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Piston recommendations?

Portagee

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I'm building a 440 for my '69 bee, and have just finished assembling the short block. For reference, I'm using a '74 block (std bore) with a standard forged crank, six pack rods, and stock flat top pistons.

I just measured the deck clearance to be 0.150", and a calculated CR of 7.8:1 (using 0.039 gasket and 906 heads, estimating 86cc chambers).

I read that this is typical for smog engines with low compression, but definitely not what I'm looking for with this engine. I plan to run comp cams' version of the MP purple cam (K21-672-4), so this compression ratio is not gonna cut it.

Any recommendations on how to address this? I've considered everything from decking the block, milling the heads, using a shim head gasket, etc...

I'm thinking that the best path forward would be a piston swap, but I don't know how to select the best aftermarket piston for this application.

Thoughts?


Thanks,

Mike
 
The best choice is absolutely a piston swap, the other methods are bandaids that bring their own problems.
At theoretical blueprint deck height, pistons with a 2.083 compression height would be zero deck. I have seen flat tops at 2.06, 2.02, and 1.99. Yours appear to be 1.93. You obviously know how to use a compression calculator. Plug in various deck heights till you get the compression you want. With open chamber heads, you dont have any quench to worry about, so head gasket thickness can be juggled to get where you want too.
I understand that the sixpack pistons really give about 9.5 to one, but.... measure and calculate yourself.
 
I agree with 33Imp. piston swap is the best way to get there. There are lots of off the shelf pistons out there today and you can also get custom pistons at a reasonable price. Just do the math and choose the compression height for your application. Not really that hard as you already know how to measure things correctly! ruffcut
 
I would recommend a piston and rod swap. Those 6 pack rods are heavy! So many pistons available today too. With those open chamber 906 heads your going to want your pistons damn near zero deck. 440'
 
Boy, it didnt take long to spend $1,000 of the OPs money.
 
Boy, it didnt take long to spend $1,000 of the OPs money.

When you gotta send out a search party to find the pistons....

He was already thinking piston swap & asking about the best aftermarket piston for the application...

440Coronet500 isn't wrong about the 908 rod being heavy & by the time you buy rod bolts & have the rods resized your probably $350 in, CNC Motorsports has the Eagle rods for $515, you can buy a number of rods cheaper but...

O/P's post. "I'm thinking that the best path forward would be a piston swap, but I don't know how to select the best aftermarket piston for this application."
 
Boy, it didnt take long to spend $1,000 of the OPs money.
:rofl:

Thanks for thinking of my wallet!

And thanks to everyone else - I figured a piston swap was the way to go, just wanted others' opinion. And don't need a whole search party to help lol, but do value the opinion of people here who know more than I.

I'm perfectly capable of finding an aftermarket piston that will fix the compression ratio (didn't mean to say I didn't know how - just that I'd appreciate feedback). However, if anyone else has swapped in aftermarket pistons to work with a stock 440 crank, six pack rods, and 906 heads, I would appreciate hearing about it!

Thanks!
 
For my 440 build I used 2355 Speed Pro forged pistons, stock forged crankshaft, LY rods, 906 heads, Edelbrock RPM Performer intake, 1407 750cfm Edelbrock carb, and a
298/303 Duration 0.466/0.488 Lift Summit 6401 cam. 440'
 
For my 440 build I used 2355 Speed Pro forged pistons, stock forged crankshaft, LY rods, 906 heads, Edelbrock RPM Performer intake, 1407 750cfm Edelbrock carb, and a
298/303 Duration 0.466/0.488 Lift Summit 6401 cam. 440'

That's great information, thanks! So looks like those pistons are for 0.030 overbore, so I'll try to find their equivalent stock bore 4.320 pistons and check the CR for my engine.

How do you like the performance of your 440 with those components? I'll be running a trick flow single plane intake, and my cam has similar duration, but with 0.509 lift - so I'd expect it will be a bit more radical (which is why I'd like the 10:1 CR).

On a side note - how does everyone feel about swapping out pistons without rebalancing the rotating assembly? I've just had everything balanced to within 1 gram, and have gone from externally balanced to internally balanced and will be running an ATI damper. I would really like to not have to re-balance everything, and hoping I can just weigh the new pistons vs. the old ones and pray they're within a few grams of each other....
 
