Boost, Autorotor and "popping" sound?

[SaberX]

I've noticed some "new sounds" from my engine area under certain conditions that have me concerned. I think I'm going to go get another A/F done, but @ $130 for the dyno w/ A/F I'd rather get some feedback before doing this.

Background - I have a new Autorotor CTSC. I have an original fuel pump but it can hold 90+ psi no problem at WOT. I also had new spark plugs and injectors fully cleaned at the time I installed the CTSC. The car is a 91 has 120,000 miles - had great compression/leakdown before the blower and makes my most recent dyno was 344 rwhp.
- I almost always see 8.5 psi of boost on my Spa electronic gauge at WOT above 5500 rpm

What has me concerned is that I am hearing some "popping" sounds coming from the engine. It's not like any "pinging" i've ever heard before. The popping only occurs between 7-8.5 psi of boost at WOT. Fuel pressure at this time is around 90psi.

I'm thinking that the blower is somehow making more boost than expected. I trust the gauge as this is a high quality electronic gauge that is mounted directly in the intake port that Comptech made for boost gauges. Additionally, the colder weather (35-50) makes the air denser and between the two could be creating a lean condition.

Any advice is highly appreciated.

 

[Vega$ NSX]

Is it a backfire? Is it constant or occasionally? Have someone follow you and see if you can recreate the pop. See if they see flames or backfire from you exhaust. I get a backfire when I let off the gas. The good news is that the detonation is occuring in your exhaust and not in your engine; its the safer condition of the two if that is what's happening.

 

[BioBanker]

Because this is happening at colder temps, Id put money on you running lean and detonating. Does it go away if you dump octane booster in there?

I have been told that in the colder temps, that detonation with the autorotor CTSC is still an issue even with the new electronics if the engine is not FULLY warmed up. ie, been running for 15 plus minutes. I was told that because the unit runs more efficiently than the old unit, that the charge is cooler and timing is not being pulled back as soon.

Id get an A/F done asap and I would confirm pulley size is correct too.

 

[Paul]

I have read other threads where owners of the new Autorotor units have seen 7 to 8 psi of boost on their gauges. CT used to have a “low boost” Whipple kit and a “high boost” Whipple kit. It’s my understanding that the older low boost kit would max out around 5.5 psi and the high boost kit would max out around 7.5 psi. I believe both the older kits (low and high boost) used the same basic "boost a pump" concept to supply about 90 psi of pressure to the fuel rail. But, the older high boost kit also came with larger injectors to get more fuel to the engine at the same 90 psi fuel pressure. I question if you are getting enough fuel through stock injectors even with 90 psi of fuel pressure at the rail for your given boost pressure. I have not found anything in writing from CT that supports what boost pressure the Autorotor kit “should” produce with the supplied pulley and FMU; however, 8.5 psi seems a little high.

I have the same recommendation as the post above about checking the pulley size. I know CT has two different pulley sizes for the new Autorotor kits. The two different size pulleys were necessary to keep both motors (3.0L and 3.2L) at the same boost level. That might imply that CT has a set boost level in mind for the supplied FMU. The smaller diameter pulley fits the 3.2L motor, while the larger diameter pulley fits the 3.0L motor. I wonder if you ended up with the smaller diameter pulley (sized for the 3.2L motor). The smaller diameter pulley would generate more boost on a 3.0L motor. To give yourself a piece of mind I too would check the pulley size and get to the dyno ASAP to check you’re A/F ratio.

Couple more questions:
What octane fuel are you using? 91 or 93?
Did you send your fuel injectors to RC Engineering prior to installing the CTSC? It could be that your fuel injectors are not flowing enough fuel b/c they need to be cleaned. Just my .02

 

[SaberX]

Great advice guys. The injectors were fully cleaned by "Dr. Injector" a local place that does this sort of thing. I got a full report detailing the results of the cleaning. I'll check my pulley size. Does anyone know the different pulley dimensions? I couldn't find them on the Comptech site. Also, we only have 91 here in Seattle. Maybe I'll pick up an octane booster and see if that does anything. Any recommendations?

 

[FIGHTERCAR]

Just a thought for discussion...could the popping sound be air escaping from the compressor through the bypass valve?

Anyone have any ideas on how to test the bypass valve?

Now that you mention it, I had a very loud popping sound back in June (Autorotor on 3.0 installed in May) under hard acceleration and have never heard it again. It occurred once as I was accelerating in second gear through 6500 RPM when boost would have been coming on strong. Of course I backed off immediately and pulled over and and checked for a broken belt or something. Nothing was found wrong. My car still runs fine to date.

 

[NA1/2-R GT]

Great advice guys. The injectors were fully cleaned by "Dr. Injector" a local place that does this sort of thing. I got a full report detailing the results of the cleaning. I'll check my pulley size. Does anyone know the different pulley dimensions? I couldn't find them on the Comptech site. Also, we only have 91 here in Seattle. Maybe I'll pick up an octane booster and see if that does anything. Any recommendations?

Brian,
I am pretty sure we have 92 in Seattle.... I don't know where you have been pumping gas at!

