Theory of 4 valve poly quad cylinder heads.

[LoganD]

"Why is it beneficial to transfer heat from the cylinder walls, piston, and combustion chamber roof into the charge on a pump gas, knock limited engine? This is not a rhetorical question."

Hot spots act like a spark plug. Controlling hot spots is more important than an increase in pre-combustion air temp. On modern high-BMEP production engines there's also the issue of material longevity, this is an issue particularly on the exhaust side.

This is the same reason they use oil squirters on pistons.

Ok, so if the problem is low speed preignition, I can see how more tumble is better. If the problem is spark knock, then more tumble is not necessarily always better.

If so, for downsized passenger car engines, or engines running very high octane fuel, more tumble the better. For a "tuner engine" running on pump gas and making power at higher rpms, there may be a point where more tumble is no longer better.

This used to be the old thinking, and it was based on the fact that as RPM rises charge motion naturally gets more chaotic so you don't need to design a port specifically for tumble at high RPM. Now we know you want to control that charge motion and design it to do things deliberately, this involves designing the entire intake system correctly.

This is how you've got Ferrari and McLaren turning 8500+ RPM with turbocharged engines making 200hp/L on 91 octane.

[hoffman900]

"Why is it beneficial to transfer heat from the cylinder walls, piston, and combustion chamber roof into the charge on a pump gas, knock limited engine? This is not a rhetorical question."

Hot spots act like a spark plug. Controlling hot spots is more important than an increase in pre-combustion air temp. On modern high-BMEP production engines there's also the issue of material longevity, this is an issue particularly on the exhaust side.

This is the same reason they use oil squirters on pistons.

Ok, so if the problem is low speed preignition, I can see how more tumble is better. If the problem is spark knock, then more tumble is not necessarily always better.

If so, for downsized passenger car engines, or engines running very high octane fuel, more tumble the better. For a "tuner engine" running on pump gas and making power at higher rpms, there may be a point where more tumble is no longer better.

This used to be the old thinking, and it was based on the fact that as RPM rises charge motion naturally gets more chaotic so you don't need to design a port specifically for tumble at high RPM. Now we know you want to control that charge motion and design it to do things deliberately, this involves designing the entire intake system correctly.

This is how you've got Ferrari and McLaren turning 8500+ RPM with turbocharged engines making 200hp/L on 91 octane.

They also have stupid fat power curves

[ptuomov]

Ok, so if the problem is low speed preignition, I can see how more tumble is better. If the problem is spark knock, then more tumble is not necessarily always better. If so, for downsized passenger car engines, or engines running very high octane fuel, more tumble the better. For a "tuner engine" running on pump gas and making power at higher rpms, there may be a point where more tumble is no longer better.

This used to be the old thinking, and it was based on the fact that as RPM rises charge motion naturally gets more chaotic so you don't need to design a port specifically for tumble at high RPM. Now we know you want to control that charge motion and design it to do things deliberately, this involves designing the entire intake system correctly. This is how you've got Ferrari and McLaren turning 8500+ RPM with turbocharged engines making 200hp/L on 91 octane.

The new quote display for this forum sucks hairy scrotum.

With port-injected engines, the "old thinking" certainly looks it has been the dominant thinking. Maybe the solutions have changed. My impression was that in the port-injected engine era, the idea was to get a lot of tumble at low rpms or low loads such that the burn would be fast enough in those conditions even with a lot of EGR. In the port-injected engine era, the high rpms and high loads would take care of themselves. At high boosts and high rpms, sometimes charge motion was considered excessive and an intent was to slow it down.

That McLaren is a low compression, port injection engine "relic" so it's of particular interest to me. What's inside there? It has long intake runners and I am guessing very much a tumble port feeding a conventional four-valve head. But that's just a guess. Another guess is that the variable valve timing and using them right with turbos is largely responsible for the wide power band.

[Corrections: Never mind, it's a flat plane engine, which eliminates the high-rpm exhaust blowdown interference: "With those log exhaust manifolds, the narrow bore spacing is going to allow it to rev higher, especially if the VVT takes out the valve overlap, I am guessing."]

[LoganD]

Ok, so if the problem is low speed preignition, I can see how more tumble is better. If the problem is spark knock, then more tumble is not necessarily always better. If so, for downsized passenger car engines, or engines running very high octane fuel, more tumble the better. For a "tuner engine" running on pump gas and making power at higher rpms, there may be a point where more tumble is no longer better.

This used to be the old thinking, and it was based on the fact that as RPM rises charge motion naturally gets more chaotic so you don't need to design a port specifically for tumble at high RPM. Now we know you want to control that charge motion and design it to do things deliberately, this involves designing the entire intake system correctly. This is how you've got Ferrari and McLaren turning 8500+ RPM with turbocharged engines making 200hp/L on 91 octane.

