diabolical1

if i may ...



i'll offer a few observations i've made as they apply to streetports. yes, many people do just go for the largest runner, latest closing port that they can cut. in a few cases, it's warranted and effective (depending on the person's actual understanding and the final setup of the engine), but in most cases it can hurt power where it counts. however, you can't convince many people that it's not helping - which it does ... at high RPM! but notice i said "where it counts" though, because on the street how often to you get to drive at high RPM outside of second gear? am i making sense?



you'll hear a lot of people say that RB's streetports are conservative, with the implication that conservative doesn't make good power. however, you may be surprised at how well a streetport based on RB's closing, a little more aggressive opening, some good contouring/blending in the bowl and simply removing the casting flash of the stock runner will perform.



that said, i actually believe RB's streetports are conservative - just without the implication that they are gutless. it's just that they are too small for my personal setups and how i drive.



so overall, i'm saying i think your observation/insight into what Lynn said is correct. at least, that's my take on it.

D1 WTF

Where did you get the porting templates from????



Cheers

Lynn E. Hanover

Well, the rule is that you can have half of anything you want. Good bottom end=poor top end. Good top end=poor bottom end. No matter where you grind, you loose something. More power requires more RPM.

(More RPM=more fuel air mixture=more power)HP= RPM X torque /5252



A Darryl Drummond 12A bridgeport uses a stock intake manifold gasket. The runners are hardly touched. The object is to make more power over a broad RPM range. So the stock runners are plenty big enough to get 245 HP at 9,400 RPM. So the stock runners can move plenty of air, and are small enough the make good velocity for just driving around with a stock engine.



In a street car you have a wide ratio transmission. So you drop maybe 1,800 to 2,200 RPM on each shift.



So let us say that you just drive normally and shift at 4,500 RPM each gear. The start of the next gear will be at 2,000 RPM. How much punch do you have at 2,000 RPM? Not much, but this points out the requirement to have good torque down low in any street car. Your cruise RPM may be 2,500 RPM and about 25 HP on the freeway. If you bridgeport that engine, it will have no torque at all below 3,000 RPM.



The race car with bridges all around is just about impossible to drive around slowly. It is towed to the false grid with a little tractor. First gear is close to a street 3rd gear. Try that with no torque. The clutch is a two disc Tilton 5 1/4" and does not slip. More like a light switch. On or off. The transmission has a close ratio gear set, so the RPM drop between shifts is about 1,100 RPM. So you can keep the engine near its best power output. Peak power is 9,400 RPM, so you shift at 9,500 to 9,600 RPM. In some cases you will find that you have pulled the RPM down below best power, but in any case, not below 8,000 RPM, (234 HP).



So, it is easy to make runners much bigger than is required for a particular HP output (NA engines only)

and the outcome is a limp poor performing engine in normal driving. To get the velocity needed for crisp performance it is then necessary to wind the engine tighter, and suffer the poor low speed performance.



Keep your eye on the prize. What is this engine going to be used for?



Lynn E. Hanover

Nateb123

Lynn: Why do you favour velocity over pressure. Upping pressure would cause VE to go up wouldn't it? Higher pressure means higher density so more air mass would make it into the working chamber before the apex seal closes it off. Is this more of a low rpm velocity is favoured, but high rpm pressure is favoured kind of thing? Bernoulli's equation still has me a bit confused though. Why would a narrower opening cause decreased pressure? Increased velocity makes sense since the same amount of air is being pushed through a smaller hole, it has to speed up to keep the flow rate constant, but pressure? The very nature of having a smaller area for air to pass through would mean an increase in pressure as well, wouldn't it? On that website, you can see that as molecules head into the venturi they're forced to squish together, yet pressure is reduced.

Lynn E. Hanover

We live in a pressurized bubble. One bar, or 14.7 PSI at sea level. We can cause air or fluids to move to locations where we want them by lowering that local pressure in a device like a pump, a rotor housing or a cylinder. By enlarging a sealed chamber from a near zero volume to some larger volume, From TDC to BDC, in a rotary or a piston engine. One side of the piston or rotor has added a small amount of pressure to our world. So a slight pressure increase is apparent in the crank case. The pressure inside the sealed volume will go way below the local pressure (14.7 at sea level). If you then open a port that leads from the outside world to the inside of the low pressure in the test volume, the local pressure will flow into the volume and equalize the pressure.



