Pressure drop - how much power does a Zavoli Zeta-S support?

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3sGTE
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Pressure drop - how much power does a Zavoli Zeta-S support?

#1 Post by 3sGTE » Wed May 14, 2014 12:27 pm

I’m experiencing a gas pressure drop on my car using the above reducer. Under everyday driving conditions it maintains a steady ~1.5bar.
When I plant my foot, above ~4500rpm with boost pressure at 1bar (approx 180-200hp) the pressure drops off – The lowest I’ve seen it go is 1.05Bar. As a consequence gas injector times shoot up to compensate.
When I bought the Zeta I read it supported anywhere between 200-300hp’worth of gas flow so I did think it could be marginal, but thought it’d cope better than this.

Does anyone have experience of this reducer?
My main reason for choosing it was it seemed very well made and compact, metal pipe fittings etc.

Also, I have noticed that during the transition from open throttle> closed throttle, the gas pressure spikes to ~3Bar and stays there during over-run until you reapply some throttle. Is this normal operation for a reducer on a turbocharged engine? It’s not causing any running issues but did strike me as strange behaviour. However the more I think about it the more it makes sense as that trapped gas pressure dosen’t have anywhere to go.

If this pressure drop isn’t in line with the norm for this reducer I guess it’s a problem with my gas feed. It is as follows:

(Standard Tomasetto multivalve) – (6mmcopper/8mm 90degree FARO adapter) – (8mm FARO pipe under car) – (8mmFARO/8mmcopper adapter) – (Valtek 8mm high-flow valve) – (8mm copper, 30cm) – (8mm/6mm copper pipe joiner) – (6mm copper, 10cm) – (Reducer)

I spent ages ensuring all pipe bend radii were nice and large and that there are no kinks. I am slightly suspicious of that 6mm Faro 90degree fitting, the internal bore looked very small.

Any help appreciated. LPG has been a steep learning curve but I have to say I’m enjoying it!

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Re: Pressure drop - how much power does a Zavoli Zeta-S supp

#2 Post by LPGC » Wed May 14, 2014 2:54 pm

This thread is on the same subject as one of your previous threads isn't it?

According to some suppliers it is rated at 183kw, which is about 245bhp depending on which version of bhp you use...

How much power does you car make? Turbo'd motors need a better gas feed than none turbo's that make the same power because the tank pressure to manifold pressure difference is lower - effectively less pressure to push the gas through the feed pipe. Was going to ask for details of your gas feed but noticed you listed that and it should be OK imo.

It is possible to see 3 bar on the over-run on a turbo'd engine... if you come straight off boost to an over-run situation. Think about it - If reducer pressure is set to 1.5 bar above manifold pressure and the manifold has 1.5 bar of boost, that's 3 bar absolute pressure.

I would try a bigger spec reducer...

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rossko
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Re: Pressure drop - how much power does a Zavoli Zeta-S supp

#3 Post by rossko » Wed May 14, 2014 3:48 pm

3sGTE wrote:However the more I think about it the more it makes sense as that trapped gas pressure dosen’t have anywhere to go.
Yes.

Zeta-S are splendid units, of course they have a ceiling but 200bhp should be within capability. You've not mentioned what's between regulator and injectors ... filter, tee, sensor?

If it was anything to do with tank static pressure you should be able to spot a difference between morning and evening performance, as tank contents temperature varies.

Problems with restriction in liquid supply tend to show up with dramatic effects e.g. a too-small multivalve works fine up until a critical demand level, then you get a total collapse like driving into a brick wall - the LPG will evaporate at the restriction and you're getting barely enough vapour up the small bore pipe to sustain idle, never mind full power. No sign of that? rule out the pipework.
A more gradual tailing off of pressure under demand does suggest more the regulator end, but treat laptop displays with caution as they are usually slugged and delayed.

We do want the mixture to go rich under full power, i.e. dose in more than 200bhp worth of fuel. It's possible to over-egg that, but difficult to detect if it is going on.
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Re: Pressure drop - how much power does a Zavoli Zeta-S supp

#4 Post by rob99 » Thu May 15, 2014 6:45 am

Hi

I have a similar issue with my Zeta S, which I posted a couple of weeks ago. It's fitted to a 208 BHP V6 Shogun.
On full chat it's started to drop the gas pressure down to about 1.05 bar and on the overrun from high rpm rises to 3+ bar.
Took it apart and everything looks to be fine, no @!## and the diaphragm and valve seat look perfect.
I'd be interested in what you find out.

Rob

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Re: Pressure drop - how much power does a Zavoli Zeta-S supp

#5 Post by 3sGTE » Fri May 16, 2014 2:58 pm

LPGC wrote:This thread is on the same subject as one of your previous threads isn't it?
Ermm may be along a similar line - I post on a lot of forums and often forget :D. Think I did ask for advice on reducers before christmas but nothing regarding pressure drop.

Max engine power is currently at ~250hp (standard turbo actuator pressure - 0.9bar)

Between reducer and injector rail is 60cm of 12mm gas pipe, with an inline canister filter and an inline pressure/temperature sensor. Both these have a similar internal bore to the zeta outlet so I don't think there is any problem there. Pressure sensing is done using a reducing tee off the vapouriser vacuum line. This combined sensor unit is supposed to go in line with both gas and vacuum pipe but the vacuum bore is only 3mm - I thought this could cause issues with the reducer reacting to rapid boost pressure rises so I ran 6mm vacuum pipe to the reducer.

Space in the engine bay is tight but I think I could fit in a 2nd Zeta. Either that or I could possibly squeeze in 1/2 magicjet reducers.
I've heard the bigas twin is a decent high power unit but I don't think it'd fit.
rob99 wrote:Hi
I have a similar issue with my Zeta S, which I posted a couple of weeks ago. It's fitted to a 208 BHP V6 Shogun.
On full chat it's started to drop the gas pressure down to about 1.05 bar and on the overrun from high rpm rises to 3+ bar.
Took it apart and everything looks to be fine, no @!## and the diaphragm and valve seat look perfect.
I'd be interested in what you find out.
Rob
Interesting, i'll let you know what find. I have noticed some reduces are specified as being suitable for turbo engines, others not. Wonder what the difference is. I've been using google translate to read lpg-forum.pl and many people there seem to mention the Zeta S pressure spiking on overrun too.

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