The new quote display for this forum sucks hairy scrotum.

With port-injected engines, the "old thinking" certainly looks it has been the dominant thinking. Maybe the solutions have changed. My impression was that in the port-injected engine era, the idea was to get a lot of tumble at low rpms or low loads such that the burn would be fast enough in those conditions even with a lot of EGR. In the port-injected engine era, the high rpms and high loads would take care of themselves. At high boosts and high rpms, sometimes charge motion was considered excessive and an intent was to slow it down.

That McLaren is a low compression, port injection engine "relic" so it's of particular interest to me. What's inside there? It has long intake runners and I am guessing very much a tumble port feeding a conventional four-valve head. But that's just a guess. Another guess is that the variable valve timing and using them right with turbos is largely responsible for the wide power band. With those log exhaust manifolds, the narrow bore spacing is going to allow it to rev higher, especially if the VVT takes out the valve overlap, I am guessing.

Well, I guess it depends on what you consider "old". You have to be careful because an engine released in 2005 had the combustion system designed at least 5 years earlier, so there's a time lag. Basically any engine with the combustion system designed in the last 15 years is going to have very high tumble due to shallow valve angles. So that would basically be any production engine after 2010. In the late 90's and very early 2000's high end CFD was still so expensive that it was being used sparingly and time-dependent CFD was virtually impossible with automotive development budgets. It was also pretty impractical from a time perspective, what used to take 6 months to run now takes 2 weeks and can be done on computers that are 1/100th the cost you would have paid 20 years ago.

I guess what I'm saying is that the drastic increase in speed and drastic reduction in cost for high end CFD has caused us to change a lot of our previous perceptions about engine design. The new Mercedes M139 is a perfect example, 20 years ago if someone were going to design a 2.0 turbo 4-cyl to make over 400 hp on pump fuel they wouldn't make it heavily undersquare (83x92) with almost no valve angle. That engine revs to 7400 RPM and makes 370 lb-ft from 121 ci.

It makes a lot of sense if you think about it. If you're knock limited and not airflow limited, which most is the case for most heavily turbocharged engines, it makes sense to design the entire engine around reducing knock instead of just trying to make it flow more. This is where the aftermarket is behind, a Coyote or LS head doesn't need more flow to make 1000 hp on pump fuel, it needs more knock resistance.

This thinking spilled over into naturally aspirated engine design. They now give the engine just enough airflow to make the RPM/power target, and then they design the rest of the engine around maximizing efficiency and cylinder pressure. That's why the new GT3 engine has 13.5:1 compression and pretty shallow valve angles for an engine that revs to 9000 RPM. They spent a great deal of time making the large bore engine very knock resistant, and that's a hard thing to do.

[SchmidtMotorWorks]

The Arao head is what I had in mind when I was talking 4vpc conversion heads. Just because it has 4 valves doesn’t mean it’s better, especially when most of what we’re talking about isn’t considered.

Curious to see who (outside the OEMs) can consistently start at a dyno pull at 1500rpm.

Supposably that Mitsubishi has ports “you can drive a truck through” and was mentioned by a tuner you can half fill it with epoxy and make more power. Logan hit on that about the 1990s trend of Honda and Mitsubishi making the ports wayyy to big to realize any real tumble, especially at lower depressions.

Typical experience with Arao

[mfdcar51]

I have a friend that bought his 4 valve SBC heads, Garbage is too kind for this product..Especially the extra pushrod for exhaust valve actuation.

[JCR]

Arao got plenty of free publicity for years from the "enthusiast" magazines.

[ptuomov]

So does anyone have a recipe how to cost effectively modify an oversized, small cam, early 1990’s dump port into a more modern tumble port? Or is that “go straight to the foundry with passing go” sort of proposition?

[LoganD]

So does anyone have a recipe how to cost effectively modify an oversized, small cam, early 1990’s dump port into a more modern tumble port? Or is that “go straight to the foundry with passing go” sort of proposition?

This is going to be completely counter-intuitive for you, but the answer is to lower the roof. You want the angle of the port generally to be more out of line with the angle of the valve. You also want to get rid of any "turn" into the valve, you actually want the port exit to have an angle relative to the valve. This will absolutely reduce your bench flow readings, the key is to minimize that loss while still getting the tumble.

This is the exact opposite of what race heads do, they always raise the port and try to bring the port more in line with the valve angle. This is very, very bad for tumble. Part of the reason this is happening is that CFM sells heads, in the aftermarket it's always more more more bigger bigger bigger. Unfortunately combustion efficiency isn't an easy sell.

