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Bob_Spidell
Yoda
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Ah, right; I remembered you had something spicy on the intake. I guess the headers alone necessitate a richer mixture. Would love to see dyno numbers on that engine.
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Colortune for HD8 Carbs?
- Thread starter wangdango
- Start date
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Ah, right; I remembered you had something spicy on the intake. I guess the headers alone necessitate a richer mixture. Would love to see dyno numbers on that engine.
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I intend a rolling road run this winter - will follow up when that happens.
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Available needles.
https://www.sumidel.com/shop/category/-0125-fixed
https://www.sumidel.com/shop/category/-0125-fixed
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I have been following this thread for a bit. Instead of spending on the "colortune" why not buy a reasonably priced air fuel meter and stick it up the tail pipe.
They are easy to use and you can just dial in the proper mixture.
If you want to get fancy and have the equipment you can weld a bung to the headers and install it semi-permanently to use while driving, when done just remove and plug up the bung
They are easy to use and you can just dial in the proper mixture.
If you want to get fancy and have the equipment you can weld a bung to the headers and install it semi-permanently to use while driving, when done just remove and plug up the bung
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Cause it's more fun to fiddle. :wink-new:
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We'll make sure you get some non-freeway driving in when you get here!
RAC68
Darth Vader
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Joe/Steve,
Although I have never used an air/fuel meter, would the separation of front and rear sets of 3 cylinders (including the exhausts) be sufficient to allow for a clear reading and adjustment of each carburetor? Since many Healey models have 1 muffler and the BJ8 has 1 resonator, I would expect the gasses would mix at these points and average any readings. As a result of the exhaust gasses mixing, I would expect that each carburetor adjustment would have an effect on the total reading at the gauge but adjusting each carburetor could become even more confusing.
Please don't misunderstand, I am looking for something simple to help adjust my carburetors and would appreciate any clarification.
Ray(64BJ8P1)
Although I have never used an air/fuel meter, would the separation of front and rear sets of 3 cylinders (including the exhausts) be sufficient to allow for a clear reading and adjustment of each carburetor? Since many Healey models have 1 muffler and the BJ8 has 1 resonator, I would expect the gasses would mix at these points and average any readings. As a result of the exhaust gasses mixing, I would expect that each carburetor adjustment would have an effect on the total reading at the gauge but adjusting each carburetor could become even more confusing.
Please don't misunderstand, I am looking for something simple to help adjust my carburetors and would appreciate any clarification.
Ray(64BJ8P1)
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Where do you find a reasonably priced Air Fuel meter?
red57
Jedi Knight
Offline
I have been following this thread and hesitated to jump in because I don't want to start any arguments.
Brief background, I raced mine from '97 till '13 when I wrecked it and am still rebuilding slowly.
I am not, and have never been, a 'professional wrench' but rather a pretty fair mechanic and wanting to understand systems & how they work is what made me a car guy originally. In the years I was racing I learned a lot about SU carbs.
Steve is right - you need real data to know what is going on and I started using an air/fuel monitor about 2001 but it took several years of still melting pistons and other problems before I did more research on air/fuel monitors and found that the inexpensive 1 wire meters are not very useful (sorry Steve). What you need is an analog wideband gage copy & paste this (I don't know how to do links
https://www.jegs.com/i/AEM/017/30-5130/10002/-1 this is Jegs but Summit & Amazon & others sell them. They are not cheap but will tell you an actual number as opposed to the one wire gages that show a row of led lights and a general rich/lean. And as Steve says, you need two, one for each downtube.
I encourage all of you to do your own research - this will give you the data the rolling roads give you. It is also what modern fuel injected cars use for input into the computer engine management.
So, I went a step further in 2009 because I was tired of going lean at 5500-6000 and not being able to correct it so I bought two of the above wide band air/fuel ratio gages and also bought an aircraft EGT gage that is made for 6 cylinder aircraft engines so I could have a probe in each header branch to know the temps of each cylinder - model I bought is Aerospace Logic EGT-100-6P & I purchased it from Gulf Coast Avionics (was $575 in 2009). With this you have a choice of showing one cylinder, having it cycle thru them all at about 2-3 seconds on each, or have it constantly scan and show the hottest. So now I can not only monitor air/fuel but also what that does in terms of EGT. Saved me several melted pistons/distorted valves. I now generate most of what a rolling road does just with out HP & Torque info.
I have found that if you change anything in your motor: cam, compression ratio, flow characteristics, etc. you will be off in fuel mix if you stick with the stock needles.
