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Hiding from the Ayatollah or making Full Metal Jac
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AutoX or hill climb.

I think the 4.7-5.1 ratios are perfect with a higher reving engine, so if you've built an 8K or 9K motor..
 

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4.44:1 & 4.57:1 are Kia ratios ;)

think the 4.44 might be an S200 ratio?
S2000's are 4.1 as standard too... i would like a 4.5 for mine!

With a stock-ish car and the 6 speed box anything over 4.3 will mean a lot of extra gear changes! 4.1 still seems to be the right balance for sprints and hill climbs up here but is track dependant. A 4.8 FD would top out at 120MPH so no use for anything powerful
 

Hiding from the Ayatollah or making Full Metal Jac
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for turbo I recommend 4.1 or less, for NA I recommend 4.3 or more, that way you get the most out of it.
 

layabout
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layabout
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Why do you want such a short gear if u dont mind me asking? Is your mx5 a dedicated autox car?
the origonal idea was a normally-asperated roadcar with sprints & hillclimbs but things (& ideas) have changed - including the engine馃お

AutoX or hill climb.
^^ sorta this(y)

Rich.
 

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for turbo I recommend 4.1 or less, for NA I recommend 4.3 or more, that way you get the most out of it.
We're only allowed to run OEM diffs so 4.3 is the lowest anyone has tried but the 4.1 is faster on certain tracks due to the extra shifts needed with a 4.3

every day is a schoolday:cool:



don't use 1st gear, lovely close-ratio dogleg '1st' (second gear through 6th as a 5 speed) gearbox:p

Rich.
You'll be rifling through it!
 

layabout
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ISTR 8k or 8.5k as long as you fit ARP Big end bolts. The original Vauxhall bolts look agricultural once you get them out.
7,750rpm with better (ARP or similar) rod-bolts, presuming the ~30 year old rods have not had a hard life, 7,250rpm if you know nothing of the engine / standard conrod life...

chineese 'forged' rods are cheap enough to avoid using old standard rods :unsure:

Yeah the redtop. Awesome engine, overlooked engine is the boost junkie z20let.
That would be awesome in a 5.
or, if you need a turbo, look at the Saab Bsomethingorother (from the vectra-esque projectiles that Saab re-engineered from origonal GM designs), bloody strong engines and easily 300hp in standard trim:cool:

^^ also, the Saab engine fits the same bellhousing pattern as the Vauxhall XE so plenty of gearbox / bellhousings around(y)

Rich.
 

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I have 4.625 with 6speed in my race car with around 220 crank hp (8500RPM limit) and the thing works awesome. It would not work well on stock motor though. With small 540diameter (13") slicks the car flew like crazy through the gears. On other set of wheels on large 225/50 R15 A052 tires the car was still fast but once I switched to small wheels it was really hard to go back (mostly because of power (or effectively torque) you get from switch to smaller wheels and car was so nimble on small wheels. So yeah high RPM builds with 15" wheels OR larger wheels will definitely benefit from those 5.x gears. Plus! you can launch the car from second gear with 6speed as first gear is just spinning wheels without much effect on your speed :-D With second gear launch and good surface you get really good launch and you can get down to 5seconds 0-100kmh times which is cool for autox or hillclimb cars always.
 
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