76FJ55

I went back and looked at this pic again. I now believe that it is indeed a Tri-Y. It is deceiving in that the last collector happens to lie perpendicular to the photo plane. if you look at the swaged sections that correspond with the inlets or each collector you will notice that they are identical between the two headers in the picture.

danglerb

I think you are correct, getting to hate these headers from just looking at them.

I get the feeling there isn't much about them that isn't wrong.

Silly of me to question you Han's, but your trick pictures should be sufficient punishment for me.

hans14914

I too think the secondarys seem a bit short. However, if they fit, it would be relatively easy to cross the runners as the thread discussed in the same space the x-pipe currently is, which is the reason I posted the pictures.

I will try and get them back from my buddy to take some pictures, or just wait until they are baked and welded so you can see what they really look like.

I got them inexpensively, and I thought they were a neat conversation piece if nothing else. Not a lot of 928D parts still out there.

hernanca

Agree that it would be easy to use the 1-4 bank from these Tri-Y's, since they seem to have the 1+4 and 2+3 primary pairings. However, the 5-8 bank seems to have the 5+7 and 6+8 primary pairings, which would not create the exhaust pulsing needed for my (evil) scheme.

The 5-8 bank would need to have the 5+8 and 6+7 primary pairings, instead, so that we could then Y-merge the 5+8 and 2+3 secondaries, and also Y-merge the 6+7 and 1+4 secondaries.

I guess it depends on how easy it would be to cut apart the 5-8 bank's primaries from their Y's. Maybe check with your friend before he gets too far - perhaps they have already fallen apart after the initial cleaning?

danglerb

I'd like to see the primary Y as close to the heads as practical, then the secondary Y located for pulse tuning, and maybe the X like Greg Brown's system toward the rear.

I have so much confidence that I am going to get around to doing that that I think I will finally send out a set of the 85/86 manifolds I have to be ceramic coated. ;(

Mark Anderson

I've been asked to pipe in on is thread but unfortunately I don't have much info. The headers and exhaust (as shown ) were off Ken Geljacks car. I did dyno them and saw so real noteworthy gains. I eventually took them off as I could not get at the clutch without removing them and that gets old.

jpitman2

Rover got some useful (but not large) improvements with headers as in Ebay item 171040103522 - stock factory items in the SD1 hatchback. Note the asymetry to stop adjacent cylinders firing into the same primary - 5,6 in the 928's case, 5,7 in the Rover (chevy cylinder sequence). Hard to get the first Y much closer to the head than this? Only downside was the loss of the V8 burble.
jp 83 Euro S AT 55k.

hernanca

I have read in several places that the secondary pipe length is the important one for Tri-Y's. Keeping the primary Y's close to the head may help in packaging/installation, too.

Regarding an X in the system, my thought is that the system will be well balanced for dual exhaust all the way back, so, if it needs anything, an H would probably suffice. However, I plan on merging both sides into a single pipe somewhere down the line to get a more exotic sound.

Unfortunately, it is low on my priority list as well. We are having a heated race, but it's too early to tell whose snail will come in first...

Heh, heh.

Good to know it came from the Geljack car, Mark, and that you dyno'd them and gave them a "Tri" on your car. Thanks!

Interesting. The assymetry throws me off, however, unless they are keeping the two sides separate and/or testing showed them this gave them a good power curve over their target RPM range. Interesting "close to the heads" configuration, nonetheless. Thanks!

jpitman2

There is no way to make a v8 firing sequence that avoids two adjacent cylinders firing in sequence (ie 90 crank degrees apart). The Rover asymmetry avoids this on the left bank by pairing 1-3 and 2-4, but right bank doesnt need this. Same applies to 928 - front two on left bank fire in sequence. Your second pic shows how long the secondary pipes were in the SD1, and that there were no 4->1 merges, just 4 of the 2->1 merges , IIRC. Curious that the right bank primary casting is longer - maybe to clear accessories? One book on the engine I have says these manifolds can only be improved on by racing extractors.
jp 83 Euro S AT 55k

hernanca

I understand that the conventional two plane/90 degree crank V8 firing sequence, in order to avoid detrimental vibration harmonics, employs a firing sequence where two cylinders from the same bank fire in sequence. This occurs once for each bank of cylinders. By employing such a firing sequence, two adjacent cylinders will necessarily have to fire in sequence in at least one of those two banks of cylinders. (We are probably saying the same thing, I just want to be sure. )

jp, I am having a tough time following! Below is the cylinder numbering and related firing sequence for the Rover V8's. The cylinders are numbered differently than the 928. Also shown are those Rover V8 cylinders assigned to the SD1 Tri-Y. I prefer to use each motor's respective cylinder numbering when referring to them, otherwise, it can get quite confusing, and we may end up disagreeing when we should be agreeing!

As it is, I am diagramming out the Rover Tri-Y set-up to help in the discussion.
(Edit: added that diagram! The "..." or ".." notation indicate which primary is the longer of a pair - I believe this would place exhaust pulses with that annotation a little closer towards the "2" and a little further from the "1" in the firing sequence. Note also that, in the picture, the secondaries seem to have different lengths as well, which should also shift the pulses a bit. It appears to me as if they are trying to bunch the pulses together, instead of spreading them apart.)

Not sure what "racing extractors" are, unless you mean "tuned headers" (long individual tubed primary pipes cut to optimal lengths based on theory and testing). However, if you mean that these SD1 Tri-Y's are considered a very good setup for the Rover, then they are worth studying further, for sure. They certainly look easier to implement!

For me, though, I still prefer my crazy idea of having Tri-Y's with certain primaries paired, so that I can downstream cross the primaries in a way that gives me a nice smooth, exotic sound. (see next post, showing it with dangler's shortie Y's..)

hernanca

Lest I get too distracted with conventional Tri-Y's, here is a depiction of the Crossed Tri-Y, with dangler's version of having "shorties" for the Tri-Y primaries: (dangler, let me know if this is along the lines that you were thinking..)

ptuomov

Can someone explain to me why the 4->2->1<-2<-4 isn't the best non-standard solution? That is, pair the primaries with shorties like in the Rover manifolds. Then bring all four pipes to a single 4-1 merge collector. Now, one can size everything (except length) close to ideal way.

hernanca

ptuomov, I believe it is a non-standard solution worth exploring, for sure. I don't know if we can determine which would be the best non-standard solution for our specific cars until we do some testing, and even then, it may depend on the intended use of the car.

Here is a diagram along the lines that I believe you, danglerb, and myself are all thinking, but combined! It makes for a very interesting pattern of adjacent exhaust pulses. The adjacent pulses will be 90 degrees apart, so it will be the same "problem" as the 4-1 primary merges experience, but the 4-1 merge will occur with larger pipes (secondaries).

I still want to do my Crossed Try-Y, but I think this would also be a very interesting experiment!

hernanca

Too bad we can't use these (we can't, right?), even if it would be for just one side...

(Note: The later 1-4 pipes have a "bellows" which allows for expansion and prevents cracking problems, which were apparently prevalent (from what I read) in the earlier non-bellows version.)

danglerb

Would expansion be less of an issue with in and out thermal coating? I don't like bellows.