flak monkey
|
| posted on 8/4/10 at 06:16 PM |
|
|
Boost dropping off
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
Sera
http://www.motosera.com
|
|
|
|
|
graememk
|
| posted on 8/4/10 at 06:20 PM |
|
|
is the tensioner up to the job ?
lets see a pic of the pulley and belt
|
|
|
02GF74
|
| posted on 8/4/10 at 06:25 PM |
|
|
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...
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?
|
|
|
flak monkey
|
| posted on 8/4/10 at 06:25 PM |
|
|
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.
Sera
http://www.motosera.com
|
|
|
02GF74
|
| posted on 8/4/10 at 06:27 PM |
|
|
^^^ 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]
|
|
|
graememk
|
| posted on 8/4/10 at 06:29 PM |
|
|
i'm going with belt slipping as well, are you using a fan belt ?
|
|
|
flak monkey
|
| posted on 8/4/10 at 06:29 PM |
|
|
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?
Charger is a Rotrex C30-94 and is capable of producing loads more boost than I really need. I do have a map for the supercharger and yes its
capable.
Boost is logged via the MAP sensor in megasquirt so yes I trust it.
There's a filter fitted on the intake of the superchager. 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.
Sera
http://www.motosera.com
|
|
|
flak monkey
|
| posted on 8/4/10 at 06:33 PM |
|
|
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....
Sera
http://www.motosera.com
|
|
|
deanwelch
|
| posted on 8/4/10 at 06:33 PM |
|
|
just don't brake it before sunday........
|
|
|
02GF74
|
| posted on 8/4/10 at 06:38 PM |
|
|
quote:
Originally posted by flak monkey
Toothed belts are very rare on supercharger installs other than monster V8 ones.
yep - that's what spring to my mind but so you can see you are more knowledgeable in this field than me.
what is belt overlap on the crank? VVVVV see below.
can you put dots on the crank/belt and run a timing light to see if there is any relative movement? no idea if that will work....
[Edited on 8/4/10 by 02GF74]
|
|
|
graememk
|
| posted on 8/4/10 at 06:39 PM |
|
|
looks like it could slip on the crank pulley to me......
|
|
|
flak monkey
|
| posted on 8/4/10 at 06:43 PM |
|
|
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
Sera
http://www.motosera.com
|
|
|
flak monkey
|
| posted on 8/4/10 at 06:48 PM |
|
|
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.
Sera
http://www.motosera.com
|
|
|
BenB
|
| posted on 8/4/10 at 06:51 PM |
|
|
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?
|
|
|
Antnicuk
|
| posted on 8/4/10 at 06:52 PM |
|
|
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
600 BHP per ton, Stylus Brought back from the dead! Turbo Rotary Powered!
|
|
|
Breaker
|
| posted on 8/4/10 at 06:54 PM |
|
|
* 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) 
|
|
|
flak monkey
|
| posted on 8/4/10 at 06:56 PM |
|
|
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.
Sera
http://www.motosera.com
|
|
|
turbodisplay
|
| posted on 8/4/10 at 06:58 PM |
|
|
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
|
NOTE:This user is registered as a LocostBuilders trader and may offer commercial services to other users
|
02GF74
|
| posted on 8/4/10 at 07:03 PM |
|
|
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.
|
|
|
sebastiaan
|
| posted on 8/4/10 at 07:34 PM |
|
|
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.
That'll only work if the belt length is 1, 2, 3, n times as long as the pulley diameterxPi, which I strongly doubt it will be.
Check the dumpvalve first, this might very well be bleeding boost. You could try fitting some packing tape over the holes and look for it coming off
at high RPM/boost.
|
|
|
boggle
|
| posted on 8/4/10 at 07:44 PM |
|
|
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....
just because you are a character, doesnt mean you have character....
for all your bespoke parts, ali welding, waterjet, laser, folding, turning, milling, composite work, spraying, anodising and cad drawing....
u2u me for details
|
PLEASE NOTE: This user is a trader who has not signed up for the LocostBuilders registration scheme. If this post is advertising a commercial product or service, please report it by clicking here.
|
carpmart
|
| posted on 8/4/10 at 08:16 PM |
|
|
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
You only live once - make the most of it!
Radical Clubsport, Kwaker motor
'94 MX5 MK1, 1.8
F10 M5 - 600bhp Daily Hack
Range Rover Sport - Wife's Car
Mercedes A class - Son's Car
|
|
|
ashg
|
| posted on 8/4/10 at 08:16 PM |
|
|
pulley is wrong. at higher rpm the engine is pulling more cfm than the charger can make with the current pulley.
Anything With Tits or Wheels Will cost you MONEY!!
Haynes Roadster (Finished)
Exocet (Finished & Sold)
New Project (Started)
|
|
|
flak monkey
|
| posted on 8/4/10 at 08:50 PM |
|
|
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
Sera
http://www.motosera.com
|
|
|
skinned knuckles
|
| posted on 8/4/10 at 09:05 PM |
|
|
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.
+1
A man isn't complete until he's married, then he's finished
|
|
|
