HJS 200 cell
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Instructor
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HJS 200 cell
Back in my day HJS made the best catalytic converters for street and race.
Does anyone know if any of the current C8 exhaust components suppliers use HJS as a core?
Does anyone know if HJS is still the highest flowing kettle converter?
Does anyone know if any of the current C8 exhaust components suppliers use HJS as a core?
Does anyone know if HJS is still the highest flowing kettle converter?
Melting Slicks
Joined: Aug 2000
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From: Early 2020 Z51 Coupe, Original Owner, Ahwatukee Foothills, AZ
I've had my HJS Cats now over 3 years, they match up perfect with my headers and the Z51 performance NPP exhaust. Fabspeed and Soul believe are the largest sellers of these Cats today. These high quality 200 cell Kevlar wrapped Cats never have thrown me a CEL, they are pricey but in my opinion worth it and second to none.
Race Director
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From: Fulshear, TX
HJS = Fabspeed & Soul
GESi = Corsa, Cicio, Kooks, aFe, Paragon, etc.
You may be thinking about Kooks headers, which have been proven to lose power when paired with the factory cats.
Race Director
Joined: Jan 2014
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From: Fulshear, TX
I've had my HJS Cats now over 3 years, they match up perfect with my headers and the Z51 performance NPP exhaust. Fabspeed and Soul believe are the largest sellers of these Cats today. These high quality 200 cell Kevlar wrapped Cats never have thrown me a CEL, they are pricey but in my opinion worth it and second to none.
Le Mans Master
Joined: Jun 2005
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From: Texas
Not true, assuming you're talking about quality cores such as HJS (German) or GESi (North American). The generic Chinese junk is a crapshoot.
HJS = Fabspeed & Soul
GESi = Corsa, Cicio, Kooks, aFe, Paragon, etc.
You may be thinking about Kooks headers, which have been proven to lose power when paired with the factory cats.
HJS = Fabspeed & Soul
GESi = Corsa, Cicio, Kooks, aFe, Paragon, etc.
You may be thinking about Kooks headers, which have been proven to lose power when paired with the factory cats.
The larger 6" stock cats out performed the higher flowing but smaller 4" performance cats. Hats off to GM for building a great cat.
Granted they didn't name the cat manufacturer so it's left to interpretation. I haven't seen anyone do a comparison that wasn't trying to sell you their product so I honestly don't know. I can state what they have done with my other cars though. Question is if anyone dynoed before and after on a C8.
Race Director
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From: Fulshear, TX
4.0" is a small-ish core at our power levels, and I think Paragon was (past tense) the only legitimate shop actually using a core that size on the C8. My guess is ARH was attempting to use the same generic 200-cell (see my earlier comment above) they used on their C7 header systems. C7 cats are much more restrictive compared to the C8's (partly because of the inlet flange design), so you could still see gains using the cheap generic 4.0" cores (C7 also had four cats from the factory vs. the C8's two).
Last edited by Kracka; Apr 19, 2024 at 09:11 AM.
Melting Slicks
Joined: Jun 2001
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Same experience with my Corsas, but yes, the HJS 200-cells will ultimately outflow my 400-cell GESi G-Sport S-Wound cores. I took a slightly different approach and had my cats ceramic coated to match my aFe headers; engine bay temps remain consistently cooler than they were when stock. I'm still happy with my setup 2+ years later
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Race Director
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From: Fulshear, TX
Same oven thermometer I used to measure trunk temps before/after adding the additional thermal barrier. It's also obvious based on how the after-run cooling fan operates after engine shutdown (especially during TX summers).
I'm > +30whp (DynoJet) vs. stock at this point, which includes all my mods, not just hot side. I haven't dyno'd since adding the Borla, but I'm due to get back on.
Driving my car vs. stock is night & day, both in my eyes, and those who own the stock cars. Headers were the single biggest power adder. Overall response and increase in top-end pull is notable. The LT1/LT2 is a total dog above 5k RPM in stock form.
I'm > +30whp (DynoJet) vs. stock at this point, which includes all my mods, not just hot side. I haven't dyno'd since adding the Borla, but I'm due to get back on.
Driving my car vs. stock is night & day, both in my eyes, and those who own the stock cars. Headers were the single biggest power adder. Overall response and increase in top-end pull is notable. The LT1/LT2 is a total dog above 5k RPM in stock form.
Last edited by Kracka; Apr 19, 2024 at 10:48 AM.
Melting Slicks
Joined: Jun 2001
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Thanks for the info, just ordered the DEI heat wrap. Next come exhaust upgrades. But first LS Fest next week. Hope to see a strong corvette presence.
Last edited by itsonlyairandfuel; Apr 19, 2024 at 11:20 AM.
Race Director
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From: Fulshear, TX
- aFe headers: Cerakote Copper ceramic coated (internal) & Cerakote Titanium V-164 ceramic coated (external)
- Corsa cats: Cerakote Glacier Titanium C-7900 ceramic coated (external)
- Borla exhaust: their standard heatshields + DEI Titanium header wrap at the inlets, below the airbox
- Trunk: DEI Reflect-A-Cool (silver) adhesive sheets on the backside of the trunk carpeting
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Great info!
Does anyone know the specs on the stock cats?
Sounds like stock maybe 6”/150mm dia, and maybe 3-400 cpsi, whereas aftermarket is 4-5” and 200 cpsi?
What is reason for the O2 spacer? Seems like he would add his hysteresis into a closed system?
Does anyone know the specs on the stock cats?
Sounds like stock maybe 6”/150mm dia, and maybe 3-400 cpsi, whereas aftermarket is 4-5” and 200 cpsi?
What is reason for the O2 spacer? Seems like he would add his hysteresis into a closed system?
Race Director
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From: Fulshear, TX
The spacer is to prevent a CEL from a cat that isn't quite efficient enough at scrubbing the exhaust to prevent a light.
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Instructor
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Wow…scrubbers indeed…700 cpsi stock vs 200 from hjs.
Has anyone measured free flow area or bench tested flow rate between stick and aftermarket?
Has anyone measured free flow area or bench tested flow rate between stick and aftermarket?
Melting Slicks
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Thread Starter
Instructor
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so this begs the question what cat Configuration wont throwing a CEO light and will equal the same flow rate as a straight ~3 inch pipe?
For example, if the stock is 700 cell per square inch, and we want to go to a 350 cells per square inch what’s the increase in cat core diameter required ?
For example, if the stock is 700 cell per square inch, and we want to go to a 350 cells per square inch what’s the increase in cat core diameter required ?
I have asked that question in the past. I suspect it it very restrictive. You Just Have To Get In The Seat | Lawn Tractors (youtube.com)
Melting Slicks
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From: SUFFIELD CT USA 2023 C8 CORVETTE UN-MODIFIED FINALIST
2023 C8 of the Year Finalist - Unmodified
Race Director
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From: Fulshear, TX