fantastixvoyage

iTrader: (1)

Well I finally popped a head to see what I'm working with on my motor before I put a small 525sc blower on it. I hope to run 6lbs or boost and make 575-600hp. This motor is just an intermediate motor till I can do a full build this winter. Figure some peeps on here may have some insite on the half-a$$ attempt. Found some good and bad. (everything does look fresh)

Pistons: GM #3999295, GM 9:1 - semi domed!
Where can I find the cc displacement of the dome???Obviously the semi-domed piston raised some concerns as flat top or reverse dome are typically used in a blower specific app. i was suprised to find these pistons advertised at 9:1. I do have VERY large chamber heads so should be close to the advertised 9:1.

Heads: GM Rec. #14096188 The internet states rect.port, open chamber (116cc), 310 runners. LS-6, IV service part and 454HO crate motors. Ok valves, roller cam springs, crane gold roller rockers.

Cam: custom Ultradyne grind (solid, roller). made a call, waiting on the cam card but they stated it as good, mild choice for a marine blower application.

Lower End: Stock GM forged, rods are 7/16"

Ignition: Full MSD

Now my questions:

-Where to find piston dome cc of a stock GM part?
-Spark timing and carb recommendations? what does a 525sc run (timing and carb cfm)
-Head Gaskests - plan to run the thickest i can find through Fel-pro. best i've found is .053 = 14.5cc. will they withstand boost?
- Max boost with 9:1 comp???

Other thoughts?

PatriYacht

Don't use the thick head gasket. Messing with the quench distance will cause worse detonation if anything. If your block is standard deck they're .015 down in the hole already. Ideal piston to head distance is .040 so with a FelPro gasket you're already at about .055. Merc used to publish the comp. ratio of those engines as 8.8 to 1. I don't see any problems running low boost with 93 octane.

rdoactive

Correct me if I'm wrong, but I think the merc 525SC was under 8:1, ran about 5psi and 32 or 34 total timing. Carb was holley dominator.
Hawk made a 525SC with higher compression, around 8.5:1, 4.5 psi, but only was able to run around 26-28 total advance. Carb was a reworked holley 850. Heard it flowed around 950.
Both used premium, 92 octane.
I had a pair of the Hawks in my old cat. Spinning the 177 blower to 7 psi gave around 575hp, but required higher octane. BTW, getting 7 psi was really spinning that blower fast.
Gary

Turbojack

You already have the head off. Just change the pistons & then you will not have to worry about the motor staying together everytime you go WOT. Detonation will finish a motor off faster than you think. Then you will be doing a major overhall before this winter.

DRIPPINWETII

7.5:1 COMP 35 degrees total timing.

articfriends

iTrader: (1)

If your going to run a 525sc blower with those pistons buy a innercooler to help suppress detonation. Guys are running whipples and prochargers with innercoolers on exactly the same motors on pump gas,Smitty

Smitty

iTrader: (1)

Comp. should be no more than 8 to 1
Do not expect that blower to make more than 5 lbs boost without hurting something. You can go with more boost if you use a superchiller or equiv cooler.
Use a good (big) cam to make good power and the blower will only help. Crane 731 or 741 are good choices.

Also make sure to have a very good oil cooler because you need to remove heat. Also do not run a thermostat and if you install a chiller make sure to feed it from its own water supply. Do not use the seawater pump.

rdoactive

Wow, I was way off!

baronbob

I said it before I will say it again Drop the max timing 1deg/# of boost. If you decide to push it have someone in the engine compartment who can hear detonation. The comments on intake cooling are all correct. I installed a duel channel T/C reader and saw 250F before the cooler and 190F after. Do this put a cooler in . I detonated a brand new motor in one pass with the knock sensor pulling the timing too late. Cost me $4,000. Detonation is your enemy. Don't let it happen!! Cam, heads, exhaust pistons, intake, carb. and boost all add up to big HP gains. The end of the trail is detonation. I think everyone is trying to tell you that. Ask Mark @ precision about carb, jetting, Fuel pressure. I hope you appreciate the input you age getting. Good luck and keep us posted.

Back4More

http://www.holley.com/data/TechServi...ech%20Info.pdf

Some good basic info