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1500 CFM anyone?
- Thread starter GregW
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anthony7777
Yoda
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Re: 1500 CFM anyone up-date
gregw,from the angle the photo was shot it didnt look as if you had all that much room,k&n,k&n,k&n,etc,etc. /ubbthreads/images/graemlins/lol.gif
gregw,from the angle the photo was shot it didnt look as if you had all that much room,k&n,k&n,k&n,etc,etc. /ubbthreads/images/graemlins/lol.gif
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Re: 1500 CFM anyone up-date
Hi Greg,
You do absolutely beautiful work. Wish I could think up something for you to make for me!
D
Hi Greg,
You do absolutely beautiful work. Wish I could think up something for you to make for me!
D
RomanH
Jedi Knight
Offline
Re: 1500 CFM anyone up-date
Greg,
That looks great! I can't wait to hear what you have to say about this setup after you fire it up.
I have a TR6 and am thinking about getting the PRIrace twin ZS replacement setup but have not been able to find anyone that has used the Mikunis so I am a bit reluctant right now.
I await your next installment on this thread! /ubbthreads/images/graemlins/grin.gif
Roman
Greg,
That looks great! I can't wait to hear what you have to say about this setup after you fire it up.
I have a TR6 and am thinking about getting the PRIrace twin ZS replacement setup but have not been able to find anyone that has used the Mikunis so I am a bit reluctant right now.
I await your next installment on this thread! /ubbthreads/images/graemlins/grin.gif
Roman
OP
GregW
Yoda
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Re: 1500 CFM anyone up-date
Thank you Dave,
There are imperfections that the camera doesn’t show. I got bored sanding the stainless so there are rough spots that I will live with. I found an alternative to modifying the steering column. I sent the carbs back and had about 3/8” milled off the adaptors. They now sit closer to the engine but lower. They clear the column with room to spare, but the rear float bowl was touching the top of the pedal box. Today, I cut out a notch out of the pedal box and welded in a new piece. That should be the end of the modifications. I’ll start the throttle cable brackets this weekend.
Thank you Dave,
There are imperfections that the camera doesn’t show. I got bored sanding the stainless so there are rough spots that I will live with. I found an alternative to modifying the steering column. I sent the carbs back and had about 3/8” milled off the adaptors. They now sit closer to the engine but lower. They clear the column with room to spare, but the rear float bowl was touching the top of the pedal box. Today, I cut out a notch out of the pedal box and welded in a new piece. That should be the end of the modifications. I’ll start the throttle cable brackets this weekend.
RomanH
Jedi Knight
Offline
Re: 1500 CFM anyone up-date
Hi Greg,
I will ask Chris next time I talk to him. Have to determine what I will have to do about passing emissions testing since I can't legally use his engine breather. Thats another reason I'm hesitating. /ubbthreads/images/graemlins/frown.gif
Hi Greg,
I will ask Chris next time I talk to him. Have to determine what I will have to do about passing emissions testing since I can't legally use his engine breather. Thats another reason I'm hesitating. /ubbthreads/images/graemlins/frown.gif
Simon TR4a
Jedi Knight
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Re: 1500 CFM anyone up-date
Hi guys,
Sorry to jump in from the Triumph board, but I found the discussion interesting, especially the figures Dave Russell quoted on how much air you actually need to flow.
Working it out from first principles is actually very easy:
1) Round up the capacity of the engine to 3 litres (to make the mental arithmetic easier.)
2) It takes 2 crank revolutions for a 4 stroke engine to complete the induction cycle on each cylinder; so we will divide the capacity by 2 to find the maximum demand for air.
3) The cylinders fill very efficiently at low revs but less so at high rpm, lets assume approximately 80% efficiency.
4) So we need 6000 times 1.5 litres times 80%= 7200 litres of air.
5) 100 litres equals 3.53 cubic feet, so 7200 litres equals 254 cubic feet per minute.
Now the problem, I suspect, is that you don't want the induction system only just able to supply enough air, or their will be a substantial power loss as the engine sucks hard to get enough air, like trying to suck a thick milkshake through a atraw. I am not sure what sort of correction factor to apply for that, but the figure of 400cfm quoted by Dave sounds pretty reasonable.
Incidentally, air weighs about 0.08 lbs per cfm, so 400 cubic feet would weigh 32 lbs.
Simon.
Hi guys,
Sorry to jump in from the Triumph board, but I found the discussion interesting, especially the figures Dave Russell quoted on how much air you actually need to flow.
Working it out from first principles is actually very easy:
1) Round up the capacity of the engine to 3 litres (to make the mental arithmetic easier.)
