I've heard of this ratio before as relating, somehow to engine performance, but I'm really not sure at all how it does. Can anyone enlighten me?
Thanks,
SWB
Runner Volume To Cylinder Volume Ratio?
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bill jones
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-first off is you need to know what you have for the total volume of the intake runner compared to the cylinder volume at BDC.
-Example is a 355ci engine equals 727cc plus the chamber volume which might be about 60 for a 13:1 compression ratio so you have total cylinder volume at BDC of about 787cc.
-So if you had 220cc intake port in the head and another 350cc or so average in a single 4 barrel manifold runner you have 570cc which is about 72.4% of the total cylinder volume.
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-Once you go thru several engines and get the numbers and then you decide to make a change, you might find a trend that would help you.
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-One thing it may lead to on a single 4 barrel engine is ideas centered around what you would do with the four long runners vs the 4 short ones, like rocker ratio and/or cam timing changes different between those short and long runners.
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-But measuring the runner volume of single four manifolds and getting accurate results is a lot of work and I found it to be a way to waste a summer or two with less than any significant rewards.
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-But if you had stack injection or an isolated intake runner system then I think this becomes a very important detail that you can change fairly easy and you can see the results.
-I pay a lot more attention to stack injection volume vs length for use at Bonneville or for sprint car engines and the rewards are much easier to find.
-Example is a 355ci engine equals 727cc plus the chamber volume which might be about 60 for a 13:1 compression ratio so you have total cylinder volume at BDC of about 787cc.
-So if you had 220cc intake port in the head and another 350cc or so average in a single 4 barrel manifold runner you have 570cc which is about 72.4% of the total cylinder volume.
---------------------------------
-Once you go thru several engines and get the numbers and then you decide to make a change, you might find a trend that would help you.
-----------------------------------
-One thing it may lead to on a single 4 barrel engine is ideas centered around what you would do with the four long runners vs the 4 short ones, like rocker ratio and/or cam timing changes different between those short and long runners.
------------------------------------------
-But measuring the runner volume of single four manifolds and getting accurate results is a lot of work and I found it to be a way to waste a summer or two with less than any significant rewards.
-------------------------------------
-But if you had stack injection or an isolated intake runner system then I think this becomes a very important detail that you can change fairly easy and you can see the results.
-I pay a lot more attention to stack injection volume vs length for use at Bonneville or for sprint car engines and the rewards are much easier to find.
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Steve Smith
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- Joined: Mon Nov 15, 2004 12:11 pm
- Location: Las Vegas, Nevada
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could you elaborate on what makes this an important detail? I have individual intake runners on a straight six motor and have wondered if I would see more than subtlties by varying runner and velocity stack length. Because of packaging a longer stack requires a shorter manifold. Does this trade off change anything.
I appreciate any insight you'll offer...
Steve
Bill,But if you had stack injection or an isolated intake runner system then I think this becomes a very important detail that you can change fairly easy and you can see the results
could you elaborate on what makes this an important detail? I have individual intake runners on a straight six motor and have wondered if I would see more than subtlties by varying runner and velocity stack length. Because of packaging a longer stack requires a shorter manifold. Does this trade off change anything.
I appreciate any insight you'll offer...
Steve
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Guest
There's no such thing as cylinder volume to runner volume ratio. Volume is a poor way to judge an intake runner unless it's in terms of relative comparison between the same cylinder head. Volume only exists as the result of runner length, and cross sectional area.
You can't determine a ratio like that for even a cross sectional area as it is all dependant on how the engine is to be utilized.
You can't determine a ratio like that for even a cross sectional area as it is all dependant on how the engine is to be utilized.
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bill jones
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-what is this 6 cylinder engine used for? type of body? rpm range etc?
-what are you using, side draft carburetors? stack injection? EFI or mechanical FI? what fuel, gas or methanol or something other?
-what rpm range? all of that WFO or is there some part throttle like in road racing?
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-If you are using something like side draft Webers, it is difficult to measure the volume of the entire intake stack using a fluid because of the places the fluid can leak away.
-then there is the issue of the length of the runner-valve to the bellmouth- that should coincide within your rpm range.
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-On the 122ci Pinto we run at Bonneville we have like Hilborn injectors with a fairly short manifold and then we have a variety of stacks that may be tapered or straight and again these are in different lengths.
