|The MGA With An Attitude
VELOCITY STACKS #3-- PP-104B
Pictures above show the new plate fixed in place with two-pack epoxy. First impression on test drive was, "WOW, nice throttle response, and quieter air intake". A second set was machined up and dynamometer tested by N McGurk in Cumbria, UK. This page shows results of that dynomometer test.
Dyno run in standard configuration, above.
Dyno run with stub stacks added, below.
Click on images for larger printable PDF images.
On 12 October 2011, Niel McGurk, Cumbria, UK, wrote:
"Well, the results are in! The car was dyno tested this afternoon a couple of runs without stacks and again with stacks. Those were the only tests I did as my car was not in particularly good tune! It was running very weak at idle, rich at mid revs and slightly rich at higher revs and so the tester recommended changing needles before doing a complete re-tune.
"I would make some comments on the design as I believe there are some (minor I hasten to add, Steve) improvements that could be incorporated. At the base of the retaining columns on the filter housing back plate there are small raised sections (that are spot welded to the back plate) to secure the columns. See picture. Providing clearance for these and a little more clearance for the columns would make the stacks a simple no modification fit. These are 3/4" in diameter and 1/16" high so the recess on the bottom of the stack should be increased from 0.68x0.07 to 0.78x0.07 minimum.
I had to file the 0.5 pillar holes slightly to fit over the pillars so would recommend increasing to 0.52 to allow for pillar thickness and position. In order to fit the stacks easily (without resorting to the grinder) I made up a couple of 1/16" thick cork gaskets. These allowed the stacks to fit flush to the back plate. There was an added benefit in that my filter elements were no longer loose and I could finally get rid of that 50 year old felt!
"Here are the results:
Peak power increased from 88.03HP at 4,641rpm to 92.31HP at 4,601rpm and peak torque increase from 104.4ft-lb at 4,350rpm to 107.4ft-lb at 4,350rpm. There were a couple of runs on each (without, then with stacks) and these were the best of both. As soon as the second set started the tester said there was a definite difference. It is possible to tell the difference on the road too. Definitely a more "lively" feel is how I would describe it".
That makes it a 4.87% increase on HP and 2.87% increase on torque. Very impressive for such a small part.
On 13 October 2011, Willem vd Veer, The Netherlands wrote:
"Will the next step be the 'flowing' of the internals of the SU carburettors? David Vizard wrote a chapter on this in his book 'Tuning the A-series engine'. With his modifications you can make any SU flow like the next larger size SU. Especially the sharp internal edges, the screws of the throttle disk and the shape of it's shaft cause a lot of flow robbing turbulence. I did most of the recommended mods on the single H2 fitted to my YA and was amazed by the increased livelyness, so I'm not really surprised by the dyno results".
On 13 October 2011, Colyn Firth in South Yorkshire, UK wrote:
"I have read in Steve Strange's amazing MGB engine tuning manual (known as "the book" on the MGB forum) that the stub stacks were worth an up to 5% improvement on the MGB engine".