Hi everyone

I posted a post a couple of weeks ago about which to buy a 460 or 429 and i've decide to go with the 429(cheaper) and i bought a set of pistons of ebay which i was told would suit a 460 or 429 and i found out since that they we're purchased for a 460 origionally.
My question is can you use 460 pistons in a 429? what about if you mix and match crank and rods?( i know with a 350 chev you can use a 400 crank with 350 rods and pistons to get 333ci but can you do this sort of thingwith a ford BB).

Also what is the diffrence between normal conrods and cobra jet rods? because i can get a set for $65. Are they worth buying for the rebuild on the 429.

Thanks for your help
Aaron,

 

The only differences in 429/460 are the crank stroke and piston compression heights. The blocks are identical, use a 460 crank/pistons or 429 crank/pistons. Rods are interchangable. CJ (or truck) rods have a beefier small end shoulder and football shaped (stronger) boltends. Be certain to have any used rod resized.

 

I totally agree with George. The only thing I would do different is substitute ARP rod bolts for the stock CJ/Truck rod-bolts first, and then have them resized.

Deen

 

Thanks for your reply's
What would happen if i used the 460 pistons and the 429 crank would the piston's foul on the heads/valves? or wouls it just drop the compression dramatically?. because i've already got the pistons i'd still like to use them if there is anyway of using them.

Thanks Aaron,

 

Its been so long since I've heard that question I can't remember the answer. Take your 429 piston and a 460 piston, put them side by side with a single piston pin in the pin boss of each piston. If the piston compression height (where the pin boss/hole in the 460 is lower than the 429, you'll suffer low compression. ?If higher, the top of the piston will stick out of the bore. You'll be able to see the difference. They won't interchange.

I'd expect it would be less expensive to buy/turn and use a 460 crank with your existing new pistons than buy new pistons for the 429 crank.

 

According to my book, 460 pistons have a compression height .130 inch shorter or lower than 429 pistons. If you need, I will dig the book out and get the measurement of each piston so you can tell what you have.

 

If you wouldn't mind jimlj that would be good, as long as it's not too much trouble to find it.

Thanks Aaron,

 

Let's see, with a .250" longer stroke on the 460 minus .130" on the shorter piston compression height with same block deck height, it should stick out the top of the cylinder by .120" or nearly 1/8" using a 429 crank?

 

According to the book, (I have never had the two pistons side by side so I'm basing this on what I have read) the compression height (center of wrist pin to the top of piston) is 1.760 on a 460 and 1.890 on a 429. If you use the 429 crank with 460 pistons, you will have low compression and a dog for preformance. Go with what George said and find a 460 crank IF you do in fact have 460 pistons.

 

So if i measure from the centre of the hole that connects the piston to the conrod with a gudeon pin to the top of the piston i'll either come up with 1.76 or 1.89 inches right?

 

So if i measure from the centre of the hole that connects the piston to the conrod with a gudeon pin to the top of the piston i'll either come up with 1.76 or 1.89 inches right?

I'm planning on supercharging it in a while so i should be able to use these pistons in that re-build and just use the pistons that are coming with the motor on this re-build?

Thanks Aaron,

 

According to the book I have thats how to measure your pistons. here is a link to the book I am using. I bought it right here from MotorHaven. There is some mis info in the book reguarding which heads are CJ or SCJ heads, but in is very informative and has been a great help to this electrician with my engine. http://www.motorhaven.com/customer/p...63&cat=&page=1

I havent a clue on your second question, but there are several guys on here that have far more experiance with these engines that may be able to answer that.

 

There are various compression heights for pistons, depending on the combustion chamber size of your cylinder heads, deck height and what final compression ratio you're after. In most cases people plan their desired c/r and then buy pistons to meet that objective within deck height and head combustion chamber sizes.

Use one of the many free formulas on the net that allow you to enter the above specifications to find out what c/r you're going to have.

Since you're going to put a blower on the engine I assume the pistons are forged, not cast and you're after 8.0-8.5:1 c/r. Identify the manufacturer of the pistons, the part number and get the actual compression height from the manufacturer. Piston compression height can vary wildly due to slight depressions, crowns and manufacturer.

 

I measured the pistons today and they came up closest to 1.760 so they must be 460 pistons then. Is it that small an increase in piston height that changes c/r that much? i always thought it would have to be a much larger increase than that.

Thanks Aaron

 

Since the 429 stroke is less, the shorter pistons will be well below your deck height. This will cause a drastic decrease in your CR. You can't use those pistons. I'd find a 460 crank and use it. You already have the correct rods and pistons. 460 cranks are cheap, (stockers are, at least). You'll love the extra cubes anyway.

JJ