Blast Arrow Kit vs Ready-to-Race: What Changes?
There are three Blast Arrow numbers worth separating before checkout. Item 18635 is Tamiya's standard MA chassis assembly kit. Item 18647 is Tamiya's MA Power Spec Starter Pack, also an assembly kit, with a different selection of motors and tuning parts. Monkee Mods' model 18647-RTR starts from that starter pack and is assembled and inspected by the store. A customer choosing between the stocked standard Blast Arrow and ready-to-race Blast Arrow is therefore choosing both a parts package and whether to do the initial build.
The common MA chassis does not make the boxes identical
Both versions use a mid-mounted, double-shaft motor on the one-piece MA chassis. The stock 18635 kit is a proper complete model, not just an empty shell or bare chassis. Tamiya lists its assembled size at 156 × 97 mm and supplies a motor, white wheels with low-profile tyres, six individual chassis rollers and 3.5:1 gears. You assemble it yourself and add two AA batteries. That straightforward box is useful if the point is to learn how the gear cover, motor contacts, rollers and body catch fit together. You also get a cleaner baseline for comparing a later motor or tyre change, because you know exactly what the standard kit did first.
The 18647 starter pack is built around the Blast Arrow body and MA platform, but Tamiya specifies a Torque-Tuned 2 motor, 3.7:1 gear set, black super-hard tyres, brake set, front underguard, mass dampers and FRP plates front and rear. Tamiya gives the assembled pack dimensions as 155 × 104 × 41 mm. The additional width reflects its included setup, so do not copy the standard kit's 97 mm width into a race registration or a parts-fit calculation. The pack is a curated set of components, not proof that one setup will be quickest on every circuit.
What the store's ready-to-race service changes
Tamiya describes 18647 as snap-together assembly. The -RTR suffix belongs to Monkee Mods' separate retail listing: the Blast Arrow body is mounted, the power-spec option parts are installed, and the car is inspected before sale. This saves the first assembly job. It does not turn 18647 into a factory-built Tamiya model, nor does it change the underlying MA motor family or make the box a remote-control car. “Ready to race” describes its build state; actual eligibility still depends on the rules of the event you enter and the car as presented for inspection.
Choose 18635 if following Tamiya's diagrams, seating gears and troubleshooting your own first build is part of the hobby you want. Choose 18647-RTR if you want the starter pack's selected brake, damper and plate parts already fitted and want to spend the first session examining and driving a built machine. The unassembled Tamiya starter pack 18647 is a third choice where available, but it is a distinct product from both store links here. If you later replace the motor, use the Mini 4WD motor guide to select a double-shaft PRO motor for MA, not a single-shaft motor intended for FM-A or VZ.
What the price comparison should include
Do not compare a bare kit's ticket against the RTR ticket as though both purchases contain the same components. The Power Spec pack includes a tuned motor, different gears and a collection of parts that a standard Blast Arrow owner would buy separately if they wanted that exact setup. The Monkee Mods listing then adds the assembly and inspection work. If you already have compatible MA option parts, 18635 may avoid duplicates; if you need every listed part, compare the whole parts basket. Neither choice removes the need for batteries or for later upkeep.
Check the car before its first run
Regardless of who assembled it, inspect that the body latches properly, tyres clear the body, the gear cover is secure and every fitted plate or damper is tight. Insert the two required AA batteries in the indicated orientation and test that the wheels turn freely before placing the car on a track. If buying the RTR listing for an event, measure the finished machine rather than using the standard kit's dimensions; the 18647 published width of 104 mm is close to the official 105 mm maximum. Add-ons, fastener position and the organiser's own class rules can matter. The technical inspection checklist explains the wider checks.
Frequently asked questions
Is Tamiya item 18647 itself factory assembled?
No. Tamiya sells 18647 as an assembly starter pack. The assembled, inspected offer is the Monkee Mods 18647-RTR listing.
Does the standard Blast Arrow include a motor?
Yes. Tamiya lists an included double-shaft motor for 18635; two AA batteries are required separately.
Which version is faster?
The published contents alone cannot answer that. The motor, gear ratio, tyres and added parts differ, while actual results depend on the track, build and batteries. Test on the course you use.
Sources checked 26 September 2026: Tamiya Blast Arrow 18635, Tamiya MA Power Spec 18647, and the linked Monkee Mods 18647-RTR listing. Availability and event rules can change.