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Saturday, February 6, 2010

New motor for the OGK

Since late Summer '09 I had been planning and piecing together version 2 of the OGK. Real gauges, better engine management, bigger brakes, less weight and a whammy one of a kind engine with the Kraftwerks supercharger. Some of the parts are here in the shop but the stumbling point has been planning the engine. I have this theory that the block can accept a much larger bore (85.5mm) than is common practice on high boost engine. So we're going to sonic test two and cut another open to take some measurements. Then comes custom made rods, cams and pistons, all of which need to be designed from scratch. This should have all been done at the end of '09 of course. It wasn't though, so I have to "throw" something together to start aero development.

This interim motor will be basic, 100% OEM rebuild with these exceptions:

84mm 9.5:1 - off the shelf Supertech's
Forged rods - M-Tuned
Billet oil pump gears in blueprinted housing - Boundary Engineering
Valve Springs - Eibach
Crank - lightened and balanced with stock damper and 949 Racing 7.25" organic twin plate clutch
CAM- BP5A intake

That's it, no custom machining other than the crank. It won't flow more than about 205CFM or so but the C30-74 Rotrex will take care of the rest. After driving William's lap record setting 230whp 99 Miata with a stone stock 100K mile engine and the same supercharger, I realize I can get by just fine with a plain engine for now. The interim motor while it won't flow much, will have no problem spinning to 7800rpm sustained and cope with 15psi/300whp.

The impetus for the Whammy engine is twofold:
1. Increasing displacement while increasing the rod ratio from the not so favorable 1.56:1 to something more like 1.66:1. That means longer rods, stock stroke and still getting 1952cc.

2. Developing what will become 949 Racing crate motors for 2011.

With the stroker conversions already available, you get higher piston velocities and end up with nearly the stock rod ratio. There are a host of benefits from keeping the stroke shorter and increasing bore. The question remains, just how far can we go with the bore and boost before it goes pop.

With enough valve lift, our new header design and prototype manifold, we can hopefully reach something like 255-270CFM from the head. Pretty weak in the Honda world but the upper end of what people get from the BP series Mazda heads. That flow should allow it to make good power between 7000-8300 rpm which is where the rod ratio comes in. An integral part of achieving that flow will be aggressively deshrouding the valves, made easier by the bigger bore.

Such a build could be run as a genuine 8000rpm 175whp N/A (non VVT) street motor with the right intake/exhaust/ECU and also be strong enough for sustained 400whpF/I track use. The long term goal is to build an endurance racer and finish the 2010 Thunderhill 25 hour with the prototype crate motor.

Hoping to get the Whammy engine built in time to do one or two 3 hour enduros between Summer and T25. Meanwhile, we can definitely get the interim motor put together in time to run the March 20 Miata Challenge event at El Toro. Can't wait to get out there. Another goal for 2010: sub 1:50 at BW13 CW on DOT slicks.

1 comment:

  1. Sounds pretty cool. I'd be curious how the N/A results turn out.


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