Compression Vs. Boost

[Sam 4]

Some of you may know I'm building a new engine for my 205 (won't be done for ages but I got most of the bits now). After speaking to the guys at Wiseco they advised me to run 9:1 compression, they said 8.5:1 is a little low for off boost and 9.5:1 usually meant melted parts on street fuel. I intend to run around 1-1.5 bar perhaps a little more. I'll have enough fuel for 400bhp and eventually thats the aim. I know I know, loads for a 205 but thats not what the topic is about so please don't use it for moaning, heard it all before.

 

After reading passion ford (they seem to build some nice 2.0 16v turbo engines so it can't be far off) they seem to think that 9:1 may be a little high on street fuel, obviously on race fuel you can get close to 11:1 or so but I'm not running it on that, probably Optimax or whatever the new one is.

 

Anyone got any input on C/R vs Boost?

 

Edit: Here's the link: http://passionford.com/forum/viewtopic.php...;highlight=gt30

Edited November 28, 2006 by Sam

[veloce200 3]

Some of you may know I'm building a new engine for my 205 (won't be done for ages but I got most of the bits now). After speaking to the guys at Wiseco they advised me to run 9:1 compression, they said 8.5:1 is a little low for off boost and 9.5:1 usually meant melted parts on street fuel. I intend to run around 1-1.5 bar perhaps a little more. I'll have enough fuel for 400bhp and eventually thats the aim. I know I know, loads for a 205 but thats not what the topic is about so please don't use it for moaning, heard it all before.

 

After reading passion ford (they seem to build some nice 2.0 16v turbo engines so it can't be far off) they seem to think that 9:1 may be a little high on street fuel, obviously on race fuel you can get close to 11:1 or so but I'm not running it on that, probably Optimax or whatever the new one is.

 

Anyone got any input on C/R vs Boost?

 

Edit: Here's the link: http://passionford.com/forum/viewtopic.php...;highlight=gt30

 

depends on:

AFR / timing / inlet temp/ coolant temp. only when you have the answers to these can you decide on compression. personally i'd opt for higher static compression, leaner mixtures, less spark and less boost with cooler water temp and inlet temp over the more common massive boost, high coolant temp, minimal spark and high inlet temp. you can get the same result with both only one sucks low down and uses massive amounts of fuel.

[Sam 4]

I've heard retarding ignition timing is quite a bad idea as it raises temperatures so didn't want to get it so high it had to be backed off.

 

I wasn't intending on running loads of boost and it being a dog off boost.

[veloce200 3]

I've heard retarding ignition timing is quite a bad idea as it raises temperatures so didn't want to get it so high it had to be backed off.

 

I wasn't intending on running loads of boost and it being a dog off boost.

 

it raises exhaust temp which shortens turbo life but may just save your pistons. low EGT's can be more dangerous than high though as heat stays in the head. my coupe turbo ran 1.5 bar peak - 1.2 6000 rpm on 95 ron no problem.

[Sam 4]

What C/R were you running ?

[veloce200 3]

What C/R were you running ?

 

std - according to carfolio 8:1 which may explain this ! so on that basis maybe 8:5:1 is safer - don't forget though they build cars to operate all round world at all heights all temps etc etc Marelli mgt had a lot of safety measures in it

[johnrobertgordon 0]

"1997.5 cm3 , water cooled turbo charged. Bore: 85mm, stroke: 88mm. Compression ratio 8.5:1 2 OHC belt driven and hydraulic tappets. 4 valves per cylinder. Oil cooler and carbon oil casing

 

Engine output: 300Bhp @ 5250rpm. Engine torque: 635Nm @ 4000rpm. Garrett/Allied Signal TR30R turbo charger and Magneti-Marelli Step 9 engine management."

 

Peugeot 206 wrc engine spec. Dunno if that helps?

[James_R 3]

all the vx boys with 2L tub's running 18-20psi are usually on 9:1 static, but dial the inlet cam out 7deg or so to reduce the dynamic CR, and run in the region of 300-330 depending n intercooling

 

 

If you want 300 then 9:1, if 400 then 8.5:1

[vern 0]

I am building a turbo engine, and had it built with a C/R of 9:1. As like you reading things the standard TT C/R of 8.5:1 seemed a little low so upped it up a bit. Will not know how it runs for a couple of weeks as waiting for the Emerald to turn up.

[Guest Ray205S16]

Engine output: 300Bhp @ 5250rpm. Engine torque: 635Nm @ 4000rpm. Garrett/Allied Signal TR30R turbo charger and Magneti-Marelli Step 9 engine management."

 

I 'm verry interested in how they get 635NM of Torque

 

grtz, Raymond

Edited November 29, 2006 by Ray205S16

[veloce200 3]

I 'm verry interested in how they get 635NM of Torque

 

grtz, Raymond

lots and lots of boost !

[Sam 4]

If you want 300 then 9:1, if 400 then 8.5:1

 

I guess I can skim the pistons to get that so not all bad. Have to see.

[TEKNOPUG 3]

I'd err on the side of caution and aim for the low side of 9:1 - 8.7:1 for example.

[jacobs53 0]

You also have to think about how far the flame front has to travel in the combustion chamber. if its quite far you need a lower CR.

