360 stroker

[Wayne Rider]

I have a 1972 360 block bored .030 I have a Scat crank with 4" stroke I called Summitt and ordered pistons KB 356.030KTM after attaching to Eagle 6.123 rods they come out of hole .120 . I am using Edelbrock RPM aluminum heads and this combo won't work. I don't know are these wrong pistons ? does everybody have this issue to stroke a 360. I am about to buy a stock 360 crank. I would liked to have stroked one but is my best option to go with stock 3.58 crank ? Can I buy pistons that will work with out milling new heads ?

 

[Plymouth 65]

You need strocker pistons with a 4.00" stroke crankshaft. Your connecting rods are correct. 65'

 

[GTX JOHN]

A stock stroke crank will work but according to
my Calculations - the pistons will be down 90 in the hole
which is not optimal for compression ratio even for a street
car. Milling 50 off the heads would help alot.

Might be easier to sell the pistons and buy a correct set for
the stroker. It would sure run better.

 

[Rocket]

Those pistons have the right compression height for a 4.0” stroke and the stock rod length of 6.123.

See the pictures below however. 1 picture is the specs but the other is a review from summit from a customer. Looks like the quench pad needs machining. I assume you are only seeing the quench pad portion of the piston sticking out and not the full diameter. No mention of that when you read the product description on several sites. That bites.

 

[DNasty777]

So they’re domed pistons meant for open chamber heads?

 

[Wayne Rider]

They are actually step head w/ valve reliefs but the entire piston was out of the cylinder. and I have closed chamber heads . I seen ad you were talking about Rocket but only after I got them. I just don't know if there is a piston to fit without machining head and still be able to run high octane pump gas

 

[Wayne Rider]

So they’re domed pistons meant for open chamber heads?

they say step head with valve relief

So they’re domed pistons meant for open chamber heads?

 

[Rocket]

If you are using a 4.0” crank, 6.123” stock length rods and those KB356 pistons with 1.465 compression height the only other variables are your blocks deck height and the head gasket you choose. How much are the non-stepped part of the piston sticking out?

Hi

 

[teringer]

I would check the top ring grove to see where it rides ,if to high they will need a larger ring gap so they won't butt and damage engine like the KB pistons

 

[dusterbing the peace]

Did you have the block machined, or did you buy it from someone? Your decks would be shaved .108 from 9.6 blue print spec…which the machine shop would have charged a lot of money for that many passes. And most factory blocks have quite a few thou over the 9.6. Not being mean but I gotta think you’re measuring the wrong part of the piston. Also, if the decks are that low you’re likely to have horrible misalignment when you drop the intake on. Can you check with the machine shop?

 

[Ottmundr]

I did not do the research or the math on your parts. My first thought was to confirm your deck height. It is kinda critical.

 

[dusterbing the peace]

Read the notes at the bottom of the table here:
https://www.hughesengines.com/Index...dGVjdGlj&level3=NC4wMzAiIEJvcmU=&partid=27880

Then read this one, which may be more in line with what you need…give them a call to confirm:
https://www.hughesengines.com/Index...dGVjdGlj&level3=NC4wMzAiIEJvcmU=&partid=26375

Also click the note for “special clearance requirements” to know more about the ring gap like @teringer mentioned.

 

[RustyRatRod]

Yup that is KB's step head piston designed to be machined for a quench distance. They will not work out of the box, unmodified. You must measure your specific quench distance and machine them accordingly.

 

[Wayne Rider]

I would check the top ring grove to see where it rides ,if to high they will need a larger ring gap so they won't butt and damage engine like the KB pistons

will do thanks

 

[Wayne Rider]

Yup that is KB's step head piston designed to be machined for a quench distance. They will not work out of the box, unmodified. You must measure your specific quench distance and machine them accordingly.

Thank you

 

[Wayne Rider]

Read the notes at the bottom of the table here:
https://www.hughesengines.com/Index...dGVjdGlj&level3=NC4wMzAiIEJvcmU=&partid=27880

Then read this one, which may be more in line with what you need…give them a call to confirm:
https://www.hughesengines.com/Index...dGVjdGlj&level3=NC4wMzAiIEJvcmU=&partid=26375

Also click the note for “special clearance requirements” to know more about the ring gap like @teringer mentioned.

Thanks for info

 

[Wayne Rider]

I did not do the research or the math on your parts. My first thought was to confirm your deck height. It is kinda critical.

okay will check thanks

 

[RustyRatRod]

okay will check thanks

Not only confirm it, but I would let your machine shop of choice also square up the deck in relation to the crankshaft center line. They are almost always too tall and crooked from the factory. Chrysler was pretty loose with their machining tolerances. One last thing. If I was building a quench engine using domed pistons and open chamber heads, I would also have the crankshaft indexed. This assures all of the throws are equal and the exact same stroke.

 

[Wayne Rider]

Did you have the block machined, or did you buy it from someone? Your decks would be shaved .108 from 9.6 blue print spec…which the machine shop would have charged a lot of money for that many passes. And most factory blocks have quite a few thou over the 9.6. Not being mean but I gotta think you’re measuring the wrong part of the piston. Also, if the decks are that low you’re likely to have horrible misalignment when you drop the intake on. Can you check with the machine shop?

I bought motor but on tear down had 1972 main and rod bearings so I assumed it hadn't been torn down . I am a rookie so I could be wrong but the piston comes out of cylinder and my measure with dial indicator was .090. I am learning the hard way and I know a lot of people have done 408's I just didn't know if this was common . Thanks for comment

 

[Wayne Rider]

If you are using a 4.0” crank, 6.123” stock length rods and those KB356 pistons with 1.465 compression height the only other variables are your blocks deck height and the head gasket you choose. How much are the non-stepped part of the piston sticking out?

View attachment 1716001581Hi

I see now where it says additional machining work needs to be done for these to work. I wondered if they sell pistons that fit out of box

 

[RustyRatRod]

I see now where it says additional machining work needs to be done for these to work. I wondered if they sell pistons that fit out of box

Yes.

 

[Demonx2]

I used forged Mahle pistons in my 408 with the 6.123 rods. Mahle p/n SBM 460030I16. These look to have been superceded to p/n 930271030. -16cc dome volume. Cut my Eddie RPM heads to get the actual measured CR of 10.5.

 

[aaronk785]

I used icon ic745.030 and they came out at .002 below deck on my untouch stock block.

 

[Max1196]

they come out of hole .120

the piston comes out of cylinder and my measure with dial indicator was .090.

but the entire piston was out of the cylinder.

Where are you measuring from? The bump on the piston will be .085 higher than the rest of the land area, so it will be above the deck an amount. What's the protrusion measurement of the non-elevated portion of the piston?

 

[dusterdoug]

I see now where it says additional machining work needs to be done for these to work. I wondered if they sell pistons that fit out of box

There are several sources for flat top pistons for the 408 combo. Google search…