Boost Pressure Question

Racer75

Tuner
Points
107
Location
Scotland, Glasgow
Car
BMW 323i (e36)
Good evening all,

I have recently completed my project of fitting an Eaton supercharger to my e36 323i. My SC is on the A/C side and uses an Intercooler. This is then fed through a BOV then into a MAF and finally into the intake. The boost gauge is hooked up to a fitting before the BOV and runs into the cabin (obviously).

My question is this, when the engine is at idle, the boost gauge is reading 0.1/2bar, on 1/4 throttle or less the gauge reads 0.5 bar and at WOT, the gauge flies back down in to the negative side of the boost gauge.

I’m starting to run out of things to look for. I looked over all my pipes to make sure they were all tight, as well as any engine ancillaries which were removed and reinstalled. I can’t seem to find any leaks.

Is there something obvious that I could be missing? Hopefully someone who knows more about this sort of thing than me has solved a problem like this before.

Thanks for reading.
 

wizzer

Road Burner
Points
202
Location
Lyndhurst, Hampshire
Car
VW Golf 2.0 TDi
Restrictive air filter perhaps?

My guess would be the wastegate is blowing open fully and sending out the boost there. Even if it has a 3psi rated spring it may be failing or not enough when you hit full boost and it pops open and stays open.
 

Racer75

Tuner
Points
107
Location
Scotland, Glasgow
Car
BMW 323i (e36)
Interesting. The BOV I use was just a generic one off eBay and I can’t remember seeing a rating on the spring. I will look about for a stronger one.

As for the intake/filter, space was a big thing for me during this, so my intake pipes are about 2” from memory.
Thanks
 

thexav

Pro Tuner
Staff member
Points
387
Car
2002 Clio 172
Drop off the entire air filter housing and see if it's still dropping boost, that will tell you if its a restrictive intake.

I would guess the BOV is the issue here. Is there a way to test it? I'm guessing it's an atmospheric vent.

Have you got a project thread on here, it will be a good read.
 

Racer75

Tuner
Points
107
Location
Scotland, Glasgow
Car
BMW 323i (e36)
The BOV is an Atmospheric one and it also has a plumb feature which I have been playing with. It only seems to increase boost at idle.


The above is my thread. It hasn't been updated since the project was completed/MOT’d, but you’re welcome to have a read
 

Racer75

Tuner
Points
107
Location
Scotland, Glasgow
Car
BMW 323i (e36)
For anyone still interested in this thread, I haven’t been using a wastegate as I was under the impression that a BOV was good enough. Clearly this was wrong but since then, and after reading your messages, I have purchased a better BOV from DemonTweeks with a stronger spring and a heap of parts so that I can fabricate a BPV operating from just after the MAF on the passenger side and run it back into the air inlet on the driver side.

Hopefully this will cure my problem but we will see.

One more thing, is there any need to run a hybrid system of a BOV and BPV together? I like the noise the BOV makes, but can live without if it’s totally detrimental to the performance.

Thanks again
 
Last edited:

obi_waynne

Administrator
Staff member
Moderator
Points
1,157
Location
Deal, Kent UK
Car
A3 1.4 TFSI 150 COD
Thanks for the update and judging by all the views of this thread it is certainly popular.

Wastegates control the flow of exhaust gases into a turbo, as you have a supercharger you won't have one I think the poster meant blow off valve.

Let us know how you get on.
 

Racer75

Tuner
Points
107
Location
Scotland, Glasgow
Car
BMW 323i (e36)
Thanks Obi.

I’ve been digging around the web since Sunday looking and lots of people fit Bypass/Diverted Valves in order to maintain pressure. I believe as I have my setup in the following order;

Air filter -> SC Inlet -> SC outlet -> Intercooler -> BOV -> MAF -> TB -> Engine

this could be creating a situation where air is being lost and fitting a BPV will help to remedy this.

