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phongshader
Justin Brown
Ca
(63 posts)

Registered:
02/19/2010 04:03PM

Main British Car:
Locost Lotus 7 2.3 Duratec

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215 crank with 1.850" rod journals?
Posted by: phongshader
Date: March 28, 2023 01:36AM

Would grinding down the rod journals to 1.850" significantly weaken the 215 crank? It's not like it's going to be making 600hp...maybe 200hp at best. Anyhow do you all think it would present any longevity problems/bad idea?


phongshader
Justin Brown
Ca
(63 posts)

Registered:
02/19/2010 04:03PM

Main British Car:
Locost Lotus 7 2.3 Duratec

authors avatar
Re: 215 crank with 1.850" rod journals?
Posted by: phongshader
Date: March 30, 2023 11:22AM

Wow, no opinions...So I bought some 6.2" Nascar rods that need 1.850" rod journals and want to install them into a Olds 215 block with Nissan KA24 Silv-O-LitePistons 9115.5MM. Is this a bad idea? I know the gains will probably not justify the cost but...will the smaller journals compromise the engine in a significant way?


Roverbeam
Chad McNeely
N.E. MO
(78 posts)

Registered:
06/09/2021 06:03PM

Main British Car:
Alpine S4 Rover 4.0

Re: 215 crank with 1.850" rod journals?
Posted by: Roverbeam
Date: March 30, 2023 12:11PM

Just based on simple section modulus formulas, a round "beam" has strength related to the cube of its diameter. Going from D=2" (d^3=8) to D=1.85" (D^3=6.3), you'll have about 80% (6.3 ÷ 8) of the crank's strength remaining. Up to you if that's "strong enough"!

Can't comment on the rest of the combination without more specifics - piston height and dish volume, block decking, gasket thickness, head volume, and whether you're offset grinding the crank to add stroke...
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ag1234
Arthur Gertz

(119 posts)

Registered:
03/29/2023 08:26PM

Main British Car:
Re: 215 crank with 1.850" rod journals?
Posted by: ag1234
Date: March 30, 2023 01:30PM

Hi Justin, many changes for little reward This weakens a cast crank, needlessly. 6.2" rod and 2.8" stroke = reduced rod angle.This is not good for your application. Better rod ratio is 1.7/1.8/1. Good Luck, Art.


7sand8s
Dennis Miller

(36 posts)

Registered:
09/21/2008 10:47PM

Main British Car:
Re: 215 crank with 1.850" rod journals?
Posted by: 7sand8s
Date: March 31, 2023 06:59AM

That should be ok.
It would reduce the journal overlap only 0.15.
Rod/stroke from 2.02 to 2.21.
Less wear on the thust side of the block.


phongshader
Justin Brown
Ca
(63 posts)

Registered:
02/19/2010 04:03PM

Main British Car:
Locost Lotus 7 2.3 Duratec

authors avatar
Re: 215 crank with 1.850" rod journals?
Posted by: phongshader
Date: March 31, 2023 10:20PM

I always thought there was more to be gained from by a bigger rod/stroke ratio than just less wear on the thrust side of the block particularly with heads with small ports...like the Olds heads ¯\_(ツ)_/¯


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