LimeyDrink

Hi all

Just wondering, if you increase power output of an EJ20 engine with an open deck block, what would be seen as the weakest link, would it be the block itself, or is it generally considred that ODB are still sufficient to withstand power that would probably cause piston/rod/other failure first.

Basically, how weak are open deck blocks.

Cheers

john banks

It is a difficult question which has been debated. There is one car running consistently over 400 BHP for some time which belongs to Harvey Smith. This has a rebuilt open deck motor with uprated internals. Bob Rawle and Andy Forrest are also consistently over 400 BHP, but both on semi-closed or closed deck blocks. I have plumped for a closed deck block for my build because I am worried about head gasket integrity at this level of power - otherwise I would have just changed rods and pistons in an open deck 2.5 and put it on my 2.0 turbo heads.

My impression from picking everyone's brains is that the pistons are the first weak link. Cast pistons do not tolerate a lot of detonation and you can hole them or crack a ring land.

However, my cast pistons and standard rods on a standard UK 2.0 motor have stood up so far, but I am only pushing it this hard because I know I have an engine on the way. I have run it up to 1.7 bar dropping to 1.5 at peak power on TD05 and at 1.6 bar flat on the TD05/06 20G so far. My main worry is the gearbox, but I receive my Lateral Performance kit fully built by Neil Engineering tomorrow, along with a 3" inch exhaust system so the fun can really start. Engine to follow, but I want to see my standard 2.0 over 400 BHP or depending on how you look at it

What has been usefully pointed out is that you cannot prove to OEM standards of reliability a method of tuning because of lack of resources. So no one can truly tell you what is safe, in these circumstances best to overspecify. With closed deck blocks pretty cheap, seems to make good sense to go for one if sticking to 2.0. If raising capacity there are bore/stroke options. Pavlo Paul is working on closing 2.5 ODB motors with welding but long term reliability results will take a while, and would really need several cars over many miles with the engine removed and inspected to prove reliability?

[Edited by john banks - 3/6/2003 12:13:48 PM]

pat

It's also worth bearing in mind that the open deck blocks are die cast, ie the aluminium is forced under pressure into the casting mold. This results in superior material density as compared to the closed deck blocks, in which the aluminium alloy relies on gravity to draw it through the mold. Also, if memory serves, the alloy composition was changed when Subaru moved to the open deck block, which further improves matters.

However, no matter how strong you make the material, nothing will compensate for the fact that there are no "bridges" between the periphery of the liner and the outer block skin preventing the bores from wandering, so the open deck blocks will never be quite as strong as their closed deck cousins.... well that's not entirely true, I'm looking at a method of making it impossible to blow a head gasket, regardless of boost levels or detonation levels.... you'll still throw a big end with lots of det, but some of the head sealing techniques I'm looking at will withstand about twenty thousand bar the whole engine would blow apart before the seal let go!

Cheers,

Pat.

Pavlo

weld the heads on...

Porsche used to do that on the Le Mans engines apparently.

Paul

pat

Paul,

it'de be a real pain if you holed a piston... how would you ever get it back out ? Needless to say, my sealing techniques would still allow complete disassembly if required.

Cheers,

Pat.

swan

And when will the "secret" be for sale and will it cost an arm and a leg?