Suck or Blow?

[That Bloke]

15-20 years ago everyone seemed to reckon that turbo set-ups just had to be suck-through(ie: Throttle assembly/carburetta mounted after the compressor, with the air being sucked through it) & you couldn't have it any other way but now Blow-through(ie: throttle assembley or carb mounted on manifold like normal with the charger blowing into it) is not only far more common(to the point that no manufacturer does it the other way anymore) but appear also appears to give better results with this in mind I still find that when you ask about Supercharging the armchair experts(Well the ones I know, well they aren't in the industry though) still insist that it has to be suck-through, but I really wanna know why? I mean how is Supercharging different to Turbocharging in regard to throttle location? They're both methods of forced induction right?(rhetorical), Therefore if turbocharging works fine(well better) with a blow-through setup shouldn't blow-through be equally suitable for Supercharging?

I guess the best thing would be to look at all the factory supercharged cars built in recent years & see how they do it.

[hooptieride]

this threads title is very misleading :eek:

[That Bloke]

Originally posted by hooptieride
this threads title is very misleading :eek:

I knew it would be & was amusing myself at that prospect, but really I couldn't have been bothered to name it anything else, it's straight to the point:D

[C0V3R]

Originally posted by That_Bloke
15-20 years ago everyone seemed to reckon that turbo set-ups just had to be suck-through(ie: Throttle assembly/carburetta mounted after the compressor, with the air being sucked through it) & you couldn't have it any other way but now Blow-through(ie: throttle assembley or carb mounted on manifold like normal with the charger blowing into it) is not only far more common(to the point that no manufacturer does it the other way anymore) but appear also appears to give better results with this in mind I still find that when you ask about Supercharging the armchair experts(Well the ones I know, well they aren't in the industry though) still insist that it has to be suck-through, but I really wanna know why? I mean how is Supercharging different to Turbocharging in regard to throttle location? They're both methods of forced induction right?(rhetorical), Therefore if turbocharging works fine(well better) with a blow-through setup shouldn't blow-through be equally suitable for Supercharging?

I guess the best thing would be to look at all the factory supercharged cars built in recent years & see how they do it.

You incorrectly defined suck through (possibly inadvertant). The fuel delivery point/throttle body is BEFORE the compressor in suck through. The fuel air charge passes through the turbo itself as well as any intercooler etc.

With blow through, the fuel delivery point is after the compressor, so that only air passes through the turbo and any intercoolers etc, thus reducing any damage done by backfiring.

[C0V3R]

671 blowers (suck through) use this method because they are directly bolted to the manifold, and dont suffer as badly from the likelihood of backfire damage due to the twin screw setup. The benefits of this is there is no pressurisation of the carburettors, and they opperate essentially as if there is a giant naturally aspirated engine sucking the mixture through them as normal. This also applies to fuel delivery, as they can be used without rising rate regulators and high pressure pumps due to there being no pressure being applied to the carb fuel bowls.

Blow through carby turbo/sc setups normally require modfication of the carby (nitrophyl floats etc) or creation of carb boxes to prevent gasket leaks (especially holleys) or both.

[That Bloke]

Originally posted by C0V3R

You incorrectly defined suck through (possibly inadvertant).


That was inadvertant, I was typing quickley, With the carburreta+ suck through it went without saying that fuel would go through the compressor, I just kinda forgot to mention the same of injection.

Now that I think of it Multipont injection makes suck-through totally redundant.

Originally posted by C0V3R


With blow through, the fuel delivery point is after the compressor, so that only air passes through the turbo and any intercoolers etc, thus reducing any damage done by backfiring.

So the statements about Suck-through being the only option for superchargers is bullshit?(as I was thinking) & like Turbocharging it is actually better do use blow through for supercharging as well?

Edit: I'd intended to use a sprintex twin screw blower in a multipoint injection application(using 2 double barrel weber style throttle bodies), someone I knew claimed that I'd have to have the throttle mounted on the blower or else (he gave 2 reasons)

1~ If I had it set up blow-through the supercharger would overload when I closed the throttle.

2~ If I had it set up blow-through the supercharger would force the throttles open.

How likely are either of these?

[ToaDady]

so now do you know why they call it a "671" blower?...i do

[Plough]

671 refers to the manufacture name of the original engine block it was built for. I had the previlige of working on these blowers during my apprenticeship.
They were originally made to suit the GM, Detriot 671D, 871D 2 stroke engines back a long long time ago. They were so popular that since then they have been used on just about anything that has a motor both petrol and diesel.
There a nice simple set up, 2 screws with or without the inserts to adjust the boost pressure amd if you are lucky your model may even have a emergency air intake shut off in case of motor runnaway. I wish I had a dollar for evertime I had to use that. The motor would go way past the redline and would not shut down, pull the emergency air shut off and watch as the motor stops as it runs out of air and at the same time sucks the blower seals into the motor and fucks everything.

