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Discussion Starter · #1 ·
Well, I decided to look up a few things today.

The 10v's all use the 056 103 419A valve guide, which is 36.5mm in length with an 8mm ID that needs to be reamed to fit the valve.

The 12v uses one of two guides. One is the very same one the 10v's use, the other is the same EXCEPT it is meant for a 7mm stem valve. Since the 12v uses the same head casting irregardless of which stem size is used, we can use the 7mm guides in our 10v as a direct replacement. Part number is 037103 419B.

Now for the other stuff.
The 12v, by default, uses a 40/33 setup in both 7 and 8mm stems. The 8mm valves are the exact same as those found in the NF/NG engines right down to the upper and lower retainers, locks/cotters, stem seals, follower/lifter and inner/outer springs. The 7mm version uses the following bits:

40x91.9mm intake valve: 078 109 601B
33x91.2mm exhaust valve: 078 109 611C
7mm stem seal: 027 109 675
7mm locks/cotters: 021 109 651
Upper retainer: 078 109 641C
Valve spring: 078 109 623C
Cam follower: 050 109 309H

Note, the 7mm setup only has a single valve spring and ONLY an upper retainer and AFAIK does not have a "sodium" exhaust valve.
 

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so we would still have to have custom inconel exhuast valves made up though, right?
also, i have a set of Ti valve retainers being made up for me 8mm stems. if i decide to switch to 7mm, would it be possible to still use the 10v retainer, or are different locks required?
i'm just trying to see if i'm gonna have to stick with the stock 8mm valves or if I can go with the more "flowdacious" 7mm :D
 

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Discussion Starter · #3 ·
The upper retainers are different as are the locks/cotters. This is due to not only the stem diameter but also the dual vs single spring thing ;-)

One thing I noticed Audi did on the 6mm valves in the 30v engine is taper the stem between where it rides in the guide and is exposed in the airflow.

The whole conversion to a 7mm stem valve will be expensive. I'd have that be the very last thing on my list to do to find the last bit of power in a 10vt.

You'll spend over $100 on the intake valves, $275 on the exhaust valves plust the cost of buying a factory valve for it to be copied (the factory E-valve is $35 new), $7.00 on stem seals, $7.50 on the locks, $75 for Ti retainers (unless you want to buy new factory ones at the dealer!), $34 for guides, find a source for valve springs (dealer, aftermarket, but not WorldPac, they don't carry them), and then the new followers/lifters are also not available from WorldPac.

You will likely spend well over $600 just to go from a 8mm stem to a 7mm stem. Like I said, I wouldn't do it unless you are trying to make the absolute most out of a 10vt. I just posted this as an FYI for those that want to know ;-)
 

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but, if all that stuff was being relaced in the first place, like on my head, i'm replacing everything anyways,valves,seats,guides,springs,retainers, so why not go for the gusto, how much more will it cost vs. just putting in the 40/35 combo with inconel exhaust valves anyhow
 

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Discussion Starter · #5 ·
Depends on what you can get the 40mm valves for. I found a set for $50 (factory valves, private seller). Also depends on what the 35mm Inconel's cost. Either way, using the 8mm stuff is going to be cheaper, how much so just depends ;-)
 

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i've been going ove this in my head, with the 7mm stem intake valve(40mm), the length is 91.9mm.

how long is the MC 8mm intake valve? and if it is longer, would it not work in the MC head?

and the 309AD lifter is designed to be used with this 7mm valve, correct? and the single spring is designed to work with it too, correct? well, what's stopping us from installing the 7mm guide,40mm seats, and using the 7mm retainers and keepers?

then all we'd need is Ti retainers that would work with the 7mm/91.9mm stem valve. no custom valves needed.
 

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I'm wondering if the difference in valve stem size is worth it? I would prefer the added strength of a thicker stem myself. What kind of flow #'s are we talking about? Will an 8mm valve stem shed more heat than a 7mm? Will the
7mm stretch more from the heat? Maybe in a turbo app its better to keep the
thicker stem? What can you possibly gain.......1hp?

Aaron
 

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i shoulda specified that i was talking intake only. leave the exhaust 8mm for durability, and the fact that you can get them in inconel.
 

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Discussion Starter · #10 ·
The 10v heads use the same length intake (91.9mm) and one of two lengths of exhaust (90.8 for the turbo, 91.2 for the non-turbo). Since you won't be using the factory 33x91.2x7 exhaust valve anyway (not sodium filled IIRC), you'll just get an inconel 33x90.8x7mm made (or 35, take your pick).
 

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The intake valve is still subjected to heat right? Heat makes things expand so I'm wondering if less metal in the stem area will make the valve stretch more. I understand that the intake valves don't see the heat the exhaust due,but I'm pretty convinced that the intake valve faces do. Ever do a valve adjustment on a beetle? Its very important since the valve gets cooling from seat contact. If the valve isnt seating porperly you loose cooling ability.
Im wondering what the thinner valve stems due to intake valve cooling.
If its not an issue than I'll put 5 intake valves on the lathe and take a mm off the stem. I wanted to see if you guys have any concerns with cooling is all......

Aaron
 

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Aaron, the cooling valve definitely doesn't get as much heat as teh exh. valve, especially if you have decent intercooling. The flow improvement is hard to say, but IMO you want to address the exh. port flow more than the intake valve flow, I think the standard 40mm intake valve will flow plenty with relation to exh. port flow, I'd put your resources towards the exh. side. What you could do, if you wanted, is just trim down the valve stem right above the valve head, what is exposed to the intake air flow, just neck that down a little and back cut the valve a little, that would do wonders for flow. I wouldn't turn the whole stem down as a first option.

HTH
 

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Discussion Starter · #13 ·
I would not worry about that. On a water cooled engine, the q, q', q" (heat flux) in the intake valve isn't nearly as important, especially on an intercooled car.

Also, there are plenty of factory valves that are in the 5.5-7mm range that are in engines that see plenty of heat (the 1.8t and 30vtt use 6mm stems). And, some of those have the necked-down portion that is exposed to the flow as Javad suggested. Given the correct "fillet" radius, you could probably take the intake valve to 6mm in that area safely.

The exhaust valves are tricky due to the sodium cores. I wouldn't turn them ;-) Now, if you had inconel's, I'd turn those down a bit.

The expansion coeffecients of these metals are not very large. At all. Think about the clearances you are dealing with in that area.
 

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Cool...uh well yea cool. I think I'll do the lathe trick and see what happens.
Thanks for all the good info on the sunject.

Aaron
 

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we all know what stuff looks like once a valve head breaks off, don't we :wink:
 
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