PolyQuad 4 Valve Head: The Best For Both Torque AND Horsepower With Small Displacement?

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PolyQuad 4 Valve Head: The Best For Both Torque AND Horsepower With Small Displacement?

Post by nicholastanguma »

Hello all, first time poster here.

I'll get right to it.

David Vizard says he favors 2 valve heads for real world street engines, including the hot rodded ones. His years of research and development have proven that up to about 4000 rpm 2 valve heads just produce better torque. But his work is traditionally biased toward big displacement low revving 2 valve V8 automobile engines. When he started working with smaller displacement higher revving inline 4s he realized he needed a way to make 4 valve heads not only horsepowerful at the top end but torquey in the low and mid ranges, too. This was the invention of his patented PolyQuad four valve head design. And the design purportedly worked.

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

A small displacement thumper (let's say 300cc) will by nature need to rev high to make good power numbers, since displacement is directly related to torque and the engine size just isn't available in only 300cc to make huge torque. But in a dual sport application the compact size and light weight of a 300cc single cylinder engine are exactly what a rider wants, and the grunty nature of dual sport riding means a rider also wants good low and mid range torque, not just high rpm horsepower.

So, basically, is a PolyQuad 4 valve head design the best way to create a small displacement thumper that will not only make good hp at high revs but also boast the fattest-n-flattest torque curve possible in the low and mid ranges?

I emailed David Vizard himself with this very question, but did not receive a reply.
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Re: PolyQuad 4 Valve Head: The Best For Both Torque AND Horsepower With Small Displacement?

Post by HDBD »

Well Harley blew the doors off of that theory with their Milwaukee 8 engine. They make much more cumulative torque under the curve then their similar displacement 2 valve twin cams. Compression! They live and work well at 235 cranking. Stock heads flow 310+ out of the box.
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Re: PolyQuad 4 Valve Head: The Best For Both Torque AND Horsepower With Small Displacement?

Post by hoffman900 »

A 4 valve head engine will make much more torque and have a flatter power curve than a 2 valve. With more valve area, valve timing can be less. This is what allowed the Ford mod motors to dominate the EMC some years ago before they had to completely rewrite the rules. They also did so with mostly OEM components compared to the bespoke components in the 2 valve engines.

Why people misinterpret this is because they’re comparing on raw numbers and not normalizing to displacement.

Imo, Polyquad is a gimic and maybe a misintrepration of what Honda did in the 1980s for some emissions engines. You don’t want swirl, you want tumble in those heads. Honda, Toyota, etc all have plenty of papers on this and is just a refinement of what Cosworth started in the 1960s with the DFV.
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Re: PolyQuad 4 Valve Head: The Best For Both Torque AND Horsepower With Small Displacement?

Post by CamKing »

A 4 valve can give you more valve area, then a 2 valve, in a given bore size.
In racing, we normally take advantage of that increase valve area to make more hp, and increase RPM. That's why some people think 2 valves make more torque. A 4 valve racing engine usually doesn't make as much torque as it's 2 valve counterpart, because it's designed to make HP at a much higher RPM.
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Re: PolyQuad 4 Valve Head: The Best For Both Torque AND Horsepower With Small Displacement?

Post by nicholastanguma »

Thanks for the replies, gents.

So I suppose general consensus is that:

1) PolyQuad is at best unnecessary and at worst a gimmick?

2) A four valve head IS going to make more torque than a 2 valve head anyway?
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Re: PolyQuad 4 Valve Head: The Best For Both Torque AND Horsepower With Small Displacement?

Post by englertracing »

Ludwig Von apfelbeck created much more extreme 4v swirl heads long long before dv
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Re: PolyQuad 4 Valve Head: The Best For Both Torque AND Horsepower With Small Displacement?

Post by englertracing »

There are some interesting posts here by a fellow named Logan d about oems implementation of high tumble and its benefits over swirl.
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Re: PolyQuad 4 Valve Head: The Best For Both Torque AND Horsepower With Small Displacement?

Post by CamKing »

englertracing wrote: Fri Apr 16, 2021 3:46 pm There are some interesting posts here by a fellow named Logan d about oems implementation of high tumble and its benefits over swirl.
About 18 years ago, I was working with a head porter. He took a well proven NHRA Pro Stock head, and redesigned the ports, so the air would swirl, instead of tumble. Flow numbers can out a little bit higher, but pretty close. There was a lot of man hours put into these heads. Put it on the dyno, and lost over 200hp.
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Re: PolyQuad 4 Valve Head: The Best For Both Torque AND Horsepower With Small Displacement?

Post by hoffman900 »

CamKing wrote: Sat Apr 17, 2021 9:51 am
englertracing wrote: Fri Apr 16, 2021 3:46 pm There are some interesting posts here by a fellow named Logan d about oems implementation of high tumble and its benefits over swirl.
About 18 years ago, I was working with a head porter. He took a well proven NHRA Pro Stock head, and redesigned the ports, so the air would swirl, instead of tumble. Flow numbers can out a little bit higher, but pretty close. There was a lot of man hours put into these heads. Put it on the dyno, and lost over 200hp.
That’s not the same thing Logan was talking about.