[ToaDady]

i whish i had a doller for every fone call i got "we can't get this 3-53 to restart." ..........well did you reset the mousetrap looking thing ?......duh is that what that's for.....

grandfather had a 8v-92 in his truck , i could find it in any parking lot omgst the cummins and catterpillar engins.

[Plough]

We would try and use a fire exstingisher on the air intake to shut down runnaway engines before we would use the mouse trap.
Try first anyway, then run, run like hell.

[That Bloke]

Originally posted by That_Bloke

Edit: I'd intended to use a sprintex twin screw blower in a multipoint injection application(using 2 double barrel weber style throttle bodies), someone I knew claimed that I'd have to have the throttle mounted on the blower or else (he gave 2 reasons)

1~ If I had it set up blow-through the supercharger would overload when I closed the throttle.

2~ If I had it set up blow-through the supercharger would force the throttles open.

How likely are either of these?

His theory was far from correct, infact I've been told having the throttles mounted blow-through(that is to say behind the blower) like I intended provides better throttle responce

[DumHed]

the factory supercharger setups have used both designs, although they are all fuel injected these days, so it's not a case of "suck through" or blow through" so much as whether the throttle is before or after the blower. The fuel is still injected at the actual intake ports - and the superchargers don't have seals designed for fuel.

The toyota 4AG-ZE engine runs the blower in a setup closer to a turbo, with a bypass valve to prevent over pressure, and to allow the engine to suck air "around" the supercharger at idle, where the ECU actually disengages the drive to the supercharger for better efficiency and throttle response.

The Eunos 800 has the throttle body before the Lysholm (scew type) blower.
I have one of these blowers, and it looks like they have some kind of bypass valve, but as I don't have the factory manifold I don't know exactly how it's set up.

Suck through (with a carby) is obviously easier, because the carby never sees any pressure so it functions 100% normally, but you can't really use long intake pipes or intercoolers because the fuel can condense out of the mix. Also a backfire can cause a major explosion in the large volume intake full of air/fuel mix!
Even the 671 style blowers mounted directly on the intake manifold blow up fairly frequently in drag racing applications.

[That Bloke]

Originally posted by DumHed


The toyota 4AG-ZE engine runs the blower in a setup closer to a turbo,

Aren't they like a cross between a Rootes & a Lysholm with Teflon rotors?

[DumHed]

almost.. they're basically a roots blower with a twist in the rotors.

They are also "fluorine resin coated" which improves sealing and friction apparently.

[That Bloke]

Originally posted by DumHed
almost.. they're basically a roots blower with a twist in the rotors.



60degrees? Sounds like it's based off the Eaton design.

[DumHed]

I haven't measured it, but it could be about that :)

[That Bloke]

Thought I'd revive this to make for some interesting discussion in here.

[DumHed]

interesting hey :)

Hmm, I'm still busy playing with turbos, but I keep trying to convince people to put one of my spare superchargers on their car :)

[BlueBoy]

Originally posted by DumHed
interesting hey :)

Hmm, I'm still busy playing with turbos, but I keep trying to convince people to put one of my spare superchargers on their car :)
Will it fit my car? :)

[flow]

The problem with turbos are the lag. Most cars as standard have their boost starting in at 2500-3000rpm. So you have to have the engine reving decently before you're in the "power" zone".

Put that on a V8 and you're in trouble. A high reving 4 and you're like a pig in shit.

Most v8s are designed from the factory such that the majority of the power is 1500-4000rpm. Bottom end power.

Superchargers work far better with lower revs and higher torque engines. And they EAT fuel.

My V8 uses 23.7L/100km I can't imagine putting a supercharger on it.

[That Bloke]

Originally posted by DumHed
I keep trying to convince people to put one of my spare superchargers on their car :)

You got a Lysholme? I don't have a car or a license right now but that doesn't matter.

[That Bloke]

Originally posted by flow_aus

Superchargers work far better with lower revs and higher torque engines. And they EAT fuel.


That's a bit of a misconception, A Modern Lysholme(twin Screw) with a good anti-friction coating has very little parasitic drag & can infact be more economical than a turbo, people just assume turbos are more efficient because they use otherwise wasted exhaust gas but what few people realise is that the turbo also disrupts the natural exhaust flow.

Turbos also can't practically give more than a 40% power increase on their own, whereas a simple bolt on installation of a Lysholme type supercharger can give you a power increase as high as 70%.

[flow]

Originally posted by That_Bloke
That's a bit of a misconception, A Modern Lysholme(twin Screw) with a good anti-friction coating has very little parasitic drag & can infact be more economical than a turbo, people just assume turbos are more efficient because they use otherwise wasted exhaust gas but what few people realise is that the turbo also disrupts the natural exhaust flow.

