Does anybody know if u can use a 1200 crank in a 1400 block? and if it can be done, what conrods should u use 1200 or 1400?

excuse my ignorance but what gains would you have?
weight reduction?

I think the gains he is more after is lower compression for boost

i think you're right phunkdoktaspok - but wouldn't using A12 rods on an A12 crank in an A14 block give you something like 5.5:1 CR with A14 pistons? i mean, it wouldn't be coming too far up the bore, would it...?

would rev nice and easy though...

If low comp is desired stick an a14 crank in an a15.

I could actually be wrong with my guess.
I was actually half asleep when I posted it and I thought it was 1200rallycar who made this thread but now I noticed its not him.

i was told a couple of years ago that this was done for a compact speedcar engine(small speedway with big m/bike or small car engine).with a bore of 79 mm,it was just under 1400cc's,& revved very hard.this was when they were on a 1400 cc limit.i don't have any more info,but the car was supposedly extremely quick.just big bore,small stroke.they now have a 1500 cc car limit,so they use a15's.

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The PISTONS from the A15 are lower in their deck height, & when used in an engine with an A14 crank, they would fall 3mm short of the top of the block, thereby lowering the compression by quite a bit.

The advantage? The lower compression would allow lots of boost, but in NSW at least, i believe that 9psi is the legal maximum permitted.

The downside? Lots of boost produces lots of heat, & these A15 pistons are just simple castings. They are known for their reasonable cost & long life in a stocker, but the BIG boost that low compression allows might just be a bit too much for them to handle.
Think twice, act once.

You would be gaining a faster revving engine. By destroking, you increase the rpm potential for your engine. The chevy guys in the usa do it by putting a crank from a 283 into a 327 block. These come out to 302 ci and will rev to 10,000 rpm no problem. use the longest con rods available and regular pistons.

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I have never actually ever heard or read anything like this. Is it only a recent thing?
How do they or how do they plan to govern something like this?

Lots of boost does create a lot of heat and if you dont have a half decent intercooler it will be hard to control the burn of the fuel in the engine
But if you do have a way of dropping the compressed inlet charges temp (ie; intercooler, water methanol injection) there is no reason why a high boost level will be detrimental to a pistons life if the air/fuel ratio is stoichiometric. Think about it, yes there is more power generated in the combustion event but if it is stoichiometric it is still a controled burn ( it cant be any hotter than a non boost combustion event as if it was detination would occur)
Think about a methanol engine, it has a more explosive combustion event creating more power but yet the engine still doesnt get hot like a petrol engine.
All this is the reason why I always say forged pistons are only security for a badly tuned engine. ( security as in they can handle the abuse for a bit longer, but still not forever)
I myself could only really justify the expense of forged pistons on a big dollar engine that if something went wrong with you would be down alot of money from the damage caused by a damaged piston.( everyone has their own price limit)
Think about this, have you ever seen a piston with a hole blown through it from too much boost? it's always a melted piston, cracked piston or broken ring lands all of which are caused by to much heat because the engine leaned out and detinated.
Thats just my views.

I remeber friends once ran a big decompression plate on a turbo a12 a few years ago now, it was like 3 or 4 mm's thick plus the 2 head gaskets, they calculated compression to be around 6:1.
The exhuast note it made at idle was awsome, it sounded hollow like a big GTR Skyline. This car handled high boost allday( high boost meaning 20psi + ) but when we compared it to a standard compression turbo a12, the power it made at high boost was equal to the stock compression engine at low boost. ( testing was only ever done on road, so there was never any actual documented evidence like a dyno test, it was just how it felt to drive)
In thought if more boost could have been made, more power could have been achievable but for a street engine to run compression like that, the amount of lag made the overall power output hardly worth it.
Just a few thoughts to consider when contemplating if its worth it to run low compression.