than that in the exhaust manifold. This naturally expidites exhaust flow out of the cylinder. The port needs to be smaller to maintain any velocity as flow begins to slow to extract the most exhaust possible. With a turbocharged engine, reversion will become a serious factor towards the end of the exhaust stroke, even without any valve overlap. If your exhaust ports flowed as much as the intake, your turbocharged engine would run like shit, IMO.

Right, flow should not be equal across the intake and exhaust valves. However, keep in mind that the cylinder head was designed for a n/a engine. The turbo has obvious benefit of pressure across the valves too. To figure out the ideal exhaust flow one needs to start with the max boost, calculate airflow, model the exhaust pressure, and then find the exhaust flow that matches the intake flow at boost.

I pondered how to calculate this in Excel until I felt my head was on the verge of implosion, then I decided to go with oversized valves on the exhaust side only. This should reduce pressure drop on the exhaust side AND increase exhaust velocity.

This was done in concert with a substantal compression increase, so I can't speak to the gains (or losses).

 

[Halsupramk3]

I ported my head myself and there are gains to be had. My low lift numbers increased significantly.

I would think with the CT and a log manifold that increasing preasure by porting out the exhaust ports would just make them back up in the manifold. Which would negate the purpose of over porting. Why expel the gases just to slow them before they hit the turbine? On the other hand velocity would not be so adversely effected by the manifold provided it makes the turns. When the turbo begins to spool would velocity be more beneficial to make the turbo work than more gases? I would think at that point velocity is better. Of course i imagine it depends on the size turbo. When boost is increased preasure is increased and the exhaust housing and manifold become restrictions. Which is why the reversion dam at the ports i think would be helpful.

It may be different with a tubular manifold. Also the up stroke of the piston helps push gases along out the ports but the down stroke isnt as effective under boost as in n/a's. I guess that makes it easier for the turbo.

I am sure there are some heavy math calculations in this whole area.
These are my numbers under the My Port sections. The street port was posted by a machine shop on SF. The full race was an option of theirs which hogged out the ports.

INTAKE
LIFT---- STOCK-- STREET---MY PORT--FULL RACE
---------CFM-------PORT
0.05-----n/t--------- n/t-----107.7-----n/t
0.100----77.4-------80.4-----160.7-----80.8
0.150----113.9-----122.4-----178.6----121.7
0.200----141.4-----159.9-----186.6----152.6
0.250----162.8-----187.9-----190.2----181.0
0.300----176.0-----202.4-----191.5----201.3
0.350----179.6-----211.2------n/t-----211.8
0.400----179.6-----216.5-----n/t------222.4
0.450----180.0-----220.0-----n/t------231.8
0.500----180.0-----220.0-----n/t------239.1


EXHAUST
LIFT-----STOCK--STREET--MY PORT--FULL RACE
----------CFM-----PORT
0.05------n/t------n/t-------86--------n/t
0.100-----60.4-----70.0----121.8------70.0
0.150-----93.0----103.4----133.3-----108.0
0.200----112.9----121.0----138.4-----135.2
0.250----123.2----131.0----141.1-----150.3
0.300----127.8----139.4----143-------163.8
0.350----130.7----143.1----n/t-------167.6
0.400----133.2----149.5----n/t-------171.8
0.450----133.2----155.0----n/t-------174.0
0.500----133.0----155.0----n/t-------188.0

(sorry for the dashes but i could not get the chart to post correctly with out them.)
n/t = not tested
My Port testing did not use a radius adapter on the flow bench to force in higher volumes of air. I did not attach the lower intake manifold.
You can see that my low lift numbers went up very much. I think this is because i left the ports smaller towards the exit than at the entrance. So i left the exhaust port exits closer to stock size and opened up the Exst bowl area more. On the intake the bowl area was cleaned up and the entrance at the manifold was opened up more to help increase velocity. By doing the ports this way i think velocity helped to keep the low lift numbers up. With my new C/R of 9:1 I think a smaller turbo would kick ass. With a large turbo it would benefit from my opening up the ports more which would be closer numbers to the Race port.

Thats my theory. It may all be total BS.

