yoo. just after a bit of an explenation really.

I've heard of people who convert a N/A engine to run boost lower the compression 2 usual ways..

2 head gaskets...

1mm decompression plate..

I've head alot of people doing these methods but never seen it on a car.

i will most likely be running a 1272cc 2g or NZ engine, and i do intend to lower the compression ratio a fraction.

but is it literally as simple as that? buy 2 head gaskets, shove one ontop of the other, and bolt up? i thought they had some sorta rivet things holding them together like on an AFH, wouldnt this affect it??

the same with decompression plates, do you have to have a head gasket on both sides?? and surely 1mm (the one i found on ebay) is massive?

on a standard NZ or 2g ect 1.3 what compression ratios am i expecting from either roughly? and what should i be aiming for? i will most likely be on around 0.5 bar -1 bar of boost.

any info would be great!

If you're running less than a bar of boost on an NZ/2G/MH/AAV bottom end I'd just leave it as is. Chris Heys' turbo'd AAV has clocked up a lot of miles on 10-12psi without issue.

yeah I've had a good look through his thread, and was going to, but I've had so many people telling me itl go bang that i was a little concerned. i am a major noob with this stuff!

in that case then i will most likely leave it! cheers andy.

for future reference though, any input? as i literally have no idea lol. gonna be a major learning curve!

The compound head gasket is about 1mm, if you used a 1mm plate and two metal head gaskets you'd be hardly any different than the standard compound. So you could use one metal and one compound with the 1mm spacer to get you an extra 1mm from standard, or two compounds and spacer for 2mm extra.

Go for the two compounds with spacer for 2mm extra and a K04 Eric, you know it makes sense

cheers mikey.

I've already got a t2/t25 hybrid going on it. was gonna run low boost at first, most likely around 6psi, then start increasing it.

need to find a supplier for the carb jets!

with a decomp plate Eric you dont run a headgasket either side just on the bottom between plate and block,

in between the head and decomp plate you use a non setting high temp sealant like Hylomar blue thats what il be using and my decomp plate is 1.5mm and knocks c.r down from 10.5 to 9.5

I think 9.5:1 compression will be reet if you're keeping it under a bar - as long as you're taking the time to get the fuelling and ignition timing correct. If you're pushing it to higher boost levels I'd consider dropping the CR - but bear in mind that stacked gaskets or spacer plates glued to the engine block introduce another potential failure mode as you wind the boost up.

Plenty of 1341cc G40 turbos on 21psi using Accralite pistons and thin HG at circa 9.3:1 compression without issues. But then I'd not be so confident if the fuelling and ignition timing weren't spot on!

Instead of using spacer plates you could always drop some G40 pistons in, they're not expensive secondhand. If it were me though I'd leave the bottom end as is, get it running on low boost and take it from there. I'd then source a spare engine, and wind the boost up. If it breaks, take your time to understand the failure mode - and then uprate the weak parts accordingly, or wind the boost down a touch.

yeah mate, i will be using my wideband sensor to help get it set up fuelling wise, and i have a turbo vaccum advance pot for the dizzy, so hopefully i wont have too many problems there.

its winstons old setup from his scirocco, not sure if youve seen it, but most likely using a hydraulic head (unless someone from manc can grab the engine on the way down)

g40 pistons, now theres an idea. do i not need the rods too? or is it the pistons alone that give it the lower c/r?

iirc the turbos set to run about 6PSI atm, so gonna start offf with that. (i dont even know how to adjust that yet either)

thanks!

The compound head gasket is about 1mm, if you used a 1mm plate and two metal head gaskets you'd be hardly any different than the standard compound. So you could use one metal and one compound with the 1mm spacer to get you an extra 1mm from standard, or two compounds and spacer for 2mm extra.

Metal head gaskets are 0.5mm compressed, so two of those and a 1mm decom-plate would see you about +1mm over a stock compound head gasket. Not that it matters because as Pete says you only use one head gasket with those plates.

I'm with Andy on this one, just start with a engine that is already suitable for boost (the standard 1.3 has been proven up to the job and are cheap and plentiful). Your gonna be paying extra money for the plate and sealant and all it will be doing is swapping one potential issue for another. Rather than your cr possibly being too high to run high boost, it will be potential failure of the plate/seal preventing you from running high boost.

You can't get different sized carb jets off the shelf. you either drill them bigger or fill them with solder then drill them smaller. Sound pikey but its what all the 5 turbo tuners do!

http://www.gt-turbo-spares.co.uk/cart/inde...amp;prod_id=268

Guide to the Solex carb

OWNED lol

You will need smaller jets for anything less than a 1.4... Thus the need to fill them and drill smaller

I was going to run a bar at 9.5:1 CR Andy

And you will hopefully be setting the timing and fuelling lol so I hope you get it right

Did you get my PM about the uprated pressure sensor too

re cut the head? gotta take it off anyway

and you can get jets, you just have to know a uk distributor, pal has box's upon box's of ren 5 fueling bits :)

Edited 29 January, 201313 yr by MiNoR cOnFuSiOn