Lack of power from LoveFab turbo kit

CB72 said:

That's very kind of you!
There also appears to be a small leak around there somewhere?
Could that be the cause?
I've ordered new gaskets to ensure everything is nice and tidy when reassembling.

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I have heard of someone installing these the wrong way around, i'm not sure if it's possible but bare that in mind just in case.

Yes the dip looks abnormal. However, what dyno is this on? Dynodynamics with no correction factors will yield about 33x rwhp on a lovefab kit running around 7.8 to 8lbs. This translates to about 39x to 4xx rwhp depending.

CB72 said:

I took my LoveFab turbocharged NSX to a local tuning shop to measure it's power as I was suspecting the car was well below it's 400 rwhp target.
In fact the car pulls very well to about 5000 rpm and then the rush goes away until you reach redline.
The graph below shows exactly what's happening:
280 hp at 5000 rpm followed by a dip to then slowly rise to 330 hp at 8250 rpm.
The torque is very generous at 410 Nm at 4800 rpm.
The engine is a 3 L model with stock internals and I'm running no more than 8 PSI of boost.
Fuel is 98 Octane.
What could the issue be?
Looking at the curve, I get the feeling that the VTEC is not working?
I'll look into the manual to determine if this could be the case?

I had a quick look at my AEM EMS calibration file and it looks OK to me?
The Vtec is programmed to come on at 4800 rpm and 60% TPS.

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nathan said:

Yes the dip looks abnormal. However, what dyno is this on? Dynodynamics with no correction factors will yield about 33x rwhp on a lovefab kit running around 7.8 to 8lbs. This translates to about 39x to 4xx rwhp depending.

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The issue is definitely with the rear cylinder bank's VTEC not coming on above 4800 rpm.
A quick and dirty look at the power curve shows that if the engine is capable of 200 hp at 4000 rpm it should be capable of 400 hp at 8000 rpm if the torque remains constant.

The O-ring gaskets were delivered today.
The O-ring that goes between the spool valve and the cylinder head has an incredibly fine mesh.
Could this be the source of the problem?
Well it isn't!
I pulled the rear spool valve apart and everything is nice and clean.
The plunger moves freely and the solenoid works fine...
Everything went back together nicely but I still don't know why the engine's power drops off above 4800 rpm???

I thought you tested the solenoid and it didn't activate?

This is why tuner shops exist. I would take it to one immediately.

E-Nough Logic said:

I thought you tested the solenoid and it didn't activate?

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I couldn't hear the rear solenoid and that's why I pulled it apart.
After reinstalling it I realized that the sound was muted compared to the front one probably due to the amount of oil present?

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Jinks said:

This is why tuner shops exist. I would take it to one immediately.

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Yes, but finding one in France that will tune an expensive engine like the NSX is something else...

Just to confirm you tested the rear solenoid by applying power and it 100% works? This is typical, they are very reliable, albeit leaky.

It seems you are left with ensuring there is enough oil pressure, and beyond that would be some type of physical interference. An oil pressure problem would be unusual on a stock untouched motor, I have seen a few built motors with missing o-rings or plug fittings cause VTEC issues.

Any chance you noticed low oil pressure on your gauge? Not that they are very reliable.

I'm not an engine expert by any means and I may be reading your dyno run incorrectly so please bear with me.

First I'm looking at your dyno chart.
As the HP is calculated from the engine's torque output the formula used always results in torque and hp being equal at 5252 rpm.
Your chart shows torque and hp being equal at about 4375 rpm.
Is this because we have HP and N.m plotted so the formula is different?

Secondly, let's ignore vtec for the moment.
Looking at the dyno chart you have a nicely building torque curve peaking at about 4750 rpm resulting in about 280 HP, then a steep drop in torque resulting in a drop in HP until about 6750 rpm.
If the engine stayed on the low lift cams without vtec you'd expect a gradual decline in torque from the peak as rpm is increasing but not a steep drop off like your dyno run shows.

To me it looks like your engine is hitting a wall of some kind to show a precipitous drop in torque like that.
Perhaps the engine is not getting a decent cylinder fill or air/fuel mix above 4750 rpm.
Is the waste gate not working properly killing your boost?
Is there an intake/exhaust restriction somewhere?
Is there a fuel restriction causing a lean condition?
Has there been a recent timing belt change?

If we come back to vtec, yes, you should get a torque increase with vtec in operation.
But to me the real problem is whatever is causing a reduction in HP from 4750 - 6750 rpm.
Non-operable vtec would be holding back some power gains (maybe 30 HP) but should not be causing you to lose power from 4750 - 6750.

Don't forget when the ECU tells VTEC to activate it also delivers a lot more fuel which compounds the lack of increased airflow. This would cause torque to drop off faster than just the low cam running out of breath.

