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Big As They Get

Tonerjockey

Tonerjockey

High Miler
GT Contributor
Joined
Oct 28, 2008
Messages
788
Location
San Jose
Well I think I finaly have managed to arrive at the largest pistons that will fit under the heads of the V7 Sport.

At first I used the stock pistons. Hemi baby! Some power but I was RACING and needed BIG COMPRESSION.

So CP Pistons made me their largest billett pistons to fit stock bore. They started off as 12:1 but flycutting for the big valve and the sinking of both valves into the heads reduced the compression considerably. Cool pistons though.

StockvsCPForgedsm.jpg


Turns out the demensions I gave CP were for the stock heads and the "hot" heads caused low pressures. ugh.

So back to CP, and with help from Terry Stewart from Shaker Products, we used the "hot" heads for the spec. we came up with this:

CPForgedvsBilletsm.jpg


The previous forged pistons were as tall as forged pistons come. If I wanted to blow the heads off I needed to have pistons cut from billett. This is what was done. The flycutting reduced the max compression, of course, but all of the combustion area should now be filled with piston. We are looking at minimal clearance to the head. I'll need to clay this thing very carefully and adjust with gaskets. The cylinders have wire o-rings for copper gaskets and I have every size available from Gaskets Unlimited.

If this doesnt get the pressure I'm looking for I think I'll move on to Tiddley Winks.

Alex
 
Looks great, but I can't help to ask: you're twin plugging this engine, no?
Cheers, JR
 
Twin Plug, recessed enlarged intakes, and am now working getting on a Czeck ignition to spark it. The heads are about 20% larger than stock ... makes getting compression tougher.

That Norris 382 grind cam might actually work with these...

The larger plug is a flat racing plug and the smaller doesn't protrude into combustion chamber. Pistons don't need relieving for plugs.

I have yet to install and clay these with either the B10 or Norris grind cams... mught hafta do some modifications to them for clearance.... we'll see.

After the cam/piston/head combination is setteled and fitted, the engine comes out and I'll get it all balanced.

Hopefully I'll be ready by May...

Alex
 
Sounds good! I might actually have a Norris 382 too (in my LM III). I hear different stories about that cam, too peaky, too hot etc etc. But then again the engine characteristics with any cam will differ with the cylinder volume. I once saw a Guzzi California easily wheely without clutch abuse with that cam and later smoke a BMW K100RS. Not too bad I thought. My bike is 1037cc and it gives me lots of midrange and high-end power(80 rwhp with stock exhaust).
It might be a peaky engine with only 750cc(no problem in your case), just like the original V7 sport cam seems very peaky for the V7 sport, but I knew a few people that used that cam in 948 and 992cc engines with sidecar rigs with good results. So I say try it and use good and well shimmed valve springs!
Cheers, JR
 
That is going to make one seriously ugly combustion chamber! I suspect the twin plug is essential as you have almost bifurcated the flame front.

It will be interesting if you get the power you hope for but I would have attacked it by serious flow bench development and some modification of the combustion chamber to increase squish.

There are gas filled copper O-rings that work a treat - sorry don't have the name of any suppliers offhand.

Good luck and it will be interesting to see how this works,

ChrisR
 
We used to run a similar piston crown shape in our Ducati racebikes, but we would machine the top of the crown flat for some semblance of a combustion chamber. We also had dual plug heads.There are two sides to the combustion chamber issue, one being that you want a good combustion chamber shape to speed combustion and the other that you want high compression to speed combustion. The trick is to find the balance point between the two.
What is your final compression ratio?
 
Dunno what the final CR is yet. Ran the engine yesterday and it seems pretty strong. Today the ignition system gets attention.

Once the ignition is stable I intend to reduce the current squish from .061' to .041". When that's done I'll measure the CR.

The heads were done by the same guy that did The Mendello Meteor's and I'm just trying to fill them up. We'll see how this goes of course.

Alex
 
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