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Theory of 4 valve poly quad cylinder heads.

General engine tech -- Drag Racing to Circle Track

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ozyfordman
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Re: Theory of 4 valve poly quad cylinder heads.

Post by ozyfordman » Mon Sep 09, 2019 5:33 pm

Thanks for the responses guys. This gives me a good place to start with research. I intended exploring established methods first in this build, just wandering if I was leaving anything on the table by not exploring the polyquad option. We currently run S109 fuel. Will look to run methanol next time. Will spend time on the bench reducing reverse flow. Steeper valve angles are also in the mix. We have a factory CNC head from a relatives race bike that blew up. The current head flows nearly the same with same std valves but much smaller csa. Looking for at least 2.5 hp per cube. There are still a few crumbs on the table but realise that they will be hard to find. Radius buckets, higher valve lift and more compression might get us there. This is a long term project. I will post results as I go if gains are worth reporting. Thanks again. Love this forum!

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Re: Theory of 4 valve poly quad cylinder heads.

Post by midnightbluS10 » Mon Sep 09, 2019 10:06 pm

Truckedup wrote:
Mon Sep 09, 2019 4:51 pm
The "poly" heads are used instead of variable cam timing ?
It reads to me like this is used on engines that had no available variable cam timing.

Not that you would intentionally disable it in order to get results from these modifications on a brand new Honda Civic or the equivalent.
JC -

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Re: Theory of 4 valve poly quad cylinder heads.

Post by GARY C » Mon Sep 09, 2019 10:32 pm

Rick! wrote:
Mon Sep 09, 2019 2:40 pm
SchmidtMotorWorks wrote:
Mon Sep 09, 2019 11:40 am
Look to see if any modern high performance motorcycle engines are biasing flow that was not done for packaging reasons. They test an unimaginable array of parameters with the best of equipment.
If they are not doing it, it is unlikely to be worth doing.
Though DV's patented system is novel, if it was that much better the single cylinder dirtcycle OEMs would be already using it. Though there is improvement one can impart to these engines, huge gains in hp are pretty hard to find. 2-3hp on a 250 4-valve single is a huge gain and it could be around 10hp on a green 450. It may be wise to look at the orange, green and red 450 bikes before committing to team blue. With available launch control and other ECU tricks, power management is of equal performance value as is raw power.
There are a lot of thing that the OEM doesn't that is better then what they do but budget and constraints do not always allow that.

GM produced one hundred million traditional SBC's none of which ever came close to what the aftermarket was doing with them.
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Re: Theory of 4 valve poly quad cylinder heads.

Post by GARY C » Mon Sep 09, 2019 10:44 pm

hoffman900 wrote:
Mon Sep 09, 2019 4:01 pm
Carnut1 wrote:
Mon Sep 09, 2019 9:02 am
pq4.png A quick search I found a few pics to show design basics. Some prefer tumble to swirl but what I like about the swirl is the energy is more intact on the compression stroke than a tumble design. Early 90's swirl testing you could see on the plug, chamber and piston the swirl burn pattern. This was good for detonation resistance and street torque. As the rpm climbs the turbulence in chamber increases and the swirl may actually use energy that could be used to fill the cylinder. Thanks, Charlie
Ducati utilizes tumble, not swirl designs, to an awesome degree.

Those who play with their modern heads say they look weird on the flowbench, but it’s super easy to mess them up using traditional techniques. We’re talking engines that make 3.3hp/ci, NA, on pump gas, meet emissions, and have long service lives, and traceable power curves. Compression is over 12:1 on pump gas with bore sizes up to 4.5” on their twins.
It seems like swirl would just force the fuel out of suspension and onto the cylinder walls.
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Re: Theory of 4 valve poly quad cylinder heads.

Post by JoePorting » Mon Sep 09, 2019 11:43 pm

I believe DV explains all this in his porting book which is about $20 on summit racing.
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Re: Theory of 4 valve poly quad cylinder heads.