[ptuomov]

So does anyone have a recipe how to cost effectively modify an oversized, small cam, early 1990’s dump port into a more modern tumble port? Or is that “go straight to the foundry with passing go” sort of proposition?

This is going to be completely counter-intuitive for you, but the answer is to lower the roof. You want the angle of the port generally to be more out of line with the angle of the valve. You also want to get rid of any "turn" into the valve, you actually want the port exit to have an angle relative to the valve. This will absolutely reduce your bench flow readings, the key is to minimize that loss while still getting the tumble.

This is the exact opposite of what race heads do, they always raise the port and try to bring the port more in line with the valve angle. This is very, very bad for tumble. Part of the reason this is happening is that CFM sells heads, in the aftermarket it's always more more more bigger bigger bigger. Unfortunately combustion efficiency isn't an easy sell.

That's not counterintuitive at all, if you mean filling the port roof around and downstream of the valve guide, installing a larger valve, sinking the valve a little more in a new bigger insert, and shaping the insert as a straight extension of the roof until very close to the seat -- all in an effort to get a straight-shot roof that is normal to the exhaust valve stem and thus parallel to the exhaust valve face. It just sounds expensive to do to an existing head.

Wasn't this what Cosworth started doing way back when?

http://www.grandprixengines.co.uk/Note_26.pdf

'Tumble Swirl' (TS) in the crank plane is likely to have occurred naturally in many engines with inclined valves and side ports, but not by design intention. In the Cosworth FVA, designed by Keith Duckworth in 1965, TS was encouraged deliberately by having the outer part of the inlet passage non-orthogonal to the valve head by 20° andby increasing Inlet Valve Maximum Lift/Head Diameter to 0.3 from the then-usual 0.25. Volumetric Efficiency (EV) was sacrificed to some extent so as to gain EC and maximise (EV x EC).By having 4 valves-per-cylinder to provide the necessary areas the valve stems could be at only 20° to the cylinder axis, so that the inclination of the outer inlet passage wall at approach to the valve head was 20° + 20° = 40°. Therefore, the biased flow did not go straight across intothe exhaust during the timing overlap period used to create extra suction. The central sparking plug made possible by four valves was placed perfectly to ignite the change whirling beneath it.

Also: https://www.sae.org/publications/techni ... 6-01-0692/

[LoganD]

So does anyone have a recipe how to cost effectively modify an oversized, small cam, early 1990’s dump port into a more modern tumble port? Or is that “go straight to the foundry with passing go” sort of proposition?

This is going to be completely counter-intuitive for you, but the answer is to lower the roof. You want the angle of the port generally to be more out of line with the angle of the valve. You also want to get rid of any "turn" into the valve, you actually want the port exit to have an angle relative to the valve. This will absolutely reduce your bench flow readings, the key is to minimize that loss while still getting the tumble.

This is the exact opposite of what race heads do, they always raise the port and try to bring the port more in line with the valve angle. This is very, very bad for tumble. Part of the reason this is happening is that CFM sells heads, in the aftermarket it's always more more more bigger bigger bigger. Unfortunately combustion efficiency isn't an easy sell.

That's not counterintuitive at all, if you mean filling the port roof around and downstream of the valve guide, installing a larger valve, sinking the valve a little more in a new bigger insert, and shaping the insert as a straight extension of the roof until very close to the seat -- all in an effort to get a straight-shot roof that is normal to the exhaust valve stem and thus parallel to the exhaust valve face. It just sounds expensive to do to an existing head.

Wasn't this what Cosworth started doing way back when?

http://www.grandprixengines.co.uk/Note_26.pdf

'Tumble Swirl' (TS) in the crank plane is likely to have occurred naturally in many engines with inclined valves and side ports, but not by design intention. In the Cosworth FVA, designed by Keith Duckworth in 1965, TS was encouraged deliberately by having the outer part of the inlet passage non-orthogonal to the valve head by 20° andby increasing Inlet Valve Maximum Lift/Head Diameter to 0.3 from the then-usual 0.25. Volumetric Efficiency (EV) was sacrificed to some extent so as to gain EC and maximise (EV x EC).By having 4 valves-per-cylinder to provide the necessary areas the valve stems could be at only 20° to the cylinder axis, so that the inclination of the outer inlet passage wall at approach to the valve head was 20° + 20° = 40°. Therefore, the biased flow did not go straight across intothe exhaust during the timing overlap period used to create extra suction. The central sparking plug made possible by four valves was placed perfectly to ignite the change whirling beneath it.

