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74K views 402 replies 52 participants last post by  mukle 
#1 ·
Do we really need them?
This is the question that I am researching right now.

Turbo or Supercharged piston engines typically use many cylinders arranged in-line and one or two superchargers. Superchargers deliver air at a relatively constant rate, while cylinders demand it in a varying manner, as the valves open and as piston speed varies through the stroke. Simple direct ducting would give problems where the nearest cylinders received more airflow. The pulsating demand from the cylinders would also show problems of either pressure waves in the duct, or a shortage of inlet air towards the end of the inlet phase.

The solution is to provide a large-volume plenum chamber between the inlet and the cylinders. This has two benefits: it evens out the difference in path restriction between cylinders (distribution across space), secondly it provides a large-volume buffer against pressure changes (distribution over time
 
#335 ·
Nice job Doug, Looking forward to see what kind of changes it made to your power band.
 
#336 ·
Ride report; Until last evening I've only done a few shakedown runs, needed to find any leaks, loose parts, etc. With about 50 miles on the new setup I got aggressive. Previously my boost would top out at a little over 8 pounds on the gauge. I felt this was because that's where I set the Hallcraft boost adjuster. Repeatedly it blows to 12 pounds now in the same time frame. This tells me that this design removes restriction on the compressor side, which is what I was trying to accomplish. Should have objective results from the Dynojet dyno at R&B Cycles and the Superflow eddy current unit at the Thundermax factory next week. We'll post both results.
 
#339 ·
This is an awesome thread with a lot of great ideas and workmanship. So wish I had a turbo, so I could try this out.
 
#340 ·
I got some ideas about hoe to use this with the trask set up.

Going to run the charge tube to the front and around to the other side.

Reroute the horn to new location and I now have room for the charge tube to the plenum.

Any suggestions?
 
#342 ·
I am thinking to increase the size of the charge tube.

Running it around the front gives me 2 options.

1 Intercooler connections
2 Longer tube means the charge air will cool just a little bit more.

I like how you did yours, but I do not think that other people will want to cut the air box.

Still trying different things.

When we did Lanes mock up here at the house. It turned out really good.
We got the turbo in nice and tight. Keeping it with the lines of the frame turned out to be the best fit. Running the exhaust pipe down low to the front keeps all the heat away from the legs.

We are working on the exhaust. It will be ready in a little bit. No pics at this time. It is not as easy as it sounds.

Time will tell.
 
#344 ·
Thank you for volunteering...
 
#346 ·
#347 ·
#348 ·
are you still using the 60mm or a 63.5mm?
 
#350 ·
60mm
There is not too much room around a tube fitting in the Plenum.
 
#349 ·
Rod, Here's the shots showing the cut out for the charge tube. Not a big deal & still plenty stiff because of the dual forming. I believe an intercooler on the GT25 is a waste of effort unless you are running over 12 lbs continuously. I feel that the larger ( 2" ) tube along with the larger radius 90 degree moved farther away from the outlet will give the biggest improvement. Per Garrett, this unit will support about 270 crank HP, so I have a way to go yet. For me, function takes precedence over form. I'd still like to see a smoked, thermoformed polycarbonate lid, but cams & headwork are my next big project.
 

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#352 ·
Gents--PHENOMENAL work and a great read. I've been away for a while so I had to play catch-up...I skipped a few pages in the middle of the thread where it started getting monotonous, but I'm certainly impressed with the results!

I'm going to plug my own thread real quick-- I've been kicking around ideas in this feeble brain of mine for a while about changing the intake port architecture. This would require major work to the head, and a completely new throttle body design...however that's the whole reason I started considering it. Take a look at the thread if you missed it over a year ago when I first started it-- http://www.1130cc.com/forums/showthread.php?t=157304
 
#353 ·
10 penny's worth

I know most of you guys are talking turbo installs here but I thought my observations on our supercharger kits development are worth sharing?
With our plenum which is approx 1.5 litres volume, plus a little in the short pipe from the blower we have virtually no bias in boost to either cylinder. This I know because of the afr in both pipes. The pipes are almost identical in volume, and the afr is the same for both cylinders with the same map for each. This makes me think that 1.5 litres head of air is enough to even out the pressure to both cylinders despite the asymmetrical inlet valve opening. Of course this is with a supercharger that is filling the plenum all the time, so there is always a residual boost behind the throttle valves when closed, keeping the plenum full and so giving the instant throttle response. With a turbo the plenum has to be refilled from off to on throttle. So plenum filling time will depend on volume which would create more or less lag depending on size but I think this would be very little difference, more to do with spool up time and turbo size. Through my 30 odd years of tuning FI I also found that if the plenum roof was closer than one times the diameter of the port the reversion of the inlet valve closing would bounce shock waves of the plenum lid and disrupt airflow. Also it was best to point the inlet of the plenum away from the inlet ports to help even flow. To make the inside of the plenum as smooth as possible to keep turbulence down and aid cylinder filling.
You can see my plenum on the TTS supercharger video I posted recently. I hope this gives you some idea's how to get the best from your install no matter what it is :)
 
#356 ·
Fabulous piece. Ever notice that turbo plenums have always tended to be round and superchargers typically are flattened ? Must be a carryover from our conceptions on cars. I understand now your references to ceiling height & reversion. For everyones benefit, what is the intake bore size and inlet ID? I upped my turbo unit to 2" because it appeared that the back pressure from such a long, narrow charge tube could be choking the turbine on the exhaust side.
 
#357 ·
The intake is for 2 inch hose so the bores going to be about .160 inch less.
We have run big tubes and bellmouths sat back in the chamber. The air disruption as hits the obstructions (bellmouths) helps even out the pressure throughout the tube but reduces flow, generally they work quite well. Working with tuned inlet lengths (more length generally more bottom end) isn't so critical, + - an inch isn't noticeable. I tried as an experiment just to run a pipe under the tank cover and split it into a Y to each inlet (so no plenum) and it was absolutely terrible, a reasonable volume is a must.
 
#358 ·
We appreciate real world results as opposed to theory, so big thanks. I had used 2 1/4" ID inlets & will be reducing them with inserts to 2" to get closer to the throttle body diameters. I'll try to ball park my volume for reference as well. Hope to hit the dyno this week for objective results to post.
 
#359 ·
Richard,
Where do you see any flaws in the plenum?

Compared to the Trask plenum, this is leaps and bounds better.

Also, If one was to just purchase your plenum for the turbo application.
What changes would you make and How much would the cost be?

This plenum will not work with the Sprintex SC.
Different monster all together.

Thanks for your input.

rod
 
#362 ·
The one that is made in this Thread. I think Karzza did a great job on this.
 
#361 ·
I had posted a question under EFI because my bike wasn't idling after the install of the new plenum. I'd incorporated the design feature of filterd air intake for the IAC. The consensus was I needed a 1/4 x 1/4 passage from each throttle bore to the pintle valve area. I can report that that is the case. I hogged mine out & it works great again, I'd had insufficient volume. Thanks to all you guys who chimed in !
 
#365 ·
Why Short Bellmouths?

Everything I read says to keep the turbulent air below the runner.

So to make sure there is enough volume of air, the plenum was raised to include the lid. Thus putting in taller runners.

Yours is flatter in height, and longer.

I say we both have the same thing. Pressure is pressure. the hard part is to equal the cylinders with that pressure! :D

Exception is that, now we have the extra ports for NoS or Meth spray and temp and IAT sensor. :notworth:

I would really like to see a combination of all the plenums.

Yes I think it still can be improved.


I am still working on mine.

No excuses here, just to darn busy to find the time.:banghead:
 
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