Decomp plate vs Machined pistons.

[Danb1987]

Again wanting some Info lol

My idea is Running a decompression plate means running 2 hgs... 2 times the problems? But only costing about £50ish

Never looked into machined pistons before but I rang a local engineering company today and told them that I could supply the pistons and a cad drawing of how I'd need them machining,

They told me they could do it at an hourly rate of £28+vat ph but they'd probably take a day to do so!

Would machining pistons not only lower the compression ratio but allow the engine to be built as a perfect low comp engine? As in reduce the risk of anything failing like a twin hg setup?

Example being a c20xe engine being high comp... Machining standard pistons making it low comp = pretty much a let engine - turbo?

[bazil]

Decomp plate is fine depending on boost, low boost your fine get into double figures and you'll be risking blowing gaskets,

Machining pistons is pretty much the same, increased boost increases heat and without under piston cooling you'll risk melting pistons at higher boost,

Understanding compression ratios and turbo sizes to suit is essential for a good build,

Your XE runs Upto 11.5:1 compression where a LET runs upto 9.5:1

Aftermarket forged pistons can drop that to 8:1 allowing more boost but more lag due to turbo size/spool up etc etc etc

There are many ways to build a turbo engine, bigger budget + quality parts = better build

Cheap build = fun for a short time.

This is all my opinion of course. I'll spend a small fortune on mine but hopefully end up with a 1.6 8V with over 200bhp and reliable due to forged internals, low compression achieved with proper pistons and fuelled by omex/dta or similar
So far my required budget will be near 3k
Roughly a grand in management and mapping, 600 ish for rods and pistons, 4-500 on head and valve work, upto 500 for rebuilt turbo, possable hybrid exchange, 200 ish on custom pipe work + downpipe, then things like oil filter relocation,

Blah blah etc and so on.

Custom building engines ain't cheep, by a converted engine or a LET if you want to avoid a money pit or headaches


Just to add to converting a XE, yes it's easier but if you use XE cams you need to alter valve timing, also you'd still need to sort fuelling, and a few other bits n bobs

[Danb1987]

Thanks for the reply bazil, I Just used an xe as an example for ease lol

My engine will be a c20ne that il turbo, web if it's just for a short while that it's in use il give it ago, by no means do I think it will be a cheap build but I'm planning on keeping it under a grand if I can,

[Andy]

Just buy a 2nd hand set of LET pistons,no need for decomp plates or machining!

[Stuart]

I'd always go for a 10:1 Compression ratio with a turbo build anyway as these days with decent management and turbo control its perfectly viable and you don't have crap off boost drivability etc.

[burgo]

also de-comp plate doesnt mean two headgaskets at all

[Danb1987]

Depends on what plate it is.... I'm looking into let pistons now thow as most machine shops want quite abit to machine pistons.

[burgo]

Depends on what plate it is.... I'm looking into let pistons now thow as most machine shops want quite abit to machine pistons.

you need to find a better machine shop my local would only charge an hours rate to machine them. thats all they charged me to deepen the valve pockets by 2mm

[Danb1987]

The guy I rang said they'd do it at £28+vat per hour and would take at least a day!

Genuinely burgo if I sent you the pistons and a drawing would your shop be able to do them?

[burgo]

you sure they didnt mean drop them off in the morning and pick them up at the end of the day instead of actually taking a whole day to do them

[MK999]

Whole day to lighten and balance 4 they've never done before maybe, machine a dish in them, er no lol

[Danb1987]

From what he said he ment hourly and all day lol "with all the setting up etc" in his words..

http://i546.photobucket.com/albums/hh431/danpuntosport/f8c447cc.jpg

Would a machine shop understand that ^ as it baffles me lol

That should lower the compression to 8.2:1 but with .5mm taken off the surface it would take it to 8:1

Taken from Vaux-extreme.

[burgo]

well i understand it so they should. its very simple lathe work so how it takes all day is beyond me

[Danb1987]

Maybe it because theyve got the word tuning at the end of there business name?

What sort of machine shop should I ring other than a car specialised one? I need a bloke in a shed with a wealth of knowledge and a lathe lol

[burgo]

search "engineering" theres two i know of with that in there name that would do it a lot cheaper than your place