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Author Subject: 7:1 compression ratio
JWP EFi

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Location: edinburgh

Registered: 07 Mar 2010

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Post #1
as title suggests, is this a bit on the low side? have been busy trying to spec a budget low comp gti6 turbo build,

Gti6 pistons fitted to 8vt (152mm) rods, pistons now sit approx 6mm below deck, the thinnest head gasket i can

find (1.2mm), slight skim, this lot gives 7.1:1 CR if my calculations are correct.

i was doing a bit of random browsing and discovered that the road spec 205 T16 ran a 6.5:1 CR, some Zetec turbo

guys are using sub 8:1 CR's.

i know off boost driveability will be rubbish, but then it is a turbo'd engine. Looking for around 250 ish bhp with

T3 0.48 / 0.42 turbo and cosworth weber marelli/pectel management plus 803 greens

Any thoughts?

ps, whats the best method of pushing pins out of pistons / con rods? tried gentle heat and light pressure on

15 tonne press but they dont want to budge
Posted 6th Feb 2012 at 21:24
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JWP EFi

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Post #2
7.3:1 to be precise

Anyone???
Posted 6th Feb 2012 at 21:59
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welshpug!

Capt Pedantic

Location: Bigend, Wales.

Registered: 27 Mar 2007

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Post #3
why not run the turbo pistons and some cutouts if required.

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Posted 6th Feb 2012 at 22:02
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JWP EFi

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Post #4
that was my original idea, but i dont have the flat top ones, have the later RGX dished set. i was told that the

dished pistons aren't suitable, something to do with squish????

so do you think RGX pistons with cut outs would be the better option? i thought i was onto something when

i discovered the the gti6 / turbo piston and rod method until i realised my CR is lower than the 8:1 i was aiming for
Posted 6th Feb 2012 at 22:07
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rich_w

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Location: Havant, Hampshire

Registered: 29 Jul 2004

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Post #5
You don't want the pistons sitting below deck, let alone by 6mm.

The pistons should be flush with the deck to provide the required squish / quench area.

This is perhaps the strongest deterrent to detonation designed into an engine. Consider it sacred and do not tamper with it!

7:1 is too low, will be very sluggish off boost.

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Posted 6th Feb 2012 at 22:53
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JWP EFi

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Registered: 07 Mar 2010

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Post #6
thats that idea donald ducked then.

btw, if pistons must sit flush, then how come the 405 T16 pistons are a good bit below, not sure how much mind
Posted 7th Feb 2012 at 18:42
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rich_w

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Post #7
jsa666 wrote:
thats that idea donald ducked then.

btw, if pistons must sit flush, then how come the 405 T16 pistons are a good bit below, not sure how much mind



The T16 isn't a particularly good or efficient engine - I wouldn't base any of your design or assumptions on that.

It's old technology and design at the end of the day. You can build a much better 16V turbo engine using the later XU10 parts, tubular manifold etc etc.

Smile

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rich@lynxpowerengineering.co.uk
07732 822546

Posted 8th Feb 2012 at 15:25
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JWP EFi

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Post #8
fair point.

but already have cast T16 ex manifold and certainly wont be shelling out £1200 on a sexy DP one!

what do think is the best solution without going forged? Quite a few chaps across the water acheiving 250 to 300 bhp

plus on stock internals. I guess i'm back to the decompression plate debate...
Posted 8th Feb 2012 at 19:53
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sosmotorsport

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Location: falkirk

Registered: 24 Jun 2009

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Post #9
if your only aiming for 250bhp why not run std comp on a low boost set up

________________________________________

SOS Motorsport
www.sosmotorsport.co.uk
450bhp 205 16v Turbo
www.facebook.com/pages/SOS-Motorsport/159917677353556
Posted 15th Feb 2012 at 22:57
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stan_306gti6 Forum Admin

Location: Kent

Registered: 18 Jan 2004

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Post #10
soundsofsilence wrote:
if your only aiming for 250bhp why not run std comp on a low boost set up


