SpeedOfLife

iTrader: (16)

I'm rebuilding a motor for my '87 TII, and I will be streetporting it myself and, well, doing everything else as well. I have some nice used components for the motor, and the ones in question right now are housings. I have a set of S4 NA housings that are extremely smooth with about 1mm chrome wear on the outer edges in the common places. I also have a set of S4 TII housings that are very smooth with about .5mm chrome wear on the outer edges. Obviously, less chrome wear on the outside is preferable, but how do I decide when the NA housings are slightly smoother? There's no deep scoring in any of the housings, and the smoothness the TII housings lack is probably less than .001" deep at any point. It is very slight, I am unable to measure it. Although I may try my dial indicator... Also, the TII housing surfaces have a bit more luster than the NA housings. I'm not sure if that indicates anything about the condition of the chrome, but figured it might. The wear pattern moves along the seal path, as in it is perfectly straight, the wear 'grain' does not cross paths as far as I can tell. I recall seeing some housings that took in lots of unfiltered air and IIRC the wear pattern looked like ants had skated along the surface in straight but random trajectories, mine do not look like that (I probably saw them on Kevin Lander's site).

Another detail to be noted about all these housings is that there is no measurable chatter. Some may have slight visible signs of chatter, but I couldn't feel ANY with my fingertips or fingernails.

Ultimately, I want to choose the housings that will last the longest and still support my eventual goal of making 350+hp with this motor. I don't know exactly why the TII housings would be a little rougher yet have less wear on the edges. Perhaps knowing possible causes could help me pick the better pair. I also wonder if the housings surfaces would smooth out a little bit, maybe after 5-10k miles, if I made sure good clean air was always entering the engine. Also, while I'm at it, I might as well ask to hear peoples' experiences with compression when using really smooth housings compared to slightly rough housings. So, after break in, what sort of compression numbers have you seen with varying degrees of housing smoothness quality?

texFCturboII

iTrader: (17)

I can't give you any numbers, but i do know, and I'm sure you do too, that there isn't any difference in those housings other than the exhaust sleeves in the exhaust ports on the N/A housings. If both are within very comparable wear, I would suggest using the TII housings simply because it would save you the pain of getting those exhaust sleeves outta there!

SpeedOfLife

iTrader: (16)

I won't be changing out any exhaust sleeves, they will be modified without having to remove them. I would like to practice on the set I don't use on the build, and then sell them to someone if they're still usable. From what I've learned, it's hard to screw up housings if you follow a safe process, but since this is my first build I want to take extra time to make sure I get things right.

blwn rtr 89'

iTrader: (5)

"smoothness" isn't exactly a attributing factor to my knowledge.

i would use the housings you took the .5mm measurement on.

SpeedOfLife

iTrader: (16)

Yeah, I've been contemplating this issue for several days and it's possible that the rougher surface would even seal better. I will probably use the TII housings as you suggest, but I won't have to decide for probably at least a week or two so I'll keep taking input.

blwn rtr 89'

iTrader: (5)

well. -.5mm of chrome surfaced inner coating, compared to -1mm id imagine the spring underneath the apex seal would push at a higher (if that little spring is considered "progressive rate") to form a better seal.

remember it could also be some minor bulid up your feeling from the housings sitting out in the open air

SpeedOfLife

iTrader: (16)

It's definitely not that. I can clearly see the texture on the TII housings, and the NA housings are visibly smoother (and palpably so as well, but we've already covered that...). I'd post pics, but none I could take would illustrate this properly, as pics are so deceiving with these minor depth issues.