14 replies to this topic

[floydrob]

i have lately been tinkering with the idea of a DIY centrifugal supercharger...nothing fancy, just in essence a belt driven leaf blower directed to the carbs. i have twin hs4 SU's ready to bolt on and a 998. my shell isnt ready to put the subframes on it yet, but i want to get all the power plant and running gear sorted ready to just bolt on (if it goes smoothly)
i was going to get my head skimmed, but that would increase CR and therefor increase the chance of blowing my head gasket.
dont want massive boost simply because this is experimental and i dont want to risk blowing up the engine!!
think i'll have a safety valve at 8psi, so if it goes anywhere above, the excess air is just discharged. would like to run it about 6 or 7psi tho, without altering the CR on the 998 other than obvi replacing the piston rings.

also, is there any cheap intercooler i could get? i have seen some on ebay around the £20 mark from things like sierras and astras, but i could make a mounting bracket if you think one of these would do the job. if not i'll just head to the scrappy and find a more robust one.

any other precautions i need to take? added cooling for example?

any help/advice is much appreciated.
Rgds, Robert

[Saxo-Fiesta-Mini]

most company pocket the head to lower cr or fit decom plate

i would add extra cooling in the for of bigger rad and oil cooler

other than cold spark plugs and a sport coil should be ok and the consensu is hif 44 carbs are best for forced induction

[floydrob]

thanks! if i was to pocket the head i'd be putting a 1275 head on...no point pocketing it and not upgrading the head in my view!
is there a cheap radiator u would recomend? tight budget here u see i'll be needing a new one anyway.

[In-a-mini]

When he said pocket the head he probably meant open up the chamber for higher cc if you are going to run any form of positive pressure through the carbs then they have to be sealed ad the fuel pressure be rising along with the positive pressure other wise you will just blow the fuel the wrong way down the jets and out the overflow! i heard there were a load of people in the us that started doing this.

[floydrob]

ahhhh, i'm confuzzzled! lol. i thought you were meaning to pocket the block, i.e. increase cc and decrease CR. like this....


the primary reason for diong this is to fit a bigger head so the valves can open properly. you would use a 1275 head gasket as a template, scribe round it to see how much of a recess needs to be removed, and then bolt on a 1275 head with the 1275 gasket. bigger valves and ports and it increases the capacity and therefor decreases CR...this what was meant?

[Guess-Works.com]

Silly question, but do you think it's actually going to work ?

[Nickh_16]

weeeeell i've seen veryveryvery crude versions done on youtube....they did work though!

[wolfie]

Silly question, but do you think it's actually going to work ?

not based on the quality of the answers in this thread

[Wil_h]

i would add extra cooling in the for of bigger rad and oil cooler

not needed, I run nearly 10psi on a totally standard cooling system, never overheated.

When he said pocket the head he probably meant open up the chamber for higher cc if you are going to run any form of positive pressure through the carbs then they have to be sealed ad the fuel pressure be rising along with the positive pressure other wise you will just blow the fuel the wrong way down the jets and out the overflow! i heard there were a load of people in the us that started doing this.

This isn't the problem with sealing carbs. Although it is a problem if you don't block the overflow.

Silly question, but do you think it's actually going to work ?

I don't really know what you are really planning on doing, but at a guess a leaf blower is not designed to create pressure eficiently, rather have massive flow at atmospheric pressure. So using it in the way you plan is probably a non starter. My first though would be how fast the blower would need to spin compared to engine speed.

Turbos and superchargers are specifically designed for automotive use and are realistically the only options.

[floydrob]

haha, i'm not using a leafblower! or any parts from one, just a similar principle in the fact it is centrifugal. there are planty of centrifugal superchaqrgers out there already.
and YES, i do think it will work, i just need to figure out what compression ratio i should be looking for to run 7-8psi.

[redhotmini]

best to take a look at the current supercharger kits, and ask the companies what the cr should be. pocketing the block doesnt increase capacity (cc) although it will lower the compression ratio a bit, depending on the head and whether its been modified or skimmed etc in the past.

edit: just noticed another thread in this forum about suitable compression ratios

Edited by redhotmini, 10 April 2009 - 03:39 PM.

[Wil_h]

haha, i'm not using a leafblower! or any parts from one, just a similar principle in the fact it is centrifugal. there are planty of centrifugal superchaqrgers out there already.
and YES, i do think it will work, i just need to figure out what compression ratio i should be looking for to run 7-8psi.

The Rotrex is the only centrifugal suprcharger I know of, are you using one of these? or are you planning on making your own. The tricky thing is getting them to spin fast enough.

For the moderate boot you plan, anywhere around 9:1 will be fine.

[floydrob]

i plan on making my own.
is it possible to do this without modifying the CR from what it was? all i really want to do internally is replace piston rings, bearings etc, balance crank and fit a kent (or similar) cam. IF all goes well with the supercharger i might get it professionally refurbed.
thanks for all the help so far!

[Dan]

What are you planning to base your supercharger on? The important thing about a supercharger is that despite being nicknamed a blower it must be a compressor. Using your example a leaf blower is not a compressor, its a fan as said above. If you try to use one to build any pressure in a closed system the pressure against the compressor vane would soon overcome its ability to seal into the housing. This is why centrifugal compressors are expensive. To maintain pressure means very close tollerances and very rigid materials. You could use half a turbo of course but you'd have to spin it very fast.

[Wil_h]

That's not strictly true Dan. The Roots type blowers are just a pump and they do not compress. all the compression is done in the fact that it's pumping in to a limited space. This is part of the reason why they are inefficient and generate so much heat.