Landracing Forum
Tech Information => Technical Discussion => Topic started by: sanger351 on May 29, 2008, 01:57:57 PM
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Anyone have some good references for a how to build your own intake manifold? I have been doing some searches but I have not really found anything useful. Links, formulas, books I am open to anything. Thanks
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Without knowing your application it’s hard to tell what will work and what wont work. I can say there are lots of variables and physics that need to be considered to get the optimal design.
Getting the correct harmonic resonance is very crucial. The second harmonic designs generally return the best performance followed by the 3rd. After the third its very minimal the gains you will get. Also there has been a shift towards more plenum volume lately, and I don’t think you can go wrong with more plenum volume, but you certainly can go wrong with less.
Some things to consider along with your engine parameters:
Type: What is the manifold configuration (EFI, Carburetors or)?
Flow with Runner%: The percent that the cylinder head flow increases or decreases when flowed with the manifold attached.
Runner Turn: The amount that the runner (excluding the turn in the valve area) turns in degrees.
Fuel Dist Rating: The quality of the fuel distribution, For example an EFI is a 10 and a typical cross ram would be a 0
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Manifold Air Temp: The manifold Air Temperature. This value is used to calculate the optimum length of the runner.
Total Throttle CFM The actual throttle CFM at 1.5 hg.
Taper Included: The runner taper from the valve seat or choke area (if it has one) to the runner opening.:
When I was running the numbers for my XO motor manifold, I found that I needed different length runners for different conditions. So I decided to make a variable runner intake where I would use spacers to increase runner length depending on the conditions. My IRL Chevy engine uses the same concept to adjust the runner length (see picture).
If you want PM and I can give you hand.
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I am a high school auto teacher so any books and info I can get my hands on that is over my head is great. What resourses are out there to learn this? Last year I took a trip to Italy and went to the Ferrari museum in Modena. They had past F1 engines out on the floor with variable length carbon fiber velocity stacks and centered injectors. As you opened the throttle on the engine a bell crank system changed the length of each runner. I could have spent days there, but some people that I was with wanted to look at more old rocks.
I am obviously not looking to build F1 quality stuff out of the chute, I am just looking for the basic info to start this learning process.
I'll PM you with some info and would appreciate any help getting pointed in the right direction.
Thank You
Sean
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Aftermarket manifolds have a ton of HP research, are dyno tested, readily available and for the most part relatively inexpensive. I have seen a motor that had a custom sheet manifold (very expensive) that would of worked great on a motor in the 7-10+K range. This motor however would never see anything over 6K and imo the reason the motor did not make the power of years before (or speed).
If you are building a rare motor without aftermarkets available making one should not be all that difficult if you have some skills and tools. If it is the case that an aftermarket is not around I would find a performance motor that is close to the bore X stroke and RPM range that you are looking for and use its manifold as a rudimentary guide to making one regarding length and size of the runners.
Maguromic is correct about the resonate tuning, but this is a black art altogether. It would be nearly impossible for someone without the million dollar engine design software to correctly ascertain the correct volume of the airbox and plenum to take advantage of 1st, 2nd or 3rd order harmonics. I build a larger airbox for my busa motor because I knew even a stock 1300cc motor can gain HP from a larger box so I increased volume 15% over stock and then increased for the % volume of the larger stroker motor (1507cc). But this is only a guess. If Maguromic has a formula for being able to correctly tune for resonate Hz I would love to know it. I have even spoke with Dr Mayfield regarding this and still don’t have any solid answers.
It again is my recommendations that you go with a good quality aftermarket as apposed to the potential gain-loss that can be made from a homemade intake.
-JH
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The class we want to run in does not allow engine swaps. All of the good aftermarket manifolds used for our engine were designed on a later head style that has a different intake bolt pattern and runner design. If we can run the later head and not be disqualified we would do that. I would be very disappointed if we were lucky enough to set a record some day only to have it protested because the intake bolt pattern is different. Valve angles, head bolts, exhaust ports/bolt pattern are all the same just not the intake.
