Intake manifold hard data (UPDATED: 5/11/12)
Oct 30, 2007 | 03:16 AM
#41
How do I change this text
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Last of it, for now
I wish I was alittle better at math
Intake Ram Pipe Diameter
This is the easiest to figure out. The velocity in the plenum intake pipe should not be higher than 180 ft/sec at maximum rpm. The formula to figure out the diameter pipe that should be used is for a given velocity is:
D = ^(CID × VE × RPM) ÷ ( V × 1130) Where: D = Pipe Diameter CID = Cubic Inch Displacement VE = Volumetric Efficiency V = Velocity in ft/sec If you're dealing with liters, change CID to liters and the constant to 18.5 so the formula will look like this: D = ^(Liters × VE × RPM) ÷ (V × 18.5) An example for a 153 cubic inch 4 cylinder with a 85% VE, revving to 6000 rpm would and a desired 180 ft/sec air speed though the intake pipe would look like this:
D = ^(153 × 0.85 × 6000) ÷ (180 × 1130) = 1.96 You would need an intake pipe that has a 1.96" inside diameter to have 180 ft/sec air velocity at 6000 rpm for that engine. In other words the engine would need a little over 3 square inches of intake pipe area.
Plenum Volume
There is not going to be a simple answer to the needed plenum volume for a given application or rpm range. The good thing about plenum volume is that there is a pretty wide range that it can be and still be effective, so general rules work well. The following guidelines are for engine operating in the 5000-6000 rpm rage. V8's with one large plenum feeding all 8 cylinders does not work all that well as far as the Helmholtz resonator goes, but if this is the case, plenum volume should be about 40-50% of total cylinder displacement. On a four cylinder engine 50- 60% works well. For 3 cylinders (6 cylinder engine with two plenums), each plenum needs to be about 65-80% of the 3 cylinders it feeds. If a boost is desired in a higher rpm range, closer 7000-7500 rpm, the plenum will need to be 10-15% smaller. To get a boost in the 2500-3500 rpm range, it will need to need about 30% larger. The plenum size of a Helmholtz resonator may go against the typical plenum size rules, but the rules change when the resonator is being used. The whole Idea of a plenum is to allow the gases to slow down and gain density. The Helmholtz plenum makes a dense charge by use of pressure waves, in the same way tuned port intake runners work. this plenum sizing method does not apply to engines that to not use a tuned intake pipe. Many engines simply have the air cleaner assembly directly on the carburetor or throttle body having very little intake length. In those cases the Helmholtz resonator system does not work.
Intake Ram Pipe
The last thing to adjust is the length of the intake ram pipe. It is possible to make an adjustable pipe that can be made longer or shorter for testing purposes. For a starting point figure a 13" long pipe will help at about 6000 rpm. For each 1000 rpm drop in rpm add 1.7" and subtract 1.7" per 1000 rpm increase. This is just a starting point. The inlet of the pipe should have about a 1/2" radius for smooth flow. Once you get a baseline (you must do a power pull and get a baseline), which can be done at the track or on a dyno. Then try moving the pipe 1/2" in either direction as see how power improves. The dyno may be a little deceiving, since peak hp my go up but average power may drop. Track testing will be best, since you will be testing in actual racing condition and can tune the pipe for the best times. It is usually best for average power if the intake ram pipe is tuned about 1000 rpm lower than the intake runner length.
Multiple Ram Pipes
Most engines will have more than 1 throttle bore feeding the cylinders. In this case you must figure out the total area of intake pipe needed to figure out what size each pipe should be. In the first example, the 4 cylinder engine needed a 1.96 diameter intake ram pipe. If that particular engine had a two barrel carburetor (or two single barrel carburetors), you would need two pipes each one having 1/2 the area of a 1.96" pipe. First off, a 1.96" diameter pipe has a total of 3.02 square inches. So we're be looking for pipes that each have 1.51 square inches of area. Using the formula for finding the area of a circle in reverse, you come up with 1.39" diameter. So a pair of 1.39" diameter pipes will act the same, or very similar to a single 1.96" pipe.
