strange turbo mod?

[S-Express]

Took my spare K24 to a long-standing turbo refurb company today for a refresh.
The place is small and run by a couple of old boys which I suspect know a fair bit about turbos. They have all the kit included balancing machine etc.
Whilst I was there, they offered to cut back the exhaust compressor wheel slightly as it would improve pick up
I don't doubt their knowledge BUT if that was the case - why didn't KKK do it in the first place!?
Any thoughts?
Thanks

Oh, and just for info - they charged £130 for rebuild and balance with all new seals/bearings etc - including a 360 deg bearing. seems like a good price?

[sam80quattro]

might be total ***** what im about to say but im seem to think at the expense of better pick up it creates more noise, as in whistles louder, might be **** but thats what my heads saying lol

[fish]

Did you get their mod?

[S-Express]

Did you get their mod?

they're doing the refurb tomorrow

[Kieron20V]

Cutting back the turbine a little is just removing a little bit of mass from the rotating assembly. It might improve the spool up slightly due to the reduced inertia, but i would imagine at the expense of some overall efficiency. Might be worth it if youre keeping it bog standard.

[Billman]

I believe it would spool later but if the turbine impeller is the limiting factor on a give turbo the cutback impeller will allow better flow.

Smaller blades, less weight (spins easier) but also smaller surface for the gasses to hit (worse spool but more flowing through).

[david]

would'nt it be better to use lighter more modern compressor wheel?

[david]

I believe it would spool later but if the turbine impeller is the limiting factor on a give turbo the cutback impeller will allow better flow.

Smaller blades, less weight (spins easier) but also smaller surface for the gasses to hit (worse spool but more flowing through).

what do you think of say 5 blades instead of 6 ?

[Gringo]

Cutback is an old rallycross trick. In the good `ol days most large turbos where made for trucks, ie. diesel engines with low revs. These turbos had large compressors and small turbines. To make these turbos work for small displacement, high reving engines they cutback the blades on the exhaust side. This allows for higher exhaust flows and higher rpms ie. making the turbo more suitable for the application.

In your case, it will make the turbo spool slower, but it will move the point where backpressure exceeds inlet pressure up in the rpm range. This is a good thing if you are building an old school rallycross engine and letting your compressor work beyond it`s limits

[Gringo]

Just to back up my statement ;

Turbine Wheel Cutback
Turbine Wheel Cutback is a machining process which enables the turbocharger to increase power output by reducing back pressure. This process does remove some blade material from the turbine wheel which normally results in a slight reduction in turbocharger response. If you're unsure of how back pressure influences a turbocharger imagine running a marathon with a finger up your nose!

From; http://www.turbodynamics.co.uk/servi...bine-upgrades/

[Sleeper_Avant]

Very common on cosworth/ford mainly garrett turbos, very efficiant and cost effective turbo tweek!

[rj scotty]

Give it a go !

If you don't like it stick it on ebay and get another k24, there are cheap after all.

[Billman]

what do you think of say 5 blades instead of 6 ?

You will not find a turbine impeller with so few blades.

On compressor impellers with same dimensions and same impeller design characteristics the fewer blades would have the following impact:

1. Less airflow on the lower turbocharger revs

2. Faster spool ( less weight)

3. Better top end flow because one less blade need to "cut" the air

[sam80quattro]

might be total ***** what im about to say but im seem to think at the expense of better pick up it creates more noise, as in whistles louder, might be **** but thats what my heads saying lol

see i was right, i am full of ***** lol

[Gringo]

I cant really understand why some of you are still recommending him to do this mod? Unless he has backpressure issues this mod wil give him poorer performance. Money wasted most likely.