-typically I like to see at least 100% to 130% of the total cylinder volume (at BDC) within the individual intake conduits.
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-we have about 540cc total in the cylinder at BDC.
-intake port is: 3.00" long and holds 91cc
-injector body is: 3.25" long and holds 128
-shortest stack is 6.50" long and holds 308
-so that gives us 12-3/4" of port length and 527CC's of volume so the intake volume is about 97.6% of the cylinders volume.
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-we have:
-a longer stack that is 9.5" long and holds 417cc's
-so this is a total length of 15-3/4" long and 636 total cc's so that is 117.8% of the cylinder volume.
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-The situation as Bonneville is like no other I know if because once you get into top gear the little engine is basically stalled and does good to gain maybe 40rpm to on a really good day maybe 200rpm for a full mile
-So we can try to get the car faster before the last shift and then we work on getting something more than 40 rpm in that last mile.
-If we can't make the car faster before the last shift whatever we do for the full mile has to be dead nuts right or the car will not gain even one rpm.
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-So the stacks can help us or hurt us maybe a full MPH before the last shift and can help us or hurt us during the full mile at WFO.
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-I think the acceleration rate of the car usually has the most input as to how fast or how quick your car is, and that would likely take something other than what we experience at Bonneville.
-We are sometimes looking for one or two tenths of one MPH out of 160 or so and when we find something that is a full MPH or more that's a happy day.
-But I can say that we run the fastest with the biggest flattappet cam that
Crane makes, and we had a set of 1-7/8" and a set of 2" headers and changing headers ALWAYS showed us something.
---------------------------------
-the big cam was something like 7 mph over the best of two other cams we tried, the 1-7/8" headers were 10 mph of a set of small street sized headers and the fuel injection was 16mph over a set of individual Mikunis.
-Granted there may have been other issues involved but I ain't going back to find out.
-what are you using, side draft carburetors? stack injection? EFI or mechanical FI? what fuel, gas or methanol or something other?
-what rpm range? all of that WFO or is there some part throttle like in road racing?
-------------------------------------------
-If you are using something like side draft Webers, it is difficult to measure the volume of the entire intake stack using a fluid because of the places the fluid can leak away.
-then there is the issue of the length of the runner-valve to the bellmouth- that should coincide within your rpm range.
-----------------------------------------
-On the 122ci Pinto we run at Bonneville we have like Hilborn injectors with a fairly short manifold and then we have a variety of stacks that may be tapered or straight and again these are in different lengths.
-typically I like to see at least 100% to 130% of the total cylinder volume (at BDC) within the individual intake conduits.
-----------------------------------------
-we have about 540cc total in the cylinder at BDC.
-intake port is: 3.00" long and holds 91cc
-injector body is: 3.25" long and holds 128
-shortest stack is 6.50" long and holds 308
-so that gives us 12-3/4" of port length and 527CC's of volume so the intake volume is about 97.6% of the cylinders volume.
---------------------------------------------
-we have:
-a longer stack that is 9.5" long and holds 417cc's
-so this is a total length of 15-3/4" long and 636 total cc's so that is 117.8% of the cylinder volume.
----------------------------------------
-The situation as Bonneville is like no other I know if because once you get into top gear the little engine is basically stalled and does good to gain maybe 40rpm to on a really good day maybe 200rpm for a full mile
-So we can try to get the car faster before the last shift and then we work on getting something more than 40 rpm in that last mile.
-If we can't make the car faster before the last shift whatever we do for the full mile has to be dead nuts right or the car will not gain even one rpm.
-------------------------------------
-So the stacks can help us or hurt us maybe a full MPH before the last shift and can help us or hurt us during the full mile at WFO.
-------------------------------------
-I think the acceleration rate of the car usually has the most input as to how fast or how quick your car is, and that would likely take something other than what we experience at Bonneville.
-We are sometimes looking for one or two tenths of one MPH out of 160 or so and when we find something that is a full MPH or more that's a happy day.
-But I can say that we run the fastest with the biggest flattappet cam that
Crane makes, and we had a set of 1-7/8" and a set of 2" headers and changing headers ALWAYS showed us something.
---------------------------------
-the big cam was something like 7 mph over the best of two other cams we tried, the 1-7/8" headers were 10 mph of a set of small street sized headers and the fuel injection was 16mph over a set of individual Mikunis.
-Granted there may have been other issues involved but I ain't going back to find out.