 

[TurboLab]

My experience with popping noises with lower ambient temp and not when it is hot is the gap on your plugs. Try moving the gap into the .026 -.028 range and see if this fixes your problem. The problem is that high horsepower cars can experience a missfire, not lose a lot of power and not "feel like a Miss". Popping is often the complaint i associate with missing under boost.

 

[ScienceofSpeed]

I've noticed some "new sounds" from my engine area under certain conditions that have me concerned. I think I'm going to go get another A/F done, but @ $130 for the dyno w/ A/F I'd rather get some feedback before doing this.

Background - I have a new Autorotor CTSC. I have an original fuel pump but it can hold 90+ psi no problem at WOT. I also had new spark plugs and injectors fully cleaned at the time I installed the CTSC. The car is a 91 has 120,000 miles - had great compression/leakdown before the blower and makes my most recent dyno was 344 rwhp.
- I almost always see 8.5 psi of boost on my Spa electronic gauge at WOT above 5500 rpm

What has me concerned is that I am hearing some "popping" sounds coming from the engine. It's not like any "pinging" i've ever heard before. The popping only occurs between 7-8.5 psi of boost at WOT. Fuel pressure at this time is around 90psi.

I'm thinking that the blower is somehow making more boost than expected. I trust the gauge as this is a high quality electronic gauge that is mounted directly in the intake port that Comptech made for boost gauges. Additionally, the colder weather (35-50) makes the air denser and between the two could be creating a lean condition.

Any advice is highly appreciated.

The standard kit for 3.0L cars we have installed make a pretty consistent 5.8-6.2 psi measured at the manifold. I'm surprised to read that your car is making that much pressure out of the box. You can always measure the pulley and confirm the size with Comptech.

Regarding your noise... detonation of any significance is a pretty noticeable high frequency "tick" that you can hear even over the noise of the blower. Not a bad idea to have a professional have a listen.

take care,
-- Chris

 

[nathan]

My experience with popping noises with lower ambient temp and not when it is hot is the gap on your plugs. Try moving the gap into the .026 -.028 range and see if this fixes your problem. The problem is that high horsepower cars can experience a missfire, not lose a lot of power and not "feel like a Miss". Popping is often the complaint i associate with missing under boost.

I would have to agree with Turbolab here. Check the gap on your plugs. On my past turbo vehicles (DSMs) I had to regap my plugs during the winter to .26 across the board. Versus running .28 in the summer.

Nathan

 

[SaberX]

I would have to agree with Turbolab here. Check the gap on your plugs. On my past turbo vehicles (DSMs) I had to regap my plugs during the winter to .26 across the board. Versus running .28 in the summer.

Nathan

Interesting. I had no idea about this. If I do decide to have the plugs gapped I can inspect them at the same time and see how the electrodes are looking. Also, can any good turbo tuner tell me about the sound? or do I need someone NSX specific?

As an aside I grabbed some Lucas Oil Octane Booster (which I read was actually good for about 2 actual octane points). I filled up with some Chevron 92 and with the +2 it should put me around 94. I was still able to hear the sound, but it didn't sound as bad....

 

[Paul]

Check the gap on your plugs. I had to regap my plugs during the winter to .26 across the board. Versus running .28 in the summer.

The CTSC kit is suppose to come with new spark plugs. You may want to call your installer to confirm if they came with the kit and if they installed them. According to CT website these spark plugs are pre-gapped and adjusting the gap will damage them???? Did you check the pulley size?

 

[nathan]

Interesting. I had no idea about this. If I do decide to have the plugs gapped I can inspect them at the same time and see how the electrodes are looking. Also, can any good turbo tuner tell me about the sound? or do I need someone NSX specific?

As an aside I grabbed some Lucas Oil Octane Booster (which I read was actually good for about 2 actual octane points). I filled up with some Chevron 92 and with the +2 it should put me around 94. I was still able to hear the sound, but it didn't sound as bad....

I dont think that you need to find someone NSX specific. Just find someone who is knowledgable about auto maintenance on forced induced cars.

 

[nathan]

The CTSC kit is suppose to come with new spark plugs. You may want to call your installer to confirm if they came with the kit and if they installed them. According to CT website these spark plugs are pre-gapped and adjusting the gap will damage them???? Did you check the pulley size?

I see that they are iridiums....funny thing is iridiums are not really worth the money. i wonder if anyone has tried using ngk BPR7ES or BPR6ES on a CTSC NSX. Iridiums really dont offer any better of a spark over the NGK BPR series plugs.

Note, that it is easy to damage the electrode when gapping/re-gapping iridiums, but you can gap them. Just becareful not to damage the electrode.

Nathan

 

[zahntech]

Yes the CT supplied Iridiums were installed...I have yet to hear the sound on Brian's car because Bill G has him working 100hrs per week!:wink:

 

[SaberX]

Just an update: I've been able to confirm that the "popping" sound was in fact detonation as evidenced by the fact that using octane booster dramatically reduced the frequency that it occurred to almost never. It looks like when its cold out ( < 40 degrees) the Autorotor is so efficient it can make lots of boost (8.5psi). Perhaps poorer winter gas octane is contributing to this as the octane booster definitely helped. I'll update as I get more info.

