Just got back to the house after dropping Mitch off at the airport and thought I’d write an update. It’s going to be long, as usual, so apologies in advance.
The dyno session was very successful after we sorted through all the usual issues. And although, we didn’t hit my personal goal of 500 HP at the flywheel, we did make 498.3 HP @ about 6800 RPM, so we were close enough to 500 to taste it. What a fantastic learning experience that engine dyno provides! But before I jump into the lessons learned, first, here's a summary of my motor build and the initial setup we had for this dyno session:
The motor is out of a 1993 SC400, and it’s been built with Lextreme forged rods, forged & coated Wiseco pistons, 9:1 compression, 460cc injectors, Lextreme Stage 1 cams, Manley SS valves, street ported heads, 2UZ piston crown oil squirters, and 12mm ARP head studs. Ignition is a wasted spark COP system of my own design, using Toyota Tundra coils. We’re exhausting through a set of S&S headers, and going into twin 2 ½” straight pipes out of the dyno cell.
The forced induction setup is an Opcon Autorotor 422 supercharger on a Richwood manifold, driven from an 8 rib serp belt. Crank dampner is a 157mm Richwood unit, and supercharger pulley is 91mm (15psi). Throttle body is a bored out GM LSx with a 78mm butterfly.
There’s no intercooler, but we initially were injecting a 50/50 methanol water mix straight into the intake of the supercharger, at a rate of around 500ml/min (375ml/min Snow nozzle running at 175psi via a Shurflo pump) at WOT & 15psi of boost. M/W injection is linear according to boost (PWM controlled from the AEM EMS, and we're running a maximum of 75% duty cycle.)
Engine management is an AEM PnP Supra unit, tuned by Mitch Pederson (ex-AEM & ex-EFI Technologies design & support engineer)
The engine dyno we've been using is a Superflow SF-901 at Faerman Racing Engines in Houston TX. (713) 686-7909. Dennis Faerman has been a master engine builder for 35 years, and a personal friend for the last 8.
For this dyno session we were initially running VP Racing fuel type C14, and then finished this afternoon with C16.
OK, here's some interesting things we've learned about this setup on the dyno (keep in mind that Mitch is a degreed mechanical engineer and has been involved with engine theory, development, and tuning before, during and after university, and has had both lab and racetrack tuning experience, and it definitely shows in his methodical process for the setup, tuning, and problem diagnosis.)
Air Distribution Problems:
As the Opcon supercharger's air discharge is directly above cylinders 1/2/3/4 we found these front cylinders were robbing the rear 4 cylinders of intake air at idle and low load. This situation smoothes out somewhat once the manifold is pressurised. A normal tuner probably would not have noticed this as Mitch used some unique techniques to pinpoint the problem and he had to richen up the front injectors by about 15%. Those of you who are running ECU's with individual cylinder injector trims can compensate for this, but those who are running batch fired injectors, well good luck. You'll probably need to fabricate something to help distribute/diffuse the air going into the cylinders better. This is not a criticism of the Richwood manifold, as it does not pretend to be optimised for every supercharger, but is a "one size fits all" manifold and owners should take this into account when using it. Any other supercharger manifold I've seen on this forum would have the same problem. Interestingly, once the manifold pressured up, Mitch had to take out this extra fuel, because the front 4 cylinders were then running too rich.
M/W Injection:
In theory, injecting the M/W straight into the supercharger should have helped us approach a very efficient case of isothermal air compression, however this did not prove out on the dyno.
We found that injecting the 50/50 M/W mix pre-supercharger did very little for our intake air temperatures, as we were seeing nearly 200 degrees F in the charge air at 15psi of boost. We changed to straight methanol, still injected it pre-supercharger, and still saw 180-190 degrees. This was with an ambient temperature of around 90-95 degrees in the dyno cell. This high charge air temperature was keeping us from running any timing, and hence we made no power.
