Piston Selection - Hypereutectic vs Cast

Matthew68

Well-known member
Hi Folks,

68 200 block build planning. I'm aiming for 10:1 compression ratio. Before I make any plans on decking the block, I'm looking into pistons. I have the aluminum head, and do NOT plan to turbo, supercharge, or run nitrous. This will be a cruiser, street driven car only, no racing.

Has anyone used Keith Black Hypereutectic Australian pistons? They can be found under part numbers 3327H (flat top) and 3328H (dished). They are sold by Summit for $150 per set. I was curious, as I don't need (or can afford) forged pistons, but I like the idea of a little more serious of a piston in case I want to stomp on pedal from time to time. At the same price as typical cast pistons, are these a good option?

https://www.summitracing.com/search?Pag ... australian

From my research, they do have a higher compression height of 1.530" vs the stock cast pistons at 1.500", but that's the only difference I can tell, aside from a pin offset of .060" (does that matter??). From the KB catalog:
Screen Shot 2019-02-28 at 12.12.41 PM.png

With a difference in compression height, would it be advised to not deck the block based on the current cast piston? I'm planning to re-use my conrods. I don't have the budget to make the bottom end turbo/boost worthy when that's not in the gameplan at all.

Also note the rings, these aren't standard sizes, so any advise on rings?

OR

Am I over-complicating this completely, and I'll be find with just using cast pistons? I figured I could save myself a few bucks in machine work if I didn't need to deck the block, but if I'm going to end up with a headache for other issues, it just might not be worth it.
 
I built an engine with the Aussie flat tops, they fit and finish just like a normal piston, I decked the block to achieve -0.005 piston in hole without problems.
There is only one issue with using these Aussie pistons, they take a special ring set, the ring set is available, but only in cast iron. I had a set of zero gap rings made at a cost of $230 so I could have zero gap and Moly.
Walt
 
Interesting find. I think I've heard about these before but thanks for bringing it up. I might need a bottom end rebuild if my suspicions of bad rings is correct and this would be a great route as my block is uncut and standard bore.

Bottom Line Up Front: I could use these pistons and a modern gasket to get where I am today with stock pistons and an NOS gasket made of unobtainium. It will also reduce the squish slightly which will provide an overall improvement in performance.

I ran my little homebrew compression ratio calculator and this is what the results are for the dished piston. Here are the results of my baseline:

================================================
INPUT - BUILD PARAMETERS
================================================
Block Specifications:
Cylinder Bore = 3.68 in
Centerline to Deck Height = 7.808 in
Rod Length = 4.715 in
Stroke = 3.126 in
Piston Dish Volume = 6.5 cc
Piston Compression Height = 1.511 in
Cylinder Head Specifications:
Combustion Chamber Volume = 48 cc
Intake Valve Diameter = 1.76 in
Exhaust Valve Diameter = 1.5 in
Rocker Arm Ratio = 1.65:1
Cylinder Head Gasket Dimensions:
Gasket Diameter = 3.81 in
Gasket Crush Height = 0.035 in
Camshaft Specifications and Events:
Intake Duration = 264 deg
Exhaust Duration = 274 deg
Lobe Separation Angle = 110 deg
Cam Intake Lift = 0.294 in
Cam Exhaust Lift = 0.3 in
Ground-in Advance = 0 deg
Camshaft Installation Advance = 4 deg
Intake Opening Angle = 26 deg BTDC
Intake Closing Angle = 58 deg ABDC
Exhaust Opening Angle = 71 deg BBDC
Exhaust Closing Angle = 23 deg ATDC
Intake Valve Lift = 0.4851 in
Exhaust Valve Lift = 0.495 in
Valve Overlap = 49 deg
================================================
OUTPUT
================================================
Engine Displacement = 199.49 in^3
Rod to Stroke Ratio = 1.51:1
Rod Angle = 19.36 deg
Resulting Deck Height = 0.019 in
Squish Distance = 0.054 in
Static Compression Ratio = 9.46:1
Dynamic Compression Ratio = 7.99:1


