MPI supercharged Apex w/ methanol injection

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Conrad Greene
5 years ago
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1 MPI supercharged Apex w/ methanol injection Woody s Performance Center (Yamaha sleds and bikes) from Topsham, ME built this 1223cc Apex drag engine for asphalt and ice dragracing. This was a high-buck project, probably $15K in engine mods as follows: 1) block bored 4mm and renickasiled, coolant passages filled with Devcon epoxy, Wiseco oversize flat top 12.5/1 pistons, larger 12mm head studs. 2) Head mildly ported, Full power valve springs, coolant passages filled w/ epoxy, oring grooves in [copper] headgasket surface (stock cams retained). 3) Crankshaft Supercrank by Falicon, stroked 6mm, liquid N2 treated, Falicon knife-edge rods. 4) MPI stage 3 centrifugal (Rotrax) non-intercooled supercharger kit 5) Autronics stand-alone fuel/ spark management system 6) Dyno tuning here to create proper fuel/ spark map Woody purchased the Autronics Australian fuel controller from Enzo Performance ( in Long Island NY with a spark management unit tacked on. This controller system measures RPM/ throttle position/ boost to provide correct A/F ratio and ignition timing for the conditions, when programmed correctly. Enzo has used these same units for many years boosting/ methanol injecting six second import dragracers. It came with four injectors large enough to pump HP worth of methanol. Woody s son did a masterful job with the wiring of the Autronics unit from TPS to crank trigger to coils/ injectors, all connections soldered/ protected with heat shrink tubing. As part of the package he supplied to Woody, Enzo came to DynoTech with his own laptop/ wideband O2 sensor equipment to help tune this engine, on methanol, to big HP. Enzo had pre-loaded an existing map into the ECU, one probably used for a four cylinder 500 HP methanol engine of some sort. I ve talked at length to Enzo and other engine builders about the benefits of methanol as a fuel. In the DTR archives I m sure we did a Rotax twin for a FL midget racer, tuning for max HP Naturally Aspirated on race gas then on methanol I think we picked up maybe 5% HP. But methanol fuel shines with boosted engines. High octane (130ish?) combined with O2 in the fuel plus very high heat of vaporization = low compressed charge temps and the ability to run high compression, and lots of timing and boost reliably. Enzo talks about some of his turbo cars running 50 psi boost with lots of compression and timing. And Enzo really likes the wide window of explosive limits of vaporized methanol/ air vs gasoline/ air. And equally important is the compressed charge mixture s resistance to detonation. On the dyno we spent some hours sorting out a misfire that turned out to be caused by improper wiring/ sequencing of the coils firing each plug. Once the engine was running cleanly with four cylinders firing in correct order, Enzo s final mapping was straightforward. I held the engine steady-state in 1000 rpm increments from RPM, varying TPS and HP as Enzo observed A/F ratio. He quickly corrected rich/ lean areas as he found them, clicking the computer keys as quickly as my nine year old son does while

2 playing Total Immersion Racing on his mom s Mac. Within an hour or so, we had good midrange fuel tuning. The rest of the tuning for this drag engine was full throttle sweeps from 5000 to wherever HP dropped off. Enzo jockeyed fuel and timing around until HP was just the safe side of maximum. But even with the overdrive pulleys supplied for big HP by MPI boost hovered around 8-9 psi from low revs to high revs, which kept HP low, and bewildered me. Centrifugal superchargers typically build boost pressure as the square of engine speed, and this was low and linear. After Autronics tuning optimized this was the HP/ boost curve of the SC Apex with 25 top, 27 bottom toothed belt sprockets. Note that since Enzo was monitoring A/F on his own equipment, we don t have that on our dyno data. mod air filter on EngSpd STPTrq STPPwr BOOST TsTim2 AirTmp STPCor BMEP RPM Clb-ft CHp IN HG second degf Factor psi

3 Even with the oversize engine, according to MPI we should have been making way more HP and boost with whatever RPM this oversize supercharger was spinning. Moreover, the flat turbo-like boost curve was perplexing. Centrifugal superchargers increase airflow/ boost as the square of turbine speed if you re making 8 psi at 7000 RPM you should make 2 psi at 3500 clutch engagement, and then should make 16 psi at 10,000! That s basic supercharger math. Rising intercooler heat will flatten that boost curve out a bit, but here we have no intercooler, deemed not necessary with the high heat of vaporization of the methanol keeping charge temperatures low. That flat boost curve indicated to me that the friction drive from the intput shaft of the SC to the compressor wheel shaft may be slipping. But Woody popped off the foam air cleaner on the inlet of the supercharger. Since this supercharger is larger than normal, there was not much room between the compressor inlet and the right frame rail, so Woody had to cut the filter down for clearance. I was leery, because small filters don t hurt turbo boost much I have the most personal experience dyno tuning turbo things, and turbos will just work harder to create the boost they re programmed to make regardless of intake restriction (up to where the turbine inlet velocity reaches the speed of sound where I ve seen airflow CFM flatline). But belt driven superchargers are more sensitive, as this dyno test shows. Here s Woody s engine, five minutes after we made the previous dyno test shown above. Note that as expected the Autronics ECU correctly adjusted fuel for the newfound airflow/ boost. This is what I call a Chicken-Out dyno run, aborted early because I didn t like something while accelerating through the engine s powerband. Something is either A/F ratio going lean, BSFC going below preset limits (computer screen gauges become bright red), real time HP curve on the screen dropping, or something awry in the dyno room from vibration etc. or small black parts flying. In this case, the digital HP gauge blew over 400 HP which I caught in my left eye which surely startled me and I stopped the test before we hit the HP peak. filter removed EngSpd STPTrq STPPwr BOOST BMEP AirTmp STPCor TsTim2 RPM Clb-ft CHp IN HG psi degf Factor second

4 Note that the HP was climbing stoutly with boost rise, with no indication that it was tailing off. Could we have made 450 or more at close to if I hadn t chickened out? The good news for me is no one ever complains when I chicken out and abort a dyno run on an engine with $15K of mods if I see something scary. After this test, we decided that indeed the chopped down air filter was the culprit! Superchargers are gear/ belt driven and any inlet restriction, as this test data shows, will cause lower boost, diminished airflow. Now the rpm/ boost curve made sense for typically slow-to build centrifugal superchargers squared is 58 million compared to squared being 100 million, and boost is now increasing as expected, as the square of RPM. So I was now mentally prepared for well over 400 CHP, and I let the engine run through its powerband again. This time, though, a ball of fire appeared behind the engine, between head and block (a fireball in the dyno room is another reason to abort a test) at 10,200. Subsequent inspection indicated that compression had been permanently lost in cylinder four between copper headgasket and head sealing surface. But the sparkplug was fine, no indication of deto. Woody recalled that the Oring grooves in the head were cut too large, requiring orings to be glued in instead of tapped in with a hammer. Then the left side of the head was late squeezing down to the block, meaning that either the oversize studs were interfering with the head or maybe the #4 oring dropped loose from its groove as the head was installed. Either situation would compromise head seal. The autopsy has yet to be performed results will be in the DTR blog.

5 Woody is psyched up now. Methanol, gonzo boost and good fuel/ spark management make 500 CHP doable with this package and Woody would get enjoyment from being the first into the 500 s. Next will be the challenge of putting 500 CHP to the ground through that skinny rubber drive belt.

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