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  #1 (permalink)  
Old 12-16-2007, 03:52 AM
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question about a 406 sbc 5.7 or 6in rods street/race car

Hey guys! sorry its been so long since i have been on here, I have been working double time and building a new 55 Chevy!!!!!

The 406 that was in my new 55 blew up a few days ago. So to make a long story short, I took it apart and am sending it out to the machine shop, of course, to have everything "freshened up."

I am going with a new combination for this engine! All it was before was a flat top 406, pro 1 aluminum heads, 2.05 valve, 64cc, 850 cfm Holley, 10.5.1 cri stock rod and crank motor that was running strong..........

HERE IS WHAT I HAVE GOING ON:
I am getting ready to buy a new rotating assembly, something around 11.5.1 flat top motor for pump gas, with 550 or so lift hyd camshaft. The car is all full interior, and it is all steel, 350 turbo trans, 3500 stall and 350 gear in a 9in ford rear-end.

What I want to do with the car is drive it as much as possible, occasionally take it too the track, and run at least VERY low 12's to mid 11's. On the street I want it to be a tire shredding monster!!!

HERE IS MY QUESTION:
I already know I am going with a good rotating assembly, with forged pistons, but I can't make my mind up whether to use stock length rods for the torque coming out of the hole because that is what i love best, or running a 5.7 or 6in rod...........I don't plan on taking this engine over 7000 rpms and I thought that is where the 6in rod came into play, but I am not really 100% sure on that fact. What would you guys build if you were in my shoes, wanting a well put together engine, with plenty of "get up and go"???

Could someone please give me the pro's and cons of sticking different rods in the 400 sbc's. I do know that it helps cylinder wall pressure, frees up extra horsepower, and makes the engine run a little smoother.

What do you guys think I should do??? Should I use stock, 5.7 or 6in rods in a street driven 11 second motor that is trustworthy?????

Thanks for any input that you may be able to give me on these 400 combos, I look forward to reading all your replies because every little bit helps, and I am ordering my parts next week!!!
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  #2 (permalink)  
Old 12-16-2007, 06:08 AM
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First off thats a nice looking 55, always loved them. Secondly since this is primarily a street car and unless you want to run expensive gas I wouldn't go over 10.5 to 1, even with alum. heads, you might get stuck somewhere and have to use 87 or 91 octane.

The 6 inch rod would probably work but me thinks the forged pistons would be pretty expensive, I personally would go with a good set of 5.7's. By the way...you didn't say what blew in the old engine...piston?....rod?
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Old 12-16-2007, 06:47 AM
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I got 6" rods in my 406
the advantage is a heck of alot more HP
disavantage is youll need different pistons
or you could go with 6" rods and a different crank but youll need some clearancing done which really isnt advisable on a 406 due to the block webbing being thin.
one thing to remember longer rods will give you more power.
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Old 12-16-2007, 07:17 AM
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Quote:
Originally Posted by 327NUT
First off thats a nice looking 55, always loved them. Secondly since this is primarily a street car and unless you want to run expensive gas I wouldn't go over 10.5 to 1, even with alum. heads, you might get stuck somewhere and have to use 87 or 91 octane.

The 6 inch rod would probably work but me thinks the forged pistons would be pretty expensive, I personally would go with a good set of 5.7's. By the way...you didn't say what blew in the old engine...piston?....rod?

IT SPUN A ROD BEARING,,, AND ALL THE MAIN BEARINGS WAS IN THE BRASS,,, WHO EVER BUILT THE MOTOR DIDNT KNOW WHAT THEY WAS DOING I GUESS, THANKS
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Old 12-16-2007, 04:13 PM
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rods

Quote:
Originally Posted by dawg
I got 6" rods in my 406
the advantage is a heck of alot more HP
disavantage is youll need different pistons
or you could go with 6" rods and a different crank but youll need some clearancing done which really isnt advisable on a 406 due to the block webbing being thin.
one thing to remember longer rods will give you more power.

In all your extensive dyno testing how much HP is a 6.0" rod worth over a 5.7"????

