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Old 02-21-2009, 10:46 PM
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383 question

My dad is building a 383 chevy and I told him I knew just where to get some answers for him so here goes. I was told that 5.7 and 6.0 rods are not actually the same length as 350-400 rods. From what I understand the 400 rods are actually something like 5.65 not sure exactly but not six inch and that 350 rods are a little shorter than a 5.7 rod something like 5.4 or 5.5 but not exactly 5.7. Keep in mind we're trying to learn here and this info I'm saying could be wrong cause im not sure. But in order to use an actual 350 piston you would have to use real 400 rods. Which this is one of the big mysteries is are the 400 rods not the same as 6.0. The 400 crank is 3.75 right? If you use a 5.7 rod you would have to use and actual 383 piston which is different than a 350 piston? I do know that if you use a 6.0 rod the wristpin will be into the oil ring. Could someone give me each scenerio. I dont need any part numbers just what each of the 3 combos need to work that way my dad get busy building so we can have the father son shootout this spring, Pretty sure the boys big block will prevail so might have to let him win but I wont tell. One more thing, Is there truth in the 6.0 rod builds more torque than the 5.7. They both end being 383's. If this is true please explain this to. He will be using vortec heads 64cc and he has a dual quad high rise with 450 carbs will this go on the vortec heads? We know it wont just bolt on. What do you have to do to make it work? He'll be using 12cc dish pistons which I think should be around 10.25 What is a good lumpy cam? It will see the strip in an s-10 pickup with 3.50 gears, turbo 350 and 3000 stahl thanksI sure appreciate all of your help thanks guys!

Last edited by ssonny34@yahoo.com; 02-21-2009 at 10:56 PM.
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Old 02-22-2009, 12:58 AM
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All small block chevy engines in the 1st generation used 5.703 inch rods except the 400. The 400 used shorter 5.565 rods. The only difference is the journal sizes. From 1955 to 1967 they used "small journal" rods and from 1968 on they used "medium journal" rods. If you used 5.565 rods you could use 350 pistons. If you use 5.7 rods (which I certainly would) use 383 chevy pistons. If you used 6.0 rods you would need a custom compression height piston. If you use the 5.7 or 6.0 inch rod, some clearencing will be required as usually the rod will make contact with a cam lobe and we usually shoot for .050 clearence.
A 5.7 rod will require a 1.425 compression height piston.
A 6.0 rod will require a 1.125 compression height.
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Old 02-22-2009, 09:20 AM
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383 question's

If you use an aftermarket eagle crank does this still require you to clearance the block. Also is there truth to using the longer 6.0 inch rod builds more torque? I was told that if you use a 6.0 rod the it is tryibg to shove the piston through the side of the block and is a high stress point. I was trying to picture this and to me it would seem that the shorter 5-7 rod would create way more piston to rod angle than the 6.0 rod. What do you guys think, just trying to help my old man out, he says thanks everyone.

Last edited by ssonny34@yahoo.com; 02-22-2009 at 09:25 AM. Reason: forgot to ask for more info
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Old 02-22-2009, 09:48 AM
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My machinest always likes to use a long rod. Now your talking just over a 1/4" actual difference between 5.7 and 6.0. Doest sound like alot but i can make for better rod ratio's. So use the longest rod you can afford to use--gennerally 6" rods aren;t to much more than 5.7".

In certian cases (mine for example), you need a super dished piston and can only use a 5.7 rod because the dish forces the pin lower in the piston thus having to use a shorter rod. Most people arent looking to lower the compression though like i am. I am doing it for use on 87 octane with just a carb, but also a a small supercharger in the future.
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Old 02-22-2009, 10:02 AM
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6" rods tend to consume more oil as the result of an inferior oil ring land (the pin goes through the bottom). Some people say taht this oil consumption is acceptable and run a 6" others use a 5.7" rod for this reason.

NOw this part is debatable, but most people agree that:

a shorter rod will give you more torque at lower RPM levels, but a longer one will give you more hp at higher RPM levels, it has to do with piston dwell and the speed of combustion. I like using GM powdered metal 5.7" rods because they are cheap and have been proven pretty durable. I would use a 6" rod if I got a good set for cheap, but the rod angle/oil consumtion issue isn't enough of an argument to make me spend more on rods when money would be better spent on a LOT of other things like better pistons, rings, cam, rockers, valve springs, valves, etc.