This is probably the best cost-efficient way of doing it, plus the setup has been tried, tested and proven many times before on the low boost SC and stayed in one piece nicely. Yes

________________________________________

"Supercharged - 454.1bhp/317.5lb/ft"
Peugeot 306 GTi-6
2000 (X), Moonstone Love
Posted 15th Feb 2012 at 23:02
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chrisd306

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Location: Perth Scotland

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Post #11
Stick 8v turbo in it cheaper than going low boost and just slightly slower than low boost

________________________________________

In my garage just now

2003 BMW M3 & 2009 L200 Raging Bull
& Audi Q5 S Line
AX stock rod & Saxo Stock rod
Sold the bike an charged rallye an bought a caravan, midlife crisis or what!
Posted 15th Feb 2012 at 23:17
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JWP EFi

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Post #12
been there done that, i will admit they are good but not quite my cuppa. but deinately a damn

site cheaper than building 16v turbo
Posted 18th Feb 2012 at 15:38
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JWP EFi

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Post #13
soundsofsilence wrote:
if your only aiming for 250bhp why not run std comp on a low boost set up


when you say low boost, how low are we talking? after much guestimating, im assuming

the 10psi mark with cossie T3??

also whats the thickest head gasket available for the gti6?
Posted 18th Feb 2012 at 15:42
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welshpug!

Capt Pedantic

Location: Bigend, Wales.

Registered: 27 Mar 2007

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Post #14
standard repauir gasket is 1.4mm.

low boost sc is 8.7 psi.
TARGET POWER: CIRCA 250 BHP
TARGET TORQUE: CIRCA 215 FT/LBS

________________________________________

need a part number? get on here - http://public.servicebox.peugeot.com

Bring on the Trumpets.

Posted 18th Feb 2012 at 15:49
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JWP EFi

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Post #15
do you think ~ 10 psi would be too much for stock bottom end?

Btw, how many LB S/C'd engines have let go? 10.8:1 CR AND a fair ammount of boost, surely these engines are

deliberately overfuelled to ensure they stay in one piece, i know superchargers and turbos are totally different

in terms of heat/back pressure etc
Posted 18th Feb 2012 at 21:24
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welshpug!

Capt Pedantic

Location: Bigend, Wales.

Registered: 27 Mar 2007

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Post #16
only those that had a fault or were already heavily worn I'd imagine, otherwise the boost levels would have been pegged back further.

________________________________________

need a part number? get on here - http://public.servicebox.peugeot.com

Bring on the Trumpets.

Posted 18th Feb 2012 at 21:41
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m306

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Location: south coast

Registered: 16 May 2011

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Post #17
jsa666 wrote:
Btw, how many LB S/C'd engines have let go?

now thats something id be interested to know too. from what ive seen and heard they seem to be very reliable, Rich designed it to be just as reliable as the standard car and has done a very good job of it. i trust it and will be going low boost soon.

i have heard whispers of one that went though, supercharger failed and took the engine with it? could be wrong though so dont take my word for it, thats just something i remember reading somewhere?

can anyone shed any more light on the subject?

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supercharged China gti6 - Thu 16th Sep 1999 - sold
2010 megane rs250
Posted 18th Feb 2012 at 22:23
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sosmotorsport

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Registered: 24 Jun 2009

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Post #18
jsa666 wrote:
soundsofsilence wrote:
if your only aiming for 250bhp why not run std comp on a low boost set up


when you say low boost, how low are we talking? after much guestimating, im assuming

the 10psi mark with cossie T3??

also whats the thickest head gasket available for the gti6?


approx 1/2 bar of boost maybe slightly more should see it around the 250 mark on std comp & T3

as for if engine could with stand it would simply be how good an engine it was in the first place if in good working order then it should take it no problem

________________________________________

SOS Motorsport
www.sosmotorsport.co.uk
450bhp 205 16v Turbo
www.facebook.com/pages/SOS-Motorsport/159917677353556
Posted 18th Feb 2012 at 22:43
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chrisd306

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Location: Perth Scotland

Registered: 26 Nov 2005

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Post #19
ive killed 2 engines low boost, 1 was because i didnt use good enough oil, and the 2nd, was a fueling issue and i put that down to the map, so not really anything to do with power, but i know russ's rallye is 260bhp and its been good for few years!

