[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