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JH, I use Lotus engineering software http://www.lesoft.co.uk that one my Indy car buddies have. The algorithms they are using are derived form all the years of F1 experience. I don’t think its that much of a black art if you have the right data to work with. This software package takes into account even the valve stem diameter. When Darrin Morgan was with Reher Morrison I ran some of my numbers by him and he said that they were within 2% of his dyno numbers. That’s close enough for me.
Sanger 351, The placemat of your nozzles will depend on what you are running, fuel or gas. I run gas and I have my nozzles very similar to the Ferrari engine you saw. Its all about trying to atomize the gas a little better. Since you are a teacher they have a free academic version. It might be worth a try to contact them. Or get one your college professor buddies to get it for you.
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The class we want to run in does not allow engine swaps. All of the good aftermarket manifolds used for our engine were designed on a later head style that has a different intake bolt pattern and runner design. If we can run the later head and not be disqualified we would do that. I would be very disappointed if we were lucky enough to set a record some day only to have it protested because the intake bolt pattern is different. Valve angles, head bolts, exhaust ports/bolt pattern are all the same just not the intake.
The different intake bolt pattern is all it takes. Thats considered a motor swap :-(
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IF everything is the same except the bolt pattern how about running the manifold that you want and changing the bolt pattern to match your heads willie buchta
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Yeah thats what I thought. The rules do say "may determine" and I have read that people look past the chevy vortec heads, and even the small block ford heads when the number of intake bolts changed. However if push came to shove I would think that the protest would win.
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I am sure I could make adapters but the port angles did change slightly. I am looking at all options. Besides as my students tell me "If it is not custom, I don't want it."
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351, send a question to the scta tech guy, tell him what you were thinking, see what he says, the worst that can happen is you find out you have to build your own manifold :| Use the system to help you, you may figure out which side of the protest you are really on. :-D
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rulebookinfo@scta-bni.org
DW
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Sure would help if you'd spill the beans on what you're building, but we understand, secrets can be fun. Keeps us guessing, anyway!
I am sure I could make adapters but the port angles did change slightly. I am looking at all options. Besides as my students tell me "If it is not custom, I don't want it."
Whipping up a manifold from scratch that flows and compliments your heads could leave you with hours of flow bench time trying to get it right. My argument for adapting an aftermarket manifold is that despite what you're trying to make it do, you're starting with a known quantity, and therefore you have fewer variables - by starting from scratch, you have almost nothing but variables.
But if you LIKE variables, here's something else to consider - If you made an adapter, would the port angle differences give you an opportunity to port-match to the heads in a way that might be to your advantage?
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Sanger 351,
I read your post with interest. I saw a magazine only last weekend,that goes into a lot of detail about fabricating custom inlet manifolds, but there is only one hitch, the newsagent is located about 13,500 miles from where you live!
I live in Australia, but i'd be more than happy to buy a copy and send it to you.
I am a member of the D.L.R.A., and i'm in the process of building a car to run in Gas Altered.The car is a Holden Torana [G.M.] coupe, very similair in size and shape to a Chevrolet Vega, and I am using a Nissan six cyl. in-line engine. This is an E.F.I. engine, and I modified a standard inlet manifold,by sectioning the plenum,machined a new flange which was then welded to the plenum, to which mounts another machined flange, which carries 3 standard throttle bodies.
If you care to send me your details, I will get the mag. away to you a.s.a.p. My E-Mail address is with my sign on name,Y.B., on the members register of Landracing.
Regards, Garry Brennan
" Life's just fine, in a straight line!"
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You can read through a website that is frequented by people that do builld sheet metal intakes as well has most everything else associated with cylinder heads. www.speedtalk.com - A lot of top line head porters post on the site. The search engine is not that great but there is a lot of information buried in their forums if you search enough.
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I just came across this site. http://www.team-integra.net/sections/articles/showArticle.asp?ArticleID=466
Do not forget to go to page 2. What do you guys think about the info?
Thankyou for all the info so far and keep it coming.
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I just came across this site. http://www.team-integra.net/sections/articles/showArticle.asp?ArticleID=466
Do not forget to go to page 2. What do you guys think about the info?
Thankyou for all the info so far and keep it coming.
These rules are very good for engines around 10,000 RPM. For lower RPM, we have to go back to the formulas and experimental evidence in Taylor and Heywood's books (what, you don't have them?!?!?).
