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Here is one of my new pistons for use with 5.5" Ford 2.3l rods. Valve notches are for 1.85" intake and 1.5" exhaust valves

-Travis
 

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Old Opeler
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Hypereutectic Pistons

These ones are what I am using for a "street" motor: KB153 with Neon Eagle H-beam rods.

Nearly fainted when they arrived as the Opel uses a left and right handed piston due to the valve sequence with the inlet and exhausts being on oposite sides of the cylinder in adjacent cylinders. Fortunately the 305 chev has the same sequence:
Ex:In:In:Ex:Ex:In:In:Ex I had thought the 305 pistons would have four notches so it was quite a surprise to find only two notches.
 

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Bump!

I'm reviving this thread because I have a question for the experts and I like what I see in these posts!
My Venolia pistons weigh 533 grams, the "stock Opel" ones max out my triple beam scale, all I know is they weigh a good deal more.
When comparing them to see why, I see the Opel slugs have some steel imbedded in the skirts beside the pin bosses. The Venolias don't.
Why is this steel in there, and can it be removed? It doesn't appear to be cast in, looks like they are just tabbed and "snapped" in maybe.
I see some extra aluminum all over the piston that could be cleaned up, this could make it a little lighter, but those steel things would be major weight as opposed to none!
The Venolias are beautiful, I wish I could use them. Maybe someday.
The previous threads by Travis and Jim show the right way to build an Opel CIH for best performance, in my opinion they are off to the right start. It's that rod length factor!
By the way, where is Travis? Seems we haven't heard from him for a while!
Alas, I have rules to deal with, the engine currently on the table must comply...
 

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Old Opeler
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When comparing them to see why, I see the Opel slugs have some steel imbedded in the skirts beside the pin bosses. The Venolias don't.
Why is this steel in there, and can it be removed? It doesn't appear to be cast in, looks like they are just tabbed and "snapped" in maybe.
I see some extra aluminum all over the piston that could be cleaned up, this could make it a little lighter, but those steel things would be major weight as opposed to none!
Jeff, Those steel bits are expansion control struts .... and are an integral part of the piston design. They physically limit/control the expansion rate of the pistons. Removing them would be a disaster ..... as they also add to the strength of the piston around the pin area.
 

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Whatever they are, they don't come out easy. I ruined a perfectly junk old dished piston finding out. One end bends out okay but the end near the pin hole won't budge.
So I'm running out of wild ideas on how to make these pigs lighter.
Sure, some cautious, tedious grinding of aluminum will take out a few grams each. Anything to reduce reciprocating weight and take a millionth of a second off the lap times...
 

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What would happen if you decked the block, then milled the same amount off the top of the pistons? Then redrilled the cam sprocket to correct the cam timing.
 

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What would happen if you decked the block, then milled the same amount off the top of the pistons? Then redrilled the cam sprocket to correct the cam timing.

If that was done you would effectively maintain both static and dynamic compression, though there would be a lighter rotating assembly with less reciprocating mass.
 

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What would happen if you decked the block, then milled the same amount off the top of the pistons? Then redrilled the cam sprocket to correct the cam timing.
What is your reason to deck the block? Is it warped, pitted or are you looking for a compression increase?

Removing a small amount from the block to clean it up, say less than .010", would need no correcting. Removing material off the piston tops would only negate the benefits from the slight compression increase. There would be no change in displacement, since that is bore times stroke and you would have changed neither. The factory pistons are, according to good sources, located below the top of the block from .004 to .007". For several reasons its good to have them .005" above the height of the block's deck.

The cam timing changes by approximately 2 degrees for every .025" removed from the block and head combined. Removing .010 would result in the cam timing being retarded by less that 1/2 degree.

If you are decking the block in conjunction with head modifications, and piston and or rod changes, then you should measure all dimensions and determine all clearances and then decide upon corrective measures...
 

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Jeff wants to have lighter pistons. So if you take say .050 off the block deck and .050 off the pistons, the compression ratio will stay the same. Nothing will change with piston to head or piston to valve clearance. CID will not change. Cam timing will be changed so it will need corrected. Jeff said he wanted wild ideas.
 

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pistons

Jeff wants to have lighter pistons. So if you take say .050 off the block deck and .050 off the pistons, the compression ratio will stay the same. Nothing will change with piston to head or piston to valve clearance. CID will not change. Cam timing will be changed so it will need corrected. Jeff said he wanted wild ideas.
My only experience with cutting stock pistons, was with our home-grown stroker motors. We welded up the rod throws on the crank and off-set ground the crank to increase the stroke .250. We used low compression pistons and cut the tops .125 which made them flat tops with valve reliefs. It moves the top ring .125 closer to the piston top, but we seen no adverse effect by do that. We built 8 or 10 of those motors and they all ran several years without a problem. The cams we ran were about .430 true lift (with 1:44 stock rockers) and we had no interference or problems with spark knock. If you angle mill the head instead of flat cutting it you have less problem with timing chain slack, and it can be made up with a longer piston on the chain tensioner. By angle milling the head it tiles the ports upward and allow a more direct shot from the intake manifold to the valves. Angle milling is the most effective way to reduce combustion chamber cc's and increase compression.
 

