Turbo-charging/Martin Luther King
Discussion
Lastnight i had a dream that one day this nation will rise up and live out the true meaning of its creed: "We hold these truths to be self-evident: that all men are created equal."[1]
seriously, i had a dream that i was driving along and a ball-bearing from my turbo (
) popped. (i know i dont have a turbo 
) I wasnt aware of any turbo-charging for the K-series and thought it wasnt possible, due it making ze engine kaput.
BUT, a little research shows that bell&colville do a turbo
Im not tempted in ANY way, but just wanted to know, is this a good idea? im thinking no.
Does anybody know anybody with it done? would you try it? why did TT go the supercharger route?
Questions, questions. opinions greatly received
[1] MLK
ING AMAZING!I'd have to disagree with the supercharging is the better forced induction arguement myself.
A supercharger is driven from the engine via a belt which is a constant form of drag. They end up using quite a bit more fuel. I think Mercedes just brought them back into fashion. They are more suiting to maintaining a certain power output. The Merlin engine in the Spitfire used it and it did sound great though.
With a turbocharger it's driven from the exhaust gases and so varies with the driving style. They are much more fuel effiecent for cruising than the supercharger. The TT figures give an mpg rating of 33 which is quite a drop. They do have lag and you have to choose the turbo to suit the application, i.e. smaller and more responsive versus huge power and an an alarm clock.
Fitting a turbo to a NA engine is not really any different to fitting a supercharger. A turbo does generate more heat in the engine bay though. The con rods need to be shortened for both to lower the compression of the engine and some form of water/air intercooling of the intake air is required to do the job right and prevent detonation.
This is what TT and the B&C kits do, although B&C have an "introductory" low pressure turbo which is claimed does not require this. Maybe, but I'd be most nervous about that one. I don't have either kit so don't have an specific knowledge.
yikes, what a rant, time to start lurking again
michael.
A supercharger is driven from the engine via a belt which is a constant form of drag. They end up using quite a bit more fuel. I think Mercedes just brought them back into fashion. They are more suiting to maintaining a certain power output. The Merlin engine in the Spitfire used it and it did sound great though.
With a turbocharger it's driven from the exhaust gases and so varies with the driving style. They are much more fuel effiecent for cruising than the supercharger. The TT figures give an mpg rating of 33 which is quite a drop. They do have lag and you have to choose the turbo to suit the application, i.e. smaller and more responsive versus huge power and an an alarm clock.
Fitting a turbo to a NA engine is not really any different to fitting a supercharger. A turbo does generate more heat in the engine bay though. The con rods need to be shortened for both to lower the compression of the engine and some form of water/air intercooling of the intake air is required to do the job right and prevent detonation.
This is what TT and the B&C kits do, although B&C have an "introductory" low pressure turbo which is claimed does not require this. Maybe, but I'd be most nervous about that one. I don't have either kit so don't have an specific knowledge.
yikes, what a rant, time to start lurking again
michael.
I had a monster turbo on my Esprit and it was terrible for driving around in. Once I got back to the smaller more responsive one it was a delight to drive. Plus there is a really thrill in that half second between planting the foot and being launched!
Having said that, I'd be partial to a TT'd Elise as it seems to be by far the most sorted conversion that would give the kind of brute acceleration my esprit had.
Reving the nuts off a car is so uncooth when you can just drop those M3s with torque
michael.
Having said that, I'd be partial to a TT'd Elise as it seems to be by far the most sorted conversion that would give the kind of brute acceleration my esprit had.
Reving the nuts off a car is so uncooth when you can just drop those M3s with torque
michael.
Bonce said:
Nor could your student overdraft, presumably?
All gone
I am a financial disaster
i worked out, that at this rate of spending, by the start of next term ill have £3.98 or something per week to live on
how/what can i drink on that? Best start getting used to the taste of special brew and kestrel "super"
Muck Savage said:
I'd have to disagree with the supercharging is the better forced induction arguement myself.
A supercharger is driven from the engine via a belt which is a constant form of drag. They end up using quite a bit more fuel. I think Mercedes just brought them back into fashion. They are more suiting to maintaining a certain power output. The Merlin engine in the Spitfire used it and it did sound great though.
With a turbocharger it's driven from the exhaust gases and so varies with the driving style. They are much more fuel effiecent for cruising than the supercharger. The TT figures give an mpg rating of 33 which is quite a drop. They do have lag and you have to choose the turbo to suit the application, i.e. smaller and more responsive versus huge power and an an alarm clock.
