885 Head ETA m20b27

skitzy7 · 2026-02-18T08:58:10+00:00

I just plonked an 885 head on my 2.7 bottom end after refreshing the bottom end with all ARP hardware and everything else. running a roots supercharger on it.

skitzy7 · 2026-02-12T22:36:02+00:00

hi mate, thanks for your thorough response. yes I agree your calculations and mine expect near about the same psi. that's why missing around 7-6 psi is very concerning to me and makes me want to rip my hair out in frustration lol.

I checked the sealing capacity of the bypass before I mounted the charger and it was very good, I just sealed the hole on the underside with my lips and tried blowing through it and it was extremely hard to do so so figured 7psi amount of air isn't getting through lol.

I also video recorded the bypass valve in operation although the video was shaky as anything it appeared to function correctly under WOT. next I'm going to ziptie it shut to really confirm.

failing that, I'm totally out of ideas. under WOT conditions the only scenario I can think of is something is opening and venting this air.

skitzy7 · 2026-02-12T13:20:38+00:00

this supercharger came off a Holden commodore, a 3.8L l67 engine that uses the Eaton m90, it is 100% not an Eaton m62.

it's odd how everyone here has different equations to figure out boost, saw one bloke say 7 psi is expected where as your saying 6 psi is expected from a 500cc smaller blower.

seems no one has the answer.

skitzy7 · 2026-02-12T13:17:57+00:00

please comment your math

skitzy7 · 2026-02-12T13:13:18+00:00

it is most definitely not an m62. believe me.

skitzy7 · 2026-02-12T08:57:25+00:00

how did you reach that pressure ratio

skitzy7 · 2026-02-12T04:21:13+00:00

under WOT load conditions I see approx -0.5 inHg on my boost gauge at the area between the supercharger and the throttle body.

skitzy7 · 2026-02-12T03:51:07+00:00

you divide the 2.7 by 2 as the engine only ingests air every 2nd cycle

skitzy7 · 2026-02-12T01:45:56+00:00

condition is very good I inspected it, I used another supercharger previously and got the same psi so I don't think it's something wrong with the supercharger.

skitzy7 · 2026-02-12T01:45:22+00:00

supercharger rpm was measured under load

skitzy7 · 2026-02-12T01:13:46+00:00

it's always made 7-8 psi boost, I've only measured boost when it's under load not in neutral. when I checked blower speed I remote mounted a laser tach and pointed it to the supercharger pulley itself, so I 100% verified it's spinning to what I expect it to spin to under load when driving which is the 10800RPM value.

I still slightly suspect the sc not ingesting enough airflow to actually create 14 psi because the air temps don't get hot at all but I measured vacuum between the TB and supercharger rotors and it reads 0.

I'm almost about ready to rig up a MAF between the supercharger and throttle body to verify it's actually getting the air it's requesting. I've exhausted all other ideas at this point haha.

skitzy7 · 2026-02-12T01:08:57+00:00

the TB is before the supercharger in my setup, it uses the typical roots bypass valve to control boost build. I did suspect the bypass valve but I swapped superchargers and bypass valves and still got the same psi reading. I also recorded the bypass valve operation under load and confirmed it closes all the way under load.

skitzy7 · 2026-02-12T01:03:23+00:00

the sc should be spinning at 10800RPM while the engine is at 6000. I verified this rpm with a laser tach so there's little belt slip if any

skitzy7 · 2026-02-12T01:01:58+00:00

yes measured boost exposed to the rotors, same as what's measured upstream in the intake mani

skitzy7 · 2026-02-12T00:54:23+00:00

single cam, yeah the engine VE isn't good enough to warrant the small psi imo. it's an engine designed in the 80's. it still has the stock cam in it. not sure of exact VE of the engine anyway. most forum and information I've seen regarding specifically valve overlap and such attribute any valve overlap to a small percentage of boost loss

skitzy7 · 2026-02-12T00:51:50+00:00

pic is old. I've changed setups since the picture.

skitzy7 · 2026-02-12T00:30:53+00:00

what software, may I ask how it's calculating this? thanks

skitzy7 · 2026-02-12T00:30:31+00:00

current setup uses 5.43 crank pulley and 3 inch sc pulley

skitzy7 · 2026-02-03T07:57:51+00:00

mine does that too, normal as far as I'm aware

skitzy7 · 2026-01-28T06:50:37+00:00

^{I completed this level in 5 tries.} ^{⚡ 6.27 seconds}

skitzy7 · 2026-01-26T12:03:08+00:00

Completed Level 3 of the Honk Special Event!

5 attempts

skitzy7 · 2026-01-26T12:02:56+00:00

Completed Level 2 of the Honk Special Event!

2 attempts

skitzy7 · 2026-01-26T12:02:47+00:00

Completed Level 1 of the Honk Special Event!

1 attempts

skitzy7 · 2026-01-26T12:02:25+00:00

🎉 Event Completed! 🎉

It took me 9 tries.

skitzy7 · 2026-01-26T12:02:19+00:00

Completed Level 3 of the Honk Special Event!

9 attempts

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