I am going along with this as lots of people have this sort of setup and my fancy BOV hasn’t really helped. Hopefully this will.

Will keep you all informed (possibly in a new thread ;))
 

Racer75

Tuner
Points
107
Location
Scotland, Glasgow
Car
BMW 323i (e36)
Here is an attached drawing I completed showing my proposed solution for the BPV fitting :)

8a6deafb-1b4a-436a-8871-0c31a67f8a4b-jpeg.8671
 

Attachments

  • 8A6DEAFB-1B4A-436A-8871-0C31A67F8A4B.jpeg
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Fabia17

Torque Junkie
Points
322
Location
Lincoln UK
Car
Fabia Monte Carlo
Good evening all,

I have recently completed my project of fitting an Eaton supercharger to my e36 323i. My SC is on the A/C side and uses an Intercooler. This is then fed through a BOV then into a MAF and finally into the intake. The boost gauge is hooked up to a fitting before the BOV and runs into the cabin (obviously).

My question is this, when the engine is at idle, the boost gauge is reading 0.1/2bar, on 1/4 throttle or less the gauge reads 0.5 bar and at WOT, the gauge flies back down in to the negative side of the boost gauge.

I’m starting to run out of things to look for. I looked over all my pipes to make sure they were all tight, as well as any engine ancillaries which were removed and reinstalled. I can’t seem to find any leaks.

Is there something obvious that I could be missing? Hopefully someone who knows more about this sort of thing than me has solved a problem like this before.

Thanks for reading.
Hi, I have been reading your post and I looked at your diagram to, and I would like to ask if you bought the charger system as a bolt on kit for your specific engine? If not, what vehicle did it come from? In your diagram you don't really show the inlet manifold, are you using the original manifold and does it have the original plenum chamber? And are you using it?
From what you describe here either you charger is not big enough to feed the motor, or the pulley is way too small, or the the total volume of the inlet tract is smaller than the swept volume of your motor. Or a combination of these issues. So when your motor is at idle and low throttle opening the boot is OK, but as soon as you open the throttle the motor sucks all the boosted air out and returns a negative boost. Time to do the maths to check.
I hope this helps
 

Racer75

Tuner
Points
107
Location
Scotland, Glasgow
Car
BMW 323i (e36)
Hi there.
Firstly, no. This unit was taken from a CLK320 and all the piping/plumbing has been fabricated to suit.

Secondly, the inlet manifold is technically an original. It was take from an older M50 Engine. For those who don’t know, this is a common alteration to the M52.

Finally, when I measured the pulley and spoke to the gent who retuned the car’s ECU, I measured the supercharger pulley at 2.3x smaller (55mm) than the crankshaft pulley (127mm). My tuner told me that this was a decent size difference.

Thanks for taking the time to reply
 

Fabia17

Torque Junkie
Points
322
Location
Lincoln UK
Car
Fabia Monte Carlo
Hi there.
Firstly, no. This unit was taken from a CLK320 and all the piping/plumbing has been fabricated to suit.

Secondly, the inlet manifold is technically an original. It was take from an older M50 Engine. For those who don’t know, this is a common alteration to the M52.

Finally, when I measured the pulley and spoke to the gent who retuned the car’s ECU, I measured the supercharger pulley at 2.3x smaller (55mm) than the crankshaft pulley (127mm). My tuner told me that this was a decent size difference.

