fdracer

remember you're feeding a huge turbo through only 2 primary tubes, whereas it would normally be fed through 6 or maybe 8 primaries in a normal piston application. two 2.25" tubes have a much smaller cross sectional area than six 1.75" tubes. the velocity will still be there when the engine is under boost because a) you're pushing out a ton of exhaust gas, and b) the rotary's inefficiency will cause some of the exhaust to still be burning as it's pushed out of the exh. port.

z8cw

Actually my biggest problem is taking all this material out, I just had such a hard time putting into the port. My concern wiht the stock port was the rate of expansion from port window in the combustion chamber to the exhaust manifold..plus the gap the exhaust sleeve created. Granted you can smoothen that transission by enlarging the exhaust port window but even than you still left with a quickly expanding diameter. There is just not enough room to port and for more timing. If I want to feed into a 2.25 exhaust the decrease in expansion rate I just gained, will change back to a less favourable rate. I guess, I want the best of both worlds and I won't get it.



On a sidenote, I saw your comment earlier about the ceramic wheel. Do you think it is possible to tune a high strung rotary for no backfire. Actually I loved it on my old set-up. This turbo will be a one off and I love the idea of trying something new and different. Unfortunanetly these pieces are very expensive and I don't like to waste money for 10 minutes of glory.



Thanks for your help



CW

fdracer

you'll need that rate of expansion in the port due to the expanding exh gas you'll be pushing through it. remember this won't be a lean burning efficient engine. the rotary's inefficiency already causes an incomplete burn, and you're excarbating that by 1) exh. opening timing is much earlier, 2) high boost requires a retarded ignition 3) and high octane gas burns slowly. your charge is still burning as the exh. port opens so you'll be literally shooting fireballs out the exh. as your a/f charge is still burning as it exits the exh. port it's still expanding rapidly. that volume of expanding gas needs room to expand or you'll quickly choke the motor. you can use a smaller exh. port outlet and run a stepped header if you'd like, that'll probably broaden your torque curve a little at the expense of top end. but personally, i'd prefer to have the extra volume as far upstream as possible, so i'd want the exh. cross sectional area to taper out quickly. by the looks of your ports, it looks like the motor's good for about 1000hp, so 500hp worth of fuel and air is a lot of mass to push through 1 exh. port, my main concern would be to evacuate that as efficiently as possible. if i were you i'd run the big diameter primaries at about 2 feet in length with as big a turbo as i can run. i'd also square out your exh. port inlet some and radius it.



about the ceramic turbine wheel, i don't see how you can keep it together for a long period of time in a drag car. lingenfelter had ceramic exh. wheels on his garrett turbos and he went through about 1 or 2 per race.

rotarygod

I disagree with that. I got a power gain from keeping velocity high. Regardless of of efficiency differences, a rotary no more requires an expansion at the exhaust port than a piston engine does. If you did to a piston engine's exhaust ports what we have with the rotaries, the piston people would think you were crazy. That would be far less velocity and terrible flow compared to optimal. They'd be right. Rotary or not, this is still an otto cycle engine. From the second the mixture combusts in the engine, it immediately starts cooling down on it's way out of the exhaust system. It's already cooled down from it's initial combustion temperature a little by the time it hits the exhaust port. The farther down the exhaust it moves, the cooler it gets. As the air gets cool, it condenses, taking up less space inside the exhaust. As this happens, you lose energy. The whole point of people doing header wrap or ceramic coating is to keep the heat and therefore the energy in the system since this is beneficial. Any area changes affect efficiency and energy in the exhaust system. For the best power, you want to keep it as close to even over the entire distance as possible and keep as much heat in as possible. Any expansions in the system should be a calculated points and be broad enough that they contribute to scavenging ability through acoustics. Just having an expanding sleeve doesn't do this as it's expansion rate is too great over too short of a distance. My large exhaust ports that use my new sleeve are actually much larger than you can go with the stock sleeve installed. Due to the constant cross section, the primary is still only a 1 7/8" pipe size. There is no point in going up to a 2 1/4" pipe if the port can't flow that much. If the port can only flow as much as a 1 7/8" hole, I may as well only use a 1 7/8" pipe to keep as much useful energy in the exhaust as I can.



