Need help with 6 port 13b race engine build
 

A little background first. I have a V6 swapped RX-7 that I have been endurance racing for 3 years. I recently bought another roller car to build a second car for our team. I want to take my pulled out 13b and use it in this second car.

I originally planned to bridgeport the motor and put this intake and throttle body on it:
https://www.efihardware.com/products...t-IDA-Manifold
https://www.efihardware.com/products...A-Throttle-Kit

For engine management I am going to use a MS3 megasquirt.

After doing some research on the 6 port, it doesn't seem very easy to put a bridgeport onto. Has anybody done this? If so where is the power band? That will let me know how much I need to do to the rotating assembly (balancing, milling the rotor thickness, adding snap rings to the rotor gears, etc...). Any other porting strategies that would work with this engine? I wouldn't mind making it a peripheral port engine either, but that is out of my budget (I think). I would like around 200 whp (or more) and as much torque as I can get with a hi revving rotary.

Any suggestions or ideas would be appreciated.

Thanks
JC

I'm pretty sure I've seen your v6 car at ChumpCar events, yeah?

So I currently own an '86 GXL with a large full bridge but it was built starting with 4-port turbo irons and housings but using s5 n/a rotors. I love the car for track days and driving around town on nice days. I plan to eventually compete in the Grid Life time attack series maybe starting next year. However, I think a bridgeport engine, and probably also a peripheral port for that matter, in endurance racing is a TERRIBLE idea. I would say on average I currently get around 13 MPG driving around town compared to 25-27 MPG with the original 6-port engine it had when I bought the car. I think some additional tuning could be done to get the cruising MPGs much better but there really isn't any way around how thirsty it is at full song. Sure it made 215 at the wheels while still using the turbo intake and I plan to move to ITBs as well but it's complete overkill for your goals and in no way shape or form could even get close to making it 2 hours on track before needing fuel.

There are a few people who have made 190 at the wheels with ITBs like the EFIHardware kit you are looking at and doing this on stock ports. If I were you I would either just clean up the ports a little and leave them basically stock or do a small street port on the secondary runners making sure you don't extend the ports any later as the 6-port shape already extends too far stock. You also have to consider that most racing bodies penalize rotary engines HEAVILY for modifying the ports at all from stock. It's usually not beneficial to try and make a largely ported high output engine versus getting a healthy, close to stock engine with ITBs and build a really good long tube collected header and then focusing on losing as much weight out of the car as possible to go faster. You aren't going to get that brap brap brap but I think you can build a mostly stock internally 13b that is extremely reliable, gets good enough fuel mileage to bump up against the 2 hour driver limit (in ChumpCar), and can be competitive by spending most of your effort on building the header with tuned length to extract the most from your ITB setup and also focusing on chassis/suspension setup and weight savings to get your speed. This all is what I am planning to build in the future for a WRL/AER/ChumpCar second gen but I don't have a close to stock N/A car anymore so I need more garage space!

I hear your concerns with the fuel milage. On shorter tracks I can go 2hrs on fuel but at larger tracks (COTA, Daytona) it won't make it with the V6 set up. The 18gal S5 tank helps. Chump Car allows up to 2 gals more with a fuel cell and a 1/2 gal surge tank (which I plan to do with this car) so that should help with getting to the 2 hr mark.

I have been doing a bunch of research on the 6 port engine and have come up with a plan. Maxdatrix sells a porting template for a bridge ported 6 port so I will start with that. I plan on using the above IDA fuel injection manifold and throttle body. Atkins sells a smoothed insert for the secondary ports that I will fit in permanently open. milled and balanced rotating assembly. Carbon apex seals. Coated rotor faces to help with oil temps. Then the standard internal mods (higher oil press regulator, pellet replacement for the oil thermostat, oil squirter mods). Racing beat racing header and exhaust.

JC

i didn't read the rules, but if mileage is the concern and not power (we used to run enduro's too, totally valid) i think i'd try the following.

overall, i would build for a broad power band, sure you can zing the engine to 8500+ every shift, but i would be looking to minimize the penalty for short shifting. also instead of power, i'd be looking to maximize efficiency. i'm assuming an FC engine, or at least the 86-03 style.

1. i'd run the turbo oil pump, but stock 71psi regulator.
2. the FD has larger diameter oil pipes, and if it wasn't big bucks to go -12, i would. i would do the FD oil pedestal, and try not to use any 90 degree fittings in the system.
3. for cooling the underdrive water pump pulleys are they way to go, both to keep it from cavitating, and to reduce the power needed to drive the water pump.
4. exhaust, i'd be looking for the widest power band. i'd want a long primary, but a smart person would see what the engine wants...
5. i have to wonder about using a ported/extrude honed stock manifold? obviously you could have an expensive paperweight here, but they generally offer a broad powerband, and just don't flow enough. ITB's would work too, i'd try a bunch of lengths.
6. i wonder about running a lower compression rotor leaner, vs a higher compression rotor. Mazda went to great lengths for mileage with the R26B, and they went high compression, so maybe thats the way. spend a lot of time tuning the whole map, the 787B starts right up with something that looks like a key, and will just idle on its own. driveability seems really good too, i've seen them use it to haul tires around

Just curious about these 190hp stock port builds, what kind of supporting mods did they have besides the EFIhardware kit? I’m working on cleaning up the MAP on my EFI REPU. It had 117hp with the stock carb and intake and a header to 2.5” exhaust. It feels quicker with the EFI, and I’ll get it on a dyno soon, but not 70hp quicker. I’m honestly contemplating a tear down for at least a street port.

After spending all that effort on the rest of the build I really think you should consider making a custom long primary header over the Racing Beat system. I loved my RB true dual full exhaust setup when the engine was stock but now that it's a full bridge I can definitely tell the exhaust isn't allowing the engine to breath like it should. Exhaust tuning can really unlock a lot of potential from the 13b. Also, I would urge you to consider only bridging the secondaries if you are dead set on doing a bridge. I really don't think you want to use a full bridge engine for endurance racing but it would be cool to see how it would perform with the fuel capacity changes you mentioned.

Another thing that can help with oil temps and pressures is to run an external oil line from the pedestal to one of the freeze plugs near the front rotor. There are a few guides out there showing how to achieve this. This gets rid of a lot of turns and potential restrictions in the oil path going from the rear of the engine to the front. Also, I haven't seen you mention dual oil coolers yet and you should 100% be doing that as well.

Has any more progress been made on this build? Interested to see what you've come up with

This is going to be a slow project as I have two other race cars that need attention for events this year. But I will post update as I go along. Right now the car is in the shop and partially gutted and the engine is out. I plan on finishing gutting and lightening the body, then putting in the roll cage, getting the suspension and brakes up to par then I'll start on rebuilding the engine. Then plan is to do the build this year and race it next year.

JC

Just in case this is still a thing I make over 200whp with a stock port gslse Na 13b. It was built for csp so porting is allowed to 1 inch of the port open(I think that's how it reads, it's been a while). Basically I just have cleaned up and slightly optimized port openings, the intake is the usual Weber and is port matched. Exhaust isn't even anything fancy. Rb twin primary.

Good to know. Thanks.

I am making some progress on the car. Just getting bogged down with my other race car right now.

Hi, if you wouldn't mind teaching me a bit, why wouldn't you run the higher oil pressure too?