2) It takes 2 crank revolutions for a 4 stroke engine to complete the induction cycle on each cylinder; so we will divide the capacity by 2 to find the maximum demand for air.
3) The cylinders fill very efficiently at low revs but less so at high rpm, lets assume approximately 80% efficiency.
4) So we need 6000 times 1.5 litres times 80%= 7200 litres of air.
5) 100 litres equals 3.53 cubic feet, so 7200 litres equals 254 cubic feet per minute.
Now the problem, I suspect, is that you don't want the induction system only just able to supply enough air, or their will be a substantial power loss as the engine sucks hard to get enough air, like trying to suck a thick milkshake through a atraw. I am not sure what sort of correction factor to apply for that, but the figure of 400cfm quoted by Dave sounds pretty reasonable.
Incidentally, air weighs about 0.08 lbs per cfm, so 400 cubic feet would weigh 32 lbs.
Simon.
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Re: 1500 CFM anyone up-date
Hi Simon,
The "brake specific fuel consumption" of the average engine is about 0.6 pounds of fuel per horsepower per hour. At an A/F ratio of 15:1, this would be 9 pounds of air per horsepower per hour. If the engine put out 167 hp at 6,000 rpm, this would come out at about 25 lb of air (313 cfm) & 1.7 lb of fuel (0.28 gallons) per minute. Assuming 100% volumetric effeciency. As you say, the carb flow of 400 cfm is somewhat higher & is a compromise between good low & high speed performance.
Incidentally, this would require around 17 gallons per hour of fuel flow.
Interesting numbers to toss around,
D
Hi Simon,
The "brake specific fuel consumption" of the average engine is about 0.6 pounds of fuel per horsepower per hour. At an A/F ratio of 15:1, this would be 9 pounds of air per horsepower per hour. If the engine put out 167 hp at 6,000 rpm, this would come out at about 25 lb of air (313 cfm) & 1.7 lb of fuel (0.28 gallons) per minute. Assuming 100% volumetric effeciency. As you say, the carb flow of 400 cfm is somewhat higher & is a compromise between good low & high speed performance.
Incidentally, this would require around 17 gallons per hour of fuel flow.
Interesting numbers to toss around,
D
OP
GregW
Yoda
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Re: 1500 CFM anyone up-date
Hi Simon,
Don’t be sorry, I don’t consider a forum to be a boundary. /ubbthreads/images/graemlins/cheers.gif The 1500 quote is a bit of an exaggeration. The three Mikunis are rated at about 630 CFM. When I was researching this little project, it probably would never have gotten past the planning stages if I hadn’t seen something similar on the market already. Talking with Mikuni, they seemed to think it would work and referred me to the guy who eventually made the adaptors. As I mentioned earlier, the 1.8L MGB with 2 Mikunis worked well, though it still needed some tweaking and a smaller accelerator pump nozzle reinstalled. I admit I’ve never attempted anything quite like this before. That’s what makes it fun. /ubbthreads/images/graemlins/thumbsup.gif
Hi Simon,
Don’t be sorry, I don’t consider a forum to be a boundary. /ubbthreads/images/graemlins/cheers.gif The 1500 quote is a bit of an exaggeration. The three Mikunis are rated at about 630 CFM. When I was researching this little project, it probably would never have gotten past the planning stages if I hadn’t seen something similar on the market already. Talking with Mikuni, they seemed to think it would work and referred me to the guy who eventually made the adaptors. As I mentioned earlier, the 1.8L MGB with 2 Mikunis worked well, though it still needed some tweaking and a smaller accelerator pump nozzle reinstalled. I admit I’ve never attempted anything quite like this before. That’s what makes it fun. /ubbthreads/images/graemlins/thumbsup.gif
Simon TR4a
Jedi Knight
Offline
Re: 1500 CFM anyone up-date
Thanks, Greg; I had realised you didn't mean it to be taken literally!
Much of this type of tech discussion about carburation and cam profiles and compression ratios is applicable to several cars of similar per cylinder displacement, so an MGB or TR4 and a Healey are all pretty close to 500cc. per cylinder. Also they all have basically similar architecture with 2 valves operating vertically, non-crossflow heads, long stroke to bore ratio, just some have siamesed ports while others don't.
So I am sure we can all learn from each other.
Regarding the Mikunis, I have no experience of them but have read good things about them, and have had a motorcycle with Amal carbs, which were sometimes used on hot Minis in the 1960's, again it was a 500cc single, a Matchless G80CS, with a 30 mm Amal carb.
Finally, thanks to Dave for the info on fuel consumption. I have noticed that lapping Mosport, as in the avatar photo, I used approximately a litre every lap. There are 3.8 litres to a US gallon, and a lap is 2.5 miles at that track, so about 10 miles per gallon. Each lap takes 2 minutes, 30 laps per hour, so 7.5 gallons will last 1 hour, at an average of 75mph!
