Slaney21

iTrader: (1)

hi all

posted this on ft.com but wanted advice from here also


Got back from a reputable tuning company yesterday and im a little upset/disappointed to say the least. Due to my frst having higher compression pistons they dont want to go ahead with the setup as they say it is causing problems with the car "pinking" and a few other issues with starting after warm and boosting etc.

are higher compression pistons not suited for turbo engine'd cars? As it stands im considering selling/breaking the car as u dont have the time/money/patience no more

thanks

xr2wishy

iTrader: (2)

higher compression pistons are fine, tell them to fook off.
however and this is a big one, higher compression puts more strain on the pistons and rods so need to be uber stong to be reliable.
with a good mapping session they should get round pinking/det with a small sacrifice of power.

JesseT

No need to give a bit more information, but generally, one can succesfully build a turbo engine with upto 10:1 compression ratio. The higher the ratio is, the more stringent requirements it will put on; ignition mapping, fuel mapping, boost mapping, IC, turbo back pressure, cam timing, plugs, knock detection, etc. In other words, you need to know what you are doing and how well all the components are doing their work. With a 8:1 ratio, there is much more room for errors.

Slaney21

iTrader: (1)

thanks for the replies gents.

its hard to know whats what as i have the tuner saying one thing and the chap who put the engine together saying the exact opposite. Im not to fussed as much about a loss of power as im not bothered about neck breaking bhp figures considering its my daily and the roads are not race tracks/rally stages etc, I just want the boost to be safe and the issue with not starting when being run sorted so i can enjoy driving it Guess its true when they say you should never own a dream car as it becomes an omen.

thought the tuner was gonna blow the bloody engine up yesterday watching it rev so high

the new was from an xr2 and had the following work done to it

ported and polished gasflowed cylinder head
lightened and balanced crankshaft
high compression pistons
standard cam (from my frst engine)
normal size valves (from my frst engine)

the engine before was around 8-10psi on a t2 turbo. So far i have covered just over 2000 miles without any hard driving and has been running ok bar the bloody starting problem and what can only be described as a high pitched sound when the boost gauge hits 10psi.

xr2wishy

iTrader: (2)

i used to run 14psi on a pretty much standard mk2 fiesta xr2 bottom end, so i wouldn't worry too much.

ben_frst

an xr2 lump with higher compression pistons? im guessing the xr2 runs arond a 10.1 comp standard so higher comp pistons than the xr2 would be a very bad idea for a turbo application

any idea on the compression ratio? ive got one motor runnin 9.1-1 and quick little car on and off boost

cossiedoc

If the engine is from xr2 you will need to have it chipped or remapped to suit new comp ratio so i can understand why they say they dont want to do it what would you prefer them to blow it up?.

Slaney21

iTrader: (1)

ben_frst:
il try and find out the ratios. not clued up on the technical side of engines so will ask about it

cossiedoc:
car is already chipped. Will also look into mapping should that be necessary or failing that its a strip down and new pistons. Of course i dont want them to blow it up at the end of the day i was a bit suprised that he said he couldnt do much with the car due to compression yet it was being given a bit of stick on the rollers thats all.

thanks for input so far

cossiedoc

No problem mate it steve of hampshirehotrides and fiesta turbo.com fella drop me a pm on ft if you need someone to look at it i have the fuelling and det monitoring stuff so could poss setup if it will on chip you have

xr2wishy

iTrader: (2)

when you say high compression, do you mean standard pistons, then the CR will be 9.0:1 IIRC, not so high really, although dropping to 8.5:1 would be better or lower if you can afford it.

Slaney21

iTrader: (1)

hey steve. cheers dude will keep you in mind

the pistons have raised edges if that makes any sense? not sure if they would come standard or not but will find out tomorrow. the ones that came outta my frst were flat i cant really remember

would i go about dropping it by using a decompression plate or by one of these "mapping" things?

JesseT

The raised edge doesn't make sense. That would be a bowl then? If the edges would be higher than standard, it wouldn't clear the head. If the edges are at standard height, and it's a bowl in the middle, it wouldn't be high comp.
The standard compression in a XR2i is 9.5:1. It's ok to turbocharge at least upto 14psi, but the T2 would be a bad companion for this. The t2 is a VERY small turbo creating high exhaust backpressure, resulting in residual heat and pressure in the cumbustion chamber which doesn't help at all fight the pinking issue that high comp might result in.
You really should find out what the high compression means in your case. Is it high in turbo engine scale or high even in N/A engine scale (over 10:1). If it's the latter, that would start to be a really bad idea.

Slaney21

iTrader: (1)

the piston on this link is very similar to the ones that im trying to explain

http://www.burtonpower.com/pic_viewe...0%20Piston.jpg

the ones which came out of the rst engine were pretty much flat. The pistons which are in now are apparently standard from an xr2. will update when i can

JesseT

That's the standard N/A piston that results in a 9.5:1 CR. Totally fine for upto 1bar of boost. Remember, that the std. RST pistons with a CR of 8.3:1 are easily fine for upto 2bars of boost.

Slaney21

iTrader: (1)

thanks for the posts jesset and everyone else much appreciated. all have a

hopefully getting it all looked at again on the weekend so will hopefully have this resolved soon enough. will update when necessary