496 to 525sc conversion ???
 

Last year i put together a nice 496 , has scat forged crank ,hbeam rods , hp 500 roller cam , rec port heads with iconell valves , balance job , forged pistons 8.5 to 1 ,main and stud girdles on rockers , it runs low 70s in a 23ft boat at 5000 with 25 prop , then i came across this on ebay

http://cgi.ebay.com/ebaymotors/ws/eB...K%3AMEWNX%3AIT

I have a few questions it came with a dominator carb i was looking at it and theres a vacuum port on the one side of the carb but nothing runs on vacuum on my boat is it vacuum or is a signal for boost to power valve ,
Next did the 525s have the same ignition as the 454 mag im thinking of going msd anyways but just curious
I also need a pulley for blower what size did merc put on from the factory id like to start low and see how it is
And spark plugs do i need a different heat range for the sc
Is there anything i should be aware of or missed to do this job right

Looks like you got a good buy. As far as the vacuum port goes I would just plug it of. From what I remember it doesn't go to anything. Don't quote me on that though. It's been a while. Sounds like you have a good foundation however are you planning to change your pistons for lower comp. I wouldn't think you'd want to run more than 2 to 3 pounds of boost. The other option would be to pull your heads and hog out the chambers. if there stock they should be 119 cc's. You can lose a lot of material there and also help performance as well. Jut not sure what would be more cost effective. I haven't looked at the profiles of the 525 sc cam but you may want to look at that for comparison of the HP 500 cam. It's been a while since I messed with blowers however there are a lot of people on the board who run them and can perhaps help you better.

Good luck,
John

PS the ignitions are different.

IMO, the 177 is really too small for anything more tan a 454. I would go with a 250 blower. The 8.5CR is not a problem and you should be able to run 5# of boost.

The 525SC has the same ignition, except the advance module is different. The 525SC also has an external rev limiter.

Stock pulley ratio is 2:1. I think 3.5" upper and 7" lower. It makes 5.5# of boost on a 454. On a 496, it would probably make 4.5# or so. You will not find any larger upper pulleys to fit the Merc 177, just smaller ones.

Couple thoughts for you since I did the exact thing to my 470cid 454s 2 yrs ago.
1. The merc came with an input shaft in the blower that was spline like. You won't be able to find any pulleys like that unless maybe you want to buy the 2 I have. Best bet though is to change the shafts to the keyed shafts. They are available at jegs and that is what I did.
2. I run 9.5:1 compression and 5 psi boost. I gained 10mph and have a achieved a speed of 91.4mph my old straight vee, so you can make good power.
3. I got greedy at the end of the season and went to 6.2 lbs boost. I ended up lifting a head and melting 3 pistons. I did get an all time record of 94mph tho so its all good and now I know my limit boost wise.
4. I run aluminum heads which allows a little more boost.
5. I run the same cam as the hp500 I believe which is the 731 crane.
6. I estimate to get my boat going 94mph each engine is making around 700hp. Not bad for that little blower and it is my compression that is crutching up the undersized blower, which is just fine in my opinion.
7. One concern is ring end gaps. You need to open them up for boost power or risk them butting. What did you set the top ring gap at?
8. Run cometic head gaskets and if you are in there, make sure your quench is set tight (.037 would be good). This prevents detonation.

I think you will be very happy with your results. Plug that vacuum port, run 98 jets all around with 4.5pvs and your a/f will be right around 11.8afr at WOT and use 93 octane or higher. I did lots of testing with an O2 meter. I use NGK vee groove #9 plugs and have no fouling issues. 30* total timing.

BT :drink:

i think someone may have already changed the shaft then because it has a keyed shaft , so what do I buy a pulley for?

That looks like one of the earlier blower units. It might even be the smaller 147 I think it was. Your not going to get alot of power out of it but their fun to play with and they sound cool. Even if you find the pullys at best you might get 5lbs out of it so I don't think comp. is going to be a problem. Seems a little strange that it has a dominator on it might be jetted way down. Could be too much carb. If you go with MSD'a, go with the marine or off road stuff. The car stuff won't hold up to the constant pounding. The B&M 250's or 420's would be the way to go. I have a pair of complete dual carbed 250's taking up space in my shop.

whats the 250 worth and what carbs

Worth? Tough one. I paid $3,500. each, too much I think but I needed them I thought at the time. The carbs are Holleys, worked by someone but at the moment I'm at my office and can't remember who. Their complete from intakes to air cleaners with linkage ect. Came off of running engines. Boat had a cabin fire and then sat for awhile. They where polished units but need a good cleaning up and polishing. I rubbed a fw places and the crud comes right off. I'll take $3000. each and I'll ship for free to the lower 48. I have a pair of 468's that I was going to use these on that are available as well. I went a different route with new 540's.