 

[flubyux2]

lol, thanks hal, for that wealth of info. i totally got you on the bowl blending and back cutting the valve seats to allow a larger chamber for the exhaust gasses to purge into when the valve lifts off the seat. keeping the exhaust port diameter the same at the manifold entrance creates more of a venturi effect as the port velocity increases due to the decrease in cross sectional area when transitioning from the valve bowls.

honestly, i know for a fact that i need to have the turbo manifold pressure equal to the intake manifold pressure. ideally speaking, if i have 15psi of boost on the intake side, i dont want much more than 15psi of back pressure on the exhaust side. its a basic law of physics; enery cannot be created nor destroyed. it can merely change forms. so, 15psi of back pressure in the turbo manifold would easily strike an equilibrium with 15psi of pressure in the intake manifold. the raw energy required to spool a turbo and cause 15 psi of backpressure is the roughly the same amount of energy USED to create the 15 psi of boost on the cold side.

a simple equation, for argument's sake;
the turbine wheel requires 15,000 kilojoules of energy to spool the turbo by 3500rpms and create 1.0 Bar of boost on the cold side. subracte 3000 kilojoules for the thermal losses and frictional losses in the bearings as well as that required to overcome inertia. there is only 12,000 kilojoules netted to turn the wheels. i guess its like how much power does it take to overcome the losses in a driveline between the flywheel and the rear wheels. if its TOO great of an inefficiency, then the losses will be too much and the benefits of boost and spool response will suffer, or top end airflow as pressure will backup inside the manifold.

this is 100% speculation though, ive got no empirical data to back up my jargon...

ideally, in order to acheive peak efficiency, air in must equal air out. granted, on the exhaust stroke, the piston is physically expelling the spent gasses. creating a higher pressure inthe cylinder and the gasses naturally tend to move towards a lower pressure area, like the manifold. however, if the turbine housing and manifold are too restrictive, then too large a volume of spent gasses cannot exit the cylinder, regardless of the pressure created as the piston moves upward.

i seem to think that a low restriction between the exhaust valve and turbine housing would be beneficial. this would allow the exhaust stroke to expel as much spent gas as possible and reduce the total dillution of intake charges.

now, the problem is, if we have too little of a restriction and reduce our velocity too much, there will be little to no inertia in the exhaust gasses. if this is the case, they can easily reverse direction re-enter the exhaust port. but, if we retain the anti-reversion step that is already engineered into the 7MGTE, we can still benefit from a reduction in total exhaust port volume improvments.

is anyone following me? anyone else think otherwise?

 

[Halsupramk3]

This equalization stuff is confusing me a little as to what benefits it would create for a turbo car. What difference does it make if the exhaust and intake manifold preasures are? I would think that buring gasses in the exhaust manifold would have very high preasures.

What does it matter if they are equal when during exhaust combustion the intake valve is going to be closed for the vast majority of time during the exhaust cycle? In a turbo car is scavaging of much benefit? When the intake opens the exhaust valves are closed.

I think i am missing some information here to understand what effect equalization is.

 

[DEFIANT 7M]

The street port was posted by a machine shop on SF. The full race was an option of theirs which hogged out the ports.

INTAKE
LIFT---- STOCK-- STREET---MY PORT--FULL RACE
---------CFM-------PORT
0.05-----n/t--------- n/t-----107.7-----n/t
0.100----77.4-------80.4-----160.7-----80.8
0.150----113.9-----122.4-----178.6----121.7
0.200----141.4-----159.9-----186.6----152.6
0.250----162.8-----187.9-----190.2----181.0
0.300----176.0-----202.4-----191.5----201.3
0.350----179.6-----211.2------n/t-----211.8
0.400----179.6-----216.5-----n/t------222.4
0.450----180.0-----220.0-----n/t------231.8
0.500----180.0-----220.0-----n/t------239.1


EXHAUST
LIFT-----STOCK--STREET--MY PORT--FULL RACE
----------CFM-----PORT
0.05------n/t------n/t-------86--------n/t
0.100-----60.4-----70.0----121.8------70.0
0.150-----93.0----103.4----133.3-----108.0
0.200----112.9----121.0----138.4-----135.2
0.250----123.2----131.0----141.1-----150.3
0.300----127.8----139.4----143-------163.8
0.350----130.7----143.1----n/t-------167.6
0.400----133.2----149.5----n/t-------171.8
0.450----133.2----155.0----n/t-------174.0
0.500----133.0----155.0----n/t-------188.0

The shop was Revolutionary Performance, that's my cylinder head. Daryle posted a few times on SF. The full race port flow numbers are a result of hours of blending and studing were the air is actually traveling. The ports aren't hogged out, I wish I had pics to show you guys. But our agreement is to respect his wishes not to devulge what took years for him to learn. But here is one trick... To see were the air was going was ingenious. Daryle used dye in the ports to trace the airflow while on the flow bench. If the route was not right he fixed it. The majority of the increase was in the bowl and we did back cut the 2J valves. Also the angles of the valve seats are something Daryle isn't willing to tell me. We have picked up a few more cfm on the intake (flirting with 240-242cfm), 205-207 on the exhaust. That increase came from unshrouding the valves and a bit more port work to the exhaust side.

