supercharged HGT

[Tom]

The overlap is too long, the exhaust and inlet valves are open at the same time for too long. The supercharger would just blow air and fuel straight into the exhaust wasting boost and fuel.

Ideally you'd really want less overlap than standard.

 

[Anonymous]

You would need low compression pistons as well as I guess HGT CR is what 10.5:1 You would need 7.5:1 and ideally forged. Also a bespoke exhaust system with manifold with long primaries and straight through silencers as superchargers are very sensitive to back pressure. Too much, as a restrictive exhaust will undoubtedly provide, will kill any additional gain you want from the s'charger.
Also a fully mappable engine management. All in all ££££££££££. That's why manufacturers spend millions developing cars to get them right and cars cost so much. Some more than others.

A paddle clutch wouldn't last 2 mins with normal road use. Plus you would probly find it undriveable. just 2 positions 'in' and 'out'. You can't ride them like an organic clutch.

Basically your project will cost a shed load of cash to do properly and TBH is a waste of time. Get an already supercharged std engine if that is your desire or one with internals to take the increased demands you will ask of it.

I would be very surprised if you got more than 250bhp out of a supercharged HGT engine. If you still want 300-400bhp that you wank over then get a turbo engine, such as an Integrale 8v with hybrid turbo, or buy a Mitsubishi Evo or Nissan Skyline R33.

For ultimate power a turbo is by far the better option.

 

[Anonymous]

Not me anon. The idea originally sparked my curiosity, but its out of the question really.
Besides, i'm more than happy with the mule just as it is. I kno what would happen if I helped it find anymore power. I'd be envolved in an accident, or someone else would envolve me in their accident, or I'd get more points and a ban.

Starting this topic is an interesting exercise in itself. Helps me learn about stuff and engines, that I was never remotely interested in before I bought my HGT. It would be cool to see a suprcharger or V8 lump fitted in any bravo. As it is, I'll happily settle for my mule just sounding like a V8 (so I'm told)

 

[Anonymous]

Well it's nice to read that some one is willing to admit they is picking useful stuff up from this forum even if they don't plan to follow their curiosities. Where would we be if we never asked questions?

Why your fascination with superchargers? They aren't that efficient and their increases in performance are more subtle than turbos. What supercharged engine or article has got you thinking that you should s'scharge your HGT? They don't give draw dropping increases in performance as turbos do. Firstly they rob the engine of power generally running off the crank pulley and at high revs their performance is marginal. They are at their best at low down and mid range revs but still don't deliver any earth shattering increases in power.

 

[Tom]

Turbos and superchargers can give very similar results. The difference is you don't get the huge WOOOSH with a supercharger and that doesn't make modduhs cream their pants as turbos do.

There isn't really a case of one is more efficient or better, they are simply different.

Anyway, peak power figures are really just numbers, they never tell the whole story.

 

[Anonymous]

I have both supercharged and x2 2.0l turbo cars and a n/a car and by far the best are the turbo'd cars - no contest. A turbo is a far better piece of kit. They might have lag, but modern sequential turbos have very little. My supercharged engine gives power in a different way up to 1.4 bar but it ain't got the got the grunt of the turbos even if you get better low down torque it is still slow by comparason. It needs a belt to run whereas the turbo works off the exhaust gases. No a turbo is better any day, pref one small and one large to spread the power input across the rev range.

 

[Tom]

Was it a turbine type supercharger or a positive displacement supercharger?

Turbos sap power just as much as superchargers, you don't get the boost for free.

 

[Josh]

as stated earleir if you take two identical cars super charge one and turbo the other you will et very similar results as both sap power in different ways. The turbo has more noticible power as you have a delay in the power where as a supercharger is a very smooth delivery.
either way you'd have to do a lot of work to the engine to accept either idea.

 

[DeanoBravo]

I really don't reckon that a T-charger saps that much. People tend to see the turbo as a massive contriction for the escaping exhaust gases, but after the initial lag (the process where by the wastegate shuts and turbo spools up) then it's really plain sailing from there! In fact when the required boost level is attained, the wastegate opens slightly (helping vent gases away from the turbo) to prevent over boosting!!

With a soooper-charger, you're running off the crank all the time! Not great for top of the rev-range stuff!!! It's almost comparible to a tiny turbo that spools up really quickly (giving more torque lower down as a supercharger would) but running out of puff up in the rev range.

 

[Tom]

A turbo is a big restriction in the exhaust. The wastegate valve is usually quite small.

 

[DeanoBravo]

The turbo would be a big restriction if it wasn't for the fact of the compressor side of the turbo was forcing air through the system! (As i mentioned when running at full boost)

So net results is that no, it's not a big restriction!!

 

[Tom]

You don't get owt for nowt.

To make x PSI of boost at y CFM you need a certain power, either it comes direct from the crank or indirectly from the crank via the exhaust.

 

[Ian]

Does anyone want my Bora for free?

.. didn't think so.

