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Old 12-01-2020, 12:17 PM   #1
abelbushey
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Default To install forge pistons or not to install forge pistons.

Hey all! Motors coming out and it’s getting a 250k refresh. To start it is a 1993 b23. The motor has a turbo on it now but I’m looking to push a little more power 250wheel range. I have a t5 and what I think is everything I need to make the swap go smoothly but we will see. The question is do I replace the factory pistons and rods to a forged option. Any input would be appreciated.
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Old 12-01-2020, 01:43 PM   #2
lookforjoe
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Based on personal experience, I would stick with cast pistons unless you're going to go much higher output (than that). Forged pistons require a larger ring gap, typically consuming more oil than a cast piston build. That has been my experience. If you are going balsl-to-the-wall build, then only forged makes sense. Your tuning will be more important in terms of longevity - often ppl say forged is stronger - they will break ring lands just the same as cast if your tuning is fkd.

You'll need to have the block checked for wear to determine what OS you need, and what cam options you are considering before you even think about what pistons are available anyway.
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Old 12-01-2020, 01:47 PM   #3
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I'd personally just toss in some FT pistons and call it good. Or just keep it as is.
At 250whp, you're not even close to stressing the stock rods or F pistons.
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Old 12-01-2020, 01:53 PM   #4
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At 250 wheel, even the 9mm rods are fine provided the tune is not stupid. Hell, the 85-89 blocks make better power at those levels from the lower internal friction.
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Old 12-01-2020, 02:10 PM   #5
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There are some huge gains to be had in piston weight savings. Mahle turbo piston assy's weight 750grams!!!

A Diamond LS2K style piston assy weighs 450grams.....
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Old 12-01-2020, 02:21 PM   #6
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Forged pistons need the proper piston to wall clearance as they will "grow" as they heat up, sloppy at first. I built and maintained SCCA production HP/FP [5] racecars and vintage [Austin Healey 100,[ 6] cars for 35 years. I used Venolia pistons made to my specs. We used Carrilo rods that were custom made, billet cranks, titanium valves, good for 8 hours,on the race motor in the FP car. Teflon coatings ceramic coatings, ceramic lifters, REM polished parts, But we would tear down the practice motor on the FP car after 3 events, the race engine used for the SCCA Run Off's would be taken apart after the race and rebuilt for the next year. This all might sound crazy, but these were full out race engines. I do not know a lot about modern engines as I work on older cars but the same rules apply, build it right the first time.
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Old 12-01-2020, 04:29 PM   #7
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piston slap with forged ones, yes.. it my opinion it is not recommened for a dailydriver
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Old 12-01-2020, 04:59 PM   #8
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Originally Posted by MadDog_945 View Post
piston slap with forged ones, yes.. it my opinion it is not recommened for a dailydriver
You can always sleeve down the block to a 92mm bore and use a stroker crank. No piston slap, hold all the boost.
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Old 12-01-2020, 06:25 PM   #9
classicswede
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I take it you ment B230 rather than B23?
1993 should be 13mm rods. 9mm rods I do not even trust in a NA build.
For under 500bhp crank forged pistons are not even worth thinking about
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Old 12-01-2020, 06:46 PM   #10
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Originally Posted by classicswede View Post
I take it you ment B230 rather than B23?
1993 should be 13mm rods. 9mm rods I do not even trust in a NA build.
For under 500bhp crank forged pistons are not even worth thinking about
I would not trust 13mm rods above 350 lbs ft, 9mm are fine to 250 lbs ft or so. Again, provided that the tune is not dog****.
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Old 12-01-2020, 07:14 PM   #11
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Or you get an iffy tank of '93 octane' gas and it pings on them a bit under boost.
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Old 12-01-2020, 09:10 PM   #12
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Replacement Mahle cast pistons aren't as easy to find, or as cheap, as they used to be. For example, lookup pistons for a '95 940 Turbo here:
https://www.skandix.de/en/spare-part...ly/piston/776/

Custom made forged pistons are available through US suppliers, e.g.
https://yoshifab.com/store/b230-perf...iston-set.html or maybe JVAB (but he's not around much anymore)

And for general info:
https://www.enginebuildermag.com/200...ston-problems/
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Old 12-01-2020, 09:20 PM   #13
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Quote:
Originally Posted by bobxyz View Post
Replacement Mahle cast pistons aren't as easy to find, or as cheap, as they used to be. For example, lookup pistons for a '95 940 Turbo here:
https://www.skandix.de/en/spare-part...ly/piston/776/

Custom made forged pistons are available through US suppliers, e.g.
https://yoshifab.com/store/b230-perf...iston-set.html or maybe JVAB (but he's not around much anymore)

And for general info:
https://www.enginebuildermag.com/200...ston-problems/
FYI, Yoshifab are currently supplying Traum pistons which are billet. At least thats what I got when I ordered earlier this year. I got the design customised slightly for my needs which Yoshifab happily arranged.
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Old 12-02-2020, 11:33 AM   #14
Jussi Alanko
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I would change connecting rods to forged, but keep the cast pistons.
In sweden they have taken over 550hp with stock cast pistons.

Good tune is what counts.
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