1268 replies to this topic

[Doctor Ed]

Not as if typing on an iPad wasn't annoying enough, but opening another tab to grab a link, taking too long, and loosing the cache of the whole page I'd just spent 1/2hr typing... Sonnoffa....

[Doctor Ed]

.... Great way to start a build thread. Not. Anyway, so the last version of this that I just wrote was far more eloquent and wordy. Now my patience and linguistical talent are running thin. Let me summarize the introduction: After much internal debate, I bought myself a wrecked and stripped chassis. An original German LHD NA, according to the vin # a 2001 build year, but first registered in 2004. A mostly cosmetic crash by the uninsured owner (windscreen surround/support leg notwithstanding) resulted in a parting out of the car. I picked it up for SFA and a day's worth of dicking around with a car trailer... and now much to my wife's delight we have a chassis in the yard. I've built a few cars before whilst living in Australia (the last a 640hp NA 4.6L V8 in a toyota supra), but since moving to Germany, I've been occupying myself with a 125cc shifter kart... all the time chewing over what kind of project I wanted to take on. Zee Churmans don't make it easy. I'd driven a 211 at the Nürburgring a few years ago, and pax' da few laps with a couple of members on here. The idea of a lotus had always been pecking at the back of my head, and although a lot more locally made cars make a lot more sense from a build and support point of view, nothing really gave me a good vibe. So this chassis came up, the timing was good, the missus didn't immediately hate the idea, and it has the potential to be dangerously quick. Tick, tick and tick. Plans? This is always embarrassing in the first post of a build thread. Goals, budgets, and reality checks kick in over time. To look back at the first post after 2 years, I'd like to avoid a massive *facepalm* (although deleting the entire post in the first instance was a decent effort). Dangerously quick Must be able to go around corners Remain registerable I don't care about show car gloss, and providence and remaining original is about the least interesting thing I can imagine, so we'll see where this goes. A blank canvas, some TÜV ground rules to play by, and a budget that precludes simply going catalogue shopping for the sake of mechanical bling. I'm handy with a welder, and know how to build a stout engine or two. Will be interesting one way or the other Cheers Ed PS - I hate the term speedster. And I guess it's not really a VX either. I'm sticking with A116

Edited by ed.oates, 30 December 2015 - 05:52 AM.

[Doctor Ed]

Let me just leave a few things here...






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[Doctor Ed]

Tesla BBK (at least for the rears): http://www.vx220.org...ter-big-brakes/ The extended upright of the tesla allows a std 308mm rotor to work with OEM rear caliper assembly. Front brakes will remain the simple 2 pot calipers, again spaced out onto 308mm rotors. Will be interesting to see if this 1) levels out the existing forward bias, 2) actually benefits braking performance in any notable way.

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[Nev]

Hi Ed,

 

I think I read somewhere on one of your other threads that your aim is around 350 BHP. If this is the case then isn't a GT35 frame somewhat large?

 

As I expect you already know, the pressure ratios that a supercharger and turbo charger make when in series are a multiple of each other (as opposed to a addition of each other). Assuming a GT35 will make 2.5 bar of boost and the M62 will make 1.5 bar, that means a total of around 3.75 bar of boost (that's 55 lb/sq inch)!! If you could build a 4 pot engine that would survive and breath all of that in, it would be circa 1000 BHP. Hence I feel your possible turbo choice above is considerably over specced for 350 BHP. If it were me, I'd look at just a GT28 or perhaps a GTX2867 after the M62, which combined together would probably still push out circa 450 BHP from a nicely breathing engine.

 

I can understand that you want a large turbo to keep the boost down and have the potential to boost with a flat line all the way to circa 8000 RPM, but even a GTX30 frame will achieve this (as I discovered on my own engine).

 

BTW, I am speculating with these numbers here (finger in the wind, rather than doing any calcs).

 

Question: Will you be mounting the S/C first, feeding boost to the T/C ?

 

 

Edited by Nev, 30 December 2015 - 08:07 AM.

