The facts.
| Part number | G9973 |
|---|---|
| Type | Open, no perforation |
| Material | Stainless steel |
| Dimensions | Ø 57.5 → Ø 40 mm, open, no perforation, straight cut |
| Fitment | Universal |
| Road approval | None — track use only |
| Fits | Spark Moto GP silencers |
| Origin | Made in Italy |
| Manufacturer | Spark Exhaust Technology, Mantova |
| Manufacturer description | MOTO GP - d.57,5 d.40 00° OPEN |
DescriptionThe whole story▼
Forty millimetres through the middle — five more than Spark's other two Moto GP inserts, and the reason this one exists.
Key Features
- dB killer for Spark Moto GP silencers.
- Ø 57.5 mm outer, 40 mm internal bore.
- Open type, no perforation.
- The least restrictive of Spark's three Moto GP inserts.
- Stainless steel, removable.
- Spark part number G9973, made in Mantova, Italy.
Forty Instead of Thirty-Five
The step from a 35 mm bore to a 40 is larger than it reads. Flow area goes up by about a third, which means this insert costs noticeably less power and takes noticeably less noise out than the other two.
It is the part for a large engine that would choke on a 35 — or for a venue whose limit is generous and where the only aim is to shave a few decibels off the top.
Three Inserts, One Case
Spark lists three plugs for the Moto GP silencer and they form a ladder. G9941 with twenty-one holes takes the most out. G9969, open at 35 mm, sits in the middle. This one, open at 40, takes the least.
Owners who run the same machine at several circuits sometimes keep two of the three in the van. They swap in minutes and they cost less than being turned away.
Choosing Without Guessing
If you know the reading your machine gives open and you know the limit at the gate, the gap tells you which insert you need. If you do not, start with the middle one — going quieter is a cheap correction, going louder is not possible once the session has started.
Fitting
From the outlet, with the silencer on the bike, using hand tools. No dismantling of the link pipe and no removal of the case.
Fifty-Seven and a Half Across
The body diameter is common to all three Moto GP inserts. It is the bore that separates them, which means the three are indistinguishable in a parts drawer unless somebody labelled them — worth doing if you own more than one.
Ordering
One per silencer, same article for a left-hand or a right-hand case. Tell us the silencer number if you would like us to confirm the bore before we ship.
Legal Status
Unchanged by this part. The Moto GP silencer is a racing article; an insert is a noise tool and not a certificate.
FitmentWhich bikes this fits▼
Universal product — Please check whether it fits your bike.
Questions, one topic at a time.
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Our team is happy to help. Use the contact button below and we’ll personally help you choose the right gear or part.
Measure your head circumference about one centimetre above your eyebrows and compare it with the size chart on this page. Between sizes? Choose the smaller one — the padding beds in with use.
Yes — it’s tested and approved to the current ECE 22.06 standard and road-legal across the EU.
Most of our touring and sport helmets are Pinlock-ready and many include the insert. Check the ‘What’s in the box’ section on this page for this model.
Yes — the cheek pads are channelled so the arms of your glasses slide in comfortably.
Take out the washable lining and hand-wash it in lukewarm water. Clean the shell and visor with a soft cloth and water only — never solvents.
Our team will personally help you choose the right gear or part — around 24h for a reply.