If you want to know efficiency differences between piston vs rotary engines, the average piston engine makes about 10 hp per pound of air ingested (not boost pressure) while a rotary only makes about 7 hp per pound of air ingested.



People keep comparing the size of the exhaust ports of the rotary to a piston engine's ports. You can't do this. They don't work the same way. On a piston engine, the exhaust valves are not constantly open. They are closed longer than they are open. This means that most of the time there is nothing flowing through them. You constantly have air exiting the engine through different alternating locations. With the rotary, you always have air flowing through the ports. You are really just maximizing the amount of port you have since you are using it full time. If the exhaust ports couldn't get enough air out, it couldn't make the power it does. Port timing is more important than just having a huge crazy good flowing port. The best flow does matter but it has to be balanced with the proper port timing for your intended needs.

z8cw

Good analysis above. I worked some on these ports and accomplished a 2 inch round opening towards the manifold and was shooting for EO 82 and EC 60.



Have a look below

fdracer

the venturi effect from a convergent divergent cross sectional area will help increase flow. big diameter primaries do hurt velocity at low speed low, but at full bore when you're moving a ton of air/fuel the decrease in backpressure should actually increase velocity vs. a smaller pipe. who knows, hopefully we can all build engines w/ ports this huge some day and we'll test what works and what doesn't.

z8cw

You think these ports are huge?

rotarygod

I fully expected that to be the answer. The next time I have a set of junk rotor housings to play with, I'll port one the Racing Beat way with the stock sleeve installed and one the same size with my sleeve installed and then I'll slap them on my flowbench to show the difference. Someone got some rotor housings lying around they don't need?

fdracer

there's no doubt you can make a small diameter primary and an optimally ported exh. port sing on the bench. but cfm isn't the key, it's the reduction in backpressure and the torque you build on anti-lag when you launch. that's why all the pro rwd guys run huge primaries, they shoot for primaries to flow about 100-150cfm more than the exh. ports flow. the bullish 2jz heads only flow about 230cfm, but they're 1 7/8" primaries each flow about 370cfm. george is now gonna run 2" primaries on his vq35 motors. all the teams that went up just 1/8" in primary diameter instantly picked up aroung 100hp using the same heads. look for pics of steph's old turbo headers vs. his new one on the nsx motor and you'll see a big difference.

rotarygod

Going up from 1 7/8" to 2" isn't a big jump in size and very little loss in velocity. What it did do was to create a slight ledge which helps reduce reversion pulses from entering the engine. Try jumping up to a 2 1/4" and see what happens to the powerband. Luckily for them, a turbo system is very tolerant to flow changes before the turbo and you can still get good power numbers. Try these changes on a nonturbo car that depends on exhaust flow and see what happens. The small size adjustment they made did nothing for venturi effect. FWIW a venturi is a restriction and you are limited with it. Carbs don't use venturis because they flow more. They use them because the pressure change through them is caused by an airspeed change through them and this helps to get the very poorly atomized low pressure fuel flowing and distributed better. If you were to remove the venturi (and obviously the carb) and replaced it with a fuel injection system and tune it properly, it would get more power.



Other things happen in exhausts in regards to pipe size changes but none of this is due to a venturi. Some people used stepped headers. These take advantage of acoustic pulses at certain frequencies. An expanding collector such as a megaphone also benefits as this also strengthens the acoustic effect in the exhaust system. In order for a venturi to work properly, it's shape has to be designed properly. You don't get it done by just changing the area at random spots.



I do have ask this so don't take it personally. I'm not trying to be an ***. Are you quoting theory or have you actually tested and tried any of these different systems for yourself? I've run my sleeves for years. I know how well they work vs the stock ones.