Don Terrill’s Speed-Talk

I have been asked to develop a race cylinder head for a 450 cc Yamaha single motocross bike. The bike will be used for beach racing over a 500 and 750 metre course over 4 laps around barrels st either end of the beach. The rider is competitive in motocross and enduros.The class is very competitive with a good deal of rule interpretation and very little scrutineering. I would like to explore the poly quad concept and better understand the benefits of this valve layout. A quick search here was unsuccessful. Not asking for a handout but would like to hear the benefits and the theories on how the benefits are achieved. I believe DV has been instrumental in the development of this technology and it is mentioned in one of his books.Is this technology making it into mainstream 4 valve performance mods, or is it still in the top secret department. Any feedback would be appreciated on this topic. I have access to an S&G machine and a flow bench. I have to admit to only working on 2 valve stuff to this point but have an experienced mentor on 4 valve motor cycle race engines. Any thoughts that you care to share will help as I am not clear on the theory.

There's quite of bit of information on the Internet from a Google search...Maybe start there?

D.V. owns the patent on the Polyquad design. You can look up the patent. The basic Idea is four different sized valves as to add swirl to what is a tumble design head. If done properly the total intake and exhaust flow will increase along with a quicker burn time. I always though careful port biasing would help this design. Taking it to the next level each valve could have a different seat angle to start flow at a different point or even a different lobe design for each valve. Expect some testing! Thanks, Charlie

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

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.

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.

But its more fun to believe in Santa Claus.

We accomplished the same thing, by leaving the valve sizes alone, and changing the centerlines for each valve.
We opened and closed one intake valve, before the other one, and opened and closed one exhaust valve before the other one.

This article by DV would be a great place to start.

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

From

viewtopic.php?t=28614

Incidentally, somebody in that thread talks about Honda and Kawasaki 450's. May be of interest or you can try to contact sbcharlie directly.

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.

I was also thinking along the lines of there being more opportunity in tuning to include gearing etc.

But his opportunity is for the head. I guess the biggest opportunity there is in refining shortcuts that were made for low cost manufacture.

When I was at Honda I saw lots of details left undone that looked like they would make a difference. They turned not to add up to much and put unwanted variables in future tests.

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.

The "poly" heads are used instead of variable cam timing ?