Idler stiffening plate 1
Nearly finished 2
Tensioner is the stock item so it could be that allowing the belt to slip I guess.
I have around half the boost I was originally planning for, around 6.5 psi but it seems to drop off after 5200rpm for some reason.
I dont think the belt can be slipping with the amount of wrap it has on the pulley.
Could it just be the supercharger isnt able to keep the boost up at the higher rpm levels with the current boost level?
I intend to change the pulley after stoneleigh anyway so I guess that will tell me whats happening for definate...
Cheers,
David
is the tensioner up to the job ?
lets see a pic of the pulley and belt
quote:
Originally posted by flak monkey
Could it just be the supercharger isnt able to keep the boost up at the higher rpm levels with the current boost level?
I intend to change the pulley after stoneleigh anyway so I guess that will tell me whats happening for definate...
Piccies:
Idler stiffening plate 1
Nearly finished 2
Tensioner is the stock item so it could be that allowing the belt to slip I guess.
^^^ intyeresting - grooved belt instead of toothed - I would have expected the latter - so yes, belt slippage is a possibility.
not sure at this mo' how you can verify that.
what sort of overlap do you have on the crank pulley?
if I were doing it, and don't takt it as gospel, #i would use toothed belt to crank/'charger and another belt for the other gubbins.
look at the overlap on crank/'charger pulley here.
[Edited on 8/4/10 by 02GF74]
i'm going with belt slipping as well, are you using a fan belt ?
quote:
Originally posted by 02GF74
dunno but you are assuming the boost is linear all across the rpm range - do you have a spec for the 'charger?
also from what engine capacity is the charger and what was the boost it provided? how is your engine different?
are you restricintg air flow via air filter or other gubbins in the inlet path?
do you trust your boostometer?
Toothed belts are very rare on supercharger installs other than monster V8 ones.
The rotrex std drive is poly vee belt. Gates recommend max of about 8bhp per rib, and I have a 6 rib belt fitted so with the proper tension it should
be able to transfer loads more power than I need. The supercharger should be pulling around 10-15bhp under full load at the moment.
A lot of the BMW custom installs running around 8psi are only using a 5 rib belt and standard tensioners too....
just don't brake it before sunday........
quote:
Originally posted by flak monkey
Toothed belts are very rare on supercharger installs other than monster V8 ones.
looks like it could slip on the crank pulley to me......
Heres the datalog and msq from tonights run for those conversant with megasquirt. The drop of is at 1330secs into the log
http://gtslocost.locostsites.co.uk/tune.msq
http://gtslocost.locostsites.co.uk/30.msl
It could be slipping on the crank pulley I guess theres more wrap than there looks in the previous pic. theres another idler in there:
Idlers
Not sure what I could do to help that to be honest.
Multi V ribbed pulleys as you say should be fine. But to check just get a little bit of tipex and mark the pulley and the belt. Rev the engine and see
what happens (ie if it moves you know there's a problem, simples 
).
A centrifugal blower should make oodles of boost at high RPM not drop off. Something's going on. Have you got a BOV set up? That might be
misbehaving and giving you boost loss?
you would be able to see signs of belt slip as you will get lots of black dusty rubbe residue around the pulleys. I dont think it will be belt slip
if you cant hear it or see it.
As said a lot of the smaller suer charger say not to use toothed belts as they have no give and can shatter the gears inside.
What guidance do rotrex give about pulley size? is it not just the pulley being too small?
One other thing to check is that you recirc valve/dump isnt bleeding boost off
* Is the pressure sensor working/designed for this kind of pressure ?
* Perhaps you can test the slipping belt at high rpm when looking at the DC ripple or AC frequency of your alternator and try to see (with oscillator)
it doesn't rise above 5000 rpm. (hope you understand what I'm trying to say) 
I do have a spring tuning kit for the BOV, the one fitted at the moment should be good for 1 bar of boost, but I can fit the next spring up and see if
that helps things.
I guessed the pulley size and started on the conservative side. I didnt think that it should drop off though, surely it should just keep increasing
boost right up to the limiter.
I'll mark the pulley and belt and see if I have any slip, dont suppose it matters which pulley I mark.
I dont think I would be able to hear it slip at such high revs anyway, theres too much noise from everything else.
Why don`t you put a trigger wheel on the charger, mount a crank sensor and connect to the dash? That way you can monitor the speed. other possibility
is a restriction before or after the charger.
Darren
looking at the last phot; i'd estimate you have belt wrapped round half of crank pulley - comapre that to about 3/4 in the photo I posted, may or
may not bne significant.
dare you run the engine with the pipe between charger and cooler removed just to see any effect?
see what other peeps say to that idea or it could be an expensive mistake.
quote:
Originally posted by flak monkey
I'll mark the pulley and belt and see if I have any slip, dont suppose it matters which pulley I mark.
if it was belt slip i would of thought you would see a boost rise and drop under load...on a turbo car i would say it was a wastegate issue, premature
opening or wastegate creep, but im not clued up on the supercharger boost controll....
try removing the bov and going out again....
I think your barking up the wrong tree with belt slip as you would spot signs.
I've had a strange problem before on my turbo Fury where by if I accelerated hard, it held boost perfectly but if I built boost slowly through
more gentle revving, I could almost induce the dump valve to open a little and bleed boost.
