After checking THIS TOPIC, I was wondering what influence a VICS manifold and a bigger TB (from 55mm to 58mm) would have on JRSC with IC... Any clues?
Venom
I asked similar on M Net regarding the entire 99 head.
They came to the conclusion that the the JRSC basically forces a set amount of air in.
With that set amount of air you can only mix a set amount of fuel...
= power output.
They reckoned that the flow benifits of a head etc in an NA are GREATER than in SC.
Not saying the benefits aren't there but not as much as you think...
Consequently I sold the head to someone with a Turbo.
This is demonstrated by Dynos of MK1 and MK2 SC'd cars they both tend to make very similar figures despite the MK2's starting with a power advantage.
They came to the conclusion that the the JRSC basically forces a set amount of air in.
With that set amount of air you can only mix a set amount of fuel...
= power output.
They reckoned that the flow benifits of a head etc in an NA are GREATER than in SC.
Not saying the benefits aren't there but not as much as you think...
Consequently I sold the head to someone with a Turbo.
This is demonstrated by Dynos of MK1 and MK2 SC'd cars they both tend to make very similar figures despite the MK2's starting with a power advantage.
Actual boost is lowered, but the SAME amount of air is forced in... power stays similar.
The problem is I know experienced people on both sides of this with different cars.
BUT I couldn't find any dyno evidence to support it in a JRSC application on an MX5 and I looked hard as I wanted to use the head I'd bought.
Be happy to be shown otherwise.
The problem is I know experienced people on both sides of this with different cars.
BUT I couldn't find any dyno evidence to support it in a JRSC application on an MX5 and I looked hard as I wanted to use the head I'd bought.
Be happy to be shown otherwise.
Well from my research for approx 10bhp.... it isn't worth it.... which is why I didn't fit it.
I think its the usual - you only get a gain if you 'uncork the blockage' the blockage for a JRSC isn't the head.
It may have more effect on am MP62 at high levels but again I couldn't find any evidence.
I'll watch Matts progress with interest but its not really relevent to a JRSC.
I think its the usual - you only get a gain if you 'uncork the blockage' the blockage for a JRSC isn't the head.
It may have more effect on am MP62 at high levels but again I couldn't find any evidence.
I'll watch Matts progress with interest but its not really relevent to a JRSC.
Makes sense to me. The blower (being a positive displacement type) forces a fixed amount of air through the engine. Any restrictions in the head or exhaust will cause backpressure - the blower will still shove the air through but it'll have to be at a higher pressure to force its way through. Reducing the restriction provides a double dividend: the blower no longer has to labour against such high backpressure so the power needed to drive it reduces and also the intake temperature will be reduced by the pressure drop, so it's possible to run more aggressive ignition timing.
Yep but the reduction is usually in the order of 1psi...
hence not much benefit.
(at JRSC levels)
hence not much benefit.
(at JRSC levels)
Sure, you can find gains from reducing restrictions before the blower too.
When BRP redesigned the intake section of their MP62 kit, adding a big (Mustang?) throttle body and a smoothly profiled throttle-to-blower transition piece (instead of the original simple plate with a circular hole), they gained around 10 hp, IIRC.
Whether the stock throttle is a significant restriction in a JRSC system, I kinda doubt, but I don't know if anyone's tried changing it.
When BRP redesigned the intake section of their MP62 kit, adding a big (Mustang?) throttle body and a smoothly profiled throttle-to-blower transition piece (instead of the original simple plate with a circular hole), they gained around 10 hp, IIRC.
Whether the stock throttle is a significant restriction in a JRSC system, I kinda doubt, but I don't know if anyone's tried changing it.
I think somebody did try a big(ger) throttle body from BRP on the JR blower, but I'm not sure if it was hotside or coldside.
IIRC, there was a benefit, but not as significant a one as seen with the MP62s. Nevertheless, "conventional wisdom" suggests that the PD blowers benefit more from "de-restriction" pre-charger than post (although obviously do benefit from both).
Might be worth dropping SOT a mail, and see if James remembers the setup that I'm talking about - I may, of course, have conjured it from my fevered imagination!
Chris
IIRC, there was a benefit, but not as significant a one as seen with the MP62s. Nevertheless, "conventional wisdom" suggests that the PD blowers benefit more from "de-restriction" pre-charger than post (although obviously do benefit from both).
