Need Help Tracking Down Pistons For Low Compression 408 Stroker

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Msmith68W

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Hello everyone,

I have a bit of an oddball situation here and I'm hoping to find off the shelf pistons that fit my needs, but so far have been unsuccessful. I am hoping you fellers can help.

Here's the deal:
360 magnum block at standard 4" bore (measured within spec and doesn't need bored) and standard deck (deck is also dead flat).
Piston made for stroker, so something probably in the 1.45" compression height range
Dish in the 30cc range
Quench pads that vaguely match the magnum head's quench pads would be ideal, but I'm willing to compromise on this
Hyper pistons are fine for this application, though if I have to pay slightly more for forged just to get the correct specs I will, though the cost for custom pistons is a no go

The biggest dish I can find in a standard bore piston is KB's 416s which is 25cc, which I could get away with if I can't find a bigger dish. Icon has the IC982 which is a 34cc dish but it's only available in overbore sizes.

Thanks in advance!
 
Last edited:
Did you try the KB356 Pistons they are available from Summit in standard bore 1.465 CH. 23.5 CC
Then run a thicker head gasket. I believe Cometic has an .051 gasket for Magnum engines.
 
SMCARNUT said:
Did you try the KB356 Pistons they are available from Summit in standard bore 1.465 CH. 23.5 CC
Then run a thicker head gasket?
Click to expand...
Trying to get the quench set right. Currently looking at what head gasket thicknesses are available. I was hoping to use the standard fel-pro .039 gasket.

With those KB 416s and the .039 gasket that makes my quench .036" (.003 deck clearance by my calculation), which is solid except that it's still slightly more compression than I want.

With a .045 head gasket (which I think was stock) that makes for .042 quench (still fine) and 9.61 static. 9.01 dynamic and 187 cranking PSI with a camshaft closing the intake valve 37 degrees ABDC. Still just a touch higher than I'd prefer, but I could probably get away with it.

Stock numbers are 9.1:1 (advertised at least) static, meaning 8.83:1 dynamic and 182psi cranking, but they also have a reputation for pinging I'd like to avoid with proper quench and ever so slightly less compression.
 
I edited my original post and let you know that Cometic makes an .051 head gasket that should put you fairly close to what you need.
Summit part number Part Number: CGT-C15535-051
 
SMCARNUT said:
I edited my original post and let you know that Cometic makes an .051 head gasket that should put you fairly close to what you need.
Summit part number Part Number: CGT-C15535-05I
Click to expand...
Thanks. I can certainly make this work with the 25cc KB dish if unable to find something with a little deeper dish, though ideally I'd like to get that quench down between .030-.040. Not the end of the world if I can't though. That 34cc offering from icon would be great if it were available in standard size.
 
This may be perfect for you and save some piston money to boot.
They also have a Part Number: CGT-C15535-060 a .060 gasket too.
 
Reviving this thread as I'm diving back into this engine build.

Turns out the block will need bored after all, which opens up piston options a bit more, but I've got another problem, which is that I think I've been operating with the wrong assumptions in terms of what I can get away with regarding cranking compression.

I've been operating on the assumption that ~180psi is going to be workable on 87 octane with good quench, but it looks like I have been wrong about that. David Vizard says one should be able to get away with 165psi on a tight quench motor with 87.

Unfortunately that presents some real problems. If I want to preserve the .039 quench, and I run the largest dish hyper piston I can find (25cc KB416), that gets me down to 9.04:1 static compression. Sounds great right? Well, I would need a camshaft that closes the intake valve 60* ABDC to get the cranking pressure down to 164psi. That's something in the 252 duration range! That strikes me as a terrible idea for a daily driven pickup truck.

The largest dish I can find at all is 34cc (Icon 9977), but it's 2618 forged which require a lot of piston to wall clearance and will significantly reduce service life, which is important in this application.

Does anyone know of a larger dish cast, hyper, or 4032 forged piston?
 
Msmith68W said:
Reviving this thread as I'm diving back into this engine build.

Turns out the block will need bored after all, which opens up piston options a bit more, but I've got another problem, which is that I think I've been operating with the wrong assumptions in terms of what I can get away with regarding cranking compression.

I've been operating on the assumption that ~180psi is going to be workable on 87 octane with good quench, but it looks like I have been wrong about that. David Vizard says one should be able to get away with 165psi on a tight quench motor with 87.

Unfortunately that presents some real problems. If I want to preserve the .039 quench, and I run the largest dish hyper piston I can find (25cc KB416), that gets me down to 9.04:1 static compression. Sounds great right? Well, I would need a camshaft that closes the intake valve 60* ABDC to get the cranking pressure down to 164psi. That's something in the 252 duration range! That strikes me as a terrible idea for a daily driven pickup truck.

The largest dish I can find at all is 34cc (Icon 9977), but it's 2618 forged which require a lot of piston to wall clearance and will significantly reduce service life, which is important in this application.

Does anyone know of a larger dish cast, hyper, or 4032 forged piston?
Click to expand...

https://www.us.mahle.com/media/usa/motorsports/sbm-dish-webpage-3.pdf
 
Disregard, I made an error along the way and have been over-estimating how much dish I need. Thanks guys.
 
It's all good. Racetec has a piston that will work great and they're under the same ownership as Scat, which is who is supplying the crank, so I actually have the option of ordering a balanced rotating assembly from them with the pistons I need. Probably going that route. Thanks guys.
 
Msmith68W said:
….
The largest dish I can find at all is 34cc (Icon 9977), but it's 2618 forged which require a lot of piston to wall clearance and will significantly reduce service life, which is important in this application.
….
Click to expand...

Is this true about forged pistons in general?
 
You could have the pocket on the piston fly cut if necessary to open up clearances and cc’s. Here’s a pic of custom Carrillo pistons I was learning how to cut on the mill for my brother.

IMG_4957.jpeg


IMG_4958.jpeg
 
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