[Doctor Ed]

Theres a couple of things I'd like to point out: firstly is I hate throwing around simple numbers... I'm a noob here, and if I poped up in my first few posts saying I want 500hp I'd get laughed out the door or ignored. The other thing to bear in mind regarding numbers is the relatively harsh TÜV certification, and putting too much info into google-index reach. I don't think there's a modified car in Germany which is producing only the stated numbers on its certification documentation, but you need to be subtle about how you go about it. Showboating and dropping numbers isn't subtle. This is a UK / English speaking forum, so prob ok, hence the thread, but I might hold back from being too specific with some things. Yes they multiply, and probably best to use the Pressure Ratio (PR) terminology when talking about twin charging. I'd only be expecting 1.4 from the M62 (see above efficient island and temps etc) and around 2.0 from the turbo. So around 26-28psi manifold could be imaginable. Turbo frame size is a dicky calculation... Which I'll thrash out in a second. Wife beckons!

[Nev]

I have a few fairly detailed spread sheets (XLS) I made and found on the internet, with all the turbo size calc formulas and expected outputs, if you PM me your email address I'll happily to send it over if it might be of use to you.

Edited by Nev, 30 December 2015 - 08:49 AM.

[Doctor Ed]

It's not the turbos themselves per se, that's easy enough to derive from the compressor maps, it's how the turbines behave, particularly when a supercharger is filling the cylinders. The amount of exhaust gas is a bit disproportionate to what you'd expect just doing the maths. More when the missus has finished

[Nev]

Am I right in thinking your intended airflow is:

 

Airbox --> supercharger --> turbo --> intercooler --> throttlebody

 

 

[Doctor Ed]

airbox->turbo->IC->throttle body->supercharger->head

[Doctor Ed]

Ok, just going back a step, what you wrote in that the pressure multiplies, is correct, but you can't just take 1.5bar and 2.5 bar and multiply 1.5x2.5=3.75 and call it 55psi manifold pressure. Need to think in pressure ratios... Atmosphere is 1 Boost of one bar is (14.7psi manifold pressure) is PR 2 Boost of half a bar (7.35psi manifold pressure) is PR 1.5 Multiply the PRs together 2 x 1.5 = 3.0 (= 2.0bar manifold pressure + 1.0bar atmo) = 29.4psi boost

[Doctor Ed]

Regarding turbo->SC setup... This applies only to positive displacement superchargers. Ie fixed volume SC like a roots/whipples which simply expels a certain volume per revolution. It doesn't care what pressure/density air is sitting against its inlet, it just goes on turning and expels a given volume per revolution.

[SteveA]

2) actually benefits braking performance in any notable way.

 

You will probably find that it is detrimental.  

[Doctor Ed]

And finally regarding turbo frame.... Think of the engine in two stages: Firstly only look at the motor and supercharger together as a unit inside a black box. For augment's sake it's a 2.2L motor, and the SC is making 7.35psi of boost (+ve manifold pressure = PR 1.5). That essentially makes the contents of the black box the equivalent of a 1.5 (PR) x 2.2L = 3.3L motor in terms of airflow in / out. Now strap a turbo to that. It doesn't know what it's being bolted to, it just sees a black box with the in/out airflow of. 3.3L motor. So you size the turbo exactly as if it actually was a 3.3L motor = huge! Well that's what maths tells you to expect. In reality, the exhaust flow doesn't seem to behave simply like a 3.3L, but intact more. So if you sized your turbo's turbine based on the 3.3L equivalency theory, in practice you find that the turbo spools a lot sooner than anticipated. As you can see, things multiply rapidly, and get very big, very quick. Generally speaking, size the SC smaller than you think, and size the turbo larger than you think. Now the m62 has a nice efficiency island around a PR of 1.4 (6psi manifold pressure). 1.4 x 2.2L = 3.08L effective flow (black box motor). You need a turbo mated to this that will flow the peak HP you want on the compressor side (10bhp per lb more or less) and a turbine that's nicely matched to 3.08L in terms of spool, if not tending a little bigger. Gt3582 on a t3 .82 would be a good example of a match to this scenario, but that's a 600hp turbo = overkill Gt3076 on a t3 1.06 would be similar in terms of turbine flow, but with a smaller compressor 450hp = not bad! The HX35 is a behemoth, but actually spools and flows well (better than the 1.06 down low), and the compressor size is again good for 450hp = I reckon that's where the money is Problem is the HX35s are enormous and not light. they're also cheap as dirt compared to a gt3076. I'm tempted to mock up a HX and see just how little room there is.

