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Author Topic:   5.5, 5.7, AND 6.0 chevy rods, what gives?
WesternAuto17
Dirt Freak

Total posts: 248
posted February 04, 2002 04:13 PM
What's the diifernce between all these chevy rods? What makes the 6.0 better? Is the 5.7 a lot better rhan a 5.5 (or whatever stock 350's are)?

If I buy a 12.1:1 Jr 406 shortblock, should I upgrade from 5.7 to 6.0?

This motor will be in a 3000 lb street stock and should see about 6500 rpm on a regular basis, but not much more.

[This message has been edited by WesternAuto17 (edited February 04, 2002).]

dirtracers
Dirt Full Roller

Total posts: 74
posted February 04, 2002 05:02 PM
First of all 400s have 5.565 rods and 350s have 5.7 rods and 6.0 are after market rods. From what I have been told 6.0 rods are the best they give more torque off the bottom end my brother had 6.0 rods and I had 5.7 rods except for that we had identicle motors and I couldnt tell much difference and my car was 200 pounds heavier

Wild Bunch Racing
Dirt Full Roller

Total posts: 53
posted February 04, 2002 05:09 PM
Well, the best way I can describe it is that you want the 6.0 rod if you plan to run 6500 rpms or lower this extends the life of your engine and gives you a more square horse power curve that is higher than the 5.7 or 5.565 rod. I really like the 6.0 rod because of the pull out of the corner. Now what rpm rannge do you plan to run this determines what lenght of rods you need?

WesternAuto17
Dirt Freak

Total posts: 248
posted February 04, 2002 05:14 PM
I should be between 5500 and 6500, but does that length make difference in how the engine is put together?

RangeRover
Dirt Maniac

Total posts: 174
posted February 04, 2002 09:55 PM
I'm sure you already know that a change in rod length will take some planning, because the crank's stroke and piston pin location will determine which rod you can use. If you already have a 350 with its 5.7 rods and just try to go with 6.00 rods, the piston will pop out of the bore .300" (if you were decked to zero, that is). This, of course, would create a catastrophe.

If you are in the planning and purchasing stage, go with the long rod set up for it's multiple advantages like: less piston side-load in the bore and with everything else remaining the same, the long rods make more power because their increased time at TDC produces higher cylinder pressures and consequently more effecient combustion. Because of this last effect, the engine, to an extent, can tolerate a bit more timing and/or lower quality fuel.

I'm for the longer rods.

hughes
Dirt Maniac

Total posts: 141
posted February 05, 2002 07:25 AM
The 6" rod gives the bottom end better geometry for High horsepower engines. It leaves the piston a top dead center for a longer period of time, and the angle at which the piston is pushing the rod down after combustion is improved. Which should equal a few more ponies with a little more reliability.
Help Me Out on this one, SD29HNC! Thats just off the top of my dome with pulling out "THE GREEN BOOK"

sdhnc29
Dirt Freak

Total posts: 467
posted February 05, 2002 10:30 PM
BINGO hughes !!! The longer the rod , the slower it moves off of TDC . This allows a for a much better cylinder fill , and yes , it will increase horse power , as well as broaden the torque band . Rod stroke ratio is often overlooked , but must always be considered when trying to get the most power for your dollar !

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Hendren Racing Engines
Rutherfordton , NC
(828)286-0780

#28
Dirt Maniac

Total posts: 154
posted February 06, 2002 09:18 AM
I think it's unanimous, go with the 6.00 rod if it's not too late.

justin
Dirt Maniac

Total posts: 167
posted February 06, 2002 10:37 AM
What kind of modifications need to be done for 6.0 inch rods to work? Also, are there any stock 6.0 inch production pieces out there or are they all aftermarket?

holeshot
Dirt Full Roller

Total posts: 53
posted February 06, 2002 10:51 AM UIN: 3728
how about a 6.250 rod in a 377 chevy combo can you go to far? will this work?

Flatlander
Dirt Freak

Total posts: 310
posted February 06, 2002 04:17 PM
I know this will sound crazy but be sure and use a piston designed for the rod the pin height is different this is on a 350

hughes
Dirt Maniac

Total posts: 141
posted February 06, 2002 05:08 PM
Justin, olsmobile had a 6 inch rod(I think it was a diesel motor), but its junk --- alot of failures on a race motor. Back in the day before all the aftermarket rods were out there (and priced reasonable), the old school guys raced them for that extra edge, but they don't compare to the aftermarket rods.