This is the easiest to figure out. The velocity in the plenum intake pipe should not be higher than 180 ft/sec at maximum rpm. The formula to figure out the diameter pipe that should be used is for a given velocity is:
D = ^(CID × VE × RPM) ÷ ( V × 1130) Where: D = Pipe Diameter CID = Cubic Inch Displacement VE = Volumetric Efficiency V = Velocity in ft/sec If you're dealing with liters, change CID to liters and the constant to 18.5 so the formula will look like this: D = ^(Liters × VE × RPM) ÷ (V × 18.5) An example for a 153 cubic inch 4 cylinder with a 85% VE, revving to 6000 rpm would and a desired 180 ft/sec air speed though the intake pipe would look like this:
D = ^(153 × 0.85 × 6000) ÷ (180 × 1130) = 1.96 You would need an intake pipe that has a 1.96" inside diameter to have 180 ft/sec air velocity at 6000 rpm for that engine. In other words the engine would need a little over 3 square inches of intake pipe area.
Plenum Volume
There is not going to be a simple answer to the needed plenum volume for a given application or rpm range. The good thing about plenum volume is that there is a pretty wide range that it can be and still be effective, so general rules work well. The following guidelines are for engine operating in the 5000-6000 rpm rage. V8's with one large plenum feeding all 8 cylinders does not work all that well as far as the Helmholtz resonator goes, but if this is the case, plenum volume should be about 40-50% of total cylinder displacement. On a four cylinder engine 50- 60% works well. For 3 cylinders (6 cylinder engine with two plenums), each plenum needs to be about 65-80% of the 3 cylinders it feeds. If a boost is desired in a higher rpm range, closer 7000-7500 rpm, the plenum will need to be 10-15% smaller. To get a boost in the 2500-3500 rpm range, it will need to need about 30% larger. The plenum size of a Helmholtz resonator may go against the typical plenum size rules, but the rules change when the resonator is being used. The whole Idea of a plenum is to allow the gases to slow down and gain density. The Helmholtz plenum makes a dense charge by use of pressure waves, in the same way tuned port intake runners work. this plenum sizing method does not apply to engines that to not use a tuned intake pipe. Many engines simply have the air cleaner assembly directly on the carburetor or throttle body having very little intake length. In those cases the Helmholtz resonator system does not work.
Intake Ram Pipe
The last thing to adjust is the length of the intake ram pipe. It is possible to make an adjustable pipe that can be made longer or shorter for testing purposes. For a starting point figure a 13" long pipe will help at about 6000 rpm. For each 1000 rpm drop in rpm add 1.7" and subtract 1.7" per 1000 rpm increase. This is just a starting point. The inlet of the pipe should have about a 1/2" radius for smooth flow. Once you get a baseline (you must do a power pull and get a baseline), which can be done at the track or on a dyno. Then try moving the pipe 1/2" in either direction as see how power improves. The dyno may be a little deceiving, since peak hp my go up but average power may drop. Track testing will be best, since you will be testing in actual racing condition and can tune the pipe for the best times. It is usually best for average power if the intake ram pipe is tuned about 1000 rpm lower than the intake runner length.
Multiple Ram Pipes
Most engines will have more than 1 throttle bore feeding the cylinders. In this case you must figure out the total area of intake pipe needed to figure out what size each pipe should be. In the first example, the 4 cylinder engine needed a 1.96 diameter intake ram pipe. If that particular engine had a two barrel carburetor (or two single barrel carburetors), you would need two pipes each one having 1/2 the area of a 1.96" pipe. First off, a 1.96" diameter pipe has a total of 3.02 square inches. So we're be looking for pipes that each have 1.51 square inches of area. Using the formula for finding the area of a circle in reverse, you come up with 1.39" diameter. So a pair of 1.39" diameter pipes will act the same, or very similar to a single 1.96" pipe.
