Low personal B.M.E.P.
Personally I'd doubt if you need a plenum on the exhaust - i thought the idea was to keep velocity up in the system before the turbo ?
On the other end, when i did the blown 500 kawa twin I used a plenum on the inlet around 1600cc volume. That worked well and gave us even mixture distribution. 180 deg twin - is yours 180 or the center two cylinders of a four - ie 360 deg ?
Anorak
For the inlet ........The guy that does the Ducati turbos in the states once said that 3.5 time total cylinder capacity is a good rule of thumb for a twin.If that helps.
One other thing i have noted is that on the 3 cylinder turbo manifolds at least one of the cylinders always seemed to direct straight at the turbo, pretty sure the log manifolds on the twin turbo skylines did the same. No idea why though.
Kinky is using a feather. Perverted is using the whole chicken
Bucket Racer/Crasher
The engine is cylinder 3&4 so it's a 180deg twin. I've thought about the exhaust plenum and would have kept it compact if it was a 4 or a 360deg twin. With the odd firing intervals it seemed like the exhaust pulses would meet quite different manifold pressure depending on which one was first or second, hence the plenum. The 2nd cylinder would exhaust into the cylinder after the first meeting more resistance to gas flow and then on the other side would suffer reduced intake pressure after #1 had done it's thing. Being injected the fuel distribution should be sweet. I know what you mean about the difficulty of fuel distribution in an intake manifold of a suck through carbed turbo system. Z1Rs would run #2 a bit lean and that was always the first cylinder to have problems. There's some comment from a few "names" in the exhaust and turbo world and they all say the same - just get the gas to the turbo in the shortest simplest way. Blake enterprises did turbo kits for Z1s years ago with a real ugly log style exhaust manifold with no apparent harm. Spaghetti style systems are for looks and style. My McIntosh has very short headers into a small dia pipe which connects to the turbo behind the engine and that works great. My turbo Cefiro had a pretty ugly exhaust manifold as well but went pretty good.
Aclass fukeruperer
Bloody hooliganOriginally Posted by speedpro
Low personal B.M.E.P.
I should have phrased it differently - the plenum gave us equality of cylinder filling...I'd been a tad worried about the first cylinder to open the inlet taking all the boost to the cost of the second cylinder.
I understand what you're saying re the pipe. If results don't match expectations it's easy enough to delete the plenum...
Another possible avenue to look at is simply different length primaries - a bit of creative pipe bending and you've got different lengths/volumes in the headers.
Bucket Racer/Crasher
Moving right along, intake plenum progress. It's taken longer than I thought but each little runner is tapered and has a hand beaten bell mouth. That's how it goes with only tin snips and a hammer or three. I've got to be careful not to do something that will stop me cleaning it up once finished. I don't want to risk crap getting into the engine. The connection to the turbo will be a cone on the end of this to a short pipe and then a piece of hose bent to the turbo where it will connect to another pipe on a flange.
No8 Wire Extraordinaire
Have you considered a 2 stroke? I hear they go quite well. No wasted cycle.
Don't you look at my accountant.
He's the only one I've got.
Bucket Racer/Crasher
bit more progress. The intake plenum is finished with help from Darren. He helped set me up with his TIG welder, his flash welding helmet(I want one) and I purge welded the end cap on with an awesome result. Got the little flange for the turbo to intake hose and have a good idea now for the exhaust plenum end cap. Talking to Darren about how to close off the intake plenum and he says to use a dome and then fishes a SS dome of the exact right diameter out of a box of bits. Of course spent more time talking shit than working at Darren's workshop but constructive as always.
Low personal B.M.E.P.
Are you putting an explosion valve anywhere on that plenum ? In my experience with 180 twins, and wasted spark ignition, it happens more than you'd like. From memory, first 3 goes at getting the blown kawa running we had to reset the explosion valve each time...winding up the spring preload each time till it would accept the odd spit back happliy. that was on meth though...and pretty rich too.
No8 Wire Extraordinaire
Pike river Plenum?
Don't you look at my accountant.
He's the only one I've got.
Anorak
the elsberg tuning site with the supercharged 50 has a good pic.
Kinky is using a feather. Perverted is using the whole chicken
Bucket Racer/Crasher
Sequential injection and ignition. It uses the MAP sensor pulses to determine which cylinder is where on the cycle and only fires that ignition.
On the dyno today there was no blowback at all at any rpm. Pretty disappointing though. For some reason it isn't tipping in the fuel it should as you open the throttle. The injector pulse width increases but only slightly and the motor sticks at say 8,000rpm. Sometimes it will catch and rev up to 16,000rpm or so. You can see into the throttle bodies when they are wide open and it isn't until the PW jumps up and you see the fuel fog jump up that the motor takes off. The TPS monitor indicates the TB opens and closes as you move the throttle but it doesn't add fuel like it should. Injector PW seems to stick at say 3.4mS whatever you do with the throttle. Almost like it's only monitoring the MAP sensor and not the TPS.
I'm familiar with supercharger blowoff panels. The "doorslammer" guys used them. Sometimes they'd completely fold them back hard against the frame of the panel. Silly bastards would double the panels if the motor popped one or two. The next thing it popped was the supercharger or the manifold.
Bucket Racer/Crasher
Finally made a bit more progress. Been learning a bit, mainly things not to do, like running the surge tank low on fuel and then not bleeding the air out. That took a night or two to figure out. Anyway, have now got it where it starts reliably on the stand just by spinning the rear wheel in 3rd. I've upped the rpm where it considers "start" to be over and the motor running from 780rpm to 1,200rpm. I also added fuel to the "Start Fuel factor", "After start factor" and the "Warm-up factor". It wasn't too hard to figure once I got a handle on which table was being used when. Once I got it idling and warm so no additional factors were affecting the fuel injected I then started adding fuel to the VE table, increasing the values from about the centre of the table up, in a single block from values of about .8-.9 up to a single value of 1.5 across the whole range. The improvement has been immediate and obvious. Whereas it didn't blip cleanly, now it sounds real sharp. So far I'm only using small throttle openings so even with the higher revs it is still using the VE table rather than the TPS table. I'll need to load it up to sort that properly. As per my crossover table at the higher revs with anything more than about 10% throttle it will switch to the TPS table. It's tempting to modify the switchover table to just use the TPS table at anything over say 5,000rpm at "any" throttle position, just to make it simple to figure which value is relevant at any load/rpm.
Pretty happy though. It starts easy, idles sweet, and throttle response so far is good.
Forum whore
Good going Speedpro.
Anorak
It occurred to me Mazda must know how to do 2 cylinder turbos.
Note the turbo inlet directly op one cylinder the 3 cylinder and twin turbo skylines do the same.
Its a sexy wee bit of Technology i had forgotten about.
Gave me another idea too....
http://www.rx7club.com/2nd-generatio...nifold-921791/
i can't post pics from there but visit it. Twin Scroll it Mazda Mitzi and Subaru all have done it.
Kinky is using a feather. Perverted is using the whole chicken
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