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Hey, great little discussion we have going here! This is my favorite thing about gt.com, how great minds come together.
The main hurdle here is keeping it stock, while interpretations of the definition of stock may be arguable. The first build of my engine was pretty much that, but did include all the usual checking and truing of critical surfaces. Well, $400 or so worth of machine shop time, put it that way! How much we deck the block or head and at what angle we may have cut things would not be discussed, as if anyone would have any dimensions to compare it to, "yeah it's stock" would be the standard statement...
I wonder how thin we'd dare have our piston crown? I'll drill into some flat tops and see how thick they are. Especially in the valve reliefs. This area could get critical as the deck gets lower and cams get wilder.
Timing chain slack, cam timing, little glitches like this are surely overcome, you guys know where I've been with all that, I think!
A half hour of careful "cleanup" of junk inside the piston skirts with a grinder took four grams of "extra" aluminum away. Hey, it's a start!
Thanks, guys.
 

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electrolysis?

Have to dig out my college chemistry texts, but you might be able to chemicly remove some of that steel without removing the aluminum. Obviously it wouldn't make it's way into the internals of the piston, but you could get rid of some fo the mass there at the ends?

So, if you melt down stock pistons and cast them in new molds, can't you still call them the stock pistons? If some guy with an Indian can do it.....?
 

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"Stock"

What you need, Jeff, is a set of +.040 Venollia forged flat top replacement pistons - maybe they have some in 'stock':yup:
 

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All right, that's it. We've gone full circle from serious, to impossible, then hilarious, now Jim's trying to be "punny".
Nice one about recasting stock German aluminum into something radical, Stephen. Do it with a huge dome and the pin holes really really high up, and a stock opel part number and blitz logo cast in, OK? Oh, and leave out the second ring groove, not needed at 7000+ RPM.
Then all we gotta do is stretch the stock rods out a little longer...
As of an hour ago, all my pistons are light enough to not max out my scale, 590 grams now. That's a little better. They don't come out as clean as the ones Travis shows earlier in the thread. I'm probably pushing my luck in terms of legality, but, they are stock...
(edit) Come to think of it, the meaning of "stock" is sometimes construed as "stock replacement", it doesn't necessarily mean it has to be an OEM part, so you might actually have a point there, Jim! But the name Venolia kind of exudes motorsports high perf, they do frown on that, in this class...
 

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Come to think of it, the meaning of "stock" is sometimes construed as "stock replacement", it doesn't necessarily mean it has to be an OEM part.
Jeff the pistons from the A400 are "stock OEM",
They are factory designed for the CIH short block but for 2400cc,
A400 & Manta400 were sold by Opel as "almost casual" cars,
So there should be somewhere a Opel ref # for these pistons.
They are Cosworth forged pistons,
dia 95mm / cd 31.5mm / pin 22mm
You just need to recarve the valve notches because it's a 16V design.
Hiro
 

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I might need some help deciphering your dimensions, Hiro. 95 mm bore, that sounds a little more than stock bore plus the .040" maximum overbore.
That 1.9 is just a tough little engine to build up within the rules!
But what we've got so far just might do the job, and the car itself has lost all it's extra weight, and some Super Late Model champs are helping with suspension blueprinting. They have a neat computer program that we input all the measurements into, from ride height to "full bump" situations and it's interesting what we see, like camber gain and bump steer. Not to go off topic, but having this figured out and corrected is really more important than more power, and to me it's more challenging. So, what if we have both? Look out, here comes "Oh-Oh", as the track announcer calls me...
Thanks guys, keep the wild ideas coming, deep thinking comes of it, and we can all use a good chuckle, too!
Dang, I have a spelling typo in my post #14. Too late to edit. Otto, help!!
 

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Hey Jeff,

Have you considered machining a tapered hole into the ID of the piston pin ends to remove some grams?

As for the suspension, I've done an Excel spreadsheet to model the 50 series front suspension, with the intent of figuring a new front Opel 50 series suspension design. Learned some interesting things about the roll centers (at least partially explaining the large front sway bars on the 50 series). I think we also figured out how to relocate the control arms for a coilover front suspension to improve suspesion geometry in turns.

Willing to exchange what we have learned for what it is worth. You can PM here or start a new string unde the suspension section. I'll be slow to respond; am in the middle of a huge project.

Regards,
Mark B.
 
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