IMO cost will be your deciding factor- if you have a good set of 5.7" rods on hand just run those, if you have to buy new rods 6" and 5.7" are usually the same cost so get the 6" for the better rod angles and reduced rotating mass. Your rod size is usually not a limiting factor on a street engine, and by usually I mean I have NEVER seen a case where it was the biggest single limiting issue.


On to the intake... Matching a standard intake to Vortc heads is usually not a good idea because the ports need a lot of work to line up. you can redril them to bolt together but bolting together and working together are two different things. A new intake would probably be the best step, or keep the tunnel ram and get different heads.
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Old 02-22-2009, 10:04 AM
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383 question's

Thanks for the info guys, He's got the eagle 3.75 forged crank, really good 5.7 rods.
Vortec heads that he'll put bigger valves in-2.02.
He also has a dual quad tunnel ram with two 450 carbs.
Can he put this intake and carb setup on the vortec heads?
I know there is something about the vortec bolt pattern?
Also he will use 12cc dish piston, with the vortec heads this should make 10.25 and run on premium gas.
He wants a good strip street cam combo to fit this motor. It will see the strip on weekends. turbo-350, 3000 stahl, he wants a good ratty sound but no plug fowling and so on.
Any recomendations?
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Old 02-22-2009, 10:07 AM
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If you look at the current popular rod ratios of the 1000+ hp big inch prostock mountain motors you'd see that the long rod ratio makeing more power is a myth for most part.
Go to the Reher and Morrision racing tech pages and read what they have to say about long rods. Essentually refering to connecting rod length they say the connecting rods sole purpose is to connect the piston to the crankshaft. End of story.

They only real way a 6" rod will make your go faster as compared to a 5.7" rod in a typical 383 SBC is by lightning your wallet.
There is a very slight difference in the piston motion/deg of crank rotation right near TDC. Optimizing the cam overlap (valve motion at TDC) will more than make up and exceed the power a 6" rod 383 will make , using a 5.7" rod in the same motor.

If you want power, put your money into the cylinder heads, first. Thats where the power is at.

Last edited by F-BIRD'88; 02-22-2009 at 10:19 AM.
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Old 02-22-2009, 10:22 AM
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The tunnel ram will not bolt up to or match the raised ports on vortec heads without extensive modification. If you want to make decent worth while power with a tunnel ram do not use small 450 cfm carbs. They will run but will make un impresssive power. Tunnel rams need big carbs to make big power. Other wise you won't make any more power than a decent single plane manifold and 1 good carb will make. Think dual 650,660 or 750cfm carbs.
The only good relitively easy way to bolt a tunnel ram on vortec heads is to use the bottom section of the new Weiand Stealth Ram EFI vortec manifold combined with the Weiand carb top for their "Hi-Ram" dual carbed tunnel ram and block off the EFI injector bosses. This is essentually a bolt on. It will work well.The top can be bought separately and this stuff can be found on EBAY etc.
Another good doable way is to cut up a Edelbrock Street Tunnel Ram (cut the runners off the base and weld it onto the base of a Professional Products Hurricane single plane manifold (vortec)
This will take carfull cutting, rewelding and probabily some epoxy work but could work well, if done right. You could also do essentually the same thing using a cheap factory L-31 vortec EFI intake manifold lower section as a new vortec base for the Tunnel Ram runners. Again cutting and rewelding is required.
Another good alternative is to trade your vortec heads for some other equally good heads with conventional port locations and intake bolt pattern. Bolt on your tunnel ram and go.
I would look at a 3500+ stall converter.
Tunnel rams like lots of RPM. If I was going to build a tunnel ram based motor for some kind of a shootout race, on a limited budget, I would build a 355ci based motor, not a 383.

Last edited by F-BIRD'88; 02-22-2009 at 11:01 AM.
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Old 02-22-2009, 10:23 AM
How fast is fast enough?
 
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Quote:
Originally Posted by ssonny34@yahoo.com
Thanks for the info guys, He's got the eagle 3.75 forged crank, really good 5.7 rods.
Vortec heads that he'll put bigger valves in-2.02.
He also has a dual quad tunnel ram with two 450 carbs.
Can he put this intake and carb setup on the vortec heads?
I know there is something about the vortec bolt pattern?
Also he will use 12cc dish piston, with the vortec heads this should make 10.25 and run on premium gas.
He wants a good strip street cam combo to fit this motor. It will see the strip on weekends. turbo-350, 3000 stahl, he wants a good ratty sound but no plug fowling and so on.
Any recomendations?

