13:1 gears; what are some things that need to be considered

Looking at doing a high speed build ona v2 gearbox with 13:1 gears. What do I need to consider to make it work as efficiently as possible? Thanks

If ya dont no start with 18s just easier first go.

Consider getting a lobotomy? noidea laughing (1)

minions laugh again


Already done 18s and 16s, wanna try 13s

yes of course, why did i not think of this :roll_eyes:

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First thing you do is use the search function.


Already have mate, not much on the topic.

That’s largely because going 13:1 there’s a much larger margin for things to go wrong. By the time you’ve gotten the hang of doing 16 and 18:1 competently you should have a good enough idea what’s required for 13:1.

So for those that do do those builds or have the knowledge on we don’t put up information publicly too often so we don’t have those who’ve barely opened a gearbox try for something that needs to be a touch higher fidelity than your basic rebuild/service. If that makes sense?


At the end of the day all you can do is buy the gears and give it a crack only way to really learn. The basics are the same as any gear set you just will have to take into account tappet timing and return spring strength. Short stroking may be required if you don’t want to go for a too powerful spring. Just alot more to consider really

What gear box is it going into?

Thabks for the advice. I just want to ask and get an answer, because I dont want to screw it up. How am I meant to learn without knowing what to learn? Its going into a v2 gearbox. I’ll cut the return spring and trim the tappet and see how it goes.

It does but if I ask a simple question I just want a simple answer. I dont want an all out guide, but at least a few things I need to take into account. I cant learn without having somewhere to start.

I’m no expert, haven’t done a 13:1 but from stuff I’ve seen mentioned around here and from my experience with 18:1 and 16:1 builds, Things to take into account would be.

Gearbox material and radiusing for heavier springs
Return spring strength
Tappet timing and shape
Short stroking (+ impact that has on cylinder volume and VE)
Spring weight
Weight of piston/head

Thank you mate, will take these into account

What v2 gear box? Cast metal? If so you will have to radius it or cnc? Cnc is you always safe option. I’d say nylon gear box isn’t an option because generally you will have to SS which then in tern you will need a larger spring which the nylon boxes won’t be able to handle

Nylon but I might buy an MK

13:1s break shit if not done right. As for tappet timing all you can really do is build-test-reopen-build-test-reopen-build-test until you get it running right or you break your gearbox. Good luck mate :crossed_fingers:


Thanks man, I appreciate the fact that you were straight forward with it. I’ll keep trying and we’ll see how it goes!

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And you’ve got to know how to shim and make your gears mesh properly. Shimming is the most important thing in a high speed build


Yes I do know how, I’ve watched a plethora of videos on how to shim flawlessly.

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You’ll be fine. It’s not as hard as people say just go slow and make sure you nail each step. My 13:1 builds haven’t needed any adjustment for tappet timing but I always short stroke the 1st tooth on the pick up side to reduce stress on the gearbox