A bit rich...but my buddy's CBR600 can't keep up!
08-07-2002, 07:04 PM
#1
Burning Brakes
Thread Starter
A bit rich...but my buddy's CBR600 can't keep up!
Hey guys...I haven't posted much in awhile, as I've been working down in Argentina. I was back home for a bit a couple weeks ago, and took the 951 up the Whistler highway while my friend had his older CBR600 along for the ride. First of all, no complaints regarding my cars performance. I had the boost dialled to a pretty conservative 15psi, and my friend couldn't pass me going up the long uphill straights. In the bends, the 951 pulled well ahead of his bike...in fact I had to slow down a few times to let him catch up. 
Anyways, my concern is that I'm running a bit rich. We took turns on the bike, so I had the opportunity to watch the tailpipe of my car as he accelerated through the gears. My car seems to produce a bit of black smoke when you first start it up and idle it (cold or hot). When accelerating, there's a noticable puff of black smoke when you step on it in each gear, and also a flame out the muffler during upshifts. I couldn't smell oil, and it wasn't blue, so I'm pretty sure the smoke was a fuelling issue.
My car has a Garrett T04E-50 trim turbo, HR Stg3 MAF, ARC2 fuel controller, adjustable fpr, 52# injectors, etc etc. I have previously tuned the air:fuel ratios using wideband O2 sensors on both the street and on the dyno, and achieved a PERFECT 12.5:1 ratio under boost, and stoichometric 14.7:1 under cruising conditions.
Okay, now some questions. Why would the car be smoking if the af ratios were dialled in so well? The af tuning was done in February, and it was at least 20 degrees celcius warmer during our drive. Could the temperature difference be affecting my mixtures? Perhaps it's normal to see some black smoke when you first get on the gas, as the af plot does initially start rich, then lean out to 12.5:1 as the rpm's build past 3000rpm. What about the flames, should I be concerned? It doesn't smoke like a diesel, but it is noticeable from behind - is any smoke a bad thing, and indicative of excessively rich conditions? The cost of my engine rebuild is still fresh on my mind, and I'm paranoid about cylinder wash. Comments appreciated.
Anyways, my concern is that I'm running a bit rich. We took turns on the bike, so I had the opportunity to watch the tailpipe of my car as he accelerated through the gears. My car seems to produce a bit of black smoke when you first start it up and idle it (cold or hot). When accelerating, there's a noticable puff of black smoke when you step on it in each gear, and also a flame out the muffler during upshifts. I couldn't smell oil, and it wasn't blue, so I'm pretty sure the smoke was a fuelling issue.
My car has a Garrett T04E-50 trim turbo, HR Stg3 MAF, ARC2 fuel controller, adjustable fpr, 52# injectors, etc etc. I have previously tuned the air:fuel ratios using wideband O2 sensors on both the street and on the dyno, and achieved a PERFECT 12.5:1 ratio under boost, and stoichometric 14.7:1 under cruising conditions.
Okay, now some questions. Why would the car be smoking if the af ratios were dialled in so well? The af tuning was done in February, and it was at least 20 degrees celcius warmer during our drive. Could the temperature difference be affecting my mixtures? Perhaps it's normal to see some black smoke when you first get on the gas, as the af plot does initially start rich, then lean out to 12.5:1 as the rpm's build past 3000rpm. What about the flames, should I be concerned? It doesn't smoke like a diesel, but it is noticeable from behind - is any smoke a bad thing, and indicative of excessively rich conditions? The cost of my engine rebuild is still fresh on my mind, and I'm paranoid about cylinder wash. Comments appreciated.
08-07-2002, 08:14 PM
#2
Race Director
The problem comes in with transient responses from the MAF sensor. The long column of air from the sensor, through the turbo, out through the intercooler and back around to the intake-manifold means that the amount of air measured by the MAF-sensor isn't the amount that's actually going into the engine at that very moment. Since air is a compressible fluid, when you crack open the throttle, the MAF picks up the increased flow and sends the air-flow signal straight to the DME (since electricity flows faster than air), and the DME along with the KLR's acceleration-enrichment signal, dumps in extra air to match the flow. However, the actual volume of air going into the chambers is much less and there's a time-delay before actual increased air-volume catches up to the extra fuel. <img src="graemlins/jumper.gif" border="0" alt="[jumper]" />
You while you can see this extra puff under acceleration, it doesn't show up on the dyno testing because that only shows steady-state average O2-sensor output after you've already got things floored. I wouldn't worry about it too much since it's just a momentary event.