If he wants it to run well without a LOT of intake work then he needs to get a different intake with port locations set up for Vortec heads. Also, going to 2.02" valves really isn't needed. In fact if you just do the valves and no matching port work he'll loose power. I would instead suggest switching the exhausts to 1.6" and doing some clean up work on the heads. Also, solid roller valvetrains are getting cheaper, you can get a lot of power swapping up to one of those, just make sure your valve job on the heads is matched to the lift.
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Old 02-22-2009, 10:27 AM
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383 q's

My dad doesnt have alot of money to sink into heads and am pretty sure that matching the parts that we have to eachother is more imortant than just dumping 3000 dollars into a set of heads for what he wants to do with the engine. I was just asking about our combination and trying to get some other info and opinions. Im sure that this combo that he is going to use will without a doubt will push an s-10 pickup plenty fast.

Last edited by ssonny34@yahoo.com; 02-22-2009 at 10:29 AM. Reason: forgot to mention
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Old 02-22-2009, 10:51 AM
How fast is fast enough?
 
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if he's planning to do street driving with it the best intake will more than likely be a Performer RPM from edlebrock. It fits the bill 95% of the time. You can do what Fbird sugested to get a tunnel ram working well, but the RPM is ahrd to beat out of the box for $200. As to the head modifications I was speaking about, you're looking at a total cost of about $400, including tools, and sending it out for the valve job, but not including springs.
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Old 02-22-2009, 11:32 AM
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383

Thanks for the info, much appreciated.
We'll stay with the 383 because we already have the rotating assembly, just need a cam. He's an old school hotrodder and has quite a few sets a early camel humps so maybe he can use them, the intake will bolt up then. I know that you get better power from on e carb and single plane intake but the tunnel ram dual quad is cool and does perform fairly well so thanks for the info.
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Old 02-22-2009, 11:45 AM
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No, you can and will make more power with a tunnel ram than a single carb manifold but to realize this power you need fairly big carbs, a fairly big cam, lots of rpm etc.
People that tell you that single carb manifolds (even good ones) make more power than a tunnel ram (when done right) just don't know how to do it right.

Here is an example of a nicely done tunnel rammed street motor. it makes very good power and does not cost an arm and a leg.

http://www.hotrod.com/techarticles/e...ems/index.html
The more cam, compression and rpm you give it, the more power you will make. Note the power this thing makes with the nitrous oxide.
Tunnel ram motors really want 14:1 cr, 280@.050"++ cam timing .650"+ lift and 8500rpm. A tunnel ram with the right carbs, cam and dyno tuning on a motor like this is worth up to 80-100 extra horsepower over the best bolt on single plane single carb manifold. But this is a starting place.
The same motor with a single plane manifold.
http://www.hotrod.com/techarticles/e...ild/index.html


You can make a very good tunnel ram motor using the Camel back heads too.
Look at this build up for inspiration. The camel back heads will need a good bit of porting to get the air flow up.


The tunnel ram makes a good bit more power and lots more torque than the single plane at all rpms.

I agree, the tunnel ram is very cool. i have my own low budget SBC tunnel ram project on the go here. I'm using two good/used cheap Edelbrock 750cfm carbs.

The little 450 cfm carbs are good for adapting a tunnel ram to very mild near stock motor with a near stock converter etc for cruising around at low rpm but won't allow the tunnel ram manifold to really work and make its potential power. It's got to breathe.

Last edited by F-BIRD'88; 02-22-2009 at 12:09 PM.
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Old 02-22-2009, 12:31 PM
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F-bird,

Would dual Holley 650 spread bores work for this set up? I currently have 450's on my SBC tunnel ram project (still very early in the making) and was wondering if the 650's would be ok or would 600's be better? Also was curious if it is better to go with mechanical secondaries or vacuum secondaries. My build will be very similar except on a 327 with some worked over hump heads at max RPM around 8k. Thanks.

Brent
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Old 02-22-2009, 02:10 PM
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I doubt the spread bore carbs are going to work well. For a 8000K rpm motor I would want 2 650 (not spreadbore) double pumpers (R4777) or two 660 center squirters or two 750's.
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