What's wrong with my torque curve?

[Gerard van Santen]

As you can see in the graph, I have a massive torque of 391 Nm (288 ft/lbs) at 3856 rpm. After that it goes slowly down to 375 Nm until 5700 rpm, which is not really bad. But then it goes into a free fall down to 312 Nm at 7800 rpm.
This costs me at least 50 hp I assume.

What is wrong? I measured boost at 7.5 psi until 4200 rpm. After that boost went down to 3 psi at 7000 rpm Boost follows the torque curve. Unlike this, the NSX feels very strong. Especially at low rpm. But is obvious.

Setup is:
- 3.0 NSX with a CTSC whipple with custom made pulley in the size used for a 97+ NSX (it is not a real high boost pulley)
- Gruppe M intake
- Comptech headers, test pipes an DC exhaust
- OEM Computer
- Type R gears

 

[amo]

fueling prob maybe
just an idea dont shoot me lol

thx amo

 

[rsevo6]

Boost goiing down in the high revs is a almost certain belt slipping problem, especially if you didn't have this prob before with the old pulley.
Fuelling could be a cause if the boost stayed normal and power/torque were dropping.
However as boost goes down, fuelling cannot have anything to do with this as that doesn't influence boost.

 

[C-speed]

Beyond your boost drop issue, it appears that the loss in power is directly related to the a/f ratio. You can see at 5600rpm the A/F drops from 12.2ish down to 10.8 by 6700 rpm. Richer generally means safer, but it all means less power. Leaner will make the most power until it starts to detonate, which means its too lean.

If you are running a boost dependant FPR (fuel pressure regulator), you are kind of SOL and they are a fixed ratio, however if you have some sort of EMS, like an AEM or AFC of some kind, try removing about 5% fuel from 5600 - 7500 rpm.

HTH

 

[Gerard van Santen]

Boost goiing down in the high revs is a almost certain belt slipping problem, especially if you didn't have this prob before with the old pulley.
Fuelling could be a cause if the boost stayed normal and power/torque were dropping.
However as boost goes down, fuelling cannot have anything to do with this as that doesn't influence boost.

I have done a run with the old pulley and had the same result. I don't think I have a slipping belt.

Beyond your boost drop issue, it appears that the loss in power is directly related to the a/f ratio. You can see at 5600rpm the A/F drops from 12.2ish down to 10.8 by 6700 rpm. Richer generally means safer, but it all means less power. Leaner will make the most power until it starts to detonate, which means its too lean.

If you are running a boost dependant FPR (fuel pressure regulator), you are kind of SOL and they are a fixed ratio, however if you have some sort of EMS, like an AEM or AFC of some kind, try removing about 5% fuel from 5600 - 7500 rpm.

HTH

I use the OEM ECU. The only thing I can do and did is to give more or less fuel rail pressure with the FPR. I have had a run with less (about 5%) rail pressure (leaner) and it gave about 10 hp more but again with the same torque curve and loss of boost after 4000 rpm. I thought it wasn't save so I gave it more fuel pressure with the A/F ratio you see on the sheet as a result.

The good thing is, that I have 300 hp at only 5550 rpm.
My best run with my 6psi pulley a few years ago gave 270 hp at 5500 rpm, but 372 hp at 7584 rpm with a normal flat slight rising torque curve (366 NM at 6077 rpm). This means that if I get my boost right, it will give more than 400 hp with new pulley.

 

[Swift]

a few things..

I have been told base on the mathmatical formula used on a dyno that the two curves HAVE to cross at 5200rpms(5500?) which yours does not, your A/F ratio is not constant..., and a few things to check would be your timing(spark),fuel pressure, and sensor readings.

good luck man. most would not complain, but then again this is an NSX made to go to 9k!

 

[rsevo6]

Gerard,
As this is a boost related problem, I remain with my opinion that something must be wrong with the charger.
Sure, the A/F may be having a problem too, but that won't influence boost in the way you describe.

Getting 10HP from a somewhat leaner mixture is to be expected, A/F of about 12.5:1 or even 12.8:1 at full boost will give you max power but also increased risk of detonation/overheating the pistons.

Have you tried to put belt spray on the SC belt (this stuff makes the belt more sticky, thus preventing possible slipping).

If you are absolutely sure that the belt doesn't slip, then there must be either a leak somewhere in the boost circuit or possibly the bypass valve or the bypass actuator is defective.

I have owned/worked on SC-ed Miata's for quite a few years and these use the same type of Magnusson whipple charger and same bypass actuator.