(I only have 1.75 inch SUs with rich needles.)
Greg, let us know how it works out!
Simon.
Thanks, Greg; I had realised you didn't mean it to be taken literally!
Much of this type of tech discussion about carburation and cam profiles and compression ratios is applicable to several cars of similar per cylinder displacement, so an MGB or TR4 and a Healey are all pretty close to 500cc. per cylinder. Also they all have basically similar architecture with 2 valves operating vertically, non-crossflow heads, long stroke to bore ratio, just some have siamesed ports while others don't.
So I am sure we can all learn from each other.
Regarding the Mikunis, I have no experience of them but have read good things about them, and have had a motorcycle with Amal carbs, which were sometimes used on hot Minis in the 1960's, again it was a 500cc single, a Matchless G80CS, with a 30 mm Amal carb.
Finally, thanks to Dave for the info on fuel consumption. I have noticed that lapping Mosport, as in the avatar photo, I used approximately a litre every lap. There are 3.8 litres to a US gallon, and a lap is 2.5 miles at that track, so about 10 miles per gallon. Each lap takes 2 minutes, 30 laps per hour, so 7.5 gallons will last 1 hour, at an average of 75mph!
(I only have 1.75 inch SUs with rich needles.)
Greg, let us know how it works out!
Simon.
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Re: 1500 CFM anyone up-date
Only if you are running at max power & max rpm continuously for more than 40 minutes at a time. Not likely in a commute, but, in your location, maybe so. I can't even think of many race tracks where you could do this.
D
Only if you are running at max power & max rpm continuously for more than 40 minutes at a time. Not likely in a commute, but, in your location, maybe so. I can't even think of many race tracks where you could do this.
D
OP
GregW
Yoda
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Re: 1500 CFM anyone up-date
Well, the plot has thickened to the consistency of molasses, and my progress has slowed to that also. I sent the carburetors back to have the adaptors shaved down as I mentioned earlier. When they eventually came back they cleared the steering column. Problem solved. I had to lower a section of the pedal box by about a half-inch to clear the float bowl of the rear carb. Welded in a new piece, no fuss. Then I bolted all the carbs on and none of the throttle shafts lined up. #2 and #3 were offset by about an eighth of an inch! Aaaarrrr /ubbthreads/images/graemlins/cryin.gif guh! Turns out that the adaptor plates weren’t milled together. The amount shaved off was different for each and the angles were different also. What to do? I mulled it over for a while. I didn’t want to send them back, ‘cause they might come back wrong again, but take a long time. I decided to tackle it myself. Trying to salvage what I had, I decided on double u-joints. I found some joints that would fit length-wise but they had a smaller bore than the 10mm throttle shafts. Also, the throttle shafts were cut to the wrong length for what I wanted to do. So I wound up getting some 10mm rod, cut it to the right length for each carb and turned the ends so they would fit into the u-joints. Next, I cut a half inch out of the middle of the u-joint and fabricated a new lever that would fit on the u-joints 5/16” shaft. Here is the progress thus far.
Well, the plot has thickened to the consistency of molasses, and my progress has slowed to that also. I sent the carburetors back to have the adaptors shaved down as I mentioned earlier. When they eventually came back they cleared the steering column. Problem solved. I had to lower a section of the pedal box by about a half-inch to clear the float bowl of the rear carb. Welded in a new piece, no fuss. Then I bolted all the carbs on and none of the throttle shafts lined up. #2 and #3 were offset by about an eighth of an inch! Aaaarrrr /ubbthreads/images/graemlins/cryin.gif guh! Turns out that the adaptor plates weren’t milled together. The amount shaved off was different for each and the angles were different also. What to do? I mulled it over for a while. I didn’t want to send them back, ‘cause they might come back wrong again, but take a long time. I decided to tackle it myself. Trying to salvage what I had, I decided on double u-joints. I found some joints that would fit length-wise but they had a smaller bore than the 10mm throttle shafts. Also, the throttle shafts were cut to the wrong length for what I wanted to do. So I wound up getting some 10mm rod, cut it to the right length for each carb and turned the ends so they would fit into the u-joints. Next, I cut a half inch out of the middle of the u-joint and fabricated a new lever that would fit on the u-joints 5/16” shaft. Here is the progress thus far.
Last edited:
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Re: 1500 CFM anyone up-date
Pardon my primitive ideas, but lots of motorcycles use multiple throttle cables. Maybe not quite as clean looking, but a whole lot easier to install & adjust. Seems like you are doing it the really hard way?