Wild Bunch Racing
Dirt Full Roller

Total posts: 53
posted February 06, 2002 09:15 PM
Justin, you need to buy pistions to use with the 6.0 length rod. The pin location is different on a 6.0 rod than on a pistion for a 5.700 rod. In other words the pistion for the 5.7 rod is longer than the pistion for the 6.0 rod.
happy racing

Flatlander
Dirt Freak

Total posts: 310
posted February 06, 2002 09:37 PM
not to disagree but the pistons aren't nessarily longer the location of the pin is just different

Hambone
Dirt Roller

Total posts: 9
posted February 10, 2002 11:45 AM
This topic is on the lines of a question I was going to ask. I'm getting ready to build another 383 and try my first 406. In my current 383 I just have stock recon. rods with heavy rod bolts. I have talked to some various friends of mine and they mostly seem to say I need to go to a better rod for reliability. What do you recomend? The problem with some rods on the 383 combo is cam and rod bolt clearance. Any suggetions? I will be running these in a alcohol modified motor turning @6500-7000 rpm.

sdhnc29
Dirt Freak

Total posts: 467
posted February 11, 2002 12:57 AM
I'd use the Crower Stroker Sportsman Rod ! They are reasonably priced , and I've never seen one fail . I sell them them for $434.63 , and I'm sure that you can find a dealer in your area that will sell them to you for the same price .

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Hendren Racing Engines
Rutherfordton , NC
(828)286-0780

istock59
Dirt Freak

Total posts: 237
posted February 11, 2002 03:45 PM
Scat's seem to work pretty well for us in claimer motors. Haven't had one come apart yet. Bent 2, but never broke them...

WesternAuto17
Dirt Freak

Total posts: 248
posted February 11, 2002 03:51 PM
Maybe, probably, this will show my ignorance, but how do you know when you've bent a rod? Also, how long does it stay bent before it breaks?

Flatlander
Dirt Freak

Total posts: 310
posted February 11, 2002 10:14 PM
i always look at my cylinder walls during freshening if you see alot of rub in one area or an intermittent scoring this could point to it but the best way is to pull them and take them to a RELIABLE shop and have them checked My luck has always been to break them and that hurts

istock59
Dirt Freak

Total posts: 237
posted February 12, 2002 07:40 AM
WesternAuto17, when I bent 2 of my Scat's, it was because the pistons on top of those rods came apart. In the process of having the motor rebuilt, I had all 8 rods checked by the machineshop. The one bent rod was pretty noticable. The other was just a minor tweak.

But...they make great paperweights now!

Hambone
Dirt Roller

Total posts: 9
posted February 16, 2002 11:51 AM
Do you recommend bushing end or press fit rods?

Eljojo
Dirt Freak

Total posts: 273
posted February 16, 2002 06:05 PM
Interesting how many people believe there is a hp/torque gain in increasing rod length. I had read a thread a couple of years back where an engine shop did some dyno work with rod length experiments. They found there was NO appreciable performance gains in using long rods (they had tested rods from 5.58 to 6.250). They did recomend the longer rods simply for the geometrical advantages leading to longer engine life. Does anyone have dyno sheets that prove them wrong? This is being written by a guy with a 6"rod 406!

Flatlander
Dirt Freak

Total posts: 310
posted February 16, 2002 06:06 PM
Bushed ends be sure and use new spriro locks on your pins also a used one can be twisted and not stay as located and the only gain on the 6" rods are reliabilty in my opinion but theres diff ideas it sort of like the pinion angle thing

[This message has been edited by Flatlander (edited February 16, 2002).]

[This message has been edited by Flatlander (edited February 16, 2002).]

neverenoughbrew
Dirt Forum Racer

Total posts: 82
posted March 02, 2002 07:12 AM
Holeshot I run 6.250 rods in 377 and run 6.125 rods in 5/8 stroke engine.

LUBEGUY07
Dirt Maniac

Total posts: 156
posted March 03, 2002 09:37 PM

Eljojo is right there is a great article about this on the isky cam web site they say there is no perfomance gain. Its just another way for us racecar drives to waste your money on lol

WesternAuto17
Dirt Freak

Total posts: 248
posted March 04, 2002 09:35 AM
If 6.0" rods improove the rotating assembly's geometry, how could that not help horse power at least a little?

sdhnc29
Dirt Freak

Total posts: 467
posted March 04, 2002 10:00 PM

The main thing that we have seen in dyno testing shorter vs. longer rod engines , is an increase in higher RPM horse power , and a torque band that is much longer and broader . The longer the rod , the slower the crank is able to pull the piston off of TDC , due to a more favorable angle on the rod as the crank swing's around . What this will accomplish is a slower vacuum created by the piston as it is pulled down the bore by the crank . This allows for a better cylinder fill . In other words , rather than jerking the piston off of TDC with a short rod , and having a rapid vacuum pulling air and fuel into the cylinder , the whole action is slowed enough by a long rod to allow a much better cylinder fill . This is where you will see a horse power gain . Better cylinder fill = more power . Engine's with restricted intake , or head's that don't flow too well , seem to benefit most from this .

We've found that shorter rod engines will have a much more , for lack of a better word , peaky torque curve . By going to a longer rod , we have found that if we lose any torque at all , it is very minimal . Generally a longer rod engine's torque band will move up in RPM , and flatten out before and after the peak torque . The shorter rod engine's will peak torque at a lower RPM , but do not seem to carry this torque out much beyond the peak .

------------------
Hendren Racing Engines
Rutherfordton , NC
(828)286-0780

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