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PollyMobiles Rebuild

SuperUno

Buy & Sell Member
Not my work but makes sense... relating to our TB discussions:-

Bigger Throttle body nonsense…
I love my dyno, it’s great.
It doesn’t suffer from any placebo effects, it doesn’t read biased rubbish on the internet, it doesn’t try to sell you anything or try to convince itself that its most recent purchase was not a total waste of money and it doesn’t flatter with “suits you, Sir” lies; it just measures what is being produced and shows it, warts an’ all.
So, now that’s out of the way, let’s look a little bit at HOW engines breathe, since that’s what induction changes seemingly set out set out to improve…..
Suck, squeeze, bang, blow right? Yes of course, mostly.
However, imagine that a given engine has a cylinder capacity of say, 3000cc, so each revolution it would DISPLACE 1500cc (1.5 litres), and that it’s running at 6000 rpm; that’s 100 revs per second so 50 CYCLES per second and thus, 150 litres per second @ 100% Volumetric Efficiency (VE). Think about that, a hundred and fifty litres per SECOND.
Well, given how fast that is all happening the VE isn’t going to be anything like 100%, is it, because there’s so little time to fill and empty the cylinders, right?
All the little restrictions along the way; air filter, trunking, intake silencer, throttle body, plenum chamber, intake runners, ports in the cylinder head, past the valves (which are closed for more than half of the time) and that’s just to get TO the cylinder, after all that it’s still got to get out….
SO…. what would you realistically expect the VE to be in such circumstances? Well, if you were to put a huge vacuum cleaner sucking at an unrestricted rate of 150 l/s (saving the piston’s uppy-downy motions from doing the job) pulling air through to the cylinders you’d get, perhaps 75% of the potential unrestricted flow. In that case there’s 25% of the potential flow lost to the restrictions.
You’re never going to get ZERO restriction because there’s far too much other necessary stuff in the engine and engine bay to fit filter, trunking, manifold and ports of sufficient proportions to have zero restriction.
A modern engine is pretty good out of the box and you wouldn’t ever expect as much as a 5% improvement in flow without drastic changes, and those very same drastic changes would likely make things worse in other ways. So, best ways up you might see 78 or 79% of the potential flow.
How come then, a typical modern high-performance road car engine has a VE of as much as 120%? Yes, a 3 litre engine would breathe as much as 3600cc in two revolutions!
With its silly uppy-downy pistons, pulling air past valves that are only open for typically 36% of the time, through ports that often have rough surfaces and uneven profiles, through often convoluted trunking and in from the outside world through a filter that only has open areas of a few microns. It cannot possibly be, surely? That’s over 50% more than the possible flow when the valves are only open for 36% of the time and the piston is only on the induction stroke for half of a revolution. “Get the ducking stool ready people, something isn’t right…..”
Well it can and it does, using PRESSURE WAVES. Tuning pressure waves is what it’s all about. Camshafts, exhausts, intake systems SHOULD all work absolutely together to harness the highs and lows of the pressure waves to best effect; so effective in fact that it amounts to a very significant supercharging effect.
Flow plays a very low second fiddle to pressure waves when it comes to tuning, because the difference that a loss of wave amplitude makes is far greater than the potential flow ‘increase’ from having a larger diameter and guess what? When the diameter of a pipe increases, the amplitude of the waves within it reduce because the molecule compression occurs over a greater area (the surface area, if you will, of the pipe section), so while the static flow may be imagined to be greater, the dynamic flow is actually considerably less.
For example, just look at a GT or F3 airbox - the airbox is huge to harness the pressure waves but the inlet FLOW is through a tiny little inlet restrictor, and despite this the engines still make PLENTY of power.
A flat six engine (all sixes actually for a specific reason that we don’t need to entertain here) is particularly well suited to harnessing the pressure waves that travel back and forth into, as well as across, the manifold if allowed to. They can make a huge difference to the VE at some engine speeds. This is why the (not stupid) design engineers at Porsche have gone to such great lengths to make best use of the pressure waves by employing various flaps in the system to either block or allow passage of pressure waves within the system.
When developing their engines manufacturers will do many, many hours of simulation work. After that they will make many test pieces, probably at least twenty different head casting designs, fifty camshaft profiles, piston crown designs, valve head shapes, compression ratios, manifold designs, you name it. At each engine test, a zillion sensors and probes are mounted all over the engine measuring everything that can be measured.
DO YOU NOT THINK THAT AT SOME POINT IN ALL THAT IT WOULD HAVE BECOME APPARENT TO THEM THAT IT NEEDED A BIGGER THROTTLE BODY?
No, of course not, they’re all stupid those Germans, right?
It takes Fred in his shed with probably zero engine design expertise, to think “Gad Daim, I can fit me a bigger throddle on there an’ life will be reeeeeal gewd….”
If only things were that simple…..
In the vast majority of cases BIGGER THROTTLE INTAKES DON’T WORK so save your money.
In every single Porsche case that I have EVER had on the dyno, NO bigger intake has made an improvement, and almost ALL has made less area under the curve than stock.
When a vendor selling parts says “There’s a 25 bhp difference with this Big-Boy Carlos Fandango intake Sonny Jim” just consider whether he means UP or DOWN!!!!!!
 