440 bore is .020 smaller than a 400, so a thirty over 440 piston is only ten over on a 440. I would look for .040 or.060 440 pistons if you wanna go that route.

First I don't know how a 400 slipped into this conversation...

Second if you don't want to re-balnce stick with the 2355, they are heavy like the stock piston.... And BTW 2355 comes in different sizes, naturally the std bore is more $$$$

https://www.summitracing.com/parts/slp-l-2355f/make/dodge

I'd buy the cheaper .030 over piston & spend the saving on boring the block...
 
I’ve got old speed pro in mine.. big heavy but 11.0:1 .. I like squeeze and with my Mr. Six Pack #4 Cam and lifter set up.
 
When you gotta send out a search party to find the pistons....

He was already thinking piston swap & asking about the best aftermarket piston for the application...

440Coronet500 isn't wrong about the 908 rod being heavy & by the time you buy rod bolts & have the rods resized your probably $350 in, CNC Motorsports has the Eagle rods for $515, you can buy a number of rods cheaper but...

O/P's post. "I'm thinking that the best path forward would be a piston swap, but I don't know how to select the best aftermarket piston for this application."

Im not saying anyone was wrong. But you can kinda tell the guy is on a budget because he just wants to "swap" pistons. Not saying that's right or wrong either.
 
so, what compression ratio are you shooting for? if the block is finished bore/hone now how will that influence piston choices? what does a 75cc edelbrock head do for you? is the cam you've picked a must have or are there other choices?
 
I agree with 1 Wild R/T, 2355 come in multiple sizes and are heavy like the original pistons. The goal of my build was basically to the 440 HP spec. I used a slightly bigger cam than the stock 440 HP. I always have the rotating assembly balanced on my builds. It makes sense when you change rotating/reciprocating mass. I would discuss this with your engine builder/machinist. The ATI damper is a great choice and the only one I recommend besides Fluid dampers. 440'
 
so, what compression ratio are you shooting for? if the block is finished bore/hone now how will that influence piston choices? what does a 75cc edelbrock head do for you? is the cam you've picked a must have or are there other choices?

Based on the original post, It's a standard bore, and I believe that initially he was not going to finish bore/hone anything.
 
For a street motor I like the Keith Black Hypereutectic pistons, not badly priced and fit tighter in the bore. I've used them on 2 motors now including my current stroker which sounds comparable to yours with no complaints. It's 9.8:1 with 452 heads but being a 400 based stroker the math won't be the same.

Are your 906's ready to go, do they need rebuilt? I ask because that alone could cost almost as much as a set of heads.
 
On a side note - how does everyone feel about swapping out pistons without rebalancing the rotating assembly? I've just had everything balanced to within 1 gram, and have gone from externally balanced to internally balanced and will be running an ATI damper. I would really like to not have to re-balance everything, and hoping I can just weigh the new pistons vs. the old ones and pray they're within a few grams of each other....

Yes, you can maintain reasonable balance by swapping the 2235 for what you have. Just check weights as you go.

But the question you should be asking (well, maybe not) is what does everyone think about putting a new piston in a used bore................
 
One of the more important considerations I would have with regards to running new pistons in a used bore is....... ring travel near tdc.
If there is really any kind of wear ridge in the used bore, you don’t want the new pistons to have the rings riding over that ridge when coming up to tdc.

“If” you can find a taller piston that has the top ring land no farther from the pin c/l than the current pistons, and the ridge is minimal, I’d consider using new pistons in the used bore, provided the wall clearance is within a normal range.

If the rings would have to ride over the ridge...... I’d have the cylinders bored oversize.
 
One of the more important considerations I would have with regards to running new pistons in a used bore is....... ring travel near tdc.
If there is really any kind of wear ridge in the used bore, you don’t want the new pistons to have the rings riding over that ridge when coming up to tdc.

“If” you can find a taller piston that has the top ring land no farther from the pin c/l than the current pistons, and the ridge is minimal, I’d consider using new pistons in the used bore, provided the wall clearance is within a normal range.

If the rings would have to ride over the ridge...... I’d have the cylinders bored oversize.

This.
 
And at that point your looking at custom pistons... Like I said before best cheap route .030 over 2355's & bore the block..
 
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