GTX B6T Motor ?'s

[mikemounlio]

So is using the small nose a bad idea? Or will i be fine when im around the 250-300 mark?

[bhazard]

Small is square and 27mm is rectangle

I thought it was the opposite?

[bhazard]

So is using the small nose a bad idea? Or will i be fine when im around the 250-300 mark?

http://www.miata.net/garage/crankshaft.html

[Advancedynamix]

If you're building an engine, use a large nose crank, period. It has nothing to do with HP levels. The small nosed crank was a design flaw, and can be a problem even at the stock 62hp b3 level (though the problem is much less common due to the lack of extra accessory load).
A large nosed crank can be sourced for under 200 dollars, and you'll need a different oil pump. You don't want to build up a trick engine, only to have to tear it down because your crank pulley came loose and ruined your crank.
Also, you'll be about as fast as a 600 cc sport bike at 200hp/200ft.lbs which you can get from a box stock B6t long block with a decent turbo and programmable management. My 180/180 b6t festiva is very close to a 600 on freeway pulls (faster than some, slower than others). Over 250hp will be tough to put down on street rubber and spinning your tires will make you slower. Keep in mind that your building a 1700lb car, not your typical 2800lb street car. 1000 lbs is a huge difference, and you can take the HP numbers that are required for most cars and cut that in half. 200hp festiva=450 hp Corvette

[mikemounlio]

If you're building an engine, use a large nose crank, period. It has nothing to do with HP levels. The small nosed crank was a design flaw, and can be a problem even at the stock 62hp b3 level (though the problem is much less common due to the lack of extra accessory load).
A large nosed crank can be sourced for under 200 dollars, and you'll need a different oil pump. You don't want to build up a trick engine, only to have to tear it down because your crank pulley came loose and ruined your crank.
Also, you'll be about as fast as a 600 cc sport bike at 200hp/200ft.lbs which you can get from a box stock B6t long block with a decent turbo and programmable management. My 180/180 b6t festiva is very close to a 600 on freeway pulls (faster than some, slower than others). Over 250hp will be tough to put down on street rubber and spinning your tires will make you slower. Keep in mind that your building a 1700lb car, not your typical 2800lb street car. 1000 lbs is a huge difference, and you can take the HP numbers that are required for most cars and cut that in half. 200hp festiva=450 hp Corvette

Perfect reply once again! Thank you.

So now on to finding a long nose crank and i guess i need to start reading on what all i need to do to change it out.
Any pointers?

[F3BZ]

thanks for the link bhazard. very interesting and it especially clears up the short, long, and big nose quagmire. interesting also is that all festiva shop manuals show torque values of either 80-85 or 80-87 ft.lb. since the big nose was incorporated in 91 i would've expected the 92/93 manuals to show the higher torque value. even in a 1992 capri shop manual which more closely duplicates a miata engine the specs also show a single range of 80-87 ft. lbs. these discrepancies might've been addressed in a TSB to dealer service depts. but i wonder how many big nose engines were installed or repaired with under torqued bolts.

[F3BZ]

So now on to finding a long nose crank and i guess i need to start reading on what all i need to do to change it out.
Any pointers?[/QUOTE]

any chance you can use an aspire crank? i dunno but somebody will. also 4G still shows a later crank for $185.

[Greywolf]

This is all fantastic info - and I will be surfing out stuff here for a long time. But in my experience the bottom end of any engine you intend to keep should be the place where you spend time and effort to get it right from the beginning.

Since a "Long Nose" crank can be had either by ordering one outright, or (if you know what you are looking for) salvaged out of a wrecking yard engine, ANY SERIOUS REBUILD even if it isn't for a monster engine should have that crank included as part of the package.

My question here though is about turbo ~vs~ normally aspirated engines, and it concerns the OTHER parts around the crank. I know from ford 2.3 engines that factory turbo and supercharger engines like the Thunderbird cars had forged rods and other hardened internals that gave strength to the rotating assembly. Is this true of Mazda 'B' engines also?

[azgtx]

I thought it was the opposite?

Nope. 27 mm has the 8 slot pulley.

[bhazard]

I mean the square vs rectangle bolt pattern

[azgtx]

Actually the long nose is still a 22 mm crank and much harder to find for sure. You want a big nose 27 mm crank. We are always on the hunt down here for B6t's in good shape and other related stuff for them...and we find them for sure. We will post them up when located. No tin worms down here in the desert so they stay on the road longer.

[mikemounlio]

So does anyone have a lead on a long nose crank?

[azgtx]

Mike if you do find one make sure you get the right bolt and key with it...or you can still get those from Mazda new.

[bhearts]

So does anyone have a lead on a long nose crank?

Big nose. Let's just call them 22mm or 27mm

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[mikemounlio]

So anyone know where i might find a 27MM crank?