 

[siman]

So all the speculation that has been spread about porting the stock head being a "waste of time" is fubar?

I was always abeliever in head work and flow bench testing...and this just increases my indulgance in proving that the 7m head is quite good in comparison to todays cars as well!

I would LOVE to see the flow bench numbers of the 1jz head, since people make the 1.5jz for track use for some reason, i am guessing it flows FASTER than the 2jz head? Quicker spool time?
No joke, but alot of the drifters that use JZ series motors build the 1.5jz ( 1jz head with 2jz bottem end) for quick spool charectoristics....ok i wont mention drifting in here again, i was just trying to create common grounds of interest

What i see is that you can adversly affect the velocity of the exhuast gases with bigger bored exhaust ports...which then intern dont push the exhaust turbine as fast as they normally would given the smaller stock spec exhaust ports?

Or can it go either way becuase a number of variables? Turbo/exhaust ports/valve sizing/valve angle.....

I know this might sound stupid....but like the ACIS ( acoustic controlled induction system) would there be a way to increase exhaust flow rates on the fly? A variable exhaust gas manifold? LOL......

or could you just gain overall performance by going with a tubulor manifold?

Ok its late...i will end my q's there.

-Jonathan

 

[Dirgle]

If I'm not mistaken the ACIS system was used to bring the volumetric efficiency of an NA engine as close to 100% as possible. With the addition of a turbo the volumetric efficiency automatically goes over 100% when pressure is introduced. Thus negating the effects of ACIS. I may be wrong about this but because the exhaust side has pressure, ACIS wouldn't have an effect.

 

[siman]

ACIS was used for:

Acoustic Control Induction System (ACIS)
“The Acoustic Control Induction System (ACIS) improves the torque in the whole RPM range, especially that in the low-speed range, by changing the intake manifold length in stages. The intake manifold length is varied in stages by optimum control of the intake aid control valve(s). The airflow in the intake pipe pulsates due to opening and closing of the engine intake valves. When an intake valve is closed, the inertia force compresses the air near the valve. This compressed air pushes off the intake valve at high speed toward the intake chamber. If the intake manifold length and intake chamber shape are set to cause the compressed air pressure to return to an engine intake valve during the intake stroke, the intake air volume is increased improving volumetric efficiency. This is called the intake inertia effect. This improves torque and horsepower.

nothing about only n/a.....

its just changing the length that the air has to flow to get to each particular runner.....basically putting a denser air charge in a smaller space...giving more HP or Tq becuase of a bigger combustion charge....I think...

here is the link to ACIS and its attributes to the motor:
http://www.geocities.com/mwsupra2003/acis.html

 

[siman]

ACIS was used for:




nothing about only n/a.....

its just changing the length that the air has to flow to get to each particular runner.....basically putting a denser air charge in a smaller space...giving more HP or Tq becuase of a bigger combustion charge....I think...

here is the link to ACIS and its attributes to the motor:
http://www.geocities.com/mwsupra2003/acis.html

of course there is a "limit" nonetheless that you can supposedly reach in the give space of a runner size....before it is just "too much" air...and something gives..."blows up" pressure wise.
Thus you are correct that a turbo will probably see a lesser degree of improvement of the sort....but if you are looking for the ultimate in power...i guess ACIS has some HP to give out....LOL

anyone, please correct me if i am wrong in ANY of this...i dont want to spread false info...i will delete these posts and theories if need be :sonic:

-Jonathan

 

[Dirgle]

True that is what it does. But Shawndude and Defiant 7m had a long argument on how it does it.
Here:

http://www.supraforums.com/forum/showthread.php?t=82444&highlight=volumetric

ACIS is only used on an NA for a reason. The Turbo defeats it's pupose. I'm sure toyota wouldn't ditch a disign that they already had in place(on th NA engine) if was more effective.than a regular turbo intake under pressure.

 

[IJ.]

