Mopar Muscle Association UK

What pistons would you recommend for a 318 with a 30 thou overbore.
Have just laid my hands on a block that's had all the machine work done, crank polished, etc.
Have never rebuilt an engine before, so any advice appreciated.
Andy

Id probably go with Keith Black Pistons.

In relaity, it depends on what you want from the new motor....250hp warm engine then you have pleanty of choice.

A 385hp screaming monster then id probably reasses what is available (Cast vs Forged etc)..........it would dictate the choices id make!

As Dave says, go KB as they provide the required compression rate to help the engine.
Heads are where the real restriction reside due to small ports. Even so, you could build a decent torquey motor especially if you selected the right camshaft to suit.

It's just going to be a mild build on a tight budget.
I've read about the KB's and some say use and others don't , seems there's a lot of issues with regards to rings.

Not head that, but mild build doesn't need to replicate the low compression aspect of the original. Decent pistons, XE262 cam and you'd have a nice motor that could run stock converter and any gears you like.

KB pistons come in cast, Hyperutectic, and Forged

id suggest if anyone had issues it would either be terrible luck or they chose the wrong material for their intended application.

you really need to get the bores measured before ordering, because the bores may have been finished to a specific set of pistons that didn't come with the purchase.

clearance is different for each material and the style of piston skirt

be a shame to get some 30 over pistons only to find that the clearance necessary for them to run "as new" is not achievable.

hypers run small clearance cast runs larger.

if the block has just been bored to size you would probably be alright but if its be finished and honed like it was nearing the build up phase i'd get it measured, someone has put in time and effort that would normally be undertaken when the pistons and specifications for them, were to hand... or they have done it when they were not to hand, in which case its an unknown quantity.

also check how much the rings are before deciding

some surprisingly cheap pistons have rings that cost a lot more than you would expect due to less popular thickness especially for the 318 when most rebuilds are just that a rebuild as standard

for example I think you can fit dodge magnum pistons to your LA 318
and they are quite cheap in cast and hyperutectic (rock hard cast)

but the magnum pistons use an oil scraper that is narrower than the LA one
and for some reason a set of rings with that size and type of oil scraper ring costs near double what the 318 LA rings cost.

summit racing

search pistons

fill in your motor and spec, bore, compression height etc in the selection boxes down the left hand side

make sure you get pistons with pins that fit your rods

find the pistons you like and shop around or try ebay first

summit prices are often very good but occasionally you can pick up new in box pistons on ebay from other people failed projects

or you find UK suppliers shifting stuff they got in for specific customer orders that never completed.


if you have press fit pins get on old ones linished down a few thou over 2/3 of the length

you can then fit piston by hand for checking purposes

the press fits pins shouldn't be pressed in and out lots of times so keep the 8 good pins for the final build up. if in doubt get an engineering shop to fit the pins

ideally you'd know the compression height necessary to achieve a flat top piston level with the deck of the block. if you don't because the engine is in bits. you can work it out from the bore of the mains
the stroke of the crank the centre to centre length of the rod and the distance from the middle of the pin to the top of the crown. draw it all out on paper.

its not ideal but its close enough

if the pistons stick out the top of the bore you might have a problem, because the edges will hit the head, however the edge can be machined down if necessary. I was dubious about this but have had no problems and discovered that the factory did it for my motor anyway....

mine takes 318 pistons but is a 6



Dave

Just found out that block was bored out for KB hyper pistons.
I assume these will be the KB167's

Whatever you buy, you will have to factor in a Recip re-balance too.

Duster1 wrote:Just found out that block was bored out for KB hyper pistons.
I assume these will be the KB167's

I used those on my last car, no problems at all and they did get a lot of stick

Duster1 wrote:Just found out that block was bored out for KB hyper pistons.
I assume these will be the KB167's

they'd be my choice

they do a similar one with a dome that begins with a KB3?? as well

but the 167s are a nice flat top. which is what I think you want.
they were too tall for me....
but if nobody has sliced too much off the deck of you motor these are designed to sit right at the top bringing CR up to 10:1

Dave