I don't have a rolling road anywhere near me so this is my DIY method.
I started with the bonnet off and measuring rods in the tops of the SUs (See Des Hamill, "How to power tune SUs" for making measuring rods). Then, with a helper - go for a drive and determine where the measuring rods are at any given rpm under full throttle up to wherever your red-line may be - for me that is 6000. Once you know where the pistons are at any given full throttle rpm, you also know where in the needle you are.... then if you show lean (by the wide band air/fuel) at say 3500 rpm, you can figure where on the needle you need to shave a bit to richen it up. At the same time I watch the EGTs to make sure I am not over cooking.
Side note here on EGTs - all my questioning around race tracks almost no one could ever tell me what is the max EGT before damage - the best consensus I got from several old timers is 1250-1300*F is about tops before damaging (a couple guys suggested 1500 should be ok?)- not sure that is true but I have tried to stay below 1300F. This leads me to Stoichiometric, which is about 14.7:1 if I recall correctly - in my case if I set to 14.7:1 the EGTs went thru the roof and I have found that I need to be around 10:1 in order to keep the EGTs down under 1300F. Again, this is under full throttle.
So, once again I will stress I am not a pro, and your mileage may vary - I have only done this with my engine which is .060 over 9.25:1 compression, headers, triple HD6, 283 degree cam (at 0 lift) but not particularly high lift and considerable flow effort on the head. I now make my own needles whenever I change anything - I know it is a bit of overkill and if your motor is stock I wouldn't go thru all this, I would just tune as the manual says.
As you can imagine, I can go on for days about this s**t but after a while my head hurts....
Dave
Brief background, I raced mine from '97 till '13 when I wrecked it and am still rebuilding slowly.
I am not, and have never been, a 'professional wrench' but rather a pretty fair mechanic and wanting to understand systems & how they work is what made me a car guy originally. In the years I was racing I learned a lot about SU carbs.
Steve is right - you need real data to know what is going on and I started using an air/fuel monitor about 2001 but it took several years of still melting pistons and other problems before I did more research on air/fuel monitors and found that the inexpensive 1 wire meters are not very useful (sorry Steve). What you need is an analog wideband gage copy & paste this (I don't know how to do links
https://www.jegs.com/i/AEM/017/30-5130/10002/-1 this is Jegs but Summit & Amazon & others sell them. They are not cheap but will tell you an actual number as opposed to the one wire gages that show a row of led lights and a general rich/lean. And as Steve says, you need two, one for each downtube.I encourage all of you to do your own research - this will give you the data the rolling roads give you. It is also what modern fuel injected cars use for input into the computer engine management.
So, I went a step further in 2009 because I was tired of going lean at 5500-6000 and not being able to correct it so I bought two of the above wide band air/fuel ratio gages and also bought an aircraft EGT gage that is made for 6 cylinder aircraft engines so I could have a probe in each header branch to know the temps of each cylinder - model I bought is Aerospace Logic EGT-100-6P & I purchased it from Gulf Coast Avionics (was $575 in 2009). With this you have a choice of showing one cylinder, having it cycle thru them all at about 2-3 seconds on each, or have it constantly scan and show the hottest. So now I can not only monitor air/fuel but also what that does in terms of EGT. Saved me several melted pistons/distorted valves. I now generate most of what a rolling road does just with out HP & Torque info.
I have found that if you change anything in your motor: cam, compression ratio, flow characteristics, etc. you will be off in fuel mix if you stick with the stock needles.
I don't have a rolling road anywhere near me so this is my DIY method.
I started with the bonnet off and measuring rods in the tops of the SUs (See Des Hamill, "How to power tune SUs" for making measuring rods). Then, with a helper - go for a drive and determine where the measuring rods are at any given rpm under full throttle up to wherever your red-line may be - for me that is 6000. Once you know where the pistons are at any given full throttle rpm, you also know where in the needle you are.... then if you show lean (by the wide band air/fuel) at say 3500 rpm, you can figure where on the needle you need to shave a bit to richen it up. At the same time I watch the EGTs to make sure I am not over cooking.
Side note here on EGTs - all my questioning around race tracks almost no one could ever tell me what is the max EGT before damage - the best consensus I got from several old timers is 1250-1300*F is about tops before damaging (a couple guys suggested 1500 should be ok?)- not sure that is true but I have tried to stay below 1300F. This leads me to Stoichiometric, which is about 14.7:1 if I recall correctly - in my case if I set to 14.7:1 the EGTs went thru the roof and I have found that I need to be around 10:1 in order to keep the EGTs down under 1300F. Again, this is under full throttle.
