Very scary compression numbers on my turbo car
10-02-2011, 09:08 PM
#21
Sounds like he's planning to replace the valves and seats anyway.
Just a thought, did you do the test on a warm engine? That can make a difference. On piston aircraft, leakdown tests are required once a year, and it is always done on a warm engine. Mind you, clearances are a lot looser when cold on air cooled engines, but still.
Just a thought, did you do the test on a warm engine? That can make a difference. On piston aircraft, leakdown tests are required once a year, and it is always done on a warm engine. Mind you, clearances are a lot looser when cold on air cooled engines, but still.
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10-02-2011, 10:03 PM
#22
Sad to see this Hustler, I hope you figure out whats going on. Might not be a bad idea to skip a few events next year and put that money towards a rebuild if it turns out things aren't so good on the inside. I just bought a compression tester so I can get this done next weekend before I make the dive for parts for TT next year.
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10-02-2011, 10:25 PM
#23
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.009" lash on the exhaust valves. Time to pull the head.
Could I have been too rich with such a long burn time that EGT is too high going out the exhaust valves? Maybe it's time to install that EGT gauge but I don't know that I can bring myself to drill into the AF manifold.
Could I have been too rich with such a long burn time that EGT is too high going out the exhaust valves? Maybe it's time to install that EGT gauge but I don't know that I can bring myself to drill into the AF manifold.
Last edited by hustler; 10-02-2011 at 11:58 PM.
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10-03-2011, 09:35 AM
#27
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I plan to pull the head off the Monday after TXMC and have it to the machine shop the next day. Forza 4 will be out that day so I will probably have some sort of a sickness that keeps me from going to work anyway. At this point with two bad engines, out of rubber for the track and out of rubber for street tires, I can't get the van. However, I can drive my ******* track car 8-hours to NOLA and be a man about it.
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10-03-2011, 10:48 AM
#28
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I have a full set of standard size supertech valves with the reduced size stem. brand new in their little paper wrappers. $259 plus ship.
you know you want that ****.
you know you want that ****.
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10-03-2011, 11:18 AM
#30
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.009" isn't bad enough to cause massively accelerated wear.
It has always been my observation that in terms of long-term durability, exhaust valve seal is the miata's weak point.
I notice this even on *bone stock* miata engines, with <50k miles. It puzzles me, that the 2 Civic I had and sold with >100k miles had perfect valve seal. One of them had mediocre ring seal in one cylinder.
So I really do think exhaust valve material *must* be upgraded for any performance builds.
<10:1 can cause sooty exhaust which traps flakes between valves and seats, which would cause seats and valve faces to start burning. It may stand to reason btw that the ability to run leaner using WI helps exhaust valve longevity; WI reduces EGT too.
You always mentioned detuning timing by 4-5* down from MBT. Did you do this on the dyno and note how much % torque this costs? Or did you dyno tune to MBT, then after the session, retard it 4-5*?
In my dyno tuning experience, at around 10 psi, 1-2* down from MBT produces noticeable torque loss, and 4-5* produces *huge* torque loss, and lots more EGT.
It has always been my observation that in terms of long-term durability, exhaust valve seal is the miata's weak point.
I notice this even on *bone stock* miata engines, with <50k miles. It puzzles me, that the 2 Civic I had and sold with >100k miles had perfect valve seal. One of them had mediocre ring seal in one cylinder.
So I really do think exhaust valve material *must* be upgraded for any performance builds.
Could I have been too rich with such a long burn time that EGT is too high going out the exhaust valves?
You always mentioned detuning timing by 4-5* down from MBT. Did you do this on the dyno and note how much % torque this costs? Or did you dyno tune to MBT, then after the session, retard it 4-5*?
In my dyno tuning experience, at around 10 psi, 1-2* down from MBT produces noticeable torque loss, and 4-5* produces *huge* torque loss, and lots more EGT.
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10-03-2011, 11:21 AM
#31
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If this car makes 245whp at 11psi on 60% leak, I'm going to be in for a real treat after a valve job.
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10-03-2011, 11:27 AM
#33
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You always mentioned detuning timing by 4-5* down from MBT. Did you do this on the dyno and note how much % torque this costs? Or did you dyno tune to MBT, then after the session, retard it 4-5*?
In my dyno tuning experience, at around 10 psi, 1-2* down from MBT produces noticeable torque loss, and 4-5* produces *huge* torque loss, and lots more EGT.
In my dyno tuning experience, at around 10 psi, 1-2* down from MBT produces noticeable torque loss, and 4-5* produces *huge* torque loss, and lots more EGT.
I don't see how at 184kpa i could possibly burn a valve. It defies the logic of everything I know.
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10-03-2011, 11:31 AM
#36
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The only thing I'm sure of is my masculinity and physical prowess.
I am not, however the car drives exactly the same as the last time I dynod it. It's kind of easy to tell, when it's over about 85*f, I won't spin the tires in 3rd leaving my apartment. This still remains true now that it's just a touch below 85* again and I made a cloud of tire-smoke in 3rd a few days ago.
I am not, however the car drives exactly the same as the last time I dynod it. It's kind of easy to tell, when it's over about 85*f, I won't spin the tires in 3rd leaving my apartment. This still remains true now that it's just a touch below 85* again and I made a cloud of tire-smoke in 3rd a few days ago.
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10-03-2011, 12:44 PM
#39
Just fyi, my car came with an egt gauge and under wot at the track it sits at 1,600 1650* f
For the last four and a half years. You think your egt's are higher than that? How hot do they need to be to burn a valve? Could they be bent? Still don't understand how your car could run so good with any of the proposed scenarios. You don't know anybody with a real compression tester? Snap-on or craftsman at least. Also as someone mentioned, was the engine fully warmed up? My buddy picked the strongest pistons when he built the engine. Unfortunately, that also meant that the alloy expanded more than the other option. So much so that you can hear piston slap when I turn on the car first time in the morning. I always let it warm up a little while before driving, and never boost until it's fully warmed up.
For the last four and a half years. You think your egt's are higher than that? How hot do they need to be to burn a valve? Could they be bent? Still don't understand how your car could run so good with any of the proposed scenarios. You don't know anybody with a real compression tester? Snap-on or craftsman at least. Also as someone mentioned, was the engine fully warmed up? My buddy picked the strongest pistons when he built the engine. Unfortunately, that also meant that the alloy expanded more than the other option. So much so that you can hear piston slap when I turn on the car first time in the morning. I always let it warm up a little while before driving, and never boost until it's fully warmed up.
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