PolyQuad - A new four valve power concept

[DavidVizard-GFN]

Randy,
Glad you like the PQ story but lets face it I had to put on a good show because you're one of the guys setting the standard!

[jerminator96]

Originally Posted by DavidVizard-GFN

Mikey, I am interested in your thoughts as to how the high performqnce street motorcycle guys might recieve PQ technology.

DV

I have a test head for you whenever you want it David.

Jeremy

[MadBill]

David's last post supports the observation that having the plug at "the eye of the (swirl) hurricane" might not the best way to go, but I had understood that under the influence of the rising piston, large scale swirl (and tumble) was thought to decay into more chaotic and unpredictable turbulence. If so, the optimum plug location would be indeterminate...

[Mikeyboy(uk)]

Hi David,
yes I can send you the whole story regarding the swirl/no swirl Mini heads and engines. It may take me a while, but I am sure I can get something sensible to you soon.

Hmm, PQ on a motorcycle head-now there's an interesting thought. I think that the main area of interest would be for off-road uses, such Moto-X and Enduro, as all out race motors need all the power they can get, along with smooth, linear power curves. With Road Racing, if you put too much mid range into the motor you just burn the rear tyre too quickly in most Superbike races. However, off-roaders like to have power "Right Now" in most instances, so I think this may be the best area to explore with PQ.

I will put my thinking cap on for you on that one!

Keep it coming David, top quality articles are everywhere on this site.

Mikeyboy(uk)

[Kenny]

Hello David,
I have a (underfunded) startup company that does high performance parts for 4-valve single cylinder engines. I mainly modify throttle bodies, I have a fairly large following, and an even larger market. I would be very interested in working with your design and if the power is there, would be more than happy to send a percentage of that "green paper" your way.
I have two totally different situations and both seem to be somewhat addressed here. The large 686cc single, that is gonna be my mainstay(for now), is a sohc roller rocker arm design that I have redesigned the rockers for, and I won't have much worry with low lift flow, since I won't be spending much time there. The 450cc factory competition type engines are of shim and bucket design that HAVE to have low lift flow numbers. One thing I notice about modding the TB's is that, on the smaller engines, they like a straight bore without any kind of entry angle, with a sharp throttle plate and a swirl polish finish. This would seem to indicate that some inlet turbulence is beneficial.
I have the capability of having a local guy CNC these heads for full on production, who is willing to make his money on the back side. The problem I have is one of limited funds so I would have to do the R&D myself. That being said.... I would like to be able to pick your brain on what you have found to work best for valve seat shapes and how does it work with steeper valve angles?
I also have the opportunity to increase this market substantially with some builders overseas, which are working the same market in their respective parts of the world.
I would welcome any input. My contact info is kdsracing@gmail.com, my phone is 540-392-4929 and my name is Kenny
Thank you very much for your time,
Kenny

[TDIMeister]

Greetings David, from Germany!

May I first say what an unusual honour is it to be able to interact directly with you in-person through this forum. I have read all your books and regard you as a celebrity! I am a 9-year member and moderator over at the TDIClub.com forums, and am myself a powertrain engineer currently working at an engine development consultancy here in Germany, after deciding to take a mid-career hiatus and go back to school to undertake grad studies in engines. Day job aside, I have done tuning modifications and amateur motorsports (Solo 2, drag racing, track days) with my former daily driver (I am not native German).

I read through your concept with interest, and had a few questions I hope you’d entertain addressing. My first is a question regarding the swirl induced by the differently-sized intake valves- and ports: It would seem to me that, given the same valve lift, and what appears to my naked eye as a relatively small amount of port division biasing, the flow through the smaller valve would actually have a greater velocity and therefore momentum to influence the swirl. Am I missing something?

Second is a comment/question, that the importance and significance of valve masking cannot be understated in your concept. In fact, may I be so bold to say that masking has as much- or more of an influence on the in-cylinder flow-field than the difference in valve diameters. Now, I’m sorry for my newbie-ness and maybe you have already covered the subject in detail elsewhere (I’m just now reading up on the multitudes of threads here, having joined only today), but I would like to read your experience and thoughts on valve masking. Also, your stated increased tendency of 4-valve heads to “cross-flow” would seem to also affect hemi-heads as well (if not more so), and is a function of valve included angle and the downdraft angle of ports.

Third relates to my sphere of interest, and that is tuning VW’s TDI Diesel engines. Here, there are some rigid boundary conditions that need to be met: the valves are completely vertical, and there is no combustion chamber in the head per sé; most of the clearance volume is in the omega-shaped piston bowl. Due to the very close clearances the pistons come to the closed-valves, the valve timing does not tolerate much if any overlap; in fact, OE specs have IVO at 16 deg. ATDC and EVC at 16 deg. BTDC at 1mm lift – yes, negative overlap of 32 degress!!! I have designed a cam that tries to minimize this negative overlap as much as possible, particularly closing the exhaust valves as late as possible before the pistons slam into them, in order to minimise the substantial residual gas recompression work that I was observing in my simulations.

To make a long story short, the ports, valve timings and flow area on the TDI are clearly not developed for high flow (tiny valves, only about 8.5 mm lift, and helical ports to induce vital swirl for Diesel combustion efficiency). If the flow can be improved while maintaining swirl, there could be significant potential for this engine.

