ever hear of 6inch rods in a chevy 400

i heard if you put six inch rods in a 400 and shave the pistons you can pull 10 grand out the rpm's. if so how much do you shave off the piston and is there any block clearancing needed.

 

Not but once if you use the stock cast crank.
And since the stock rods are 5.565, I guess you'd have to shave about 1/2" off the stock pistons.

You can build a 6" rod 400, but it takes a custom crank (if you wanna turn lots of rpms) and pistons.
Larry T

I got to thinking about this after I posted. To build a 10,000 rpm engine is gonna take more than replacing a part or two. Everything in the engine is going to have to be designed to work at that rpm and (just as important) to work together. There probably wouldn't be many production line pieces in the engine. And this stuff isn't cheap.

 

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And you add about 30 grand in parts and machine work that could be possible.

 

I wish it was that easy...but wtf do I know....

 

Why the hell would you want to turn a 400 cid engine 10,000 rpm's anyway? Seriously?

Whoever told you that was retarded.

 

Longer rods mean LESS RPM and slower piston speeds BUT better breathing and torque. Shorter rods mean more piston speeds and cylinder wall loading and also accelerated wall wear.
Thats why the stock 302 Chevy screams when the 350 doesnt.
You will need special pistons when you use the 6 inch rod. Both are pretty cheap nowdays. The benefits are there but RPM isn't one of them until you do what was posted earlier and thats spend major Thousands of dollars.

 

that's basically an exaggeration. The stock rod length of a 400 is 5.65", which is considered to be short. A short rod length creates higher stress angles. A longer rod relieves this. I'm pretty sure that you need specific pistons for this conversion, and not necessarily a crank-- But don't quote me.

The 2 bolt main block is most preferable (even over the 4 bolt main)- but is really only good for about 5500-6000, without adding splayed 4 bolt main caps.

 

By adding the rods will not make it spin 10k
But does have plenty of advantages performance wise...
By adding a longer rod it makes less leverage against the side of the cylinder walls like the smaller factoy rods and makes for better piston quench and adding a lil more torque,
And yes you need a certain piston for 6" rods notice how pin is moved up higher in the piston near the rings also makes for a lil lighter piston.
If you ever ride in a well built 6" rod 400-406 you will remember it! they make some bb's envious.
Heres a few pics of my 406
11.1 Mahle forged flat tops
6" scat rods and internally balanced scat crank

 

it wouldn't be a 400 " motor to go 10k....a 3" stroke crank or smaller would probably get you there with the right cam and a big pair of heads. you'd be in the same boat as those comp eleminator guys....changing valve springs every 2 or 3 passes......

as for 6" rods in a 400. they do it every day. if you have a 400 block , you could use the crank , and those 6" rods you have ...buy some off the shelf pistons and build a pretty decent motor. not a 10k motor , but a usable 6500 rpm motor that will make good power and torque. last 406 i had in the shop was a handfull on the street and definently would leave you smiling .......

 

World of Outlaw 406s go between 8,000 and 9,000 rpms. Lap after lap after..............................
and how many RPMs do the 500 inch Pro Stock engines turn? Yea, I know it's a whole other deal.
Larry T

 

Great input and not to get off topic about 400's but heres a friend of mine that has a true 10k motor and actually launches it at 10k
small cube 282 motor 15.1 comp. heres the specs on it, http://www.watsonruppelperformance.com/id5.html

 

10K takes cubic money Displacement is almost irrelevant. The valve train alone will set you back $8~$10K. Billet crank, ...

Big SBC is cool, but you have inches and torque so just gear it accordingly and and go melt some pavement

 

This is not correct either. The 302 and 350 have the same length rods and share the same 4" bore. The difference is in the stroke...3.0" for the 302 and 3.48" for the 350. The shorter stroke is what makes the 302 a quicker winding engine than the longer stroke 350. 6" rods are readily available for the sbc and you can easily buy pistons to work in your 400. Oh, to answer the original question. NO. You cannot put 6" rods in a 400 sbc by shaving the stock pistons down.

 

I've been thinking about building a 6" rod 350, where do I get the correct pistons?? thanks-

 

The long rods require that the wrist pin sits high in the piston. The internal angles are lessened by using longer rods, so there are fewer stresses on the crank.
10 grand isn't unheard of but you've gotta have a bulletproof valvetrain.