With these cars I have seen several bypass actuator problems occur over time:
-mounting bracket shearing off due to vibration
-actuator coming loose from it's bracket due to vibration
-actuator linkage to the bypass valve wearing out (this is a unlubricated rod/hole in plate connection, rediculous design in my opinion, failure waiting to happen).
When this happens, the bypass butterfly valve will not fully close anymore at boost, sometimes up to the point of it's connecting rod completely slipping out of the bracket so disconnecting the actuator from the valve thus leaving the valve open.

When I saw the Whipple charger NSX Comptech kit for the first time and saw the same bypass valve linkage, I must say I was surprised not to have read about problems with this linkage from SC users.

On the SC Miata, after a few years, this linkage wearing out became a well known problem waiting to happen.
Solution that I and some others invented was to change the unlubricated rod/hole in the plate linkage to a ball joint connection, making it a lubricated ball connection, problem solved.

I will monitor this linkage on my newly bought SC-ed NSX and will probably be replacing it in due time, as based on my previous experience I expect it to fail in the future.

 

[Gerard van Santen]

Gerard,
As this is a boost related problem, I remain with my opinion that something must be wrong with the charger.
Sure, the A/F may be having a problem too, but that won't influence boost in the way you describe.

Hi Rene,

I also think it is a malfunctioning supercharger.

In the lower graph you can see the dyno with my low boost pulley a few years ago. If you compare this with my present situation, you can clearly see the difference.
You can imagine what happens if boost is steady

This is the present situation with loss of boost from about 4500 rpm:

This is the low boost graph a few years ago. A steady boost of 6 psi:

 

[rsevo6]

Hi Rene,

You can imagine what happens if boost is steady

Ehh.......... PSSSHHH- BOOOMM??????:tongue: :biggrin:

 

[Gerard van Santen]

Fuelling could be a cause if the boost stayed normal and power/torque were dropping.
However as boost goes down, fuelling cannot have anything to do with this as that doesn't influence boost.

Fueling doesn't influence boost. But boost surely influence the fuel mixture!
If boost goes down while using a static (boost dependant) FPR, the a/f ratio will also go down. So with a normal steady boost, the a/f curve should be more flat in this case in the range of 12.0 to 12.5

Ehh.......... PSSSHHH- BOOOMM??????:tongue: :biggrin:

I hope not. I was refering to a situation that the hp numbers would go over 400 hp

BTW. thanks for using your pulley as a master for making an exact copy of it.

 

[Jap4RE]

Not to pick on you but why would you spend so much money on your setup and then go cheap and not get an EMS? the factory ecu can only adjust for so many conditions, you have such a specific setup that I would guarantee a good tune from a respected tuner such as autowave would yield more and safer power levels.

 

[Gerard van Santen]

Not to pick on you but why would you spend so much money on your setup and then go cheap and not get an EMS? the factory ecu can only adjust for so many conditions, you have such a specific setup that I would guarantee a good tune from a respected tuner such as autowave would yield more and safer power levels.

I don't feel picked on. You're right. That is the way I will go. I am looking for a programmable ECU. But that doesn't solve the initial problem of my loss of boost.

 

[coldhammer]

three things come to mind.

1)slipping belt. you say you did a run with the old pulley on but could just as easily be that when you put the old pulley on you tightened the belt down more.

2)Boost Leak. When I was running the old elbow with my bbsc kit i would get flucuating boost readings. Ended up being that after a run or two with the higher boost levels the elbow would loose its seal and only hold about 4psi. an easy check is spray a mild soapy mixture on the piping and see if you get any bubbles. If not you could still have a leak from somewhere else in the system.

3)the bypass valve diagphram has gone out. It could have weakened to the point that it will only hold 5psi. Again an easy test is cap one end and hook the other end to a compressor, turn up the pressure slowly and make sure it holds what its supposed to.

 

[Gerard van Santen]

three things come to mind.

1)slipping belt. you say you did a run with the old pulley on but could just as easily be that when you put the old pulley on you tightened the belt down more.

2)Boost Leak. When I was running the old elbow with my bbsc kit i would get flucuating boost readings. Ended up being that after a run or two with the higher boost levels the elbow would loose its seal and only hold about 4psi. an easy check is spray a mild soapy mixture on the piping and see if you get any bubbles. If not you could still have a leak from somewhere else in the system.

3)the bypass valve diagphram has gone out. It could have weakened to the point that it will only hold 5psi. Again an easy test is cap one end and hook the other end to a compressor, turn up the pressure slowly and make sure it holds what its supposed to.

Thanks for the advice. I will check on point 2 and 3. I don't think I have belt slippage. Because with the old pulley I loose also boost. The graph you see with the old pulley is from a few years ago. The run I did now with the old pulley gave the same boost loss as with the new smaller pulley.

 

[Cees-Jan]

Hi Gerard,

If you have a (small) leak the influence will be larger at lower revs. since at low revs the boost pressure is good you can rool out number 2 and 3.

