What is the Best Rod Length for a 383?

[81Cheyenne]

I'm building a 383 with 64cc Vortec heads,6" rods,RV cam,carb,headers...etc. Will be used for hunting,fishing,daily driver,pulling a boat with a slide-in camper on the back sometimes.  I would like to run pump gas (probably 87 octane) but might be tempted to go higher octane on occasion if I want to have a little fun. I have heard differing opinions from some local knowledgable professionals on whether to go with a flat top piston or a dish top. I've used the available calculators to determine compression ratio. I guess that the question is what is the max compression ratio that I should shoot for in this situation? Also what is the max that you would run on the street using pump gas?

[Captkaos]

Not really sure why you started another topic, we answered that already in this one....

[Blue 82]

KB makes a "D" reverse dome that should fit the bill if using a 6" rod


Here's the specs... note the 1/16 rings
http://kb-silvolite.com/performance.php?action=details&P_id=57

the above come out to 9.2:1 with a .010" deck clearance

If you want some save some $ and go with the 5.7 rods
save a few bucks with 5/64" rings
and use the money saved to deck the block .015" (Piston to head clearance at .010")

these would work fine  -12cc D
Compare the position of the piston pin location to the above photo


http://kb-silvolite.com/performance.php?action=details&P_id=155

This would make a detonation fighting, torque beast even at 9.4:1

[VileZambonie]

I wouldn't be too concerned with keepint the piston to wall clearance too tight if you are going to run 6" rods because you are going to see a noticable ridge and cylinder wear. I agree keep your compression ratio under 10:1 if you plan on running pump gas and a good timing curve. Bumping up the compression ratio and retarding the timing isn't going to help you.

[81Cheyenne]

Not really sure why you started another topic, we answered that already in this one....

I thought that I may be drifting from the original topic on rod length to a discussion on compression ratios so I thought that I was doing the right thing by starting a new topic.  Sorry about that.

[81Cheyenne]

KB makes a "D" reverse dome that should fit the bill if using a 6" rod

Here's the specs... note the 1/16 rings
http://kb-silvolite.com/performance.php?action=details&P_id=57

the above come out to 9.2:1 with a .010" deck clearance

If you want some save some $ and go with the 5.7 rods
save a few bucks with 5/64" rings
and use the money saved to deck the block .015" (Piston to head clearance at .010")

these would work fine  -12cc D
Compare the position of the piston pin location to the above photo

http://kb-silvolite.com/performance.php?action=details&P_id=155

This would make a detonation fighting, torque beast even at 9.4:1

Blue,
Looks like these are for a 5.7 (3.48 stroke).

Update: Uh....never mind. Guess that I should have scrolled down a little.

[Blue 82]

I guess I can't read...

Here's a D-cup for a 383
http://kb-silvolite.com/performance.php?action=details&P_id=161

If you are going to do the whole stroker deal,
might as well find a kit with everything
and save a few bucks...

[81Cheyenne]

If you are going to do the whole stroker deal,
might as well find a kit with everything
and save a few bucks...

Well, I would, but I already have the crank. It's a SCAT 9000 for 6" rods. Bought it from the same guy that I got the roller block from as a package deal. Had never been out of the box.

[Blue 82]

Well, I would, but I already have the crank. It's a SCAT 9000 for 6" rods. Bought it from the same guy that I got the roller block from as a package deal. Had never been out of the box.

I posted a slug that fit's the bill,
I'm sure there are others,
GM has used the circular dish pistons for decades
The D-cup is just one option
A chamber matching reverse dome is an option too, although pricy....
http://cgi.ebay.com/ebaymotors/SRP-PISTONS-SBC-350-INVERTED-DOME-383-138103_W0QQcmdZViewItemQQcategoryZ33623QQihZ002QQitemZ120255798225QQrdZ1QQsspagenameZWDVW

Find anything else you like?

Here's a compression calculator that might be of assistance
(remember, a stock SBC slug is approx .025" in the hole)
http://www.race-cars.net/calculators/compression_calculator.html

[81Cheyenne]

(remember, a stock SBC slug is approx .025" in the hole)

Are you counting the head gasket here? I'm plugging in zero clearance with .040" for head gasket thickness just for the sake of argument. Sound pretty resonable?

[Blue 82]

For a "zero" measurement,
you gotta remove anywhere from .020" to .035" from the deck
standard deck height on a 5.7 is 9.025"
If you do the math, it puts the slug below the deck approx .025"/.035"

Here's the math
(1/2 x stroke) + Rod length + piston compression height - deck height = distance above/below deck

let's do a stock 350 (it works the same for all engines)

(1.74") + 5.7" (rod) + 1.550" (Piston pin centerline)  = 8.990

Now subtract 8.990" from the GM deck height (9.025) and the piston is theoretically .035" below the deck

I've seen .005" difference bank to bank
and .005" diff from front to back on the same bank

After the block is Bored & Honed
After it's line bored/honed
After it's stroker clearanced
and surgically cleaned
you have to put in the crank, pistons and bearngs, then measure the piston depth at all 4 corners (cyl's 1,2,7,8)

then you know how much you have to take off for your desired piston to head clearance

Lopping  .020"  or even .030" off of the deck is a gamble on an unknown block.....

Some shops will trim .010" off and call it a day
you can still measure the depth and adjust the head gasket thickness accordingly (say you wind up with an average of .020 in the hole..... a .022" gasket will give you .042" piston to head clearance so you can get your desired comp ratio where you want it)


However if you preform a post mortem on a shortblock before you take it apart you have a good idea of what what you are up against.....