Advanced Engine Theory and Design
- Thread starter Alky V6
- Start date
Maybe a little too rich on the Meth there man. Lean it down a little. :wink:SPEEDSTAR said:Meth,10c114,6.5acet,15ni,tel,nipro15,
Lets start out with the difference between momentum (inertia) tuning and pressure wave tuning. Some may think they are the same, but actually they are two different tuning tools. Momentum tuning has to do with the intake port runner shape, volume and length, while pressure wave tuning deals with the plenum and intake tube to the plenum. When things are setup correctly they can both work together to enhance cylinder filling. One point to bring up is the importance of exhaust system pressure wave tuning to make this whole thing work at its best. During valve overlap you want a high positive pressure wave entering the combustion chamber while a strong negative pressure wave is hitting the combustion chamber from the exhaust side. In my opinion, if your not willing tune both intake and exhaust, don't waste your time with Helmholtz plenums. If your going to bother calculating your intake system, don't do half the job. Some may feel that tuning the exhaust side on a turbo engine is a waste of time. I and others feel that turbo engines respond to pressure wave tuning just as naturally aspirated engines do. Just at higher working pressures. My feeling is that because the working pressures in the intake and exhaust are higher, pressure wave tuning can have a larger affect.
Inertia tuning only helps in a very narrow rpm band. 600 to 700. In an effort to widen this window variable length intake runners were developed. An expensive proposition for most. Another alternative is the Helmholtz resonator. By setting up the Helmholtz resonator to enhance cylinder fill before the point where the intake runners are working at their best, then you have just extended that narrow rpm band where intake tune is at its best.
Suggested Helmholtz plenum volumes for various engines.
V8 engines should use a flat plane crankshaft so that the firing order is bank to bank. In essence you've created two four cylinder engines. Use split plenums. One plenum for each bank of cylinders. Use plenum volumes that pertain to a 4 cylinder engine.
4 cylinder engines should use a plenum volume of 50 to 60 percent of the volume of all 4 cylinders.
V6 cylinder engines should use split plenums. Each plenum should have a volume of 65 to 80 percent of the volume of all 3 cylinders.
2 cylinder engines should use a plenum volume equal to the volume of the 2 cylinders.
These are recommended volumes to boost intake charge between 5000 and 6000 rpm and cylinder sizes between 400 to 600cc. To tune to say 3,000 rpm increase plenum volume 30%. To tune to say 7500 decrease the volume 10 to 15 percent.
These are only guidelines and extensive testing would need to be done on each individual engine setup to determine the best combination. Plenum volumes do not need to be right on the money. You can compensate to some extent for a wrong plenum volume by tuning the intake pipe to the plenum. The intake pipe to the plenum is an integral part of the Helmholtz resonator. Do not build a Helmholtz plenum without properly calculating the diameter and length of the pipe that will feed the plenum.
V8 engines should use a flat plane crankshaft so that the firing order is bank to bank. In essence you've created two four cylinder engines. Use split plenums. One plenum for each bank of cylinders. Use plenum volumes that pertain to a 4 cylinder engine.
4 cylinder engines should use a plenum volume of 50 to 60 percent of the volume of all 4 cylinders.
V6 cylinder engines should use split plenums. Each plenum should have a volume of 65 to 80 percent of the volume of all 3 cylinders.
2 cylinder engines should use a plenum volume equal to the volume of the 2 cylinders.
These are recommended volumes to boost intake charge between 5000 and 6000 rpm and cylinder sizes between 400 to 600cc. To tune to say 3,000 rpm increase plenum volume 30%. To tune to say 7500 decrease the volume 10 to 15 percent.
These are only guidelines and extensive testing would need to be done on each individual engine setup to determine the best combination. Plenum volumes do not need to be right on the money. You can compensate to some extent for a wrong plenum volume by tuning the intake pipe to the plenum. The intake pipe to the plenum is an integral part of the Helmholtz resonator. Do not build a Helmholtz plenum without properly calculating the diameter and length of the pipe that will feed the plenum.
intercooler
Don, I am not a turbo guy but you may want to do a litte research on the latest trend in alky injection. no IC !!! reason being that alky does not vaporize very well at low temps. I am hearing that intake temps betweeen 110 and 130 seem to be the target temp!! food for thought mike
Don, I am not a turbo guy but you may want to do a litte research on the latest trend in alky injection. no IC !!!
reason being that alky does not vaporize very well at low temps. I am hearing that intake temps betweeen 110 and 130 seem to be the target temp!! food for thought mikeBlownV6 said:Don, I am not a turbo guy but you may want to do a litte research on the latest trend in alky injection. no IC !!!
