1973 Rebuild

[Captain Obvious]

  And that's what it's all about!

[Takhli]

On 9/24/2018 at 7:06 AM, Captain Obvious said:

  And that's what it's all about!

You betcha! 

Beyond polishing, I can't say that there's any measurable benefit with a swirl except that they look pretty and you get bragging rights. They might also be easier to clean next time the head comes off, if ever, but the valves are running a little less than 2 grams lighter after the work is done.

Still need to have them refaced but would like honest opinions on the swirl... as if it matters at all.

Cheers.

Edited October 2, 2018 by Takhli

[Captain Obvious]

My honest opinion is that you're working in the minutia. I don't think there's any meaningful performance benefit to what you did to the valves.

Looks pretty? Certainly. Bragging rights? Absolutely! Performance gains? I would have to see the dyno sheet before and after.  

I'm no engine builder, but I think there are waaaay bigger fish to fry before you start seeing any changes from the surface finish on the valves. Cam changes. Intake tract improvements. Combustion chamber design improvements. Exhaust tract improvements. All that stuff. I think the valves are in the .1% at the very end once everything else has been optimize.

The NASCAR and Indy guys who have already squeezed out the other 99.9% elsewhere might see a tiny improvement, but not us. That's my uneducated non-expert read.

[wheee!]

Very pretty. A real pain to take apart to show people at car shows though....

[Captain Obvious]

And don't get me wrong... I'm not poo-pooing the work. I think it looks cool. And it would certainly be on the "build sheet" of things to tell people about the motor.

Would look great on the mods list if the car is ever sold (but let's hope that doesn't happen.   )

[Takhli]

15 hours ago, Captain Obvious said:

My honest opinion is that you're working in the minutia. I don't think there's any meaningful performance benefit to what you did to the valves.

Looks pretty? Certainly. Bragging rights? Absolutely! Performance gains? I would have to see the dyno sheet before and after.  

I'm no engine builder, but I think there are waaaay bigger fish to fry before you start seeing any changes from the surface finish on the valves. Cam changes. Intake tract improvements. Combustion chamber design improvements. Exhaust tract improvements. All that stuff. I think the valves are in the .1% at the very end once everything else has been optimize.

The NASCAR and Indy guys who have already squeezed out the other 99.9% elsewhere might see a tiny improvement, but not us. That's my uneducated non-expert read.

With what I've read on swirl polished valves since starting this, I'll agree.

One reason I went this far is to learn what kind of results can be accomplished in a home shop. A business wouldn't normally do it and I wouldn't do this for the normal daily driver, but hey.... It's my son's engine, and I have the time.

In the Z's hay-day, this kind of work was for engines that lived at the top end - where that last 0.1% is important - and engines were often torn down after a race. Since the car will live on the street, I think we'll just face them with the factory angle and back cut, and call them done. As you mentioned, de-burring and cleaning up the pockets and tracts will do more for performance.

They do look pretty, though and we're still happy with the combustion side.

Thanks, Captain.

[Captain Obvious]

All that said, I'm intrigued by the reduction in valve mass. I don't know what a typical valve weighs, but you mentioned that you took off 2g of material. What is that in percentage of total? Anything significant? And if so, are there any performance gains possible from such a change? (Thinking less valve float at high RPM for example due to the reduced momentum?)

I'm beyond my pay grade with evaluations like that, but it seems possible. Have you experience that deep with engine details?

[Takhli]

After polishing the face and attempting the swirl pattern the mule weighs 79 grams - a little more than 97.5% of its original weight.

After cleaning, but before any polishing and with no appreciable wear on the stems, the Eighteen intake valves we have weighed in at between 81 and 84 grams. But the mule was the only one at 81 grams, where the others were all 82 grams or more. The mule is also the shortest by 0.004-inch so it stood out as the odd ball I could use for experiments.

The set of six intakes valve I chose for the engine all weighed 82 grams and had the same length before any polishing, and now weigh 80 grams each. Polishing the combustion face seems to remove about 0.001-inch of material. They have polished combustion faces but no work on the backside. 

Grinding the faces and dressing the stems will remove more material but I don't know how much. I'm guessing about one gram's worth. 

Edited October 3, 2018 by Takhli

[Zed Head]

In real life usage the backs of the valves tend to get coated with crud.  From the PCV system and back-flow of exhaust gases and fuel vapor.  The fuel additive industry makes a fortune claiming to be able to clean them.

Not to be a downer, it's cool for that first dyno run or individual races or drag strip runs but long-term might not stay effective.

There's a neat thread over on Hybridz about weight reduction and balancing of rocker arms.  Lots of grinding of non-critical areas.

[siteunseen]

22 minutes ago, Zed Head said:

There's a neat thread over on Hybridz about weight reduction and balancing of rocker arms.  Lots of grinding of non-critical areas.

Can't remember the number of grams off hand but mine were all over the place.  I ground the underside to get them all the same weight before sending them to Delta for resurfacing.  Luckily they all weighed the same when they came back.  Happy with that but they sit in the box still, life reared its ugly head but I'm going to get it put together this winter after I shine up my valves. 

My Dad told me about shining up the back side of his valves back in the '60s.  He also told me, and of course I played dumb, to grind all the casting marks off the runners and smooth them as best I could.  That will be much easier today with a Dremel and the flex cable attachment.  He used a rod wrapped with rough sandpaper back then he says.

 

Edited October 3, 2018 by siteunseen

[Captain Obvious]

Thanks for the info guys. Maybe next engine I overhaul will get a similar treatment.  

[Matthew Abate]

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