Kenku

All righty. I'm just wondering if some people who have messed with these things more than I have would be so kind as to answer a few questions I have. Lasse wankel's post a page back provided a lot of help, and I've read various others... anyway.

First off, would a 51mm diameter port flow enough air that it would warrant going all the way up to a 58mm Gene Berg IDA, as opposed to the more normal 51mm IDA? Or should I be looking at going a little bit smaller than a 51mm port? Even though this is going to be going into a street car, I really am looking for mid-high RPM power. Next, is it necessecary to go over to carbon seals, or will the stock 2mms live reliably enough at high RPMs? I'm not really against carbons, but I'd prefer the longer life span of the normal seals. And finally, what about off-throttle vacuum? Will it still generate enough manifold vacuum to work the brake booster, or should I be looking at moving to a non-boosted master cylinder, with the various other modifications that go along with that?


Disclaimer:
Yes, I said street car. Yes, I realize I'll have shitty fuel economy in city driving (not that I do much; 95% of my miles are on the freeway) and will have to have a really loud exhaust to avoid choking the motor. Yes, I realize that it won't make much / any power at the lower part of the tachometer. Yes, I think I have a pretty good idea of what I'm getting myself into. No, I don't want you to tell me that I should go with a street or bridge port. I'm not trying to be snotty or an ******* with this disclaimer; it's just that I've seen a lot of times where questions like this make people assume that the poster doesn't know what they're talking about.

Okay. Anyway, any help that people give would be appreciated.

voodooracing

2mm steel seal will be fine... but since you are going to be spining at such a high rpm, you want to use the carbon seal. The carbon seal is lighter, and you use a stiffer apex seal spring. This will help a little in preventing seal float.

Grizzly

I would say go Ceramic rather than Carbon? Carbon's dont tend to last long but your right in saying they are light and good for high revs.

Chris

Lasse wankel

I would say go for it! I had a RX-3 12 years ago that had a PP w/ large runners and a 51mm Weber it was really streetable w/ RB headers and a 3" exhaust w/ 2 mufflers. Sure the mpg was poor and the idle lumpy but it sure was streetable. Best ET w/street tires was 13.27s-104mph with a weight 2200lbs. I would suggest that you port the minimum ID in the rotorhousings no more than 44mm to achieve good flow and hi velocity that a street engine must have. The beginning of the rotorhousing port should be around 48-50mm then tapered to 44mm. Use the 51mm carb w/ 43mm chokes and you will have a fun PP engine to drive! In this set up i prefer Mazdas 3-piece apex seals or the Hurley ones. Had carbon seals in older engines i built but they suffer from low rpm torque. This is my experience so far, hope it will help you a little bit

EScalade

There is no point in destroying good PP housings with steel seals.
Run 3mm carbons and just pull the engine down more often - or run ceramics if you've got the folding.

Kenku

Grizzly: *snicker* I *WISH* I could go ceramic.

Lasse: Thanks, that's exactly what I was looking for in terms of advice. I don't know that I'm going to do it exactly that way though, but I'm a self described nut. I figure if worse comes to worst and it's undriveable, I pull a new pair of rotor housings out of the boneyard and try again, and the motor with too little low-end for street use goes in the race car. From what I've heard, it's possible to retune IDAs to a lot of different configurations, so I could just detune the bigger 58 down to 51 for the smaller ports if necessecary, right?

EScalade: Why do you say the 3mm carbons, out of curiousity? More lifespan because they're thicker? And I don't know about "destroying good PP housings" as I am going to be making the things myself.