________________________________________

In my garage just now

2003 BMW M3 & 2009 L200 Raging Bull
& Audi Q5 S Line
AX stock rod & Saxo Stock rod
Sold the bike an charged rallye an bought a caravan, midlife crisis or what!
Posted 19th Feb 2012 at 02:00
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stan_306gti6 Forum Admin

Location: Kent

Registered: 18 Jan 2004

Posts: 21,768

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Post #20
chrisd306 wrote:
ive killed 2 engines low boost, 1 was because i didnt use good enough oil, and the 2nd, was a fueling issue and i put that down to the map, so not really anything to do with power, but i know russ's rallye is 260bhp and its been good for few years!


Yes Chris, its a reliable setup, you just broke yours twice being an animal. LOL Razz

________________________________________

"Supercharged - 454.1bhp/317.5lb/ft"
Peugeot 306 GTi-6
2000 (X), Moonstone Love
Posted 19th Feb 2012 at 07:57
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m306

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Location: south coast

Registered: 16 May 2011

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Post #21
chrisd306 wrote:
ive killed 2 engines low boost, 1 was because i didnt use good enough oil, and the 2nd, was a fueling issue and i put that down to the map, so not really anything to do with power, but i know russ's rallye is 260bhp and its been good for few years!

your mistakes have proved to be very helpful Chris, to me they are anyway. its proved why you should get the best stuff on a conversion like that

________________________________________

supercharged China gti6 - Thu 16th Sep 1999 - sold
2010 megane rs250
Posted 19th Feb 2012 at 10:16
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JWP EFi

Turbo Legend!

Location: edinburgh

Registered: 07 Mar 2010

Posts: 2,163

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Post #22
soundsofsilence wrote:
jsa666 wrote:
soundsofsilence wrote:
if your only aiming for 250bhp why not run std comp on a low boost set up


when you say low boost, how low are we talking? after much guestimating, im assuming

the 10psi mark with cossie T3??

also whats the thickest head gasket available for the gti6?


approx 1/2 bar of boost maybe slightly more should see it around the 250 mark on std comp & T3

as for if engine could with stand it would simply be how good an engine it was in the first place if in good working order then it should take it no problem



my engines a good one (arent they all lol!) came from 2002 xsara vts with only 52k, bores are perfect, as is crank etc

engine currently stripped as i was planning to fit different pistons, so will be going back together with new rings,

shells etc etc. I'm guessing it would be a wise move to use ARP big end bolts? I've always reused the originals

over the years and never had a problem, but seeing this one's a boosted engine then i need to give it every

chance its got.

Posted 19th Feb 2012 at 13:02
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stan_306gti6 Forum Admin

Location: Kent

Registered: 18 Jan 2004

Posts: 21,768

Status: Offline
Post #23
You could go ARP bolts, although the low boost SC engines are standard lumps with standard bolts and have been no problem.

However, if you decided to go with standard I personally would buy new ones rather than use the old ones. Yes

________________________________________

"Supercharged - 454.1bhp/317.5lb/ft"
Peugeot 306 GTi-6
2000 (X), Moonstone Love
Posted 19th Feb 2012 at 13:35
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JWP EFi

Turbo Legend!

Location: edinburgh

Registered: 07 Mar 2010

Posts: 2,163

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Post #24
Cometic do a 1.8mm head gasket, true or false???

before this engine goes back together i'm considering all possible ways of lowering the c/r, even if its only a small

amount

i really don't like the idea of a decomp plate
Posted 19th Feb 2012 at 18:10
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birk

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Location: Doncaster

Registered: 24 Oct 2005

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Post #25
I Killed 3 engines on low boost.

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Posted 19th Feb 2012 at 18:15
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