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The intake manifold is our big plenum design. We found long ago that the MINI had very poor air distribution though the intake manifold. #1 cylinder didn't get enough air and #4 got to much air, this caused #4 piston to melt even when the average AFR was correct. So we designed the big plenum manifold to fix the problem. Now with the intake the average AFR is correct and the engine makes more power and lives longer. We sell them here - http://www.sneed4speed.com/r53-mini-...take-manifold/
...We found long ago that the MINI had very poor air distribution though the intake manifold. #1 cylinder didn't get enough air and #4 got to much air, this caused #4 piston to melt even when the average AFR was correct. So we designed the big plenum manifold to fix the problem. Now with the intake the average AFR is correct and the engine makes more power and lives longer...
I'm not disputing any of the above, but I'd be interested in Unbreakable Lump's thoughts as pertains to the problem that manifold redesign addresses.
I'm not disputing any of the above, but I'd be interested in Unbreakable Lump's thoughts as pertains to the problem that manifold redesign addresses.
I can't speak to the final production design configuration's F/A distribution directly (I don't have that data). Rover group, who was in charge of the Supercharged adaptation (included Supercharger & intercooler packaging, intake and exhaust manifold), had a very poor initial prototype intake manifold design with terrible part load F/A distribution problems and turned to Chrysler for help since they couldn't meet emissions requirements with such poor F/A distribution. Their design had extremely short runners (40mm if I remember right) and was cross talking between cylinders as a result.
I personally worked directly with a Chrysler CAD designer to give Rover a design that would work. We rapid prototyped a part in a few weeks, tested it and it worked perfectly. F/A distribution was something like +/- 2% cylinder to cylinder (I think that I have actual data on this somewhere that I can look up later). The design that we gave them did not have the flat surface on the forward edge that ended up in the production part and had more "dead head" volume at the end of the plenum (at #1 cylinder) which is important to airflow on that cylinder (especially for a log type manifold). The manifold that we designed would not fit without Rover moving the radiator further forward (which they did by 20mm), but it appears that Rover took this initial design and modified it by putting in that flat spot, which reduces the plenum volume and reducing the dead head volume. It also looks like they pinched down the plenum at the end, washing out the nice bellmouth entry radii, which would hurt flow into the #1 cylinder. I left the program right after production launch of the base engine but before the final production release of the supercharged engine. So I don't doubt that the final production version, with reduced plenum volume, flat spot on front, and less than ideal dead head volume, causes a F/A distribution issue at WOT.
Holing a piston is almost always a result of pre-ignition (not to be confused with detonation, which is completely different). And pre-ignition is due to a hot spot in the combustion chamber (almost always the spark plug electrode). And that hot spot almost always is due to running too lean, raising combustion temperatures and EGT's. This is what always gives me pause about aftermarket tuners doing tunes based on AFR and not EGT's or basing AFR's on seat of the pants experience or general guidelines. EGT's when you're making 250 HP are going to be a lot higher at say 12:1 AFR than they will be at 12:1 when you're making 170 HP, although reducing backpressure and opening up the exhaust ports helps quite a bit.
Last edited by Unbreakable Lump; Mar 18, 2016 at 11:45 AM.
The intake manifold is our big plenum design. We found long ago that the MINI had very poor air distribution though the intake manifold. #1 cylinder didn't get enough air and #4 got to much air, this caused #4 piston to melt even when the average AFR was correct. So we designed the big plenum manifold to fix the problem. Now with the intake the average AFR is correct and the engine makes more power and lives longer. We sell them here - http://www.sneed4speed.com/r53-mini-...take-manifold/
I have heard of this as well with some models creating more power using spacers for the intake manifold. Does it require any modification to upper radiator hose ? Just realized that is the Larry Phaff designed MINI !
