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TOPIC: SBC 350 Easy Mod

SBC 350 Easy Mod 25 Aug 2017 00:32 #1

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SBC 350 Easy Mod 25 Aug 2017 14:58 #2

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Impressive!
How's that comp cam compair to our "Mercruiser" marine cams? Gotta llove that vortec top end. I wonder what the numbers would be if they would've put in a quench type piston.

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SBC 350 Easy Mod 25 Aug 2017 19:41 #3

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Yup pretty impressive!
up until this dyno video, it has been an everyone's guessing game like what is my Vortec top end conversion is going to add? well evidently a lot more than you would think.
it is amazing what an aggressive cam and a pair of Vortec heads can do... what? they increased like 125.5 HP :)
Dave, Mercruiser's cam in our OEM SBC engine is pretty mild... duration @ .050 200 / lift .400 pretty close to their original 192 cam.

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SBC 350 Easy Mod 25 Aug 2017 20:37 #4

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According to the guy narrating the video, the 64cc Vortec chambers replaced the older 76 cc chambers, and is what gave him the additional point in the static compression ratio .
This suggests to me that cylinder block was fitted with Flat Top pistons. ( you would not see Full Dished pistons used with 76 cc heads)

For those of us with the Marine version SBC that is fitted with the dreaded GM Full Dished pistons, please understand that you cannot expect this type of performance increase.

Also, and while I love to see modifications like this, this is not a suitable build for a Marine SBC Cruiser Engine!


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SBC 350 Easy Mod 25 Aug 2017 22:23 #5

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Rick, I have to disagree with you & you suspected wrong.
You can clearly see in that video around 8:17 mark, that engine block is fitted with typical GM DISHED PISTONS.
I'm seeing dished pistons with 76cc non-Vortec heads.
You can choose from flat-top, flat with reliefs, dished, or domed, as well as change the gasket thickness and deck height.
There are several volumes to determine CR...All of these components will play an important role.
Using 64cc chamber volume Vortec heads on a 383ci stroker engine. 64cc chamber with a flat-top, 6cc valve relief piston, a 0.015-inch deck, & a 0.041-inch thick gasket creates 10.6:1 ratio...a bit too much for my comfort zone. by using a 20cc dished piston drops the ratio to a more E10 suitable 9.2:1 compression.
is the flat piston always better? are those GM's dished pistons always bad? not necessarily.

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SBC 350 Easy Mod 26 Aug 2017 11:01 #6

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Ruffryder wrote: Rick, I have to disagree with you
Understood!

& you suspected wrong.
You can clearly see in that video around 8:17 mark, that engine block is fitted with typical GM DISHED PISTONS.
Ah..... I stand corrected. Those are indeed the dreaded GM Full Dished.

I'm seeing dished pistons with 76cc non-Vortec heads.
IMO, that would be a rather poor combination for any performance.

You can choose from flat-top, flat with reliefs,
Yes...... F/T's with single valve reliefs, the 76cc chambers along with the correct Q/E dimension (deck height & gasket thickness), would work well for the 5.7L in the Marine version.


dished, or domed, as well as change the gasket thickness and deck height. There are several volumes to determine CR...All of these components will play an important role.
Understood...... I've been involved with the SBC since the mid 60s.

Using 64cc chamber volume Vortec heads on a 383ci stroker engine. 64cc chamber with a flat-top, 6cc valve relief piston, a 0.015-inch deck, & a 0.041-inch thick gasket creates 10.6:1 ratio...a bit too much for my comfort zone.
And certainly incorrect for a 6.3L Marine build...... but aren't we discussing the 5.7L in this thread???

by using a 20cc dished piston drops the ratio to a more E10 suitable 9.2:1 compression.
Just a note on that........ we most definitely DO NOT want to use the GM F/D pistons in a 6.3L Marine build.............. regardless of the cylinder head selection.

is the flat piston always better?
Joon, the F/T piston can create a Q/E if all else is done correctly.

are those GM's dished pistons always bad?
Yes.... IMO they are a poor choice, and should NEVER be used in a SBC Marine build.


The video is very interesting and impressive. I would agree that the "easy mods" would be great for use in a street machine.

IMO, this build would not necessarily be a good choice for a SBC Marine Cruiser Engine. For me, the GM Full Dished pistons would have to go bye bye!



For those of you who may be building or modifying a SBC marine version in the near future, the 5.7L SBC w/ the Vortec cylinder heads needs a good Quench Effect combustion chamber...... especially for Marine Cruiser use!



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Rick E. Portland, Oregon
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