Show us some numbers....

Keith
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Old 12-16-2007, 04:37 PM
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Quote:
Originally Posted by tiresmoke55
Hey guys! sorry its been so long since i have been on here, I have been working double time and building a new 55 Chevy!!!!!

The 406 that was in my new 55 blew up a few days ago. So to make a long story short, I took it apart and am sending it out to the machine shop, of course, to have everything "freshened up."

I am going with a new combination for this engine! All it was before was a flat top 406, pro 1 aluminum heads, 2.05 valve, 64cc, 850 cfm Holley, 10.5.1 cri stock rod and crank motor that was running strong..........

HERE IS WHAT I HAVE GOING ON:
I am getting ready to buy a new rotating assembly, something around 11.5.1 flat top motor for pump gas, with 550 or so lift hyd camshaft. The car is all full interior, and it is all steel, 350 turbo trans, 3500 stall and 350 gear in a 9in ford rear-end.

What I want to do with the car is drive it as much as possible, occasionally take it too the track, and run at least VERY low 12's to mid 11's. On the street I want it to be a tire shredding monster!!!

HERE IS MY QUESTION:
I already know I am going with a good rotating assembly, with forged pistons, but I can't make my mind up whether to use stock length rods for the torque coming out of the hole because that is what i love best, or running a 5.7 or 6in rod...........I don't plan on taking this engine over 7000 rpms and I thought that is where the 6in rod came into play, but I am not really 100% sure on that fact. What would you guys build if you were in my shoes, wanting a well put together engine, with plenty of "get up and go"???

Could someone please give me the pro's and cons of sticking different rods in the 400 sbc's. I do know that it helps cylinder wall pressure, frees up extra horsepower, and makes the engine run a little smoother.

What do you guys think I should do??? Should I use stock, 5.7 or 6in rods in a street driven 11 second motor that is trustworthy?????

Thanks for any input that you may be able to give me on these 400 combos, I look forward to reading all your replies because every little bit helps, and I am ordering my parts next week!!!
In test, after test, after test of 5.7, 6 inch, and 6.2 rods on the dyno, the best that's ever achieved is about 1%-2% which isn't outside the error range of the readings from one run to the other.

Rod length is mostly an exercise in mental masturbation rather than a producer of power. Just use what makes assembly easy and minimizes compromises in other places.

I would suppose that if you started an engine design exercise that first picked a rod length and then sized the other components around that decision, you might see something. Certainly Chrysler went down this road with the early Hemi, the poly-sphere, the R and RB, the LA and on. But trying to stuff 6 inch or longer rods into a 9.025 inch SBC, especially with a stroker crank, causes to many other compromises such as the pin invading the ring lands of the piston, trying to get the big end past the cam makes for using an inadequately strong (physically) cam that wanders the timing all over the place. If you're going to bust some bucks for a Rocket Block or some pro racing aftermarket block with a raised deck and cam bore, you've got some space to go exploring long rods without having to cobble everything else to get 'em in. For a stock block, you're just wasting money and time.

Bogie
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Old 12-16-2007, 09:16 PM
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Wasn't there a recent article on the board from some renown (or was it infamous) engine builder that essentially said to forget about rod length in the expectation of major hp gains?

I have to agree with Bogie.
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Old 12-16-2007, 10:18 PM
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Rod length ??

I agree with Bogie. But I would go with the 5.7" Rods rather than stock 400s. Most use 5.7" to reduce the thrust load on the cylinder wall with a better Rod to Stroke ratio. 6" Rods will put the piston pin into the Oil Ring land and may contibute to poor oil control on a street engine.
Although I'm building a 406 with Scat 4340 I beam Stroker Clearanced 6" Rods, 4340 Scat Crank, Wiseco PT019H3 Forged -20cc Pistons, ProTopline 64cc Chbr. 220cc Itk. Run. 10-1 Comp. maybe some N20. This will be mostly Strip some Street engine. After talking with Wiseco Rep he assured me with the ProTru Pistons oil control has been greatly improved.
This link will tell you way more than I can think about. LOL. Anything you can ask about 5.565, 5.7 & 6" rods etc. A very good read.
http://www.rustpuppy.org/rodstudy.htm
Another Good read.
http://www.purplesagetradingpost.com...%20engine.html

Last edited by SSedan64; 12-16-2007 at 10:38 PM.
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Old 12-16-2007, 10:35 PM
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I agree. The only real advantage i can see for a longer rod is less side loading on the piston, rings, cylinder wall. This reason alone makes them choice.

