All I need now is a TIG welder...
Turbo Mini Forums

The purpose of the plenum is to slow down the velocity of the air so that there are no momentum effects influencing which port it goes down.

Here's an analogy - stick with me.

Imagine a crowded underground station and the train has just arrived. There is a queue of people moving at walking pace trying to get on the platform. The platform is full of people at virtual standstill but at the carriage doors all hell is breaking out as people scramble to get onto the train!

All the carriages fill at the same rate - no problem.

They wont all end up at the last carriage.

The main factors affecting flow in any system are rapid changes in velocity due to change in area or sharp changes in direction.

Hence, the intake system should be designed to take this into account. The outlet of the plenum into the intake runners is where you get a sharp increase in velocity, the more you can accelerate the flow over a longer the length the better. Hence a long tapered inlet to the runner would be ideal but impractical.

The is a tendency to think that if it's turboed then why bother. Well if you want to get every once of boost in the cylinders, you need to minimise pressure losses due to flow restrictions through the system.

Pressure loss is a function of mass flow not velocity. If you are moving twice the mass due to boost you will have twice the pressure loss. Hence, I think it is more important to get it right.

TDs design of Plenum and inlet is about spot on. The tangential outlet of the runners creates a taper affect and a slow acceleration of flow into the runner.

Dave - can you make me one?

Saul Bellow - "A great deal of intelligence can be invested in ignorance when the need for illusion is deep."
Stephen Hawking - "The greatest enemy of knowledge is not ignorance, it is the illusion of knowledge."

So i guess the idea of a turbo then would be the guy at the back of the queue shouting BOMB!!!! :) in the packed under ground station and all the folks in front panicking to get on the train.

Two things are infinite: the universe and human stupidity; and I'm not sure about the the universe.

Been a while since ive been here....

Interesting ideas. Werent there issues with fuel injection that lead many to suggest the carb worked better ??

Have you considered mounting the injectors closer to the plenum, rather than right at the cylinder head ?? Might help dampen out any injection timing issues ?

Ive been thinking of working on mine later this year once I finish the Granada.

I was considering bringing the turbo manifold over the top, with longish tubes, and mounting the turbo above the drop gear casing. This would create very un-equal length runners, but does that really matter ??
Then the inlet manifold, albeit with short runners underneath, with TB/inlet towards radiator side.
might even be possible without bulkhead mods, although its just a thought at the minute.

What diameter of pipe are you going to use for the exhust manifold ??

O2 sensors mounted before turbo, wont last long. Temps will be far too high.
Ideally you dont want to palce the sensor where it will be much more than about 750degC

Pre turbo could reach as high as 1000degC.

For the Tig welder, Ive heard Miller Syncrowave mentioned many times...
Also check here.
http://www.fab-forum.com/default.asp

9.85 @ 145mph
202mph standing mile
speed didn't kill me, but taxation probably will

Hey Stevie, Long time indeed.

Basic probs with running the injectors that far away is that you're increasing the time 'variance' between the fuel leaving the injector and reaching the valve.
Imagine 1000 rpm - port velocity is approx 1/6th of it at 6000rpm (it isn't, but let's keep theoretical...)
Now, fuel is carried in the charge-air.
So, if your injector is next to the valve, there is little 'real' difference in timescale between the fuel leaving the injector tip and reaching the valve, weither at 1000rpm or 7000rpm.

If you now mount your injector 12" (say) away from the valve, and optimise it for 1000rpm air velocity, then at 7000 rpm, the velocity has increased by a huge amount so the fuel will get there to the valve much sooner.
Basically - the difference in TIME between the injector opening and it reaching the valve is a lot different.

This will REALLY screw up trying to get the thing to work with the conventional 'start and follow' injection event.
Ways to get round this:
1) Have an injector start event that alterswrt RPM - such that the fuel always reaches the valve at the same 'crank degree' no matter what the RPM.
2) Have a fixed injector event at (say) 100 degrees ATDC and open the injector symetrically about this event (eg, for 20degrees, it'd open the injector at 90 degrees ATDC and close it at 110 degrees.
This concept is the most interesting - as it uses the fact that at low RPM (and hence port velocity) you're only at really small injector duty...

We've actually got a guy on-board the forum who is a programming enthusiast, and he's already started writing the software for Megasquirt for a few options.
I'll be running a different ECU - one that is more of a 'piggy back' unit. It'll basically replicate the injector duty output from my DTA ECU, but (simply) put it in the right place such that this who thing will hopefully work...

I'll be setting it up with two O2 sensors - but let me assure you that this will be done with just a few psi - no more than 5 for example - just until we get the cylinders balanced. Once we're up and running, then the O2's will be gettign switched out for bungs, and they'll be fitted into the downpipe.


The 'runners' on the exhaust is a subject of much discussion - It makes sense for me that they should be equal length (volume) once they meet the turbine. How much of a difference - I don't know.



Tig is going to be down to cost and cost alone. I'll probably going for the Lincoln Precision Tig 185. It's on wheels - so is movable around the 'shop at least. Has various soft-start features and other stuff. pretty much ideal for my needs.

Edited by TurboDave16V on 17th Apr, 2006.

Very interesting this, Will be nice to see it working, I know you've spent a lot of time researching this, and, ooh tigged stainless manifolds, are they being polished? Its always handy to know some one who can TIG.

Just wondering what sort of throttle you will be using. A twin? one on each port, or a single before the plenum.

I have an 820 turbo TB with stepper motor for idle control, its (52mm though) incorrect info) 58mm. Got it for the 16valver but have mow changed to another. Its yours if you want it

Edited by Sprocket on 17th Apr, 2006.

With tubular manifolds, or simply ones with larger runners, and large plemum inlets, I assume it could lead to new ground with regards to camshafts ?
I have a spare mini turbo exhaust manifold, and I know the ports were extremely small, then again, it is a small engine.

And in case anyone doesnt know already, you can weld stainless veyr well with a MIG. obviously it doesnt look as nice as profesiionally done TIG, but it works just the same.
Alu is a different matter. There was a nice used Murex machine went on ebay a few weeks ago. Ended up a little over £1000. It had all the gadgets, water cooled, HF start etc I was sooo tempted, but its a bit beyond my budget.
But same as you, if spending anywhere near, may as well buy the right welder first time around.

I assume you are going to try and run sequential ?? I was thinking by moving the injector away, and running batch fire, you would nearly always have an injector firing to each port.
It may fire against a closed valve, but does that matter so much ? Adding that distance, would make fuel distribution more akin to a carb, but with much finer overall control on fuelling.

Comparing Subarus...their aftermarket manifolds are far from equal length, but good sized tubes, free flowing do give good gains.

Shorter runners usually help spool, but would longer runners perhaps help overall flow making a more efficient system ?

9.85 @ 145mph
202mph standing mile
speed didn't kill me, but taxation probably will

Edit my last post the TB is not 52mm but 58mm. Doh.

Lots of good points there Steve - but like you say - it's all new ground (or for us grass-roots folk anyway)...

Turbo-camshafts are something that are totally undeveloped IMO. But - the cam you'd optimise for a 0.25 turbine is not going to be optimal for a 0.35 turbine, so where do you draw the line?

it will batch all injectors once every 360 crank degrees. It means that you've got dead-fuel sat in the intake on 3/4 when 1/2 are doing their stuff (and vice versa) but that isn't the issue at this time. Sequentialising is 'Icing on cake'.

At this time, I still need to get it in the oven... LOL!

Sprox - I'm goign to source a US throttleBody - just for ease of replacement. I'm trying to do all of my bits this way - just to make things simpler for the future. Thanks for the offer all the same.