MWMIata

Currently building an NA VVT engine to compete in SCCA Max TT class. OEM 10.5;1 I planned to use have the piston rings frozen on. Engine will have f cams, under bucket lifters, dual light springs, stock valves l, itb's

I am now boring to 84mm for 11:1 CR Supertech pistons. Already have the head shaved ..045, block decked ..010


Q1 Has anyone had experience with a .010 deck / .045 shave and ST 11:1 pistons replacing jdm? Any red flags with this combination?
Q2 94 Octane and E85 at this assumed CR of 12.5:1 or do I need to rethink this?
Q3 How do you do the clay test for piston to valve clearance on a VVT motor?


Thank You

bimmerboy

All the power to you and best of luck with your engine build. You may want to google Quin and his ITB Miata. His youtube is The Slip Angle. His thought process involved stock block and head castings (for ease of replacement) except for the decking/shaving.

However, if SCCA Max is your goal, modding a 1.8L bumps you one class up from Max5 into Max4 and you will then be competing against K24s. In order stay in Max5 you have to stay 1.9L or below and have a motor built with factory "equivalents" and "spec" in mind.

MWMIata

Agreed, this started as a similar build but my OEM 10.5:1 pistons had the rings frozen and a scratch on the cylinder wall. Still want to keep it a Miata for other events.

emilio700

iTrader: (3)

1. Retain at least OEM quench. On our engines we would tighten the quench area narrower than OEM, which helps power. Eliminating quench area completely really hurts power though.
2. 11.0:1 is about the max you can run on 94. Our experience, BP's don't respond much to compression. Our 200whp ITB motor ran 13.2:1 but we made about the same power with 10.4:1. All else equal, cams are the biggest gain, ITB's next.

If I have a choice between a mega prepped engine with 14.0:1 and stock cams, or a bone stock engine with huge cams, I'll take the latter. EP engines are heavily "blueprinted" (lol) stock style engines with massive cams making nearly 200whp on 100. It's all the cams.

MWMIata

The observations and responses were much appreciated on Q1, and Q2

Couple more ?'s

Q3, How do I perform the clay test and take into account the VVT advance ? Or can I expect no issues with .055 removed?

Q4, Any downside to installing a .060" Head Gasket to lower compression ratio slightly?
Assumptions .045 Head Shave / .010 block deck = + .12, Supertech Pistons (11:1) - .2 with .040" head gasket.= approx 12:1?
with a .060" head gasket 11.8:1? I am assuming that this increase in the distance between the head and piston would aid in restoring "quench area"?

Thank You

emilio700

iTrader: (3)

Research quench area