CTSC timing

[donwon]

Has anyone with CTSC measured the timing on their systems or know what stock timing is?

The reason I ask is because when I went to the dyno yesterday, my timing was between 27-30 degrees throughout the band. I was told this was high, but the CTSC doesnt have a timing adjustment.

 

[Yellow Rose]

Be Careful !!

For the NSX engine under steady-state conditions such as cruising along, timing is approximately 40° BTDC.

For a naturally aspirated NSX engine at WOT, the timing is approximately 27° BTDC.

For a forced induction NSX engine, the rule of thumb is to retard 1° per 1 PSI of boost. Assuming a 9 PSI kit, timing at WOT should be 18° BTDC.

You were told correctly.....that is too much timing advance at WOT on a forced induction NSX. Using Comptech's 6 PSI supercharger means that if timing was adjustable with their kit, you should be at 21° BTDC. The problem is that Comptech's kit does not adjust timing. There is a way around this. You can manually retard timing by up to 3° on the NSX. Unfortunately, this 3° is during the entire RPM band - even at idle and cruising. Gas mileage and drivability is affected. However, at WOT the resulting timing is 18° BTDC, which is within guidelines of the abovementioned rule of thumb.

 

[sjs]

The stock standard boos CTSC is intended to work with stock timing. For one thing, boost tends to fall off a bit at higher RPM, but in any case they apparently considered it safe on decent gas. (not that there haven't been failures which appear to be detonation or heat related )

As for the old "rule of thumb" on timing for boosted cars, most such generalities range from "reasonably close" to "dangerously wrong" but are rarely if ever "right". There are too many variables, and without careful monitoring of all the vitals during tuning you may find out the hard way that what you thought was a safe and conservative approach is actually quite the opposite.

 

[donwon]

For one thing, boost tends to fall off a bit at higher RPM

Thats exactly what is happening.

 

[sjs]

Thats exactly what is happening.

That's "normal" and helps explain the power curve of the CTSC. It is sized to get boost early but then runs out of steam, yielding a fat torque curve relative to peak HP.

 

[Lud]

While I am admittedly going more on guts than extensive nsx-specific data here, I am inclined to agree with sjs. Andy what are you basing your numbers on? That sounds like an awful lot of timing retard to me, based on the CTSC boost profile.

 

[Yellow Rose]

Andy what are you basing your numbers on?

Previous posts to different threads by Gerry Johnson (of the TT fame) and Devin Pierce (known here as PaynNSX).

GJ once posted that steady-state timing is around 40°.

DP also posted some graphs (perhaps from an AEM recording) of timing at steady-state and at full throttle.

Lastly, earlier this year I plugged a Honda data scanner into my OBD-2 diagnostics port. Steady state timing was 37-38° BTDC.

 

[Lud]

I'm sorry, I should have clarified that I meant where/how are you coming up with your recommended numbers of 21° for a standard ctsc and 18° for the "high-boost" ctsc.

 

[Yellow Rose]

I'm sorry, I should have clarified that I meant where/how are you coming up with your recommended numbers of 21° for a standard ctsc and 18° for the "high-boost" ctsc.

If we begin with the baseline timing of 27° BTDC for a naturally aspirated NSX engine at full throttle, and follow the general rule-of-thumb of retarding timing by 1° per 1 PSI, 27-6=21 and 27-9=18.

Several things to keep in mind.

1 - the CTSC does not make a legit 6 PSI or 9 PSI; however, I used those numbers for simple math.

2 - the guideline of 1° retard per 1 PSI is just that...a guideline. It has been suggested to me by a reputable engine builder that with the stronger pistons, good gasoline, proper aftercooling and accurate timing control, that one could use ½° retard per 1 PSI. I honestly do not recall where here on PRIME it was posted to use 1° retard per 1 PSI, but a few months ago I was thumbing through a forced induction book at a local tuning shop and saw the 1° recommendation there as well.