Your absolutely right. Alcohol does not like to be too cold. The trick is to find the fine line and dance it. I'll have to check my data logs, but I believe my air temp at the up pipe, just before entering the plenum is inline with what you've stated. That is with an intercooler too. I'll get back to you with some exact numbers. I have no temp measurement in the intake port itself after the nitrous nozzles. Your right that alky doesn't vaporize well. That is why I port inject everything. Nothing is sprayed before or into the plenum. Also keep in mind that the higher boost and static compression ratios that alcohol fuels allow give you back a lot of that necessary heat during the compression stroke before ignition. Heat is generated as you compress a gas. Only its happening right in the cylinder. I'm also using a head that is less than optimum so it is important to have as dense a charge as I can get away with. The small port size does give me higher than optimum charge velocity too. Maybe that is helping to break up the alcohol? All I can tell you is, the combination is working. I was aware that people were eliminating the intercooler on alcohol installations, but I thought, I have this intercooler sitting around. I'll install it and see what happens. If it's too cold, I'll just remove it. At this point, I have no intention of removing it. One more note. I use ambient temperature water in the intercooler. I have not tried icing it yet.
Intake temps, measured 8 inches before the throttle body, start out at 33 degrees Celcius at the start of the run. By the end of the run it's 54 degrees Celcius. My Celcius to F conversion is at the shop. Maybe someone can help us out. The next post I'll explain how to calculate the very important intake pipe for the helmholtz resonator.
Ok. Lets build our plenum intake pipe. Air speed through the pipe should not exceed 180 ft/sec. I'll use my engine as an example. Since we would be splitting the plenum, we will calculate for half the engine. The formula for calculating the diameter of the feed pipe follows:
Diameter equals the square root of [(CID x VE x RPM) / (V x 1130)]
235 CID / 2 = 117.5
(117.5 x .85 x 7400) / (180 x 1130) = 3.6336037
square root of 3.6336037 is 1.9062013"
The intake pipe to each plenum should be 1.9" diameter.
Now let's boost and change our VE number. Let's use 2.7 (270% VE)
The intake pipe diameter is now 3.397357 or 3.4".
Assuming you want to tune the resonator for a point 1000 rpm before the point that your intake runners are tuned for, say 5000 rpm, the length of the intake pipe needs to be around 15.5". Increase the length 1.7" for every 1000 rpm less tuning point or decrease the length for every 1000 rpm higher tuning point. The throttles should be in each intake runner or prefferably at the front end of the plenum intake pipe. There should be a large increase in plumbing volume in front of the plenum intake pipe and throttle body, if the throttle body is placed at the front of the intake pipe.
Boy, I hope I didn't bore the heck out of everyone.
Diameter equals the square root of [(CID x VE x RPM) / (V x 1130)]
235 CID / 2 = 117.5
(117.5 x .85 x 7400) / (180 x 1130) = 3.6336037
square root of 3.6336037 is 1.9062013"
The intake pipe to each plenum should be 1.9" diameter.
Now let's boost and change our VE number. Let's use 2.7 (270% VE)
The intake pipe diameter is now 3.397357 or 3.4".
Assuming you want to tune the resonator for a point 1000 rpm before the point that your intake runners are tuned for, say 5000 rpm, the length of the intake pipe needs to be around 15.5". Increase the length 1.7" for every 1000 rpm less tuning point or decrease the length for every 1000 rpm higher tuning point. The throttles should be in each intake runner or prefferably at the front end of the plenum intake pipe. There should be a large increase in plumbing volume in front of the plenum intake pipe and throttle body, if the throttle body is placed at the front of the intake pipe.
Boy, I hope I didn't bore the heck out of everyone.
So you are saying to use big, 5" or bigger, pipes from the intercooler to the throttle bodies to serve as a large plenum, then 3.4" pipe 15.5" long from throttle body back to intake plenum? Would you use a 3.4" throttle body as well? At wot does it really matter where the throttle body is? Seems to me you could still put the throttle bodies at the start of the plenum and just feed them with the smaller pipe, at wot, anyway.
On a slight tangent, for someone who is now running a more standard setup with one plenum and the throttle body on the front of that plenum, and feeding it with 3-5" pipe, could you "tune" it by inserting a short length of smaller tubing just in front of the throttle body? That would be an easy piece to make and install so back-to-back testing runs would be easy at the track or dyno. Course the first requirement would be to already have enough plenum volume since the stock manifold is pretty tiny, and I'm not sure how uch bigger the Champion is.
