Porsche 993 twin turbo

[hoffman900]

Speaking of NA hemi chamber or 4 valve 4 -bangers, I havent experienced, or seen a case where the exhaust port size has made that big difference, however timing may have been sensitive (Lancia/Fiat TC engine for example).

Friends tell me all the time wedge chamber is a different animal.

Most vintage hemi designs have exhaust valves and ports way too big, so you’re working around that.

[ptuomov]

Speaking of NA hemi chamber or 4 valve 4 -bangers, I havent experienced, or seen a case where the exhaust port size has made that big difference, however timing may have been sensitive (Lancia/Fiat TC engine for example).

If you run a four-valve pentroof ITB engine with real race cam with a lot of overlap, I believe that an oversized header primary extending an oversized exhaust port is going to hobble the whole thing to be a dog at the lower end of the powerband. If you don't have much camshaft overlap, then the exhaust port and header primary size matter less, but then you're not making anywhere near the powerband average power that you could make and the engine is not competitive.

[juuhanaa]

Guys, please show me an example where that too big exhaust primary is the case. Beeing on track this year and seeing people run different headers on a class where they started messing with those engines before i was born. Doesnt make that difference? Also evolution of kitcars, interesting stuff. Honda make torq big time with a 4-1 headers...

[ptuomov]

Guys, please show me an example where that too big exhaust primary is the case. Beeing on track this year and seeing people run different headers on a class where they started messing with those engines before i was born. Doesnt make that difference? Also evolution of kitcars, interesting stuff. Honda make torq big time with a 4-1 headers...

Cross-cart Xtreme Junior racing class is an example in your neck of the woods.

[juuhanaa]

Guys, please show me an example where that too big exhaust primary is the case. Beeing on track this year and seeing people run different headers on a class where they started messing with those engines before i was born. Doesnt make that difference? Also evolution of kitcars, interesting stuff. Honda make torq big time with a 4-1 headers...

Cross-cart Xtreme Junior racing class is an example in your neck of the woods.

My point is, if the rules limit letsay cid, and we notice something doesnt make a difference, then we can try build the engine different.

[juuhanaa]

Speaking of NA hemi chamber or 4 valve 4 -bangers, I havent experienced, or seen a case where the exhaust port size has made that big difference, however timing may have been sensitive (Lancia/Fiat TC engine for example).

If you run a four-valve pentroof ITB engine with real race cam with a lot of overlap, I believe that an oversized header primary extending an oversized exhaust port is going to hobble the whole thing to be a dog at the lower end of the powerband. If you don't have much camshaft overlap, then the exhaust port and header primary size matter less, but then you're not making anywhere near the powerband average power that you could make and the engine is not competitive.

Please tell me some dimensions. I know how fast 180degree@1mm lift cams can go itb or without.

[ptuomov]

Please tell me some dimensions. I know how fast 180degree@1mm lift cams can go itb or without.

viewtopic.php?f=1&t=63194

That ended up with about 145hp/l with a 9300rpm rules-imposed rev limit (with way oversized ports and cams for the 9300 rpm engine speed).

[juuhanaa]

Please tell me some dimensions. I know how fast 180degree@1mm lift cams can go itb or without.

viewtopic.php?f=1&t=63194

That ended up with about 145hp/l with a 9300rpm rules-imposed rev limit (with way oversized ports and cams for the 9300 rpm engine speed).

Okay you were stuck with the cams, but i like you can make it better

Thats a another thing to mention, we tend to learn things when we are stuck with the cams. Now, the cams i were stuck had 180degree@1mm, and because im a rocket scientist i figured im in a hurry? I made up a 26cm long cone really, started 55mm dia. round and made it smaller towards the cylinder head where it matched 38mm round. Later we design better exhaust and gain like 30hp@7000rpm to my friends car which had OEM parts in it!

Anyway, a car that looked like junk and and bad headers in it, ended up with this result: (digger dont like M3 was only the second fastest 2wd rally car, but we do now have same duration cams)

https://oopsware.org/Sprint619/Syote210 ... 106res.htm

[ptuomov]

The moral of the story is that I believe now that the header folklore about head vs. header flange is all wrong. If the header pipe is larger than the exhaust port in the head, then you have to pull all stops trying to make the transition efficient. If the right size header pipe is much smaller than the exhaust port one is stuck with, then any sort of reasonable transition seems to work very well and time is better spent optimizing something else.

[juuhanaa]

ptuomov,

there has been numerous events when the BMW:s has been faster than me.. Its just me thinking loud that a wedge head could be more "sensitive" about the port size. I am aware of what David Vizard says about the lobe center angle being a? It makes sense to me and i would be very careful about widening the lobe centers what ever the engine is.

