Finally got my carb'd LS project on the street
01-17-2012, 10:38 PM
#61
Well guys, I was doing some thinking tonight about the way I calculated and presented my track results after removing the exhaust. It occured to me that I was only comparing my best run with the exhaust to all of my runs without. What that came down to was that my best run with exhaust was equal to my worst runs without. So instead I went back and looked at the corrected times for ALL the passes through the exhaust on 19 November, and this is how it looks:
First Pass
11.12 @ 120.65
Second Pass
11.21 @ 120.52
Third Pass
11.17 @ 120.93
Fourth Pass
11.07 @ 122.34
Fifth Pass
11.13 @ 122.52
So the average ET and MPH for all these passes is 11.14 @ 121.39
And since I've already listed the corrected times for my "without exhaust" passes in a previous post, I'll just list the average of those runs. I'm only averaging the first three passes since the fourth pass was made with the HVH spacer.
The average ET and MPH for the "without exhaust" passes is 11.03 @ 123.16
So when looking at my data this way, I had an average gain of .11 sec and 1.77 mph by removing the exhaust. This is still not enough for me to want to pull the exhaust off the car regularly to hit the track and it still makes me feel good about the efficiency of my exhaust system. However, it's also good to know that my car is at least consistent enough to show a gain when 71lbs is removed (that had me confused), and it shows there is a modest amount of horsepower to be freed up if I ever need that last little bit to push me past an ET goal.
First Pass
11.12 @ 120.65
Second Pass
11.21 @ 120.52
Third Pass
11.17 @ 120.93
Fourth Pass
11.07 @ 122.34
Fifth Pass
11.13 @ 122.52
So the average ET and MPH for all these passes is 11.14 @ 121.39
And since I've already listed the corrected times for my "without exhaust" passes in a previous post, I'll just list the average of those runs. I'm only averaging the first three passes since the fourth pass was made with the HVH spacer.
The average ET and MPH for the "without exhaust" passes is 11.03 @ 123.16
So when looking at my data this way, I had an average gain of .11 sec and 1.77 mph by removing the exhaust. This is still not enough for me to want to pull the exhaust off the car regularly to hit the track and it still makes me feel good about the efficiency of my exhaust system. However, it's also good to know that my car is at least consistent enough to show a gain when 71lbs is removed (that had me confused), and it shows there is a modest amount of horsepower to be freed up if I ever need that last little bit to push me past an ET goal.
01-18-2012, 06:22 AM
#62
Launching!
Join Date: Jun 2011
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Did you re-jet for the pulled exhaust to keep things at the same AFR?
If not you don't have a perfect comparison. When you pull the exhaust, typically you are going to get more suck from the headers without the back pressure and intern pull more through the carb. Not in all cases but most the time it requires some minor tinkering with the carb to keep the air fuel ratios the same..... Once you get a wideband on your car you can better access the situation. you might also be able to do some more tuning and get a small amount of et there. It will also allow you to see were you are across the whole power band to ensure your AFR is as close to the desired value as possible.
In terms of reading the plugs was the car shutdown right at the top end? If not you could be getting misleading results if you drove it back to the pits... Also reading plug with unleaded fuel is not as good a tool as it was with leaded gas. It can still be used (I don't like to) but it takes more time to color a set of plugs.
We used to when a car was going to the track for the first time get some leaded gas so we could read the plugs better before wide bands became more affordable.
Bruce
If not you don't have a perfect comparison. When you pull the exhaust, typically you are going to get more suck from the headers without the back pressure and intern pull more through the carb. Not in all cases but most the time it requires some minor tinkering with the carb to keep the air fuel ratios the same..... Once you get a wideband on your car you can better access the situation. you might also be able to do some more tuning and get a small amount of et there. It will also allow you to see were you are across the whole power band to ensure your AFR is as close to the desired value as possible.
In terms of reading the plugs was the car shutdown right at the top end? If not you could be getting misleading results if you drove it back to the pits... Also reading plug with unleaded fuel is not as good a tool as it was with leaded gas. It can still be used (I don't like to) but it takes more time to color a set of plugs.
We used to when a car was going to the track for the first time get some leaded gas so we could read the plugs better before wide bands became more affordable.