Any internal problem in the charger is also not possible for the same reason.

Leaves only the belt slipping option there....

Off topic: Everything Ok with you and family ?

 

[Gerard van Santen]

Hi Gerard,

If you have a (small) leak the influence will be larger at lower revs. since at low revs the boost pressure is good you can rool out number 2 and 3.

Any internal problem in the charger is also not possible for the same reason.

Leaves only the belt slipping option there....

Off topic: Everything Ok with you and family ?

Hi Cees-Jan,

Long time no see or heard of.

You know, a few years ago I had this blown up engine. First I thought the loss of boost I started this topic with, was a result of the damage in the blower caused by the remains of the valve stem we found in the blower. But than again, how is it possible that I have 7.5 psi until 4.500 rpm? If the damage is severe than it should be lower in the lower rpm's also.

I will look again into the belt.

Off topic also: Family OK :biggrin: Work as usual I myself have the same spinal problems as a few years ago and wear a corset for the last three months now :frown: Is your family OK? We have to meet soon.

 

[coldhammer]

If you have a (small) leak the influence will be larger at lower revs. since at low revs the boost pressure is good you can rool out number 2 and 3.

I completely disagree based on first hand experience. I had a small boost leak and the system would hold steady until about 5psi. Seeing as how a superchargers boost is directly tied to an increase in rpms this shows that at higher rpms the influence was quite large. Once the boost leak was fixed i climbed from 5psi @ 8k rpms to 8psi @8krpms.

 

[Gerard van Santen]

I think it is solved :smile:
At least I think.

I was afraid to tighten the SC belt to tight, because I had some pulley bearing issues in the past. But now I did tighten the belt more than I had at the moment I did the Dyno. And what...?

I have around 7.5 psi all over the rev range now:biggrin: I haven't tested the NSX on the dyno yet, but it feels stronger than ever!

If I make a rough calculation with this formula: HP=(torque x RPM)/5252 than it should make with a flat torque curve (it feels like flat now): (288 x 8000)/5252 = 438 hp. This is a rough calculation. I have to verify on the dyno.

So everyone saying I only had to tighten the belt was right. Thanks for that advise. Others also thanks for the other possible options.

 

[rsevo6]

I think it is solved :smile:
At least I think.

I was afraid to tighten the SC belt to tight, because I had some pulley bearing issues in the past. But now I did tighten the belt more than I had at the moment I did the Dyno. And what...?

So everyone saying I only had to tighten the belt was right. Thanks for that advise. Others also thanks for the other possible options.

Should I :redface:

yes

WE TOLD YOU SO!!! :biggrin: :biggrin: :wink:

Glad to hear you finally resolved this problem, and without having to spend any money:smile:

 

[Gerard van Santen]

Should I :redface:

yes

WE TOLD YOU SO!!! :biggrin: :biggrin: :wink:

Glad to hear you finally resolved this problem, and without having to spend any money:smile:

Psssst....... Not so LOUD... Why are you so hars on me :wink: :biggrin:

The NSX is very fast and strong. But I am carefull now. I'm still waiting for my Walbro fuel pump and new bigger injectors I have ordered. So I can play it more safe.

 

[rsevo6]

Gerard,

I don't get one thing:
You use the car to it's full potential, you already lost one engine to lean mixture, why don't you permanently install a wideband A/F measuring device, so you can see when something fuelwise is goiing wrong and can probably prevent bad things from happening.

My Comptech powered NSX is on it's way to me now and immediatly when I have it on the road, I for one will be installing a wideband A/F.

 

[Gerard van Santen]

Gerard,

I don't get one thing:
You use the car to it's full potential, you already lost one engine to lean mixture, why don't you permanently install a wideband A/F measuring device, so you can see when something fuelwise is goiing wrong and can probably prevent bad things from happening.

My Comptech powered NSX is on it's way to me now and immediatly when I have it on the road, I for one will be installing a wideband A/F.

It is all planned. Everything is on order now.

BTW I lost two engines. One because of a glocked fuel filter and one because of a failure of the harmonic balancer. That's not bad for 5 full NSX Trophy competition years. These races were driven with an OEM low boost CTSC setup. This setup was highly reliable over the years.

 

[goldNSX]

BTW I lost two engines. One because of a glocked fuel filter...

After how many miles/years?

 

[Gerard van Santen]

After how many miles/years?

I do about 20,000 miles a year with a lot of track miles. The engine I am running now has more than 290,000 miles behind its wheels :biggrin:

 

[my1stnsx]

The engine I am running now has more than 290,000 miles behind its wheels :biggrin:

Holy smokes!!!! You definitely drive your car for sure!!!:smile: