Tran

Hi All,

Some of you may have seen me struggling with EGTs on my turbo Miata in the Megasquirt section. In short, I found much time (even on the road!) in double digits psi of boost quickly got the EGTs near the region where I should be concerned with my OEM exhaust valves burning up. In the end, this was a combination of a retarded map and spark latency making it even more retarded.

My car
Stock BP6D head with Supertech heavy doubles
9:1 forged bottom end
GTX2860, FM manifold + DP, 2.5" exhaust, flattop
99 RON UK fuel (similar to US 93)

I got a tune a few weeks ago and asked the tuner to calibrate to 880C (1616F) max on my EGT channel in the Megasquirt (measured in the turbine housing, just after the collector). Interestingly, at spring (8psi), even tuned to MBT, EGTs were already in the 860-870C (1580-1600F) ( range in a slow pull, when I've read OE valves to only be good to 900C (1650F). The tuner kept going to 16psi, at which point in a painfully slow 25 second pull, the EGTs would just reach 900C at the end, despite still being able to achieve MBT.

I did a trackday last week at Brands Hatch. I didn't have my boost table fully dialled, but it was wet and I ran 9-10psi all day. Interestingly, almost immediately my EGTs got to 870C (1600F) at the end of the straight, but didn't go much further. I was expecting some kind of heatsoak effect after a few laps, but perhaps the wet weather helped.

My questions here are, what EGTs do people see on track and what have people found the limits of various valves to be? Am I being over cautious or perhaps optimistic thinking I can run 16psi on pump fuel on track with stock exhaust valves? Is 900C (1650F) a sensible limit to have in the Megasquirt protections?

codrus

I have run 1600-1700F on track and it's been fine. I have aftermarket valves, though.

--Ian

Tran

Thanks, that's a useful data point. Is that with stainless valves?

codrus

Uhhh. Probably. This head was built somewhere around 2005, so it's whatever FM was selling then. Pretty sure they're not inconel.

--Ian

Tran

Thanks, so that proves those can stand long term use up to 1700f in a turbo miata on track. Now the key information for me would be what OE valves can take...

codrus

Well, it wasn't running quite that hot for that entire time. Still, the car has run near those temps for the last 3-4 years of track days with no issues that have cropped up yet.

OE exhaust valves are much less strong.

--Ian