Use your mouth to suck some air out of a pop bottle, then while holding that low pressure in the test volume (the inside of the bottle) stick your tongue over the hole to hold the vacuum in the bottle. Now quickly think about what is going on. Don't take too long or your tongue will hurt for a week. You are on the outside of the bottle in our world and the pressure in our world is trying to equalize the pressure inside the bottle and your tongue is in the way, so the 14.7 PSI in your tongue is being forced into the bottle. Now get you tongue out of there, your mother is going to see you doing that stupid stuff.



It is difficult to deal with and seems a bit backwards at first. The reduced section cannot just be a hole in a surface and still work. It has to fallow some rules like the ideal inlet and outlet angles. This is what you see in the choke area of a carburetter. So you get a high flow rate in the choke area (Venturi) and a very low pressure. The booster venturi (that little pipe looking thing that hangs down close to the choke, and the bottom end of that tube is connected to the fuel in the float bowl through the main jet, and has an air leak to meter that depression through an air corrector jet. So the effect is that of holding a siphon hose in the shop vac hose. No mechanical connection is required for fuel or water to be removed from the siphon nose. It is not being sucked from the hose, and fuel is not sucked from the booster venturi.



You cannot suck a Slurpie up a straw. You cannot suck the air out of a pop bottle.



Don't feel bad. Nobody can do it. It just seems like we can. You can lower the pressure inside the straw and inside your mouth by spreading your jaw and pulling your tongue to the rear of your mouth. Increasing the volume in your mouth, and thus lowering the pressure in your mouth to a point lower than that in our world. So our 14.7 pounds becomes slightly higher than the pressure in your mouth and forces the fuel, or water, or better yet the slurpie up the straw. Or the air from the pop bottle flows into your mouth to equalize the pressure. And so it is with the engine, or a pump, or a compressor.



The mechanical device generates a low pressure, by increasing the volume inside a closed chamber, and then through the intake port connecting that low pressure to the intake runner, and then to a carb or throttle body. So as the engine or compressor runs, an unending supply of low pressure is exposed to the intake runners. So, how much pressure is available to force air, or and air/fuel mixture into the runner?



Always just one bar. Or 14.7 pounds at sea level, and less as you go higher above sea level. At very low engine speeds there is time for a good amount of air to enter the chamber before it closes. This is called cylinder filling. As the revs go up, less time is available to fill the chamber before it closes. Cylinder filling goes down inverse to RPM. And never more than 14.7 pounds to push the stuff in.



Even with a tuned intake system, like the pipe organ looking Renesis intake, there will be only two ROM where cylinder filling gets back close to 14.7 pounds and both of those RPM are of no value in performance. Good for freeway cruise and not much else.



So if the time factor is killing total volume at any test RPM, you need the highest possible velocity available using only 14.7 pounds. Then if you increase runner diameter, you drop velocity. The face of the charge may have increased in area, but not enough to cover the volume lost as a result of the loss of velocity. So why do people doit anyway? If the higher RPM required to get back to the same velocity, is not a problem for you, then there is HP available by increasing runner diameter. And it is an easy step to miss the point that higher RPM yields more HP anyway, so the statement :I increased runner diameter and got more HP sounds like it is true. It will be true for a higher RPM, but not true for the same RPM you test at before the change. So let us say that peak torque was at 3,000 RPM 100 foot pounds. We grind out the runners so that you can stick your arm through them. Now we dyno again and find peak torque at 7,000 RPM and its still 100 foot pounds. Way more power. HP=RPM X torque/5252. But what is the torque at 3000 RPM now? Maybe 60 foot pounds. 5th is now too tall for 65 MPH. You need to slip the clutch a bit to get away from the lights. The stock runners are capable of quite sporty performance, even at very high revs.



There are ways to have it both ways. Just port the end irons. Most of the driving is on the primaries anyway so when you want to show off, you call up the secondaries.



Turbo engines are completely different.