Bruce
01-18-2012, 09:11 AM
#65
Did you re-jet for the pulled exhaust to keep things at the same AFR?
If not you don't have a perfect comparison. When you pull the exhaust, typically you are going to get more suck from the headers without the back pressure and intern pull more through the carb. Not in all cases but most the time it requires some minor tinkering with the carb to keep the air fuel ratios the same..... Once you get a wideband on your car you can better access the situation. you might also be able to do some more tuning and get a small amount of et there. It will also allow you to see were you are across the whole power band to ensure your AFR is as close to the desired value as possible.
In terms of reading the plugs was the car shutdown right at the top end? If not you could be getting misleading results if you drove it back to the pits... Also reading plug with unleaded fuel is not as good a tool as it was with leaded gas. It can still be used (I don't like to) but it takes more time to color a set of plugs.
We used to when a car was going to the track for the first time get some leaded gas so we could read the plugs better before wide bands became more affordable.
Bruce
If not you don't have a perfect comparison. When you pull the exhaust, typically you are going to get more suck from the headers without the back pressure and intern pull more through the carb. Not in all cases but most the time it requires some minor tinkering with the carb to keep the air fuel ratios the same..... Once you get a wideband on your car you can better access the situation. you might also be able to do some more tuning and get a small amount of et there. It will also allow you to see were you are across the whole power band to ensure your AFR is as close to the desired value as possible.
In terms of reading the plugs was the car shutdown right at the top end? If not you could be getting misleading results if you drove it back to the pits... Also reading plug with unleaded fuel is not as good a tool as it was with leaded gas. It can still be used (I don't like to) but it takes more time to color a set of plugs.
We used to when a car was going to the track for the first time get some leaded gas so we could read the plugs better before wide bands became more affordable.
Bruce
01-18-2012, 09:15 AM
#66
Thanks Bob for the compliment.....I'm glad you like the car. Oh, and I hope your back is better......I know mine is much better after surgery!
This is true. Like I said before I tested this.......even if it's just enough to push me over that little extra bit, it's worthwhile. I just probably won't pull it off for every trip to the track. I'll keep that option in my hip pocket for when I get to a track much closer to sea level and if the car is running 11.0's, the exhaust will come off..........
This is true. Like I said before I tested this.......even if it's just enough to push me over that little extra bit, it's worthwhile. I just probably won't pull it off for every trip to the track. I'll keep that option in my hip pocket for when I get to a track much closer to sea level and if the car is running 11.0's, the exhaust will come off..........
01-19-2012, 08:49 PM
#71
Tonight I put the exhaust system back on and screwed in a couple narrow band O2 sensors into my new bungs, just to be sure I got the bungs positioned where I intended to have enough clearance for the sensors. Looks like they'll work just fine. I have a couple plugs coming from Summit in a few days to screw in until I have access to a wideband.
02-14-2012, 04:35 PM
#76
Yep, just finally getting around to picking one up. This is my first carbureted car in over 15 years, so I didn't have one on hand. Prosystems said they set the carb up for my altitude out here, but at 76/86 at this altitude.......I have to think it's rich. Time will tell I suppose. How did your Prosystems 950 come jetted for your 6.0L at sea level?
02-14-2012, 04:42 PM
#77
Yep, just finally getting around to picking one up. This is my first carbureted car in over 15 years, so I didn't have one on hand. Prosystems said they set the carb up for my altitude out here, but at 76/86 at this altitude.......I have to think it's rich. Time will tell I suppose. How did your Prosystems 950 come jetted for your 6.0L at sea level?
02-14-2012, 04:47 PM
#78
They have pretty much nailed the main jetting on the 3 versions of my carb that they sent. They just have not done very well on the idle mixture, cruise mixture and tip in. From what I can tell, their strategy is to just fatten up the idle until any hesitation is gone and call it a day. IF that happens to be 11:1 AFR then "that is what it wants" LOL. If you want clean plugs and any type of fuel economy, that will be up to you. But, it gives me something to play with.
02-14-2012, 04:51 PM
#80
By the way......I'm going to be looking to guys like you when I really do start fine tuning the driveability of this thing because I'm new to all that. But I think (unless I really get bored) I won't be messing with anything out here except optimizing the idle and WOT because I'll be moving back to near sea level in less than 6 months and will have to go through it all again anyway.