Having spoken to him a couple of years ago when I had my engine / manifold failure, he was running a slightly different manifold (scara) than I was, running a GT30 and a 38mm ext. wastegate with a lot of boost, approx 2 bar IIRC, but alas, I don't have the email from him anymore

Ok maybe a bit more then, but really not much more to be honest.

Everytime when i finish something, i see what i should have done different. Easy when things are done, but pff, hard when you are working on it, and it has to be finished within an certain period. (always to late .

Time and patience are vital if you ask me.

Tried to cut some corners with software, but when i went to hec ( holland engineering consultants ) i got some serious doubts about the parameters that were put into the programm, so much for timesaving sadly enough.

Btw. was there not an very very nice evo with about 570 bhp, running with 38mm od on pistonheads if i remember correctly?


You are finished with your mani project then, if you are already 95% happy with it?

Time and patience I have and so true, absolutely vital.

No, it's not finished but it's only a little bit of welding needed and that'll be fine, the guy doing it won't mess it up.

Weak, was an unfair use of the word. I've known about that car for some time and like it very much (like all delta's) and in truth hope my own car makes those kind of figures, my point in response to juergen was about the breathing efficiancy of an engine, wether it be the exhaust or inlet side or the camshafts abillity to control pressures accross the cylinder.

Unless you have an insanly large hotside, choking will always occur behind the turbine wheel at higher revs and dependant on the boost level needed (exhaust mass) a properley sized wastegate should not choke at these higher points. I would expect the outlet from the collector to easily cope with the full situation.

Thanks - good answer. So, if the turbo inlet of CSA 2426mm^2 will not choke the mass flow from five cylinders, surely any primary with a CSA 1/5th of that area or larger wouldn't choke the flow from one cylinder either? Or am I missing something?

Your missing what gases would prefer whilst maintaining enough velocity

Obviously! - can you tell me then?

Instead of winding yourself up trying to fight some corner your wanting to camp in I think you should read what I've written, the answer to your last question is in there.

I just want some numbers so I can get a handle on it. At the moment it doesn't make sense to me - but I hope it will do after you or Tricky explain. So, if you could be a little less cryptic I would appreciate it!

p.s. to be clear, I have no corner to fight!

What number would you like?

Well, the ones that I can use to calculate the area relationships between valve/primaries and primaries/collector. The first part you have covered i.e. valve/primaries - so just the second part I guess.

Let the collector MCSA be determined by the turbine housing entry, you are about right with the area as I said.

So, are you saying, there is no science behind it - it is just whatever it is?

There is an exact science to collector outlet D in a N/A engine, I don't know it off the top of my head but I will look it up later on. On a turbo unit, from what I can gather the dimension is'nt as critical as the former.

Flow not being at choking point does not nesacerilly mean no restriction either. You can still have sub-optimal flow and not be at choke.

Thanks Tricky. But what would indicate a sub-optimal design. Is there some critical gas speed to look for in the primaries and/or the collector maybe? And, if you have selected your primaries based on valve size, if you then switch to a T4 turbine housing (which has a larger inlet area than a T3) should the primary size be re-considered? Or, if the primaries are the correct size, does it not matter what happens at the collector?

What do you mean by science? a sum? No equation for that I've ever seen but likely someone could work the numbers into somehow matching various turbo flanges but it'd be a mind flexer. When push comes to shove it has to suit the turbo so within those constraints maybe you mean subtle sculpted radius and the science involved in that? At fabrication stage the detail is at the mercy of the craftsman (or is he a tradesman who couldn't be called that), has he any gray matter applied to his job or is it a repetitive skill? Maybe he takes a lot of time on a never noticed detail or maybe he wondered what it was that he was making that day or hell, he might of been up all night reading something related. Science I suppose is in every detail if you let it.

If it's a definative answer you crave you'd wait a long time, nothing ever could be to my mind as no two builds are the same even by the same person. To be in the ball park area is possible and in this case plenty enough, after that the devil is in the detail. Only after multiple manifolds with extensive testing could it be dialed in closer to optimum. Maybe you can amaze us all with a modular manifold that can be chopped and changed to the best results, on that application.

Hopefully your going to side swipe us all with a fantastic sum

Sub-optimal is the skinny runner theory, think of the engine as N/A - gas needs to expand it's way out of the cylinder. The turbo does it's own job of speeding it back up again, no need to do it right after the port.
I don't think there is a critical gas speed to look for in the tubes but maybe in the collector yes, which is what a proper merge collector is partly about.

I don't think the pri. size need be reconsidered for a turbo swap, but going from say a gt3071 with a .63 AoverR to a 3582 or a big T4 says a lot about how your use of the car has changed and prehaps a different runner length might be more suitable and indeed the outlet area at the housing could need to change too, possibly meaning a new collector if there is a big area increase.

Highly unlikely, I'm afraid. Everything I had thought I understood to be true about turbo exhaust manifold design criteria has been totally debunked by you and Tricky, so I can offer nothing constructive.

That is exactly the case. Doing a straight swap of the existing turbo and manifold (design parameters, not the physical manifold of course) onto a 16V 2.1 litre engine from a 2.0 litre 8 valve engine will give too much torque (for the drivetrain) at 4000 RPM but run out of flow before 7000 RPM with the better breathing engine, never mind supporting the 8000+ RPM target. The T4 I have would seem to match the torque and power objectives and eliminate boost creep problems, so I have to amend the design to that. Lengths I am not worried about, as I have confidence based on previous efforts that I can get that right - pulse tuning is no different between NA and turbo engines except for the effect of higher EGTs.

Are you bound by regs, why are you using a T4 ?

'cos I have one! - And it matches the flow I need.

Thats fair enough, but I would have thought a more up to date unit would be top choice ?

I can't stretch to a ceramic BB unit... there is a recession going on you know...

I hadn't noticed one ! Save up, theres tons of choice on tubbys these days and the eficianys are sooooooo much better than the old skool. Even the smallest frame billet gt30 can flow enough for nearly 600 hp at lower boost and around 6-8% less heat input .

What I have is more of a T4 plus - it's a bit special... It has current design "aero efficient" turbine and compressor wheels. The cost of ceramic BBs and non-plastic cages is the big problem... If you can find me one for less that a grand I'd like to know where...

I know what your saying, I just spent twice that on the same item, not cheap with all the extras.

Just spend the money with Burns and get a double slip, they'll get one of the craftsmen to do all you could wish for in a collector. I'd run the turbo and see how it behaves, sounds capable of the target power without being pushed too hard so unlikely to disappoint and hold the blame on it's own.

Of course they are expert craftsmen and could make a very pretty one - but I can't tell them what I wish as I can't define a specification at the moment.

I guess I will have to find some expertise somewhere, or do some reverse engineering.

That's the beauty of Burns, they'll take all of that under their wing and provide you with what you need rather than what you tell them. It is expensive I know but well worth it on a number of points.