I wish I was alittle better at math
Jan 24, 2008 | 03:41 AM
#43
Great comparison!!! It would be nice if you got the graphs from https://www.performancetrucks.net/fo...d.php?t=392089 in this thread.
I think whats funny is how many times I have heard people claim that Swaping to an LS1 manifold Makes more power.
I almost got banned on another forum over this argument. I showed real world comparisons using things like That comparison in Chevy high performance. All he talk about was every last drop of HP at the top end. I also tried to discuss things like the added weight for truck applications and the time, Modifications necessary, and cost to swap an LS1 intake in to a truck VS any Possible potenial gain IF any. All the data I came across pointed that you would not have any real benifit. Even when they tesed different cams you might gain something like 2 HP around Peak rpm or you might reach your peak RPM slightly sooner at a loss of torque. I have to dig up that Issue if I can find it but I did scan the page with the graph on it. Thought I had all the Info scanned but I may have lost when my computer crashed a few months Back.
I also don't think alot of people relize there are alot of other factors to consider when picking a manifold. How large is your cam, How much are your heads capable of flowing, what size throtle body are your running or do you plan to run, what other modifications have been done to your engine, Whom did you get your information from, people with real experince and true racing credit or people that know everything but dont have any real credit to there name and so on???
At any rate great to see the data presented so that People can make a more educated choice.
I think whats funny is how many times I have heard people claim that Swaping to an LS1 manifold Makes more power.
I almost got banned on another forum over this argument. I showed real world comparisons using things like That comparison in Chevy high performance. All he talk about was every last drop of HP at the top end. I also tried to discuss things like the added weight for truck applications and the time, Modifications necessary, and cost to swap an LS1 intake in to a truck VS any Possible potenial gain IF any. All the data I came across pointed that you would not have any real benifit. Even when they tesed different cams you might gain something like 2 HP around Peak rpm or you might reach your peak RPM slightly sooner at a loss of torque. I have to dig up that Issue if I can find it but I did scan the page with the graph on it. Thought I had all the Info scanned but I may have lost when my computer crashed a few months Back.I also don't think alot of people relize there are alot of other factors to consider when picking a manifold. How large is your cam, How much are your heads capable of flowing, what size throtle body are your running or do you plan to run, what other modifications have been done to your engine, Whom did you get your information from, people with real experince and true racing credit or people that know everything but dont have any real credit to there name and so on???
At any rate great to see the data presented so that People can make a more educated choice.
Jan 24, 2008 | 06:54 AM
#44
ok so theyres alot of info flying through here so im gonna stick my neck out and hope i dont et insulted.lol.ive been in search of an intake tb swap for my truck ,ive got the intake that came with my lq4 and stock tb.in youre professional opinions what intake and tb would be most benificial to my application ?i dont like the looks of the intake on my truck i have alot of mods and looking to do more so i thought id go for this next,i do have abrand new n2o setup im planning on installing on my setup too help get her out of the hole just alittle 30 - 50 shot,although itll do 125,i dont want all the variables that go with that.most of my driving is street racing 1/4 mile and 30 rolls .my setup works well but i know theyres more hidden hp ive dropped to 10 psi boost and no stall now .i was thinking of the victor with the 90 mm setup or a fast setup.i really like the looks of the victor with elbow,but not so sure how it will line up with my a/w intercooler setup underthe hood maxcooler.i have a ton af money into this whole setup and i feel it def has alot more potential.im not real happy with my low end response dbw,of course but im not going too use a large converter i jst dont like them.been theyre done that .but i also feel weak high end rpm and mph i can feel it it levels out some around 80-90 mph in the rpm band.idk y, probly tuning.so in closing im looking for a benificial int/tb swap.if any bcaause of forced ind,ive sen alot of people say dont bother.i usually dont run up past 6500rpm .i open for sugg.i hope this isnt jacking the thread but it seems like the 1 i need to be in to get my answer,ive ask numerous times b4 on other boards but never really got a solid answer but people trying to sell me stuff .im looking for a solid answer i dont want too waste more money just too loose power.if i loose the thread cause i dont know how to find it again please pm me i want too get too the bottom of this.any ?please ask .but dont critisize im looking for professional answers.
