Piston Dish limits

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gordon
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Piston Dish limits

Post by gordon »

In order to get comp. ratio where I want (10.0:1+/-.2) on a 500" 4.350" bore Cad engine I need 32cc volume in the piston. Head gasket thickness .043 and chamber volume of 76cc. With the piston forgings available is 32cc reverse dome design possible? Or do I need to go to a full dish or donut dish design with no quench. Obviously this is a relatively low rpm engine ( 5500rpm max) and needs to run on pump gas. I am concerned with detonation due to fuel octane tolerance especially at low rpm and under load. I am thinking a reverse dome is more desirable here but If it can't be made for a reasonable cost then I will have to go to a full dish or something else.
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Re: Piston Dish limits

Post by Walter R. Malik »

gordon wrote: Sat Jan 30, 2021 10:56 am In order to get comp. ratio where I want (10.0:1+/-.2) on a 500" 4.350" bore Cad engine I need 32cc volume in the piston. Head gasket thickness .043 and chamber volume of 76cc. With the piston forgings available is 32cc reverse dome design possible? Or do I need to go to a full dish or donut dish design with no quench. Obviously this is a relatively low rpm engine ( 5500rpm max) and needs to run on pump gas. I am concerned with detonation due to fuel octane tolerance especially at low rpm and under load. I am thinking a reverse dome is more desirable here but If it can't be made for a reasonable cost then I will have to go to a full dish or something else.
Maximum crown volume will depend upon dimensions of the compression height, pin diameter and rod thickness over the top.
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Re: Piston Dish limits

Post by PackardV8 »

gordon wrote: Sat Jan 30, 2021 10:56 am In order to get comp. ratio where I want (10.0:1+/-.2) on a 500" 4.350" bore Cad engine I need 32cc volume in the piston. Head gasket thickness .043 and chamber volume of 76cc. With the piston forgings available is 32cc reverse dome design possible? Or do I need to go to a full dish or donut dish design with no quench. Obviously this is a relatively low rpm engine ( 5500rpm max) and needs to run on pump gas. I am concerned with detonation due to fuel octane tolerance especially at low rpm and under load. I am thinking a reverse dome is more desirable here but If it can't be made for a reasonable cost then I will have to go to a full dish or something else.
Back in the day, we wasted a lot of time and money making casts of the combustion chamber and sending them to have a matching reverse dome (your term, not mine) machined in custom pistons.

Image

They worked OK, but then we came across some research out of NASCAR shops in which they had better results from an easy-to-make-less-expensive full dish with an outer circumference squish band in the piston.
Image

There's a full discussion on a thread here.
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Re: Piston Dish limits

Post by gordon »

Thanks Walter and Jack for chiming in. Pin dia. is .980" and 1.645" for pin height. This is my first Cad motor. Going into my 53 Stude. This will be my slightly more modern version of the original Studillacs . Modern engine, Man transmission, 9" rear, Corvette front suspension and steering. AC etc. Most of the places that sell and promote Cad performance I have found to be less than dependable and truthful. I am stuck trying to go direct to the manufactures for stuff I want . I no longer enjoy the benefit of being in the business fulltime anymore and am stuck paying full boat $$. I am now in need of pistons and for $1000 + prices can't afford mistakes. I had one piston guy say I could not get a 4.350" 32 cc reverse dome or dish piston unless it is of a donut design with bump in middle. The design looks kool but will it keep me out of det. at the low rpms this cad runs? Trying to do my home work before I spend money and waste it. I think probe used to make what I need except wrong pin height and they went out of business. I think Ross is my next stop for custom pistons.
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Re: Piston Dish limits

Post by gordon »

The rods are Molner 7"CtoC , pin dia.980 ,pin end is 1" wide and wall thickness on top of pin dia. is .195" .These were originally marketed as Olds 425 style rods. I was trying to get the aftermarket 7.1" rods offered for Cadillac engines but the source dried up. Big end dimensions are same on rod journal 2.5" dia. This thing has to be pump gas friendly as I plan on driving this thing cross country with AC on. Gotta keep the old lady comfortable on the road trips.
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Re: Piston Dish limits

Post by BOOT »

I like the idea of D-dish. I wonder what NASCAR's exact reason was? Piston total weight or maybe piston rock due to the offset weight for the reverse dome?