Big rules for intakes:
1. Runner length and diameter should be based on the tables in Taylor.
2. Velocity stacks are critical.
3. Position the runners in the plenum by at least 1/2 the diameter of the runner.
4. Minimum plenum volume should be 1X engine displacement, 2X is better, more doesn't matter.
Hope this helps. :-D
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Blue I beg to differ with you on plenum size that bigger does not matter. Everything matters and have had first hand experience with engines with to much plenum and they were very evil running things.
The guys in the article for the b-18 stuff are almost dead wrong on many things as well especially the stuff about the itb setup not resonating.. the use of sound waves is easy to understand but has little to do with intake tuning. I have designed this stuff for a living for over 30 years and have a small clue of what works..LOL..
Dave
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"have had first hand experience with engines with to much plenum and they were very evil running things."
Dave was this a wet plenum with fuel separation problems? What size plenum/displacement ratio do you like?
John Burk
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Too large a plenum will lag a driver request for more or less power a small one will lead think capacitor low pass filter sort of thing.. If you do some simple math and see what the plenum sees for demand per degree of crankshaft rotation it becomes obvious. It equally depends if the air metering device is before or after the plenum. After the plenum the plenum is invisible before and it is an active component.
Dave
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Too large a plenum will lag a driver request for more or less power a small one will lead think capacitor low pass filter sort of thing.. If you do some simple math and see what the plenum sees for demand per degree of crankshaft rotation it becomes obvious. It equally depends if the air metering device is before or after the plenum. After the plenum the plenum is invisible before and it is an active component.
Dave
My comments reflected two givens that I should have stated:
1. Dry manifold with sequential port EFI where the fuel doesn't hit any wall before the intake valve. To stay sequential the injectors need to be at <30% duty cycle. Not to many people do this and it really whacks the idle control unless it's a dual injector per cylinder setup.
2. Throttle response doesn't matter. For aircraft and LSR, this is a good idea. For almost any other form of racing or street driving, it's a bad one! <LOL>
LSR is one of the few forms of racing that lends itself to optimizing for continuous power at a narrow RPM range and letting the rest of the power band fall where it may. Of course, we have to get up to speed and fewer gears are simpler, stronger and lighter. The only un-compromised vehicle I can think of with regard to throttle response is aircraft. On a point design, resonance makes a huge difference that hurts the performance at any lower throttle or RPM setting.
Other than plenum volume, my experience shows the other 3 points are valid even needing good throttle response. Trade offs are everywhere.
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Mr. Delaney's article (Integra site) completely confuses:
1. individual throttle bodies without a common plenum (ref: Weber IR, etc.)
2. individual port runners ending in a common plenum with a single throttle body (Edelbrock JG manifold as shown)
3. individual throttle bodies with or without a plenum fed from a Helmholtz resonator box
A sheet metal manifold is (generally) a "tunnel ram" design with tuned length port runners ending inside a sized plenum (plenum = storage device). If multiple throttle bodies/carbs are used, their air-horns may also end in a Helmholtz box (box = tuning device).
An important distinction: Helmholtz boxes are always dry, plenums are either dry (TB) or wet (carb) depending on the mixer - not on the manifold design.
Tunnel ram plenum volume is critical to power and response. If the volume is too low, peak demand cannot be satisfied by the flow rate of the throttle bodies (the obvious conclusion: if the TB flow rate is high enough, you don't need a plenum except as a connecting passage). If the volume too high in carburated apps, velocity and vacuum at the venturi drops and fuel drop-out occurs, fuel curve will be weird, poor response etc. In injected apps this is (obviously) not a problem but high volume may still cause other problems such as bad TB sensor readings.
The statement "ITB's do NOT use ram theory to get that extra kick at peak torque because they usually in race form do not have a plenum" is of course incorrect since it premises all ram theory on the "spring" and elasticity of air in a box.
What is given as "David Vizard's rule" for runner length is, in fact his rule for the intake pipe length of a Helmholtz box - not a runner at all.
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Too large a plenum will lag a driver request for more or less power a small one will lead think capacitor low pass filter sort of thing.. If you do some simple math and see what the plenum sees for demand per degree of crankshaft rotation it becomes obvious. It equally depends if the air metering device is before or after the plenum. After the plenum the plenum is invisible before and it is an active component.