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pollyp

pollyp

Club Member
Not my work but makes sense... relating to our TB discussions:-

Bigger Throttle body nonsense…
I love my dyno, it’s great.
It doesn’t suffer from any placebo effects, it doesn’t read biased rubbish on the internet, it doesn’t try to sell you anything or try to convince itself that its most recent purchase was not a total waste of money and it doesn’t flatter with “suits you, Sir” lies; it just measures what is being produced and shows it, warts an’ all.
So, now that’s out of the way, let’s look a little bit at HOW engines breathe, since that’s what induction changes seemingly set out set out to improve…..
Suck, squeeze, bang, blow right? Yes of course, mostly.
However, imagine that a given engine has a cylinder capacity of say, 3000cc, so each revolution it would DISPLACE 1500cc (1.5 litres), and that it’s running at 6000 rpm; that’s 100 revs per second so 50 CYCLES per second and thus, 150 litres per second @ 100% Volumetric Efficiency (VE). Think about that, a hundred and fifty litres per SECOND.
Well, given how fast that is all happening the VE isn’t going to be anything like 100%, is it, because there’s so little time to fill and empty the cylinders, right?
All the little restrictions along the way; air filter, trunking, intake silencer, throttle body, plenum chamber, intake runners, ports in the cylinder head, past the valves (which are closed for more than half of the time) and that’s just to get TO the cylinder, after all that it’s still got to get out….
SO…. what would you realistically expect the VE to be in such circumstances? Well, if you were to put a huge vacuum cleaner sucking at an unrestricted rate of 150 l/s (saving the piston’s uppy-downy motions from doing the job) pulling air through to the cylinders you’d get, perhaps 75% of the potential unrestricted flow. In that case there’s 25% of the potential flow lost to the restrictions.
You’re never going to get ZERO restriction because there’s far too much other necessary stuff in the engine and engine bay to fit filter, trunking, manifold and ports of sufficient proportions to have zero restriction.
A modern engine is pretty good out of the box and you wouldn’t ever expect as much as a 5% improvement in flow without drastic changes, and those very same drastic changes would likely make things worse in other ways. So, best ways up you might see 78 or 79% of the potential flow.
How come then, a typical modern high-performance road car engine has a VE of as much as 120%? Yes, a 3 litre engine would breathe as much as 3600cc in two revolutions!
With its silly uppy-downy pistons, pulling air past valves that are only open for typically 36% of the time, through ports that often have rough surfaces and uneven profiles, through often convoluted trunking and in from the outside world through a filter that only has open areas of a few microns. It cannot possibly be, surely? That’s over 50% more than the possible flow when the valves are only open for 36% of the time and the piston is only on the induction stroke for half of a revolution. “Get the ducking stool ready people, something isn’t right…..”
Well it can and it does, using PRESSURE WAVES. Tuning pressure waves is what it’s all about. Camshafts, exhausts, intake systems SHOULD all work absolutely together to harness the highs and lows of the pressure waves to best effect; so effective in fact that it amounts to a very significant supercharging effect.
Flow plays a very low second fiddle to pressure waves when it comes to tuning, because the difference that a loss of wave amplitude makes is far greater than the potential flow ‘increase’ from having a larger diameter and guess what? When the diameter of a pipe increases, the amplitude of the waves within it reduce because the molecule compression occurs over a greater area (the surface area, if you will, of the pipe section), so while the static flow may be imagined to be greater, the dynamic flow is actually considerably less.
For example, just look at a GT or F3 airbox - the airbox is huge to harness the pressure waves but the inlet FLOW is through a tiny little inlet restrictor, and despite this the engines still make PLENTY of power.
A flat six engine (all sixes actually for a specific reason that we don’t need to entertain here) is particularly well suited to harnessing the pressure waves that travel back and forth into, as well as across, the manifold if allowed to. They can make a huge difference to the VE at some engine speeds. This is why the (not stupid) design engineers at Porsche have gone to such great lengths to make best use of the pressure waves by employing various flaps in the system to either block or allow passage of pressure waves within the system.
When developing their engines manufacturers will do many, many hours of simulation work. After that they will make many test pieces, probably at least twenty different head casting designs, fifty camshaft profiles, piston crown designs, valve head shapes, compression ratios, manifold designs, you name it. At each engine test, a zillion sensors and probes are mounted all over the engine measuring everything that can be measured.
DO YOU NOT THINK THAT AT SOME POINT IN ALL THAT IT WOULD HAVE BECOME APPARENT TO THEM THAT IT NEEDED A BIGGER THROTTLE BODY?
No, of course not, they’re all stupid those Germans, right?
It takes Fred in his shed with probably zero engine design expertise, to think “Gad Daim, I can fit me a bigger throddle on there an’ life will be reeeeeal gewd….”
If only things were that simple…..
In the vast majority of cases BIGGER THROTTLE INTAKES DON’T WORK so save your money.
In every single Porsche case that I have EVER had on the dyno, NO bigger intake has made an improvement, and almost ALL has made less area under the curve than stock.
When a vendor selling parts says “There’s a 25 bhp difference with this Big-Boy Carlos Fandango intake Sonny Jim” just consider whether he means UP or DOWN!!!!!!
very fascinating, thanks for sharing Matt :)
this applies to both NA and forced right?
 
