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Thread: twin turbo Vs Big single?

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    twin turbo Vs Big single?

    here is good video to do the comparison

    https://www.youtube.com/watch?v=45ZODU3XWlg

    Last edited by Humpty's Revenge; 29-05-2020 at 02:10 PM.

    Bye for Now!

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    Thanks for linking the video! Modern turbos are very good! Have definitely not been thinking about that for my Legnum, no, not at all...

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    it has been some thing that has been discussed before but i watched this video and it changed my mind in what could possibly be best for performance, not necessarily cost.

    you have to bear in mind this is a set up on an RB26 and not a 6a13TT so i dont know how that effect the situation. but people have done it and ended up with good results.

    the single route also means if you wanted to go smaller to start with than change up to a bugger exhaust housing later then it is a bolt on change.

    i am still not convinced about the lower down rev range spooling, but you are using the 2.5L to spool the turbo and not 1.25L to spool a smaller turbo. you would probably have to scrifice the some of the top end and go for a small A/R thean the 1.01 that they used but it does sound good.

    goes to find out price of a GTX3576 or GTX3582

    you are looking at £2k Plus just for the turbo.
    before any fabrication costs. way out of my budget.

    you can get china copies of the GTX35 but you would want a twin scroll housing.

    i think this is the way adam findlay went with his big single build.

    but as i say totally out of my budget ragng on a car that is worth £3K or less
    Last edited by Davezj; 30-05-2020 at 11:59 AM.

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    I was a big fan of TT setup until I dig deeper and see other builds now I'm completely converted into a single turbo. Yes you absolutely right Dave it will not cost £2.50 :-) to do it, but modding with twins would not be cheap either as simple refurb each of them will cost no less than 200 each.
    How I see this is, after conversion to one single you will have car with very close to 500 bhp, now show me 500 bhp car for less than say 6k? They are exist but, I'm taking about newish bmw or other cfappy audis you will need to fork out 20k+ that's my way of looking at this.
    His FL Legnum VR4 running 238.8 ATW HP and 500Nm @1.05 bar on LPG
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    you might have 500hp with the turbo setup, but it will not last long without spending money on the bottom end rods pistons etc.

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    Quote Originally Posted by Davezj View Post
    you might have 500hp with the turbo setup, but it will not last long without spending money on the bottom end rods pistons etc.
    Well yes and not, Greg bend forged rod on crappy tune, too early boosting too much, and drive bigger power on standard engine with proper tune, yes its always better to Forge our engine but in case 'up to' 500 with sensible tune i would keep stock (refurb Ed) bottom end

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    yes you can manage it with a properly controlled tune but you really need an aftermarket ECU to do that and that will be about another £1k for a link G4+ , haltech elite 2500, or something like that. it starts getting really expensive when you add more and more stuff.

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    it is still a good price for performance car with the power of a £20K equivalent car. you just have to have about £10K budget to start with. to buy the base car the turbo and engine upgrade (rods pistons cams), after market ECU.
    and you will have one hell of a car.

    3K car
    sort the mechanicals £1K
    £1K ecu (you will have to do some wiring yourself)
    £2K turbo
    £2.5k pistons rods and Cams
    this leaves £500 for the fabrication, you will have to be handy with a welder and cutter and the fabrication, but it will be satisfying to do.

    but i think to do this you have to have a very good plan and not use the car at all until the mods are done. it is a big round of mods to do but it would be the quickest way to do it.
    Last edited by Davezj; 30-05-2020 at 04:56 PM.

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    Well yes as usual every stick have two ends, if someone looking for affordable 500bhp then daftest idea is to go with vr4 :-) there is much better options out there, search what ppl archive with dirt cheap saab or tons of cars with group VAG 1.8T engine.
    We stuck with the vr4s here and need to think how we can upgrade them, so we all have car in various state so that 3k saved, I'm pretty sure you can get decent turbo in 500-1000 bracket so another 1k saved, then is the ecu, why spend 1k on something which we have decent tunable ecu? If we can adjust fuel ign and boost what else is needed to tune bigger tubs? Yes so far in my example fabrication will be biggest expense, but again, is never to late to learn.
    Just to make it clear I'm not here to argue, just show my point of view with hope someone can show their and may we all have constructive debate.