Fitting a turbo to a NA engine is not really any different to fitting a supercharger. A turbo does generate more heat in the engine bay though. The con rods need to be shortened for both to lower the compression of the engine and some form of water/air intercooling of the intake air is required to do the job right and prevent detonation.
This is what TT and the B&C kits do, although B&C have an "introductory" low pressure turbo which is claimed does not require this. Maybe, but I'd be most nervous about that one. I don't have either kit so don't have an specific knowledge.
yikes, what a rant, time to start lurking again
michael.
Fuel schmuel...if we were bothered about fuel consumption we'd be driving diesels!
You are quite right, of course, in saying that superchargers are inherently less efficient, because actually driving them soaks up quite a bit of horsepower.
I don't agree that they are better suited to constant speed though. In variable speed applications, turbo lag more than counterbalances any advantage in fuel efficiency, IMHO, and if you fit a smaller/light pressure turbo to reduce the lag, you may as well not bother, given the extra heat and complexity. The only true solution I am aware of to completely alleviate lag is a hyperbar system, in which case the fuel efficiency side of the argument goes out the window anyway!
For what it's worth, the Merlin engine used a centrifugal supercharger (basically a very large version of the compressor side of a turbo, but driven by the engine). The failed 1950's BRM V16 used a centrifugal blower, too. These are only really suitable for constant engine speed applications, as they produce negligible boost at low speed. Didn't matter in the Spitfire, as the engines were run in a narrow RPM band and speed controlled by varying the pitch of the prop as much as by the throttle. The main reason (other than reliability) that the BRM flopped was that the power delivery was stupid - nothing at low revs, then and incredible surge of power as the supercharger came in, which the tyres of the day simply couldn't cope with.
If anyone is sad enough to care, the main reason that the Spitfire wasn't turbocharged is that we didn't quite have the metallurgy to handle the very high temperatures that the exhaust side of a turbo has to cope with. This was developed later in the war, and planes like the American Lightning (powered by an Allison engine which was basically a licence-built Merlin anyway) were turbocharged.
Most modern superchargers are either Roots-type (which have a nice, progressive boost delivery), or small centifugal blowers (turbo sized), driven by step-gearing at a constant high speed so that they are always running withing the 'boost band'.
There are other ways of reducing compression ratios as an alternative to shorter con-rods, of course - low compression pistons or even just an extra thick cylinder head gasket - and detonation isn't such a major problem on low boost/no internal engine mods. conversions provided the engine has a knock sensor which can back off the ignition if detonation is encountered. Boost (hence power output) will be limited compared to 'full house' conversions, though.
>> Edited by Martin_S on Thursday 19th February 19:23
good post. 
Turbos are bloody good as they dont put drag on the engine like a supercharger does, and they use waste energy (exhaust gases).
So whats the solution to the lag problem?
Dumpe valves help a bit with the response but not with the lack of power down low.
Variable blade pitch turbos? ie high angle of attack at low rpm to maximise speed, then slowing changing to a low angle of attack at as rpm increases, so the turbo doesnt over boost where theres heaps of gas to drive it.
Who ever can pull this off without it self destructing will become VERY VERY rich.
So whats the solution to the lag problem?
Dumpe valves help a bit with the response but not with the lack of power down low.
Variable blade pitch turbos? ie high angle of attack at low rpm to maximise speed, then slowing changing to a low angle of attack at as rpm increases, so the turbo doesnt over boost where theres heaps of gas to drive it.
Who ever can pull this off without it self destructing will become VERY VERY rich.
At one point there were several turbo conversions for the Elise but they went massively out of fashion. Andrian Newey of Mclaren f1 fame has some insane turbo charged Elise IIRC.
Guy at work also has the orginal turbo elise that was featured in lots of magainzes. Plate was 'B10WN K' or something. Anyway the turbo was ditched and a QED race engine replaced it. Now he's dropping that and putting in a vtec...
Izza said:
Turbos are bloody good as they dont put drag on the engine like a supercharger does, and they use waste energy (exhaust gases).
So whats the solution to the lag problem?
Dumpe valves help a bit with the response but not with the lack of power down low.
Variable blade pitch turbos? ie high angle of attack at low rpm to maximise speed, then slowing changing to a low angle of attack at as rpm increases, so the turbo doesnt over boost where theres heaps of gas to drive it.
Who ever can pull this off without it self destructing will become VERY VERY rich.
'Ye canna change the laws of physics, Capt'n', as Scottie would have put it. All the variable geometry turbines and bypass (dump) valves in the world can't overcome the fact that the compressor in a turbo has both mass (therefore inertia) and aerodynamic drag. When the gas flow through the engine slows down, the turbo slows down, and it takes time to spin up again. Dump valves, small turbos and variable geo minimise the problem, but they don't completely eradicate it.
