Drago86

actually thats 157 pound feet of torque, which is pretty darn good for that high of rpm. to figure out what Ve that is you would have to know how much torque 100% VE is in a 13b, then you could have an estimate of the VE. I'd say delaying the port closing will eventually be limited by the compression stroke of the motor, you need to have enough mass and interia in the intake charge to make enough pressure to overcome the pressure of the compression stroke. high RPM VE comes from intake area, intake timming and intake tunning. the faster it spins, the less time you have to fill the chamber, thus you must increase the mass of air avaliable to flow into the engine in one stroke (increase port area), increase the time the ports are open to flow more air in (increase timming), and use tunned runners to force more air in at the specified rpm. I'd think generally BSFC would decrease with high rpm tunned motors, because the charge has less time to expand fully, and the exhaust ports generally open earlier reducing the power stroke on high rpm engines.

bill shurvinton

Posted last night but it seemed to get lost somewhere. Depending on the type of racing you are doing, putting max VE near max RPM is not always a good thing. You often want to have max VE near the revs you drop to after a shift. This is because power will continue to climb as torque begins to fall off. So you shift at 12000 and drop to say 9000. In this imaginary engine torque is 200lbft at 9000 and 150 at 12000. This gives you 342HP at 9000 and 342HP at 12000. In terms of power under the curve it would be a very fast car.



ISTR some dyno figures for the Guru saying that they had tested to 14000, but can't find a reference.

Drago86

I'd love to see the dynos.



Sesshoumaru, May i ask what you used on the runners? I'm still porting my motor and am having a hard time with the runners, my burrs are to small and stones take to long. I think im going to try an 80 grit flap wheel next. Thanks.

83turbo

Don't you mean BSFC would _increase_ for those reasons? OTOH, there's less

time for the cooling system to sap heat out of the burning gases, so this may

counter that somewhat.

Bill-

I understand your point about having a strong powerband, but if you were so inclined, could you move that 200 lbft to 10, 11, 12K? This gets back to the

question of whether BSFC necessarily goes up with RPM in that range, or whether

it is possible to attain the same VE at 12k that you can get at 9k.

Lynn E. Hanover

Wow, this is fun.



The big thing I think is that everything affects everything. If you add a factor here, it disappears from over there.



Moving the closing line is exactly the same as a late closing intake valve in a piston engine.



It is done to take advantage of a underutilized induction track. For example, the runners are round, of good diameter, the carb is bigger than your head (or the air valve) and the engine seems to go a bit flat at 8,000 on up.



So you whip out the new die grinder and move the closing line from 45 degrees to 85 degrees. Being sure to radius and polish the closing line. Hey this is great 25 more HP at the rear wheels.



However, it seems a little tired just driving it to work. I didn't used to downshift just for this sweeper onto the freeway, what gives?



Gives indeed. The torque you added to the top end, is just about exactly removed from the bottom end. Now a bit more like a turbo engine just off idle. Not much steam at all.



The new engine overcomes this very problem with three complete sets of inlet tubing. So you could have a small high velocity intake port, and tuned runners that can maintain high velocity right through the RPM range.



No help for the rest of us.



The actual effect is that you can make the engine smaller with a die grinder.



(Where does he come up with this crap?)



Remember that the rotary has two bottom dead centers just like a piston engine, with the only difference being that the two are in different places where on the piston engine it is the piston at the bottom of the stroke both times. But the definition is "maximum volume" and the rotary has two of those. The one at the top is the "maximum volume" of the intake stroke, and the intake port (a valve) closes after that volume has started to get smaller. The cute thing about a rotary is the crank degrees are used to describe things that are happening at one third that speed. Piston people are lost on this stuff. But I wander off again.



Closing the intake port later, leaves you with a smaller volume of mixture to compress before ignition. There are ways to close it late and hide that fact from Mother Nature by having high runner velocity, so that mixture is still pouring into the closing chamber even though the pressure is going up because the chamber volume is decreasing. The high runner velocity could be because of your genius porting job, or the giant turbo from Germany, it makes no difference.



So in that case, you close the port late and get giant HP numbers because you have provided a longer period of time/number of degrees per revolution for intake opening. So if you have ingested a larger volume of mixture per revolution, is this not the same as an engine that is a bit larger in displacement that what you started with? And have you not heard that there is no substitute for cubic inches? Or CCs?



So where is that smaller thing?



When the engine is running slower than high revs WOT. Like when you drive it to work. At low RPM the tuned effect of runner velocity is just about nonexistent, or the turbo is just barely spinning, that same late closing intake is now spitting out a good part of the inducted mixture back into the inlet tract and making a mess for that runner and the other runners, and the usual 10% of exhaust dilution is now 15% because you are rebreathing the same crap that just went the wrong way in the intake. So low speed power is down around Briggs and Stratton numbers, And you have manufactured a very small rotary with your die grinder.



Congratulations.



Lynn E. Hanover

83turbo

Yes, I am aware of the downside of late closing (which is why I kept the closing

time fairly early when I did the ports for my turbo engine). Also the peripheral

intake ports I made (for another project) close around 50 degrees ATDC - same thing.



The real question is one of where and how the point of diminishing returns applies.

Ignore the "minor detail" of low end, decent powerband, etc for the moment -

assume that a way around that can be found (or that the engine is for an

application other than a car). Bump the intake closing to 85 degrees, and you

probably get an high RPM power increase. Does this trend continue at 95 degrees?

More? If VE can be maintained at ridiculous RPM, is HP gain hampered by a drop

in BSFC?

I noted while helping someone with a Suzuki GSXR engine that intake valve closing

was very very late - it seemed like halfway through compression. (My comment

was something like "are you sure this is the intake port?" - as he turned the engine

it seemed like it spent more time blowing out the intake than sucking in).

RETed

Screw it...

Variable intake runners, with variable apeture ports...

best of both worlds

Now to be able to take that idea and execute it's to work in the real world...

Priceless.





-Ted

Sesshoumaru

Drago86 i used some carbide bits then used a grinding bit. All of the bits i picked up at wal-mart. I also used a flex shaft on my dremel.



I'll be doing some more work on those ports............

Drago86

what diameter are the bits? my biggest carbide is 1/4th an inch and it seems to take forever.

83turbo

Dremel's kind of small for that kind of work. I use a much larger die grinder for

removing most of the metal, and a smaller one with a flex shaft for finishing.

Air powered ones work well too.