Hi, I have a 2007 Copen 1.3 with the K3-VE engine.
I am currently working on the car and I have a new intake (manifold and filter), exhaust manifold and exhaust system; and I am thinking of also upgrading the throttle body and potentially cams (as I have read elsewhere in this forum that is a good upgrade for the stock engine).
I was wondering if anyone had any idea at what point I should look to upgrade the gearbox (as I have no idea how solid these are, and I am not adding forced induction so do I really need to?).
As per your other new thread, itâd be good to see some pics of your car and see a short intro about you.
To answer your question though - Typically Daihatsu gearboxes are fine with high revs, its torque which kills them, which is why they dislike turbos. 1st and 2nd gear are quite strong, though a lot of people have issues with synchromesh between these gears. Problems typically manifest with 3rd gear soonest.
I have a K3-VE2 Sirion Rally 2 which has/once had 110bhp, its done 120,000 miles/150,000km and as far as I know its still on its original gearbox which is fine (other than 1st/2nd gear synchro) so with a sample size of one, your car with rally cams and intake + exhaust mods ought to be OK essentially forever. I suspect youâll only be getting 110-115bhp at most with those changes which will be fine Iâd have thought.
(I say âonlyâ - its plenty in such a lightweight car and believe me, youâll want to look at brakes more than engine power mods!)
TL;DR - upgrade the gearbox when you break 3rd gear. Ideally buy a spare gearbox now for when this happens so youâre not out of action for too long, as you can swap the replacement gearbox in, take the broken one out and THEN buy a gearset from Compact Motorsport or KC Technica to rebuild the broken one.
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Listen to Grangerâs good advice. The question of âat what point I should up grade the gearboxâ, also begs the question of âwhat ratios are availableâ? First is way too low.
Not much to gain in upgrading the throttle body. If you go more than a few mm bigger, even with cams, more compression etc, then youâll loose some throttle sensitivity and make it more like an on off switch with barely any gain/maybe even going backwards. My recommendation, from experience working with a k3-ve racecar, is to get the factory throttle body to someone with a lathe and get it bored out to suit a bigger butterfly. Kinsler might have something in stock or they will make one for you THROTTLE PLATES Archives - Kinsler Fuel Injection
. Keep in mind you want one that has the same opening angle (the angle can be changed and is done so when vacuum or boost is found to hold them shut - so the finished item is more ovalised. Iâve attempted to make my own but had little success, and thought I am certain I could have, from a time point of view it became an onerous task that I have up on). Failing a bigger butterfly get the thing in a lathe and taper the bore leading up to the butterfly, mill the spindle down thinner and replace the button head screws with counter sunk Allen key type. A lot of this sort of thing Iâve done has been done so while reading a rule book so as not to fall foul within a motorsport class.
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