You while you can see this extra puff under acceleration, it doesn't show up on the dyno testing because that only shows steady-state average O2-sensor output after you've already got things floored. I wouldn't worry about it too much since it's just a momentary event.
08-07-2002, 09:42 PM
#3
Burning Brakes
Danno, for my part I'd give you the gold star for fund of Porsche knowledge but this one's a bit difficult to grasp:
"Since air is a compressible fluid, when you crack open the throttle, the MAF picks up the increased flow..."
I'm sure the American Institue of Physics would like to know more about the convertible states of matter within a 951 engine! <img src="graemlins/beerchug.gif" border="0" alt="[cheers]" />
Ian good to see you back.
Mike
"Since air is a compressible fluid, when you crack open the throttle, the MAF picks up the increased flow..."
I'm sure the American Institue of Physics would like to know more about the convertible states of matter within a 951 engine! <img src="graemlins/beerchug.gif" border="0" alt="[cheers]" />
Ian good to see you back.
Mike
08-07-2002, 09:51 PM
#4
Burning Brakes
Thread Starter
Thanks Danno!
I was hoping to get your opinion on this. That makes a lot of sense. What about the flame thrower on upshifts - similar phenomenon? I must admit...it looks pretty damn trick. It must look kinda disconcerting to drivers behind me at night though...
I was hoping to get your opinion on this. That makes a lot of sense. What about the flame thrower on upshifts - similar phenomenon? I must admit...it looks pretty damn trick. It must look kinda disconcerting to drivers behind me at night though...
08-07-2002, 10:08 PM
#5
Nordschleife Master
I think I can chime in with a reasonably intelligent response on the flame thrower...
Essentially it's my understanding that when you step off the throttle to shift at WOT...air is cut off instantly, but fuel continues flowing for a split second. That fuel flows through the exhaust and hits the hot turbo and ignites...thus the flames.
If you have an air/fuel gauge...drive around at part throttle (easier to pay attention to the gauge than when at WOT...hehe), then step off the gas...see the gauge bounce to full rich or near it for an instant?
Correct me if I'm wrong
Essentially it's my understanding that when you step off the throttle to shift at WOT...air is cut off instantly, but fuel continues flowing for a split second. That fuel flows through the exhaust and hits the hot turbo and ignites...thus the flames.
If you have an air/fuel gauge...drive around at part throttle (easier to pay attention to the gauge than when at WOT...hehe), then step off the gas...see the gauge bounce to full rich or near it for an instant?
Correct me if I'm wrong
08-07-2002, 10:38 PM
#6
Race Director
[quote]"Since air is a compressible fluid, when you crack open the throttle, the MAF picks up the increased flow..." <hr></blockquote>
I'm sure the American Institue of Physics would like to know more about the convertable states of matter within a 951 engine! "
Well, by 'compressible fluid' I don't mean a liquid; some of my favorite refreshments <img src="graemlins/drink.gif" border="0" alt="[cherrsagai]" /> ! A fluid has:
- volume, mass and therefore density
- viscosity (very important)
This is important because cohesion between the fluid molecules creates viscosity (they tend to stick and pull on each other). So it's not like a laser light-show where each beam is independent. Streams of a traveling fluid (gaseous or liquid) affect each other. It's just that water isn't compressible whereas air is, both being fluids. In fact, more accurate mapping of air-flows particularly in regards to gains in head port & polishing can use water as the medium.