I'd agree that I'd be very careful changing much on a performance orientated car such as a porsche, if I was looking to modify for increased performance (if I were looking for increased drivability then there might be things to tweak but I doubt it).
Sadly or not? that's not the case with the CG13DE or CG10DE the CG is supposed to stand for clean and green or so I've read!

So given the manufacturer is going to optimise towards a particular use or sets of use then they will make design choices to suit that use, they will also make design decisions to suit a particular price point.
So apart from the clean and green what was Nissan's motivations when developing the CG? Well the only vehicles it's in are small cheap motorised shopping trolleys, their primary purpose is a small, cheap, reliable, bare bones, runabout that is easy to drive, economical to run, so all the design decisions were made with this in mind.

On the other hand if tuning for performance this means there's some easy and cheap gains to be had, in my case a new exhaust and inlet manifold as well as a larger throttlebody (dubious benefit maybe) has given close to 33% more power (Nistune tune as well although a ECU would be tuned from factory to suit), if Nissan engineers were chasing performance then they didn't try very hard!

Look at the weight of the flywheel, the twin cats, tiny exhaust and restrictive cast manifold, small brakes, beam rear axle, spartan interior. Don't get me wrong I like micras but they weren't designed as performance cars, of all it's cars it's one where I'd guess Nissan was least concerned about performance.

Now if we look at Paul's application: Track day car, performance over comfort, heavy braking and acceleration, high cornering forces, turbo putting out 160 hp? vrs the factory 75hp, we are pretty far from the intended purpose Nissan had in mind.
Yes I know there were Nissan supported Micra rally cars and performance Micras that probably got factory backing but I'd argue the initial design didn't have any of those in mind.

The contrast between the CG and a VG30DETT (3ltr twin turbo z32) that I've been helping with lately is HUGE! the VG is complicated as, unreliable as, and goes like stink if you get it running, Nissan at the time weren't afraid of complications and going all out for performance. I'd change those motors for greater reliability, I doubt you'd easily get much more performance out of them without bypassing emissions or using technology they didn't have back then.
 

SuperUno

Buy & Sell Member
It was for interest reading, I didn't say it fully applied to Micras which as you say would have been tuned to a price more than performance. But given some of us have found little to no gains from using an increased TB size it is interesting reading. I suspect the reason for the standard TB being better for our application is that we are stuck with the standard inlet manifold (road rally regs and cost reasons) so the standard TB is 'tuned' to the standard inlet manifold. Moving away from the standard inlet manifold may see more gains.
 
you have to address the bottleneck first, the most restrictive area, and then when that is opened up you can probably fit a bigger t/b.
calculate the cross sectional area, for instance the inlet throats in the head are 18mm dia iirc, so pi x r x r multiplied by 8 throats that are each open for about 200 deg (depending on what cams you are running)
it they = less than the t/b then no gains
 

Low Rider

Poindexter
Moderator
Club Member
The elephant in the room here is that, it's already been proven (on an N/A CGA3DE at least) that increasing the standard throttle body from 45mm to 48mm does yield an increase, even on a bog stock intake, engine and cam. All testing done by one person on the same dyno. Anything more however resulted in a loss. Granted it's perhaps small gains when compared to those seen on a well proportioned manifold with ITBs for example, but it's a gain none the less.

Likely very true on a high end performance car that's enjoyed decades of progressive development with large budgets. In Paul's case however, if he's pulling a leaner AFR at WOT at any given point, the charge air density has increased. There's really nothing more to discuss.
 
That's what this (in results text):
http://www.hipermath.com/math_center/racing_calculations
Throttle body size calculator reckoned when I was playing with some numbers.

Curiously it's 'race' numbers correspond with the standard TB size it's not until you move the peak power figure to 7500rpm you get 48mm. 8300rpm before it deems a 50mm throttle body necessary.

It was for interest reading, I didn't say it fully applied to Micras
Sorry I can tend to make the point forcefully.
 
Useful calcs there. Anyone want to buy a GA15 TB????
I'm thinking of next time I get Spot tuned of quickly putting on the standard TB to see what difference it makes, trouble is that engine is going to be better able to make use of the GA15 TB. I remember the tuner being unconvinced about putting the GA15 TB on, Matt Argent has also gone back to a smaller TB as he said they were getting max air readings before the throttle was fully open so the smaller TB gives better throttle control.
 
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