So, once again I will stress I am not a pro, and your mileage may vary - I have only done this with my engine which is .060 over 9.25:1 compression, headers, triple HD6, 283 degree cam (at 0 lift) but not particularly high lift and considerable flow effort on the head. I now make my own needles whenever I change anything - I know it is a bit of overkill and if your motor is stock I wouldn't go thru all this, I would just tune as the manual says.
As you can imagine, I can go on for days about this s**t but after a while my head hurts....
Dave
Last edited:
Bob_Spidell
Yoda
Offline
"... in my case if I set to 14.7:1 the EGTs went thru the roof ..."
Yup. Stoichiometric should produce max EGT; although timing has a big effect as well. Max EGT is known as 'peak EGT' in an aircraft--if you plot EGT vs fuel flow there is a distinctive peak in the curve--and many aircraft have charts which can tell you the percentage of max power based on RPM, EGT and manifold pressure. Max power is found 'rich of peak,' 'max economy' is found lean of peak, but operating LOP requires careful monitoring--EGT goes down--lest you suffer detonation. Operating LOP often requires careful balancing of fuel flow to each cylinder, and at least one company will sell you a set of injectors to perfectly balance the combustion in all 6.
Yup. Stoichiometric should produce max EGT; although timing has a big effect as well. Max EGT is known as 'peak EGT' in an aircraft--if you plot EGT vs fuel flow there is a distinctive peak in the curve--and many aircraft have charts which can tell you the percentage of max power based on RPM, EGT and manifold pressure. Max power is found 'rich of peak,' 'max economy' is found lean of peak, but operating LOP requires careful monitoring--EGT goes down--lest you suffer detonation. Operating LOP often requires careful balancing of fuel flow to each cylinder, and at least one company will sell you a set of injectors to perfectly balance the combustion in all 6.
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Just finished the 1000 mile run for Monterey Healey Week Rendezvous on my UN (Moss rich) needles. Car ran great on the freeway and I achieved > 19 mpg on level roads if I kept it around 65. However the idle is bad with a fast blurping and continuous small backfiring going downhill at low speed.
There is an air leak in the slip joint of my #1 header downpipe and the rear carb doesn't seem to be tunable so I'm removing both carbs for overhaul.
Have received both the new edition of the Des Hammill book and Brooklands: SU Carburetters Tuning Tips & Techniques so I have a lot of reading ahead - thanks Dave for the Hammill recommendation above.
There is an air leak in the slip joint of my #1 header downpipe and the rear carb doesn't seem to be tunable so I'm removing both carbs for overhaul.
Have received both the new edition of the Des Hammill book and Brooklands: SU Carburetters Tuning Tips & Techniques so I have a lot of reading ahead - thanks Dave for the Hammill recommendation above.
red57
Jedi Knight
Offline
Steve, I think you will enjoy your reading - you seem to me like someone who enjoys this kind of challenge.
Maybe I'm just not as smart others but in my years of fiddling with SUs, there have been several times when I had an 'a hah' moment and felt I finally understood how they work......Then something else would happen and I would feel like I just don't get it.... Then another 'a hah' and repeat. Over the years I would ask questions of all the hot-shot race engine gurus I could find and most revealed they really didn't understand them either but convinced you they did by their confidence.
An example is the large number that recommended removing the dashpot springs for racing since the piston would rise faster and open the bore to allow more air sooner (the holy grail of horse power)- only problem is if the piston is at full height at say 3500rpm, then there will be no metering of fuel as the revs go up - a sure way to go lean at high rpms.
I'll bet you will be making your own needles soon!
Dave
Maybe I'm just not as smart others but in my years of fiddling with SUs, there have been several times when I had an 'a hah' moment and felt I finally understood how they work......Then something else would happen and I would feel like I just don't get it.... Then another 'a hah' and repeat. Over the years I would ask questions of all the hot-shot race engine gurus I could find and most revealed they really didn't understand them either but convinced you they did by their confidence.
An example is the large number that recommended removing the dashpot springs for racing since the piston would rise faster and open the bore to allow more air sooner (the holy grail of horse power)- only problem is if the piston is at full height at say 3500rpm, then there will be no metering of fuel as the revs go up - a sure way to go lean at high rpms.
I'll bet you will be making your own needles soon!
Dave