 

Would recommend Probe pistons from cnc motorsports

 

Pistons for running 6.00" rods in 3.48" stroke 350 and 3.75" stroke 400 SBC engines are readily available from any of the major parts outlets like Summit Racing.

The 400 used a 5.565" rod, so it's not going to be feasible to cut .435" off the top of a regular 400 piston. You'd be literally cutting the entire top off the piston.

Making a 400 turn 10-grand on the tach takes a lot of 'spensive internal and especially nice valvetrain goodies as well as a great set of cylinder heads, the 6" rod length has little if anything to do with that. The longer rods reduce the side loads on the cylinder walls.

 

some of the titainium valve springs are 150 each and last maybe 5-6 1/4 mile runs....so i've heard from reliable sources...
way outta my price range

 

It's kind of like putting a six-inch rod in your girlfriend, if you don't do it just right, you won't get the desired result.

 

Spinning 10 grand with a 6" rod 400? Yeah your head will be spinning cuz you spent 10 grand and it ain't done yet! Then there's "why?" when there are many ways to make monster power at lower engine speeds. Long rods are good for that too not just big RPM. I wouldn't go so far as to call the person who said it a retard. Engine dynamics isn't a subject one can grasp in a simple conversation. Frankly anyone but the most hardcore racers here have little need for custom engine combinations.

 

I agree....some times the things that are asked are so f--ng dumb.

 

the rod length has no effect on piston speed, that is the effect of the stroke, the longer distance ( longer stoke ) means faster piston speeds.

 

One point not mentioned is the rod length to stroke ratio. The six inch rod in a 400 brings this ratio back into the acceptable range of 1.6:1, which is very close to what the 350 has stock. Putting this in perspective, all small blocks have a 5.7" rod except the 400, so in comparison the 302 Chevy has an exceptionally long rod, especially when looking at the differences and similarities between it and the Ford. The Ford deck height is so short that there is little room and it takes a custom piston and a longer rod to get a desirable rod:stroke ratio, just like in a Chevy 400! This is to be expected because the Chevy began life in a larger form with room to grow designed in.

 

Uh oh, get out the pop corn!

 

There's a whole bunch of KB slugs for this build ...

http://kb-silvolite.com/forged.php?action=details&P_id=337

Another function of this setup is that the intake vacuum pulse becomes longer and less sharp.
Larry Widmer has a bunch of p00p on theoldone.com regarding breathing and rod length/stroke ratio.

 

Dan,
If you are thinking about building a 350 with 6" rods (BTW, good engine) and don't really know where to start or get the parts, I'd suggest you get with a good machinest and talk to him about it. He can recommend parts and you can buy them through one of the mail order companies or (you might be suprised) maybe the machinest will meet their prices.
Larry T

 

Think about the pistons movements near TDC and BDC. Longer rod reduces the acceleration of the piston in this area.

Jukka

 

I've got a 6" aluminum rod 406 and it takes all kinds of special stuff, back when i first built he engine it was a lot of manual labor cutting the block and getting a specail cam because the rod beams actually hit the camshaft. Nowadays there are better aftermarket blocks that have clearance and different cam locations, i think you can go to a 6.125 rod if you want (maybe longer on the really big small blocks). I built mine to run B/A in comp eliminator, all cyls were close to 17:1, 1.625 pro stock valve springs, crower crank, cam, lifters, Brodex -12 heads angle milled, 40 couple cc pockets, 2.10/1.60 titanium valves, 3/8 pushrods, jesel - you name it. Don't ask the cost. This little whore made close to 1000hp, sidestep clutch at 9K (tried all the way up to 11.5K), shift at 8.5K go thru traps at 7.70's. And it wasn't competitive, there were more powerful ones out there, spent all that money and did all that work and came up a day late and nickle short. But thats okay, i've still got the engine and the car is right here. Obsolete or not she's an impressive piece.
There is a big advantage to a 6" rod motor, because of the length of the rod the piston lingers longer at both TDC & BDC (with head off and wrench on crank you can really see it) and whenthe crank rolls around the piston accelerates like a rocket so that the, either intake or compression, signal is very strong and positive. It is much quicker than a 5.7" rod. The total revolution time is the same for either engine, the 6" rod motor lingers longer at TDC/BDC and makes the time up in rod speed.
If you want to read about the effect of a longer rod, go to the guy that exploited it best, Smokey Yunick. He is still way ahead of eveybody, even offset ground his piston pins to get a longer rod.

 

WOW! That's cool!

 

Excellent info- Thanks.