What sort of effect does the heat have on the exhaust turbine in turbocharged applications?

 

I did this with my 12A streetport when I was trying to get more out of a stock carb. From what I remember this didn't seem to hurt the low end much, but this was about 14 years ago. The idea was originally to get more out of the stock carb by having each rotor draw from all barrels instead of just two, essentially doubling the size of the carb. I left the primaries separated from the secondaries to minimize velocity loss and consequently hurting the bottom end. If you think about it... this may also work like a dynamic effect intake manifold. I recommend making a carb spacer to bridge the ports before experimenting on one of your rare manifolds. This would probably workout better down low anyway because runners would be longer. With shortening the runners moving the powerband up and all. Better yet...You could keep the primaries separated to guarantee good low rpm carb draw and bridge the secondaries for the boost in topend. Here's another thought based on longer runners being better for torque. If you use a squarebore you can swap the carb around and have the primaries feed the secondary ports through the long runners and have the secondaries on the short runners. You may want to look at some second gen manifolds to get a feel for good runner lengths.

 

You absolutely MUST have an inconel turbine wheel. If you don't, it will melt! Fortunately this isn't hard to come by anymore. The added velocity really gets a turbo spinning up quickly which is nice. You can use a larger a/r and still keep good spool.

 

Jeff, you have too many parts to play with and too many options between all of them. I'm having touble keeping track of all of it.


Personally, for the REPU, I would try the tall port center iron with the reverse runner intake. That would give you the longest primays out of the bunch for low rpm torque and a short run, higher volume for the secondarys, depending on how much you port the runners.

 

what type of material would be appropriate for the pipe? would it do just to have it ceramic coated like the header or would you have to use something special, like Inconel?

 

Too much good info in here to waste. Lets get this archived soon!

 

Not yet. I still need to finalize everything.

 

You don't need anything special here. Just ceramic coat it. The nice thing is that a header is easy to remove and replace.

 

Seeking to finalize my projects.

REPU:
3B plates smoothed etc
rotor housings to T2 or there abouts

MG:
Y plates to '74 spec
rotor housings unported

Baja:
Y plates smoothed etc
J-spec rotor housings unported

Reasons REPU:
I'd prefer a Y intermediate for forced induction, but I may never get around to it. Besides, if I can afford a supercharger, I can probably also afford a quickie rebuild. Moreover, a nitrided set of sideplates would hold up better to boost, I'd think, under normal circumstances (as long as it doesn't exceed the strength limitations of the rear plate, which the lighter, weaker Y plates and S4 are known to fail at the dowel pin area near the oil filter pedestal, which on the 3B plate is reinforced like later S5, S6 etc). Or I could have a custom manifold ported to match the '74-'75 short port plate, maybe. I'm thinking too much. The soon to be T2 ported rotor housings have 99% perfect chrome so they should last a while and have better compression than the stock ported ones. Only the really low RPM torque will be affected - not really a big issue in a '74 REPU with 4.625 gearing, stock heavy flywheel, and it won't be hotrodded much. My other REPU with D ported rotor housings, missing chrome, nitrided R5 plates, streetports etc. can tow things pretty well, and it's NA.

Reasons MG:
Some missing chrome. One housing was junked. Its replacement is in similar shape to the other, and can be reused. No plans to go forced induction on the MG. Liked the way it took off on primaries with the Cosmo manifold. For safety, I should limit or govern the high end power/high speed driving capabilities until such time as I can afford to redo the suspension, brakes etc. Keeping the exhaust ports stock should help. I feel the '74 spec intake ports are ideal as there is no need for the ultra low end of stock intake ports, they happen to be compatible with the small exhaust ports, and there is not enough carburetion available for street ports with the current setup (which actually fits). A good middle of the road with room for future improvement once the suspension and brakes are sorted out.

Reasons Baja:
I've already stated the reasons for the baja, but I should touch on them again. I'm obviously not happy with the bug engine. If I was, I wouldn't have invested the time and effort you've seen here over the last two weeks asking all these questions about ports and all that. It can barely break 'em lose in snow! It takes so long to respond to throttle inputs that by the time it finally gets up there, the oppurtunity has already passed. Not happy at all. I'm willing to invest time and effort to make a reliable watercooled swap work. Not a fan of piston engines in general, and I'm discovering I'm not a fan of air cooled either. It's quirky, but quirky has little staying power, you know?

I could go on ranting about it all day, but I won't. Ok, Y side plates for lightness, no porting for ultra low end, J-spec exhaust port timing for better low end peaking at like 4k RPM, 97% perfect chrome (good enough for me), S4 T2 waterpump for lightness and hopefully efficiency too, beehive for ease of installation and no oil lines to tear off, tall radiator mounted in the front for best cooling. I'll get a bus tranny for it some day.

I've been over this project mentally dozens of times and it always comes down to time and money, effort and desire. If I have all four, I'm good to go. Just gotta finish two projects first.