Individual throttle bodies need to be size for PEAK flow, not average flow.
Basically, 6 throttle bodies would need to be the same size as 1 throttle body.
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| Throttle Body Size https://slantsix.org/forum/viewtopic.php?t=42828 |
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| Author: | Supercharged SL6 [ Thu Dec 09, 2010 5:31 pm ] |
| Post subject: | Throttle Body Size |
The calculator in the megasquirt manuel says a throttle body with 4 45.5mm bores that flows 1000 CFM would only support a 455HP engine. That dosn't seem overly large for a supercharged engine that may make 300-350HP or is it. |
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| Author: | Joshie225 [ Thu Dec 09, 2010 9:17 pm ] |
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I think you probably looked at the requirements for individual throttle per cylinder, independent runner manifolds rather than plenum manifolds. |
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| Author: | Sam Powell [ Wed Dec 15, 2010 4:37 am ] |
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He must mean 1000 total? The post is unclear about that. You would think 1000 cfm would support more than 450HP. Just a seat of the pants response based on the reported hp figures for carbureted cars with 1000 cfm Demons and such. If you are right about the configuration of the TB's then you would also think 6x45 mm bores would supply more than 1000 CFM. Again, just a seat of the pants response without doing the math. The 60 mm TB on my engine is the same size as the one on the Buick GN which put out around 300 HP. Published figures of 275 were short of actual dyno figures for insurance reasons at the time. Sam |
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| Author: | emsvitil [ Wed Dec 15, 2010 3:18 pm ] |
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Individual throttle bodies need to be size for PEAK flow, not average flow. Basically, 6 throttle bodies would need to be the same size as 1 throttle body.
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| Author: | Sam Powell [ Wed Dec 15, 2010 8:15 pm ] |
| Post subject: | |
I think I can see that. Each individual one flows only while it's valves are open. Which is true of a single one as well. But are there not times when more than one intake valve is open at a time. If so then maybe the total flow of a single TB would be slightly higher than each individual one on multiple runners. This is just ruminations on my part, based on no real knowledge. It is kind of like the wise a** kid at the back of the class saying "Yeah but". Sam |
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| Author: | emsvitil [ Wed Dec 15, 2010 9:18 pm ] |
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The graph shows individual cylinders, average flow and total. You can see the total is the sum of the 2 cylinders next to each other in the firing order and is slightly above and below the average. Also the average is just about the same as individual peak and the total. For > 6 cylinders, the total and average will be above individual cylinders peaks. For less than 6, the total and average will be below the individual cylinders. So you need to size your carb at whatever is greater. For less than 6 cylinders, size the carb as if the engine has 6 cylinders (whatever displacement of your cylinders) For greater than 6 cylinders, size the carb on total displacement For 6 cylinders, either way works. |
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| Author: | emsvitil [ Wed Dec 15, 2010 10:36 pm ] |
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Let's see if this works........ here's a spreadsheet to look at: See if you can open Intake_CFM (may have to save it, never tried this before, let me know if you can get the file) http://cid-935e825b2a66d084.office.live ... ublic?uc=1 |
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| Author: | Sam Powell [ Thu Dec 16, 2010 5:48 pm ] |
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I think it worked. I saved it to disk. It seems like cam profile would effect the shape of things. Is that not right? Sam |
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| Author: | emsvitil [ Thu Dec 16, 2010 6:17 pm ] |
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Quote: I think it worked. I saved it to disk. It seems like cam profile would effect the shape of things. Is that not right?
yes, that's on sheet 1...........
Sam |
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| Author: | Sam Powell [ Fri Dec 17, 2010 5:20 am ] |
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Oops. I didn't notice. Thanks. Where did you get that? Sam |
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| Author: | Sam Powell [ Fri Dec 17, 2010 5:29 am ] |
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Actually I went back and tried to open it from my saved files, and it would not open. I got a page with four titles in blue, and they were not in a spread sheet. Or did not appear to be. One said "Skyline" or some such thing. I think instead of saving the spread sheet, it saved a group of titles. I left the letters HTML after xls when I saved it. Should I have deleted those last four letters? This all does not really matter, it has just become an interesting curiosity at this point. Sam |
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| Author: | emsvitil [ Fri Dec 17, 2010 1:34 pm ] |
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Quote: Oops. I didn't notice. Thanks. Where did you get that?
'download' is underSam 'more' when you scroll over the file save as .xls I made it. Although not quite true, I assumed a sinusoidal curve from valve open to valve close with peak flow in the middle. Figured it was close enough to get an idea of what was going on........ |
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