supercharger boost problem

[GreenV8S]

Without a recirc/bypass fitted, the supercharger is going to be trying to force the full air flow past the closed throttle. The pressure upstream of the throttle is going to be very high, I wouldn't be at all surprised to see 14 psi of boost here when the throttle is closed, it could easily be a lot higher. I haven't followed all the details of where your gauge is connected and what figures you're seeing when, but if you're seeing very high boost figures under no load / part load conditions then I think the most likely explanation is that you're measuring the boost upstream of the throttle.

Edited by GreenV8S on Saturday 3rd May 13:38

[Crofty2011]

Ok, need a bypass valve, thanks for that (and the web address)
On the Fuel regulator, have seen them advertised (FSE?)and will buy one of those also. I assume the existing reg is removed and blanked off?
Thoughts on whethher the Lambda/ECU is going to "adjust" the mixture?

[GreenV8S]

Crofty2011 said:

Ok, need a bypass valve, thanks for that (and the web address)
On the Fuel regulator, have seen them advertised (FSE?)and will buy one of those also. I assume the existing reg is removed and blanked off?
Thoughts on whethher the Lambda/ECU is going to "adjust" the mixture?

FSE are well known for supplying what they call 'rising rate' fuel regulators where the fuel pressure varies by more than the manifold pressure. Used correctly in the right application there can be some benefits to this, but more often it just seems to be used to make the engine run richer under full throttle conditions, which is not usually what you want.

I don't know what engine management system you are running, but I certainly wouldn't assume that the stock system is going to provide the correct fuelling under boosted conditions. You would need to know whether the AFM has enough range to cope with the full power, and whether the ECU map extends far enough (or can be adjusted to extend far enough), whether the injectors and fuel pump have sufficient flow rates.

Forced induction makes it ever so easy to detonate your engine to bits, and if you're keeping the stock compression ratio and stock bottom end you are likely to be especially vulnerable. In that case you need to be absolutely paranoid about getting the fuelling and ignition timing right and bear in mind that faults which might just cause a bit of rough running on the stock engine are more likely to destroy yours with forced induction, so you need to be monitoring for faults as well as making sure the components are up to spec.

For basic protection I would suggest wideband AFR monitoring, fuel pressure alarms, knock detection as a minimum, and at 7 psi with no charge cooling you're probably going to benefit from water injection.

[stevieturbo]

You do not need an FSE reg.

On a low boost setup, I would not be overly concerned about a bypass yet. That is nothing to do with your problems IMO.


Forget calculations for a minute. Lets talk real world. How do your pulley sizes, and boost compare to other similar engines this blower might be fitted to.

[Crofty2011]

Supercharger is off a Cooper S (5th generation) which runs a 66m vs 140mm combination. I am running the standard 66m against a 125mm pulley which drops the ratio from 2.1 down to 1.9 but mine is a 2 litre as opposed to a 1.6 litre engine (dont know whether that matters). Dont know if the Cooper S is a standard compression or lowered?
Thanks for your comments so far

[kenmorton]

Thought the Eatons had an internal bypass ?

[GreenV8S]

stevieturbo said:

On a low boost setup, I would not be overly concerned about a bypass yet. That is nothing to do with your problems IMO.

The problem is that the boost gauge is reading higher than he expects, and surely the cause is that he's got a downstream throttle with no bypass/recirc and is measuring the pressure upstream of the throttle. It shouldn't be any surprise to see very high pressures here given his layout. This seems like a fundamental characteristic of the layout rather than a miscalculation on the gearing.

As I see it there are two issues: the gauge would be more meaningful if it was connected downstream of the throttle, and a bypass would remove the high off-load pressures he's seeing currently and give the blower a much easier time.

[Pigeon]

kenmorton said:

Thought the Eatons had an internal bypass ?

Don't think so. The one I've got certainly hasn't.

Another vote here for some means of unloading the blower on part throttle. Otherwise it's just going to make everything hot, waste fuel and shorten component lifespans.

[stevieturbo]

GreenV8S said:

stevieturbo said:

On a low boost setup, I would not be overly concerned about a bypass yet. That is nothing to do with your problems IMO.

The problem is that the boost gauge is reading higher than he expects, and surely the cause is that he's got a downstream throttle with no bypass/recirc and is measuring the pressure upstream of the throttle. It shouldn't be any surprise to see very high pressures here given his layout. This seems like a fundamental characteristic of the layout rather than a miscalculation on the gearing.

As I see it there are two issues: the gauge would be more meaningful if it was connected downstream of the throttle, and a bypass would remove the high off-load pressures he's seeing currently and give the blower a much easier time.

from what I gather, he is measuring boost at the intake manifold..same as FPR. So that gauge source should be fine.

[Crofty2011]

Thanks for all your comments, you all obviously know your stuff and have all raised valid points. At the start the problem was the gauge reading and as far as I can see that has been caused by the siting of the "pickup" and is now resolved thanks to your help. The next thing that I will need to consider is the bypass valve (which is built in to the cooper S pipework and I will cut down and weld into my pipework). Third will be fuelling and fourth (my biggest cost) will possibly be ECU and re mapping. As I have only started it briefly and run on tick over ther may be more issues once I load the engine!
Thoughts on the fuelling and ECU etc?

[stevieturbo]

Full standalone ecu would be best. Budget will dictate what you use, and who you intend to do the tuning.

A piggyback ecu is another possibility. These could control additional injectors, or larger injectors to a degree to try and sort fuelling. This should be cheaper than most stand alone ecu's. As to how good they actually are....Im not 100% sure, as Ive never used one.