[ptuomov]

What's a good exhaust header primary inside diameter for this twin turbo engine?

Parameters:
3.6 L displacement from 6 cylinders, so 600 cc per cylinder
6800 rpm redline
Stock 408 hp at 0.7 bar peak power boost, target 500 crank hp at 1.1 bar boost
Exhaust valve diameter 42.5mm
Exhaust port diameter at the flange 38mm
Twin turbo K16/24 hybrids with each getting three 240 degree separated pulses
Turbine housing inlet 40mm being fed from three cylinders
Exhaust valve peak lift 10.9mm
Exhaust valve events at 1 mm: EVO 44 degrees BBDC, EVC 4 degrees ATDC
Exhaust camshaft duration: 228 degrees at 1 mm, 218 degrees at 0.05"

36mm primary ID, 40mm collector outlet ID that matches the turbine inlet ID, with this flow path shape? That’s a 23% increase in the area at the collector, which is a little on the high side for these cams.

97C326A5-8D33-4B16-8920-4AF78658C159.jpeg

7A42F3F9-4018-424C-B379-DC73406B8A52.jpeg

A580E112-BD20-481D-AFD0-C27B7F338E47.jpeg

C9AC964A-9D4F-440C-8034-F82179050E6C.jpeg

[juuhanaa]

What's a good exhaust header primary inside diameter for this twin turbo engine?

Parameters:
3.6 L displacement from 6 cylinders, so 600 cc per cylinder
6800 rpm redline
Stock 408 hp at 0.7 bar peak power boost, target 500 crank hp at 1.1 bar boost
Exhaust valve diameter 42.5mm
Exhaust port diameter at the flange 38mm
Twin turbo K16/24 hybrids with each getting three 240 degree separated pulses
Turbine housing inlet 40mm being fed from three cylinders
Exhaust valve peak lift 10.9mm
Exhaust valve events at 1 mm: EVO 44 degrees BBDC, EVC 4 degrees ATDC
Exhaust camshaft duration: 228 degrees at 1 mm, 218 degrees at 0.05"

36mm primary ID, 40mm collector outlet ID that matches the turbine inlet ID, with this flow path shape? That’s a 23% increase in the area at the collector, which is a little on the high side for these cams.



97C326A5-8D33-4B16-8920-4AF78658C159.jpeg7A42F3F9-4018-424C-B379-DC73406B8A52.jpegA580E112-BD20-481D-AFD0-C27B7F338E47.jpegC9AC964A-9D4F-440C-8034-F82179050E6C.jpeg

Are you restricted with the primary length? 240 degree separated pulses and 228 degrees at 1 mm sounds you could be safe by making the length you need to get it flow, and then find the size for the given length?

[ptuomov]

Are you restricted with the primary length? 240 degree separated pulses and 228 degrees at 1 mm sounds you could be safe by making the length you need to get it flow, and then find the size for the given length?

It’s a turbo street car, so the correct length is the shortest length that gives long enough turn radii for the pipes. The diameters still need to be decided, though.

What do you mean by this? “…you could be safe by making the length you need to get it flow”

[juuhanaa]

Shortest length sounds like turning the turbo supercharger using a back pressure. Im wondering how the turbine change things at the collector area, but remember it is the length what makes NA header flow, and it has something to do with the harmonics. I have modified the "streetable" NA to be better throughout the rpm band, by changing 4-2-1 headers to 4-1. It had 180 firing order and 180degrees@1mm duration cam. We had to cut some metal to make it fit

The newer engine had 4-1 headers in the same engine family when it came from the factory.

[ptuomov]

Shortest length sounds like turning the turbo supercharger using a back pressure. Im wondering how the turbine change things at the collector area, but remember it is the length what makes NA header flow, and it has something to do with the harmonics.

I don’t understand that either.

Yes, the exhaust manifold pressure does indeed drive the turbocharger. Are there other kinds of turbochargers?

Whether the exhaust manifold drive pressure that the turbine sees is smooth or spiky depends on the exhaust manifold. Spiky can make the turbocharger more efficient at harvesting the exhaust energy and the overall engine more powerful for the given cylinder displacement. That’s why the short, low volume exhaust manifolds work so well.

The most relevant back pressure from the piston engine’s perspective is at exhaust port during the valve overlap. The exhaust “back pressure” doesn’t matter that much before the intake valve opens, I mean it matters a bit but not hugely.

The short and big pipe is going to flow better than long and narrow, so getting the pipe to flow by making it longer doesn’t make sense. However, making the pipe longer may or may not get the cylinder head flow more, which will then force the poorly flowing long and narrow pipe to have to flow more.