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Old 05-12-2012, 11:08 AM
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355 SBC Build Questions / Help

Hello Rodders new to the forums So I am looking to build a 355ci SBC
I acquired a long block from the salvage yard I believe it is a 880 casting says Hecho en mexico, been at the machine shop for a few months now so not quite sure. I know that it is a 4bolt main hyd roller 1 piece main seal with the swirl port heads (meh), had it all cleaned up and pressure tested its good to go. So before I can have some Machine work done need to get some piston, have them mic bore hone. This will be built for a DD no Bottle no Drag and never spin past 5500 just a Very Torquy Tough Engine
I plan on reusing the stock crank and rods as there in good shape, hoping I can get it all internal ballanced with the pistons ect.. now lets talk pistons "FLAT TOPS"

KB Pistons KB120-030 4.30 I know about there bigger then "normal" ring gap
Flat top, with two valve reliefs + 7cc
Compression Distance 1.561 in.
Piston Ring Thickness 5/64 in. x 5/64 in. x 3/16 in.

So a little bit of math if I a doing it correctly 3.48 / 2 = 1.74 + 5.7 = 7.44 + 1.561= 9.001 so if the deck height is truly 9.025 although it can vary.. Basically I would like the pistons .005 in the hole or should be 0 deck?

And now will be the Head selection...and that been cast into stone on my decision for me a true aftermarket Vortec head RHS / EQ / Dart? with 170-180cc intake runners keep the velocity high for torque? I know they advertise them as 64cc chambers and can vary from 68cc to 62cc just have to stick the valves in and use a beaker and check... I am not sure on how accurate summitracing compression calculator is but it gives me 10:1 with a .040 4.030 gasket with true 64cc. Might Be pushing it with iron heads and pump gas..heard you can be okay due to vortec's fastburn combustion, good squish, octane, timing and nice shinny combustion chambers, Did I mention this will be going in a 5000+lbs Sedan?

I am not highly educated on cam selection I have very basic knowledge about them but know how they work. (Going to have alot of suggestions) about this I want to keep the hyd roller I was thinking of GM's ramjet 350 / HT383 cam as I seen on GMPP its got a great torque curve nice and flat

GM Ramjet / HT383 Cam

Will this cam even work with a 10:1 engine.. works very well in the ramjet with 9.4:1

So the main questions is the pistons good .005 in the hole at TDC with .040 head gasket and real "64cc combustion chambers" and would that cam work with a 10:1 compression if my setup is correct? or could i even squish it more with a .030 gasket?, It might have been answered here before but spent a good time digging around and could not find anything, esp about the cam, only in L31 stock truck engines.

Want to get this done within the next 2 months so the machine shop does not think I flaked out, so I can order the Pistons and have them do all the machining to get the short block out and on the engine stand

Input would be greatly appreciated, thanks again!

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Old 05-13-2012, 11:44 PM
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10:1 static CR could work with your cam, but you are pressing the limits for pump gas. Anything that helps keep the engine from "lugging" will help deter detonation, low gears, high stall torque converter, light weight vehicle, etc. A cool running engine also can tolerate more compression. Computer controlled fuel injection also lets you get away with higher CR because the computer will retard the timing if it senses detonation, but you don't say whether you're going to be running carb or FI (or I missed it). You do state that this build is going into a 5000+ lb sedan, which is HEAVY, and there is my concern.

My suggestion would be to change your piston choice from the KB120 flat top piston to the KB193 . This is a 12cc D-cup (reverse dome) piston that will still give you a good quench just like the flat-top piston. Using the KB193 will drop your static compression ratio a little over .5, from just over 10:1 to 9.5:1. The difference in HP would only be about 6-7 HP due to the CR difference, but you will gain more by being able to make sure you tune for max power than you will lose from the CR difference. This gives you some leeway for the motor running a little hot, a hard grade, or even a bad tank of gas.

The other thing I would change in your build is NOT to zero deck the block. I would have the machine shop deck the block just enough to get a flat, true surface and adjust the quench with head gasket thickness. That leaves the decks as thick as possible, less prone to warping/cracking. Instead of decking to .005 in the hole or zero deck with a .040" thick head gasket, maybe deck the block to 9.015. That would leave the KB piston (with 1.561 compression height) .014" in the hole. Combine this with a GM 10105117 composition head gasket (used in the Ramjet 350) that is .028" installed thickness. .014" + .028" = .042" quench with a thicker deck. The 10105117 gasket is $15.99 at Jegs

This build duplicates the 350 Ramjet longblock with pistons that will give slightly more CR, but better quench characteristics, than the dished pistons used in the Ramjet, and better breathing heads.
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Old 05-14-2012, 10:41 AM
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Quote:
Originally Posted by BigEd36
The 10105117 gasket is $15.99 at Jegs
That gasket is for a 4.000" bore. He is building a 355, so that would mean he would have .030" of gasket hanging in the bore, turning red hot and causing pre-ignition.
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Old 05-14-2012, 10:57 AM
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My apologies folks as for the car weight it is 3600-3800lbs I was not sure the info sticker in the door is old and fadded, not sure where I got 5000+lbs from But good'ole google helped me with that.

And for the top end, Yes it will be Fuel Injected (TBI Holley 670cfm) with megasquirt ECU and Ignition control with a Ford EDIS 8 (36 -1 crank triggered) with hotter after market coils so it will be quite precise ignition control, just curious about the wasted spark messing with the O2 readings

I plan on putting a beefed up 700r4 with lockup

As for the heads I was almost sold on the Summit/Dart Heads..Then after a few photos and digging around I hear there not real vortec's and if you look on Summit the intake runner looks really funky and on 1 post fella said he had to grind the tar out of it to gasket match, and saying it nothing like a Vortec runner.. sure a good number of us want to do a bit of cleaning up on some iron heads, but that sounds ridiculous

Just save my pennys and buy some RHS Vortecs
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Old 05-14-2012, 03:45 PM
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Quote:
Originally Posted by Silver Surfer
That gasket is for a 4.000" bore. He is building a 355, so that would mean he would have .030" of gasket hanging in the bore, turning red hot and causing pre-ignition.
According to info I've seen the actual bore on the 10105117 gasket is 4.10", so it would be suitable for a 4.030" bore 355.

From the Scoggin-Dickey Parts Center listing for the 10105117 head gasket:
Quote:
Compressed Thickness (in.): 0.028
Gasket Bore (in.): 4.100
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Old 05-14-2012, 03:57 PM
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And Summit says:

"Notes: Not for use on engines having larger than a 4.000 in. cylinder bore."
http://www.summitracing.com/parts/NAL-10105117/
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Old 05-14-2012, 05:57 PM
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This discussion really raises questions due to different specs noted on the internet, so to hopefully get info we can count on I contacted Pace Performance about the gaskets. They took my contact info and said their product advisor would be better able to answer my question. This is the email I just received from them:

Quote:
Hello Ed, I measured the bore on one of these gaskets and they are a 4.085" so there is no problem at all with .030" overbore, would even be okay with a .060" overbore. Mark
While I've never used these gaskets I have a 355 that I will be freshening soon, and the piston deck height is such that I could use these and gain a little over .2 CR compared to the Fel Pro 1003's that are in it now plus save some money. Think I'm gonna give 'em a try.
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