[eliot]

Crofty2011 said:

Thoughts on the fuelling and ECU etc?

Do you want to learn the subject (Megasquirt) or Just get it fitted and sorted (Emerald, amongst others)

[Crofty2011]

Good question! I guess I want to know enough to buy without getting ripped off and without buying something too good for what I need. Once I've bought the ecu who do I get to "tune" it to the car? I guess all the other bits (fuelling, bypass etc) would need to be completed before the ecu is mapped? I'll google the names you've put forward

[GreenV8S]

stevieturbo said:

from what I gather, he is measuring boost at the intake manifold..same as FPR. So that gauge source should be fine.

I thought from the original post that he was measuring at the blower outlet. If he's measuring downstream of the throttle then he should be getting an accurate reading. But if that's the case I'm at a loss to see how he could be seeing high boost figures when the engine is unloaded.

[chuntington101]

Crofty, just a quick question, how is all this aranged in the engine bay?? where is the throttle body in the system?? have you tried fitting a larger pully and seeing if that has any effect??

Cheers

Chris.

[Crofty2011]

Chris,
I've fitted the supercharger and pipework to a std F7R (Williams) engine and so far I haven't changed anyhing from standard. The guys that have contributed so far have determined the problem (me not thinking, and taking a reading from pre throttle body against a nearly closed valve), now that I've taken the reading from the vac point used for the fuel pressure regulator the pressure starts at minus 8 psi and rises with revs applied. I'll be starting a new discussion on programmable ECU's next as I need help on that side too!
Thanks for your interest and suggestions
Crofty

[chuntington101]

Crofty2011 said:

Chris,
I've fitted the supercharger and pipework to a std F7R (Williams) engine and so far I haven't changed anyhing from standard. The guys that have contributed so far have determined the problem (me not thinking, and taking a reading from pre throttle body against a nearly closed valve), now that I've taken the reading from the vac point used for the fuel pressure regulator the pressure starts at minus 8 psi and rises with revs applied. I'll be starting a new discussion on programmable ECU's next as I need help on that side too!
Thanks for your interest and suggestions
Crofty

cheers Crofty,

what i was getting at was why is the throttle down stream of the SC?? its normal to fit the throttle in front of the SC as then its not fighting against a closed throttle plate. its is traditionall how positive displacement blowers like your have beenoperated.mounting this way also remvoes the nead for a bypass valve when you come off the throttle.

Cheers

Chris.

[Crofty2011]

well now,
I've never heard of fitting the throttle body between the airfilter and supercharger (I assume thats where you are talking about?). The only knowledge that I have is from looking at production vehicles such as the Cooper S and Merc Kompressor where the bypass valve relieves the pressure, and since i'm a complete novice I thought I would actually use the Cooper S bypass valve (welded into the alloy air tube) and fitted just after the intercooler that I haven't got round to designing or fitting yet. maybe I should have read up on the subject before I started, maybe I was just a bit too keen to get away from the missus at Xmas!!
quick question for you, - with the supercharger running there's quite a bit of pressure being pushed out of the crankcase breather? Is that normal and if so is there anything in the "aftermarket" that I can put in the pipe (like a filter or something) as I obviously can't block it off?
I can still change the supercharger set up if there is a benefit to installing another throttle body and connecting the pipe straight into the airbox??

[chuntington101]

Crofty2011 said:

well now,
I've never heard of fitting the throttle body between the airfilter and supercharger (I assume thats where you are talking about?). The only knowledge that I have is from looking at production vehicles such as the Cooper S and Merc Kompressor where the bypass valve relieves the pressure, and since i'm a complete novice I thought I would actually use the Cooper S bypass valve (welded into the alloy air tube) and fitted just after the intercooler that I haven't got round to designing or fitting yet. maybe I should have read up on the subject before I started, maybe I was just a bit too keen to get away from the missus at Xmas!!
quick question for you, - with the supercharger running there's quite a bit of pressure being pushed out of the crankcase breather? Is that normal and if so is there anything in the "aftermarket" that I can put in the pipe (like a filter or something) as I obviously can't block it off?
I can still change the supercharger set up if there is a benefit to installing another throttle body and connecting the pipe straight into the airbox??

yes if you take the MINI as an example they run the throttle body, then the Supercharger (SC), thenthe intercooler and finally the intake manifold. this mean the SC is allways restricted (apart from WOT) by the throttle body. this, im told, drimatically reduce pumping losses and stress on the SC drive system (ie belts). also it menas you dont need a blow off valve.

a blow of valve is what tipically fitted to turboed cars. its design to vent the the air from the turbo and stop the turbo from stall or causing damage to it.

the bypass valve you talk about is what is used to bypass the SC when crusing and light throttle to reduce emmission, noise, etc. this valve (basically a small throttle body) will snap shut once you go WOT.

there is some info on superchargering in the last few practical performance car mags. might be worth back ordering some (or i might beable to get them scanned) for some more info.

Hope this help some, sounds like a really cool project!!

Chris.

[Crofty2011]

Thanks Chris, yes I already have PPC because I'd heard about the articles and will send them some photos at some point (if I can get it to work).They focussed on types of supercharger etc but little on actual fitting and any other bits that were needed (I guess they wanted to talk about other things as well as superchargers!!). Is there a rule of thumb when talking about superchargers/turbos ie when talking about them you start from the engine and work back towards the filter? If so then mine will be set up throttle body/bypass valve/intercooler/supercharger/ air filter - which I think is the way the mini is set up (and what you are descibing)??