D
Pardon my primitive ideas, but lots of motorcycles use multiple throttle cables. Maybe not quite as clean looking, but a whole lot easier to install & adjust. Seems like you are doing it the really hard way?
D
aeronca65t
Great Pumpkin
Offline
Re: 1500 CFM anyone up-date
I am enjoying reading about these various carb ideas, since it is a subject of real interest to me.
The tri-carb set looks great...that 6 carb set was very neat, but I guess, not practical.
Since some of you have mentioned the use of carbs used mostly on bikes (Mikunis and Amals) may I also suggest that you look at some of the carbs that are fitted to Harleys.
My car is a 1500 Spridget (Spitfire engine) and I am presently running one "S&S Super G" carb. It has a 2-1/8" almost straight through bore...very little "bump" for the venturi. I have fitted this carb with an adjustable main jet (an easy adaption from a smaller S&S carbs). It comes with an adjustable idle mix and adjustable acelerator pump. Very simple to adjust (no jets to replace) and even idles better than the the original Zenith/Stomberg single carb. Tuning the carb is like ajusting an old lawn mower.
You can also get the S&S 1-7/8 carb (again, with adjustable main jet, idle jet and acelerator pump). Most bike places will try to sell you an S&S with the Harley manifold, but if you talk to them, you should be able to get just the carb for $225 to $300. I worried about the float bowl flooding in hard corners (in my road racing application), but no problems at all.
Another similar carb is the old American-made Bendix carb available in 38 and 40 mm. Again, with a fully adjustable main jet and idle jet. You can get the 38 mm for about $250.
J&P Cycles sells all this stuff and also SU carbs (for bikes) and adjustable main-jet kits for Kehnin carbs.
More info about these carbs here:
https://www.jpcycles.com/productdetail.as...ge=&search=
https://www.jpcycles.com/productgroup.aspx?GID=0FB71CFD-05FC-40F4-807D-18266DAA8BD
I am presently looking at the Megasquirt fuel injection home-brew system and I have heard that someone out there has "hidden" the injectors in an SU carb. That isn't so important to me, but it seems that some of you guys might find that idea interesting.
By the way, my car 1500 cc car uses about 5.5 gallons per hour when racing on the single 2-1/8" carb. . Average rpm is likely to be about 5500
Here's my single S&S carb fitted to my car. This is not the best representation, since it shows a hasty "repair" when a carb stud came loose and we vise-gripped the carb on just before the start of a one hour enduro (it held up...I got second).
I am enjoying reading about these various carb ideas, since it is a subject of real interest to me.
The tri-carb set looks great...that 6 carb set was very neat, but I guess, not practical.
Since some of you have mentioned the use of carbs used mostly on bikes (Mikunis and Amals) may I also suggest that you look at some of the carbs that are fitted to Harleys.
My car is a 1500 Spridget (Spitfire engine) and I am presently running one "S&S Super G" carb. It has a 2-1/8" almost straight through bore...very little "bump" for the venturi. I have fitted this carb with an adjustable main jet (an easy adaption from a smaller S&S carbs). It comes with an adjustable idle mix and adjustable acelerator pump. Very simple to adjust (no jets to replace) and even idles better than the the original Zenith/Stomberg single carb. Tuning the carb is like ajusting an old lawn mower.
You can also get the S&S 1-7/8 carb (again, with adjustable main jet, idle jet and acelerator pump). Most bike places will try to sell you an S&S with the Harley manifold, but if you talk to them, you should be able to get just the carb for $225 to $300. I worried about the float bowl flooding in hard corners (in my road racing application), but no problems at all.
Another similar carb is the old American-made Bendix carb available in 38 and 40 mm. Again, with a fully adjustable main jet and idle jet. You can get the 38 mm for about $250.
J&P Cycles sells all this stuff and also SU carbs (for bikes) and adjustable main-jet kits for Kehnin carbs.
More info about these carbs here:
https://www.jpcycles.com/productdetail.as...ge=&search=
https://www.jpcycles.com/productgroup.aspx?GID=0FB71CFD-05FC-40F4-807D-18266DAA8BD
I am presently looking at the Megasquirt fuel injection home-brew system and I have heard that someone out there has "hidden" the injectors in an SU carb. That isn't so important to me, but it seems that some of you guys might find that idea interesting.
By the way, my car 1500 cc car uses about 5.5 gallons per hour when racing on the single 2-1/8" carb. . Average rpm is likely to be about 5500
Here's my single S&S carb fitted to my car. This is not the best representation, since it shows a hasty "repair" when a carb stud came loose and we vise-gripped the carb on just before the start of a one hour enduro (it held up...I got second).