Kenku

OK, don't have a flowbench adapted to prove this out to myself one way or another yet so I'm throwing it out there. End project is a roadrace 13B; streetport (in the sense that it's not a bridgeport, not in the sense that it's especially streetable) with 42mm chokes on an IDA. Anyone have any sort of back to back on, say, S4/S5 Turbo end irons vs earlier 4-port ones? I know the hogged out EProd style 6 port end irons work but have downsides - I strongly suspect that without stupid amounts of effort filling in the runners they lose a lot of midrange, and I don't think there's any advantages to those castings compared to the 4-port ones. Either way the intent is to use 12A style center iron because holy cow am I not impressed with the dinky ports on all of the EFI center irons. I know there's a lot of positive results with the 13B-RE irons but I strongly suspect that the runner volume isn't really as big as it looks, and everything is just angled to better miss the turbos.

I know the 13BT irons have more runner area but I'm just not sure if that helps, basically.

peejay

The best side housings are FD end housings and 13B-RE intermediates, objectively speaking.

Subjectively, I'm looking into the 4 port RX-8 engines. If Mazda did what I think they did, those engines are 6 port engines that you can port any way you want without hitting water or having to add material, and best of all they are next to worthless on the used market.

Kenku

Hm - see, again, I though the FD runners were mostly optimizations to have the velocity vector coming down instead of straight in.

I suppose I know what the answer is... oh well, diy flowbenches aren't that expensive.

j9fd3s

iTrader: (3)

i'll have to fire up my old computer, but there was a guy many years ago who posted flowbench tests of the irons.

you are correct the FD and Cosmo intake runners are very close to the same size/shape as the T2, they are just tilted up to clear the turbos. they look bigger, but we are seeing a diagonal cut, and not a straight one.

i do like PJ's idea, use the Rx8 high power center, and low power end irons. block off exhaust (maybe only in the center), port as needed. there was a Japanese tuner car that was running an Rx8 engine with blocked off exhaust ports and GSL-SE rotor housings.

mustanghammer

iTrader: (3)

Okay so looking at the same thing and Peejay, I have been thinking about a 4 port RX8 engine too.

Kenku, do you think 4 port RX 8 Irons pared with GLS/SE housings meets the definition of a "13B" with respect to the STU rule set? The STU rules don't specify the source engine's intake port count like the EP rules do. They just say 12A or 13B. The STU rules do state that the RX8 engine cannot be ported.

Kenku

Ah... hm. I'm not on the comp board obviously, but I think what they're targeting with the "unported Renesis" rule works out to the improved intake manifold with EFI - it would probably be a significant performance benefit to an S5 motor if it could be made to work. (which makes me think of an S5 keg with enough work to mount a Renesis intake manifold dropped into an RX-8 but I'm already set on my plans) On the "if it quacks like a duck" front, if it's not using side exhausts and not using that intake manifold, I'd say it's not a Renesis, and I don't think they really want to import the more fiddly Prod rules over. You'll notice annular discharge carbs aren't outlawed either.

The practical problem though... looking at parts on ebay, some of the 4-port housings have the casting for the aux ports roughed in (IE a smaller-than-finished-machined hole) ala 04-08 mazda rx8 13b OEM front iron steel Renesis engine plate 4 port and some it looks like they finally revised the cores to eliminate the extra area for the runner ala 2004 Mazda RX8 13B 4 Port Front Iron So I don't know if that would work out as well as planned as far as not needing to add material, and I wonder what it would take to get the exhaust ports to not torch the side seal springs. I'd be happy to cast a manifold if anyone wants to try it - yes, I need a project to get me back on track with that.

Personally, I'm sitting on 3 engines worth of pro built (I think Sunbelt but not sure) Prod GSL-SE housings and irons, plus I have at least a few Prod 12A iron sets kicking around... may just try the obvious combination.

Do you have any idea what Prather was doing on his car? I watched the in-car he posted and it looked like he was shifting around 8700rpm, which seems low for Prod.

peejay

Kenku, YGPM.

mustanghammer

iTrader: (3)

Have not seen the ports on the inside. Will have to watch the video.

Kenku

I meant more in a general sense... from the video, one of the boxes mounted to his dash looks like an ECU, and the lower RPM range makes me wonder if he's trying to go "hacked up GSL-SE manifolds plus EFI" instead of the defacto standard Weber IDA. Also wonder what he's doing for shocks/struts.

mustanghammer

iTrader: (3)

He is running a carb - likely one that he modified heavily. Shocks are double adjustable Konis. There is allot going on with this car. Give him a call, he will talk to you about what he is doing.

Gilgamesh

I agree that 4 port Rx8 irons just look like the 5th and 6th ports are cast closed.

Your idea is to take a 4port rx8 iron and port it out somewhere in between a hogged out 6 port iron and the standard ports right?

I would call Kevin at Rotary Ressurrection, he has been doing ALOT of rx8 stuff as you can imagine. He probably has some rx8 4port irons headed to the scrap pile he would sell you for scrap prices.

Kenku

Because I'm just thinking about stuff at work, any guesstimates of EP-ported-12A irons vs EP-ported GSL-SE irons on a 13B? I mean, I have the parts, so might be fun to test.

I meant to have my dyno going by now, but suffice to say that 2018 kicked my butt pretty hard.

peejay

What are the current EP rules for porting? My rules-weeniedom is limited to RallyCross anymore where the engine rules are either "must be 100% stock spec from the throttle body to the exhaust ports" or "must be internal combustion and run on gasoline, Diesel, or E85" and no in-between.

I can attest that you can make the GSL-SE secondaries very, very large... see my thred below for details.

Kenku

EP says "street port" and no material added; https://i.imgur.com/LrvoqTy.jpg is one of my EP GSL-SE irons.

Latest plan is an intermediate tube chassis (GT-3 instead of GT-2) and skip the unibody classes because I'm tired of dealing with unibody race cars. GT-3 engine is unrestricted street port 13B, bridge with 44mm chokes and more weight, or peripheral with a single 37mm restrictor. For me right now it's between 12A irons and the GSL-SE irons because I have them - later on may move over to T2 irons plus coolant-grooved 12A center.

peejay

Ah. I did add material to the port.

I wonder if you could add material to the SLEEVE and then make the sleeve part of the intake manifold. Kind of like the header tongues that Paul Yaw used to make for 12As to fill the dead area at the top of the exhaust port... 33% more flow without porting.

Kenku

It's explicitly not allowed to have part of the intake manifold project into ports, actually.

I'm thinking a good apples to apples would be build one either way, cast an intake manifold with the same runner length for both and try it on the dyno.

BLUE TII

iTrader: (9)

Right.
However, some of the aftermarket intake manifolds seem to put the full runner bend before the interface to the engine on the 13B-REW and 13B-RE intake manifolds. Some of these like the old RX7Parts manifold were an all new design and some have this feature like the JW intake because they are adapted from the same mold as the older 13B intake manifold design which had to have the full bend before the engine.

Interesting- now you have bigger runner leading to the intake port face which may help peak flow.