|
|
|
|
|
Hi Need to pick your brains on how to work out a compression ratio. It is for my 205 turbo which is receiving much attention recently and will need the C/R improving. The engine is a 2 litre 8 v 1998cc 4 cylinder engine from a 406 sri. The engine code is XU10J2TE. I know the standard C/R is 8:1, I know that this is quite low to start with but with the increase in boost and etc it will need to change. My real issue is working out the capacity within the head, the bore and stroke are both 86 mm which gives me a capacity of 1998 but I need to know the other bit. Cool picture of mad JDM 205 as Thanks  |
| |
|
|
|
|
jasonj
Part of things
Posts: 220
|
|
|
|
|
If you type compression ratio into wikipedia there is a formula on how to work it out there. You should be able to run a reaonable amount of boost with 8:1 compression though with good ignition and fuel management.
|
| |
Team Supercharged Opel Ascona 400.
294bhp - 235 lb/ft
|
|
|
|
|
|
|
|
turn the head upside down with the cams out,,,you'll need a flat bit of glass or perspex,,,drill a small hole in the middle of this,,,blank off the plug hole with and old plug stuff with something to block off the space between the inner and outer electrode...
now get an accurate fluid measuring device such as a pipette or a very accurate measuring jug,,,fill this up to about 150ml's place the flat glass on the block face of the head and slowly pour the fluid (i normally use parrafin or red diesel) thro the hole so it fills up the combustion chamber until the fluid just starts to come up the hole you drilled,,,now check your pipette/jug and you will know how much fluid it took...
that amount of fluid in ml's is the same as the chamber capacity in cc's
oh and btw running @ 8:1 you will need to work out some very good knock protection otherwise this will pink like mad if it runs lean under boost and load.
|
| |
if at first you don't succeed...use a gas axe!
|
|
|
|
|
|
|
Hi Moving forward with this now Thanks for the replies. If you type compression ratio into wikipedia there is a formula on how to work it out there. You should be able to run a reaonable amount of boost with 8:1 compression though with good ignition and fuel management. I haven't done this because I need to work out the combustion capacity within the head and the low compression (Dished) pistons. These number are needed in order to work out a C/R. Thanks for the replies to this post, I sourced some perspex from a local sign company and a measuring syringe from our Vet. The combustion chamber within the head is 35cc per cylinder. turn the head upside down with the cams out,,,you'll need a flat bit of glass or perspex,,,drill a small hole in the middle of this,,,blank off the plug hole with and old plug stuff with something to block off the space between the inner and outer electrode... now get an accurate fluid measuring device such as a pipette or a very accurate measuring jug,,,fill this up to about 150ml's place the flat glass on the block face of the head and slowly pour the fluid (i normally use parrafin or red diesel) thro the hole so it fills up the combustion chamber until the fluid just starts to come up the hole you drilled,,,now check your pipette/jug and you will know how much fluid it took... that amount of fluid in ml's is the same as the chamber capacity in cc's oh and btw running @ 8:1 you will need to work out some very good knock protection otherwise this will pink like mad if it runs lean under boost and load. I will be running adjustable fueling and ignition timing, and it will b e mapped with knock protection in mind. If it gets to the point of water injection then so be it. I am only running a gt28r with ceramic internals so am limited to around 1 bar of boost. I would not think that with this turbo the engine will knock that bad. But hey it is French and I have been wrong before. I will be putting up a build thread with the full spec and a countdown until rrg12 (The deadline). Thanks Again Alex |
| |
|
|
|
|
|
|
|
I guess you're not on the 205gtidrivers forum? there's tons of info on there, all you need and more, use google to search the site  the head is the same as the n-a XU10J2, as are the rods IIRC, only the pistons and cam differ. |
| |
|
|
RobinJI
Posted a lot
"Driven by the irony that only being shackled to the road could ever I be free"
Posts: 2,995
|
|
|
|
|
I'd be cautious of lowering the compression ratio much below 8:1. There should not be any need to do so running 1 bar of boost, or in fact considerably more than 1 bar with the correct management and cooling. There's a direct relationship between thermal efficiency and compression ratio, and as such lowering the compression ratio really should be the last ditch option in an attempt to keep things safe, as reducing it will directly reduce power and increase fuel consumption. Sometimes peak power can be increased as the reduction in thermal efficiency is over-ridden by the increase in volumetric efficiency you get by being able to wind the boost up a touch more, but then you will directly reduce the engines performance at everything but full boost, worsening lag, as well as increasing fuel consumption at full boost, and reducing the power produced for any given boost pressure, so you end up needing more boost to get the power you're after. Remember more boost = more heat, which just goes to make things even worse. Basically what I'm trying to say is high compression ratio is not the enemy.
