PERFORMANCE

For a couple of years now we have been working on and developing some bolt-on performance parts for the SR250 engine.  Without opening up the engine, we have been able to extract an extra 20% in both power and torque.  

 

To achieve this, we used several exhaust and intake calculators, ran multiple simulations, and most importantly conducted real world testing - over 20 hours of it actually, spread across two different rolling road dynamometers with two different operators and two different bikes - just to make absolutely sure that the parts worked, that the tests were repeatable and to achieve the results we wanted  - and are now able to promise our customers.  

What are the parts, what do they do and how do they work?  Read on to find out!

 

EXHAUST

The stock Yamaha SR250 Exhaust is a complete system - meaning both the header and the silencer are a single part.  This design is chosen to reduce sound and exhaust emissions, but has the huge downsides of added weight and reduced performance.  The system is a double walled design - meaning the thick outer wall you see is only there for appearance.  The pipe that actually caries the exhaust away from the engine is inside this external pipe and is therefor much smaller in diameter - creating a cork in the system for the engines output.  This means the effective diameter of the exhaust is a mere 26mm.

 

The header we developed is a single wall design, made from high quality Stainless Steel and has an effective diameter of 32mm - allowing for a much greater flow of exhaust gas and an increase in power of 10%+.  Used with a suitable silencer, weight savings are upwards of 1.5kg!

Length also plays a large factor in header performance and the Jadus design is 130mm longer than stock - lifting power and torque low down in the rev range.

INTAKE

The stock intake system is also a compromised design and in the case of the SR, is another bottle neck for airflow through the head, meaning a strangled engine and less power potential.  This is why we decided to design and develop a high performance intake system - to unlock some extra power!

 

Our tuned intake design has a specially formed bell mouth entry that fits inside an oversized high performance clamp on foam air filter.  This filter has a large surface area and allows a high volume of clean air into the engine at high velocity.  The length of the intake takes advantage of the 3rd harmonic, giving a huge spread of power through the midrange. 

 

When combined with the Jadus header we managed to squeeze out a further 10% in power and torque from the engine - making for a total increase of 20% over stock with the whole kit.

IGNITION

Through research and testing, we found the SR's peak ignition advance to be a little conservative.  So we developed a special advance bracket kit to raise the ignition curve a few degrees.  

The extra advance helps raise cylinder pressure at the correct time in the combustion process and translates to a cleaner more efficient burn and more power - giving higher milage and crisper throttle response.

What we found was that the kit only had an affect on engines with less than 130psi of cylinder compression. This is logical because engines with reduced compression tend to benefit from slightly advanced timing - to make up for lost static compression, the dynamic compression can be raised.  At this time, we only intend to sell a kit for the earlier SR250 Specials.

THE KITS

The Jadus SR250 Full Performance Kit comprises of:

- Jadus SR250 Low Slung Header

- Repacked Dunstall replica silencer (optional)

- Jadus SR250 Harmonic Intake

- Jadus oversize performance foam air filter

- Applicable Mikuni jets for carb adjustment

The kit, as shown in the above dyno graphs, gives a 20% increase in power and torque, reduces weight by at least 2.5kg and it is all bolt on!  

 

Buy here starting from €280 (exc. VAT)

The Jadus SR250 Exhaust Kit comprises of:

- Jadus SR250 Low Slung Header

- Repacked Dunstall replica silencer

- Jadus oversize performance foam air filter

- Applicable Mikuni jets for carb adjustment

This kit, as shown in the first dyno graphs, is good for a 10% increase in power and torque and a 1000rpm lift in the power band.  This kit will also save at least 2.5kg.

 

Buy here for €212 (exc. VAT)

The Jadus SR250 Intake Kit comprises of:

- Jadus SR250 Harmonic Intake

- Jadus oversize performance foam air filter

- Applicable Mikuni jets for carb adjustment

This kit has been tested on the dyno by a third party and achieved a 10% boost in power and torque across most of the rev range, with a 15% increase at 6500rpm.  The kit will save a little over 1kg in weight

(by removing the stock air box).

 

Buy here for €140 (exc. VAT)

DEVELOPMENT

Below is just some snap shots of the development process.  From some very technical surface analysis CAD tool images to raw shots from the dyno testing days.  You can see some of the process in which the exhaust was finalised in 3D, plus the various types of intakes we prototyped and tested.  If you have any questions at all about any of the parts, the process or the testing, hit us up on any of our media channels, we would love to engage with you.  And finally, thank you for checking out our work and supporting us!

