Superchargers vs Turbochargers.
Discussion
Having been fed a diet of tuning books to make up my own mind about forced induction. I settled on supercharging as a method of going for about 150hp from my old mini. I plan to go the route off a 750ml pass Eaton M45 blower. Not being a big fan of lag (after all minis are about going around corners really fast, I don't really want the boost to kick in half way around the corner), I felt at home with my choice to not go for a turbo.
However, I have been made aware that turbo developments have come a long way since my books were published. How far can we overcome the lag?
I was looking at the supercharger figures and it takes 30hp to produce 10psi at 6000 RPM. Basically, this sort of means that I could have more with a turbo.
Lets have a good debate about the latest of both technologies and see which is the best for each purpose.
However, I have been made aware that turbo developments have come a long way since my books were published. How far can we overcome the lag?
I was looking at the supercharger figures and it takes 30hp to produce 10psi at 6000 RPM. Basically, this sort of means that I could have more with a turbo.
Lets have a good debate about the latest of both technologies and see which is the best for each purpose.
I don't know too much about turbos, (and nothing about superchargers at all...) but for what it's worth here's my experience.
The lag will always be there with a turbo to a lesser or greater extent, unless you opt for some kind of anti lag strategy (a whole topic in itself) The supercharger is always going to win in the lag stakes simply because of the way it is driven. (ie no waiting around for exhaust gas)
But, ask yourself: when was the last time you saw a rally car with a supercharger?
You're after quick cornering - I don't have too many problems with this in my tuned Impreza turbo. All you have to do is be in the right gear to keep the revs up. (No, I don't run it with antilag!!)
There are far too many parameters to discuss in one post about turbos - but generally, a smaller turbo gives less lag but also it'll give less HP at high RPM as it won't flow enough air. The converse is true about a large turbo. You then get into mixing and matching compressor sections and turbine section, A/R ratios and everything.
You'll need to cover things like intercooling, compression ratios and fuel supply for both cases, so I'll leave these alone for now.
I'd recomend reading something like "Forced Induction Performance Tuning" by A G Bell if you haven't already. It's not all that old and is easy to follow. There are other modern books too, but their names escape me...
Getting back to your mini application, what about fitting the MG 1.3 engine (with big valves) I know this fits and gives acceptable performance It would be a simpler excercise, although it wouldn't give you the oppertunity to play with forced induction.
It's a bit of a rambling post, but it should hopefully stimulate some more ideas...
The lag will always be there with a turbo to a lesser or greater extent, unless you opt for some kind of anti lag strategy (a whole topic in itself) The supercharger is always going to win in the lag stakes simply because of the way it is driven. (ie no waiting around for exhaust gas)
But, ask yourself: when was the last time you saw a rally car with a supercharger?
You're after quick cornering - I don't have too many problems with this in my tuned Impreza turbo. All you have to do is be in the right gear to keep the revs up. (No, I don't run it with antilag!!)
There are far too many parameters to discuss in one post about turbos - but generally, a smaller turbo gives less lag but also it'll give less HP at high RPM as it won't flow enough air. The converse is true about a large turbo. You then get into mixing and matching compressor sections and turbine section, A/R ratios and everything.
You'll need to cover things like intercooling, compression ratios and fuel supply for both cases, so I'll leave these alone for now.
I'd recomend reading something like "Forced Induction Performance Tuning" by A G Bell if you haven't already. It's not all that old and is easy to follow. There are other modern books too, but their names escape me...
Getting back to your mini application, what about fitting the MG 1.3 engine (with big valves) I know this fits and gives acceptable performance
It would be a simpler excercise, although it wouldn't give you the oppertunity to play with forced induction. It's a bit of a rambling post, but it should hopefully stimulate some more ideas...
What I am going to do myself is to run a stock MG Metro non-turbo engine with turned pistons and scooped out chambers, about 8:1 CR, open the ports right out, use a 260 inlet 285 exhaust cam, standard valve sizes, high lift rockers. Looking like having a suck through setup....due to space.
Antilag looks like a bad thing. Rally cars get rebuilt regularly. Turbos seem a compromise of getting the power/lag balance right (offset by lots of gears-narrowER power band). Superchargers, from what I gather are limited at the top end, due to the power consumption associated with the resistance of the inlet tract/valve timing. I'm looking at getting as much as I can out of my engine (below 7000rpm) thus avoiding the need for EN40 crank, etc, etc.
Antilag looks like a bad thing. Rally cars get rebuilt regularly. Turbos seem a compromise of getting the power/lag balance right (offset by lots of gears-narrowER power band). Superchargers, from what I gather are limited at the top end, due to the power consumption associated with the resistance of the inlet tract/valve timing. I'm looking at getting as much as I can out of my engine (below 7000rpm) thus avoiding the need for EN40 crank, etc, etc.
