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525 SC build questions

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Old 09-12-2017, 11:30 AM
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Default 525 SC build questions

Hey there...I have a 28 Nordic heat with a 525 sc(1997) and im going to do some building on it this winter...I have a couple questions as I am in the process of part buying...

1. For a cam I'm planning to go with one from Bob at marine kinetics...a custom grind I guess?? He seems to know exactly what I need lol
2. He's trying to sell me on AFR heads however I'm having a hard time justifying the money so I'm considering sticking with the stock 088's and do a little porting myself, clean the valves up, throw a new set of springs on them, and mill them to up the compression a little...I've been told I can safely be in the 8.4-8.8 range...does anyone know how to figure out how much to mill off the heads to get in this ballpark?? I'm going to do the milling myself at work just not sure how much to take off??
3. Going with a refurbed 6-71 from Dyers blowers as I had an old GMC blower laying around from a swap meet so for the money I cant pass it up...plant to run it at 7-8 lbs of boost at the most
4. Plan to pull the pistons, rering it, hone it, and put in new rod and main bearings while I'm there so that leads me to another question...would I be in better shape to replace the pistons vs. milling the heads?? Keep in mind I can mill them for free just need to figure out how much to take off..but I also want this built as "right" as possible for the money I'm willing to spend
5. What kind of power difference can I expect with my stock heads vs the AFR's??
6. I'm planning to run twin holley carbs off of an older 8 or 900 sc cant remember which it was...planned on jetting them to 700's...would that be sufficient for my setup?? also if anyone has jet size suggestions I'm all ears

Sorry for the long post just looking for as much help as possible...I'm a mechanic for a living however this is my first go at building a blower motor honestly so I want to make sure I don't make a pile of scrap metal hahaha

Thanks in advance!!

Stewart
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Old 09-12-2017, 02:42 PM
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I have never used Bob M nor ever had any contact with him. With that said, there are quite a few threads here about him. Some for, some against. Do some searching and make up your own mind.

Good luck
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Old 09-12-2017, 03:44 PM
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Oh really?? I've read nothing but good about him and that's why I was gonna go with him...I'll have to do some more searching I guess!!

Thanks!!!

Stewart
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Old 09-12-2017, 05:42 PM
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How much power are you trying to make?? what drive do you have??
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Old 09-12-2017, 06:27 PM
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No real power goal in mind...boat does 75 now stock...I'd love to see 80-85....according to that bob fella this combo should make a reliable 700 hp roughly...that was with the heads tho but I'm pretty confident I can get there on stick heads and still be "safe and efficient"

Drive is a bravo 1 with xz gear "upgrade" from cp performance...has a nose coned lower with a drive shower...boat had external steering as well....1.50 gears 28 p bravo 1 4 blade prop

stewart
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Old 09-12-2017, 06:59 PM
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no matter what you do to the gm heads they will never make power like a set of afr,s will.i built a pair of 454s for another oso member that made 691 hp with dyno headers.custom pistons at 9 to 1 c/r,a set of afr 305 heads with cnc chaimbers and a cam from bob madera.i was out in the boat with the owner last month and it runs very good.ps,the blowers are weiand 177s with singel holley 1025 carbs and mercury marine gen4 ignitions.with a 6.71 i would expect even better performance.
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Old 09-12-2017, 07:05 PM
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700 hp is going to eat bravos for breakfast.

Instead of milling heads, I would go with better pistons.. well I did go with better pistons lol....

You have a lot more blower than the 177. The combo Im putting together with a 731 roller cam, Al's heads, 8.5 compression and the 177 blower at 5 psi is supposed to come out over 600hp.
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Old 09-12-2017, 07:09 PM
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So I suppose the real question is are the heads worth the 2500-3000 right now...I totally understand yes they would be better hands down but are they gonna make the boat 750 hp and run 85 vs 600 hp and run 76?? I guess I'm really wondering as a best guess what the difference would be

thanks!!
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Old 09-12-2017, 07:12 PM
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Yea I'm kinda worried about the drive too however I'm hoping I can nurse it next summer and possibly do at a minimum an xr upgrade or better next winter...that's why I'm thinking maybe skip the heads for now and do the drive and heads next winter?? Idk thoughts?? Trust me I've been a boat mechanic for a looong time I understand what power does to bravos hahaha

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Old 09-12-2017, 07:15 PM
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Not offering any advice here, only info. I had a pair of bone stock 525 SC's years back, put the Superchillers on, changed out the pulleys to up the boost, little carb adjustments. All else left as Merc built them, never even took a valve cover off. Ran at 10 psi boost +/- and made 638 on a dyno in full in the boat trim. I ran them for many seasons with no issue before selling.

P.S. Was a Bravo killer.
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