i hear constantly about how people have their pistons machined to lower the compression of the engine

but, what are the actual gains of this? just allows for more boost capacity? does it affect day to day running?

also, what sort of compression should i be looking at having it machined to? i have everything ready for my engine to be rebuilt, but wanted to look into compression lowering before i have it all assembled. i have brand new mahle pistons, so it would be these i wud have machined

any advice would be appreciated

 

It will let you run more boost with more advance. This will lead to more power in high boost (22+psi) engines. Downside is less power when boost isn't available, worse fuel economy (who cares), more difficult cold starting, etc. but nothing major.
If you end up machining the pistons, don't machine too much and don't machine close to the edge of the piston as this will reduce the flame's distance to the first ring. The piston crown thickness is around 7mm btw.

 

if i only ever want to run about 1 bar boost, and around the 200bhp mark at most really, is there much point in lowering the compression, or will standard compression be fine? i know its a bit of a vague question, but i want the car to remain as driveable and reliable as possible, even tho it is only a 2nd car

 

RSandy

Jesse is right in what he says. But in practice, lowering comp isnt so bad. Mine is well below 7.5:1. It's very driveable - i use it every day, and it starts v quickly in all conditions.

But, if u want 200hp, then do not lower the compression. No point at all. ive seen 230 on std comp with reliability many times.

 

Rick ive heard some rumours your car doesn't start at all at this precise moment in time

 

SafeChav

Dont even TRY and start with me

 

keep it standard compression

 

Many have even used the CVH's standard 9.5:1 compression with 1 bar boost.

 

Too late, BITCH

 

that conpression ratio a big high, i always thought the standard RST compresion was about 8.3:1, i maybe wrong tho

 

Ditto

 

For a genuine 200bhp, you need a suitable chip (eg: AB), a 0.48 A/R exhaust housing on the turbo, a suitable cam like a CVH34 and about 1.1-1.2 bar boost..

 

engine mods wise i have:

piper 285t2 cam kit, superchipped ecu, turbo technics stage 1 t3, -31, radtec FMIC, cossie fuel pump, uprated oil pump, mahle pistons +.29 with block rebored to suit, reground crank with heavy duty bearing kit, mongoose exhaust, induction kit.

shud this lot, with standard compression and 1 bar boost, not make 200bhp??

iv previosuly made 200bhp on the same enigne at jamsport holding about 16psi, and with fewer engine mods, so i wud have thought with the new stuff, i shud make the same agen, just with more reliabilty?

but anyways, the general concensus is that i shud stick to standard compression anyways. i dotn have the money to keep rebuildin the engine when it goes pop, so thats why 1 bar and 200bhp suits me

 

If thats your engine spec mate you could take about 19psi through
that engine.

When jamie done my red S2 it made 214bhp 227lb torque.

My mods where as follows

Standard engine+head
Jamsport chip
-34 act
Standard T3 turbo
Pro Alloy Intercooler+ Rad
Full Mongoose
PX induction kit.

Went like a train ill see if i can post up my print out later.

 

i no of a escort turbo runnin 9.5 compression and gotech it makin over 250bhp @1 bar of boost

 

9.5:1 is the standard CVH's compression for all 1.3, 1.4 and 1.6 N/A variants. RST sure had the 8.3:1.