Thanks for taking the time to reply
Hi, I have been taking a look around, and not able to find any details of a clk320 which had the "Kompressor". I see your inlet manifold upgrade, it looks good, but to help further we need to establish the charger number or the doner engine code. This should provide the information needed to establish you have the right size unit. You see "C230"s (not 320s) had Kompressor 's but they also had two engine sizes, a 1.8 and a 2.3l. I hope this will help a little more, because if by accident you have been supplied the smaller compressor this would account for your problem immediately, because as you open the throttle the compressor will not have enough volume to feed the demands of the engine. You need the compressor from the 2.3 - 2.5 litre engines. Regards Kev
 

Fabia17

Torque Junkie
Points
322
Location
Lincoln UK
Car
Fabia Monte Carlo
Hi, I have been taking a look around, and not able to find any details of a clk320 which had the "Kompressor". I see your inlet manifold upgrade, it looks good, but to help further we need to establish the charger number or the doner engine code. This should provide the information needed to establish you have the right size unit. You see "C230"s (not 320s) had Kompressor 's but they also had two engine sizes, a 1.8 and a 2.3l. I hope this will help a little more, because if by accident you have been supplied the smaller compressor this would account for your problem immediately, because as you open the throttle the compressor will not have enough volume to feed the demands of the engine. You need the compressor from the 2.3 - 2.5 litre engines. Regards Kev
I know, this is probably going back to the beginning of your project and seems a pain, but we are working blind, so hope you don't take it personally. To help in any real way, we need information, sorry. Going back to basics and rechecking everything in sequence is the best way forward.
 

Fabia17

Torque Junkie
Points
322
Location
Lincoln UK
Car
Fabia Monte Carlo
I did manage to blag this image if it helps you at all, you may be able to say if it's this one or not? Nope I can't upload it, sorry...
 

Racer75

Tuner
Points
107
Location
Scotland, Glasgow
Car
BMW 323i (e36)
Hi Kev. You are totally right, it was actually from an SLK230 ‘98 ( I just checked back on my ebay purchases).
Originally I thought this was an Eaton M45, but I believe it is actually an M62. Eaton report these are good in applications of engines 3.5L or bigger.

Hopefully this provides you with enough info. Cheers.
 

Fabia17

Torque Junkie
Points
322
Location
Lincoln UK
Car
Fabia Monte Carlo
Hi Kev. You are totally right, it was actually from an SLK230 ‘98 ( I just checked back on my ebay purchases).
Originally I thought this was an Eaton M45, but I believe it is actually an M62. Eaton report these are good in applications of engines 3.5L or bigger.

Hopefully this provides you with enough info. Cheers.
Hi, OK so we need to establish the pulley diameters, now there is no point in measuring across the pulley face, because the belt does not run on the shoulders. So you'll need to to put a vernier gauge across the lands of the pulley, make sure you don't get the blades in the valley's. We need thecrank and compressor drive pulley sizes, and we'll check the ratio. You need a minimum of 2.5 :1, because the chargers volume per revolution is 1.016 liters per revolution, so at 2.5:1 it'll be pumping 2.5 litres per revolution. Which should be about right. So let me know when you are positive it's an M62 and you have the pulley measurements. Then we'll move forwards again. Did you use any of the old inlet, or did it arrive bare? Did you check the rotors for damage etc. Some of the roots type compressors have Teflon seals to help maintain the positive pressure, but I'll try and find out if this model does, the little one off the 1.2 toyota corolla does, and if the rotors are or the seals are damaged they won't hold boost at high rpm. So this too is a consideration. Also was the oil changed? Its not seizing or belt slipping at high tourqe? Just my thought process.....
 

Fabia17

Torque Junkie
Points
322
Location
Lincoln UK
Car
Fabia Monte Carlo
Just taking a look around and the M series compressors do not have rotor seals, so that's a relief in the sense of one less thing to worry about. I'm assuming the thing is quiet, like no rattling, or no oil leaking from seals? If there is any, stop now and rebuild the charger, else you may irreparably damage the rotors or rotor pack bearing, which are not technically replaceable. If it has done anywhere near 50,000 miles then you need to change the oil, without further ado. You can obtain a seal and bearing kit from www.superchargerrebuild.uk
They have all the gear, and if you can't do the job they will do it for you. However, as with all things supercharger, it's not cheap. And you'll need access to a Hydraulic press for the bearings and seals. Oh, they do pulleys too....
 

