just to add to this and feel free to correct me if i'm wrong. I haven't had THAT much to do with turbo engines but from memory of the mind of useless information, I don't think you need to worry about tuning the length of the inlet manifold. usage of forced induction negates the need for it, IIRC
Also, I think you would be well advised, due to this being a 6 cylinder, to use a turbo with a twin entry on the hot side (exhaust). This is only if you're using a single turbo, it will make it easier for you to control the exhaust gases entering the turbo. you can plumb each bank into different entries
Have you explored the vast world of injector sizing and positioning yet? again correct me if i'm behind the times here. Positioning of the injectors can affect torque and HP, people who run big power turbo engines usually run with the injectors further up the inlet path, as opposed to having port injection. IIRC the theory behind this is greater atomisation of the fuel/air mix, the further up the track the better.
When twincharging would the OP be best to run with small injectors at the port entry (for low end) and then switching to larger injectors further away as the turbo starts to blow?
If i'm confusing the situation feel free to delete my post
Assuming 20 psi will reach your power goal, and that does sound quite reasonable, but you would know a lot more about the capabilities of Porka engines than I do.
So starting out with a well intercooled 20psi as our goal, which is a pressure ratio of 2.36, let's assume we want to end up with equal pressure ratios across both turbo and supercharger. That would be the square root of 2.36 or 1.53 pressure ratio across each.
So we end up with 14.7 Psia absolute pressure going into the turbo, multiplied by 1.53 which will be 22.49 psia absolute coming out of the turbo. Or 7.79 psi boost pressure.
Pressure going into the supercharger will be 22.49 psia absolute, multiplied by 1.53 which will end up as 33.41 psia absolute in the inlet manifold. Or 19.7 psi total boost pressure.
If you want 800 Hp that will require 1,200 CFM of air at a pressure ratio of 1.53 from the turbo.
There would be many advantages of twin turbos at that power level, especially with a flat six.
The reason being that we need a LOT of airflow at what is realistically a quite low pressure ratio.
Eye balling flow maps will quickly tell you that 600 CFM flow at 1.53 is much more sensible goal than trying to match one monster turbo with 1,200 CFM flow at 1.53.
Also the exhaust manifold design and general installation problems will be far fewer, and turbo response vastly better with much smaller twins.
Turning now to the supercharger. Engine capacity 3.2 litres, or 1.6 litres per revolution engine displacement.
A pressure ratio of 1.53 may require about 1.6 x 1.53 = 2.448 litres of blower displacement.
As your blower has 1.3 litres per rev, first guess at the blower drive ratio might be about 1.88:1
That is a very acceptable drive ratio to have, it should all work out very well.
The beauty of all this will be 20 psi of boost pressure, but the turbine back pressure is very likely to end up being no higher than maybe 8psi, (similar to the turbo boost contribution).
With 12psi positive pressure differential across the engine its going to make a lot of power, and the exhaust heat will be able to escape.
Especially important with what I am assuming is to be an air cooled engine.
As far as inlet manifold goes, you definitely don't need long tuned intake runners with a roots blower.
The cylinders are going to fill at low rpm regardless. So there will not be the loss of low end torque that you might normally expect with a turbo or normally aspirated engine with short or no intake runners.
At high rpm, and 12 psi positive engine differential pressure, ram tuning is not going to make much difference.
If you have insufficient room, just put a big box over the intake ports with bell mouth entries.
The Top Fuel guys are making 8,000+ Hp with just a big ugly open box between the blower and the heads.
No fancy induction tuning needed on those things, just raw boost pressure. And it works fine.
One final thought.
The turbos dont "know" that there is a supercharger there.
The 1.53 blower pressure ratio effectively makes the engine seem like a 4.9 litre engine as far as the turbines go.
For selecting a turbine housing for twin turbos, each turbine would effectively be being driven by a 2.45litre engine up to only 8psi boost. The turbo supplier should be able to recommend a suitable a/r for that.
If still in doubt, go up to the next larger size, it will certainly not be lacking low end boost !!
Also known as the infamous "Warpspeed" on some other Forums.
Thanks about your inputs Jibo and Tony! All comments are welcome!
It's going to be twinturbo+supercharger setup and Yes it is air cooled.
I was planning to use single injectors for simplicity; fuel rails, room etc. For my understanding it is possible to get good idle with modern 1000cc injectors?
And place them after separate throttles. ECU (Finnish Hestec) will support twin injectors if needed.
I found that Audi engine where the charger is from has very short intakes. The package is very neat, it has water intercoolers as well integrated but naturally sized for different Audi models, up to 400 hp I think. Those charge coolers have 15,7 sq inch area to flow with high density turbulators. With nearly double hp/flow they might be quite of restrictors?
Probably need to open up the housing to install bigger ones. Before have to make some kind of temporary end plate and flow test the original cores
What's are your opinions for my exhaust port and header sizing, intake/exhaust ratio ---> overlap and cam selection ideas?
From the results others are seeing, modern 1,000cc injectors, along with a good engine management system should in theory be able to reach 1,000 Hp at 100% duty cycle with good idle characteristics.
That assumes petrol. Ethanol will require something larger.
