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.