You can just buy wieand 10 rib pulleys then off jegs or summit. They are $120 each. I started with 3.75 diameter with about 3.5psi, then to 3.5" pulleys at 5psi and last was 3.25" pulleys that made 6.2 psi.

BTW, the 525sc came stock with the 1050 dominators with close to the jetting I called out above. I'm pretty sure you will be pleased with the pop this blower gives you although if you could bump your compression up a bit it would be even better.

Somebody stole that blower in the auction-$809!!. That IS a Weiand 177 made for merc, with the Dominator flange cast on the case instead of the smaller flange the street blowers used.

If you want to run one of those you would be better off getting a marine weiand 177 set up, parts much easier to come up with, merc specialized some parts and now some imposssible to find....I ran one on a 489 worked awsome...Rob

ya i bought it off ebay it took 3 weeks to get but im satisfied now, i was worried for awhile seller wouldnt return any emails then 1 day it showed up

Sorry Stingray for the incorrect info. To my knowledge - After thinking about it with 7.5 pds of boost it would in effect only bump your compression to near 9.5/1. It's been several years but I did look back and realized that I had used the 731 cam with the 177's on one set up and it worked fine. It wasn't long after that set up I went to 420 mega blowers and different cams 741's. (FUN) Those made just over 660 HP on the dyno. I still like the 177's though. Like Griff mentioned you may be just a tad small for a 496 CI however set up properly you'll have a good reliable package and make some noticable power also. Regardless of what you do though I would consider boost retard. You never know what kind of fuel you might get stuck with. Just a little insurance depending on what you do with pullies. You kind of got me thinking now. I still have the 525 SC blowers with very low hours. I might have to strap those on my 496's next year. HMMM.

Good luck and have fun.

That would be a good thing. It will give you a lot more pulley options. With your 8.5 static comp ratio, you should easily be able to run 5# of boost. That will give you an effective compression ratio of about 11.5:1 under full boost and you will be able to run 92-93 ocatne fuel.

Here is a good tech pdf from Holley's website. http://www.holley.com/data/TechServi...ech%20Info.pdf

"Regardless of what you do though I would consider boost retard"
Not sure what this means , is that part of a msd setup or just set the timing back? Because before i even put the blower on im going to put a msd on i have been fighting a top end miss all last season when i get to last 200 rpms it sounds like im hitting rev limiter i chaged props back to 23 then i revved higher and the last 2-300 rpms same thing i think i have it narrowed down to ignition , as i have a stock thunerbolt on a high performance engine , figure a marine msd can't hurt anything,

MSD offer a nice one that is easily controllable either at the dash or in the engine compartment.

Boost retard = retards (pulls out) ign. timing as boost goes up. If you try to run higher amounts of boost with same total timing #'s you will have detonation and that can lead to pistion, rings, bearing failure. So your options are to set timimg lower and live with less preformance under low boost cond. Set timing norm and limit boost so you don't get detonation. Or install a boost retard, so you can run your norm timing settings and as the retard box see's a pressure on it, it pulls timing out.

Most are adjustable for boost and degrees of timing. So you can set it for say.. For every 1 psi boost, it retards timing by X amount of degrees

GOOD INFO>

I really don't see any reason for a boost retard system in a low boost application. Just set total timing to about 30*. You could probably just run the timing locked at 30* or maybe set up the distributor with 10-15* of advance all in by 3500rpms and then set base timing at 15-20*.

could not retarding the timing cause head gasket failure?

I started cleaning and inspecting all my sc components lately and everything looks good but the intake it has been in salt water and its very corroded t stat is all ate out of intake and coolant jackets entering intake have been dev coned and someone did a terrible job doing it then there is a blower stud snapped off flush tried drilling it, it will not drill cant tell if its stainless or if someone broke a bit off in it anyways , I guess i either need a used intake or can you still buy these from b and m or weind , not sure what to do but id like to get things organized before long it will be time to start working on it , any help would be appreciated

The 525SC intakes are very hard to come by used and Merc wants about 4 times the $$$ that they are worth. Mine had salt usage before I got it and was flushed and well taken care of. Still it had some heavy salt damage around the water ports and Tstat. I think it cost me about $300 to get it all welded up. I think the studs are stainless, but not sure. Chances are its seized because of salt and being dissimilar metals.

would this work , the only diff i see is the thermostat location is slightly diff but i have a holley strip dominator on there now with the same location, i dont know maybe the sc will interfere with the 4 port housing

http://www.holley.com/6130WIN.asp

Put some pics up of the corrosion. If that is ok, I'm sure we can get the stud out one way or another. For much less than $550.