I see a new engine in the Wren lineup - the model 70. I guess this is a hand selected MW-54 MK IV which puts out 70N, rather than the nominal 66N?

Yes, that's right. The 70s are a version of the MW54 built by us (not available as a kit), and they put out over 7kg. A little less thrust and a little less expensive than a SuperSport, we're widening the range of options open to our customers.

Sara Parish
Wren Turbines

is a mk4 54 upgradable to a 70 then?

It's not an upgrade that we would usually consider doing, as there is not a huge difference in thrust and it would be expensive, entailing a complete rebuild of the engine. The only time it might be feasible is after a nasty crash, if the engine had to be rebuilt at Wren the guys might rebuild as a 70 rather than a standard Mk 4.

Sara Parish
Wren Turbines

I'm sure that much of the difference is due to closer tolerances, but are there any hints that you could give us that might allow some of our kit engines to be brought closer to the specs of a 70? Like make mine a 68?

Awww c'mon Mark ... tell the truth. You won't be satisfied with a 68, what you REALLY want is a 69 !

But I'd settle for a 68.5! [8D]

No, that's not possible. I think yours is a Mk 2 or 3? There are quite a few differences between that and the Mk 4, and the 70 is a further development of that. You really need all the changes because they add up together to produce the increase. Making just one or two changes wouldn't make enough difference, and if the engine is running happily taking it apart and changing a few things might actually have a negative effect.

Sara Parish
Wren Turbines

Mine is a Mark 3 Sarah. What were the changes from a Mark 3 to a Mark 4?

Thanks.

If I remember right the Mk1 was a 12lb engine kit leaving the threads to be tapped and the turbine wheel and compressor needed balancing and had the case made of sheet.

The Mk2 was the same with threads tapped.

The Mk3 had the one piece stainless case and a proper green front cover and still 12lb and was the first of the pretty looking Wrens.

The Mk4 was as the Mk3 but with a fully balanced rotor and bigger compressor giving 14lb.

I'm 100% there were many other upgrades from model to model and I'm sure Sara will elaborate on my rather poor descriptions..
Jason

No, I thought that the Mk 3 was 14 pounds with a pre-balanced set of spinning stuff.

My Mk 3 kit was specified as 14 pounds, with turbine wheel, compressor, and shaft pre-balanced...

Woketman is correct. The Mark 3 was 14#. They sometimes advertised it as 14+#. The Mark 4 has a number of refinements to get it to 14.5#.

Joe

According to Sara, the Mk 4 gives 14.5 lbs minimum, while the average Mk 4 is "comfortably" over that (15?)

Yes, I was quoting their advertised numbers. Wren is conservative in their thrust numbers and most of their engines will output better than advertised.

Joe

Then there was the super secret Mk2.5 that had the Mk3 compressor in a Mk 2 case...apparently closer to 14 than 12 lbs of thrust...

Have to agree with Gordon. 69 is what we want sometimes [8D]

Could´nt recist this one

There are quite a number of changes from the Mk 3 to 4, which is why we don't offer upgrades. The complete rotor assembly (shaft, turbine, compressor etc) is different, and that's an expensive item. The parts which fit closely against the rotor - front intake and NGV - would also need to match the new rotor, and there are other items too.

All our thrust figures are conservative, we give figures that all engines should be able to achieve but most do better.

Sara Parish
Wren Turbines