Also i think, as the torque and hp goes up with mods so does this side loading.

Im using 6" rods and the gudgeon pin is in the oil control land but thats only a concern with build it once engines who i think should use 5.7 rods.
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Old 12-17-2007, 01:56 AM
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Quote:
Originally Posted by SSedan64
I agree with Bogie. But I would go with the 5.7" Rods rather than stock 400s. Most use 5.7" to reduce the thrust load on the cylinder wall with a better Rod to Stroke ratio. 6" Rods will put the piston pin into the Oil Ring land and may contibute to poor oil control on a street engine.
Although I'm building a 406 with Scat 4340 I beam Stroker Clearanced 6" Rods, 4340 Scat Crank, Wiseco PT019H3 Forged -20cc Pistons, ProTopline 64cc Chbr. 220cc Itk. Run. 10-1 Comp. maybe some N20. This will be mostly Strip some Street engine. After talking with Wiseco Rep he assured me with the ProTru Pistons oil control has been greatly improved.
This link will tell you way more than I can think about. LOL. Anything you can ask about 5.565, 5.7 & 6" rods etc. A very good read.
http://www.rustpuppy.org/rodstudy.htm
Another Good read.
http://www.purplesagetradingpost.com...%20engine.html

THANK YOU VERY MUCH FOR THE INFO,,,, thats just what i wanted to be reading.. i learned a little bit from reading that,, i might just go ahead and run just the 5.7 rod for better cyl psi, but for a race/street motor i might save some money and not run the 6in rods,, that and i want more tork out of the hole and doing some fun burnouts more then being able to rev the motor in the really high rpm's thanks
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Old 12-17-2007, 07:05 AM
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More Rod Info

Quote:
Originally Posted by tiresmoke55
THANK YOU VERY MUCH FOR THE INFO,,,, thats just what i wanted to be reading.. i learned a little bit from reading that,, i might just go ahead and run just the 5.7 rod for better cyl psi, but for a race/street motor i might save some money and not run the 6in rods,, that and i want more tork out of the hole and doing some fun burnouts more then being able to rev the motor in the really high rpm's thanks
This is from the database. More Info.
stroke to rod ratio
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Old 12-17-2007, 07:18 AM
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Quote:
Originally Posted by k-star
In all your extensive dyno testing how much HP is a 6.0" rod worth over a 5.7"????

Show us some numbers....

Keith
easily get 75 to 100 hp gain depending on heads.
possibly more
and the torque will move up aswell with a longer rod.
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Old 12-17-2007, 07:23 AM
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Actually, the shorter rod is favorable for the street because they tend to reduce detonation by allowing the piston to dwell at TDC for a lesser amount of time. The shorter the TDC dwell time, the less chance of detonation. Short rods for pump gas.
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Old 12-17-2007, 07:51 AM
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Quote:
Originally Posted by Greg T
Actually, the shorter rod is favorable for the street because they tend to reduce detonation by allowing the piston to dwell at TDC for a lesser amount of time. The shorter the TDC dwell time, the less chance of detonation. Short rods for pump gas.

I not so sure about shorter rods reducing detonation. Check out this Old HotRod article.
http://www.purplesagetradingpost.com...%20engine.html
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Old 12-17-2007, 10:22 AM
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Quote:
Originally Posted by dawg
easily get 75 to 100 hp gain depending on heads.
possibly more
and the torque will move up aswell with a longer rod.


No not be an ***** but


there is no way....
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