Post by gruntguru » Tue Sep 10, 2019 12:08 am

GARY C wrote:
Mon Sep 09, 2019 10:44 pm
hoffman900 wrote:
Mon Sep 09, 2019 4:01 pm
Carnut1 wrote:
Mon Sep 09, 2019 9:02 am
pq4.png A quick search I found a few pics to show design basics. Some prefer tumble to swirl but what I like about the swirl is the energy is more intact on the compression stroke than a tumble design. Early 90's swirl testing you could see on the plug, chamber and piston the swirl burn pattern. This was good for detonation resistance and street torque. As the rpm climbs the turbulence in chamber increases and the swirl may actually use energy that could be used to fill the cylinder. Thanks, Charlie
Ducati utilizes tumble, not swirl designs, to an awesome degree.

Those who play with their modern heads say they look weird on the flowbench, but it’s super easy to mess them up using traditional techniques. We’re talking engines that make 3.3hp/ci, NA, on pump gas, meet emissions, and have long service lives, and traceable power curves. Compression is over 12:1 on pump gas with bore sizes up to 4.5” on their twins.
It seems like swirl would just force the fuel out of suspension and onto the cylinder walls.
There must be several billion 2 valve engines with swirl out there.

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Re: Theory of 4 valve poly quad cylinder heads.

Post by hoffman900 » Tue Sep 10, 2019 6:45 am

gruntguru wrote:
Tue Sep 10, 2019 12:08 am
GARY C wrote:
Mon Sep 09, 2019 10:44 pm
hoffman900 wrote:
Mon Sep 09, 2019 4:01 pm


Ducati utilizes tumble, not swirl designs, to an awesome degree.

Those who play with their modern heads say they look weird on the flowbench, but it’s super easy to mess them up using traditional techniques. We’re talking engines that make 3.3hp/ci, NA, on pump gas, meet emissions, and have long service lives, and traceable power curves. Compression is over 12:1 on pump gas with bore sizes up to 4.5” on their twins.
It seems like swirl would just force the fuel out of suspension and onto the cylinder walls.
There must be several billion 2 valve engines with swirl out there.
We’re talking about 4 valve powersport application with power goals of 2.5hp/ci here. Not truck engines.
-Bob

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Re: Theory of 4 valve poly quad cylinder heads.

Post by ozyfordman » Tue Sep 10, 2019 8:12 am

Yes. I agree. Currently at 2.1 hp per cube. Need 2.5 or better with good reliability. More would be better. I was looking to see if there was a way to get there without the maintenance requirements of prostock. In order of importance, how would you rate the following pursuits. Minimising reverse flow (given reaching near max theoretical of valve size in forward direction.) steeper valve angles, ( ties into reverse flow buy reducing low lift flow in both directions). Minimising cross flow through exhaust. Valve heights and valve seat angles. Offset bottom angles, (I know from experience that this works) with 2 valve stuff) Swirl and tumble? I don’t have a swirl meter but would get one if it was high on the list. All open ended questions I realise. Any help with priorities? Have room to move on max theoretical with current valve size before going to bigger valves, currently 38% of bore area for intakes.Too many questions I know, willing to do the testing. Where are the gains for 2.5 + cfm per cube best sought? I’ve never been past 1.5 hp per cube with junk 2 valve stuff. Asking the right questions never hurts. We are way past cams, carbs and compression here. I am a newby to 4 valve stuff , hence all the questions.

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Re: Theory of 4 valve poly quad cylinder heads.

Post by LoganD » Tue Sep 10, 2019 10:10 am

You don't want swirl in a gasoline spark ignition engine. If you're seeing combustion efficiency improvements with the introduction of swirl then the system simply didn't have enough charge motion to begin with. Tumble is what you want in a gasoline SI engine. High swirl rates produce fuel/air separation and move the fuel away from the spark plug (centripetal acceleration) producing a localized lean zone by the spark plug....and that's the exact opposite of what you want.

This is why you've seen the move away from steep valve angles in 4-valve cylinder heads to much shallower valve angles without a major change in port angle. The amount of tumble in a new 4-valve cylinder head (anything post 2018) is crazy, and this is how they're getting 32 bar BMEP on 91 octane.

