How long should my Wren 54ss run on powermak before it runs on jet-a? Most of the starts I have on the 54ss run on start gas for 10-20 seconds before it runs off of jet-a. Is this normal or shoul it run on the jet-a much quicker??

On mine, the fuel ramp starts somewhere around 27,000and by time is gets to around 35-ish, I can shut the start gas off. I have an off board gas system. If I shut the gas off too early the rpms will sag down below 30K and slowly work their way back up. The engine is remarkably consistent and once you learn its behaviour patterns. FWIW, I have had very little luck with powermax - especially in cooler weather, if you get liquid PM in your system the gas pressure goes down and it is tough to keep the fire going (this is from a number of different engines). Straight ordinary propane works wonders for me, though.......

10 secs sounds ok to me, 20 perhaps a little long. Mine takes a bit longer on the first start of the day probably waiting for fuel to pump through the line.

What is inconsistent on mine is when it lights, sometimes it spins up, comes to a complete stop then whoomp & then spins up, today it just went whoomp without a prior spin up. John.

Between 10 and 20 seconds soundes about right. I agree with John, Mine will light up on gas, spin up a little then almost stop. Then the starter kicks in again and the motor will spin up again (Gas still burning) then the fuel ramp will start.
After the fuel ramp starts it is probably less than 10 seconds to idle. Mine does the same every time. The first start of the day, the fuel ramp may take a little longer.


Great running engine.

Regards

this is IME an indication of time to replace the glow plug. if it's a fairly new plug usually it's the coils aren't pulled out far enough or too low a voltage applied.

That sounds like my 54. Thanks for the help. I have 8 hours on my wren this year. For my first turbine, this one was a very good buy!!!

WOW, 10-20 seconds normal??? I've been running mostly AMT turbines for 7 years and it seems to me the longer the startup the worse off you are on bearings as they are only seeing heat/rpm's and no lubrication until the Kero starts.

Since there is a Wren in my future this season, I've read on RCU a few post referrence WREN's using non turbine oils and also refferences to using minimal oil as it does nothing for power to fuel ratio. So it would be my intentions on the wren that I see it get to benchmark rpms and heat degrees in a consistent ramp up time frame as quick as feasible given the ECU allowance. 10sec seems on the long side to me .02

FWIW, A SWB Mamba on air start is as quick of lite em up as I've ever seen its almost as linear as the rise in rpms when ramped up properly. less than 4seconds total can be achieved.

But, it it lit off, then the glow plug is working.....

Gosh, I'm not sure what you are trying to say here....But there are a couple of things to consider....
The idle speed on these little engines is high, so it is going to take a little longer to get there......
If the fuel ramp is too high to get a faster start, there is a chance that liquid fuel will pool in the bottom of the combustion chamber...when that lights off, it will errode a big hole through the chamber....no need to ask how I found that out (on a totally different engine)
I haven't timed my start, but at jet meets, mine is at idle as fast as any other trubine there...faster, if they are using powermax...

Thats kind of what I'm saying, I would not consider more liquid fuel flow but would consider a hotter gas so insure temps were comensurate with RPMS as it ramps up so the ECU can turn on the kero. feel free to add others in the proper order of burn temp as a gas.

As for gases as I understand and use based on outside temps is:

Propane gas lowest temp, highest pressure in summer

MAP gas, next hottest temp,

Powermax, HOT HOT,

yes but an old/poor plug or one that doesn't have the coils extended far enough out has a big lag and then a pop rather then immediate propane ignition. i don't own a Wren but on my JetCats if i hear the clicking of the propane valve several times and a few seconds after starter has engaged before i hear ignition of the propane then the plug is in need of changing. as soon as it's changed i get immediate ignition of propane as soon as the starter has engaged.