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Thanks guys, I will measure my pistons and current bore size and will take the block into have the machining done the right way (of course)... I'm already into it for 8k... now is not the time to start saving a few hundred...
Will let you know if I have any more questions before the assembly. (will start a new thread to capture the build).
If God is your co-pilot, change seats!
Acts 2:38, the perfect answer to the perfect question.
Last edited by flatwater; 12-19-2018 at 08:29 AM.
snow on the ground here, so would like it to warm up before I start.. its a pain stocking up the wood stove for a couple hrs work at a time...not to mention keeping everything clean.
thanks again for the feedback...really appreciate it!
No prob. I have learned so much from others I feel it is my duty to share when I can.
Just trying to firm up my CR numbers to make sure I’m whereI want to be.
I have been reading up a bit on “D” shape pistons vs dishedfor marine use and the “quench”. Saw a few threads that guys were pretty set onthe “D” shape piston style. (of course I have dished already)… so just want tomake sure I don’t have to exchange anything.. (I have the time now to do so ifneeded).
I’m trying to finalize my CR ratio but am left with notknowing my deck height. Do I need to assemble the crank, rod and piston to getthe deck height? Sounds like I would need to go that far to determine 100%.
I asked my parts supplier to set me up for around 9:1Cr as Iwant to run 87 octane fuel pulling the kiddies around on skis. No need to run premiumfuel and the cost at this point as they are only starting out. (Fuel costs inCanada are absolutely ridiculous)…
If I have my numbers right this is what I have so far.
Compressed head gasket .041”
Stroke length 3.75”
Bore 4.03” (new block, clearance machined, but not machined .030”in the bore, so will a 377 build).
the info is borrowed from another site. this is what I'm worried about...
If building one with the standard 4.000" bore 5.7L block, you end up with 377 cu in (6.2L ).
If you go with a .030'' over-bore 5.7L block, you end up with 383 cu in (6.3L ).
There's 33 more cu in of displacement with this engine due to the .270" longer crankshaft stroke.
(GM's 6.6L (aka 400 cu in) stroke is 3.750" ....... 5.7L stroke is 3.480")
The main journals must be turned down in order to fit the 5.7L block.
The rod caps do need to be modified for clearance as does the 5.7L block in certain areas.
With the stroker kits that you can buy, you'll likely get components that are suited for the auto guys.
If you don't specify, very likely you'll get the full dished pistons, of which I'd not wish on anyone for a SBC.
While the full dished pistons do bring the C/R into a correct range, these cannot possibly create a quench or squish within the combustion chamber. The quench or squish is important for a Marine build, and especially important for a mild stroker for Marine cruiser use.
Quench effect or squish zone
Note the dotted lines that show the locations of the piston dished areas while underneath the "wedge" area.
Note where the full dished piston "dished" area is under the wedge.
In order to gain a quench/squish, the piston deck surface needs to "mirror" the wedge area best it can.
A Low Compression Quench, a D-dish, or a Reverse Dome style piston offers this deck surface.
(the flat top piston can also create a quench effect w/ a 5.7L build, but makes for an excessive C/R if used in the stroker build for Marine use)
The piston profile selection can't actually be made until a cylinder head is chosen, and the chamber volume is known.
Piston profile -vs- combustion chamber and wedge area
Note the full dished piston at the bottom, and the two quench style pistons regarding the piston deck surfaces.
With a good quench dimension, C/R can be increased a point or two, and the ignition advance can also be increased with little concern for increased detonation potential.
More spark lead places the LPCP closer to 12* or 14* ATDC, where torque is born.
(if a lousy combustion chamber is created, ignition advacne must be held back, which makes for a lazy LPCP...... perhaps as late as 16, 17 or 18* ATDC)
The Hot Rod guys tend to like the longer rods. The longer rods raise the wrist pin location in the piston, effectively creating shorter skirts. Ring landings are now closer the piston deck.
While the longer rods are an advantage, the changes to the piston are somewhat counter productive for the Marine build.
Since we run under heavier loads, and don't run at high RPM, the longer skirts are an advantage for us.
Both the longer rods and longer skirts would be ideal, but unfortunately, we can only have one or the other with this build.
Point being... if you're going to do this, do it correctly.
The added cost for the correct pistons won't break the bank.
Other than the correct compressed head gasket thickness, nothing else out of the ordinary is required.
BTW, this is not necessarily limited to the Stroker engine build..... all of this can also apply to a Marine SBC 5.7L build.