Also: https://www.sae.org/publications/techni ... 6-01-0692/

Precisely. You want the air to come into the cylinder with inertia towards the exhaust side heavily. This means the part of the intake valve closest to the cylinder wall won't be utilized well at all, but it will create a low pressure area there that encourages the air to tumble perpendicular to the cylinder. This is what you want.

If you visualize it that way, you can see why it's so hard to design tumble into parallel valve heads. To do this correctly you want the part of the valve closest to the cylinder wall to be at the very bottom of the port exit. Generally in a parallel valve engine the part of the valve closest to the cylinder wall is on the side of the port, not the bottom. This causes swirl.

[ptuomov]

That's not counterintuitive at all, if you mean filling the port roof around and downstream of the valve guide, installing a larger valve, sinking the valve a little more in a new bigger insert, and shaping the insert as a straight extension of the roof until very close to the seat -- all in an effort to get a straight-shot roof that is normal to the exhaust valve stem and thus parallel to the exhaust valve face. It just sounds expensive to do to an existing head.

Precisely. You want the air to come into the cylinder with inertia towards the exhaust side heavily. This means the part of the intake valve closest to the cylinder wall won't be utilized well at all, but it will create a low pressure area there that encourages the air to tumble perpendicular to the cylinder. This is what you want.

Just to be clear, this sort of tumble port is what doctor orders for "overvalved" four-valve heads that have valve sizes that could easily flow the engine flow demand with very low pressure loss. Furthermore, it's even more of a prescription for engines run on low-octane fuel where the burn speed is at a premium (pun intended). In contrast, if the four-valve head is "undervalved" because of displacement/rpms being sky high high, and especially so if the engine is run on race gas, then one would prioritize the flow and deprioritize tumble. Is this an accurate representation of your views for high-performance engines?

[SchmidtMotorWorks]

Does anyone have valve timing data for the Ducati and other engines with high tumble designs vs more conventional ports of similar performance purpose?
I am interested to know if overlap is reduced to minimise intake flow directly out the exhaust.
I suppose a well designed exhaust system might have a well timed pulse to block that, but only for a narrow range.
I do know that some of the Coyote tunes have negative overlap at some conditions, but I did not dwell on that to figure out why as it was not relevant to my project. Never enough time.

[hoffman900]

From Kevin Cameron:

Yes, mainstream. For this is a production motorcycle to be ridden every day, not a collector’s curiosity to be hung in static ignominy above some hedgie’s fieldstone fireplace. A major goal of V4 engine development was rideability. In general, the greater the valve event overlap in an engine’s cam profiles, the fussier and peakier its performance becomes. At the height of racing two-valve sophistication (Manx Norton, Velocette KTT, etc.) valve overlaps of 90 to 100 degrees were commonplace. The other end of the spectrum is Harley-Davidson, whose big twins have valve overlaps near zero. Close on its heels is Ducati’s Diavel power cruiser with just 11 degrees overlap. At the other current extreme is Suzuki’s GSX-R1000, with something like 70 degrees of overlap.Where does Ducati’s V-4 fall in this spectrum? Twenty-six degrees. That means good strong torque and drivability. A look at the actual curve shows peak torque maintained from 9,000 to 11,500 rpm with plenty below. That’s drivability.

Not sure where that is measured at though. You could always email Kevin Cameron. Yoshimura, Dan Crower, Honda, YEC (Yamaha), all advertise some racing camshaft numbers if that will help.

[SchmidtMotorWorks]

I have just re-scanned this entire thread and there is a lot of ignorance regarding swirl vs tumble. For most of history nearly all automobile engines had swirl and no tumble. I am talking of course about 2 valve engines. In the correct dose, swirl is highly beneficial. All the texts from Ricardo, Taylor, Heywood etc have sections on optimum swirl rates.

The link below was posted elsewhere in this thread. If you haven't read it yet I recommend you do. It tells you a lot about polyquad.

http://www.motortecmagazine.net/the-fut ... e-engines/

From the article:
POLYQUAD – THE FUTURE OF 4 VALVE ENGINES
Posted by David Vizard | Jan 7, 2017 | Cylinder Head School, Engine Builds

Back in 1999 a patent application was started and these were, at great expense, granted about 2003. If you are a professional head porter and wish to use the PolyQuad concept a license can be issued. A test head is royalty free unless it is subsequently sold. A royalty of 7% will be charged on each PQ head sold. This will be based on the honor system but in case someone thinks it unlikely I will ever find out just remember I have not tens, but hundreds of thousands of readers out there that are, for all practical purposes, undercover agents!

From patentcut:
https://patentcut.com/4703734

Oct 31 1999 EXP: Patent Expired for Failure to Pay Maintenance Fees.