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Engine, Exhaust, Transmission Discuss the FR-S | 86 | BRZ engine, exhaust and drivetrain. |
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03-10-2023, 12:08 PM | #29 | |
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For the NA graph I found it under products / engine / capacity upgrade kit / pick Scion / select the detail on 21004-AT002 - PISTON FULL KIT FA20 2.1L and it will bring you to: http://hksusa.com/products/21004/AT002/583 One thing to note, the CR shown on the capacity kit page is 12.4 which is less than what is listed on their complete engine which uses the capacity kit. Makes no sense. |
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03-10-2023, 12:23 PM | #30 | |
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https://www.motortrend.com/how-to/05...-stroke-ratio/
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03-10-2023, 01:43 PM | #31 | |
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Do we know for sure the kit does make it worse? They don't list the length of the rods so we can't do the math. All we know is stroke increases from 86mm to 90mm. According to the MT Article, there are ways of offsetting the ratio problem with longer rods/shorter pistons in a stroked engine. Maybe they did that to keep things closer in line. [EDIT] They actually say in the spec sheet: "Specific connecting rods have been designed to suit the longer stroke." Seems like they might have addressed the issue. |
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03-10-2023, 02:20 PM | #32 | |
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https://www.ft86club.com/forums/showthread.php?t=63901
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03-10-2023, 03:41 PM | #33 | |
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03-13-2023, 11:32 AM | #34 | |
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It's not impossible, but it's unlikely there's that much room to raise the wrist pin / reduce piston height without compromising piston strength. Bear in mind that a 10:1 CR piston in an otherwise stock motor would have a piston height only about 2mm shorter than stock, so over 7mm difference is a LOT. More likely the "specific connecting rods...designed to suit the longer stroke" are simply shorter than stock to maintain the piston height, making the rod to stroke ratio worse than stock. EDIT: it does say on the spec sheet that the pistons are "shorter height", and they use a 1.5mm smaller connecting rod bolt size, so maybe they've been able to maintain near-stock rod to stroke ratio...again, it's not impossible. That said, does a shorter rod to stroke ratio necessarily make a design "bad"? Not really. It means it will be more biased toward low-end torque vs. high-revving power, and *may* be subject to a bit more wear over time due to the additional side-loading, but it doesn't make the motor an instant hand grenade...
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Last edited by Tatsu333; 03-13-2023 at 11:39 AM. Reason: Added info from HKS spec sheet |
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03-13-2023, 11:46 AM | #35 | |
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03-13-2023, 02:39 PM | #36 | |
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03-13-2023, 04:08 PM | #37 |
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There was I guy here I am going to say he was from South Korea iirc, a few years ago that had a fully HKS stroked engine but also with reduced compression pistons and forced induction.
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03-13-2023, 05:16 PM | #38 |
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Someone on FB in New York is selling the low comp HKS 2.1 kit right now too. No idea how to link a FB post but it is in the group named FRS/BRZ/86 Marketplace.
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03-13-2023, 07:38 PM | #39 |
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Yeah, you are right, I am wrong on that. I dunno where I got 1.2:1 from.
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03-13-2023, 10:10 PM | #40 | |
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They do some interesting things with the full S1-S3 engines for FI, like oil jets to help cool the pistons. |
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