Thanks, Bryan.Bryan Maloney wrote: ↑Thu Sep 23, 2021 5:47 amThe swirl control was tied in with keeping the tumble moment arm value low. I don't recall the BSFC being improved much, but the engines seemed to better utilize the .894 net intake valve lift we were running at the time.hoffman900 wrote: ↑Wed Sep 22, 2021 7:14 pmBryanBryan Maloney wrote: ↑Sat Sep 18, 2021 11:20 pm We had swirl, tumble, and wet flow test equipment available as part of Dodge's Nascar effort from 2000 to 2012.
We measured swirl as rotational torque with a honeycomb insert and a rotary strain gauge. Tumble was measured on another fixture with a perforated plate and three load cells. Data from the three load cells gave us total combined tumble torque, and more importantly, the force location defined as distance from the bore center and clocking in degrees.
We found that the swirl and tumble combined define the helix of the incoming air column in a two-valve chamber.
As Mummert stated, the swirl tends to jump up at low lift, lag behind in the mid-lift, and ramp up again at high lift. The tumble curve tends to do the same. The tumble force location (we called it "moment arm") moved closer to the bore center as the intake valve opened, and moved away from the bore center rapidly at high lift, when the swirl was spiking.
Our conclusion was we needed a smooth, linear increase in the swirl as the valve opened; not a set value.
To manage the swirl, we worked with chamber containment of the flow cone, runner trajectory, and some slight steering with the fin behind the guide. The flow must stay attached to the short-turn; swirl and tumble go out of control if there is separation. The modern steep seat and top angles really helped.
Reverse swirl fins behind the intake guides can improve burn uniformity, BSFC, and help prevent the swirl from spiking at high lift.
If you can do some wet flow testing on your cylinder head, you will be mesmerized by what you see. It will tie in with your swirl and tumble observations.
What did you guys see by focusing on tumble after the swirl intensity was contained? Improved BSFC? Did you guys every get as far as getting the tumble portion modeled in a CFD program with a modeled piston top? How did you guys go about managing tumble short of moving the entire intake port angle?
Thanks
We didn't see any CFD modeling on our race engines back in 2004, but later I saw a simulation on a production engine that showed a dished piston allowed better tumble continuation after BDC. We ended up running a small chamber and a shallow spherical dish in our race engines; as many others had.
Tumble management boiled down to chamber containment, and runner short-turn/ roofline height. Twist in the intake port floor can have some affect, too.
There are some good papers on tumble in engines, the self-published ones from Honda (free) are interesting. There is also a SAE one during the design process of the "new Hemi" about mixture motion / tumble. Interesting comment about being able to use the valve lift, I'll have to think about that for a minute...
Here is what Randy Gillis (formerly of JE Pistons, now at Racetec. Also ‘piston_guy’ on here) said eons ago here about dish shape.
I suspect a good part of what they were seeing was keeping tumble active longer due to the dish design.I did the first "tapered" or conical dish pistons for (then) Busch series engine builder Frank Leeson of Bill Davis Racing . He approached me with the idea and we made some test parts for him. Several dimensions were changed and those changes had a very clear affect on performance. One critical aspect was the width of the "perimeter squish band". Frank and I morphed the piston into the "spherical radius" from the conical due to the need for increased negative volume. After a couple of weeks I was contacted by Bob Fisher ( then of Ernie Elliott Inc) who was building engines for Bill. I gave both of them a 1 year exclusive on the design and development. Both did extensive back to back ( spherical to mirror image dish) testing . The spherical required at least two degrees less timing and always made a significant improvement to torque with a smaller improvement in HP. We figured combustion efficiency was responsible for that. There was also a stability condition. the feeling was the load was focused in the center and not offset by the mirror image dish. After the year was up , I offered the design to a west coast Craftsman truck ( then) engine builder. He was extremely skeptical and wanted no part of this "dumb design". I offered to ( and did) make two sets of equal pistons weight , rings, skirt profile, dish volume , etc . except for the dish design. The deal was to test the "conventional" design he was using first and then ( while still on the dyno)) pull it down , change the pistons and use the same used rings , and test it again. The result was a 10 hp 13 ft lb increase in power with 2*s less timing required. We didn't "invent" the concept , it was already out there on Hondas and other imports, we just adapted it to the V8 engine. There would eventually be a few cases where results were neutral as far as power increase but we did the design on all kinds of pistons. None made LESS power. I still use it today
Warp speed should remember when the concept hit and how soon it became available from every piston supplier. He might even have some comments on it.
Your work, Randy's comments, etc. are pushing 20+ years old now, so certainly not new concepts in the racing 2 valve V8 arena at the top end of things, and certainly not in the OEM / racing 4 valve world (though they seem to have figured it out a lot better in the last 15 years). I don't think enough builders beyond the top pro world pay attention to it.
I'll have to dig up Honda's tumble meter design. They have an illustration in one of their papers and they were using it to validate their CFD models.