On a slight tangent, for someone who is now running a more standard setup with one plenum and the throttle body on the front of that plenum, and feeding it with 3-5" pipe, could you "tune" it by inserting a short length of smaller tubing just in front of the throttle body? That would be an easy piece to make and install so back-to-back testing runs would be easy at the track or dyno. Course the first requirement would be to already have enough plenum volume since the stock manifold is pretty tiny, and I'm not sure how uch bigger the Champion is.
- Joined
- May 28, 2001
Mac in SD said:
Wisdom from the high priest of Stage 2 abstenince.
On another note.
Don I have seen some good results using LS-1 springs on Buick heads. Both iron and aluminum. I will have to get some pics for show and tell here. Have you thought about that on your motor?
Thanks for the conversion.The Swede said:33 Celsius= 91F
54Celsius= 130F
You guys really should start using the metric system :biggrin:
I'm trying to get into this metric thing, but it's hard to teach an old dog new tricks. I'd be lost without all my conversion tables I made up for myself.
ijames said:
Throttle body should be the same diameter as the intake pipe. I would think it would be OK to have the TB at the plenum. I'm just worried about the throttle blade disrupting the resonate wave action thing a ma jig. I have seen others suggest putting the TB in front of the intake pipe too. You have the right idea about the size of the piping before the tuned intake pipe.
On your tangent idea. I would first use the formula to calculate the needed diameter on your intake pipe for a single plenum setup for all six cylinders. That's a pretty large pipe.
Reggie West said:Wisdom from the high priest of Stage 2 abstenince.
On another note.
Don I have seen some good results using LS-1 springs on Buick heads. Both iron and aluminum. I will have to get some pics for show and tell here. Have you thought about that on your motor?
Hey Reggie, good to see you joining in.
The LS-1 spring is way to light. I'm running an aggressive mechanical roller so I need 210 on the seat and 635 on the nose. The ramp rate is on the ragged edge and my lift is at .714". I'm currently using a Crane dual spring w/damper.
The Helmholtz plenum is a good tool to enhance the engine's torque curve, but keep in mind that they are not known to be the best setup for peak HP figures. While the resonance wave tuning can be an advantage at the particular target rpm band that the system is tuned for, it can disrupt cylinder filling in other areas of the power band.
My thinking when I was choosing whether to go helmholtz or independent runner (large plenum) led me to the question, if I chose to pick a rpm range somewhere before peak torque to enhance turbo spool up time, how long would the engine be at that rpm range for the duration of a 1/4 mile run? The answer was in the low, low tenths of a second. The tuned plenum would be helping for a split second and then possibly hurting cylinder fill at some other points in the power curve. During a 1/4 mile pass, the engine is going to be within a 1000 to, at the most, 1500 rpm range, straddling the peak HP point of the rpm band, for a vast majority of the run. I made the decision to focus on peak HP. Remember, I had made the decision to use the magic gas to spool the turbo anyway.
My thinking when I was choosing whether to go helmholtz or independent runner (large plenum) led me to the question, if I chose to pick a rpm range somewhere before peak torque to enhance turbo spool up time, how long would the engine be at that rpm range for the duration of a 1/4 mile run? The answer was in the low, low tenths of a second. The tuned plenum would be helping for a split second and then possibly hurting cylinder fill at some other points in the power curve. During a 1/4 mile pass, the engine is going to be within a 1000 to, at the most, 1500 rpm range, straddling the peak HP point of the rpm band, for a vast majority of the run. I made the decision to focus on peak HP. Remember, I had made the decision to use the magic gas to spool the turbo anyway.
DonWG said:
Did you do your own tables?
Here yu have some.....
http://www.convert-me.com/en/
http://www.megaconverter.com/mega2/
http://web.200sx.nu/Projekt/konvertering.asp
The Swede said:
And there is www.pwr-tools.com, a great program with built in conversions and lots of mechanical, electrical, and HVAC calculations. Need to find the critical speed of a driveshaft? How much the walls of an intake plenum will flex given the thickness and boost? How much deflection a piece of channel you want to use as a frame rail will have under say 3000 lbs of load at launch? What size beams to use so that big block in the attic won't fall through the ceiling of your office? Etc, etc. Well worth the under $50 for the full version - the free version works forever, just doesn't have all the features.
The Swede said:
I made up some conversion tables that I can refer to real quick instead of having to calculate each time I needed some number converted.
Thanks for the resources everyone. Ain't the internet wonderful.
