actionmarineguy

I am gathering parts to put together a 525 sc engine to put into a 25' warlock cat.
I have all the specs from merc. figured I would copy them since they did the r & d
anyone have opinions on the 7.5 :1 comp ratio and the smaller intake valves 2.190
Was planning to use a 454 like they did. Possibly alum heads.
I also have a 502 with alum heads wondering how much that would affect the boost?

Any opinions would be appreciated. thanks Guy.

wanted to post pictures? can't figure out how

phragle

Im not an engine guy, nor do I play one on TV... but a lot has changed since the 525sc was set up. From what I have researched, your better off with a 250 blower than the 177, less heat buildup. Cams and heads are lightyears ahead of 525sc. with semi decent heads, the 250 blower and a better cam you should be over 600 in a realitvely low state of tune and it should be pretty bullet proof.

Rbesola

I just built similar engines. I started with hp500s though. Dropped compression to 7.6. Used a 525efi cam. Original heads. And 420 blowers, intercooled. Basically hp600 clones but intercooled and pushing more boost. I know you have to draw the line somewhere but id definitely overbuild it that way you have room to grow. Start with the 502 and the biggest blower you can get your hands on. Nobody said you have to use it to its limits. Heat is the enemy!

mike tkach

when mercury designed the sc525 they had longevity in mind more than performance.the 7.5 compression ratio is to low imo and gives up a lot of power and the camshaft is very mild.i agree the 177 blower is to small for a 454 and a b&m 250 would be better.an 8.71 or a b&m 420 will do wonders with the right components.the gm rectangle port heads do not flow very good. mild thunder has .060 over 454s with b&m 420s making 800+ hp and are very reliable.if i remember correctly his compression is near 9 to 1 and he only runs about 6 lbs of boost and he has dart aluminum heads and fairly aggressive hyd roller cams.im sure he will see this thread and chime in on the subject.

mike tkach

im curious as to why you went with 7.6 to 1 compression ratio and a 525 efi cam?

MILD THUNDER

What you don't want to do, is drop the compression way down, AND use a small blower like a 177. If, the 177 is the only option, than I would build the engine with at least around 8.5:1 compression, to keep the engine making more power ''ON MOTOR", rather than relying on the blower to make the power.

The 525sc was a good engine in its day, but far from a powerhouse by todays standards. With a 454, modern heads, modern hydraulic roller camshaft, you can make that power N/A no problem. I would prefer not to have the compression at 7.5:1, unless it was gonna be a very high boost style setup. If you shop the internet, usually you can find a very good deal on a 420 B&M blower setup, for not much more than a 177/250 blower. The key to power in these engines is in the cam/cylinder head/blower combo. Don't be led into the theory that cylinder heads don't matter as much on a forced induction engine, because they are critical. A good set of aftermarket aluminum heads, a large underdriven blower, the right tune, the right cam, and you'll have a reliable setup that will snap your neck when you hit the throttles and last a very long time.

Ive had the same engine combo for a long time, with different blowers, starting from 177, then 250, then 420. Each time I upgraded the blower, the boat went faster, at the same or less boost. 5psi with 177 netted me 79mph. 7psi with a 250 blower, netted me 83mph. 6psi with 420 blower netted me 88mph.

badluck

I would bump up the compression to 8.5:1 along with 5psi boost.

ezstriper

I agree with run more compression, not to mention those pistons are hard to come by, and switch over to a Hyd roller cam...Bob M. can dial you in on that...I did a 525SC clone a few years back and worked well, I used a different blower cam and a 850, also be very careful on a flame arrester, used a nice one from a high performance marine place and made NO boost...

JRider

I think you would be better off with a HP500 carb style motor. You can pull 600hp out of an NA 502 or 509 easily, possibly with iron heads. Single carb, single plane, hydraulic roller and 9.5:1 aluminum headed motor...simplicity at its best.

actionmarineguy

Thanks for all the input,
I know there are better options but have 2 complete setups sitting on a shelf.( Minus 1 lower pulley if anyone has one). just looking for a reliable setup with the Cool factor of the blower, I would be fine with the 525 hp but since I am building a engine anyway small improvements would be great as long as reliability is not affected. It does seem to be hard to find an off the shelf piston under 8.0:1 cr.