Bellmouth Intake Simulations

Here we ran simulations to optimise the intake bell mouth shape.

Stock SR250 Exhaust

This is the stock SR250 complete exhaust system - heavy and restrictive.

SR250 Silencer

With a cut-away, it is possible to see where the stock header pipe ends into the large collector silencer.

Cut SR250 Exhaust

Cutting up the two components for closer inspection.

SR250 Split Header

Here is the outer cosmetic pipe separated from the functional inner pipe.

SR250 Jadus Header Comparison

Here is a side by side comparison of the stock header and the Jadus header.

SR250 Header Cad

Here is a screen shot from some of our 3D modelling development.

SR250 Header 3D

We overlaid all of the designs we prototyped to help understand where to make adjustments to lengths and bends.

Header Tweaks

Small adjustments had big implications.

3D Printed Exhaust Prototypes

Here are some of the prototypes we made to test fitment and design.

3D Printed Header Prototype

Here is a test fit of one of the header prototypes.

Stainless Header Prototype

This was the first stainless steel prototype. Note that at this stage we had decided to weld on the reducer - later to be added as a separate sleeve instead, for flexibility.

Exhaust Silencer Packing

Here is our repacked exhaust silencer. This helps reduce noise a little without affecting exhaust gas flow.

O2 Sensor Install

We installed a modern O2 sensor and air fuel ratio kit to be able to get optimal jetting settings for the carburettor.

SR250 Mikuni Jets

Yes, we bought a lot of jets for testing. So you don't have to!

SR250 O2 Sensor Placement

Installed O2 sensor.

SR250 Oxygen Sensor

Sensor placed in a position to get reliable readings.

SR250 Air/Fuel Meter

Modern air/fuel ratio gauge.

Tuned Intake Length

Among hundreds of others, this was one of our inspirational and reference images for our harmonic ram intake design.

Bellmouth Design

Some screen shots from the different bell mouth designs displayed with different surface analysis tools.

CV Carb Intake Design

A collection of images, filters and prototypes of the various intake designs we went through.

SR250 Tuned Intake

At front are some stubby bell mouth designs, in the middle are some 4th harmonic designs and at rear are some 3rd harmonic designs.

SR250 Harmonic Intake Lengths

In practice, it was more effective to test the different harmonic tunings like this - with a bolt on removable bell mouth and various length tubes.

SR250 Tuned Intakes - Ram Intakes

So when installed looked like this.

SR250 Intake Bell-mouth Prototype

Just one of those many prototypes in context - mounted in position.

SR250 Classic Ignition Spark Advance

Just the beginnings of developing the spark advance brackets - calculating in CAD what the resulting full advance would be.

SR250 Spark Advance Brackets

The billet machined aluminium ignition advance brackets for the SR250 Special.

SR250 36 Degrees Peak Advance

Testing some prototypes on the SR250 Classic.

Advanced - Initial

Establishing initial advance with a timing light.

Advanced - Peak

Establishing peak advance with a timing light.

SR250 Special Advanced Ignition

Mounted advance brackets.

SR250 Dyno Run - Baseline

Day one of dyno testing with the Jadus Test Mule 1.0.

Jadus Dyno - Day 1

Establishing a baseline with a completely stock set up.

Jadus Dyno Day 1.0

Now onto the Jadus header!

Jadus Dyno Day 1.2

The header alone had a big impact on performance.

SR250 Tuned Intake Testing

Then with adding the intake bell mouth, things really starting picking up.

Dyno Remote Fuel Tank

Remote fuel reservoir set up.

Jadus Dyno Graph

Final results were very satisfying after all the hours of work.

Jadus Dyno Day 2.0

The Jadus Test Mule 2.0 on the dyno ready for a full 8 hours of testing.

Jadus Dyno Day 2.1

Sophisticated sensors and software to dial things in.

Jadus Dyno Day 2.2

Advancing the ignition on this bike yielded no gains.

Jadus Dyno Day 2.3

But the intake made a huge impact again.

Jadus Dyno Graph - At Rear Wheel

This is rear wheel power as opposed to engine power - showing stock vs full Jadus kit. Over a 20% gain across the rev range.

Jadus Dyno Graph - At Engine

Dotted lines = stock power and torque, first solid lines = Jadus header power and torque, second solid lines = Jadus Full Performance Kit.

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