"A" in ASIC is acoustics so I'm guessing the sound waves/frequencies generated by the turbo compressor would negate any benefits.

 

[limequat]

So all the speculation that has been spread about porting the stock head being a "waste of time" is fubar?

Absolutely not. Increasing the head flow is documented and proven. A good port job can improve flow. What HASN'T been proven is that extra head flow is necessary. A stock intake will flow 400 cfm. A stock head will flow over 1000 CFM. The head will be the last bottleneck in your system.

I know this might sound stupid....but like the ACIS ( acoustic controlled induction system) would there be a way to increase exhaust flow rates on the fly? A variable exhaust gas manifold? LOL......

Actually, it's not stupid at all. You've basically described variable vane turbochargers.

 

[Boostedstr8six]

lol, thanks hal, for that wealth of info. i totally got you on the bowl blending and back cutting the valve seats to allow a larger chamber for the exhaust gasses to purge into when the valve lifts off the seat. keeping the exhaust port diameter the same at the manifold entrance creates more of a venturi effect as the port velocity increases due to the decrease in cross sectional area when transitioning from the valve bowls.

honestly, i know for a fact that i need to have the turbo manifold pressure equal to the intake manifold pressure. ideally speaking, if i have 15psi of boost on the intake side, i dont want much more than 15psi of back pressure on the exhaust side. its a basic law of physics; enery cannot be created nor destroyed. it can merely change forms. so, 15psi of back pressure in the turbo manifold would easily strike an equilibrium with 15psi of pressure in the intake manifold. the raw energy required to spool a turbo and cause 15 psi of backpressure is the roughly the same amount of energy USED to create the 15 psi of boost on the cold side.

a simple equation, for argument's sake;
the turbine wheel requires 15,000 kilojoules of energy to spool the turbo by 3500rpms and create 1.0 Bar of boost on the cold side. subracte 3000 kilojoules for the thermal losses and frictional losses in the bearings as well as that required to overcome inertia. there is only 12,000 kilojoules netted to turn the wheels. i guess its like how much power does it take to overcome the losses in a driveline between the flywheel and the rear wheels. if its TOO great of an inefficiency, then the losses will be too much and the benefits of boost and spool response will suffer, or top end airflow as pressure will backup inside the manifold.

this is 100% speculation though, ive got no empirical data to back up my jargon...

ideally, in order to acheive peak efficiency, air in must equal air out. granted, on the exhaust stroke, the piston is physically expelling the spent gasses. creating a higher pressure inthe cylinder and the gasses naturally tend to move towards a lower pressure area, like the manifold. however, if the turbine housing and manifold are too restrictive, then too large a volume of spent gasses cannot exit the cylinder, regardless of the pressure created as the piston moves upward.

i seem to think that a low restriction between the exhaust valve and turbine housing would be beneficial. this would allow the exhaust stroke to expel as much spent gas as possible and reduce the total dillution of intake charges.

now, the problem is, if we have too little of a restriction and reduce our velocity too much, there will be little to no inertia in the exhaust gasses. if this is the case, they can easily reverse direction re-enter the exhaust port. but, if we retain the anti-reversion step that is already engineered into the 7MGTE, we can still benefit from a reduction in total exhaust port volume improvments.

is anyone following me? anyone else think otherwise?

You would be correct if there wasn't combustion going on in the engine. The intake charge itself represents a small percentage of the energy involved. Fuel is the the major contributor. IIRC, even on big turbos you won't see a 1:1 intake/exhaust pressure ratio but the bigger the turbine housing a/r the closer you get (along with massive *peak* output). It's probably more realistic to see between 2:1 and maybe 3:1 ratios. That's why the gte exhaust cam is fine for all but the biggest a/r hot sides. The reversion you'd see with a long duration cam would likely negate a lot of the flow potential increase on relatively quick spooling turbines. There are a lot of dynamic variables but that's my understanding.

 

[Dirgle]

Actually, it's not stupid at all. You've basically described variable vane turbochargers.

More info please

 

[siman]

More info please

http://www.tytlabs.co.jp/english/review/rev353epdf/e353ab_uchida2.html

http://www.toyota-europe.com/technology/engines/d_4d_2.html

here is the best description with a cutaway:
http://www.turbochargedpower.com/Control%20System.htm

....I didnt even know they existed! Pretty sweet if you ask me! I wonder if they use them in race car applications? JGTC? IRL?.....do they? :icon_conf


-Jonathan