73-87chevytrucks.com
73-87 Chevy _ GMC Trucks => Performance => Topic started by: 81Cheyenne on June 06, 2008, 09:39:17 am
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I'm building a 383 for my C10. Is it better to use 5.7" or 6" rods? I have a chance to buy a new crank that uses 6" rods at a reduced price and wanted opinions on rods before I bought it. I'll be buying new rods either way whether I get this crank or not.
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You'll never notice a difference performance wise. Hardcore racers like to go with a longer rod due to dwell and thrust angle but for a street engine just go with the most affordable balanced rotating and reciprocating assembly.
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I have 5.7" rods in my 383 and will go with at least 6" next time... Often times you either have to clearance the rod bolts or get a reduced-base circle cam (that's my choice) and corresponding pushrods with the 5.7's... For the money, check into building a 396 small block. Just a little more stroke than a 383, but quite a bit more power.
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What are you building the truck for, a drag truck or street? For the street, you won't be able to tell the difference as most of you driving will be spent between idle and 2500rpms.
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I'm building the truck for the street. I'll be using it for hunting and fishing. Pulling a boat (occasionally with a slide-in camper on the back), hauling my motorcycle,goofing around,etc. I like the idea of the torque that a 383 will give me on hills,boat ramps and so forth while pulling some weight.
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If that is the case, I would build the cheapest rod configuration and put the money elsewhere for longevity/dependability.
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Yep just go with what's most cost effective. If you buy a matched set you most likely won't have any major clearance issues and the cost will be much lower. I'll be building another one very soon with some Vortec heads. I will post the whole build when I do it but I'm also going to go the more cost effective route.
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Some pistons (for 6" rods) have the pins running through the oil ring area
(http://gearsandrears.com/123picsforindex383piston.jpg)
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here's a good article from many years ago
it gives a few tips on how to get a handle on detonation
I think this article is more important now, with the price of fuel heading toward the sky.
a few bucks spent on machine work and attention to detail will pay off in the long run.
http://www.chevyhiperformance.com/howto/47075/index.html
here's a torquey 383 that might be of interest
http://www.chevyhiperformance.com/techarticles/148_0207_ht_383_chevrolet_crate_engine_build/index.html
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i'm going to use 5.7's
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here's a good article from many years ago
it gives a few tips on how to get a handle on detonation
Speaking on detonation....(Maybe I should start a new thread what do you think Capt?)...I'm probably going to go with 6" rods since I picked up a SCAT 9000 that uses them. I have had conflicting opinions (from guys whose opinions that I trust) on whether I should go with flat top pistons or a dish. I'm using 64cc vortec heads. On second thought, I WILL start a new thread on this one.
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Just calculate your compression ratio. Figure out which pistons you have available and find out what the -cc volume is
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Just calculate your compression ratio. Figure out which pistons you have available and find out what the -cc volume is
Yup. Done that already. I guess the question is what's the max compression ratio that will run on pump gas and still give me plenty of power with this setup(vortec,383,C10,etc)?
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I would strive to stay at or near 9:1 unless you are going with aluminum heads. By pump gas are you talking about 87 or 92? I would build it to run on 87 it it were mine.
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here's a good article from many years ago
it gives a few tips on how to get a handle on detonation
Speaking on detonation....(Maybe I should start a new thread what do you think Capt?)...I'm probably going to go with 6" rods since I picked up a SCAT 9000 that uses them. I have had conflicting opinions (from guys whose opinions that I trust) on whether I should go with flat top pistons or a dish. I'm using 64cc vortec heads. On second thought, I WILL start a new thread on this one.
Using a flattop with 64cc heads with a .030" over piston .025" in the hole will put you at 9.8:1 with a -5cc flattop with a .040" gasket
If you zero deck it it's close to 10.8:1
Deck it .015" and use a dished slug for better detonation resistance... with the piston .010" in the hole that gives you .050" piston to head clearance with a .040 gasket.
some people say that .050" piston to head is tight, but I've run the slugs .003" above the deck with a .039" gasket with no problems in a 383 for a Ski Boat. You gotta use hypereutectic pistons for that, and keep the piston to wall clearance tight.
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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?
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Not really sure why you started another topic, we answered that already in this one....
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KB makes a "D" reverse dome that should fit the bill if using a 6" rod
(http://kb-silvolite.com/images/piston/LKB169.gif)
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/images/piston/LKB193.gif)
http://kb-silvolite.com/performance.php?action=details&P_id=155
This would make a detonation fighting, torque beast even at 9.4:1
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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.
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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.
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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. :-[
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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...
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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.
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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
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(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?
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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.....