MC8 boost port ...

[Jeff Campbell]

I decided to build a new motor to take to the TBO to play with. The project motor for this week is a MC8. Last night I decided that instead of extending all three 3rd port holes up as boost ports (as the MC90 had) ... that I would try something different. Since I am using a MC91 type piston which has a built in port passage for feeding a boost port ... I figured that I could do this:

MC8 boost Port 500b.jpg

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I extended the center 3rd port hole up into a wide single boost port, with the 91 piston, the 2 remaining 3rd ports will feed the boost port. This way I do not have to cut the 3rd port wall out in the block (less work), I only need to cover it with a non-3rd port manifold.

Jeff

[Scott Kneisel]

Hey Jeff,
I will be interested to see how that works. It is actually inverted from what I am used to seeing.
See pics:

Mc30 Boost Port1.jpg

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Mc30 Boost Port2.jpg

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[Jeff Campbell]

Scott, I don't think I have seen one done like that ... maybe that block started out with a gully ported 3rd port?

A lot of the 3rd ported motors were boosted by extending each of the 3rd port holes upward, as was done by McCulloch on the MC90 motor:

Mc90 Boost Ports-500.jpg

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Also, many of the 3rd ports were opened up to improve 3rd port flow, by gully porting it, cutting out the ribs between the holes, but leaving some to prevent ring snagging

MC30 block NOS - opened 3rd port-500.jpg

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another boost porting option, is to cut 2 boost ports feed through holes in the piston or a cut away 3rd port wall:

MC9 modified 2-500.jpg

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..anyway, it will be fun to see how my motor runs at TBO.