This WAS a debate for a long time, but it turned out that the steep valve angles and large ports in 90s 4-valve heads, particularly those from Honda and Mitsubishi, just didn't have any charge motion at low pressure drops. Modern heads to not have this issue. You do sacrifice some flow for any charge motion, so some manufacturers have compromised with moderate valve angles and some sort of flap that will help charge motion at low pressure drops. Ford did this with the Coyote V8, it has "CMCV" plates or charge motion control valves.

We measure this now with a flow index. We have a tumble meter on the flow bench and we rate the heads by (flow*tumble)/valve size. You're looking to maximize tumble while still utilizing as much of the valve curtain area as possible with a given valve size. Mercedes are the absolute leaders in this, it's borderline witchcraft how good they've gotten at balancing this.

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Re: Theory of 4 valve poly quad cylinder heads.

Post by BobbyB » Tue Sep 10, 2019 10:16 am

LoganD,

Thanks for the very informative information.

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Re: Theory of 4 valve poly quad cylinder heads.

Post by hoffman900 » Tue Sep 10, 2019 10:17 am

Thanks, Logan.

Someone mentioned that the modern Ducati heads look weird on a flowbench and they’re really easy to mess up using traditional porting methods.
-Bob

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Re: Theory of 4 valve poly quad cylinder heads.

Post by Stan Weiss » Tue Sep 10, 2019 12:15 pm

Experimental study on an IC engine in-cylinder flow using different steady-state flow benches

https://www.sciencedirect.com/science/a ... 6817302582

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Do you use engine simulation software that uses cylinder head flow files?
We have a package of more than 3025 DFW or FLW Files

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Re: Theory of 4 valve poly quad cylinder heads.

Post by gunt » Tue Sep 10, 2019 4:07 pm

Gona make a show of myself here , but i thought these differences , swirl / tumble etc also greatly depended on working rpm range , so the to me the high rpm bike engine will only lose to this and the poly quad

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Re: Theory of 4 valve poly quad cylinder heads.

Post by SchmidtMotorWorks » Tue Sep 10, 2019 4:23 pm

With regards to return on tuning investment:
1 gearing
2 exhaust pipe
3 intake duct
Optimised fuel and spark throughout.
http://www.schmidtmotorworks.com Prototypes, Tooling, Molds.

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Re: Theory of 4 valve poly quad cylinder heads.

Post by ptuomov » Tue Sep 10, 2019 7:33 pm

LoganD wrote:
Tue Sep 10, 2019 10:10 am
You don't want swirl in a gasoline spark ignition engine. If you're seeing combustion efficiency improvements with the introduction of swirl then the system simply didn't have enough charge motion to begin with. Tumble is what you want in a gasoline SI engine. High swirl rates produce fuel/air separation and move the fuel away from the spark plug (centripetal acceleration) producing a localized lean zone by the spark plug....and that's the exact opposite of what you want.

This is why you've seen the move away from steep valve angles in 4-valve cylinder heads to much shallower valve angles without a major change in port angle. The amount of tumble in a new 4-valve cylinder head (anything post 2018) is crazy, and this is how they're getting 32 bar BMEP on 91 octane.

This WAS a debate for a long time, but it turned out that the steep valve angles and large ports in 90s 4-valve heads, particularly those from Honda and Mitsubishi, just didn't have any charge motion at low pressure drops. Modern heads to not have this issue. You do sacrifice some flow for any charge motion, so some manufacturers have compromised with moderate valve angles and some sort of flap that will help charge motion at low pressure drops. Ford did this with the Coyote V8, it has "CMCV" plates or charge motion control valves.

We measure this now with a flow index. We have a tumble meter on the flow bench and we rate the heads by (flow*tumble)/valve size. You're looking to maximize tumble while still utilizing as much of the valve curtain area as possible with a given valve size. Mercedes are the absolute leaders in this, it's borderline witchcraft how good they've gotten at balancing this.
I think that generating enough tumble is important at party throttle and low rpms. But isn’t the four valve head automatically generating enough tumble at high loads and high rpms, especially if turbocharged? Is this a practical concern?

I agree that one still wants to generate whatever tumble one needs efficiently.

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