-
Steve Smith
- Pro
- Posts: 266
- Joined: Mon Nov 15, 2004 12:11 pm
- Location: Las Vegas, Nevada
Hey Bill,I fear Guest provided the answer for my level of understanding. I'm using triple sidedraft Webers on a roadrace engine running from about 4000-8000 RPM.
I've read repeated references to tuning the motor with differeent length tracts and or velocity stacks. Your message triggered the question of just how much effect can we see with variations of plus or minus an inch or two. I suspect it'll be a 300 RPM max peak variation but I've no dyno experience to support that. Does that agree with your observations or are results more dramatic.
frankly, I don't think I'm a good enough tuner or driver to exploit a 300 RPM variation.
Steve
I've read repeated references to tuning the motor with differeent length tracts and or velocity stacks. Your message triggered the question of just how much effect can we see with variations of plus or minus an inch or two. I suspect it'll be a 300 RPM max peak variation but I've no dyno experience to support that. Does that agree with your observations or are results more dramatic.
frankly, I don't think I'm a good enough tuner or driver to exploit a 300 RPM variation.
Steve
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bill jones
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- Joined: Sun Sep 05, 2004 6:38 pm
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-Carburetors are an entire different deal than dealing with FI because you still have to waste some airflow to get the fuel out of the float bowls, and typically the fuel takes a lot more of the space when it's a carburetor.
-I can tell you this about a asphalt oval track sprint car that I build the engine for, it likes long tall stacks and that is for an rpm range of about 4500 to 8500.
-The one thing we have that beats the high buck engines is the throttle response off the corners but we still have all the power we need on the rest of the track.
-I attribute our success to the fact we run smaller and longer stacks than any of those guys, our heads and injectors are flowed and ported etc as a unit, I have my own ideas on how the throttle blades should open and I don't see anybody else doing their linkages from the left side to the right side the way I do.
--------------------------------
-Guest is right in the fact you have to know how the engine is used and tune around those factors, such as you can't apply much of drag racing tuning ideas to road racing or to Bonneville or viceversa.
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-There are so many people who have dynos and use'm every day but I don't see much that I can apply from their 600rpm per second results to what I deal with.
-------------------------------------
-With most vehicles, if you wanted to change the individual stack length you always end up with the stacks hitting something and limiting the excersize or you can't get the stacks sealed up inside an airbox so you lose the ram air effect.
-Same thing with headers, how do you get all that tubing diameter and length to fit?
-I wonder how many people can tell you the actual air box pressures at speed or even know what they have for fuel flow or fuel pressure.
-I believe that the greatest help in any of this tuning is data acquisition.
--------------------------------
-As far as an inch or two making a difference, when you have that inch or two to play with and you try it you usually find that one change may not do anything until you change something else, so you need to keep good records and be able to analyze the results.
-Lots of times I've seen where every change I've tried makes the car slower, so then you have to rethink what happened and maybe try the same changes in a difference sequence.
-I can tell you this about a asphalt oval track sprint car that I build the engine for, it likes long tall stacks and that is for an rpm range of about 4500 to 8500.
-The one thing we have that beats the high buck engines is the throttle response off the corners but we still have all the power we need on the rest of the track.
-I attribute our success to the fact we run smaller and longer stacks than any of those guys, our heads and injectors are flowed and ported etc as a unit, I have my own ideas on how the throttle blades should open and I don't see anybody else doing their linkages from the left side to the right side the way I do.
--------------------------------
-Guest is right in the fact you have to know how the engine is used and tune around those factors, such as you can't apply much of drag racing tuning ideas to road racing or to Bonneville or viceversa.
-------------------------------------
-There are so many people who have dynos and use'm every day but I don't see much that I can apply from their 600rpm per second results to what I deal with.
-------------------------------------
-With most vehicles, if you wanted to change the individual stack length you always end up with the stacks hitting something and limiting the excersize or you can't get the stacks sealed up inside an airbox so you lose the ram air effect.
-Same thing with headers, how do you get all that tubing diameter and length to fit?
-I wonder how many people can tell you the actual air box pressures at speed or even know what they have for fuel flow or fuel pressure.
-I believe that the greatest help in any of this tuning is data acquisition.
--------------------------------
-As far as an inch or two making a difference, when you have that inch or two to play with and you try it you usually find that one change may not do anything until you change something else, so you need to keep good records and be able to analyze the results.