Lynn E. Hanover

Lynn E. Hanover

We live in a pressurized bubble. One bar, or 14.7 PSI at sea level. We can cause air or fluids to move to locations where we want them by lowering that local pressure in a device like a pump, a rotor housing or a cylinder. By enlarging a sealed chamber from a near zero volume to some larger volume, From TDC to BDC, in a rotary or a piston engine. One side of the piston or rotor has added a small amount of pressure to our world. So a slight pressure increase is apparent in the crank case. The pressure inside the sealed volume will go way below the local pressure (14.7 at sea level). If you then open a port that leads from the outside world to the inside of the low pressure in the test volume, the local pressure will flow into the volume and equalize the pressure.



Use your mouth to suck some air out of a pop bottle, then while holding that low pressure in the test volume (the inside of the bottle) stick your tongue over the hole to hold the vacuum in the bottle. Now quickly think about what is going on. Don't take too long or your tongue will hurt for a week. You are on the outside of the bottle in our world and the pressure in our world is trying to equalize the pressure inside the bottle and your tongue is in the way, so the 14.7 PSI in your tongue is being forced into the bottle. Now get you tongue out of there, your mother is going to see you doing that stupid stuff.



It is difficult to deal with and seems a bit backwards at first. The reduced section cannot just be a hole in a surface and still work. It has to fallow some rules like the ideal inlet and outlet angles. This is what you see in the choke area of a carburetter. So you get a high flow rate in the choke area (Venturi) and a very low pressure. The booster venturi (that little pipe looking thing that hangs down close to the choke, and the bottom end of that tube is connected to the fuel in the float bowl through the main jet, and has an air leak to meter that depression through an air corrector jet. So the effect is that of holding a siphon hose in the shop vac hose. No mechanical connection is required for fuel or water to be removed from the siphon nose. It is not being sucked from the hose, and fuel is not sucked from the booster venturi.



You cannot suck a Slurpie up a straw. You cannot suck the air out of a pop bottle.



Don't feel bad. Nobody can do it. It just seems like we can. You can lower the pressure inside the straw and inside your mouth by spreading your jaw and pulling your tongue to the rear of your mouth. Increasing the volume in your mouth, and thus lowering the pressure in your mouth to a point lower than that in our world. So our 14.7 pounds becomes slightly higher than the pressure in your mouth and forces the fuel, or water, or better yet the slurpie up the straw. Or the air from the pop bottle flows into your mouth to equalize the pressure. And so it is with the engine, or a pump, or a compressor.



The mechanical device generates a low pressure, by increasing the volume inside a closed chamber, and then through the intake port connecting that low pressure to the intake runner, and then to a carb or throttle body. So as the engine or compressor runs, an unending supply of low pressure is exposed to the intake runners. So, how much pressure is available to force air, or and air/fuel mixture into the runner?



Always just one bar. Or 14.7 pounds at sea level, and less as you go higher above sea level. At very low engine speeds there is time for a good amount of air to enter the chamber before it closes. This is called cylinder filling. As the revs go up, less time is available to fill the chamber before it closes. Cylinder filling goes down inverse to RPM. And never more than 14.7 pounds to push the stuff in.



Even with a tuned intake system, like the pipe organ looking Renesis intake, there will be only two ROM where cylinder filling gets back close to 14.7 pounds and both of those RPM are of no value in performance. Good for freeway cruise and not much else.



So if the time factor is killing total volume at any test RPM, you need the highest possible velocity available using only 14.7 pounds. Then if you increase runner diameter, you drop velocity. The face of the charge may have increased in area, but not enough to cover the volume lost as a result of the loss of velocity. So why do people doit anyway? If the higher RPM required to get back to the same velocity, is not a problem for you, then there is HP available by increasing runner diameter. And it is an easy step to miss the point that higher RPM yields more HP anyway, so the statement :I increased runner diameter and got more HP sounds like it is true. It will be true for a higher RPM, but not true for the same RPM you test at before the change. So let us say that peak torque was at 3,000 RPM 100 foot pounds. We grind out the runners so that you can stick your arm through them. Now we dyno again and find peak torque at 7,000 RPM and its still 100 foot pounds. Way more power. HP=RPM X torque/5252. But what is the torque at 3000 RPM now? Maybe 60 foot pounds. 5th is now too tall for 65 MPH. You need to slip the clutch a bit to get away from the lights. The stock runners are capable of quite sporty performance, even at very high revs.