My bet is dump valve
pulley is wrong. at higher rpm the engine is pulling more cfm than the charger can make with the current pulley.
Ok, thanks, not really narrowed it down but never mind. Will just eliminate one thing at a time. I will change the spring in the BOV tomorrow and see
if that helps hold the boost in. If not I will be changing the pulley in a month so will see what effect that has.
Will be interesting to see if it will still cruise off boost if I increase the boost and spring pressure in the BOV as it only just cruises off boost
at 70mph now.
Cheers,
David
quote:
Originally posted by ashg
pulley is wrong. at higher rpm the engine is pulling more cfm than the charger can make with the current pulley.
Surge? Impeller isn't big enough.
I know you said the map is big enough but depends on pulley ratios.
[Edited on 8/4/10 by GBaggott]
This is the map for the charger
Should support around 400bhp with ease.
The pulley ratio at the moment gives me an impeller speed of 80,000rpm, so yes it looks like as the kg/s rise with engine RPM then boost could drop
off. For 350bhp I should be looking at a flow of around 0.3kg/s which actually puts me almost bang on that map for 6psi of boost.
I will be trying a smaller pulley soon, so I guess time will tell.
What revs is the 80 000 rpm achieved at?
Just wandering where you are on the curve for various engine revs.
[Edited on 9/4/10 by Ivan]
Pulley is sized to give 80,000rpm impeller speed at 6800rpm.
95mm SC pulley, 118mm crank pulley if you want to do the calcs
I am getting 6.5psi at 5300rpm then it starts to drop off.
David
quote:
Originally posted by flak monkey
Other than that theres no restrictions other than the intercooler etc which will give a slight pressure drop across the rev range rather than causing it to drop off.
surely your peak power wont be far from that....on a turbocharged car boost climbs, peaks and then drops as the car goes through its peak output....
Hmm thats interesing. I am in the process of speaking to rotrex uk to see if they have any suggestions. Their initial reaction was indeed belt
slip.
As the crank RPM increases, the impeller speed continues to increase too so boost should still continue to rise, at least thats my understanding
anyway.
quote:
Originally posted by boggle
surely your peak power wont be far from that....on a turbocharged car boost climbs, peaks and then drops as the car goes through its peak output....
Looking at the chart you need at least 86000 rpm on the compressor to achieve a PR of 2 @ .3 kg/s and that will keep you on the right side of the
surge line at low speeds.
In fact to allow for temperature and other losses I think 90000 rpm would not be unreasonable.
It will also mean that you stay on the chart as low as 3800 engine rpm rather than falling off it at 4300 at present - also help keep you away from
the surge line and in more efficient territory.
But hey - I'm no expert - just applying a bit of logic rightly or wrongly.
[Edited on 9/4/10 by Ivan]
Meant to say I would bet that it's not really belt slip, just wrong pulley size - however if it is, all you need is a Turbo to solve any belt
slip issues
Of course a smaller compressor pulley will exacerbate belt slip issues but bigger crank pulley might help.
[Edited on 9/4/10 by Ivan]
Have just checked Corky Bell - on p 29 he talks about selecting a compressor and using those guidelines and the curves provided by you, you are
risking surge at any boost ratio above about 1.8.
Maybe that doesn't apply to superchargers but I think it will as in this case the compressor is a turbo compressor - maybe worth discussing with
the agents.
quote:
Originally posted by MikeRJ
quote:
Originally posted by boggle
surely your peak power wont be far from that....on a turbocharged car boost climbs, peaks and then drops as the car goes through its peak output....
That really depends on many variables, the (standard) turbo in my car holds 1 bar all the way to the red line. Very often a turbo in a production car will be a little undersized to reduce lag issues, which limits the amount of boost it can provide at higher RPM, and/or the boost control system will deliberately roll off boost at higher RPM to reduce thermal stress on the engine.
are there any noticeable changes in the map (ecu) @ the rpm the boost drops off?
what camshafts are you using?
compression ratio?
how much is the psi drop? are you monitoring air temp?
- colin.
[Edited on 9/4/10 by atspeed racing]
Think I have found the problem, just got back from a long run, everything really hot. When you blip the throttle the belt whips and goes slack around
the supercharger idlers and main pulley. So looks like I will be making a new tensioner system
As for CR its running 10:1, cams are standard which are very low overlap anyway. Air temps are consistent at around 30deg when moving, and around
45deg in traffic so the intercooler does its job
I changed the spring in the BOV before noticing the whip and it made no difference, unsuprisingly!
I guess the crank pulley turns clockwise as you look at it from the belt side? That would mean the automatic tensioner is on the "tension" side of the belt, rather than the return side where tensioners are usually placed (not that you have much room between the Rotrex and the crank pulley!).
Yes, the pulley turns clockwise looking from the front of the engine (conventional).
You can see the tensioner move when you rev the engine - its in a stock location for the duratec and is just a spring loaded one.
I'll look into designing and making a manual tensioner that can be locked solid if thats going to solve the problem. I would then assume that it
wouldnt matter whether the tensioner is on the tension side or not?
quote:
Originally posted by flak monkey
I'll look into designing and making a manual tensioner that can be locked solid if thats going to solve the problem. I would then assume that it wouldnt matter whether the tensioner is on the tension side or not?
manual tensioner should be fine yo uwill know when to adjust it too everytime you start losing boost