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    I do understand it can be done. A lot cheaper. I would yes we have a car already in good condition ISH. So I would say £4k saved.
    I think the ECU is a good way to spend £1k as it means tuning for max timing for best torque is possible you can't really do this with a reflash ECU. This sort of tuning is a must for a proper setup and tune.
    Yes turbo can be had for 350-1000 but not gtx35, depending on type and quality.
    Engine would have to be strengthened if we are talking 500hp. So I still think you will need to spend about £2.5k at some point to make the engine last. You can risk not doing any engine mods
    Then the fabrication cost, you could all of it yourself which would be the best thing to do. As you know exactly what has been done and to what quality/standard. So you are only paying for materials which would probably eat up the whole £500 budget in all reality.
    Pipes, plate and flanges and fabrication consumables . You will have to do inlet pipework, exhaust manifolds, dump pipes, merge collector, wastegate pipe and flanges, wastegate. Mounting brackets, heat shielding, etc. So lots to consider.
    So yeh you could do it cheaper.but not many people will have all the required skills to do it all and save the substantial amount of cash that doing this yourself would achieve.

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    Thumbs up

    double post
    Last edited by Davezj; 31-05-2020 at 10:33 AM.

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    the tuning is a funny one , there are quite a few people on here that have aftermarket ecu link g4+ and i dont believe anyone has done the Max Brake Torque (MBT) tuning for the VR4. once it has been done i believe it is possible to transfer the MBT figure to any engine of the same type. as it is not dependant on AFR air flow, boost pressure, cam lift, etc. It is effected to a small degree by the actual fuel used, E85 will require about 3 degrees less timing to produce the same torque figure as petrol and i am not sure about LPG but that is easy to test with a petrol/LPG car. i think that once you know the MBT timing point for an given engine geometry, it is applicable to all types of tunes, boost pressure, porting cams, etc. the issue you have is getting to the MBT point as most setups are limited by knock before they reach MBT. which is why ignition timing is still a tunable parameter on most engines. every engine will have a different torque and power figure at the MBT point based on how much air and fuel is being burnt but the MBT point will be the same. however most engines are knock limited and will never reach the MBT point. but with high octane race fuel or LPG gas or liquid LPG injection you can use much more ignition time and get to the MBT point or just very good charge air cooling can be used to prevent knock (water/meth injection or very good intercooling could be used).

    but if you could use a a more knock resistant fuel to do the MBT test and then compare to petrol and get a consistent timing difference on tested cell to MBT you could creep up on the MBT ignition timing point and when knock occurred you can back off the timing but you would know how far away you are from the full potential of the engine and make a choice to chase more torque or be happy that you are only a few degrees off the max torque achievable.
    It can make choices for you with respect to investing in additional charge cooling equipment or switching to a different fuel. cost vs reward.

    to do an MBT tune for one cell in the ignition map you need to be on a load cell dyno and have control of the rpm by the dyno and control the load cell selected by throttle, so for a set RPM you change the ignition timing one degree at a time in quick succession on a recorded run. so the graph on the dyno will be torque vs ignition timing at a given RPM. As the ignition time is increased for range 10deg to 40deg BTDC, the torque will rise and keep going until MBT point then the torque will drop off. so for this cell you now know the MBT point for this one cell in the ignition map. but there are something like 15 by 9 = 135 matrix of cells not all need to be tuned for MBT but a lot will.
    so that is one cell tuned for MBT. but if you don't have a ecu that can be adjusted on the fly as the car is running on the dyno you will have to reflash the ecu for every time the ignition timing is adjusted and it is just not possible to do this with a reflash ECU.

    so i have been desperately waiting for one of the lucky link g4+ ecu owners to have the MBT tuning done on a dyno and then share the results, i have even offered to go halves on the cost of the dyno time required to perform the MBT tune but no one seems to want to do it, or understands the importance of doing it. it would make the ignition time tuning so much easier for everyone.

