12G295: Hardened seats important?
Turbo Mini Forums

I've got a couple of 12G295 heads and am wondering, with a small bore (either 998 or 1098) running 8psi possibly 12ish psi (8:5:1 compression and gt1544 turbo), am I tempting fate by not using hardened valve seats and just running the fresh cut but otherwise stock seats and large collet stock valves (uprated springs and caps, though)?

I'm not particularly worried about 40K miles of longevity-- this is for a "road race" car that will likely blow up after about 60 hours or less of track time because something always "times out". I'm running unleaded fuel here in the US without any "lead additives".

As long as you use some kind of fuel additive then it won't be a problem.

Fastest 998 mini in the world? 13.05 1/4 mile 106mph

www.twin-turbo.co.uk

I've run 5 years/4000 miles turbo but non-hardened seats w/out recession.

'Where does the engine go?'

addative added steve ?

No,Steve,unless you count some rather volatile octane improver! I run big valves and have always been more concerned about head cracking across the valve bridge area than recession.Cutting into that area to fit inserts can only increase the risk of cracking.

'Where does the engine go?'

right

I had hardened valve seats put in mine when I had it skimmed and new valves put in, but there's a wealth of anecdotal evidence which suggests it's not really worth it.

unleaded inserts are fitted as standard to all my heads, but in your case steve, theres not enough meat,

tetraboost brings to mind but rather expensive! .... but if your hands are tied as your are steve & your fueling and timing is spot on .......... i cant see why not under 10 k miles but if you want a head to last and save a small fortune on addative ......... go for the inserts for sure

Edited by BENROSS on 10th Jul, 2013.

Once again, I appreciate the varied and first-hand experience responses. I've run heads without seats and without additive for quite a long time. My largest concern was regarding the specifics of the turbo application. My perhaps irrational thinking was that since the exhaust valves can or perhaps do get hotter then the "blowtorch" effect could apply more quickly and burn through an exhaust seat in short order.

This car will most certainly NOT be in an optimum state of tune. Time and finances (and more importantly someone who knows how to dyno tune blow-through SU carb setup here in Southern Califormia) won't permit it.

My fear (again perhaps irrational) with exhaust seats is that they can fall out or fall loose with the increased and sustained temperatures involved in endurance racing a $500 A-series turbocharged car. I know, in the days of yore, seats fell out with some degree of regularity-- I have some destroyed heads that are witness to this. However, with modern materials and improved understanding I suppose that is less of an occurrence than it may have once been.

I did have some seats installed by a local shop about 5 years back and they were so small in diameter they actually choked off the throats considerably more than had they not been installed. Had I not pulled the valves out to check their work, I never would have seen it. They made zero attempt to blend them in. I recall the throats on the 12G295 head being smaller than the CAM4180 head I had.

What I'm doing is trying to resolve my internal conflict and balance out my perceived risk of blowtorching unhardened seats with the perceived risk and real expense of installing hardened seats. My natural tendency is to "just run it".

If valve seat recession is the only concern/fear, then I'll not install seats until the head is hammered enough to require new seats. Again, this thing will not run longer than 60 hours without needing some major work either to the transmission, the bottom end (stock), the pistons, or the head. SOMETHING will go kablooey. Actually, In 4 years of doing this, I've not had a complete powerunit (NA or turbocharged) last longer than 30 track hours.

Sorted!

I once bough a mini that jhad been run for a few years on only unleaded. It had not been thrashed. The exhaust valves were fooked with almost no sealing on 3 cyinders.

Now, even if people are 'getting away with it' I suspect that to some dergee the valve seat is degraded.

As I originally said, if you don't put seats in, use an additive. Also, with a turbo motor, and additive with an octane boost is always a good thing.

Fastest 998 mini in the world? 13.05 1/4 mile 106mph

www.twin-turbo.co.uk