HKS Engine Specs

[Uplink]

Originally Posted by terboboost

Where did you find this dyno chart? I can't find anything on US or Japanese site.

It was kinda buried. If you go to hksusa.com under products / engine / camshafts then select the one for our cars you'll get this (which was run with their SC kit): http://hksusa.com/products/22002/AT005/678

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.

[NoHaveMSG]

Originally Posted by Uplink

Ok, mystery solved. So after a bit of digging around their site (they have still not responded to my e-mail) I was able to find some ballpark numbers indirectly. If you look at the page for the camshaft they use in the Stage 0 engine, they have a dyno graph. Unfortunately, that graph is the 2.1L capacity kit + cams + supercharger... because of course it is. But if you look at the 2.1L capacity kit used in the Stage 0, it has a dyno graph of just that and the cams, NA. It's basically a little better than going with a 2017 FA20, netting +12hp and +18ft/lbs (209 & 169) over a stock 1st gen. But you're also getting a beefed up engine rated to well above the transmission's reliability plus it's a complete drop-in replacement. All-in, it's not a terrible option.

It's been said before, so I will repeat. FA20's already have a kind of poor rod/stroke ratio. The HKS capacity kit makes this worse.

https://www.motortrend.com/how-to/05...-stroke-ratio/

[Uplink]

Originally Posted by NoHaveMSG

It's been said before, so I will repeat. FA20's already have a kind of poor rod/stroke ratio. The HKS capacity kit makes this worse.

https://www.motortrend.com/how-to/05...-stroke-ratio/

Good read, thanks!

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.

[NoHaveMSG]

Originally Posted by Uplink

Good read, thanks!

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.

It's a long read, but the info is in here. I think our rod to stroke is like 1.2:1 or something. I can't remember.
https://www.ft86club.com/forums/showthread.php?t=63901

[Uplink]

Originally Posted by NoHaveMSG

It's a long read, but the info is in here. I think our rod to stroke is like 1.2:1 or something. I can't remember.
https://www.ft86club.com/forums/showthread.php?t=63901

Yep, that's stock, 103.3mm rods / 86mm stroke. On the HKS spec sheet they are using a custom rod / 90mm stroke but they don't give the actual rod length so we can't figure out what the ratio is in the upgrade. If they're able to counter the math a little by going with a slightly (5mm) longer rod that would bring the ratio in line with stock and you'd be no worse off.

[Tatsu333]

Originally Posted by Uplink

Yep, that's stock, 103.3mm rods / 86mm stroke. On the HKS spec sheet they are using a custom rod / 90mm stroke but they don't give the actual rod length so we can't figure out what the ratio is in the upgrade. If they're able to counter the math a little by going with a slightly (5mm) longer rod that would bring the ratio in line with stock and you'd be no worse off.

Unless they've moved the wrist pin at least 7.1 mm higher in the piston body (relative to the piston top), there's no way to match the stock rod to stroke ratio. You need a 4.8mm longer rod to match the ratio with the increased stroke, plus allowing for an additional 2mm of travel (half the stroke increase), plus about 0.3mm additional combustion chamber height (I.E. shorter piston height) to match the stock compression ratio.

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...

[NoHaveMSG]

Originally Posted by Tatsu333

Unless they've moved the wrist pin at least 7.1 mm higher in the piston body (relative to the piston top), there's no way to match the stock rod to stroke ratio. You need a 4.8mm longer rod to match the ratio with the increased stroke, plus allowing for an additional 2mm of travel (half the stroke increase), plus about 0.3mm additional combustion chamber height (I.E. shorter piston height) to match the stock compression ratio.

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...

I believe he had the measurements in the NA build thread for the HKS stroker and they did what they needed to make it fit, not improve the ratio. It's one of the reasons he did his own custom rod and piston kit, along with wanting more displacement.

[Tatsu333]

Originally Posted by Uplink

Yep, that's stock, 103.3mm rods / 86mm stroke. On the HKS spec sheet they are using a custom rod / 90mm stroke but they don't give the actual rod length so we can't figure out what the ratio is in the upgrade. If they're able to counter the math a little by going with a slightly (5mm) longer rod that would bring the ratio in line with stock and you'd be no worse off.

Originally Posted by NoHaveMSG

I believe he had the measurements in the NA build thread for the HKS stroker and they did what they needed to make it fit, not improve the ratio. It's one of the reasons he did his own custom rod and piston kit, along with wanting more displacement.

Also worth noting, everything I've found says stock FA20 rods are 129.3mm long, giving a rod to stroke ratio of 1.50:1.

[wbradley]

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.

[RedReplicant]

Originally Posted by wbradley

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.

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.

[NoHaveMSG]

Originally Posted by Tatsu333

Also worth noting, everything I've found says stock FA20 rods are 129.3mm long, giving a rod to stroke ratio of 1.50:1.

Yeah, you are right, I am wrong on that. I dunno where I got 1.2:1 from.

[Uplink]

Originally Posted by wbradley

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.

They do some interesting things with the full S1-S3 engines for FI, like oil jets to help cool the pistons.