Hi All, need some help with a tech supercharger question that l have had in from a Mag, Glenn, Carl, Bill, anyone.
Here you go,
This is it
The magazine is great and has prompted me to write with a technical
question. I have aquired an Eaton M45 supercharger from a Mini and intend to
fit it to my Mazda MX-5. Most of the parts I need are readily available
either here or in the US and fuelling/igniton issues should not be a major
problem. The one point I\'m not too sure about is the position of the
throttle body. All reports I have read have this sited upstream of the
supercharger which sucks through it. For various reasons I should prefer to
keep my throttle where it is, downstream of the supercharger. This means
that when the throttle is closed, the butterfly will be subject to around
6psi of boost pressure which I suspect is not a good idea. To solve this I
propose to fit a dump valve to vent the boost. Will this work? Do I fit it
before or after the intercooler? Is there any benefit to fitting a
recirculating type to feed the boost back into the circuit?
Please let me know what you and your experts think.
Hi Clive,
Recirculating the air is the way to go with this type of setup where the throttle is placed after the supercharger.
The car should not need an intercooler for this type of setup as there is no real boost (6 psi or less)pressure of any significance,so the charge should not be too hot,if over 6 psi then yes consider an intercooler.Since the Eaton Supercharger is a roots type the basic boost pressure should,be pretty much the same throughout the rev range once the engine starts to get some revs on,the boost would pretty much be dictated by the gearing ratio of crank pulley to supercharger pulley.It may need some careful experimentation.This is because for one given revolution of any Roots type of supercharger the displacement remains constant unlike centrfugal types.
Most roots type of blowers(Superchargers)have the throttles or carbs placed before them rather than after,unless intercooled,if it is setup that way round then the fuel helps to cool the inlet charge a little as it starts to vapourise,absorb some of the heat that is made by the blower compressing the air molecules.
The very best setup has the inlet,supercharger,intercooler,and throttle in that order,and has a recirculating system for the air when the throttle is shut.
I have tried to keep it as simple as possible but there are many other things that can and should be considered for a setup like this,but i have purposely left them out so as not to over complicate or confuse the issue.
Kind regards
Carl
Many Thanks, Carl your a Star for coming back on this.
I realised the above i.e. Roots type blower plumbing etc etc, but still not to sure when you got to this bit,
\'\'recirculating system for the air when the throttle is shut\'\'
Surely he will always have some pressure up against the butterfly\'s, but is it even worth worrying about, personally l have never seen a conventional Turbo Dump valve used, which leads back to the original question of which side of the butterflies does he need to fit one, if at all, as l can\'t see how or why you would fit a Dump valve on the inlet side of the butterfly as this is open to atmosphere with a supercharger.
To me the \'\'boost\'\' is controlled mechanically by the gearing and if there was a need for a Dump valve, the ideal place would be in the inlet manifold, problem is then though, it would spit out fuel mixture when relieving pressure!.
Hi Clive,
We are supercharging the 20B FD we have, the way we are going to do it is to leave the throttle body in place and use something similar to a recirculating dump valve, this will read vacume in the plenum chamber between the engine and the throttle body when the butterflies are closed, when it sucks, the dump valve will dump the charge in the inlet track back into the front of the s/charger. At least I think that is what carl is getting at.
Regards
Tony
QuoteOriginally posted by antnicuk
Hi Clive,
We are supercharging the 20B FD we have, the way we are going to do it is to leave the throttle body in place and use something similar to a recirculating dump valve, this will read vacume in the plenum chamber between the engine and the throttle body when the butterflies are closed, when it sucks, the dump valve will dump the charge in the inlet track back into the front of the s/charger. At least I think that is what carl is getting at.
Regards
Tony
Hi Tony,
Your superchager is not a positive displacement type but is the centrifugal type so will create more and more boost (Almost exponentialy) as the revs of the engine increase.That being the case you will need to vent excess manifold pressure too when the throttle is open,or you will simply overboost.
If you want to know more then pm me.
Kind regards
Carl
didn\'t some of the yank systems use bypass valves to relieve pressure and load from the \'charger when not in use. I think Weind use to do a system.
I seem to recall seeing it on //www.toohighpsi.com (worth a read anyway as its cool)
i thought centrifugal type supercharges are dependant on the size of the pulley so you can set the max boost presure by the pulley size. Please correct me if i am wrong.
QuoteOriginally posted by gilbert
i thought centrifugal type supercharges are dependant on the size of the pulley so you can set the max boost presure by the pulley size. Please correct me if i am wrong.
That is quite true,but the problem is that if you want say a max boost of 10 psi then you can only have that maximum boost at maximum revs because of the gearing,if on the other hand you want more boost in the midrange of the revs then you need to be able to bleed off excess boost at higher revs.
Regards
Carl
basicly you need to make some kind of wastgate and run a boost control to put it in very simple tearms.
QuoteOriginally posted by gilbert
basicly you need to make some kind of wastgate and run a boost control to put it in very simple tearms.
superchargers do not have a wastegate,only turbos can have a wastegate.
The wastegate on a turbo vents exhaust gas and bypasses the exhaust turbine on a turbo which in turn slows the turbine wheel down and that obviously in turn slows the compressor down thus making less boost.
A supercharger can have a charge relief valve that can vent excess boost though.
Regards
Carl
QuoteOriginally posted by Carl
superchargers do not have a wastegate,only turbos can have a wastegate.
The wastegate on a turbo vents exhaust gas and bypasses the exhaust turbine on a turbo which in turn slows the turbine wheel down and that obviously in turn slows the compressor down thus making less boost.
A supercharger can have a charge relief valve that can vent excess boost though.
Regards
Carl
i know that a supercharger does not have a wastegate,tahts why i said some type of wastegate meaning some thing to releive excess pressure henst producing wasted boost pressure. i could have worded it a bit better i must admit.
You and me both mean the same thing, a pop off valve like on the indy cars is the same sort of thing as charge relief valve.
so that when the boost reaches a desired pressure and the valve is pushed open to release the access pressure and the boost level is kept at the desired amount.
If thats is right.
That\'s right James.
great minds think alike eh?LOL!
regards
Carl
Ok.
Can I use the greddy type R as s charge relief valve ?
Cause it have valves on the both chambers.
Quote from: cliveHi All, need some help with a tech supercharger question that l have had in from a Mag, Glenn, Carl, Bill, anyone.
Here you go,
This is it
The magazine is great and has prompted me to write with a technical
question. I have aquired an Eaton M45 supercharger from a Mini and intend to
fit it to my Mazda MX-5. Most of the parts I need are readily available
either here or in the US and fuelling/igniton issues should not be a major
problem. The one point I\'m not too sure about is the position of the
throttle body. All reports I have read have this sited upstream of the
supercharger which sucks through it. For various reasons I should prefer to
keep my throttle where it is, downstream of the supercharger. This means
that when the throttle is closed, the butterfly will be subject to around
6psi of boost pressure which I suspect is not a good idea. To solve this I
propose to fit a dump valve to vent the boost. Will this work? Do I fit it
before or after the intercooler? Is there any benefit to fitting a
recirculating type to feed the boost back into the circuit?
Please let me know what you and your experts think.
Hello,
Just wondering if anything ever came of this? I\'ve considered putting this same supercharger on my MX-5 but I\'ve been informed that it\'s quite difficult due to the shape of the Mini\'s version of this supercharger?
Cheers,
R.
:eek:
Classic Resurrection !! :D