A 4 valve engine can always make the same or more torque than a 2 valve engine for the same peak. Packaging, economics, and tradition is what keeps the 2 valve alive.
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Re: PolyQuad 4 Valve Head: The Best For Both Torque AND Horsepower With Small Displacement?

Post by englertracing »

CamKing wrote: Sat Apr 17, 2021 9:51 am About 18 years ago, I was working with a head porter. He took a well proven NHRA Pro Stock head, and redesigned the ports, so the air would swirl, instead of tumble. Flow numbers can out a little bit higher, but pretty close. There was a lot of man hours put into these heads. Put it on the dyno, and lost over 200hp.
That is interesting.
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Re: PolyQuad 4 Valve Head: The Best For Both Torque AND Horsepower With Small Displacement?

Post by CamKing »

hoffman900 wrote: Sat Apr 17, 2021 12:40 pm A 4 valve engine can always make the same or more torque than a 2 valve engine for the same peak.
That's what I said in my other post.
My comment about swirl, was to show that high swirl isn't always the answer.
$ valve engines don't make power, because of swirl, they make it because of valve area.
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Re: PolyQuad 4 Valve Head: The Best For Both Torque AND Horsepower With Small Displacement?

Post by digger »

CamKing wrote: Sat Apr 17, 2021 9:51 am
englertracing wrote: Fri Apr 16, 2021 3:46 pm There are some interesting posts here by a fellow named Logan d about oems implementation of high tumble and its benefits over swirl.
About 18 years ago, I was working with a head porter. He took a well proven NHRA Pro Stock head, and redesigned the ports, so the air would swirl, instead of tumble. Flow numbers can out a little bit higher, but pretty close. There was a lot of man hours put into these heads. Put it on the dyno, and lost over 200hp.
Not sure you can attribute that to swirl without having all the information on air velocity as far as peaks, gradients etc as a big loss of power can be shown when those are incorrect even if you arent trying to maximise swirl.

I'm in the camp that a high rpm race engine should already have enough mixture motion in its useful operating band that it does not warrant specific things to encourage excessive mixture motion .
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Re: PolyQuad 4 Valve Head: The Best For Both Torque AND Horsepower With Small Displacement?

Post by Momus »

nicholastanguma wrote: Fri Apr 16, 2021 9:34 am Hello all, first time poster here.

I'll get right to it.

David Vizard says he favors 2 valve heads for real world street engines, including the hot rodded ones. His years of research and development have proven that up to about 4000 rpm 2 valve heads just produce better torque. But his work is traditionally biased toward big displacement low revving 2 valve V8 automobile engines. When he started working with smaller displacement higher revving inline 4s he realized he needed a way to make 4 valve heads not only horsepowerful at the top end but torquey in the low and mid ranges, too. This was the invention of his patented PolyQuad four valve head design. And the design purportedly worked.

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

A small displacement thumper (let's say 300cc) will by nature need to rev high to make good power numbers, since displacement is directly related to torque and the engine size just isn't available in only 300cc to make huge torque. But in a dual sport application the compact size and light weight of a 300cc single cylinder engine are exactly what a rider wants, and the grunty nature of dual sport riding means a rider also wants good low and mid range torque, not just high rpm horsepower.

So, basically, is a PolyQuad 4 valve head design the best way to create a small displacement thumper that will not only make good hp at high revs but also boast the fattest-n-flattest torque curve possible in the low and mid ranges?

I emailed David Vizard himself with this very question, but did not receive a reply.
What is the specific engine you are working with?

Modern 4 valve 250 MX bikes have remarkably good characteristics.
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Re: PolyQuad 4 Valve Head: The Best For Both Torque AND Horsepower With Small Displacement?

Post by CamKing »

digger wrote: Mon Apr 19, 2021 6:42 pm
Not sure you can attribute that to swirl without having all the information on air velocity as far as peaks, gradients etc as a big loss of power can be shown when those are incorrect even if you arent trying to maximise swirl.
This whole test was done, trying to keep everything else the same.
The original port was done by the same head porter that was trying to make a high swirl version of it. It was also on the most dominant engine at that time.
Velocity was almost the same, Same for cross-sectional areas.
The test was to keep everything the same(or as close as possible), but introduce swirl.
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Re: PolyQuad 4 Valve Head: The Best For Both Torque AND Horsepower With Small Displacement?

Post by BLSTIC »

How do you modify an inline valve engine for tumble anyway? Or is it just "not swirl"? I'd love to modernise some old engines...

Also it's worth noting the Mitsubishi Astron engines here. Apparently their combustion chambers and ports were copied from WW2 Mitsubishi engines and are very high swirl for a hemi (even the exhaust ports are swirl inducing). They work great at 3000rpm but not so well above 4500 despite adequate port flow. Apparently a large part of the problem is at high rpm a high swirl port has a problem with clearing the cylinder at overlap, along with wet fuel hitting cylinder walls. Kind of like when you empty a bottle by spinning it where the water gets forced onto the walls vs flow through an open funnel the same size. Their heads flow 175cfm at .500 for a 40ci cylinder, have equivalent valve/bore ratio as 2.02 and 1.6 on a 4" bore (so, you know, enough), but they don't make high rpm power.
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