There are ways to have it both ways. Just port the end irons. Most of the driving is on the primaries anyway so when you want to show off, you call up the secondaries.



Turbo engines are completely different.



Lynn E. Hanover

royal

Hi Lynn, Thanks for going to the trouble of explaining all that. Would you be able to explain the differences with a turbo engine as I'm trying to learn stuff and then think I'm getting there and someone says 'but its completely different on a turbo!'. My first thoughs would be that its the same principles but I guess not?!

oldone

All of the above that you have described I have experienced in my N\A race engines Lynn.I have even gone as far as to square the runners off by milling them,increasing the ports a fair bit.To be honest the result was only 184 horses on the wheels.I then opened the opening timing and closing timing on the ports and the power went down to 158 horses on the wheels.Low rpm driving just sucked.

However on experimenting on a 12a motor I cut a bigger bridge port on all plates,just cleaned up the runners and flowed some angles towards the ports,the lil motor feels so strong at 3000rpm and really gets on song at 5000rpm and pulls like a steam train from there onwards.Be interesting when I do some power runs on the dyno.



[attachment=45213SCI0007.jpg]



[attachment=45214SCI0040.jpg]

oldone

Pics are of the 12a obviously.

Lynn E. Hanover

The main difference is that 14.7 pounds of boost of the NA or, Normally Aspirated engine has to work with. With a turbocharged or supercharged engine, you can force feed mixture at nearly any rate you might want. Now thw breathing will be limited by the strength of the engine, and your ability to remove the excess heat.



The engines are about 28% effiecient, so about 72% of the heat from burning fuel escapes as waste heat. Mostly through the exhaust heat and then some as oil heat and some through the water or coolant. So, less than 30% of the energy ingested is available to do anything with. There are some losses that are the same for piston, rotary and turbo rotary engines. Oil shearing, mechanical drag, and chamber shape losses.



So for every 10 gallons of fuel, you get to use 3 and 7 go down the drain. So there is still an opening for a more effiecent engine design, and even the use of ceramics and other material changes that can limit heat losses.



The turbocharger recovers a small amount of energy from the waste exhaust flow, to drive the compressor. In WWII the Wright (the company the Wright Brothers started) aeronautics company built a radial airplane engine that had dual stage superchargers, and three exhaust turbines that recovered energy from the exhaust flow and added that power back into the cam ring in that engine. This engine had 3,350 cubic inches of displacement. There was also a 4,360 cubic inch engine.



One method of dealing with the excess heat of the boosted engine is to just use it for s few seconds.

So the heat does not get high enough to damage the engine. The other problem is that you are chaning the compression ratio of the engine as you add boost pressure. The engine stays the same size but you double or triple the volume of mixture you force into it, so the actual compression ratio goes off the charts. So boosted engines might have an ignition advance of 5 degrees or less at full boogie, while a NA engine might have 25 degrees at that same load and RPM.



So, the NA engine is difficult to detonate, and the boosted engine is easy to detonate. So boosted engines have all kinds of things going on to prevent detonation, that are not required on an NA engine.



Since the velocity of the inlet tract is now a function of boost, the runner size is just as big as you can get it. If you want more velocity, you turn up the boost.



To keep the engine together you need an intercooler. Since detonation is a function of charge temperature, you do all kinds of things to keep that temp as low as is possible. You inject water. Latent heat of evaoporation cools the charge, and water slows the flame front so it mimics higher octane fuel.

You reduce ignition lead because the much higher compression, has the flame front moving very fast and chamber pressures are very high. The oil is cooler. The water is cooler. The location where air is collected for the engine to breath is cooler. Once compressed (heated) air is inside the car it is run through a cooler. (intercooler). Just to keep the engine alive.



So, there you are. Runner size is not reducing power, it is increasing it. The reverse of the NA engine.



Lynn E. Hanover