Anyways if you can't find a piston with the CC you need, maybe cut(soften) the head deck some. IDK what would be more cost effective but just thought I'd bring it up.
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Re: Piston Dish limits

Post by gordon »

It is not just a matter of cc's , half way through a build and money spent on a combo,parts suppliers run out of parts and sometimes town. It is a tuff business to stay in business. I will call several of the bigger piston places now and just pay the big ticket price after I verify if they can make what I want or how close they can get. I understand making running changes that is why I ended up with Olds spec rods and not the spec I started with. Originally was going to use 7.1" rods made to fit the 2.5" factory journal and .990" wrist pin. They became unavailable after I placed order. Pistons for these Rods also. With the Idea of running longer than stock Cad rods (6.75") I found the Olds rods available (7")but with .980"pins. Now I have to find someone to make pistons similar to what the vendors were offering but with .980" pin and slight diff in pin height. The now unavailable pistons had the modified D cup dish and valve reliefs to give the the 10:1 ratio I was after, so I know it can be done. The pistons were being sold for $699 not $1299 a set. Should not be this complicated or expensive in my book but WTF do I know. If they want to call it custom even if they have already made them and charge custom prices so be it. Just make them and don't tell me I need some other design. I don't like chewing my tobacco twice. Not good the second time.
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Re: Piston Dish limits

Post by PackardV8 »

gordon wrote: Sat Jan 30, 2021 5:31 pmIf they want to call it custom even if they have already made them and charge custom prices so be it.
No worries. Just order five sets; then it's a production run and the price will be back to $699.
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Re: Piston Dish limits

Post by gordon »

Jack, on the factual side about ordering five sets , already know and understand that. On the sarcastic humor side, did not ask for it and don't welcome it. From one Studebaker person to another, next time you need a special Snap on Carb adjusting tool I will just give you unneeded humorous advice instead of sending the one I have had and used for years to get you out of a jam. Did not even know you except that you were a stude guy in need.
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Re: Piston Dish limits

Post by BillK »

Dont take this wrong but it seems like it would have been a lot easier to just do a real nice basically stock 500 Caddy. We did one almost 20 years ago that went into a 57 Caddy with all modern driveline and AC etc. That guy has put almost 50K miles on that car with absolutely no issues. I would have to look in my records to be sure but I am almost certain we used the Eldorodo 10 to 1 pistons. If I was doing one today I would use the Keith Black reverse dome pistons. They are 28.5cc Puts you right where you want to be.

Just my opinion :)
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Re: Piston Dish limits

Post by Walter R. Malik »

As far as I am concerned ... a "custom" set of pistons is the best deal in the high performance industry today.
Not much more than they were 40 years ago.
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Re: Piston Dish limits

Post by PackardV8 »

Walter R. Malik wrote: Mon Feb 01, 2021 11:28 am As far as I am concerned ... a "custom" set of pistons is the best deal in the high performance industry today. Not much more than they were 40 years ago.
For true; as well as lighter, better dimensional control, always within two grams, thinner rings and much, much easier to get a true custom order done.

As the industry consolidates, this golden age might not last long, but today is the best it's ever been for pistons.
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Re: Piston Dish limits

Post by piston guy »

Gordon,
There are custom piston manufacturers that will make you a -32cc dish piston in 4032 alloy for your Cad. At that volume , "I" would recommend a round dish with a specific width "squish band". I was the first one to "adapt" the conical ( first) and spherical ( later for more volume less depth) to Nascar pistons along with Frank Leisson , then of Bill Davis Racing doing "Busch" engines. I say "adapt" because the Japanese were already using the design on four cylinder engines.. The concept's premise was to smooth air entry on intake , focus the "charge" on the compression stroke to the center of the piston , and again smooth air flow out on the exhaust stroke over a mirror . Interestingly the "basic" design made more torque improvement than HP ( consistently) and usually with 2*s less timing.
Purpose designed round dishes are making a comeback.
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Re: Piston Dish limits

Post by DCal »

Your round dish is approx. .180 deep. CpPistons has three D-shaped profiles for FE Fords with various diameters and squish pads placements. There are other profiles of course but these three are for the laid down valves reliefs such as yours and will make a good looking part. It is custom. I can suggest a dealer if you need.
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Re: Piston Dish limits

Post by gordon »

I am willing to listen to reason, I am talking to Ross pistons now but not committed to any one yet. Who do you suggest?
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