We then pulled the manifold & charger off and relocated the main (375ml/min) methanol nozzle to the front underside of the manifold so that it's spraying the methanol vertically, straight into the discharge of the supercharger. Then we added a 2nd (225ml/min) nozzle at the rear of the manifold, so it's blowing the meth forward. Ideally we would have mounted this one in the underside of the manifold as well, but the starter motor blocks this area. Both methanol nozzles produce a cone shaped pattern, which is fine for the vertical nozzle, but probably isn't optimum for the rear mounted one, and I'll need to change that one to a fan pattern.
With this setup we were able to cool the charge air to within 10 degrees of ambient, and after a couple of light load pulls, we actually saw a "bounce" in air temps to 20 or 30 degrees below ambient.
Supercharger Drive:
With the 91mm (15 psi) supercharger pulley, the 8 rib serp belt arrangement held up fine, although we were getting a fair amount of belt "flapping" on the slack side. To be fair, we don't have any of the "normal" accessories installed, so we had probably 18-20" of unsupported belt there. Too, we only had perhaps 140 degrees of wrap on the charger pulley for this test setup. Still, a 10 rib setup would be preferable, or possibly a dedicated 6 or 8 rib drive belt "just" for the supercharger as Zuffen is doing for his setup.
Outstanding issues:
We didn’t make my personal goal of 500 BHP, even after changing the 91mm charger pulley to a 78mm (18psi), however with the 18 psi pulley, we did find the limit of the 8 rib serp belt setup, as it was consistently slipping over about 16-17 psi of boost. I am now thinking that to run higher than 15psi, even with these efficient twinscrew chargers, will require at least a 10 rib serp belt setup (if shared with the other accessories), or a dedicated 6 rib belt just for the charger, or a toothed Gilmer belt setup.
We did find that with the 18psi pulley, the charger was working so hard above 470 HP, that it was way too hot to touch following a dyno pull, so I’m thinking that it should still have a meth nozzle at its intake, just to keep it cool.
We had some inconsistent fuel pressure issues, which I think we can safely blame on a worn out SX fuel pump that just couldn’t deliver the goods at 60 psi.
The 460cc injector duties approached 90% as we hit 498 HP, even with us dumping 600ml/min of straight methanol into the system, so to go much higher than 500 HP even with meth injection is going to require larger injectors. This could be a bit exaggerated, however, considering the unstable fuel pressures we were seeing.
We were blowing the dyno cell’s exhaust pipes off the headers no matter how well they were clamped on, so we seem to be moving a lot of exhaust energy! Dennis commented that in all the years he’s been running this dyno, he’s never had the exhaust pipes consistently blow off a motor like they did on this one. So for the next run, I think I’ll have to have some special headers with larger primaries and collectors. The S&S units are great for a naturally aspirated street motor, but I don’t think they’re large enough to handle this blown UZ.
Our compression tests produced some odd results. The left bank of cylinders consistently gave us 160psi of cranking compression, while the right bank produced 175psi. While a number of things could cause this, both Dennis & Mitch felt it was probably coming from an intake camshaft that was indexed or ground slightly off. This was borne out by comparing the actual injector duty cycles of both banks in order to achieve the same AFR’s.
Summary:
I’ll put up some videos, photos, and curves of the HP and torque tomorrow (I left Dennis’s shop in such a rush this afternoon to get Mitch to the airport, I forgot to get the dyno sheets!), but I think it’s safe to say that if you want an engine with balls and balls of torque, a supercharger setup will deliver it, however if it’s peak horsepower that you’re after, you may be better off with a turbocharger. 498 HP is certainly nothing to sneeze at, but when you consider the engine is really producing that 498 HP, plus another 80 HP or so to drive the blower, you start thinking “hmm, I could have that missing HP back, if I put a turbo on this motor.” But then with a turbo, you wouldn’t have all that wonderful low end torque that the superchargers produce, and it’s actually the engine’s torque that presses you back in the seat, not its HP.
congrats and here's hoping you can squeeze a few more hp out of it yet