    as long as you dont have knock you can set the ignition timing to the MBT point .
    the MBT point corresponds to the maximum cylinder pressure point needing to occur at about about 16-18 degrees after top dead centre. which is the point where the combustion event gets the maximum mechanical advantage to push the piston down and turn the crank. This point does depend on the configuration of you engine but can be calculated precisely by analysing the conrod journal separation on the crank and conrod length, plus some other stuff. but it is about 16-18 degrees after top dead centre.
    you might think this is easy to do and it will be a fixed value but due to the speed of the engine rotation changing as you climb up the rev range, so the ignition timing applied must be earlier in the engine cycle as the revs climb to ensure the the max cylinder pressure due to the burn of the air and fuel occurs at the 16-18 degrees after top dead centre.
    the general rule of thumb is as the rpm increases, the ignition timing can be increased to gain more torque. but it is not a linear relationship.

    hope this makes sense. you will have to watch the MBT tune video from HP academy, which explains to much better then i can.
    watch the entire video to understand what and why he is doing the stuff he is doing.




    Last edited by Davezj; 31-05-2020 at 11:18 AM.

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    Bloody heel Dave, I wonder if Carroll Shelby knew that's possible when designing his cobras or GT40 which win Le Mans couple of times, tbh there's a saying that there's some kind ppl that can find problem for any solution, I try to find easiest way to improve my car, let's let rocket science for Elon Musk to launch his rocket properly, w hat I'm trying to say, and by any means I have i dig on you Dave as I like your way of looking at things is so much depth as no one else know to me personally, by this what's stated above its not very useful in real life, as if we go this way we will have to work in what dirt air car suck in, at what altitude and what condense air was that day. Sorry for being sarcastic but we not try to brake world records for the best 2.5 v6 engine or get the crown for fastest vr4 on the planet. The point is, we all have about 20 years old cars and trying to improve them as 99% of them needs a better tubs or at least rebuild of 20 years old ones. To me all tuning is about how much fuel you can squeeze in cylinder to make as big bang as possible without damaging the rest, so is i can tweek timing and fuel and boost im happy man not need fancy lc or any other crap, my TV can play uhd, so what I don't Wath uhd anyway

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    you can have a spark lug with a pressure sensor built into it and you can measure the max pressure in the cylinder and adjust the timing to make the max pressure point at 16-18 degree after top dead centre. but a spark plug like this cost about £1500 so it is a bit out of my price range. but that is one of the best way to tune your car. but nobody seems to do this either. it does mean if you are tuner you have to have almost every different type of spark plug on the market with a pressure sensor fitted. which is not really piratical.
    i looked into getting a machine shop to modify a spark plug for me but they talked a lot and never delivered.

    there are lots of things on the market that can help a lot when tuning a car but not many people know about them.

    i will try again in the future but for now just getting my engine back together will be enough.

    i do appreciate where you are coming from and i understand you line of thought, it is healthy to have different ways of doing things and have an active debate about how to go about putting thing into motion.

    let the fun begin.
    i have a spear engine in the shed that needs to be built, so once my black vr4 engine is put back together. i can think about building that one, but it will probably be bigger twins as i have at least 8 to choose from. lol

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    @Davezj, I think I have already said during one of our other conversations that I am planning on having my Anglia on the dyno for a full, proper, whole-range tune, including timing/MBT, at all load points, not just full throttle! But, I've just not got round to it yet, as there's been some other issues that need sorting first, and lack of time! Although the lockdown has given me the opportunity to sort a couple of other issues, mostly my handbrake, which would have caused a big issue on the dyno had I left it as is... you'll see the details of that in episodes 9-11 of Garry's Garage!

    But, that aside, my additions of coilpacks and fuel pressure sensor means that I should have great spark, and much better known values for fuelling, which should definitely aid the MBT tuning to ensure it's making safe power. Running on 98/99 octane I may start to be knock limited - but short of fitting a full LPG system...


    Getting back on topic of single turbos... if I go down the bigger single route on my Legnum, then I'm also considering a Link ECU (because I know how they work now, from my experiences with the Anglia), so the tune should be mostly transferrable from my Anglia to the Legnum - though it might just need an additional tune for the higher load cells it might be reaching, and retune of any transient fuelling changes due to the differing way it will come on boost. I'll also then need to sort the auto box out, as we've not yet figured out the torque reduction request signal from the original autobox ECU, to limit torque in the engine ECU - this will be a must for me, as I'm planning on keeping the auto, and definitely don't want to kill it due to the torque staying high during gear changes!