 

[Westrock]

I think I'm going to go get another A/F done, but @ $130 for the dyno w/ A/F I'd rather get some feedback before doing this.

You would be doing yourself a huge favor by buying a wideband guage for your car. They are very invaluable when it comes to diagnosing issues as well as keeping an eye on things. Now that I have had one, I can't see how I went so many years with out getting one as an intial mod.

Is this just an audible pop or is there an actual disruption of power or something else noticable? That would tell you alot about what is happening.

I had spark blow out occur a couple times on my car (not an NSX) when I upgraded to a larger turbo. It felt like the engine exploded and I would immediatly take my foot off the gas. And the car would run just fine afterwards. The spark gets blown out, so its basically like taking your foot of the gas, except your not ready for it. I had to gap from 0.040" to about 0.032". 3rd gear was OK, but top of 4th would do it everytime.

 

[BioBanker]

This is a big warning for me as Ive driven my autorotor CTSC tons of times around freezing (94 octane).

Thanks and keep us updated.

 

[TurboLab]

Another thing you might consider is the fact that as volumetric efficiency goes up and intake temps come down an engine needs more timing. Same concept as someone dyno tuned on 91 and sticking in 110, raising the boost ,staying on the same ignition map and running a full second slower in the 1/4 because its choking. Im not saying add 3 degrees and spray titanium all over the place but sometimes octane booster can change the timing requirements making it run better even though it was never really detonating.
I had a GTR at my shop i was tuning on the dyno that had Knock voltage, a big power dip on the graph 11.0 AFR's and ran with a popping noise and i spent 8 hours trying to figure it out. Turns out i had to add 5 degrees of timing to set the peek timing at peek torque around 36 degrees!!!! Scary but the car made only 19whp but picked up 50 ft-lbs of torque.
Having a wideband in my mind is the most important piece of equipment you could have on a boosted car, then stick it on a dyno with an experienced tuner. As a side note.. Detonation sounds the same inside the cylinder wall, but the sound you may hear differs from one car to another based on exhaust, engine configurations, and whether it is detonation or pre-ignition.Pre-ignition is what makes cute shapes out of expensive parts very quickly, where-as light detonation can happen for awhile, im not saying detonation is a good thing but most engines can handle alittle. The problem is that detonation creates burning embers in the motor whicj is the cause of pre-ignition. Sorry for the rambling but i was trying to paint a picture of why it still may not be detonation you are experiencing, even though you are probably right and it is pinging. If it sounds like a ford taurus Climbing a hill, then thats detonation. Good luck.

 

[Bob Kenney]

Detonation on the stock pistons can be a real problem. The stock pistons are cast and are NOT very robust when it comes to dealing with detonation; the ring lands can fracture leading to scored cylinder walls. Forged pistons afford a higher tolerance level to this condition but are not failure proof just more robust. Approach any knock, ping or pre-ignition sounds with concern, engine tear downs and rebuilds are expensive.

 

[TurboLab]

I agree detonation is bad and should be avoided at all costs, however engines are made to handle small amounts of detonation. If not a "knock sensor" wouldnt be worth a whole lot. Even with the parameters predetermined to know the difference between engine noise and an acutual event, the ecu is giving timing back to the engine to restore the lost power after it has taken measures to stop the knocking. There fore it is acceptable to have light detonation. Honda's are tuned aggressively to use the knock sensor to pull during an event and not before and give back timing much more quickly than other makes. You can log a stock obd2 ecu have knock and giving timing back very quickly. At least this has been my experience on the dyno. Evo's on the other hand like to play it a little safer at the sacrifice of power, after an event they are slow to reintroduce timing. But they suck...(I sold mine because my wife wanted a new kitchen so i have to dilute myself into thinking they suck even though i usually get dominated by them )

 

[ScienceofSpeed]

Just an update: I've been able to confirm that the "popping" sound was in fact detonation as evidenced by the fact that using octane booster dramatically reduced the frequency that it occurred to almost never. It looks like when its cold out ( < 40 degrees) the Autorotor is so efficient it can make lots of boost (8.5psi). Perhaps poorer winter gas octane is contributing to this as the octane booster definitely helped. I'll update as I get more info.

I'm surprised and intrigued that you'd be seeing that pressure even with your air density. Have you double checked your gauge readings with another sensor (perhaps the one at the dyno?) and confirmed the pulley size is correct? The runs I've seen at sea level in cool conditions do not come close to 8.5 lbs.

cheers,
-- Chris

 

[zahntech]

The system is producing 8.5lbs regularly..and it is detonating lightly only under full boost and load.

We will be addressing the issue, another NSX Tuner is also having this issue with couple of other cars and we will post the results of our efforts.

 

[BioBanker]

WHere is Shad in all of this? Although no longer connected to CT, I suspect that he would be an incredible resource with this.....

 

[Bob Kenney]

The system is producing 8.5lbs regularly..and it is detonating lightly only under full boost and load.

We will be addressing the issue, another NSX Tuner is also having this issue with couple of other cars and we will post the results of our efforts.

Just my own curiosity here; but what rwhp are you making from a 3.0 with stock iinternals at 8.5 lbs of boost?