Let me try and clarify the situation as of today.
1) Is there a VTEC issue?
The only thing I haven't done yet was to monitor the oil pressure switch output on the solenoid valves.
On a std NSX this would correspond to CEL 22 or 52.
It would be a pain to do as the AEM ECU sits behind my Comptech harness bar.
I could try to access the signal directly from the switches if I had a correct plug...
On the other hand my oil pressure is absolutely normal so I believe the problem must be elsewhere.
2) Is it a tuning issue?
This seems now more and more probable.
I compared my Ignition table with one of the two other NSX turbo owners here in France and he runs 19.9° of advance above 6K rpm for boost levels above 5 PSI while I'm running 20.3° at 5 PSI and then only 18.5° at 6.6 PSI to drop off at 16.8° at 8.36 PSI.
The boost on my car is limited to 8 PSI.
The temptation is enormous to advance the ignition a little to see what happens but I'm concerned about knock.
Is it correct to believe that within reason if the AFR remains around 11 to 1, I can advance the ignition by 1°?
What's the process the guys go through on their dyno?
Hold the engine at a certain rpm and tune the advance to reach peak HP while watching AFR?
I'd like to understand the process so that I can monitor what the guy does when I get the car tuned.

E-Nough Logic said:

Don't forget when the ECU tells VTEC to activate it also delivers a lot more fuel which compounds the lack of increased airflow. This would cause torque to drop off faster than just the low cam running out of breath.

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Isn't the fuel supply governed by the map and the mass air sensor?
If the ecu activates the vtec but air intake flow is restricted in some way would extra fuel be added if the air sensor shows lower than ideal flow?

I couldn't resist advancing the ignition so I added 5%to the whole 6.6 psi line and 10% to the 8.36 psi line.
To play it safe, I reduced the boost to 7 psi and went for a ride.
I know, it's not scientific but I want to determine where the issue is coming from.
During the ride, I started accelerating hard above 5000 rpm in third to avoid the rising rate torque that tends to blurr the acceleration feeling.
Seat of the pants, I believe it's far better than before.
I get a strong pull all the way to redline.
The appointment for the dyno is now in order!

CB72 said:

I couldn't resist advancing the ignition so I added 5%to the whole 6.6 psi line and 10% to the 8.36 psi line.
To play it safe, I reduced the boost to 7 psi and went for a ride.
I know, it's not scientific but I want to determine where the issue is coming from.
During the ride, I started accelerating hard above 5000 rpm in third to avoid the rising rate torque that tends to blurr the acceleration feeling.
Seat of the pants, I believe it's far better than before.
I get a strong pull all the way to redline.
The appointment for the dyno is now in order!

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Looks like you're on your way to finding out what's really wrong and getting it sorted.

CB72 said:

Let me try and clarify the situation as of today.
1) Is there a VTEC issue?
The only thing I haven't done yet was to monitor the oil pressure switch output on the solenoid valves.
On a std NSX this would correspond to CEL 22 or 52.
It would be a pain to do as the AEM ECU sits behind my Comptech harness bar.
I could try to access the signal directly from the switches if I had a correct plug...
On the other hand my oil pressure is absolutely normal so I believe the problem must be elsewhere.
2) Is it a tuning issue?
This seems now more and more probable.
I compared my Ignition table with one of the two other NSX turbo owners here in France and he runs 19.9° of advance above 6K rpm for boost levels above 5 PSI while I'm running 20.3° at 5 PSI and then only 18.5° at 6.6 PSI to drop off at 16.8° at 8.36 PSI.
The boost on my car is limited to 8 PSI.
The temptation is enormous to advance the ignition a little to see what happens but I'm concerned about knock.
Is it correct to believe that within reason if the AFR remains around 11 to 1, I can advance the ignition by 1°?
What's the process the guys go through on their dyno?
Hold the engine at a certain rpm and tune the advance to reach peak HP while watching AFR?
I'd like to understand the process so that I can monitor what the guy does when I get the car tuned.

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My car made plenty of power with conservative timing in the ballpark of what you are working with. do you happen to have the map I can take a look at and compare?

JD Cross said:

Isn't the fuel supply governed by the map and the mass air sensor?
If the ecu activates the vtec but air intake flow is restricted in some way would extra fuel be added if the air sensor shows lower than ideal flow?

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Our cars do not have a Mass airflow sensor. The calculations are performed using a map sensor and RPM. If you change the VE of the engine then the ECU will not be able to detect any increase/decrease in airflow directly. The only method of detection at that point would be the air fuel ratio. A richer than expected air fuel ratios would tend to indicate a reduction in airflow, and a leaner mixture indicating an increase in airflow.

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CB72 said:

I couldn't resist advancing the ignition so I added 5%to the whole 6.6 psi line and 10% to the 8.36 psi line.
To play it safe, I reduced the boost to 7 psi and went for a ride.
I know, it's not scientific but I want to determine where the issue is coming from.
During the ride, I started accelerating hard above 5000 rpm in third to avoid the rising rate torque that tends to blurr the acceleration feeling.
Seat of the pants, I believe it's far better than before.
I get a strong pull all the way to redline.
The appointment for the dyno is now in order!

Click to expand...

any chance you logged your AFR during the pulls? Was it leaner at all indicating a change in airflow? Perhaps the rebuild or re-connection of your VTEC solenoid has fixed your issue.

E-Nough Logic said:

Our cars do not have a Mass airflow sensor. The calculations are performed using a map sensor and RPM. If you change the VE of the engine then the ECU will not be able to detect any increase/decrease in airflow directly. The only method of detection at that point would be the air fuel ratio. A richer than expected air fuel ratios would tend to indicate a reduction in airflow, and a leaner mixture indicating an increase in airflow.

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I used the wrong term with mass airflow sensor.
Our engines have sensors for atmospheric pressure, intake air temp, manifold pressure, speed and throttle position, O2, knock, coolant and so on.
Doesn't the ecu take in all these inputs and use them to select the best fit fuel map?
If air flow is restricted in some fashion wouldn't the ecu get input on this and reduce fuel accordingly?

I finally managed to create a log in third gear from 2500 to 8000 rpm.
Not easy on an open road when the car gets to 110 mph at the end of the run...
Most parameters were OK except that the load gets at a high of 7.1 psi at 4350 rpm ( I had it programmed at 7 psi) to then gently decline to 5 psi at 7900 rpm.
No wonder the power is lacking at high rpm!
The obvious cause to me is that there is an air leak somewhere?
The area I suspect is at the junction ahead of the blow off valve where the V clamp doesn't fit very well.
I'll try to tape it and go for another run.

JD Cross said:

I used the wrong term with mass airflow sensor.
Our engines have sensors for atmospheric pressure, intake air temp, manifold pressure, speed and throttle position, O2, knock, coolant and so on.
Doesn't the ecu take in all these inputs and use them to select the best fit fuel map?
If air flow is restricted in some fashion wouldn't the ecu get input on this and reduce fuel accordingly?

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Unfortunately none of those sensors are capable of determining airflow. Even the map sensor can only measure pressure which is an indirect but reliable way that we use to calculate airflow and therefore fuel demand. I could easily manipulate the engine airflow in such a way that all of the sensor readings could accurately read exactly the same but reduce airflow by 25%. The only sensor that would indicate the change would be a wideband O2 sensor.

If properly set up the ecu can trim the fuel to maintain the target AFR. This is meant for mostly minor deviations and for efficiency. Most don't enable fuel trims at WOT. The stock NSX does not have a wideband so it can't even detect changes in AFR at WOT anyway.

E-Nough Logic said:

Unfortunately none of those sensors are capable of determining airflow. Even the map sensor can only measure pressure which is an indirect but reliable way that we use to calculate airflow and therefore fuel demand. I could easily manipulate the engine airflow in such a way that all of the sensor readings could accurately read exactly the same but reduce airflow by 25%. The only sensor that would indicate the change would be a wideband O2 sensor.

If properly set up the ecu can trim the fuel to maintain the target AFR. This is meant for mostly minor deviations and for efficiency. Most don't enable fuel trims at WOT. The stock NSX does not have a wideband so it can't even detect changes in AFR at WOT anyway.

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Thank you for taking the time to explain this to me.
Good to learn more about our cars.

Sounds like a boost leak to me.
I'd say check your plumbing, connections, blow off valve, and wastegate operation.

Following the loss of boost, I reworked the positionning of the pipe going to the throttle body to make sure that the V-clamps can hold tight.
Clearly each time you apply or release the throttle the engine will rock back and forth making a hard life for the couplers.
When everything was finally secure, I drove the car and ...it was like magic!
The power just oozes from the engine desperately trying to brake the traction from the rear tires.
I'm convinced I've never had this much power.
The car just rushes away like a 1000 cc motorbike.
I'll do a dyno run next and keep you posted.

That's great news! Glad it appears to have been something fairly straightforward. And now you know the solenoid is clean. [emoji57]

jwmelvin said:

That's great news! Glad it appears to have been something fairly straightforward. And now you know the solenoid is clean. [emoji57]

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For sure, but the most significant part of the story is that it's an immense confidence booster.
On many tracks, I would blame my driving skills when my lap times were not as good as some of the GT3's.
They might still not be on par but the difference will be so much smaller

CB72 said:

For sure, but the most significant part of the story is that it's an immense confidence booster.
On many tracks, I would blame my driving skills when my lap times were not as good as some of the GT3's.
They might still not be on par but the difference will be so much smaller

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Awesome so the issue was down to a boost leak.

Glad it's sorted