slitherz90gxl

I am designing something in CAD right now that I plan on attempting on my throwaway engine. A lot of the parts are barely in spec and this will be my first official rebuild; sort of just to get the hang of putting everything together so I don't blow money and then have it explode because I didn't fully seat an apex seal or something.

Would it be possible to have someone weld extra material to the exhaust port to make it close earlier? I am wanting to open the intake earlier and make the exhaust close later; to get rid of the extra overlap from opening the intake earlier.
I was thinking this, or to save more money since this is purely an experimental project, using some extremely high temperature putty like Thermosteel? It is supposedly good for up to 2,000 degrees Fahrenheit.

From what I've seen from threads and reading Kenichi Yamamoto's book; the earlier the intake opens the better low rpm torque/hp. I assume some of the rotary gurus have probably already tried this out so I'd like to see what they have to say about it.
(If you've tried this, how'd it go?)

I'm also considering leaving the exhaust stock(just polishing the surface up some) and then trying a buttterfly or a half-bridge; keeping the secondary intake port the same size.

j9fd3s

iTrader: (3)

RE: earlier intake opening, it works, this is basically what they did with the Rx8.

with the Exhaust on the Rx8 they open it later and close it later, and mostly make up for that by having two ports instead of the one port, so area is actually larger.

i don't know about modding rotor housings, putty won't work, as the seal has to slide over it AND there are some big pressure waves from the opening/closing of the port

slitherz90gxl

Hm, I guess I should read up on the Renesis design. I am just going off of old rotary manuals that I have collected.

Well, what I was thinking was that I could use the putty and sort of mold a funnel-esque exhaust port. I'd just start the putty a mm or so before the lip of the port on the inside of the housing. And then sort of build it with a slope heading towards the exit. By slope, I mean a very, very gradual slope.

I'm not looking to make the exhaust port smaller by more than a few mm. Just enough to offset the overlap of the intake. I might not even bother with it. I was only putting the idea out there. Assumed someone else had tried it already.

While this will be my first build and I am really just aiming to experiment. I want it to at least run long enough for me to make sure I built the engine correctly. I don't need the car drive-able until April for DGRR.

j9fd3s

iTrader: (3)

i'm certain that putty would last about 2 seconds, welding risks warping stuff. it may be best to make a new exhaust sleeve, although that's the hard way….

every Rx8 has less overlap than the previous engines, so in a sense there are 266,000 people that have tried it, it does a couple of things. primarily it reduces the amount of exhaust gasses that get cycled into the intake stroke.

this improves power in the low rpm, and low throttle areas. also it lets you set the mixtures in these areas leaner, idle can be 14.7:1, this is all good for mileage and emissions, and throttle response/power is better too.

so the less overlap, early opening intake works great in a street car. on the street you spend most of your time at part throttle, and under 4000rpm.

there are two SAE papers on the renesis, you should check em out.

RotaryEvolution

iTrader: (30)

never seen a rotor housing modified in such a way. mainly because you can't add chrome to the area that is now missing, even though you could add the aluminum back in.

the stock port timing is what it is and you can only realistically enlarge it from there and shift it earlier or later.

Jeff20B

iTrader: (13)

If you really want an exhaust port that closes sooner, you will need to switch to the 85 and older "form factor". Any US-spec 13B rotor housing from the 70s will have this port timing that opens at T2 spec but closes WAY EARLIER like what you're asking for. The other available option is to use GSL-SE rotor housings which open a lot later than T2 spec, but close right at T2 spec, so not helpful to you. Just fyi.

If you're trying to do this on a fuel injected 6 port, the GSL-SE irons will work. If you're doing a 4 port, you only have the old school carbed 4 port option (Y or R5 castings) which has a different bolt pattern so your T2 intake mani will not fit, unless you like doing extensive mods in aluminum. I suppose you could swap in a GSL-SE intermediate plate for the injector bungs, if keeping EFI.

One more option is to fill in the coolant seal grooves in one side or the other, depending.

As much as I still love the rotary engine, these are mods I would never do.

RotaryEvolution

iTrader: (30)

the early engines do have much more to work with, mainly because the ports are smaller so you can shift in either direction you choose.

the 74-75 housings though have the smallest ports, smallest exhaust casting and the inserts are pressed in and held in place by banjo studs. you can modify them rather extensively but there will no longer be an exhaust sleeve. on a fully bridged 74 spec i moved the leading edge down earlier and the low end response is great but the top end hits a wall.

slitherz90gxl

So GSL-SE 13b's had smaller ports? From the papers I read they had the same port opening as the s4/s5 13b's. You guys have more experience though so, I trust what you are saying.

I'm going to look in to finding 74-75 housings. The one that I found on ebay was $400. I don't really want to dump that much in to something that I'm experimenting on. I'll probably just ditch this idea. Thanks for the assistance though.

RotaryEvolution

iTrader: (30)

i don't have as much experience with the GSL-SE housings as Jeff, but i still somewhat recall them being smaller than the 86 spec housings. the 74-75 13B housings are rediculously small in comparison.

Jeff20B

iTrader: (13)

The very best housings to use in this experiment would be the US-spec 76-78 Cosmo and RX-4 housings. They open at T2 spec but close way early, but they have sleeves and castings that are bigger than 74-75, even though port timing is exactly the same. You could port these as big as T2 spec and it still leaves a tiny anti-reversion lip which is helpful if you're going to turbo them (or it should, not 100% on this). You don't need to remove the sleeves from 76-78 housings. Infact they use the same sleeves as GSL-SE housings (I'm 97% certain about this) which are plenty big enough for excellent flow. All around the very best choice, if you can find them.