3 - just like fuel control is adjusted to achieve a nominal air-fuel ratio of 12:1 under boost, timing control is adjusted so there is no pinging. However, there is another parameter that timing control must also satisfy, and that is exhaust gas temperature. I do not know (I’ve only begun to study this) what an acceptable exhaust gas temperature is for a boosted NSX engine. I suspect it is in the 7-900 °F range. The point being is that I suspect timing retard also affects how hot things get in the combustion chamber. Thorough aftercooling is negated if timing is off and valve parts break. I had valve guide failure with my CTSC, which as we all know is not aftercooled and does not compensate ignition timing. While I was never able to prove it, I strongly suspect that things got too hot. I know, there are perhaps hundreds of CTSC kits out there with virtually no failures, but eventually the odds catch up with a user.

 

[Lud]

I guess all I can say at this point is my gut tells me the numbers you are arriving at via your rule of thumb make me uncomfortable. And I would be concerned about the potential for an EGT issue as you mentioned with that much timing retard on a CTSC NSX. As sjs said people often go overboard trying to be "conservative" by pulling more timing, but that can end up being just as dangerous as too much advance. I would be interested to hear from someone who has real-world info.

 

[Yellow Rose]

I guess all I can say at this point is my gut tells me the numbers you are arriving at via your rule of thumb make me uncomfortable.

Actually, I did not arrive at the 1° rule-of-thumb. Someone else (I do not recall who) here on PRIME posted it. I don’t think that the person’s post contained a basis; however, I have also seen this number in a printed publication. Therefore, while it may be a "dangerous" number, it appears to be a "starting point". Contradictory, indeed.

And I would be concerned about the potential for an EGT issue as you mentioned with that much timing retard on a CTSC NSX.

As I understand it, tolerable ignition timing and EGTs are partially a function of combustion chamber geometry. So what works on a Honda will most likely be invalid for a Chevy.

I would be interested to hear from someone who has real-world info.

Most definitely.....as would I. Let’s have it folks.

 

[WOODY]

what is the accepted procedure for dialing in timing? adjust til no change in horsepower then back it off a little? retard til it pings then back off a little?

 

[Yellow Rose]

what is the accepted procedure for dialing in timing? adjust til no change in horsepower then back it off a little? retard til it pings then back off a little?

This is how it was explained to me.

Dyno pull.....read plugs.....add 2° of advance.

You should see approximately 5 HP increase.

Repeat until power gains diminish.....remove 2° of timing.

This method adjusts timing to the threshold of pre-detonation. That is why there is an intermediate step of reading the plugs, looking for specs of aluminum which indicates pre-detonation. What this does not address is the effect of ignition timing upon exhaust gas temperature. As I mentioned in another thread, I think the range of 7-900 °F is an acceptable value for our engines.

Another forced induction NSXer introduced me to a laptop software that plugs into the OBD-II diagnostics port. It displays intake air temperature, fuel trims (Kendall, this is for you), coolant temperatures, timing advance, exhaust gas recirculation valve position, throttle position, oxygen sensor output and many other parameters. What I am hoping is that one of the multiple values read from a single oxygen sensor is voltage, which can be correlated to temperature. The software has data logging and playback capability. An AEM can do all of this too, but they are available only for OBD-I vehicles. I have not priced an AEM, but for the NSX it is in the neighborhood of $16-1800. The abovementioned software is $200.

 

[sjs]

I think you mean 700-900 °C.

As for timing, it should be mentioned that it's a complete map of advance in a grid of load vs RPM, similar to the fuel map. Changes relative to the stock map may vary at different parts of the map, so the "ideal tune" (power + safety) can be pretty complex.

 

[Ryanmcd2]

The best way to do timing is to do it on a GOOD dyno and you will see where the stock ECU pulls timing if it get's any kind of det. Timing get's you good TQ but causes heat and needs a lot of fuel. Best thing I have seen is running more boost and go easy on the timing. On a shop car that I am working on NOT a NSX it's a evo but same thing applies and it's getting tuned with a AEM. We were running 19PSI starting out and ended up at 36 PSI of boost with C16 and 712 WHP. The TQ was about 390 because we did not go crazy with timing but adding 1 timing gains about 30 TQ BUT it needs more fuel and causes more heat. It's all a balance really, I say run a AF of 11.8:1 or .82 .84 lambda if you are doing that, get it on a dyno and you will see it on the dyno chart if it pulls timing or get's det because the power will drop. Also on newer cars you can hook up an OBDII scanner and watch timing and it should increase with RPM if you see it pull 1 you may be getting knock or det. I hope this helps. I think people take tuning as some black magic, once we turn up the boost and add the 150shot this car will be over 1000whp on a 2.4 liter 4 running to 8500 RPM.