I had stated earlier that I would let you guys know what length intake runner I am using on the stage I engine. It is 7 inches including the head port length. The intake manifold section of the intake runner is tapered at 5.4 degrees included. The length is actually very close to the length of the intake runner of a stock GN intake manifold. I picked that length for various reasons. The most important reasons being the rpm range I was tuning for (the upper rpm band), and the compensating effect for the shortcomings of the breathing ability of the head. If you are using a head that is giving less than adequate flow numbers for the target rpm and HP numbers you are shooting for, by shortening the intake manifold runner and using the proper taper, you can somewhat compensate for the heads shortcomings. This can, and should be done along with your choice of crankshaft stroke, and camshaft specifications. Next, I will outline my idea of the intake for a Stage II drag engine.
This is my idea of the ultimate drag intake for a Stage II application. Constructive criticizm is welcome.
Port matched at the head, of course.
Length would be 2 - 2.8". No less than 2". For a variable length runner setup, the length would start at 4" up to 6400 rpm then quickly adjust to 2.8" up to redline.
Runner taper would be 7.3 degrees included.
A 2.8" length would concentrate on an rpm range between 6250 to redline. In my configuration example, redline would be 8250 rpm. That's a 2,000 rpm band where the engine is generating a solid HP curve. More than adequate for a drag engine.
The plenum would be large. 200 to 300 percent of total engine cylinder volume. There would be two large throttle bodies. Two 90mm's. The plenum size and dual throttle bodies are meant to ensure that the intake manifold would be a non-resonant unit.
The entry of each intake runner would be shaped to ensure the least turbulence possible. Either a fully shaped bell mouth or an eliptical flare if space constrants don't allow a full bell mouth. By the way, that is why I used an eliptical flare on the Stage I engine. With short runners it's hard to incorporate a full bell mount type port entry.
Of course, for this unit to work at its peak, the cam specs and exhaust system would have to match the intended power band target.
One of the main problems with runners being so short is the mounting of the fuel system. My configs target is 1803 HP @ 7500 rpm on Methanol. That would mean four 160 lbs/hr electronic injectors. That just isn't a viable option. The next thought is a mainly mechanical injection system with one 160 lbs/hr injector per cylinder used to trim the fuel system. It would be similar to the system I'm presently using on my Stage I engine, but the mechanical side of the system would be much, much larger. The need to run a belt driven mechanical fuel pump to supply the mechanical side of the system would probably be the best bet. Where to feed the mechanical is another problem. Do I take up valuable runner volume with the large fuel volume that would be needed or do I inject it after the choke spot of the head port, aiming it directly at the back of the intake valve?
Port matched at the head, of course.
Length would be 2 - 2.8". No less than 2". For a variable length runner setup, the length would start at 4" up to 6400 rpm then quickly adjust to 2.8" up to redline.
Runner taper would be 7.3 degrees included.
A 2.8" length would concentrate on an rpm range between 6250 to redline. In my configuration example, redline would be 8250 rpm. That's a 2,000 rpm band where the engine is generating a solid HP curve. More than adequate for a drag engine.
The plenum would be large. 200 to 300 percent of total engine cylinder volume. There would be two large throttle bodies. Two 90mm's. The plenum size and dual throttle bodies are meant to ensure that the intake manifold would be a non-resonant unit.
The entry of each intake runner would be shaped to ensure the least turbulence possible. Either a fully shaped bell mouth or an eliptical flare if space constrants don't allow a full bell mouth. By the way, that is why I used an eliptical flare on the Stage I engine. With short runners it's hard to incorporate a full bell mount type port entry.
Of course, for this unit to work at its peak, the cam specs and exhaust system would have to match the intended power band target.
One of the main problems with runners being so short is the mounting of the fuel system. My configs target is 1803 HP @ 7500 rpm on Methanol. That would mean four 160 lbs/hr electronic injectors. That just isn't a viable option. The next thought is a mainly mechanical injection system with one 160 lbs/hr injector per cylinder used to trim the fuel system. It would be similar to the system I'm presently using on my Stage I engine, but the mechanical side of the system would be much, much larger. The need to run a belt driven mechanical fuel pump to supply the mechanical side of the system would probably be the best bet. Where to feed the mechanical is another problem. Do I take up valuable runner volume with the large fuel volume that would be needed or do I inject it after the choke spot of the head port, aiming it directly at the back of the intake valve?
Here's a problem I'm going to be looking into solving soon. The entry into my T76 compressor is the type that allows a tubing to be clamped to it. The high end turbos have special bell mouths built into them. This makes for less flow loss at the entrance into the compressor, but makes attaching a filter to it impossible. I'm a strong believer in air filters. I don't have the finances to just allow junk to be injested into my engine. I want to design an attachment I can use with my standard T76 compressor housing that will give me a bell mouth entry and allow me to draw cool air through a filter. I have studied turbo F1 systems and figure there has to be some way to make a similar system that will attach easily to a standard compressor inlet.
