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Upgrade Crankshaft?


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#1 Hughieboy

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Posted 07 August 2018 - 08:19 PM

I have an old 1275GT block which I am considering re-boring out to 1380cc. If I fit a stage 4 head and Kent 286 cam, would I need to upgrade the crankshft too? 


Edited by Hughieboy, 07 August 2018 - 08:34 PM.


#2 Retroman

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Posted 07 August 2018 - 08:38 PM

No just make sure it is checked by an engineer for being straight and that the journals are good.

 

I would also consider 73mm to 1360 as it leaves another overbore, and the difference in output is nothing

 

to be honest a tuned 1330cc is plenty for the road

 

I think you mean a 286 cam...

 

The only performance related 186 I know was my uncles F1 stock car number, and another relatives Ministox number



#3 Retroman

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Posted 07 August 2018 - 08:43 PM

Check too that the block has no hole above the centre main bearing, they are to be avoided.



#4 cal844

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Posted 07 August 2018 - 08:43 PM

No just make sure it is checked by an engineer for being straight and that the journals are good.

I would also consider 73mm to 1360 as it leaves another overbore, and the difference in output is nothing

to be honest a tuned 1330cc is plenty for the road

I think you mean a 286 cam...

The only performance related 186 I know was my uncles F1 stock car number, and another relatives Ministox number


I agree with this, a 1330 will be more than adequate for road use, plus you'll still have plenty rebores left

#5 Hughieboy

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Posted 07 August 2018 - 09:35 PM

Thanks all, appreciate your replies. Will definitely consider the 1330/1360 options. 



#6 slidehammer

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Posted 08 August 2018 - 01:19 PM

If you are planning on hi horse power outputs and rpm I would get the crank tuffrided and a center main strap fitted to prevent crank flexing.at hi rpm.



#7 Moke Spider

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Posted 08 August 2018 - 05:53 PM

A stock Crank as Retroman has suggested will be fine. About the only thing other than a balance is to consider having the Crank Wedged.



#8 sonikk4

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Posted 08 August 2018 - 06:49 PM

Why not start at 1293, get a really good head, decent cam, ignition system, exhaust system etc then a good rolling road set up.

 

Now you will have a really good setup, loads of life left in the block for rebores and potential.

 

The head, cam, fueling , ignition and exhaust system is where the power is at. Yes an increase in CC's will help with torque but not outright power.



#9 Cooperman

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Posted 08 August 2018 - 10:04 PM

Best advice, unless building a full-on competition car, is to always go to the next bore size up. Then, after you get to 1330 cc (+0.060" overbore) at the next re-build sleeve back to 1275 cc. That way there is no need for offset boring (= expensive) and no risk of scrapping the block.

Power and torque come more from accurate build and good gas flowing than simple increase of capacity.






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