Daves Compound Twin turbo XUD

[ginge191]

I LOVE the fact this runs on a TMIC!
Can't wait to see some videos of this running!

[Anton]

Congratulations for finding the motivation to keep going! Looks awesome.

Well done.

[Dave]

TMIC's are for bosses.

I have had to search high and low for the motivation to build the engine, but getting it into the car took all of 3 days - some prep work had to be done, and some is still not finished. Moved the battery, modified gear linkages, moved electrics, bypass heater matrix, cut parts of chassis, on the to do list is bigger air pipes, jolly good clean inside and out (my gf hates it at its best, let alone with engine parts all over inside) and sort out solenoid for the reverse on the 6 speed box... and I have MOT due in 1 week. I did replace lots of front end bushes too which has made it handle amazing with coilies on the front too

Long way off being something amazing, but its gathering speed now

[Mattcheese31]

i like it . . . . .who am i kidding i'm jizzing over here . . . . . .hope it holds together mate, you seem to be doing it properly this time so hopefully it'll stand strong . .

[Poodle]

Haha yeah, just put those figures up as examples, the potential is incredible. Two 30psi turbos..? 120psi at the inlet... O.o

Look forward to seeing how you get on with this, looks promising!

[Xud Missile]

fupping awesome. Shame I missed first fire up, can't wait to see it on the road

[Jtrigga]

Good to see that you are still going with this, that block wont stay blue for long. I look forward to the usual youtube videos.

[ginge191]

What rods are you using this time around?

[ash23]

looking good dave ! i need a ride when its up to full potential

[silverzx]

Oooh, tasty XUD.

[zx_volcane]

Holy crap,

This will be an absolute beast when its all setup, compound ftmfw!

[darrenjlobb]

No, the big turbo feeds the little turbo. Little turbo boosts up first, once that's going it effectively creates more exhaust gas - enough to spool the bigger turbo.

The best bit is when the bigger turbo comes on blow, it's not exactly what you'd expect. Two turbos boosting at 15psi makes 30psi right? Wrong. The little turbo is now compressing air that's already compressed, this creates super-awesome boost (technical term). With one blowing into the other they "compound" their pressure ratios and produce more boost than their individual capabilities added together. Say both turbos individually boost at ~2bar absolute pressure (absolute pressure = boost pressure + atmospheric pressure; ie what we know as 15psi of boost), expressed as a ratio to atmospheric pressure this is 2:1. So we have two turbos compounding their pressure ratios of 2:1 each, multiply the ratios together and we get a final pressure ratio of 4:1. Knock off a bar to account for atmospheric pressure and you're left with 3bar or 45psi of boost...

This is kinda incorrect, without going in pages trying to explain.

The only things to consider with compound setup are PR (pressure ratio) and flow in say cfm, these are the things you will find on any turbos compressor map.

Boost pressures (psi) are totally irrelevant here as it means nothing. The turbo wont make x psi, it will make x PR, when i say PR, i mean the ratio between the pressure entering the turbo (so normally atmopsheric) or in compound whatever the other turbo is making) vs the outlet pressure.

You can quickly calculate what total mani pressure you can make, and by using compressor maps you can work out what pressure ratio to run each turbo at to keep both turbos near peak efficiancy.

Flow is also critical, as its stupid having a big turbo that can flow more air than the small turbo can make at peak, as it will just surge (hence why i was changing my 2256v for a 2260vk. The whole point of compounding is to allow the small primary turbo to sit CONSTANTLY in its PEAK effiancy band (which will be at a lower PR than you need to make the power), thats where it can FLOW its most air, which is most important, but normally on there own, you cant do this as you need more boost / manifold pressure, so by using a compound, you can get the full PEAK FLOW from the primary, and still get your high manifold pressure.

Turbos are happy, engines happy everythings happy, im crap at explainging things but thats my attempt as I think there is some confusion here.

[cwspellowe]

So basically what you're saying is.. epic amounts of win for reasons noone really understands but that doesnt matter because you won't be able to wipe the smile from your face?

Where do i sign up?

TBH it's about time someone took on the compound boosted crown since the bus' XUD disappeared a while back. I'd thought of it but can't justify the costs and would have nowhere near enough fuel at the mo.

[Dave]

^ What darren said

There is rough compressor map matching going on here, but the lorry turbo was a scrapyard find so cost next to nothing, and may not be ideal! but its got a high flow/low spool down the back which should accommodate for the large lorry turbo.

Anyhow, sorry for this atrocious video, and I also missed the very first fire! but we did have power issues, and fuelling issues, and valve seating issues, but after she struck up the valves drove home nicely!

---

No MBC on yet, and vanes basically wide open, making 14psi at about 3.5k-4k.. LDA not even dropping so no danger of her spitting a rod yet

[Poodle]

Sorry, was trying to explain it in terms that didn't involve me sitting at the keyboard thinking for half an hour, too lazy for that.

Looks awesome anyway, how long until we get an in car vid?

[darrenjlobb]

No, the big turbo feeds the little turbo. Little turbo boosts up first, once that's going it effectively creates more exhaust gas - enough to spool the bigger turbo.

The best bit is when the bigger turbo comes on blow, it's not exactly what you'd expect. Two turbos boosting at 15psi makes 30psi right? Wrong. The little turbo is now compressing air that's already compressed, this creates super-awesome boost (technical term). With one blowing into the other they "compound" their pressure ratios and produce more boost than their individual capabilities added together. Say both turbos individually boost at ~2bar absolute pressure (absolute pressure = boost pressure + atmospheric pressure; ie what we know as 15psi of boost), expressed as a ratio to atmospheric pressure this is 2:1. So we have two turbos compounding their pressure ratios of 2:1 each, multiply the ratios together and we get a final pressure ratio of 4:1. Knock off a bar to account for atmospheric pressure and you're left with 3bar or 45psi of boost...