Might be worth dropping SOT a mail, and see if James remembers the setup that I'm talking about - I may, of course, have conjured it from my fevered imagination!
Chris
True the MP62 benefited...
They don't like sucking...
Probably as much benefit sorting the inlet tract (pre blower) or finding a bigger TB than boring the old one.
Again though on a dyno day there was Linked cars (no afm etc) and they only made 10bhp more than mine.
I played with loads of stuff and hardly anything made an appreciable difference.
Best value was DIY Water Inj used on hot days.
They don't like sucking...
Probably as much benefit sorting the inlet tract (pre blower) or finding a bigger TB than boring the old one.
Again though on a dyno day there was Linked cars (no afm etc) and they only made 10bhp more than mine.
I played with loads of stuff and hardly anything made an appreciable difference.
Best value was DIY Water Inj used on hot days.
Interesting thread, how did i miss it??
![Image]()
I just jump in and make meself at home
![Image]()
Seriously though i think one thing that not really bin mentioned and is mega important is Volumetric Efficiency (Ve) of the SC.
Yes the MP62 does move 62 cubic inch of air each revolution, but only when Ve is at 100%.
Any restrictions to the inlet will reduce Ve.
Likewise the more boost you make the more resistance the SC is working against so the less Ve.
Take a look at this roots efficiency map:
![Image]()
The column up the left is the pressure ratio, which is the ratio of the air pressure pre and after blower.
No boost is 1.0 as intake pressure equals outlet pressure.
The bottom row is blower speed, basically the smaller the blower the more you spin it for the same boost level.
So a M45 would be more over to the left than say a MP62.
As you can see the higher the boost levels the less efficient the SC gets, this makes sense as your blowing into more resistance and fighting against heat and mechanical losses.
Now you you reduce you boost pressures but still keep your blower speed your SC will be working a lot more efficiently.
As the lower air pressure also means everything is cooler it also helps your engine a lot better as well.
Now for most of us MP62 powered mere mortals, we are not really spinning our SC's to within a inch of their lifes, so the gains to be made by reducing our intake restrictions to the point of dropping say 2 psi will not be much.
But the higher the boost levels the more gains we see.
What that means in real world power i don't know, but i'd hazard a guess that if you were at 15psi and you improved your intake flow enough to drop 3 psi, i'd bet you'd see 10 - 20bhp.
On a M45 you have the problem that your not really moving enough air to the get to the higher boost levels, but again i'd say a 2-3 psi drop due to a better flowing intake would have noticable results.
All guess work really i'll be the first to admit, but if you've taken it as far as you can go like Rockdoc for example it's gotta be worth a shot
![Image]()
Cheers
Mark
I just jump in and make meself at home
Seriously though i think one thing that not really bin mentioned and is mega important is Volumetric Efficiency (Ve) of the SC.
Yes the MP62 does move 62 cubic inch of air each revolution, but only when Ve is at 100%.
Any restrictions to the inlet will reduce Ve.
Likewise the more boost you make the more resistance the SC is working against so the less Ve.
Take a look at this roots efficiency map:
The column up the left is the pressure ratio, which is the ratio of the air pressure pre and after blower.
No boost is 1.0 as intake pressure equals outlet pressure.
The bottom row is blower speed, basically the smaller the blower the more you spin it for the same boost level.
So a M45 would be more over to the left than say a MP62.
As you can see the higher the boost levels the less efficient the SC gets, this makes sense as your blowing into more resistance and fighting against heat and mechanical losses.
Now you you reduce you boost pressures but still keep your blower speed your SC will be working a lot more efficiently.
As the lower air pressure also means everything is cooler it also helps your engine a lot better as well.
Now for most of us MP62 powered mere mortals, we are not really spinning our SC's to within a inch of their lifes, so the gains to be made by reducing our intake restrictions to the point of dropping say 2 psi will not be much.
But the higher the boost levels the more gains we see.
What that means in real world power i don't know, but i'd hazard a guess that if you were at 15psi and you improved your intake flow enough to drop 3 psi, i'd bet you'd see 10 - 20bhp.
On a M45 you have the problem that your not really moving enough air to the get to the higher boost levels, but again i'd say a 2-3 psi drop due to a better flowing intake would have noticable results.
All guess work really i'll be the first to admit, but if you've taken it as far as you can go like Rockdoc for example it's gotta be worth a shot
Cheers
Mark
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