[Mikeyboy(uk)]

Hello David,

I have read the article relating to your Poly quad head and think I ought to point out a couple of things which I think may provoke a bit more discussion.
I think that the swirl velocities found toward the outside of the cylinder would be a better place in which to site the plugs (I think you would need two small plugs sited in a higher speed zone to take more advantage of the swirl). This is based on the effect I have seen over here with none other than the good old A series engine. I had a motor in that gave very good top end horsepower but useless torque compared to one of mine, even though they both used 310 scatter cams. The most notable feature of this engine was that the port had no where close the same amount of swirl as my head, but the same overall flow. My motor was reluctant (by comparison) to rev, but made massively more area under the curve and felt much, much stronger to drive. The other one however made its power past my peak power speed and was the faster engine on fast circuits. I attributed this trait to the lack of swirl on his head. It is my belief that swirl is RPM related, too much and you cannot rev the engine as high as you can with a lower value ( in this case 7600 for mine, 8700 for his), BUT you get way better driveability with swirl.
My point here David is that the plug position being out farther from the centre may lead to even more low end torque than PQ currently shows (on the PQ head). My head required less ignition timing than his for the same CR. The plug was in the line of fire of the swirl, his plug was effectively in a stagnant area due to lack of swirl.Plug position is important relative to the swirl axis. My belief is that if you swirl on cylinder centre line, your effective swirl at the plug (lets face it-that is where it counts!), is zero. This would seem to me to be a non-desireable situation.

However, I think you would need two plugs to get the job done. What would be useful is to know the ratio of tumble to swirl shown in your PQ charge motion drawing. If swirl was the dominant force (not tumble, trumble?!) then I feel the above is justified. If tumble pre-dominates, then no, leave the plug where it is in the centre.

My second point is regarding the valve periphery. With any 4 valve engine, the long timeframe (low rpm) allows much more reversal to take place at low rpm compared with a 2 valver. It is even worse with a 5 valve- a head design I have 20 years experience of playing with.(Old now you see!!!) A 5 valve is hyper sensitive to cam timing and in particular, seat duration. The excessive peripheral flow means that motors are sensitive to tiny cam timing changes. To give you an idea, on the flow bench, a 5 valve flow chart looks as though you have missed a station out and everything is moved one lift increment early. So what I am leading up to is, I think your article should have pointed out that the valve circumferences with PQ are less than a conventional 4 valve, so therefore this may account for some of the low end torque gains.

I have some more ideas for you on this subject but I am so slow a typist that I will save the discussion for when I see you or when we talk on the phone.

Keep up the good work, great online magazine full of interesting articles.

Regards Mikey.