Ok, back to the topic, since the air-column coming into the car is about 5-6ft long, the head of this column can be experiencing some condition that affects it. Like being squeezed through some half-open valves. This causes all the air behind it to push and you have higher-pressure in a localized spot. Meanwhile, air coming out of the intercooler might be experiencing a pressure-reduction and an increase in velocity, thus lower pressure here at the same time. And at the MAF sensor itself at the same time, you might have the highest velocity and lowest pressure. So if you draw a stretched out picture of the intake air-column and plot it, you might have something like this:
Air at low-pressure, low-velocity is sped up and pressurized by the turbo into a high-pressure, high-velocity stream. Some of velocity and pressure is lost going through the intercooler. Another restriction is the intake valves where air slows down alot and experiences more pressure.
As you can see, the air-column in the intake-tract experiences changes in velocity, pressure, density, volume, temperature, etc. as it moves through the system. However if you pick any single point along this plumbing to measure at steady-state conditions, you will find a constant mass of air moving through for any given time period.
"What about the flame thrower on upshifts - similar phenomenon?"
Same thing, different conditions at the MAF-sensor vs. what's actually going into the engine. Let's say you're at 6000rpm and do a shift. When you close that throttle, air-flow and mass behind it is shut off; very little makes it into the engine. However, the intake-air column is still moving at 350cfm and the turbo is still spinning madly. This air-column slams into the throttle-plate and compresses, allowing room to open up in back of the column, thus flow is still occuring across the MAF sensor. The MAF-sensor still sends a signal to the DME to inject a certain amount of fuel for that flow, even though much, much less air is actually ingested through the intake valves. Thus the overly rich mixture that shoots flames out the tail-pipe.
Only when the intake-column in front of the throttle-plate has compressed enough to stop the tail-end from moving does the MAF-sensor indicate slow-flow conditions. The compressor-bypass valve also also keeps the same amount of air circulating, thus prevent any additional air from entering the system, thus the sensor indicates low-flow and the DME finally turns down the fuel.
So what you're experiencing is a time-delay reaction between what the MAF-sensor is reporting vs. what's actually happening in the engine.
I'm sure the American Institue of Physics would like to know more about the convertable states of matter within a 951 engine! "
Well, by 'compressible fluid' I don't mean a liquid; some of my favorite refreshments <img src="graemlins/drink.gif" border="0" alt="[cherrsagai]" /> ! A fluid has:
- volume, mass and therefore density
- viscosity (very important)
This is important because cohesion between the fluid molecules creates viscosity (they tend to stick and pull on each other). So it's not like a laser light-show where each beam is independent. Streams of a traveling fluid (gaseous or liquid) affect each other. It's just that water isn't compressible whereas air is, both being fluids. In fact, more accurate mapping of air-flows particularly in regards to gains in head port & polishing can use water as the medium.
Ok, back to the topic, since the air-column coming into the car is about 5-6ft long, the head of this column can be experiencing some condition that affects it. Like being squeezed through some half-open valves. This causes all the air behind it to push and you have higher-pressure in a localized spot. Meanwhile, air coming out of the intercooler might be experiencing a pressure-reduction and an increase in velocity, thus lower pressure here at the same time. And at the MAF sensor itself at the same time, you might have the highest velocity and lowest pressure. So if you draw a stretched out picture of the intake air-column and plot it, you might have something like this:
Air at low-pressure, low-velocity is sped up and pressurized by the turbo into a high-pressure, high-velocity stream. Some of velocity and pressure is lost going through the intercooler. Another restriction is the intake valves where air slows down alot and experiences more pressure.
As you can see, the air-column in the intake-tract experiences changes in velocity, pressure, density, volume, temperature, etc. as it moves through the system. However if you pick any single point along this plumbing to measure at steady-state conditions, you will find a constant mass of air moving through for any given time period.
"What about the flame thrower on upshifts - similar phenomenon?"
Same thing, different conditions at the MAF-sensor vs. what's actually going into the engine. Let's say you're at 6000rpm and do a shift. When you close that throttle, air-flow and mass behind it is shut off; very little makes it into the engine. However, the intake-air column is still moving at 350cfm and the turbo is still spinning madly. This air-column slams into the throttle-plate and compresses, allowing room to open up in back of the column, thus flow is still occuring across the MAF sensor. The MAF-sensor still sends a signal to the DME to inject a certain amount of fuel for that flow, even though much, much less air is actually ingested through the intake valves. Thus the overly rich mixture that shoots flames out the tail-pipe.