A half sorted metro turbo engine should give you what you need, with very little lag, if you choose the turbo properly. Even a std turbo isnt too bad, although Id say 150bhp would be pushing it hard.
Considering they run very low boost as std to produce about 100bhp ( or whatever they have ), and use 9.4:1CR, its easy to get a bit more power. They run 4.5psi midrange, upping to about 7psi above 4500rpm.
Lower the CR, get a good head, high lift rockers, cam Ive already mentioned elsewhere, but stock is fine, intercooler, and you should be knocking on 150bhp with good torque.
A lot depends on budget...Are you buying everything from scratch ?
Have you considered a centrifugal SC ? Very compact, and quite efficient, and you can also use an intercooler with them.
What do you intend using it for ? short slow tracks ? do you need good low down torque, or chasing midrange and top end power ? Will traction be an issue ?
Considering they run very low boost as std to produce about 100bhp ( or whatever they have ), and use 9.4:1CR, its easy to get a bit more power. They run 4.5psi midrange, upping to about 7psi above 4500rpm.
Lower the CR, get a good head, high lift rockers, cam Ive already mentioned elsewhere, but stock is fine, intercooler, and you should be knocking on 150bhp with good torque.
A lot depends on budget...Are you buying everything from scratch ?
Have you considered a centrifugal SC ? Very compact, and quite efficient, and you can also use an intercooler with them.
What do you intend using it for ? short slow tracks ? do you need good low down torque, or chasing midrange and top end power ? Will traction be an issue ?
I suspect you might run into problems if you try to get that much boost from an M45. The Eaton blowers get less efficient as the back pressure increases (because they have no internal compression) and the baby M45 is the least efficient of the lot. Just because the blower can flow as much air as you want at the pressure you want, doesn't mean it is going to produce the extra power you are expecting. Most of the power taken by the supercharger is going to end up as heat in the charge air, and unless you have a good intercooler this will mean you have to back the ignition off, or use excessive fuelling to prevent detonation. Both these measures will cost power. Unless you are very careful/lucky, by the time you subtract power consumed by the blower and power sacrificed to avoid detonation you may end up with little more than you started with - and you can even end up with less in some situations! If you're looking for this sort of boost level, a screw compressor, centrefugal supercharger or turbo might be a better bet.
Esp with a small engine heat issues will be a major factor in the power/boost trade off.IMO a well chosen & matched turbo will prob give you more bang for your bucks-esp if its mid-top end that you want.I had some experience 'upping' the turbo on my skyline recently.Good I/c & (prob an oil cooler too)will really help with charge temps,I cant see lag being too much of a prob,with a small,quick spooling turbo,esp if you keep the pipework as short,smooth & stiff as poss.A good electronic boost controller really helped me to utilise available boost,& can also help with adjusting spool/open gate time,safety etc.
GreenV8s,
Good info about Rootes blowers. That has got me thinking seriously. I will have another look. A T2 turbo is a good choice but unless I plan to do some pretty novel siting of everything, it ain't gonna fit. I'm not going to start sawing my bulkhead about. The volumetric efficiency dropping off is probably why the guy who sells kits uses them on serious overbores/higher compression engines.
I will have a think about the maths and see what 12PSI should get assuming I have an ultimate cyl head.
I like the idea of efficiency and a cool charge.
Thanks guys.s
Whilst you're at it, anyone know a model of screw blower roughly equal to an M45?
>> Edited by kneegrow on Friday 24th September 20:44
Good info about Rootes blowers. That has got me thinking seriously. I will have another look. A T2 turbo is a good choice but unless I plan to do some pretty novel siting of everything, it ain't gonna fit. I'm not going to start sawing my bulkhead about. The volumetric efficiency dropping off is probably why the guy who sells kits uses them on serious overbores/higher compression engines.
I will have a think about the maths and see what 12PSI should get assuming I have an ultimate cyl head.
I like the idea of efficiency and a cool charge.
Thanks guys.s
Whilst you're at it, anyone know a model of screw blower roughly equal to an M45?
>> Edited by kneegrow on Friday 24th September 20:44
kneegrow said:
Whilst you're at it, anyone know a model of screw blower roughly equal to an M45?
Not off hand, but maybe a search for Sprintex, Opcom, Whipple will turn up some specs. Might not be easy to get find a supplier though because they aren't used in any production cars over here.
Have you thought about using a centrefugal supercharger (Vortech etc) instead? Far easier to package than the big positive displacement blowers, and similar efficiency to a turbo even at high boost levels with no lag or exhaust heat issues and none of the installation complexity of a turbo. Downside is lack of boost at low rpm, if you can live with that?