Lastly, I have been working on an engine design that would have a displacement of 500 cc per cylinder. My goal is to achieve a specific power output of 167 HP/L naturally-aspirated! I have calculated that peak power would have to be developed at 9250 RPM and a BMEP of 16.1 bar (234 PSI) at this operating point. My question is, in your experience, are such BMEP figures attainable, particularly at such RPM without too much sacrifice at lower RPM? I have read Cosworth’s DFV engine of 1967 making 203 PSI at 8500 RPM, and Cosworth-prepared Super Touring race engines claiming 254 PSI (!!!) at max. power RPM.

All the best, I greatly look forward to hearing back from you.


Cheers,
Dave

[TDIMeister]

Greetings David, from Germany!

First of all, allow me to say what an unusual honour it is to be able to interact directly with you in person through this forum. I have bought and read all your books, and I consider you a celebrity! I am a 9-year member and moderator over at the TDIClub.com forums, and I am myself a powertrain engineer currently working in Germany at an engine development consultancy, after deciding to take a mid-career hiatus to go back to school and undertake grad studies in engines. Work aside, I have been involved in performance modifications and amateur motorsports (Solo 2, drag racing and track days) in my former daily driver (I am not native German).

I read your Powerquad concept with interest, and hope that you would entertain some questions I have. First, it would appear to me, given the same valve lifts and what appears to my naked eye to be a relatively small amount of port division biasing, that the narrower port and smaller intake valve would have a higher flow velocity and therefore momentum to influence the swirl direction rather than the bigger valve. Am I missing something?

Secondly, I have a comment/question that the influence and importance of valve shrouding cannot be understated in this concept. In fact, if I may be so bold as to say, I think shrouding has as much- or more impact on the in-cylinder flow-field than the difference in valve diameters. I’m sorry for the newbie-ness (I’m still going through the large number of threads, and I just signed-up today), and maybe the subject has already been covered in detail elsewhere, but I would love to read more on your experience and thoughts on valve shrouding.

Thirdly you mentioned the greater tendency of 4-valve heads to “cross-flow.” Looking at the illustrations, it would seem that this would affect Hemi heads as well, if not to an even greater extent, and this tendency would be more functions of valve included angle and port downdraft angle, as well as shrouding.

Fourth, is a question related to my sphere of interest, and that is tuning VW TDI Diesel engines. These engines have some special rigid boundary conditions that need to be adhered to: the valves are perfectly vertical and virtually flush to the cylinder head deck surface, so shrouding plays little role. The intake ports are helical-shaped to induce a high amount of swirl that is vital for combustion efficiency. There is no in-head combustion chamber per sé, but most of the clearance volume lies in the omega-shaped piston bowl. Because of the very small clearance between the pistons at TDC and the closed valves, these engines tolerate very little if any overlap without machining deeper valve relief pockets on the piston. In fact, OE specs have IVO at 16° ATDC and EVC at 19° BTDC at 1mm lift – yes, that’s right, 35 degrees of negative overlap!!! Some years ago, I designed and made a small run of cams that tried among other things, to minimise this negative overlap as much as possible, particularly closing the exhaust valve as late as possible before the pistons crash into them, in order the reduce the substantial amount of residual gas recompression work I was observing in simulations.

To make a long story short, the TDI cylinder heads are far from being designed for high flow out of the box (conservative valve timing, tiny valves, only about 8.5 mm lift, helical swirl ports). If anything could be done to improve the flow of these heads while maintaining swirl, there is great potential for performance improvements. A write-up on this subject would be amazing, and I can provide a large number of illustrations in support of that, and even arrange to send a head your way for you to do your magic on it.

Lastly, I have been working on an engine design with a displacement of 500 cc per cylinder. My goal is to achieve 167 HP/L naturally aspirated with the broadest possible torque curve. I have calculated that peak power will have to be at around 9250 RPM, with a BMEP of 16.1 bar (234 PSI) at rated power. I have read that the Cosworth DFV of 1967 developed 203 PSI BMEP at 8500 RPM, and Cosworth-prepped Formula 3000 and Super Touring race engines based on production castings have been claimed to make 238 and 254 PSI at peak power, respectively. My question is, in your experience, are the BMEP figures I am targeting achievable at this RPM level for a street engine without too much sacrifice at lower RPM? To rephrase, what is the highest BMEP that you’ve seen at the lowest RPM?

Thank you very much in advance, and I greatly look forward to hearing back from you!




Cheers,
Dave

[Dusty]

If the pressure head is roughly the same at each valve the velocity should also be roughly equivalent. If my thinking is right the difference in kinetic energy between the two ports is caused by the mass flow rate difference. That being said maybe thinking of the bias between the two ports as a difference in energy as opposed to flow may be beneficial.

[williamsmotowerx]

I had tried something similiar to this with a different approach at the time. '04 was the year... and 4 strokes really became popular in the motocross community.

Because of the rear shock, the airbox snorkel is biased to the left. The 4v head has a common intake port that splits in the middle. Because of this bias, the left port is shorter than the right port by a fairly large margin. To compensate for this I used an oversized valve on the left shorter port to try and equalize flow. This is pretty much exactly the opposite of what you're accomplishing here David.

My conclusion on the dyno, it ran exactly the same... no change.

Just thought I'd share my findings on the opposite of what this article is showing.

[DavidVizard-GFN]

Bill at motorwerx,

Did the bigger valve equal the flow of the two valves? if so the flow should now be greater - why then did the power not go up.What are your thoughts here? Wedre there other factors interacting?

DV