I used the measurements from your post for the dish size to come up with a volume of 7.7cc and my standard build parameters with the exception of the thicker 0.050" gasket than the 0.035" that I have on there today. Here are the results:

================================================
OUTPUT
================================================
Engine Displacement = 199.49 in^3
Rod to Stroke Ratio = 1.51:1
Rod Angle = 19.36 deg
Resulting Deck Height = 2.22e-16 in
Squish Distance = 0.05 in
Static Compression Ratio = 9.37:1
Dynamic Compression Ratio = 7.91:1

Substituting in the flat top pistons would then yield:

================================================
OUTPUT
================================================
Engine Displacement = 199.49 in^3
Rod to Stroke Ratio = 1.51:1
Rod Angle = 19.36 deg
Resulting Deck Height = 2.22e-16 in
Squish Distance = 0.05 in
Static Compression Ratio = 10.5:1
Dynamic Compression Ratio = 8.84:1
 
fast64ranchero":3l7g0zty said:
I built an engine with the Aussie flat tops, they fit and finish just like a normal piston, I decked the block to achieve -0.005 piston in hole without problems.
There is only one issue with using these Aussie pistons, they take a special ring set, the ring set is available, but only in cast iron. I had a set of zero gap rings made at a cost of $230 so I could have zero gap and Moly.
Walt

Thanks for the feedback Walt. Where did you get the ring set? I’d prefer moly, but that cost gets me over budget. Any potential issues using cast with this piston?

Also, with the offset pin, did that cause you any issues? Or is that standard? I ask because I don’t know.

Cheers,
Matthew
 
cr_bobcat":2ryrgduw said:
Interesting find. I think I've heard about these before but thanks for bringing it up. I might need a bottom end rebuild if my suspicions of bad rings is correct and this would be a great route as my block is uncut and standard bore.

Bottom Line Up Front: I could use these pistons and a modern gasket to get where I am today with stock pistons and an NOS gasket made of unobtainium. It will also reduce the squish slightly which will provide an overall improvement in performance.

I ran my little homebrew compression ratio calculator and this is what the results are for the dished piston. Here are the results of my baseline:

================================================
INPUT - BUILD PARAMETERS
================================================
Block Specifications:
Cylinder Bore = 3.68 in
Centerline to Deck Height = 7.808 in
Rod Length = 4.715 in
Stroke = 3.126 in
Piston Dish Volume = 6.5 cc
Piston Compression Height = 1.511 in
Cylinder Head Specifications:
Combustion Chamber Volume = 48 cc
Intake Valve Diameter = 1.76 in
Exhaust Valve Diameter = 1.5 in
Rocker Arm Ratio = 1.65:1
Cylinder Head Gasket Dimensions:
Gasket Diameter = 3.81 in
Gasket Crush Height = 0.035 in
Camshaft Specifications and Events:
Intake Duration = 264 deg
Exhaust Duration = 274 deg
Lobe Separation Angle = 110 deg
Cam Intake Lift = 0.294 in
Cam Exhaust Lift = 0.3 in
Ground-in Advance = 0 deg
Camshaft Installation Advance = 4 deg
Intake Opening Angle = 26 deg BTDC
Intake Closing Angle = 58 deg ABDC
Exhaust Opening Angle = 71 deg BBDC
Exhaust Closing Angle = 23 deg ATDC
Intake Valve Lift = 0.4851 in
Exhaust Valve Lift = 0.495 in
Valve Overlap = 49 deg
================================================
OUTPUT
================================================
Engine Displacement = 199.49 in^3
Rod to Stroke Ratio = 1.51:1
Rod Angle = 19.36 deg
Resulting Deck Height = 0.019 in
Squish Distance = 0.054 in
Static Compression Ratio = 9.46:1
Dynamic Compression Ratio = 7.99:1