Dave
My comments reflected two givens that I should have stated:
1. Dry manifold with sequential port EFI where the fuel doesn't hit any wall before the intake valve. To stay sequential the injectors need to be at <30% duty cycle. Not to many people do this and it really whacks the idle control unless it's a dual injector per cylinder setup.
2. Throttle response doesn't matter. For aircraft and LSR, this is a good idea. For almost any other form of racing or street driving, it's a bad one! <LOL>
LSR is one of the few forms of racing that lends itself to optimizing for continuous power at a narrow RPM range and letting the rest of the power band fall where it may. Of course, we have to get up to speed and fewer gears are simpler, stronger and lighter. The only un-compromised vehicle I can think of with regard to throttle response is aircraft. On a point design, resonance makes a huge difference that hurts the performance at any lower throttle or RPM setting.
Other than plenum volume, my experience shows the other 3 points are valid even needing good throttle response. Trade offs are everywhere.
not to question obvious authority, but my observation at bonneville is that the "peajy" power plants have the hardest time getting to their max speed, because of an on/off nature to their powerband. It is (might be was) my opinion that having a nicely-variable, drivable powerband is not only a good idea, but almost necessary, for a driver to be able to ease up to their top speed...
Correct me where I am wrong! thanks!
-scott
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What is a peajy engine??
This will be an EFI manifold and I would like the discusion to continue. What are the thoughts on injector placement? If I put the injector up the runner or in the bell vs in the head pointed at the valve, how will this affect injector timing?
One thing to consider is that this is a purpose built engine operating between 4000-8500 rpm with a manual transmission. Idle quality and lower rpm driveability are not a priority like many of the manifolds used for street use.
Thank you everyone for the help so far, I am learning alot and I respect everyones input and experiances.
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What is a peajy engine??
Thank you everyone for the help so far, I am learning alot and I respect everyones input and experiances.
Peaky with a typo, they are close together, the k and j
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oops, yes: "peajy" = "peaky" typing way too fast.
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For some of us, those who run Harley's or the vintage GMC/Chevy's with siamese intake ports, the problem of manifold tuning becomes even harder. Are there any programs out there that simulate these designs? I've had limited success with different length stacks on a Chevy 6 but would like to do a little research before logging up too much dyno ($) time. I absolutely hate the concept of "It can't be done".
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Vintage Four Fords!
Exhaust Intake Exhaust Exhaust Intake Exhaust
Most intakes designed in the 30's.
I'm leaning towards a 4-barrel Holley mounted sideways.
Mike
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Mike, worked for me. JD
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Nobody has mentioned how intake runner tuning actually works . A negative pulse starts when the intake cycle starts and turns into a positive pulse when it bounces off the upper opening . For most engines the runner length would be way too long but it works to let the pulse bounce up and down the runner multiple times and get to the valve as it's closing . When waves bounce back from the open end they change sign and maintain the sign when they bounce off a closed end . Acoustically an open valve is like a closed end so on the odd cycles (1st , 3rd) it comes down as positive pressure and negative pressure on even cycles . On 3rd cycle intake tuning the 1st and 2nd cycles happen during the intake stroke and cancel . The timing of the 3rd cycle is important which I think should be at bottom center.
It's basic math , 6000 rpm is .01 sec/ rev and 180 deg is .005 sec . At 1100 ft/sec x .005 sec is 5.5 ft divided by 6 (3 up and 3 down) is a runner of .92 ft or 11" . Air speed adds about 10% to the round trip time the 6000 rpm length is actually 9.9".
At 2/3 and 4/3 of tuned rpm the negative pulse arrives at bottom center so it's important to pick a runner length that avoids these .
Exhaust tuning works the same but sound travels faster in hot air so the lengths are longer .
John
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Re: excess volume - the peaky-er the engine is (narrow power band, falls off the planet below the band) proper volume becoms more important.
Too much volume kills recovery after a shift (~ RPM drop: very close ratios not too bad, Powerglide = terrible).
Bill Jenkins' rule for carbureted apps: find max power, then reduce plenum volume by 10%.