12 replies to this topic

[G'Racy]

Read a lot on here about supercharger systems, but could someone please explain in layman’s terms the main differences, pros and cons of suck through and blow through supercharger systems, cheers.

[mini13]

With a suck thru you have fuel going through the charger meaning you then can't intercooler the air to regain density (well you can, but fuel will puddle in the intercooler, and if you ever get a backfire it makes a right mess of it...)

[Turbo Phil]

In a suck through system the carb/injectors are placed before the supercharger, so the fuel passes through it. Blow through is basically the opposite with the carb/throttle body after the supercharger.
Suck through is the simplest as the carb operates under vacuum just the same as when fitted to a NA engine, on a blow through the carb is under pressure when boost is introduced, so the carb needs to be sealed and made boost sensitive so there is a pressure differential between the float chamber and carb throat. You’ll also need to use a fuel pressure regulator than increases fuel pressure to compensate for boost.
The commonly used roots type blowers are not very efficient and although efficiency is improved due to better rotor sealing in a suck through install charge temps can still get very high. A blow through configuration on the other hand can employ an intercooler as fuel is introduced after the position of it.

Phil.

[DeadSquare]

 

BLOW:-

As the air is compressed, the compression warms it and it expands a bit.  because the warm air takes up more space than cool air, less air would get blown into the cylinder head, so the air gets passed through pipes to a 'radiator' (called an inter-cooler) to cool it before it comes back to a special carb that works under pressure.

 

SUCK:-

As the air is sucked through the carb, picking up fuel, the air is cooled as the fuel evaporates;  it also gets well 'chopped up' as it is compressed by the supercharger and the compressing warms it so that it is more like a gas than a mixture as it is blown into the cylinder head and this makes it explode better.

 

Because suck does not require a special carb, it is simpler, even if an inter-cooler is incorporated between the supercharger and the cylinder head.

[timmy850]

I helped install a suck through vmax kit and they are very simple in comparison. Basically the supercharger/carb is all one piece and bolts on the back of the cylinder head. Then you just add on the new bottom pulley and the new belt and it's pretty much done. Air goes into the carb + mixes with fuel then is sucked into the supercharger and then into the engine. 

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Blow through is much more complicated - air sucked into supercharger - then normally to the intercooler, then back to the carb/throttle body and then into the engine. As mentioned above you need to increase the fuel pressure as you increase boost, and you also need a blow off valve to release boost when you close the throttle. 

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I think for a normal road mini the suck through is the better option.

 

[G'Racy]

Thanks guys thats a lot clearer, another question though if I may.
Read a lot on here previously about charge temperatures and inter cooling, on a suck thro system just how critical are these to the reliability and performance of the vehicle in everyday use?

[dyshipfakta]

Thanks guys thats a lot clearer, another question though if I may.
Read a lot on here previously about charge temperatures and inter cooling, on a suck thro system just how critical are these to the reliability and performance of the vehicle in everyday use?

You can’t intercool a suck through or atleast not really a blow through with intercooler will be more efficient and make more power but is much more complex. To be honest if going to all that trouble a little turbo will work better and be simpler I would imagine.

[mini13]

this is geared toward turbo's but itll give an indication of the temps you'll be seeing with a charger,

 

basically turbo's are around 65-75% themaly efficient, with an Eaton charger this drops down to around 60%, even lower if wou want to run much more than about 8 psi,  you'll easily be sing inlet temps to the engine of 100deg C upwards, this is all edging closer to detonation, run close and you only need an iffy bit of fuel or a hot day and you'll kill the motor.

 

 

 

https://www.motorgee...e&page=flowcalc

 

[Gr4h4m]

You can reduce the intake temps using water injection.

The other thing to mention IMO if you run the engine like you stole it and without mechanical sympathy it’s going toe greatly reduce its life, especially when you are pumping greatly increased power outputs.

[G'Racy]

I’ve read that water injection isn’t that effective?
Are there any other options?

[DeadSquare]

I’ve read that water injection isn’t that effective?
Are there any other options?

 

Methanol, but it is expensive if you are doing more than 1/4 mile drags.

[Turbo Phil]

I’ve read that water injection isn’t that effective?
Are there any other options?

I’m not sure where you’ve read that, but water injection done properly is hugely effective at lowering charge temps.

Phil.

[Gr4h4m]

I saw in take temps drop to 45deg on the rollers with a simple home brew water injection system