Does it have the be the actual manifold that came on the car, or an OEM mazda piece? The best bet if you could do it would be a S5 TII lower and FD UIM. It can be port matched to the 5 port block, and then extrude honed for best flow.



Due to your uses for the car, I would recommend not using the 6 port system. You want a strong midrange and top end, and some short gears. A Miata 3rd member will bolt up to a n/a rear diff housing, and allow you to bolt in a wide range of gears including 4.88 and 5.12's. All youll need is a custom front mount, and a lengthened driveshaft. Another option would be to cut and weld the pinions to put the gear end of the pinion onto the long pinion FC's use. The miata and FB use the same ring gear and LSD units, but have a shorter pinion and 3rd member. If youre interested in that , let me know. I was very very close to doing that to my car. I already have the Miata 3rd member and S4 clutch type LSD.



Maybe someone else with personal experience with bridgeports can chime in here, but my current SP engine has a hell of a midrange. And it would be much stronger with a standalone and even a S4 intake manifold. My S5 intake manifold and ecu are killing my power.



This is somewhat of an aside, but at that weight, 450 lb springs will be too heavy. There wont be enough compliance to take up bumps, and the car will lose cornering grip and stability on less than perfect surfaces. Jims5543 thought 450/250 lb springs were too stiff for his 2800-2900 lb car for autocross.

 

yeah we almost did the 1st gen pumpkin into fc with 4.77's but thats not legal. the gears are but we cant change the pumpkin

 

I don't think I will be allowed to use turbo pieces, since the car is NA. Infact I'm not even sure if it would be legal to start with turbo rotor housings to save me some time in porting, even though the dimensions are the same.

Would there be better midrange on a 4port? What does the intake look like for one of those? Was that motor carbed or FI? I do not want to go carb... that's the other slight advantage I have: fuel injection.

Bumps usually aren't too much of an issue in autocross, they are generally pretty smooth. Those spring rates have been suggested as a good place to start by a couple of different people, Steve O'Blenes being one of them. They may not be perfect, but I gotta start somewhere.

 

You need to read through the rule book and see exactly what you can and cant do.



If you cant run a different 3rd member, but gears are legal, you can do the other option I suggested. Splicing the gear end of the short pinion onto a long pinion shaft, and using that in the stock diff. Its been done before.



The old 13B's were carbed. J9, do you know if the mounts were different?



Midrange will be determined moreso by the porting than what housings you choose. The intake and exhaust will also have a strong effect on it.



Travis, whats your power goal?

 

I think I will need no less than 200hp to the wheels to be competitive.

Obviously I could get more with a different engine config (peripheral), but I need to keep some power down low(er). With a broader torque band I will have to shift less, which is a good thing in my book. Fewer opportunities for me to screw up.

Diffs are open for me, as well as trannies. I was actually thinking about running a T5 out of a mustang since they are so abundant. They should easily be able to handle the kind of power I'm making too. I haven't really researched it a lot. It was just a thought I had the other day.

 

Since the tranny and rear end are open, you have a world of options open to you there. Id stick with mazda trannies because there is a wide range of them that will bolt in. Check out this page for the transmission information. That page is a goldmine of information on mazda trannies.



I think a SP similar to mine would meet your needs, and be easy to tune. Exhaust porting is very important though. A bridgeport will have a weaker low end more similar to a PP than a SP. Im really interested to see how an aux bridge would perform with a setup better than what I had. Im having much of the same problems with my SP, but just to a lesser extent.

 

Thanks for the link.

That's why I thought an aux. bridge would work well. Good low/mid range with the ports closed then a pretty good top-end with the ports open... the problem is I can't make it work with the stock manifold.

So the basic dillema becomes: Is the weight penalty worth the trade off of driveability. It's very close in my mind, but I honestly don't know what kind of midrange power I'm looking at. I've only drive rotaries a couple times.

 

yes but you could build one from a t2 block.



what kinda of car is this motor going in? fc?

 

Yup, an FC.

https://www.nopistons.com/forums/index.php?...CODE=12&CID=205

 

you're prolly stuck with a 6 port motor, huh?