This is kinda incorrect, without going in pages trying to explain.

The only things to consider with compound setup are PR (pressure ratio) and flow in say cfm, these are the things you will find on any turbos compressor map.

Boost pressures (psi) are totally irrelevant here as it means nothing. The turbo wont make x psi, it will make x PR, when i say PR, i mean the ratio between the pressure entering the turbo (so normally atmopsheric) or in compound whatever the other turbo is making) vs the outlet pressure.

You can quickly calculate what total mani pressure you can make, and by using compressor maps you can work out what pressure ratio to run each turbo at to keep both turbos near peak efficiancy.

Flow is also critical, as its stupid having a big turbo that can flow more air than the small turbo can make at peak, as it will just surge (hence why i was changing my 2256v for a 2260vk. The whole point of compounding is to allow the small primary turbo to sit CONSTANTLY in its PEAK effiancy band (which will be at a lower PR than you need to make the power), thats where it can FLOW its most air, which is most important, but normally on there own, you cant do this as you need more boost / manifold pressure, so by using a compound, you can get the full PEAK FLOW from the primary, and still get your high manifold pressure.

Turbos are happy, engines happy everythings happy, im crap at explainging things but thats my attempt as I think there is some confusion here.

Have just re read poodles post, and he is acaully correct, infact we are both saying the same things, I just read it to fast first time and thought you were adding psi+ psi together, but you are in fact using PR, and i missread, sorry!

[Ruan]

I just had to recheck myself there that I was actually getting this right...

I noticed this and was WTFing for a few minutes...

And yeah, it multiplies the PRs minus atmospheric pressure.

[Dum-Dum]

Long story short:

charger + charger + charger = boost x boost x boost = WIN

Or

Its not a pressure adder its a pressure multiplier.

[cwspellowe]

It's a WIN multiplier

Plus it makes you 10x more attractive to all women ever

[Ruan]

Long story short:

charger + charger + charger = boost x boost x boost = WIN

Or

Its not a pressure adder its a pressure multiplier.

Doesn't multiply the boost, multiplies the RATIO

[Dum-Dum]

OK so i slightly over simplified it but the pressure ratio is basically boost divided by flow (or something like that) so it is kinda boost.

[cwspellowe]

Er, pressure ratio is just the ratio of output pressure to atmospheric.

[Dave]

Typical high powered XUD, gotta come to bits again now for a repair :p

It will rest in pieces, eventually

[darrenjlobb]

Nah its pressure ratio from in to out taking into account atmospheric (atmos + boost) you include atmos in the calculations by using ABSOLUTE pressures...

Also superchargers which work as positive displacement blowers work differently

[Dum-Dum]

Yeah, your right of course. I've got man flu or monkey aids or something so my brain dosent work.

[Ruan]

Pressure Ratio is simply the ratio of the inlet pressure to the outlet pressure...

So say a turbo is working at a PR of 2 (at atmospheric that's 1bar(14.7psi) of boost above atmospheric) That essentially multiplies atmospheric pressure to make 29.4psi Absolute (Since atmo is 14.7psi ...) Feeds into another turbo working at PR2 - That turbo then multiplies the inlet pressure (29.4psi absolute) by a ratio of 2 = 58.8psi absolute... Convert back to atmospheric = 44.1PSI...

So the way you work it out is ALL in Absolute

Atmospheric multipled by LP pressure ratio - 14.7 x 2 = 29.4psi
LP side multiplied by HP side - 29.4 x 2 = 58.8psi
Convert to Atmospheric - 58.8 -14.7 = 44.1psi

[cwspellowe]

It's all the manhoods battering your brain via the back of your throat. Unfortunately it only gets worse from here.

Back on topic though, what's happened now Dave?

[Ruan]

Or another more realistic example in Bar this time...

Atmospheric multiplied by LP pressure ratio - 1 * 2.2 = 2.2bar
LP side multiplied by HP side - 2.2 * 2.8 = 6.16bar
Convert to Atmospheric = 5.16bar of boost...

That's from a turbo making 1.2bar and 1.8bar of boost individually.

f*cking love compounding.

[Dave]

It's all the manhoods battering your brain via the back of your throat. Unfortunately it only gets worse from here.

Back on topic though, what's happened now Dave?

Cooked my damn £300 VNT, very unhappy - well just a new seal I think, but its just annoying having to pull all the custom mani back off etc. Hopefully havent fried anymore fins ect, but I took it out for a dash after it was blue smoking and still pulls hard so couldnt have done more than the seal....

[cwspellowe]

It's all the manhoods battering your brain via the back of your throat. Unfortunately it only gets worse from here.

Back on topic though, what's happened now Dave?

Cooked my damn £300 VNT, very unhappy - well just a new seal I think, but its just annoying having to pull all the custom mani back off etc. Hopefully havent fried anymore fins ect, but I took it out for a dash after it was blue smoking and still pulls hard so couldnt have done more than the seal....

I feel your pain.

When i was at Jonny's house I thought i'd killed the GT2056 with some of the weird ass noises coming off it and the complete lack of boost. Imagine my delight when I found the old turbine wedged in the exhaust

That was a £300 blower too. I'm rather precious of it now after the cheaper versions didn't agree with me...