Turbos also can't practically give more than a 40% power increase on their own, whereas a simple bolt on installation of a Lysholme type supercharger can give you a power increase as high as 70%.

Which bit is the misconception?

I'm talking about a supercharger using more fuel than your normal engine. Nothing about turbo vs Super - they BOTH eat fuel... especually at 103.9 as I saw it today!

Power will always/often include more fuel used. It just had to be said to people about to think about this that they've got to realise this. They may not be able to run their car day-to-day.

[That Bloke]

Originally posted by flow_aus
Which bit is the misconception?

I'm talking about a supercharger using more fuel than your normal engine. .

My mistake, still a supercharged engine will use less fuel than an atmo that could produce the power & torque, It's all relative.

[flow]

No ad. Never used them, but:
http://www.capa.com.au

[DumHed]

Originally posted by That_Bloke
You got a Lysholme? I don't have a car or a license right now but that doesn't matter.

Sure do :)

It'd be on my car right now except that it's longer than my engine so it won't fit without very major work!

[That Bloke]

Originally posted by DumHed
Sure do :)

It'd be on my car right now except that it's longer than my engine so it won't fit without very major work!

Longer than your engine? What do you drive?

[scathing]

Originally posted by flow_aus
The problem with turbos are the lag. Most cars as standard have their boost starting in at 2500-3000rpm. So you have to have the engine reving decently before you're in the "power" zone".

Put that on a V8 and you're in trouble. A high reving 4 and you're like a pig in shit.

That's a matter of setup, anyway. As you say, having the boost building at around 2500RPM suits 4 pots. On the bigger cars, they have it boosting from lower.

The Audi RS's run twin turbo setups on their V6's and V8s, and they boost from low down. The RS6 makes peak torque from below 2000RPM, which means the turbos have to be providing some boost. For a petrol engine with twin turbos isn't too bad. It still pumps out 331kW from a 4.2L V8, so the turbos are doing a reasonable job.

[scathing]

Originally posted by DumHed
Sure do :)

It'd be on my car right now except that it's longer than my engine so it won't fit without very major work!

The damned thing won't fit on my engine either. :(

[That Bloke]

Originally posted by scathing
The damned thing won't fit on my engine either. :(

My tafe auto teachers always said "you can make anything fit anywhere if you want it enough"

[scathing]

Originally posted by That_Bloke
My tafe auto teachers always said "you can make anything fit anywhere if you want it enough"

I tried that line on my girlfriend once, too.

Lets say that not only did I not manage to fit it where I wanted it, but apparently the bed was too small to fit me and I had to spend the night on the sofa.

[DumHed]

the supercharger is from a Eunos / Mazda 2.3L miller cycle V6.

It's a transverse mounted engine, so there's plenty of room for the long supercharger - which has the throttle body on the end, and quite a long gearbox section.

My engine's an inline 4, longitudinally mounted (Nissan SR20), and there's not really enough space to put the supercharger without some mods to the S/C's intake piping, and also to the SR20's intake manifold to provide some space (unless I put in on the exhaust side, but then it's in the way of the crank angle sensor / distributor.

Also, the turbo setup was easier to get working nicely. Superchargers are a bit harder to match to the engine, and don't allow easy control over boost level, etc to keep it tuned safely when it's first put together.
I'd still like to try it one day.

[That Bloke]

How much money to take it off your hands?

[DumHed]

hmmm...

I'd have to think about it :)
I still have a couple of possibilities for it.

I also have a toyota SC14 (from a 2L six), which has the advantage of a self contained oil system and easier piping - but it wouldn't have the same power potential or efficiency.

[That Bloke]

Here's a question, 7-8PSI(roughly half a Bar) is considered to give a power boost of 50-60%, so would ramming a full Bar(14.7psi/ One atmosphere) into the engine make it produce equivalent power to an engine twice the displacement(having now twice as much air rammed in)?

[Crazy_Vaclev]

She sucks for 5 to 10 minutes & then I blow.

[Sagacious]

talk about thread necromancy this thread was kicked off by That_Bloke in July of 2003!

[That Bloke]

It was me who Necromanced it, with a relevent question

Here's a question, 7-8PSI(roughly half a Bar) is considered to give a power boost of 50-60%, so would ramming a full Bar(14.7psi/ One atmosphere) into the engine make it produce equivalent power to an engine twice the displacement(having now twice as much air rammed in)?

[Salted_Chipmunk]

Wouldnt it also come down to your fuel maps, injectors and that as well?

It wouldnt be a matter of simply upping the boost cause you would need the corret amount of fuel to mix with the air or its going to go boom.

[DumHed]

In theory a bar of boost will give double the power, but only if you're getting the same relative volumetric efficiency as you are at your "no boost" power level.
That obviously has to include extra frictional losses and flow restrictions caused by the extra air.