 

[Yellow Rose]

°F vs °C

I think you mean 700-900 °C.

No.

700 °C = 1292 °F and 900 °C = 1652 °F. Even one of the strongest grades of aluminum.....6061-T6.....has an approximate melting point of 1080 °F. The melting point of the lesser grades is even lower, in the 900's °F.

 

[sjs]

Re: °F vs °C

I think you mean 700-900 °C.

No.

700 °C = 1292 °F and 900 °C = 1652 °F. Even one of the strongest grades of aluminum.....6061-T6.....has an approximate melting point of 1080 °F. The melting point of the lesser grades is even lower, in the 900's °F.

Yes.

Which is why we don't make things like valves and headers out of aluminum. The exhaust temp gasses do get that high, fortuantely the metal around them does not. Heck, most EGT gauges don't even read below 700 °F and ~1300 is mid-gauge. But 900 °C is too high in any case.

 

[Ryanmcd2]

Most EGT = 1200-1600F on turbo stuff that I have seen. Turn on antilag and watch it hit 1800

 

[Ryanmcd2]

Re: °F vs °C

lol Andy I though you knew it all man have you seen a exhaust glow before? I can tell you it's over 900F

I think you mean 700-900 °C.

No.

700 °C = 1292 °F and 900 °C = 1652 °F. Even one of the strongest grades of aluminum.....6061-T6.....has an approximate melting point of 1080 °F. The melting point of the lesser grades is even lower, in the 900's °F.

 

[Yellow Rose]

have you seen an exhaust glow before?

Yes.....headers on my naturally aspirated Chevy V-8.

I can tell you its over 900 °F

How.....calibrated palm surface?

 

[WOODY]

Actual Test Results (run 10-02-00) FOUND ON NET @ http://www.aera.org/Techside/exhaust gas temp.htm

Elevation: 600 ft above sea level (bearutiful Chicago)
Barometric Pressure: 29.05 uncorrected weather station reading
Air Temperature: 35°F
Vehicle Weight: 3500 lbs with a full tank of 93 octane Shell gas and skinny driver

Cold start @ 1200 RPM 5-600°F 20" of vacuum

Warming up@ 900 RPM 7-800° F 20" of vacuum

Normal Temp@ idle 750 RPM 8-900° F 18" of vacuum

City @ 3000 RPM 3rd 1100° F 14" of vacuum

Highway @ 3000 RPM 5th 1400° F 10" of vacuum

Coasting 850°F 24" of vacuum

WOT 3000 to 7000 RPM 1550° F 12 lbs. of boost

 

[sjs]

The thing about turbos is that they rely on high temps to generate boost, which generates more power, etc., so you tend to tune fuel and timing to build EGTs fast then taper off at higher loads. These days with sophisticated controls I think 1500 or a bit more is very common for turbos, but with an SC you may be much lower since it doesn't "feed" off the heat.

 

[WOODY]

Isnt It The Velocity Of Exhaust Gases That Spools The Turbo? How Does The Temp Of The Gas Factor In?

 

[Yellow Rose]

One of the laws of gas chemistry is that as a gas cools it expands. Expanding gas becomes “more gas available” to exert work onto the turbo’s impeller, because this adds to the baseline velocity of the exhaust gas. This in turn results in quicker spool-up. Sometimes the exhaust system of a turbo’ed car is wrapped with insulating fabric to contain as much heat as possible within the piping upstream of the turbo. As the above link’s write-up says, the exhaust gas temperature cools quickly after exiting the cylinder head.

 

[Sig]

Isnt It The Velocity Of Exhaust Gases That Spools The Turbo? How Does The Temp Of The Gas Factor In?

see above instead