Stamped vs. Machined water pump impellers

[geesamand]

I'm evaluating a new water pump for a sports car. The stock water pump is known for cavitation at high rpm, so traditionally the track dogs changed to an underdrive pulley.

Now a shop is producing a water pump replacement that has an impeller built from CNC'd billet aluminum. Supposedly it does not see significant cavitation all the way up to red line.

Questions:
1) Given that this car was considered to be a very well sorted sports car, why would the OEM still use a stamped design that cavitates? (The car is known for an insufficient stock cooling system)

2) Could there be any downsides to a water pump that is more efficient? Perhaps more hp draw?

Thanks in advance for your thoughts.

Dave

 

[oldrotary1]

oldrotary1 geesamand I have some ideas you can try. since 40% of the cooling is done with oil and an oil cooler try increasing or adding to the oil cooler capacity or add another cooler which will increase your oil volume,this can also be done by adding a modified deeper or wider pan as well (to increase volume)which will help to keep the engine cooler as a , or if you can afford one moroso makes a beautiful alum pan with baffles for racing. you should also remember that if you base your rad capacity against the factory rated horsepower and you modify your horsepower say by 50% you should also icrease your rad by the same amount,I think you could ad some ducting to force extra air to the rad, I have done a lot of research on this as I am curently building a waterpump that will not cavitate even as high as 20000rpm

 

[Tmoose]

The stock impeller was always stamped steel? I'm not aware of street driven RX-7 having a bad rep for cooling issues, unless 100,000 mile seal reloads of legend are related.

Mike H, do you believe any product is engineered to expire at the end of the warranty period?

Exceeding the warrantee period is certainly important for a manufacturer's cash flow, short term and longer. A friend was a zone tech rep for GM, and used to say the Fire-maro T-Top warrantee issues were burning thru his pension plan.

But I get the feeling today's most successful mfrs are the ones whose products' have earned reputations for appliance-like reliability well beyond the 100,000 mile mark, factory warranty be hanged.

 

[NorthJ]

If its a track car have you thought about running an electric water pump. Did this on a Mini (classic) solved all my cooling problems.

 

[evelrod]

Electric pumps may be the hot setup, I won't argue that. They require quite a bit of plumbing and modifications and, in the clubs I race with, are technically NOT legal...This is not to say I have not seen some of my competitors using them...I just don't push the issue as I don't see any great performance advantage in their use. My 63 Austin Cooper uses a stock type pump with a slightly modded impeller and a smaller dia pulley with the aforementioned restrictor for decent cooling at Socal tracks...read that as some pretty hot days in the summer.

Rod

 

[geesamand]

Thanks for the ideas. Water pump upgrade is only part of the cooling package, of course. For price and classfication reasons I'm not adding extra oil coolers, oil pan size, or radiator. Ditto on the electric pump - installing this improved water pump was just too easy by comparison.

Thanks for the suggestions. I have it installed currently, and while it will be hard for me to demonstrate an improvement, others have found that this unit helps.

Regarding general rotary reliability, this is only a problem at high RPM. So warranty is a non-issue, this only comes up when on the track, and those guys have traditionally upgraded the rest of the cooling system or gone electric since there was not a drop-in water pump upgrade before.

 

[kevindurette]

"1. It gets through the warranty. End of discussion.

2. Costs more money."

Yep. That's the end of it. Cars are made to sell. Dreamers and enthusiasts end up spending more money than they'll ever make. The companies aren't run by engineers; they're run by accountants, investors, and other business people.

I wish this wasn't the case. There are many things that would make a car so much better that might all add up to only a few extra grand in the end, and avoiding the free use of stamped components is definitely one of them.

 

[Tmoose]

kevindurette repeated
"1. It gets through the warranty. End of discussion."

I'm pretty sure I'd heard of some vehicles or products actually lasting beyond the warrantee. Actually I question the ability to engineer and manufacture a product to last precisely X hours or miles. Certainly there are plenty of examples of products expiring before the warrant ended.

Lots of mission statements include something about exceeding customer's "expectations". That is not complete nonsense. Brilliant marketing and buyer's incentives can only sell so many ---------- (insert name of extinct product).

 

[patprimmer]

The great impact of the Japanese cars was largely due to them being trouble free for at least twice the warranty period. In my opinion, that raised the bar enough so others had to follow to keep some market. Warranties then escalated from one to three years or more.

The stock parts work fine for the use they were designed for. If you change the use it up to you to solve the consequential problems YOU caused.



Regards

eng-tips, by professional engineers for professional engineers
Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.

 

[GregLocock]

Twice? My horrible Corona is now 24 years old. Last year I had to replace the the clutch master cylinder ($70). Two years before that is was the thermostat housing ($20). When will this unreliability end?



Cheers

Greg Locock

SIGlease see FAQ731-376 for tips on how to make the best use of Eng-Tips.

 

[kevindurette]

It goes back to the saying "Good enough is best." The cavitation point of the water pump pulley won't affect its longevity when loafed around on the street.

I think it'd be cool to design a car with "Easter eggs" throughout... such as a valvetrain that uses exotic materials to survive 20 000 rpm. Nobody will know until they start playing with it, but once they do, the popularity of the car will explode among enthusiasts. This same thing happened to the Toyota Supra's 7M-GTE, which can handle 800 horsepower on the stock bottom end.

I think GM should make a new Nova. They should put the ECOTEC in an expansive engine bay, sitting on an adapter engine cradle. Once you take the cradle out, it'll open up to the stock mounting points for a Chevy Big Block. That'd be cool as hell. The car would survive EPA testing but be a complete "Easter egg" to enthusiasts.

 

[Artisi]

In a pressurised closed circuit such as an automotive cooling system with an impeller running is a casing with such wide clearances etc, it is unlikely what you see is cavitation. Unfortunately cavitation is a poorly understood phenomenon used by many to describe actions/effects which are not cavitation.

In a automotive water pump it could well be recirculation of the flow round the impeller or corrosion-erosion or a combination of both.

A few photo's either posted here or preferably in the pump engineering forum would achieve some knowlegable comments.