I used the measurements from your post for the dish size to come up with a volume of 7.7cc and my standard build parameters with the exception of the thicker 0.050" gasket than the 0.035" that I have on there today. Here are the results:

================================================
OUTPUT
================================================
Engine Displacement = 199.49 in^3
Rod to Stroke Ratio = 1.51:1
Rod Angle = 19.36 deg
Resulting Deck Height = 2.22e-16 in
Squish Distance = 0.05 in
Static Compression Ratio = 9.37:1
Dynamic Compression Ratio = 7.91:1

Substituting in the flat top pistons would then yield:

================================================
OUTPUT
================================================
Engine Displacement = 199.49 in^3
Rod to Stroke Ratio = 1.51:1
Rod Angle = 19.36 deg
Resulting Deck Height = 2.22e-16 in
Squish Distance = 0.05 in
Static Compression Ratio = 10.5:1
Dynamic Compression Ratio = 8.84:1

Bobcat,

When you ran this, did you account for the taller compression height of these pistons? Didn’t see that in your calculations, but perhaps you cut that out.

That’s my goal, to save some budget and some block height. I sure hope these work, but I still want to do some more research.

Cheers,
Matthew
 
I changed the compression height for the new computations, I just didn't copy/paste in the new input data, just the outputs. Here is the output for the 7.7cc dish, 1.530" compression height.

================================================
INPUT - BUILD PARAMETERS
================================================
Block Specifications:
Cylinder Bore = 3.68 in
Centerline to Deck Height = 7.808 in
Rod Length = 4.715 in
Stroke = 3.126 in
Piston Dish Volume = 7.7 cc
Piston Compression Height = 1.53 in
Cylinder Head Specifications:
Combustion Chamber Volume = 48 cc
Intake Valve Diameter = 1.76 in
Exhaust Valve Diameter = 1.5 in
Rocker Arm Ratio = 1.65:1
Cylinder Head Gasket Dimensions:
Gasket Diameter = 3.81 in
Gasket Crush Height = 0.05 in
Camshaft Specifications and Events:
Intake Duration = 264 deg
Exhaust Duration = 274 deg
Lobe Separation Angle = 110 deg
Cam Intake Lift = 0.294 in
Cam Exhaust Lift = 0.3 in
Ground-in Advance = 0 deg
Camshaft Installation Advance = 4 deg
Intake Opening Angle = 26 deg BTDC
Intake Closing Angle = 58 deg ABDC
Exhaust Opening Angle = 71 deg BBDC
Exhaust Closing Angle = 23 deg ATDC
Intake Valve Lift = 0.4851 in
Exhaust Valve Lift = 0.495 in
Valve Overlap = 49 deg
================================================
OUTPUT
================================================
Engine Displacement = 199.49 in^3
Rod to Stroke Ratio = 1.51:1
Rod Angle = 19.36 deg
Resulting Deck Height = 2.22e-16 in
Squish Distance = 0.05 in
Static Compression Ratio = 9.37:1
Dynamic Compression Ratio = 7.91:1
 
keith black gets good marks as the 1st step up frm stock (fit'n finish, durability, etc).
Great for budget builders like me...
8^0
 
I can’t seem to find a ring set to go with these. Their catalog skips the piston part numbers when giving reference parts, of course. I’ll give them a call tomorrow and see if I can locate a set.
 
Why are you looking for a 10.0:1 CR?

Are you going to be able to run pump gas?

What carb and exhaust are you planning?
 
Georgia200":316znrz7 said:
Why are you looking for a 10.0:1 CR?

Are you going to be able to run pump gas?

What carb and exhaust are you planning?

Hi Georgia,

In short, why not?

I have an Autolite 2100 1.23. Hooker long tubes to Vintage Inlines dual 2” imposter exhaust.

I run pump gas, exclusively premium 93.
 
