Exhaust Valve thoughts ?
Turbo Mini Forums

I know most people stick to the tried and tested 29mm exhaust valves, but has anybody had much success using a larger one ?
Is it worth favouring the exhaust a little more because of the heat of the gases ? Or the inlet, to get more charge in ?
Any thoughts ?

Phil.

Edited by Turbo Phil on 30th Apr, 2004.

WWW.TURBO-MINI.COM

I know Jukka is using larger ones, I was thinking to use 35/31 but the difficult is to find reliable exhaust valves to deal with the eat, so i decided to use36/30 valves .
if I could choose a different valve size i would certainly try what a very good mini turbo specialist do, (the one who came back from japon last year , or av..... ),
but this said the std turbo head with dished pistons and 10/12 psi are giving very good hp numbers (120/130).so mods are required only for big hps
fab
fab

i donk really know an awfull lot about valves etc, but i am sure i have read somewhere that the problem with getting bigger valves in a turbo head, is that it is very difficult to find bigger valves with thicker stems?

Having said that, i cant see why you couldnt use valves from a completely different engine, modern ones are almost always sodium filled these days, so it would be a matter of finding the right size and length..........

Also the way ive always understood turbo engines is that the exhaust side is actually more important than the inlet, due to the fact that the mixture is getting shoved in there under pressure, but the exhaust is just leaving due to the force from the piston. So if thats correct then a larger exhaust valve would be beneficial. on the other hand i could be completely wrong!! LOL

Pete

And on the 7th day........... God created turbochargers!

Yes, I run 36/31 mm Rimflos with std stem (7,1 something mm). No problems whatsoever. The exhaust valve is offset to leave enough meat between ports to reduce cracking. I like rimflos because they are one piece items and relatively bulky stainless valves. Good thing considering the heat.

I know of a local turbo mini that uses 32 / 32 mm valves. The owner naturally states that it runs strong like he**. I really cannot comment before I see some reliable RR printouts.

Making the head breath is vital and I feel that larger exhaust valves are essential with higher boost levels. Like Fab said if the goal is somewhere around 120 hp then the std valves can be retained. But every head shop has their own ideas, like K. Calver who does not like big exhaust valves that much.

Jukka

Thanks for that guys !
That's pretty much what i was thinking, that the bigger exhausts would become beneficial if higher power outputs are sought.
But i just wonder how restrictive the standard exhaust valve is ? i'm sure Dave is still on the 29mm zaust, he has 150+hp....
Jukka didn't you run 32mm zausts once upon a time ?

Cheers
Phil.

WWW.TURBO-MINI.COM

Hi There!
I am doing a 33/32mm head at the moment and will try it this season. At the moment I am using 36/31 (without offset) and had no cracks so far! I am also thinking that the turbo does his work to get a lot of charge into the chambers and therefore a big exhaus valve is necessary to get rid of the big amount of exhaust gases.

Bimmer Twinky headed and turboed A-Series:
http://www.minifreunde.at/harry/projects.htm

Yes, I had originally 32 mm exhausts (also offset) but ran with unleaded some 20000 miles and literally ruined the whole valve gear and head. Valves seemed fine but bought 31 mm Rimflos instead. I did not feel like boring / honing the ex guides to 8 mm. Also, the feedback from MED etc adviced that normal stem is quite OK which it has been.

Note that el cheapo valves most likely will self destruct so it is wise to buy good quality. BTW, I don?t remember what I did with the large valves, possibly put them in a bin. It?s always difficult when you need 2 different collets, and top caps to match towo different stem diameters.

im running 33in 32ex, but as the car isnt working yet i dont know what this is like
its a vmax head

I also had a problem with bronze guides and SS valves: the valves are a lot more worn than the guides - I guess that is the reason why MSC hardened the valves. This season I am trying the hardened valves - I will see what will happen to them - next time I will try rimflo because of their chromed stem.

Bimmer Twinky headed and turboed A-Series:
http://www.minifreunde.at/harry/projects.htm

Speaking now about my 1380cc the valves were 37.5 mm and 31.5 mm off set and they still cracked a few times, just a thought to add.

Best 1/4 mile 13.2 seconds @116 mph
First 5 port miniturbo to make over 200 bhp on a carb?
First 5 port miniturbo to make over 200 bhp on Injection?

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my old head was 33 inlet and 32 exhaust..it worked!