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Old 08-19-2009, 07:43 PM   #1 (permalink)
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Default High RPM Power Loss

Setup:

Stock D16Z6
D15B Cam
Greddy 15g, stock wastegate - 5psi
2.5" downpipe, 3" exhaust
... stock injectors...
Crome basemap - 170% turbo efficiency, 1.25* per psi retard. Runs close to 100% indicated duty cycle in VTEC / 5psi (Crome duty cycle calculation is whack anyway...)


So, the weirdness. When I start it up in the morning, I let it warm up 5-6 minutes. The first couple WOT pulls, it pulls very well all the way up to the rev limiter. Everything feels excellent.

After a couple more minutes, power starts dropping dramatically after 6000 rpm or so. Boost still comes on just as fast, it just falls flat on it's face - with tires spinning it won't even tag the redline.

Fairly certain the A/F is in a safe range, there is no pinging or detonation. Just not certain why it only does it when the engine is hot, and sometimes it is fantastic? Can't see any ECT-related corrections that might cause this.

I'm open to any ideas... and yes, I know I need new injectors and get a wideband on it.

Thanks.
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What is it and will the doom hit the valve when vtec is engaged?
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Old 08-19-2009, 08:01 PM   #2 (permalink)
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at redline a 15g is way out of its efficiency range.
the reason why it runs great the first time is cause its not all heated up yet.
after the turbo is hot just from running and the engine is up to norm operating temp
the turbo will just blow hot air at the higher rpms.
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11.2 @121mph 1.9 60ft missing 4th
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Old 08-19-2009, 08:03 PM   #3 (permalink)
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i missed the basemap part.
thats got a lot to do with it aswell. its not tuned properly. it prolly gets to much fuel at those rpms to keep it safe from detonation.
basemaps are not made to drive on and beat on the car. made to get to a tuner.
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My boost lag gives your V8 a chance
best times
11.01 @ 129mph 1.8 60ft
11.2 @121mph 1.9 60ft missing 4th
1.77 is the best 60ft so far

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Old 08-19-2009, 08:03 PM   #4 (permalink)
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At 5 psi? I don't think it's ever in it's efficient range at 5 psi.

I'm starting to think it's fuel pump failure at high demand. Maybe main relay going bad?
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What is it and will the doom hit the valve when vtec is engaged?
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Old 08-19-2009, 08:06 PM   #5 (permalink)
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Originally Posted by shifty35 View Post
At 5 psi? I don't think it's ever in it's efficient range at 5 psi.

I'm starting to think it's fuel pump failure at high demand. Maybe main relay going bad?
even at 5psi.
when i had my 15g it only made power until about 6200rpms at 10psi and then fell on its face. i mean you could feel it fall off. the small turbos are made for the low end power. and quick spool.
__________________
My boost lag gives your V8 a chance
best times
11.01 @ 129mph 1.8 60ft
11.2 @121mph 1.9 60ft missing 4th
1.77 is the best 60ft so far

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Old 08-19-2009, 08:12 PM   #6 (permalink)
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So you're suggesting it's just getting heat soaked and efficiency goes to crap.

I can buy that. This is my second 15g car, I do remember that my last one felt pretty weak after 6k or so, come to think of it, even at higher boost...

I think the thing that bothers me is it can't even hit the rev limiter with the tires spinning in second when hot. *That* just seems wrong...
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Quote:
What is it and will the doom hit the valve when vtec is engaged?
'00 Honda Insight - the commuter, 70+ mpg
'90 Mazda Miata - Weekend Fun Car
'04 Toyota Prius - Wife / family car
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Old 08-19-2009, 08:18 PM   #7 (permalink)
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Quote:
Originally Posted by shifty35 View Post
So you're suggesting it's just getting heat soaked and efficiency goes to crap.

I can buy that. This is my second 15g car, I do remember that my last one felt pretty weak after 6k or so, come to think of it, even at higher boost...

I think the thing that bothers me is it can't even hit the rev limiter with the tires spinning in second when hot. *That* just seems wrong...
yup mine never would spin to the rev limiter in 2nd at 10psi.
get a real tune and i promise it will help out a ton.
even turn up the boost when its tuned and you will be much happier
__________________
My boost lag gives your V8 a chance
best times
11.01 @ 129mph 1.8 60ft
11.2 @121mph 1.9 60ft missing 4th
1.77 is the best 60ft so far

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Old 08-20-2009, 04:34 AM   #8 (permalink)
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Bah, maybe I'll just take it to the dyno tomorrow. I have free access anyway :P

Going to resolder the main relay connections in case it's dropping voltage to the fuel pump when hot, and resolder the VTEC conversion in the ECU to make sure it's not dropping VTEC when hot either.

Plugs do look filthy rich. We'll see how it goes.
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Quote:
What is it and will the doom hit the valve when vtec is engaged?
'00 Honda Insight - the commuter, 70+ mpg
'90 Mazda Miata - Weekend Fun Car
'04 Toyota Prius - Wife / family car
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Old 08-20-2009, 06:35 AM   #9 (permalink)
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After more research, thinking...

I think the valve lash is too tight, leading to valve float. This would explain why it only happens when hot.

Guess I'm adjusting lash when I get home.
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Quote:
What is it and will the doom hit the valve when vtec is engaged?
'00 Honda Insight - the commuter, 70+ mpg
'90 Mazda Miata - Weekend Fun Car
'04 Toyota Prius - Wife / family car
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