With an already low starting point of 8:1, proper management and intercooling should be able to keep knock well under control. If it does not I'd suggest looking at combustion chamber design or methods such as water injection before resorting to reducing the compression ratio further.
|
| |
Last Edit: Jan 10, 2012 1:20:52 GMT by RobinJI
|
|
|
|
|
Jan 10, 2012 13:33:53 GMT
|
|
If your cc is 1998 and its a 4-pot, then you’re at 499.5 cc per cylinder. Thats 499.5 cc of swept capacity, so then with an 8:1 comp ratio, your combustion chamber volume (inc gasket) must be 1/8th of 499.5, so 62.44cc.
Is that the number you’re looking for or have I misunderstood something?
|
| |
1974 Lancia Beta Saloon
1975 Mazda 929 Coupé
1986 Mazda 929 Wagon
1979 Mazda 929 Hardtop
1982 Fiat Argenta 2.0 iniezione elettronica
1977 Toyota Carina TA14
1989 Subaru 1800 Wagon
1982 Hyundai Pony 1200TL 2-dr
1985 Hyundai Pony 1200 GL
1986 Maserati 425 Biturbo
1992 Rover 214 SEi 5-dr
2000 Rover 45 V6 Club
1994 Peugeot 205 'Junior' Diesel
1988 Volvo 760 Turbodiesel Saloon
1992 Talbot Express Autosleeper Rambler
2003 Renault Laguna SPEARS OR REAPERS
|
|
RobinJI
Posted a lot
"Driven by the irony that only being shackled to the road could ever I be free"
Posts: 2,995
|
|
Jan 10, 2012 16:39:16 GMT
|
If your cc is 1998 and its a 4-pot, then you’re at 499.5 cc per cylinder. Thats 499.5 cc of swept capacity, so then with an 8:1 comp ratio, your combustion chamber volume (inc gasket) must be 1/8th of 499.5, so 62.44cc. Is that the number you’re looking for or have I misunderstood something? Close but not quite, that would be a ratio of 9:1, because the TDC volume would be 62.44cc, and the BDC volume would be: 499.5cc + 62.44cc. = 561.94cc. If you know what ratio you're aiming for, then your combustion chamber volume can be worked out as: swept volume / (target compression ratio - 1). So at the standard 8:1, your combustion chamber volume must be 499.5 / (8-1) = 71.36cc. If for example you want to reduce it to 7:1, then your target volume would be 499.5 / (7-1) = 83.25cc. So you'd need to find an additional 11.89cc, As I'm sure you're aware there's a few places you could find the extra space. Although I would refer to my post last night about how you probably don't want to reduce it any more. If you're getting issues with knock at 1 bar of boost on 8:1 CR, then I'd be looking for another solution that's not as detrimental on the engines efficiency and performance when not at full load. |
| |
Last Edit: Jan 10, 2012 17:09:54 GMT by RobinJI
|
|
|
|
|
Jan 10, 2012 19:28:09 GMT
|
Hey you're right! I wondered about that while sat at my desk, then typed out a load of b0ll0x.  |
| |
1974 Lancia Beta Saloon
1975 Mazda 929 Coupé
1986 Mazda 929 Wagon
1979 Mazda 929 Hardtop
1982 Fiat Argenta 2.0 iniezione elettronica
1977 Toyota Carina TA14
1989 Subaru 1800 Wagon
1982 Hyundai Pony 1200TL 2-dr
1985 Hyundai Pony 1200 GL
1986 Maserati 425 Biturbo
1992 Rover 214 SEi 5-dr
2000 Rover 45 V6 Club
1994 Peugeot 205 'Junior' Diesel
1988 Volvo 760 Turbodiesel Saloon
1992 Talbot Express Autosleeper Rambler
2003 Renault Laguna SPEARS OR REAPERS
|
|
RobinJI
Posted a lot
"Driven by the irony that only being shackled to the road could ever I be free"
Posts: 2,995
|
|
Jan 12, 2012 17:58:53 GMT
|
Yeah, no worries, it's an easy mistake to make, and I wasn't all that confident correcting you until I'd checked the answers I'd got to make sure I was definitely right! Just thought I'd post this up as an example that you don't always need megga low compression ratios. This is a dyno plot from a 1.8l 20vt VW engine running an upgraded turbo, tubular manifold, FMIC ect.. and importantly, a compression ratio of 9.5:1. Link to Dyno plot, as it's a biigg picture.As you can see that engine's making ~280bhp at the 1 bar boost you're planning, and ~325bhp at 1.6 bar boost. That's from a 1.8 liter engine with a 9.5:1 compression ratio. I'm not sure what sort of figures you're aiming for, but I'd say that's pretty respectable. OK, it's a different engine, but it shows that you don't always need a super low compression ratio to run decent boost figures, and decent power, and you're already at a much lower compression ratio. |
| |
|
|