Only when the intake-column in front of the throttle-plate has compressed enough to stop the tail-end from moving does the MAF-sensor indicate slow-flow conditions. The compressor-bypass valve also also keeps the same amount of air circulating, thus prevent any additional air from entering the system, thus the sensor indicates low-flow and the DME finally turns down the fuel.
So what you're experiencing is a time-delay reaction between what the MAF-sensor is reporting vs. what's actually happening in the engine.
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08-08-2002, 12:13 AM
#8
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[quote]Originally posted by Leo Chappell:
<strong>Is there a way to eliminate or compensate for this delay so that you don't get the sudden rich a/f mixture?</strong><hr></blockquote>
Danno, if there ever was an opening for your map conversion kit, here it is!
<strong>Is there a way to eliminate or compensate for this delay so that you don't get the sudden rich a/f mixture?</strong><hr></blockquote>
Danno, if there ever was an opening for your map conversion kit, here it is!
08-08-2002, 03:11 AM
#10
Addict
Rennlist Member
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[quote]Originally posted by Leo Chappell:
<strong>Is there a way to eliminate or compensate for this delay so that you don't get the sudden rich a/f mixture?</strong><hr></blockquote>
Ofcourse, the map conversion kit danno is selling would pick up on the amount of air the engine is taking in (at a given moment)quicker than anything else since the measurement is done right IN the intake manifold by the (intake)valves.
Something less often excercised is putting the air flow meter by the throttle plate (under boost), instead of infront of the turbo. This would be far superior to the factory set-up in this aspect but still not as quick to respond as a sensor placed inside the manifold.
Ahmet
<strong>Is there a way to eliminate or compensate for this delay so that you don't get the sudden rich a/f mixture?</strong><hr></blockquote>
Ofcourse, the map conversion kit danno is selling would pick up on the amount of air the engine is taking in (at a given moment)quicker than anything else since the measurement is done right IN the intake manifold by the (intake)valves.
Something less often excercised is putting the air flow meter by the throttle plate (under boost), instead of infront of the turbo. This would be far superior to the factory set-up in this aspect but still not as quick to respond as a sensor placed inside the manifold.
Ahmet
08-08-2002, 10:19 AM
#11
Burning Brakes
Thread Starter
Thanks for the responses!! I've got a warmer and fuzzier feeling now. But it certainly does lead me to question whether the next step is to chuck out the MAF. Could that fact that I repositioned my MAF sensor directly after the air filter (rather than after the 90 degree elbow) be contributing to these issues? I know it's not a big distance, but it sure helped remove my lift-throttle bucking problem.
In case you guys are interested, I've got some really great photos that my buddy took of my car during our ride to Whistler. I'll select my favourites and put a post together later today.
In case you guys are interested, I've got some really great photos that my buddy took of my car during our ride to Whistler. I'll select my favourites and put a post together later today.
08-08-2002, 09:55 PM
#12
Intermediate
Okay, okay, let's get one thing straight about Ian's BOASTING about losing me on my CBR600 in the twisties and my not being able to pass him up the long hills en route to Whistler!
1) I WAS able to gain ground on him going up hill ... just not as quickly as I thought I'd be able to. Not only that, but at full twist, it took me a good 20 or 30 seconds to catch him, having started from a couple of car-lengths behind (I was giving him a real-time verbal report regarding his smoking, flaming tail pipe over our 2-way radios ... man did that flame look wild!). Let it suffice to say that I could not by any means pull away from his 951.
Oh, and I was NOT on full throttle ... I was just toying with Ian ... Yeah! That's the ticket! That's my story and I'm stickin' to it!
Alright, alright, I wasn't pegged, but I was damned close, so I might as well have been. Man is his 951 impressive!!! Kind of makes me reconsider the $3K (Canadian) that I paid for my bike ... oh wait, that's a trip to the shop for Ian! Suddenly I feel a little better! <img src="graemlins/roflmao.gif" border="0" alt="[hiha]" /> (Sorry, buddy ... a little too close to home for you, perhaps.)
