Steel Crank
Turbo Mini Forums

Im just wondering the outline of BHP and Rpm you'd need to introduce a steel crank at. there must be more to it than just power and revs? Does the amount of time held at high revs and high power and/or the total running time have an effect.

You guys running turbos seem to be able to run high power and high revs without problems on a worked standard crank, whereas the circuit racer engine builders advise a steel crank from around 150-160bhp.

What are people running, and what are your thoughts on this?

Matt

Matt W

The main thing to remember is that compared to an NA engine which really does need to turn high RPM to make the power, a turbo motor does the job at typically a lower RPM. Hence as you rightly say most people using a standard or worked standard crank.

So its the high revs that effectively kills the crank. What sort of Rpm does the Don produce peak power at? or is that a secret? :)

Matt W

dunno about peak but they shift the don at around 9300 IIRC, there is a dyno print on the site somewhere.

the dons a special case though,

and yep its rpm that kills cranks rather than power,

Edited by Joe C on 8th Sep, 2011.

Sorry i should have used the search button, ive answered my own question.

Matt W

We spun a couple of KAD headed 1440s to 10k for a while but the where very quick to brake the crank if you got wheel spin anywhere near that i.e. Hitting a yump in the road flat in 3rd these where arrow steel cranks we now Spin to 8500 and reworked the heads to make the power earlier

so paul ,if one had ,say,a set of very light longman offset dish forged omegas and a set of arp big end bolts ..is 8k livable with a a+ crank n rods ? :)

Medusa + injection = too much torque for the dyno ..https://youtu.be/qg5o0_tJxYM

I'm at the "where do I set the rev limiter" stage. Worked standard crank, A+ rods, ARP bolts, and forged omegas.. I figured 7500 is ok based on nothing but guess work. Any raise on that?

Rev limit is pegged depending on what cam you are using. There is no real point having a cam that has a power band up to 8k, setting the rev limit to 7500. If you set the rev limit to 7500 because you are worried about the internals, then you need to change the spec of your cam. That said, there should be no real probem with 8500 rev limit on modified standard internals, but it all depends on how long you intend to hold the engine at 8k. standard rods and crank have been said to be good for one race season in a Miglia spec engine.

There are no gaurantees though, and alot depends on the quality of the build.

I believe we regulary run up to 8k. Just bladed std crank (wedging not allowed), worked A+ rods, APR bolts & forged Omegas running low boost.

Mine gets rev'd to 8k and has been for the past 4 years with no problems. But with being a turbo it doesn't take a long to get there before your in the next gear, so you're not reving at high revs for long periods.

Im hoping to give mine some stick around coombe in a few weeks, may raise the limiter for that though.

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1/4mile in 13.2sec @ 111 terminal on 15psi

All of my engines I build with prepared stock cranks/re sized big ends and arp rod bolts are limited to 7200rpm. Anything twin kam I build over 8000rpm has steel crank. Bearing clearance and big end re-sizing along with a thorough balance job are the key to a reliable bottom end.

Jk

If Carling made Mini engines
it would probably be like this one!

There seems to be no predictable pattern as to what standard cranks will take. some people have broken them in standard engines, while others i.e the don rewrite the rule book as to what it is believed the parts can take.

As long as the fillet radii are good and the rotating assembly is well balanced it seems that they do infact take a lot more punishment then they get credit for.

Edited by minimole23 on 9th Sep, 2011.

A worked OE crank will happily go way over 9k, well mine does anyway, admitted it doesnt do it often anymore but it used to almost daily for over 6 years with new shells and a polish every couple of years and oil changes every 1000 miles.
Its sustained high rpm that causes problems, like in a 20+ minute race where its flat out constantly.

I seriously doubt it!

That is defiantly the key Robert the lighter the piston and rod the longer the crank will live at high rpm a slightly longer rod in the A series make quite a difference to crank.
7k on a standard crank seems to work fine for at least 2O hours I personal have never run one for longer

i'll just have to find out then ,damn , more pioneering .

Medusa + injection = too much torque for the dyno ..https://youtu.be/qg5o0_tJxYM

I have those lightweight offset forged Omegas that you speak of Robert, they are 100g each lighter than my old diecast Omegas plus a thinner ring for less friction. There was definately a difference in the way the engine picks up so we know theyre the way to go

I seriously doubt it!

Thanks for the info guys, this is a lot of help.

My peak power is produced at 7500rpm anyway so i dont think ill be going much above that. I think my setup is as good as its going to get without changing the rods and pistons. Baring in mind ive not had it running in the car yet.

Matt W

Medusa + injection = too much torque for the dyno ..https://youtu.be/qg5o0_tJxYM

Had this chat with Joe C today about forged Amegas. Noticed theres not many people running them for high boost turbo applications. Two questions, can they actually take high boost and are they actually worth using for a daily runner?

Im running forged omegas on 25psi on a 9:1 CR. Probably covered about 5-6k of hard mileage so far too. So I would say they are good for both.

Oh yeah they have also been hydrauliced once too...but we won't go there!

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1/4mile in 13.2sec @ 111 terminal on 15psi

This is true for an NA motor, but the maximum limit for a turbo car is somewhat extended.

Fastest 998 mini in the world? 13.05 1/4 mile 106mph

Where is the best place to get your rotating assembly balanced down south Bedford area?

No point doing this thing half measured

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