[Doctor Ed]

2) actually benefits braking performance in any notable way.

  You will probably find that it is detrimental.  

Why?

[SteveA]

Lots of people have done it before with no benefits. Search for 308mm to see what others have found.

[Doctor Ed]

As far as I'm aware no one has done 308 rears, retaining the OEM brembo caliper? Lots of caliper swapping going on, which is questionable, but using the stock calipers with pagid pads put on a 10mm bigger radius with a bigger heatsink, I can't see how it could be detrimental? Lots of folks opinion that they can't feel a big difference, which is fair enough, it's not a huge upgrade, but physics says it's still a bigger torque, and a bigger (albeit heavier) heatsink.

[Nev]

And finally regarding turbo frame.... Think of the engine in two stages: Firstly only look at the motor and supercharger together as a unit inside a black box. For augment's sake it's a 2.2L motor, and the SC is making 7.35psi of boost (+ve manifold pressure = PR 1.5). That essentially makes the contents of the black box the equivalent of a 1.5 (PR) x 2.2L = 3.3L motor in terms of airflow in / out. Now strap a turbo to that. It doesn't know what it's being bolted to, it just sees a black box with the in/out airflow of. 3.3L motor. So you size the turbo exactly as if it actually was a 3.3L motor = huge! Well that's what maths tells you to expect. In reality, the exhaust flow doesn't seem to behave simply like a 3.3L, but intact more. So if you sized your turbo's turbine based on the 3.3L equivalency theory, in practice you find that the turbo spools a lot sooner than anticipated. As you can see, things multiply rapidly, and get very big, very quick. Generally speaking, size the SC smaller than you think, and size the turbo larger than you think.

 

Yes, this sounds like good logic to me,  I hadn't really thought of it in those steps.

 

Question: Once at high revs (say 6000 RPM+) how can you determine if the S/Cer become a resistance (as you are not bypassing it). When the turbo is working harder than the S/Cer then won't the S/Cer will reduce efficiency?

 

[Doctor Ed]

i don't know if it's possible for the supercharger to 'restrict' things. It just takes what's there and multiplies it. It prob get a little out of efficiency somewhere, so makes a bit more heat than it should, but i don't think it's a restriction per se. Only example that's comes to mind... One bloke I know with a 4L v8 twincharged motor ended up making another 50hp top end (600hp) when the supercharger was removed (lost all the bottom end though) but neither he nor I are convinced it was necessarily the SC restricting things, rather it's possible his bypass valve was somehow recirculating and pissing hp away.

[Exmantaa]

Just reading all your various postings, I'm getting a bit confused with your power goals and what you want with your car/engine...

 

The debate between a 2.2 Turbo- or Supercharger-conversion will always be, but to keep this simple:

 

250Hp    => M62 supercharger install; Simple, proven and reliable. And can be on stock 2.2 engine...

300-370 => Build engine! (or stock B207, but I shall not open that can of worms here...) Harrop SC or Turbo conversion.

400>      => Turbo all the way. (Look at twin scroll to keep good low end throttle response?)

 

500+      => BigTurbo and maybe then think about "twin/compound charging" for low end response, but at that powerlevels the standard SC manifold will probably restrict airflow. (I remember that on a US(LSJ) turbo conversion, they gained quite some Hp's by changing the stock SC manifold for another bespoke turbo intake manifold..)

 

My own opinion on 2.2 turbo conversions; because of the lack of space down there, they seem to always look a bit like a bodge with all the piping and silicone hoses everywhere...  Best option (i.m.o.); try to fit OEM stuff (A20NHT etc) in there and use proven uprated turbo's (ZFR/EFR type)

 

Or; relocate the gearbox cables (and maybe more stuff) and fabricate a really well thought out turbo manifold that creates space for a decent turbo and doesn't try to melt the car. (Even better when casted)

Look f.i. at the Swindon TOCA engines... 

 

 

 

Edited by Exmantaa, 31 December 2015 - 12:08 AM.