chevy 400

[hotrodnharleys]

hello guy's and gals.... I'm not to smart when it comes to some things. I have a chevy 400 bored 40 over I would like to know can I put 6'' rods on to any piston I'm going with dish type. this engine is nothing fancy, just a 400 been bored going to put 3/4 race cam in it. I have to use stock heads 76cc. I just want it to sound good just a cruiser. thanks

[jerry clayton]

Yes-there are lots of pistons for 400 with 6 inch rod

[glennsexton]

Welcome to CHR:
I like the idea of an internally balanced crankshaft assembly for a 400 using 6” rods and a short-compression-height piston to allow room for larger crankshaft counterweights. This will typically cost a bit more than the standard rod and crankshaft but by using 6” rods, experts say that the rod-length to stroke-ratio is better. Assuming that you are staying with the stock stroke of 3.75”, you can certainly use a 6 inch rod in a 400 block but there are a few questions that you should answer first.

What is the block deck height? Stock for a 400 is 9.025 and if the block has been bored it may have been resurfaced or cut to square thing up. Stock 400 rods are 5.565. This is important as you need to calculate compression height.

Compression height = block deck height – rod length – (.5 x stroke)

For a bone stock 400 it would be: 9.025 - 5.565 – (.5 x 3.75) = 1.585
For a 6” rod with a stock block: 9.025 – 6.0 – (.5 x 3.75) = 1.150
For a 6” rod with a 9.010 block: 9.010 – 6 – (.5x 3.75) = 1.135

The difference between stock everything and a block that has been resurfaced to 9.010 using 6” rods is .45” – which can be really significant. Several manufacturers make a piston with 1.133 compression height for the intended purpose of using a 6” rod (like this one for a .030 over 400 http://www.summitracing.com/parts/ue...make/chevrolet)

As is the case whenever “other-than-stock” components are used, clearances will need to be vetted prior to final assembly to make sure all the rod bolts clear block and camshaft.

One last note – please do not choose a cam before hearing from Techinspector on how to calculate the “stack” and correctly determine your compression ratio. This, combined with heads (don’t forget you have to have steam holes) you select, the intended RPM range of the engine, type transmission, rear end ratio, and weight of the car and what you want to do with it – cruise or race – all need to be sorted out before cam selection. Don’t make the rookie mistake of thinking you need a bad ass sound when such typically indicates an over cammed and poor performing engine. For anything driven on the street, a healthy throb is always better than a rumpty-bump that signals to an educated ear that you really don’t know what you’re doing.

Have fun and give us some more information so we can help you out.

Best,
Glenn

[hotrodnharleys]

thanks for all your help. got it together runs great!

[techinspector1]

thanks for all your help. got it together runs great!

I'm sorry I missed out on this build. There's a ton of stuff I could have taught you.

.

[glennsexton]

thanks for all your help. got it together runs great!

So what all did you end up with? Always love to hear how things came together.