 

[DeanoBravo]

Yes - with a turbo it's called "lag"! This is the one true time the exhaust flow out of the engine block has it's greatest pressure.
But as i've stated, once a turbo is on full boost, the wastegate actually has to open to prevent over-boosting. This means there is more exhaust gas than the turbo needs! Where's the extra strain on the engine there??!?

When on full boost there is a nice balance of flow between compressor side and exhaust side...

 

[Tom]

The 'strain' is that its still creating boost and to create boost it takes power. You don't suddenly get free boost.

Lag is caused by the inertia of the turbo internals and the fact the turbine and compressor don't work well at low exhaust flow rates and low compressor RPM.

Measure the size of your wastegate valve and compare it to the size of your exhaust.

 

[DeanoBravo]

I still feel you are more concerned about the spool up/lag time here. Until that point many factors get in the way. And of course there is the inertia of the turbine wheels, but this is only really a big factor during the spool up process.

But again, once the cars boost limit has been reached, the wastegate has to open to prevent more boost than is needed. It is at this point where the balance comes in and the strain is no-where near as great. (And as a note, there are MANY things that affect spool-up - not just the size of the turbo!)

And in comparison with the wastegate, the exhaust exit to the turbo down-pipe is pretty damn big!!
But why would i need to compare exhaust size with the wastegate - i know the wastegate is in-comparison quite small. (I have three at home!!)

This is all quite different to a supercharger than needs the direct crank power all through the rev range.

Once at full boost, turbo's rule!

 

[Tom]

As I said before, it still saps the same amount of power for a given amount of boost & flow no matter if the wastegate is open or not. The wastegate does not reduce any 'strain', just stops the turbo destroying itself and the engine.

Centrifugal compressors make good boost over a narrow range of RPMs. Too slow and they do nothing much, too fast and the efficiency drops off again. This is why you get lag and why centrifugal superchargers are a bit crap. You've got to get the thing spinning at about 50% of its maximum RPM before it does anything useful.

On a turbo car the compressor RPM and engine RPM are not really linked so it can reach a good boost early. On a centrifugal supercharger they are linked so at low RPM you always get poor boost. With a positive displacement supercharger you get boost at idle.

 

[DeanoBravo]

I didn't say the wastegate reduced the strain!! I'm saying there mere fact that it's open means that any possible backpressure from the turbo is at a complete minimum!!! And thus the point that at full boost the turbo NO-LONGER BECOMES the massive block in the exhaust gases path!
(This initially started on the turbo just being a "block" in the exhaust gas flow)

And i'm afraid to say that if the foot is pushed down and kept on the accelerator to the top of the rev range, the boost will correspond to a certain number of revs through the rev range all the time! (Barring boost-leaks or any other oddities...)

 

[Tom]

But the boost is not linear with RPM. If you get 20PSI at 6000RPM you won't get 10PSI at 3000RPM and 5psi at 1500RPM.

 

[Anonymous]

Having the luxury of driving two almost identical engines, one turbo'd and the other supercharged, I can reliably report that the turbo engine has by far the greater performance and potential for releasing yet more power.

The s'charged engine is by no means a slouch but it readily loses ground to the turbo'd unit.
The supercharger engine makes for effortless driving providing respectable additional low down torque. Yes low down extra power delivery is immediate. In a sense this allows drivers who are unable to keep an engine reving and on boost or perhaps don't like to constantly rev an engine to exploit more power. The s'charger therefore is delivering extra power in a very different way and for a different purpose.

Driving a 2 litre supercharged engine feels very much like driving a 3 litre engine as progress can be relaxed and stress free. This is where it scores over a turbo but then this is where the advantage ends.

At higher revs the turbo can create alot more boost and hence power. Turbo design can determine lag and boost characteristics using smaller, bigger or sequential units.

I am not an engine designer so my understanding is only that of an enthusiastic layman but I can still appreciate basic engineering concepts such as turbo and super charging.

If as Tom argues there is indeed little to choose from between turbo and s'charged methods of forced induction why have the majority of manufacturers and serious engine tuners chosen to turbocharge rather than supercharge? Have they been toiling under a misunderstanding? I don't think so.

Real answer: Because turbocharging saps far less power from an engine and in return can deliver alot more 'bang' for your buck so to speak.

For small engines turbos make alot more sense. For larger engines s'chargers are employed to boost low down torque.

Turbos are also alot easier to incorporate into an engine. The revolutions that a turbo can achieve are far greater than a s'charger which is governed more or less by the speed of the crank pulley. They are belt driven which will also limit their revolution speed despite having a specific pulley gearing to increase spin speed.

At idle the supercharger is not producing positive but negative boost. Mine produces around -0.8 bar at idle and only becomes positive at about 2,500 rpm. Max boost is about 1.2 bar if I ever tested this generally planting the throttle in the Wilton produces about 0.8 - 1.0 bar boost.

In comparison the turbo spins according to the speed of exhaust gases leaving the cylinder head. Thus it can create a lot more boost when the gas flow is high.

Perhaps s'charger technology is set to make a huge leap forward. For the technology to catch up with turbos it would have to be an enormous leap. Great if it can be done, but some how I don't see it. I think s'charging will remain secondary to turbos on engine designers' drawing boards.

Andy