73 rally charger. blowen motor? piston questions.

[JHolslin]

I was driving my charger on the freeway last night, when I gave it some gas I could hear a bad knock. I limped it home. sitting at idle there is a little knock but when a rev it it sound like a horrible knock. I assume I lost a connecting rod bearing. so now.... I planed on rebuilding the motor after I redid the body but now ill have to pull it. with the factory heads is there a piston that will up the compression ratio? or will I need to shave the heads? and with a bigger cam is there room for all this shenanigans?

[EccentricMagpies]

Not an expert but you might want to add some information on your motor size
Big block / small block / stock / etc...

[Nacho-RT74]

Yes is posible to use higher CR pistons... allmost any engine have that option on the performance market

[JHolslin]

o jez!! I thought I put that in. it has a 400 magnum. all factory. I was hoping to get the compretion up and install a bigger cam. my concern is valve clearance with a bigger cam and a (Domed) piston?

[Nacho-RT74]

I don't think there are domed pistons off the shelf to 400s

On an affordable price rate, hypereutectic pistons keith black KB240s. They are able to get pistons 0.020" down the hole on a blue printed block deck height. That is around 0.1" higher than stock. This allong metallic headgaskets should raise the CR IN 1 to 1.2 ratio from stock

Cut the heads around 0.020" will help even more. The quench area should be around 0.095" per some specs I have read around but I have measured up to 0.110" on some combustion chambers of the 452 heads I got NOS. I cc'd these NOS heads combustion chambers and got 92 cc where should be per blue printed values around 84 cc, so cut the heads will get you on those numbers or close.

All these together could get you on around 9.5 CR
-KB240 pistons
-Block deck height cut to blue printed values.
-Metallic headgaskets
-Heads cut around 0.020"

If you want to get more juice and money is enough, bigger valves and light bowl blend job to the new valves size. This won't raise the CR but will allow more admision and exhaust flow.

[JHolslin]

That's great info.
Thanks.

[RECHRGD]

A collapsed lifter can sound like that. 

[c00nhunterjoe]

The 240 has valve reliefs. Even with all that milling labore, you will still be lucky to have 9:1. Might as well spend that money on a 451 rotating assembly. Street friendly strokers are 2k, comes crank, rods, pistons, bearings, rings, rod bolts, etc. The whole rotating assembly, brand new.

[Nacho-RT74]

The 451 pistons have same valve reliefs and they sit ( under blue printed specs ) a same block deck height... just the quench step makes difference. Of course will get more displacement too.

On the affordable world, KB240 is just like a regular rebuild job, but with the plus of a higher CR.

Still getting around to 9:1, is a good option.

But if you want to invest more, go for the stroker kit

A collapsed lifter can sound like that. 

True

[JHolslin]

that seam reasonable for the strocker kit. I am starting to think the noise maybe in the valve train. It only knocks once every other rotation. so the lifter or rocker or valve issue is my next step in locating the noise. I have not yet done anything since it happened this weekend. but I plane on pulling the valve covers and running it and watching the rockers. if it is just a Lifter, valve or rocker issue I can put my money into the body first instead of pulling the motor (Rebuild motor 2019 itinerary). thanks for all the great info. I like the idea of a rotating assy. for $2000.