2) I am admittedly a wuss on my bike, especially on un-tried twisties ... I am deathly afraid of gravel on little-used mountain highways! I am a family man with a couple of kids at home, so I'm pretty tame on my bike for the most part.
Ian, on the other hand, is an ANIMAL!!! He has taken his (former) bike to track days and was far more aggressive on my bike than I will likely ever be! So let the following example be a testament to Ian's car. With Ian riding my bike agressively and really tossing it around, I was easily able to stay on his tail in his 951, in both the straights and the twisties. I'm far more experienced and confident driving aggressively in a car (especially his 951) than on a motorcycle, but I'm certainly no seasoned rallye driver.
At any rate, his car's performance knocked my socks off, even when I had it dialed down to 12psi (the car is far better balanced and less twitchy at lower boost). The car felt as though it was pivoting around the seat of my pants, with instant throttle response and plenty of power to keep me out of trouble with a bit of on-demand oversteer.
Sorry for the long-winded post ... just wanted to make sure that you all got a balanced report on our outing! You've done a great job on your car, Ian. Thanks for sharing the driving experience with me.
Cheers,
- Brian
1) I WAS able to gain ground on him going up hill ... just not as quickly as I thought I'd be able to. Not only that, but at full twist, it took me a good 20 or 30 seconds to catch him, having started from a couple of car-lengths behind (I was giving him a real-time verbal report regarding his smoking, flaming tail pipe over our 2-way radios ... man did that flame look wild!). Let it suffice to say that I could not by any means pull away from his 951.
Oh, and I was NOT on full throttle ... I was just toying with Ian ... Yeah! That's the ticket! That's my story and I'm stickin' to it!
Alright, alright, I wasn't pegged, but I was damned close, so I might as well have been. Man is his 951 impressive!!! Kind of makes me reconsider the $3K (Canadian) that I paid for my bike ... oh wait, that's a trip to the shop for Ian! Suddenly I feel a little better! <img src="graemlins/roflmao.gif" border="0" alt="[hiha]" /> (Sorry, buddy ... a little too close to home for you, perhaps.)
2) I am admittedly a wuss on my bike, especially on un-tried twisties ... I am deathly afraid of gravel on little-used mountain highways! I am a family man with a couple of kids at home, so I'm pretty tame on my bike for the most part.
Ian, on the other hand, is an ANIMAL!!! He has taken his (former) bike to track days and was far more aggressive on my bike than I will likely ever be! So let the following example be a testament to Ian's car. With Ian riding my bike agressively and really tossing it around, I was easily able to stay on his tail in his 951, in both the straights and the twisties. I'm far more experienced and confident driving aggressively in a car (especially his 951) than on a motorcycle, but I'm certainly no seasoned rallye driver.
At any rate, his car's performance knocked my socks off, even when I had it dialed down to 12psi (the car is far better balanced and less twitchy at lower boost). The car felt as though it was pivoting around the seat of my pants, with instant throttle response and plenty of power to keep me out of trouble with a bit of on-demand oversteer.
Sorry for the long-winded post ... just wanted to make sure that you all got a balanced report on our outing! You've done a great job on your car, Ian. Thanks for sharing the driving experience with me.
Cheers,
- Brian
08-08-2002, 11:25 PM
#13
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excellent reporting both of you, i have been able to pull away from 900 and 1100 cc bikes after 70 mph many times with my maf equipped 944 turbo, 600 cc bikes really dont hold up at all though once im at full boost, but im running it to 20 psi not 15 like you ian, again great story, send in some video if you can, if someone wants to send me their digital camera i could make some great videos to download to this site with my maf equipped car, ill buy one soon if they arent too pricey, any ideas on a cheap 1 minute type camera/video thingy i might look into...
08-11-2002, 01:57 AM
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I'm runnin the powerhaus K29#8 with 52 pound injectors, but i need bigger ones still, so im getting 72 pounders i believe, i got a bigger fuel pump and the adj. reg set to 3.5 bar at idle