    I got a small bit of advice from a UK YouTuber/Facebooker, Stav-Tech, who seems to know his onions when it comes to turbos! He suggested a 12cm Holset HX35, plumb it up in twin-scroll mode so that each bank is feeding one half of the turbo, and he reckons full boost by 3500rpm and extend the usable rev range a bit too over the TD-03s. Could step up to the bigger 16cm with a little sacrifice low down to gain up high.

  16. #16
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    Hi garry, that is good to know.
    my comment still stand about contributing to the dyno time as i know money is tight in these times of reduced pay and stay at home rules.
    i presume the HX 35 is quite comparible to the GTX35, one to holeset one from garret/honeywell

    holset HX35
    https://www.speedingparts.co.uk/p/tu...lset-hx35.html

    HX35 5477 (Compressor wheel 54mm inducer, 77mm exducer, Turbine wheel 70mm inducer, 60mm exducer)

    https://www.garrettmotion.com/racing...x3576r-gen-ii/

    GTX35 5876 (Compressor wheel 58mm inducer, 76mm exducer, Turbine wheel 68mm inducer, 62mm exducer)

    so they are similar ish sizes

  17. #17
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    That's a very generous offer, Dave, thanks!

    Yep, the Holset is similar, just a bit cheaper than the Garret as it's not necessarily an "aftermarket" brand. Could step up to the 16cm one to get more flow for less boost - which might be better if we're boost limited on our engines!

  18. #18
    Davezj's Avatar

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    yeh the holset seem to quite a bit cheaper the GTX3576 was just short of £2K and the gtx3582 was a bit more than £2K

    the HX35 although a bit old tech is on sale new at a bit less than £600.

  19. #19
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    @adaxo

    if you want to do a cheap big single turbo check out these to videos for Stav-tech
    and here is the turbo for £85 (buy 3 and have 2 spares, it is tempting.)

    i am very tempted to see what can be done, keep the original manifold and just make a pipe from there to the centrally mounted turbo over the gear box. all we would need is a couple of td03 flanges (rind out to as big a possible along with the manifolds T3 or T4 flange whatever it is and connect with pipes the exhaust pipe would go down the back of the engine and meet up with the normal place for a cat back. it seems to simple to be true. mounting bracket for the turbo and some heat shielding but then there is the inlet pipework to the throttle body.
    other peoples builds have cut the throttle body off the plenum and put it on the other end but is that really required.

    food for thought.

    https://www.ebay.co.uk/itm/T3-T4-T04...4AAOSwzxldxR3X

    or with all the oil lines for £111

    https://www.ebay.co.uk/itm/New-T3-T4...AAAOSwYk5d~K1d


    https://www.youtube.com/watch?v=zM-u91P5OQo&t=268s

    https://www.youtube.com/watch?v=kAYe8Cjz2wI&t=835s
    Last edited by Davezj; 01-06-2020 at 06:29 PM.

  20. #20
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    Quote Originally Posted by Davezj View Post
    @adaxo

    if you want to do a cheap big single turbo check out these to videos for Stav-tech
    and here is the turbo for £85 (buy 3 and have 2 spares, it is tempting.)

    https://www.ebay.co.uk/itm/T3-T4-T04...4AAOSwzxldxR3X

    or with all the oil lines for £111

    https://www.ebay.co.uk/itm/New-T3-T4...AAAOSwYk5d~K1d


    https://www.youtube.com/watch?v=zM-u91P5OQo&t=268s

    https://www.youtube.com/watch?v=kAYe8Cjz2wI&t=835s
    This whole conversion thing is very tempting, and since my car is on stands anyway and about to receive refreshed engine and gearbox, is all getting closer than ever? IF Im going to do it, will rather go with holset unit, or other known brand, even if second hand and needs to be refurbed prior install instead of Chinese ones, didn't watch videos how to improve them as im busy watching videos how to weld manifolds :-)
    I will be very happy if the whole conversion cost about a grand, I think its possible IF we can knock some pipework, there is where your contribution with hand become handy Dave, not to bother to see welds to be pretty like victoria secret models as it will all be wrapped in thermo bandage anyway, and as I said earlier, ecu will stay original until im completely sure that I exhausted whole possibilities to tune with it, remember we have piggy back fitted already to control fueling. When its need to be change I will probably go with them

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