Hi All.

Julian mentioned in another thread that Saab possibly replaced the cast iron water pump impeller on the factory 99 16V with one made of aluminium.

This raises the question as to whether there would be any real world benefit for existing 99 owners to replace their existing impellers with one of a lighter (stronger?) material such as aluminium (or similar)?

Would having a lighter impeller help reduce the load on the gear teeth / jackshaft or does the weight of the water being pumped negate any benefit?

Could you (would you) redesign the shape of the impeller blades to improve the efficiency of the pump - or would this put additional load back on the unit?

If the answer is yes to either of the above questions, could a machine shop produce the part or would it need to go to a specialist manufacturer?

Happy for anyone with more engineering knowledge that I to chime in...

Just my 2 cents worth.

Neil

I believe they did this on the Triumph performance engines.

Thanks Jordan

Now would this fit a Saab 99?

http://www.sprintparts.com.au/news.cgi@ ... 480705.htm

Regards
Neil

Neil, I was going to post a link to that aluminum impeller in the other thread where Julian mentioned it. You beat me to it! I've been thinking about contacting that place and asking about dimensions. I think it would fit some pump shafts, but I seem to remember different impeller/shaft combos have different mating schemes (tapered fit, O-ring, etc.) I'm not sure which mating scheme that Triumph unit utilizes.

I don't think an aluminum impeller would be a great choice for street driven 99s, though it might be just fine. My concern is that the water seal (seats against the underside of the impeller) wears into the impeller. I'd imagine it would wear quicker on an alloy unit resulting in quicker leaking. The interesting thing is that these water seals are a generic component and when you buy them from a general mechanical components source catalog the seals come with a ceramic disk (surrounded by a rubber boot/ring for fitting/sealing). The ceramic disk would sit at the face on the underside of the impeller where the water seal currently seats. I wanted to know if these ceramic disks could be fit to a custom-designed impeller so I designed one in CAD. Unfortunately there isn't really room to fit the ceramic disk into a B engine water pump impeller.



I think the shape of the impellers could be improved upon to reduce cavitation and/or increase efficiency. It would be best done using Computational Fluid Dynamics Finite Element Analysis software. This is something that's been rattling around in the back of my head as an interesting project to do but I haven't focused time on it. The other half of the equation is the water pump cover. This dictates the angle (and potential curvature) of the impellers. It could also be beneficial to look at the design of the underside of the pump cover.

Whom could build them (machinist vs. specialist machinist) really depends on impeller design and the capability of different suppliers.

From my experience I'm not too concerned with load on the teeth when everything else is set up well. I'm more concerned with sudden stops due to failed bearings, lack of lubrication, cavitation etc. I've seen destroyed gears but they're usually due to mismatched gears or stress on assembly/dissassembly. The lower rotating mass from an alloy impeller could possibly be helpful for lowering rotating masses in a high power/high revving engine.

Geoff wrote:.....I think the shape of the impellers could be improved upon to reduce cavitation and/or increase efficiency. It would be best done using Computational Fluid Dynamics Finite Element Analysis software.....

I hate to throw out some voice of reason, but what is wrong with going to an electric pump again? Do some rally homologation rules not allow you to convert to a remote mounted electric pump?

Electric pumps are legal by usa rules but dont work for most foreign rally rules.

Got it.