What blower are you running?? Might want to do the math and make sure your not spinning it too high.

My bad. I misread where you were getting the vacuum reading from.

I'm curious to what blower as well. I had a small b&m 250 on my 509 and I ran a 30p bravo (4blade) to 5500 on my 280 velocity. I would think a blown 500ci engine would spin a bigger prop in a 23ft boat. Maybe I'm missing something?

Nope. Its a SMALL 174. Merc Had a rev limit of 5200 with that blower (from what I can find out). I don't want to push my luck with running it at 5600/5800. If I had a 250 I'm sure I could spin a 30. CP, how much did you velocity weight and what kind of speed were you hitting? 77/78 feels great. Im sure 85 ish would fell better...lol

Im also only running 26 total timing.

By trying to run it safe by retarding timing, fat jets and not overdriving it.
I think you have a small restrictive heat pump on that engine. It might be hurting you more than helping.

omg, those exhaust valves must be glowing red.

Running so little timing will cause the EGT's go way up and increase the risk of detonation. I would bump the timing to 30*.

The blower is also small for for a 496. What size pulleys are you running and how much boost????

The rev limiter on a 525SC was 5350rpms and the blower was overdriven at a 2:1 ratio for a blower rpm 10,700rpms.
The max rated rpm for the 177 blower was 13,500rpms.

The plugs show no signs of detonation and the burn on the plugs electrode look good. (mark is on the bend). I have about 30 hrs or so on this setup. I was going to bump up the timing up to 30 but the plate on the blower (Hawk Marine/ old blower/new Teflon/ great shape) listed timing at 25. I am learning as I go with a blower setup. I am one size smaller from stock on the top pulley to compensate for the Supper Chiller. Temp gun on blower intake is about 130 and I want to say the manifolds are about 170 at the base and warm on the riser. Engine temp never over 120. Run hard and have never lost boost due to heat. Griff, If you were to run 30 would you keep the V6 module (14 total) with 16 base or go back to the V8 (24 total) and base @ 6.

You want to keep the V6 module. But keep in mind it does not provide 14* of advance on a V8. I forget, but I wanna say it's like 8-10* when used on a V8. Just set the total and let the initial fall wherever it does.

Big block Chevys love ignition lead. Back in the early days of supercharging marine engines, guys thought it was being safe by retarding the fuk out of the timing. The #1 reason engines with superchargers fail is lack of fuel. Make sure you have a safe AFR, then give it some timing. This is where a dyno comes in handy.

I like to get the AFR where it needs to be, then add/subtract timing and watch the EGT. Just a FYI , mercury ran 35* total on the 525sc, and 33* total on the 600sc. Granted they were low static compression. Going from say 30 to 32 might pick up a measly 5-10hp, but it's about keeping the exhaust valves cool and cylinder temps down