I hear there are a lot of new Mini Superchargers going on ebay from time to time. Perhaps something like that would be a cheap option. They are putting put around 200bhp on the new mini, so I dont see that gearing one to suit an old 1300 mini shouldnt be too difficult ?
Not sure about pulleys etc or availability, but Im sure they are.
Whats the big deal with cutting the bulkhead ?? Its not that bad of a job really. Tho, it does look a bit odd, when you have a gaping big hole there..
If you were to splash out on an 8 port head, or some sort of X-flow head for a mini, turbo positioning may become easier, along with any power benefits the head may offer. No idea what these cost at the minute.
Not sure about pulleys etc or availability, but Im sure they are.
Whats the big deal with cutting the bulkhead ?? Its not that bad of a job really. Tho, it does look a bit odd, when you have a gaping big hole there..
If you were to splash out on an 8 port head, or some sort of X-flow head for a mini, turbo positioning may become easier, along with any power benefits the head may offer. No idea what these cost at the minute.
kneegrow said:
Looking like having a suck through setup....due to space.
You sound like you're not keen on the idea... It doesn't work well with dump valves or with intercoolers, but it has its good points - the evaporation of the fuel droplets as the mixture passes through the supercharger gives you a measure of "built-in" intercooling, and you don't have to piss about with a sealed and pressurised carb and a high pressure fuel pump.
I went to "le pub" with my engineer mate last night. We had a chat about pressure drops, loading and heating of rootes pumps. I initially thought that it would be a good idea to fit something like an M62 instead. But, the pressure differential actually causes direct loading on the rotors. As the area would be bigger at a lower RPM (To achieve the same boost) if anything, the resistance would be bigger. Rootes blowers are not the choice for anything over pretty limp boosts. This will have a brilliant effect, but I am looking for something which I can develop without having to alter all my gubbins for.
Looking for screw blowers is very difficult. They are astronomically expensive. I saw an Autorotor one come up ages ago but I have forgotten the model number. The websites are quite scanty as to which model does what. Whipple only go down to a 1.2L pass which is too big. A Mazda Millenia has a 1L pass which at 1:1 would give scope. But, I think it has a load of crap cast with it. They are also cheaper than Bini blowers. They are a bit on the big side. I might have to go with the M45 as they are cheap and I am probably going to destroy it anyway.
How about using a Wankel motorbike engine as a supercharger? I also though, an old church organ in our village was powered by a "Supercharger" I think it was a shorrocks! (They binned it)
Looking for screw blowers is very difficult. They are astronomically expensive. I saw an Autorotor one come up ages ago but I have forgotten the model number. The websites are quite scanty as to which model does what. Whipple only go down to a 1.2L pass which is too big. A Mazda Millenia has a 1L pass which at 1:1 would give scope. But, I think it has a load of crap cast with it. They are also cheaper than Bini blowers. They are a bit on the big side. I might have to go with the M45 as they are cheap and I am probably going to destroy it anyway.
How about using a Wankel motorbike engine as a supercharger? I also though, an old church organ in our village was powered by a "Supercharger" I think it was a shorrocks! (They binned it)
If you don't want to cut your bulkhead, then you need to buy a set of manifolds from Mirage Motorsport which allow the T2 series of turbos to be fitted without bulkhead mods.
I've developed my mini over the last 5 years, and have tried lots of stuff, from Weber alpha, DTA injection (now just using DTA for ignition as injection the A-series properly is not possible with any ECU currently available) and of course, the smaller T2 turbochargers.
The best T2 to go for is the stock Renualt 5GT unit (50 trim compressor, 0.35 turbine A/R). These spool up very quickly, and flow more than enough air for a low-14 second pass on the quarter. You can go further than the stock turbo of course, but don't let anyone tell you that you need a T3 for big power... I'm already running Sub 14's on an open diff, and in a heavyweight car with full soundproofing, recaor's and other road-going essentials.
Adopting the T2 gives supercharger like performance - there really is nothing to beat it for the A-Series.
>> Edited by turbodave on Thursday 30th September 13:23
I've developed my mini over the last 5 years, and have tried lots of stuff, from Weber alpha, DTA injection (now just using DTA for ignition as injection the A-series properly is not possible with any ECU currently available) and of course, the smaller T2 turbochargers.
The best T2 to go for is the stock Renualt 5GT unit (50 trim compressor, 0.35 turbine A/R). These spool up very quickly, and flow more than enough air for a low-14 second pass on the quarter. You can go further than the stock turbo of course, but don't let anyone tell you that you need a T3 for big power... I'm already running Sub 14's on an open diff, and in a heavyweight car with full soundproofing, recaor's and other road-going essentials.
Adopting the T2 gives supercharger like performance - there really is nothing to beat it for the A-Series.
>> Edited by turbodave on Thursday 30th September 13:23
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