rod question

hi wanted to know what rod lenght do I need for my engine. kb short deck block, crank 3.750 stroke, 4.310 bore, using older veney fuel heads for blown appl. thx. wally

 

you might want to give a little more information. what is the piston compression height? what compression do you want to end up with? what head gasket thickness? this will help get you the right answer, there are a lot of variables when figuring rod length.
Darren

 

sorry for the vagueness on my motor combo, but I dont have much infor for you, just its a short deck with 3.750, veney older fuel heads. think 170 cc, as for what I want to do is, wanted to put it together with the most compression posible to run it injected(with a thin copper gasketon alky) then when I get mid season I want to switch copper gaskets to get less compression and run the blower 14-71. have my altered and want it to run in the 7.50s class not exactly sure how much hp that will take

 

It seems you have 2 things you don't yet know, rod length and piston pin height.
The basic formula is;
Deck Height - (stroke/2) - Rod length = Pin Height
or
Deck Height - (stroke/2) - Pin height = Rod length

Both of these are assuming the piston to block deck are the same at TDC. (adjust as you see fit)

Hey hemi guys, what are some common lengths to help "mopar" through this?

 

Contact the piston mfg. and get the specs on them , a good place to start .

 

thx still need pistons for this set up 4.320 bore. old TAD block

 

If you look on this page:

Hemi piston information

The list is from Brendan Murrays site, gives you information about different pistons, their pin heights, part numbers etc.

You say you run 4.31" bore, check out the two pistons listed at 4.31" bore, the OEM chamber and veney head, and read it's comp height. I assume you'll want the veney head piston compression height if your running veney heads. Once thats determined you can use SoDak's 2nd equation to work out your rod length. Note the rod lengths listed on this are for standard deck blocks, so ignore those lengths if using a short deck and use the equation with .5 off the standard height.

Then once thats worked out, you will know that the piston on that page will work with the rod length you have calculated. Order that piston with the part number listed, order your rod length and you should be well on your way.

That combination will give you more than ample power if you want to run 7.50's in a altered. We ran a similar combination to what you want to run but with a 8-71 and ran 7.1's without breaking a sweat. We put a 14 on it and it ran 6.8's without leaning on it.

Hope that helps a little by removing a few unknowns. Good luck

 

http://www.ariaspistons.com/products/chrysler.html
Need to scroll down a little until you find the B/Alky Hemi section.

The chart that BB/FA posted from Brendens site looks like an older version of an Arias chart. For what you're doing, the 1.428" CH piston is more than adequate, since you're running the 170 cc head. Arias more or less considers these a "shelf" piston and sell them at a pretty decent price, and usually will have a set ready within a week or two, plus you can buy replacements 2 at a time instead of 4 if you're on a budget. Nothing trick about them, but they'll work with just about any 170cc head. Once you know your compression height, you can do the math to figure your rod length. Just quick figuring with a .060" head gasket, looks like you need around a 6.98" rod.

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Just saw where you're wanting to run injected first, probably won't be able to get much more than 12-1 with a std. stroke, even with thin gasket, but it should run OK, just not optimum, plus side should be about zero maintenance. Also, for whatever reason, they won't make the shelf piston in a 4.320", at that price. I tried back in the fall, had to go with the 4.375" piston. Also the price on the chart is a little confusing, I paid $69 a piston, think they call it a decal package price, fwiw.....