Which is better for a rebuild, FD housings, or FC housings? I have a 13bt S-5 mounted in a 1st gen, and am rebuilding a spare motor to play with.

I have heard (but can't remember which) of them had a better exhaust port and sleeve to start with and made a little more power.

I have also heard that certain years had different spark plug timing (spark plug holes were shifted which changes timing slightly)

so which would be better to start with if I am buying new housings?

doug

 

Any answers for this? is there a difference?

doug whalen

 

I am not 100% sure on any of these questions.

You'd probably get a better response in the Rotary Performance forum. It is a little bit below this one.

 

As far as ports they are all the same 86+. The later housings tend to wear less and be in better condition due to a slightly harder coating. Keep in mind FD housings have no passage for the LIM/turbo coolant flow, so it's not worthwhile to swap to them unless you can easily machine the bevel and hole into them for the passage and o-ring.

 

The later housings look like a good upgrade for folks running an aftermarket (read oil only) turbo.

 

They're not an upgrade...you won't see any more power or compression with them vs. the stock FC ones in equivalent condition. The only time it's worthwhile is when you have access to a used set very cheap and your stockers aren't so nice.

 

I must not have been specific enough. If the later housing have a harder coating, and they tend to wear less, then the later housings are superior to the earlier. I know there isn't a difference in compression or horsepower. This looks like an upgrade for a longer lasting engine, if the previously quoted is known to be true. Anyone have any personal experience using FD housings instead of FC housings. I have very little experience with 3rd gens or their motors, but I know a few guys around here that could attest to the stronger coating, I shall inquire with them.

 

Okay, so in 100k miles when you tear the engine back down and the chrome isn't worn quite as much as it would have been with FC housings, you can call it an upgrade. In the meantime, they're identical, except that the FD housings require modification to work with a turbo 2, and they also cost more (both new and used). I think the FD housings are around $50-75 more per housing new, last I checked.

Bottom line, it's a moot point, but you seem to be the type that would lose sleep wondering about the slightly stronger coating on the FD housings, so you are probably better off spending the money for those plus the machine work to make them work with the FC LIM.

EDIT: FWIW there are 4 "levels" of harness on the stock rotorhousings that I know of. The 85 and earlier housings were quite weak and exhibited large chunks of chrome flaking off anywhere after 50k miles, and are generally not reuseable for a solid build.

The 86-88 were better, but still wore and chrome flaked consistently, though nowhere near as badly as the older ones. They are usually reuseable up until the 150k mark.

The 89-91 were even better, and are usually in substantially better condition than the older ones. They are pretty much always going to be reuseable unless apex seals damaged them.

The 93+ were a hair better than the last one, and the wear is usually about the same or *slightly* less than the 89-91s. Not enough of a difference to worry about.

 

Kevin,

correct me if I'm wrong but I thought there some differences in the location of the spark plug holes between model (changes ignition timing). maybe between the S-4, and S-5?

kenn

 

keep in mind REW engines tend to be more abused than a S5 engine would be put under, if i was given 2 sets of housings in the same condition i would choose the S5 over the S6 so take that how you want.

housings usually are not a prone failure point when in decent condition but the fact it has seen more abuse is the main thing i try to avoid when possible.

 

To answer Kenn's question, the s4 has one style of plug timing, and the s5/6 have the leading plug lowered about 1/8". Not really a big deal...not so much timing, as location changed. Timing, after all, is ultimately controlled by the ecu, and it would take a drastic change in location to affect timing. IT is really nothing to worry about, I would shy away from mixing an s4 with an s5/6 in the same build, but other than that, build with whatever you find in the best condition at the best price.