29 replies to this topic

[1cobrav8]

Guys how many of you have got Dyno plots or data traces of your boost pressure on WOT? After running my setup again yesterday I'm keen to understand why the boost pressure just flat lines after about 5k. All previous supercharger projects I've worked on before have a boost curve that follows revs all the way to the limiter. Just keen to know if this is something to do with my car alone or all of ours? Any help/advice wouldn't be appreciated. FYI I'm on a harrop with. 70mm pulley and I'm seeing about 1.1 bar max boost pressure.

[fezzasus]

That'll be the restricive manifold

[1cobrav8]

That'll be the restricive manifold

I don't think it can be as my m62 did exactly the same. But at a much lower boost pressure.

[fezzasus]

That'll be the restricive manifold

I don't think it can be as my m62 did exactly the same. But at a much lower boost pressure.

Surely that's the argument for a restrictive manifold. M62, lower boost (lower rotor sealing too) means pressures become balanced at a much lower point than with a tvs.

Edited by fezzasus, 10 July 2016 - 08:24 AM.

[siztenboots]

do you have verniers on the intake cam , to adjust that for more overlap?

[1cobrav8]

It's just such a wide rpm band to maintain boost pressure 5k-7.5k! The charger speed increases dramatically between the two points but yet no additional boost. Odd.

[Exmantaa]

Remember it's a fixed displacement charger you have there, so the flat boost line is pretty normal on our SC conversions

If you boost rises sharper at the top end, then the head/cams/exhaust beging to cause you powerloss.

ps; boost is a measurement of restriction...

 

ps2; your 1.15bar max boost is very very good for the pulley size and powerlevel!!

[Exmantaa]

This is a log of my 2.0 Harrop engine on the dyno with a 80mm pulley, stage 2 cams and 2,5" exhaust.

Same flat pressure curve but a bit higher than yours (MAP/boost pressure 227KPa=1.27bar) due the smaller displacement, cams and exhaust:

Edited by Exmantaa, 10 July 2016 - 11:58 AM.

[FLD]

It would be interesting to see boost measured before and after the laminova.

[1cobrav8]

im presuming that the bypass valve is what's causing the pressure to stablise. I may have a play around with it when I'm next on the Dyno

[Bargi]

Didn't think the bypass worked that way for these setups. It's more just to kick in for crusing and startup. Didn't think it was like a turbo where it can bleed off excessive boost? I may have this all wrong though. I'm sure Exmantaa will explain Sent from my cuntyfuckbollock phone by Twatatalk

[Exmantaa]

im presuming that the bypass valve is what's causing the pressure to stablise. I may have a play around with it when I'm next on the Dyno

 

No, it's a fixed displacement pump...

[1cobrav8]

im presuming that the bypass valve is what's causing the pressure to stablise. I may have a play around with it when I'm next on the Dyno

  No, it's a fixed displacement pump...

Exactly so surely the higher the revs the higher the boost? if I find the time I'm going to take the laminovas out and do a run without them. I think this will answer a lot of questions for people

[909]

The bypass valve should stay open at idle and low throttle application and stay closed under full throttle.

 

I have checked this action in the past, using a cheap security mini video camera, aimed at the bypass valve actuator.  You will need lighting in the engine bay as well.

 

The efficiency of an Eaton type blower will also fall off as it reaches its designed upper rev limits.  They will not keep pumping air, at the same rate relative to rpm, above their design limits.  

Edited by 909, 10 July 2016 - 07:59 PM.

[Exmantaa]

 

 

im presuming that the bypass valve is what's causing the pressure to stablise. I may have a play around with it when I'm next on the Dyno

  No, it's a fixed displacement pump...

Exactly so surely the higher the revs the higher the boost? if I find the time I'm going to take the laminovas out and do a run without them. I think this will answer a lot of questions for people

 

 

No.

 

The SC displacement is fixed to the crankshaf, so for simplicity; let's say for every crank revolution the SC makes 2 revolutions. (determined by pulley size)

In your engine that's 1.2litre engine displacement  while the Harrop crams 2 x 1.32litre inside. That means the pressure in the manifold is raised by a factor 2.2. Whatever the rpm is...

The real boostpressure is a lot more complex with sc leak paths and thermal efficiency etc., but you get the point.

 

But doing a run without the laminova's will be an interesting test. Or fit a pressure gauge before the laminova's to see the pressure loss they create.  

Edited by Exmantaa, 10 July 2016 - 08:06 PM.

[909]

Belt slip at higher rpm's is also a point to consider.  It is quite suprising how tight a multi rib belt has to be to prevent slip on the supercharger pulley, especially on a smaller supercharger pulley.

 

I chased a low boost problem for quite some time, not on a VX220, before somebody else suggested checking belt slip.

 

Checking this on a dyno, using an optical rpm meter, could perhaps be possible.

[1cobrav8]

 

 

im presuming that the bypass valve is what's causing the pressure to stablise. I may have a play around with it when I'm next on the Dyno

  No, it's a fixed displacement pump...

Exactly so surely the higher the revs the higher the boost? if I find the time I'm going to take the laminovas out and do a run without them. I think this will answer a lot of questions for people  

  No.   The SC displacement is fixed to the crankshaf, so for simplicity; let's say for every crank revolution the SC makes 2 revolutions. (determined by pulley size) In your engine that's 1.2litre engine displacement  while the Harrop crams 2 x 1.32litre inside. That means the pressure in the manifold is raised by a factor 2.2. Whatever the rpm is... The real boostpressure is a lot more complex with sc leak paths and thermal efficiency etc., but you get the point.   But doing a run without the laminova's will be an interesting test. Or fit a pressure gauge before the laminova's to see the pressure loss they create.  

Just ordered a fitting to go in my ZZP sandwhich plate pre laminovas, so when it's next on the Dyno I'll measure the pressure drop to give us a better idea what's going on

Edited by 1cobrav8, 10 July 2016 - 09:03 PM.

[1cobrav8]

Belt slip at higher rpm's is also a point to consider.  It is quite suprising how tight a multi rib belt has to be to prevent slip on the supercharger pulley, especially on a smaller supercharger pulley.   I chased a low boost problem for quite some time, not on a VX220, before somebody else suggested checking belt slip.   Checking this on a dyno, using an optical rpm meter, could perhaps be possible.

Just ordered my 6pk belt as was still only on my 5pk when I Dyno tested

[CHILL Gone DUTCH]

I think you get less slip on a 5 Pk than a 6 pk Because it's spring tension the 5 pk has more pressure on the pulleys than a 6 pk because the 6 pk puts the same pressure over a wider surface

Edited by CHILL Gone DUTCH, 10 July 2016 - 09:09 PM.

[chris_uk]

if the size of the belt is the same, then then pressure applied would be the same wouldn't it? 

 

the 6pk belt would offer more surface area to grip to.