Racer75

Tuner
Points
107
Location
Scotland, Glasgow
Car
BMW 323i (e36)
Just off the phone with the company who supplied me with my unit, who are small parts company just up the road from me. Confusingly, they claimed that the charger was from a '98 SLK 230, but when they checked their records, It appears to have come from an early 2000's SLK230. This would make the SC an M45, not an M62. Which is a bit annoying, but maybe I should have double checked before starting.

Reading the Eaton website, they claim that the unit is suitable for 3.0L engines and it flows .45CI (or .750ml) of air. I am unable to check the shoulders of the pulleys as I don't have the necessary tech, but outside diameters are certainly at a 2.3:1, which I know doesn't mean much. Push comes to shove, I could hunt around for an M62 unit and fit that instead. I am sure, however, from the information I have found online regarding BOVs and BPVs, is that a BOV only setup (such as mine) is detrimental to the performance of the engine. I will be changing the valve later for a BPV and will see if that makes any difference.

Thanks for the help on this one, I really mean it. It's so helpful for me to engage in discussions with people who know more about these sorts of things than I do. That's how you learn after all! As I said in a previous post, this particular car had been sat up for a couple of years and was a perfect candidate for a major project that I would never have had the skills to carry out a few years ago.

Thanks again to everyone who has taken the time to view my tread and to those who have left comments/advice. As always, it is so much appreciated.

Cheers :)
 

Fabia17

Torque Junkie
Points
322
Location
Lincoln UK
Car
Fabia Monte Carlo
Before you disappear, I just did a quick calculation based on the M42 @ 737cc per revolution. You would need to spin this at 3400 rpm just to make the equivalent current engine displacement. So if you are relining at say 6000 rpm the charger will be spinning upto close on 19000 rpm, it will disintegrate, especially when you need a bit more than engine displacement to allow for losses.... Sell that on, you shouldn't have too much trouble, and get an M62. Sorry its been a hassle, but at least we got to the bottom. My door is always open if you want to churn ideas. Regards Kev. PS. Buy a set of digital vernier calipers. Invaluable. From Amazon... 20 quid is enough....
 

Racer75

Tuner
Points
107
Location
Scotland, Glasgow
Car
BMW 323i (e36)
Thanks again Kev, will certainly take what you have said onboard.

in the meantime, as I don’t track the car and it’s rarely ever at >5000rpm on the street, would you consider it to be dangerous in its current state? It’s been fine over the last couple of months and M62 chargers are getting harder to come by.
 

Fabia17

Torque Junkie
Points
322
Location
Lincoln UK
Car
Fabia Monte Carlo
Thanks again Kev, will certainly take what you have said onboard.

in the meantime, as I don’t track the car and it’s rarely ever at >5000rpm on the street, would you consider it to be dangerous in its current state? It’s been fine over the last couple of months and M62 chargers are getting harder to come by.
I really would not like to say without doing the proper maths. I can't judge, I have not seen or been a part of the build. I would say keep the rpm away from the top end until you are 100% sure of what it's doing. If you follow the page link I posted, and you find your numbers which shouldn't be too hard, you can follow the maths through and you will get an accurate picture of pulley speeds and power losses. On the Eaton site, in the archives I noted they used the M42 on the 2.3l engine, although this is a four cylinder and you are on six pots so although the total size is similar, the demand characteristics will be very different. If you want help with the maths, if you find all the number required, I'll crunch them for you. But you'll need to read the page, list which numbers are required,then we can see whats going on. You will notice they talk about motorcycles, but the maths is the same so don't be put off. But you'll need those verniers to get the pulley diameters accurately for a start....
 

Fabia17

Torque Junkie
Points
322
Location
Lincoln UK
Car
Fabia Monte Carlo
I used to have an amazing book years ago all about the dark art of supercharging, but alas its gone, however there is a great looking book on Amazon called Supercharged by guy called Corky Bell, its not cheap but would be of great benefit to you. About £35
 

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