 

I wouldn't skim the pistons especially if there the standard items. I'd look into getting a custom gasket made or the possibility of shorter custom rods. The problem with machining the piston is that you lose some material which would normally disipate the heat in the combustion chamber. As pistons in turbo applications act as heat sinks. Also i'd worry about making it the crown too thin. Much easier to get a custom gasket made.

[PumaRacing 1]

I 'm verry interested in how they get 635NM of Torque

 

grtz, Raymond

 

With some difficulty I imagine given that 635Nm is 468 lb ft which at 4000 rpm is 357 bhp - 57 more than the engine actually has at peak. I suspect the correct figure is 435 Nm.

[veloce200 3]

With some difficulty I imagine given that 635Nm is 468 lb ft which at 4000 rpm is 357 bhp - 57 more than the engine actually has at peak. I suspect the correct figure is 435 Nm.

found 540nm elsewhere. I didn't seek to calculate it as I know they run a lot of boost low down to make up for the fact they have a 300hp limit which would explain the low output but large torque. mind you if they only tested the output at max rpm maybe they do cheat and get away with it !

[Sam 4]

Jacob. I'm using custom wiseco pistons - hence the phone call to them, they run an 18cc dish, apparently I can skim them a little (of course this won't effect the thickness of the crown). I'm also using a 1.7mm Cometic HG. He said the pistons in the XU10 are quite long anyway.

[pugrallye 0]

In the subaru (i know its not a pug), but it runs forged pistons etc etc and compression was calculated to 8.6:1 which is capable of running to 2 bar of boost (it only runs at 1.3 though) (2.2 ltr engine) but its ignition was mapped so its always on the point of detonation - although its prob a degree or two off of actually pinking if you know what i mean, to gain maximum power, and off boost drivablity is still all there.

I remember I had a cossie years ago and the pistons were skimmed to drop the CR to 7.5:1 and that was an absolute pig to drive off boost but boost levels were higher so it was a necessity

[rich_gti6 0]

Mine has a 9.3:1 static compression, with a peak boost of 1.3BAR.

 

When I built the engine I was only expecting the SC to give 1BAR; if I had my choice the CR would be lower.

 

For 2BAR I reckon you'd need to be near 8, or even high 7's.

 

I wouldn't be worried about low RPM responiveness due to the low compression, a bit more advance will make up for that.

 

It maybe worth speaking to Ashford Motorsport; they have built some of the most powerful XU turbo engines in this country, some over 400BHP.

 

Rich

[Sam 4]

I'll have to do some calculations when I have all the bits in front of me, its going to be a while before it all gets built I think anyway. I don't want to run a shedload of boost. 1-1.5 bar really if I can avoid having to drop compression too low I will, I realise it means less safety margins though.

 

Rich: are you on msn? sam@dcoe.net if so.

[welshpug 1,623]

I think someone needs to look into why VW think 11-1 with a turbo on a 2.0 engine producing 200bhp on "street fuel" is perfectly feasible, where many other manufacturers and tuners run such low figures.

 

also worth bearing in mind that when american tuners refer to "street fuel" it is of much poorer quality to the fuel over here in europe, but the race fuels mentioned wont be too far apart in specification/quality at all.

[Sam 4]

When you go to get fuel in the states though 92 isn't a ron figure, its RON + MON / 2, not sure how that compares to ours?

[B1ack_Mi16 67]

I really think 9:1 is the way to go.

We're not longer in the mid 80's with simple enginemanagement systems.

 

Mate of mine were (on the old turbo-setup Sam, as you saw in some pics I sent) was running 9.2:1 compression in a bored and stroked 1.8T Audi engine (which now is a 2 litre). Was running 2.2 bar of boost on that with no problems with knock. That was on 98 octane pump-fuel.

 

Pushing out like 550bhp on the old setup.

 

As long as you get the ignition-timing correct you can still run high compression and quite some boost.

Especially as your turbo won't deliver very much boost until approx 4000rpm you really should go 9:1.

 

It's in the low revs it's most likely to start knocking anyway, at 2-3000rpms. As revs increases the chance of knocking decreases.

 

So piston with optimised squish height for good combustion efficiency like you're getting from Wiseco is the way to go really.

 

Just put it togeather and I think you'll find it will work good.

[pdd144c 0]

As long as you get the ignition-timing correct you can still run high compression and quite some boost.

 

Hence why my TT used standard 1.9 pistons with good results, although everyone dismissed that as being stupid

 

Just out of interest, what is the standard T16 comp ratio? Seem to remember the setup being good for 1.8 Bar according to Hilgie when we spoke last on MSN.

 

Sam, if you want to speak to someone in the know I can put you onto the man who used to build Will Gollops engines... If you are still popping down tomorrow we can chat then.

[petert 554]

I've been reading this for a while and no-one has mentioned squish height. If your using the Wiseco pistons I designed a few years ago they will have a 37.50mm compression height and an 18cc dish. Keep the squish band high and make the dish bigger if you want lower CR. A good example of this is the 1.9L 8V DFZ engine. It's only has 8.4:1 but has excellent throttle response, due to the 37.50mm comp. height. Design the piston correctlyin the first place and resist skimming the piston.

 

I've just realised you're building an XU10 so the deck height will be incorrect but the theory remains the same.

Edited November 30, 2006 by petert