GBaggott
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| posted on 8/4/10 at 09:21 PM |
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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]
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flak monkey
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| posted on 9/4/10 at 06:53 AM |
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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. 
Sera
http://www.motosera.com
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Ivan
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| posted on 9/4/10 at 08:10 AM |
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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]
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flak monkey
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| posted on 9/4/10 at 08:52 AM |
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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
Sera
http://www.motosera.com
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MikeRJ
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| posted on 9/4/10 at 10:22 AM |
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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.
Pressure drop across a fixed restriction (such as your intercooler) will be proportional to the square of the flow, so dont discount this!
A pressure gauge before and after the intercooler would let you know if this is a problem.
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boggle
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| posted on 9/4/10 at 11:15 AM |
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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....
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
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flak monkey
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| posted on 9/4/10 at 11:31 AM |
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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.
Sera
http://www.motosera.com
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MikeRJ
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| posted on 9/4/10 at 12:02 PM |
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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.
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Ivan
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| posted on 9/4/10 at 12:12 PM |
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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]
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Ivan
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| posted on 9/4/10 at 12:23 PM |
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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]
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Ivan
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| posted on 9/4/10 at 02:23 PM |
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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.
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boggle
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| posted on 9/4/10 at 02:36 PM |
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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.
also depends on the the boost controll system...i have found with ebc's they can sometimes cause fluctuations as the solonoids cant keep up....
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
|
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atspeed racing
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| posted on 9/4/10 at 02:41 PM |
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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]
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flak monkey
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| posted on 9/4/10 at 05:54 PM |
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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!
Sera
http://www.motosera.com
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MikeRJ
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| posted on 9/4/10 at 06:24 PM |
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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!).
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flak monkey
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| posted on 9/4/10 at 06:51 PM |
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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?
Sera
http://www.motosera.com
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sebastiaan
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| posted on 10/4/10 at 12:41 PM |
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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?
That is correct. Locking the pulley should not be that hard to do and should solve the problem. Make sure you check the belt tension regularly though!
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dlatch
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| posted on 10/4/10 at 03:52 PM |
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manual tensioner should be fine yo uwill know when to adjust it too everytime you start losing boost
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