Howdy Matt and All:

A critical bit of info missing is the compression height of your stock block/piston. Without that you will be making a pretty big guess. Typical 200 blocks have about .030" compression height, but can vary for .025" to .035". The compression height of a stock piston in a stock block is 1.5". The new piston are 1.53". The difference between a stock steel shim head gasket at .025" and an aftermarket composite at approximately .050", could make up for the difference in pistons.

To answer your original question, all indications are that hyereutictic pistons are a good idea for an upgrade from stock cast pistons. That will be especially true if you are going for 10:1 CR. You listed your carb- what distributor are you using? If you do have to machine your block, I'd suggest that you, at least, step up to better ARP rod cap bolts.

What is the elevation where you are?

I'll sure be anxious to hear what you find on rings and all the critical dimensions. So, keep us posted on your progress.

Adios, David
 
CZLN6":2mgcdirv said:
Howdy Matt and All:

A critical bit of info missing is the compression height of your stock block/piston. Without that you will be making a pretty big guess. Typical 200 blocks have about .030" compression height, but can vary for .025" to .035". The compression height of a stock piston in a stock block is 1.5". The new piston are 1.53". The difference between a stock steel shim head gasket at .025" and an aftermarket composite at approximately .050", could make up for the difference in pistons.

To answer your original question, all indications are that hyereutictic pistons are a good idea for an upgrade from stock cast pistons. That will be especially true if you are going for 10:1 CR. You listed your carb- what distributor are you using? If you do have to machine your block, I'd suggest that you, at least, step up to better ARP rod cap bolts.

What is the elevation where you are?

I'll sure be anxious to hear what you find on rings and all the critical dimensions. So, keep us posted on your progress.

Adios, David

Hi David,

I haven't measured just yet. By first compression height of my stock block/piston, do you mean deck height? I'll be running the slightly thinner Victor gasket, which as advertised is .044" crushed.

I'll be using a DUI distributor, custom curved by Bill (wsa). I'm at 482' elevation in Ohio.

So far, the manufacturer (UEM - who makes KB, Silvolite, etc) doesn't sell a ring set for these pistons. I found one company, Hastings, based out of Michigan that makes them. They will sell direct to consumer, but they are pricey at $222 for a chrome set. It's about half that at a re-seller, but I can't find anyone who will order them from me. I also called Total Seal, who stated they can make up a set of Moly ones for $230. Both of those prices are $70 more than the pistons themselves, so I may rethink my decision here altogether.

Cheers,
Matthew
 
"... can't find anyone who will order them from me.
the machinest
 
Howdy:

Yes Matt. The measurement from the topmost part of the piston to the deck of the block. This dimension varied from block to block. Be sure to check it out.

Adios, David
 
So I found a somewhat economical set of rings, but they are cast. The chrome ones are around $250, while I can get cast ones for around $80.

My question - is using cast rings on the hypereutectic pistons ok? I realize they are not as good, but again the chrome or moly blow my budget. Is it better to use hyper pistons with cast rings or hyper pistons with chrome/moly rings?

Cheers,
Matthew
 
Chrome Moly are much better choice for a longer lasting engine with a little less rotating friction too. Good luck (y) :nod:
 
Plasma-Moly are the best. They require a very slick cylinder wall finish. 500 grit++
The cast will seat on anything around the 320 Grit area.
If you don't plan to race it or put over 100,000 miles on the engine go for the cast.
Make sure you end gap them to perfection, especially the top ring. The second ring is mostly an oil scraper.
 
Matt, IMO cast Iron works fine and is what you engine came with stock. Moly breaks in like Cast Iron and wears like Chrome. It'll be fine if built with Cast Iron, if that is what your budget allows.
 
Walt/Bill,

Thanks fellas. I may have a lead from one source on the chrome that will keep me in budget. If that falls through, I’ll just go with the cast. Won’t be doing any racing, and definitely won’t be putting over 100,000 miles in my lifetime on it.
 
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