Jan 24, 2008 | 07:04 AM
#46
I am no profesional but have you had any head work done or do you plan on having some done in the future... I would say probally The F.A.S.T with a 90mm on it... Curious on other input Too!
Jan 24, 2008 | 07:45 AM
#47
no head work yet but im looking for input on that too ,i dont want too raise c/r at al l cause of the f/i .im pushing the envelope on boost.im not sure if i need or if it would even be benificial to do so.KEEP IT COMING GUYS.
Jan 24, 2008 | 07:59 AM
#48
I hate to throw another option out there, but there is another intake on the horizon that is promising to flow better than the FAST 90 and looks to be cheaper. It is suppose to be released for sale in the next couple of months, so I don't know if you will want to wait that long for it to come out and and for the data to be verified that it is as good as they say. Anyway here is a link to what I'm referring to. https://www.performancetrucks.net/fo...d.php?t=409589
Jan 24, 2008 | 08:25 AM
#49
TECH Veteran
Joined: Sep 2003
Posts: 4,534
Likes: 3
From: Las Vegas, NV
Great comparison!!! It would be nice if you got the graphs from https://www.performancetrucks.net/fo...d.php?t=392089 in this thread.
I think whats funny is how many times I have heard people claim that Swaping to an LS1 manifold Makes more power. I almost got banned on another forum over this argument. I showed real world comparisons using things like That comparison in Chevy high performance. All he talk about was every last drop of HP at the top end. I also tried to discuss things like the added weight for truck applications and the time, Modifications necessary, and cost to swap an LS1 intake in to a truck VS any Possible potenial gain IF any. All the data I came across pointed that you would not have any real benifit. Even when they tesed different cams you might gain something like 2 HP around Peak rpm or you might reach your peak RPM slightly sooner at a loss of torque. I have to dig up that Issue if I can find it but I did scan the page with the graph on it. Thought I had all the Info scanned but I may have lost when my computer crashed a few months Back.
I also don't think alot of people relize there are alot of other factors to consider when picking a manifold. How large is your cam, How much are your heads capable of flowing, what size throtle body are your running or do you plan to run, what other modifications have been done to your engine, Whom did you get your information from, people with real experince and true racing credit or people that know everything but dont have any real credit to there name and so on???
At any rate great to see the data presented so that People can make a more educated choice.
I think whats funny is how many times I have heard people claim that Swaping to an LS1 manifold Makes more power.
I almost got banned on another forum over this argument. I showed real world comparisons using things like That comparison in Chevy high performance. All he talk about was every last drop of HP at the top end. I also tried to discuss things like the added weight for truck applications and the time, Modifications necessary, and cost to swap an LS1 intake in to a truck VS any Possible potenial gain IF any. All the data I came across pointed that you would not have any real benifit. Even when they tesed different cams you might gain something like 2 HP around Peak rpm or you might reach your peak RPM slightly sooner at a loss of torque. I have to dig up that Issue if I can find it but I did scan the page with the graph on it. Thought I had all the Info scanned but I may have lost when my computer crashed a few months Back.I also don't think alot of people relize there are alot of other factors to consider when picking a manifold. How large is your cam, How much are your heads capable of flowing, what size throtle body are your running or do you plan to run, what other modifications have been done to your engine, Whom did you get your information from, people with real experince and true racing credit or people that know everything but dont have any real credit to there name and so on???
At any rate great to see the data presented so that People can make a more educated choice.
I remember that article. The numbers that they posted beside each intake listed were incorrect. You have to read the whole article and look at the actual graph to see what happened.
Jan 24, 2008 | 04:32 PM
#50
What do you mean there incorrect... I breafly remember reading and re reading it a while back... Still looking for the magazine so if you could fill us in.