-Lots of times I've seen where every change I've tried makes the car slower, so then you have to rethink what happened and maybe try the same changes in a difference sequence.
As I have even seen a few others in here state, average cross sectional area is what I go by. That takes into account the length of the port too.
Over the last 15 years I developed an Excel Spread Sheet that has avg cross sec vs piston speed. If this is done properly, I feel as though "Trends" can be established. Not absolutes, but Trends.
Hope this helps.......
Over the last 15 years I developed an Excel Spread Sheet that has avg cross sec vs piston speed. If this is done properly, I feel as though "Trends" can be established. Not absolutes, but Trends.
Hope this helps.......
Jay Allen
CAMSHAFT INNOVATIONS
www.camshaftinnovations.com
CAMSHAFT INNOVATIONS
www.camshaftinnovations.com
On another thread I asked for some opinions about computer simulation programs. I have several, but no real engine building experience so can't say how good they may be predicting things. However, Engine Analyser and Dynomation both (others too I expect) allow adjusting areas/volumes and intake tract length. Dynomation also calculates taper in both the intake and exhaust. If you have an engine and know parameters and dyno numbers that can be plugged in, you can determine how well they may predict. Then, as was pointed out in that thread, the computer may suggest what happens with a change. Intake length, taper and areas, thus volume, can have a big impact on peak numbers, rpm at peak etc and may allow an educated guess at what happens when you change a part. As Bill says, may be easy to waste lot of time measuring and not accomplishing much. In the end, have to see on the dyno or race track though.
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bill jones
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-The main thing I learned with the computer programs is to get any decent answers you had to know what you had everywhere inside your engine.
-I made up a printed work sheet for Allan's Engine Expert and for Dynomation so I could keep all the data on a page in columns, and I entered all the engine parameters that the program asked for as the first column with a section below that allowed me to enter the results spit out by the programs.
-Then I could go along and make one change at a time in each of the next columns and see the results.
-You can get about 8 changes to a page.
--------------------------------------------------
-Once you get to where you can compare these single or maybe even two or three change combinations at one time you can chase the results around pretty good and usually find the upward trends.
--------------------------------------
-I do believe the programs are severely limited as to the quickness of rpm that your engine may accelerate at and if you are at altitude and could a sh-t less about sea level numbers you HAVE to take the program results as only a somewhat generalized trend.
-I made up a printed work sheet for Allan's Engine Expert and for Dynomation so I could keep all the data on a page in columns, and I entered all the engine parameters that the program asked for as the first column with a section below that allowed me to enter the results spit out by the programs.
-Then I could go along and make one change at a time in each of the next columns and see the results.
-You can get about 8 changes to a page.
--------------------------------------------------
-Once you get to where you can compare these single or maybe even two or three change combinations at one time you can chase the results around pretty good and usually find the upward trends.
--------------------------------------
-I do believe the programs are severely limited as to the quickness of rpm that your engine may accelerate at and if you are at altitude and could a sh-t less about sea level numbers you HAVE to take the program results as only a somewhat generalized trend.
The reason I brought this up, was because Darin Morgan had posted a reply to a question in which he stated that this was an important ratio to keep track of. I have heard this before and I have also heard about "throttled volume", however I believe that mostly relates to EGR performance at the OEM level and has little to do with racing (or does it?).
I do realize the importance of tuned lengths and also cross sectional sizing for maximum efficiency etc. These two elements however do not necessarily mean different induction volumes. We could have a long, small cross section runner or a short, large cross sectional runner, with both tuned to a different RPM range but of the same volume. If you had a "rule" for volume, it might make picking the length/area relatively simple?
I've also seen it stated that in plenum type manifolds, the plenum volume is dictated by the displacement of the engine? Again I'm aware of helmholtz formulas and such, but haven't really figured any ratios out.
Thanks,
SWB
I do realize the importance of tuned lengths and also cross sectional sizing for maximum efficiency etc. These two elements however do not necessarily mean different induction volumes. We could have a long, small cross section runner or a short, large cross sectional runner, with both tuned to a different RPM range but of the same volume. If you had a "rule" for volume, it might make picking the length/area relatively simple?
I've also seen it stated that in plenum type manifolds, the plenum volume is dictated by the displacement of the engine? Again I'm aware of helmholtz formulas and such, but haven't really figured any ratios out.
Thanks,
SWB