Like turbos, injectors are getting better and better as time goes on.
I like the six throttle body idea, its going to have razor sharp throttle response, and you can then fit really large volume plenums and intercooler cores to it, whatever will fit into the available space.
Not familiar with the Audi intercoolers, but the Jaguar V8 also uses a pair of air/water intercoolers, and the latest blown Jag is quoted at 500Hp. I suppose its a matter of what you can get, and what fits.
You may also need to think about some cooling between the turbos and the supercharger.
The rear supercharger bearings are going to run hotter than in a normal supercharger application, where ambient air usually enters the rear of the blower.
Its just something to keep in the back of your mind.
I have never tried it, but it may be possible with an air/water system to conduction cool the bearings and the rear of the blower case by circulating water around the bearing area through a hollow sandwich plate bolted directly to the back of the blower case.
I believe the Eaton specification for rear bearing temperature is 50C continuous or 70-80C for short bursts, and that is probably being very conservative.
None of this may actually be necessary if your supercharger bypass flows air around through the main intercoolers when the supercharger bypass is open at engine idle and small throttle constant speed running.
But if the blower case heat soaks and becomes too hot to touch, something will need to be done.
As far as the cylinder heads go, Madmac had the cylinder head of his twincharged EVO5 extensively ported with larger valves fitted and it made absolutely no difference to the dyno numbers. It seems that engine airflow has more to do with the supercharger and turbo capacity than the cylinder head, so I would not get too carried away initially.
There are guys making similar power to your goal with one litre less engine capacity and only four cylinders.
Its always something you can do later on.
Similar thing with valve timing. A lot of overlap is just going to blow fuel out through the exhaust.
And this is going to be a torque monster with a very strong top end with just about any valve timing.
Making very large power numbers with twincharging is a lot easier than most people expect.
As mentioned earlier in the thread, with three cylinders feeding each turbine, if you use no more than 240 degrees seat to seat exhaust duration, one valve will close fully before the next one cracks open.
You can give it a bit more duration than that, with lengthened exhaust runners, but a lot more exhaust duration will have one cylinder blasting exhaust back into the previous cylinder during TDC overlap, which is definitely not going to help.
Your best bet might be to use one of the computer engine simulation packages and play around with that.
If you tell it the engine is supercharged with about 12 psi positive pressure differential with a positive displacement supercharger, it should be able to come up with suitable inlet valve timing.
Valve timing is not going to be a critical feature.
Think about it this way.
With a positive displacement supercharger, once the air has passed through the rotors, it MUST flow through the engine regardless of inlet valve timing !
So you can be a bit conservative with valve timing, have a very well behaved engine, and lose nothing power wise.
The main thing is to initially correctly size the supercharger and turbos, and provide efficient intercooling.
With the throttles placed after the positive displacement supercharger, the design of a very smooth progressive air bypass system becomes extremely important.
Everything else is surprisingly a lot less critical than you are probably expecting, its a very forgiving system.
Also known as the infamous "Warpspeed" on some other Forums.
in 91. it was a twin staged turbo v8 .a little whle ago I took the small turbo out and tried it on the big single , which is very big .a holset hc8-3 with a 67mm ind.
comparing the performance of the two setups was interesting .. with the small turbo in line , it would make 9 psi by 2500 ,and the big turbo start making boost by 3k then by 3500 the big turbo was making almost all the boost,as the ex pressure differential over the small one reduced . unfortunately by 5500 rpm the lack of flow through the small turbine would limit top end , it needed a bigger small turbo turbine side to compensate , but the driving response over its operating range was electric .
trying it with just the big turbo produced exactly the effect you would expect , without the small one to make lots of exhaust gases ,it would amble up to around 5 psi by 6500 rpm .and definitely poor response . my next plan is to try a split housing valve .(one day)
my point is that the supercharger will kick a much bigger turbo than you might expect into action in a big way ,as it creates so much more ex gas .
A roots blower sitting on top of that beast with the BIG turbo would absolutely transform it.
Its all really interesting, and exactly as Robert says.
The roots blower provides the exhaust mass flow at amazingly low rpm to really stir a big exhaust turbine into action.
Even absolutely minimal boost up stream of a roots blower really fills those rotors at any rpm, but especially at the top end where blower Ve is usually starting to roll over.
And right through the entire rev range, boost is going to plateau at much higher than turbine inlet pressure, so complete total exhaust scavenging at TDC overlap is a slam dunk.
Total scavenging means excellent exhaust heat removal, complete cylinder filling (free of exhaust dilution) and a much reduced tendency towards detonation.
This is where the massive low end detonation free torque comes in, these things pull like a steam engine at low rpm.
Very easy to drive especially from a standing start, and you will be doing a lot less gear shifting, the engine flexibility is incredible.
Compounding enhances the characteristics of both the roots blower and the turbo, while at the same time eliminating the separate disadvantages that each of them has.
And its all a lot less critical to get working really well than most first timers expect.
Also known as the infamous "Warpspeed" on some other Forums.
I have an old Turbocharging book by Hugh Macinnes. Probably from late 1980's. Is it still a good reference. Should I just forget it and move into a more recent book?