You can fit a hyperbar (basically an afterburner which injects fuel into the exhaust on the over-run to keep the turbo spinning - bye, bye fuel economy!), but other than that you just have to live with the fact that turbos suffer lag if operated over wide engine speed ranges.
My personal favourite idea (waiting with all the other brainwaves to be developed when I retire), is to use a valveless pulsejet in the exhaust system, arranged to keep the turbo spinning when off the throttle, and to provide a little extra jet propulsion when you have your foot down. With the addition of a simple oil injector, you could have and optional smokescreen, as well, for when the rozzers are chasing you! I suspect there might be a problem with silencing, though - apparently a reasonable sized valveless pulsejet can be heard about six miles away on a calm day!
FWIIW, and contrary to popular belief, exhaust gasses are not 'free' energy. The exhaust side of a turbo significantly impedes exhaust flow and so reduces the the efficiency of scavenging. Hands up any Elise owner who hasn't yet fitted a cat bypass pipe and a sports exhaust to improve exhaust flow, yet we all think that hanging a bloody great metal (or ceramic) impellor right in the exit from the manifold (and then forcing the air it compresses through an intercooler)won't cost us anything?
>> Edited by Martin_S on Friday 20th February 19:56
"I'd have to disagree with the supercharging is the better forced induction arguement myself. "
You would be wrong to think that, and Gordon Murray himself will tell you that supercharging is the way to go. There are multiple factors working against turbochargers:
1) A supercharger is powered by the motor's belt, so it absorbs some power this way. However, a turbocharger is a severe restriction in the exhaust. For whatever X kPA you see in the inlet, you have X+Y in the exhaust tract... a higher pressure in the exhaust tract, than in the inlet, is extremely undesirable.
2) Even if we can remove much of the lag turbos are known for, turbo engines will always have to create exhaust in order for the turbo to spool and generate speed. A supercharger simply scales better at lower RPMs because it is directly coupled to the crank. Instantaneous is the key for supercharging.
3) Did I mention Gordon Murray says so? See the EVO issue from last year interviewing good ol' Gordon. The cover of that EVO issue has the 1000HP new Bugatti.
4) It is possible to recover much of the supercharger's power consumption, by really messing with the tuning of the exhaust. It is hard to do that when you put a turbo and dumpb valve just downstream of the cylinder head.
5) Reliability... superchargers simply do not have to deal with the extreme temperatures and superheated gases that turbos do. Supercharger technology will always be more reliable than turbo technology.
The only time turbos are still advantageous is when the engine in question is expected to run in a very narrow power band, where exhaust velocity and therefore turbine speed is maintained.
The big OEMs know it, only VW/Audi/Porsche seems to be holding out... no doubt from their bad reliability experiences with the G-Lader superchargers in the last decade.
You can never completely negate turbocharger lag, you can reduce it and reduce it some more, but it will always be there...
You would be wrong to think that, and Gordon Murray himself will tell you that supercharging is the way to go. There are multiple factors working against turbochargers:
1) A supercharger is powered by the motor's belt, so it absorbs some power this way. However, a turbocharger is a severe restriction in the exhaust. For whatever X kPA you see in the inlet, you have X+Y in the exhaust tract... a higher pressure in the exhaust tract, than in the inlet, is extremely undesirable.
2) Even if we can remove much of the lag turbos are known for, turbo engines will always have to create exhaust in order for the turbo to spool and generate speed. A supercharger simply scales better at lower RPMs because it is directly coupled to the crank. Instantaneous is the key for supercharging.
3) Did I mention Gordon Murray says so? See the EVO issue from last year interviewing good ol' Gordon. The cover of that EVO issue has the 1000HP new Bugatti.
4) It is possible to recover much of the supercharger's power consumption, by really messing with the tuning of the exhaust. It is hard to do that when you put a turbo and dumpb valve just downstream of the cylinder head.
5) Reliability... superchargers simply do not have to deal with the extreme temperatures and superheated gases that turbos do. Supercharger technology will always be more reliable than turbo technology.
The only time turbos are still advantageous is when the engine in question is expected to run in a very narrow power band, where exhaust velocity and therefore turbine speed is maintained.
The big OEMs know it, only VW/Audi/Porsche seems to be holding out... no doubt from their bad reliability experiences with the G-Lader superchargers in the last decade.
You can never completely negate turbocharger lag, you can reduce it and reduce it some more, but it will always be there...
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