fiestaturbo.com

[Chetski]

Im after a bit of help, i know what compression ratio is and stuff and i was wondering if anyone knows what kinda compression ratio i could change too to improve performance, and if its worthwhile doing it [ERRR] so far its been fairly reliable.

Currently im on standard c/r 11.0:1 on my zetec-s 1.6 with t25 turbo and at the moment i have an oppertunity to lower the c/r of my car for free properly so i need your thoughts on whats best.

Possible compression ratio i could change too:

9.9:1
7:1
9.4:1
9.0:1
8.6:1
8.25:1


Thanks

Chetski

[heeman10]

Who did the turbo conversion on the engine? If it was a company/tuner as opposed to a DIY job, I'd get a suggestion from them

On something small like a 1.6 I wouldn't advise dropping it too much, otherwise your off-boost running will be crap, and you'll have to live in the revs all the time to get any kind of tractability.

What boost are you running now, and what do you want to increase it to? I wouldn't drop the C/R below 9:1, and something as high as 9.9:1 might be a happy trade-off. Speak to someone like Van Aaken, they have a fair amount of experience with supercharged 1.6 Zetec engines

[Chetski]

The turbo is from van aaken developments with boost set at 0.3bar which gives me 140bhp an torque. Van aaken say they wont undertake any major engine interal work an that running higher boost = big loss in reliabilty with the bottom end.

You mentioned off-boost driveabilty could you explain what you mean? currently the turbo reachers an holds peak boost from 1800rpm giving almost lag free, sharp throttle response.

As for boost this may sound funny to you guys but i want to run as low as possible, basically have the turbo providing the optimum boost for the c/r to give a balance of performance, reliabilty an economy, i dont want to whack it upto 1bar just for the sake of it. Im happy to increase say 0.4bar if that what gives me what im looking for which isnt all out power.

One company estimated if i drop to 9.0:1 it should keep off boost drivability whilst giving me a reliable 160bhp but i duno who to beleive?

[heeman10]

Hi,

When I talk of off-boost driveability, I'm talking about the power available to you when the engine speed isn't high enough for the turbo to be making useful boost. You say yours is fully up to speed at 1,600rpm, so you clearly don't have any issues at the moment. That in mind, I don't think a compression ratio would dull it down too much. Like I say though, I wouldn't drop it below 9:1, otherwise it'll be really sluggish accelerating from low revs, so you'll end up having to downshift more than you'd want, for overtaking etc. I can't comment on the reliability of the engine, but it's good to know you're not wanting to run big big boost, as you'll no doubt cause problems with the relatively standard internals you'd be using.

Best bet is to ring around tuners, preferably those who have worked on such engines (tricky as there aren't all that many turbo'd Zetec Ss out there), and get their opinions.

James.

[Chetski]

Heeman10 thanks i get what your saying now, like i said it peaks so low its almost always on boost apart from when im parking! SO if i lowered the c/r it may get more sluggish until boost is built up which is exactly the kinda info im looking for!

As for reliabilty i think it be safe to go as low as 9.7:1 on standard internals, but as im rebuilding the engine at the moment with uprated interals i think i will go for 9.4:1 as im confident the new parts can easily cope with the increased strain.

As for the boost i know from experience big boost means big bhp but sometimes resulting in a less driveable car, an driveability i find is more rewarding than knowing i got 200bhp.

Thanks very much!

Chetski

[ianFRST]

how do you plan on lowering the compression? new pistons that were designed 2 do it are the best and most reliable

[thehuzman]

If you are happy with the power you have, then I wouldn't bother changing the C/R. At that boost level you may get a bit of extra power going to something like 10:1 just because you're ignition is probably retarded a bit at 11:1 on full boost to stop det.
However this will mean a remap for not a lot of extra gain.
If you are going for higher boost more power, do you know at what power/boost level you need to upgrade your management, as I think the VAD stuff generally runs fairly a standard ECU setup that can't handle big boost.
I'd defo look into all the other implications before stuffing the boost up though, because not a lot of people know the limits of the Zetec SE (rods,crank etc)
More to it than meets the eye

[Chetski]

Well if im lowering the c/r i might aswell go for the optimum c/r for the engine, besides i might get a unichip to take care of the management side of things although on paper the VAD chip seems very similar to a unichip interms of mapable points, features and tunability.

I know that 150-160bhp is the limits of the rods with forced induction, the pistons an crank can handle upto 220bhp which is highly debateable itself, but in reality the rods are the 1st thing to blow a big hole through the block around 150-160bhp after a few thousand miles. With the engine rebuilt it will handle the power i could chuck at it so im not worried about how much power i get i proberly have it less for everyday driveabilty and more for track days.

Like i originally side im not after big boost, im happy if it stays the same or just goes up a couple psi, aslong as it runs how i want it too with nice torque an minimal lag.

[PhilM]

8.25 is the best on that list really....low comp so fine for turbo and most boost pressures, and still retains a hint of offboost torque!

[heeman10]

Do you not think that'll completely kill it Phil? He's not wanting to run silly boost or anything.