525 sc ?
 

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

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.

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!

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.

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

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.

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

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...

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.

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.

I just did a 600 hp/ 600 tq 502 for 242LS, pretty easy mild mannered.

That changes things if you already have the setups but you could always peddle them and go a different direction. Do you have blocks? If so what displacement.

Here is my 509, Dart Pro1 heads, Dart intake, 10:1, built by Jim Valako.

622tq, 684hp

Better start stashing some money for drives while you are at it. I'm starting to wonder how long out poor old Bravo's are going to last when they have 600+ ft/lbs going through them. :eek:

Cool. Are they in the boat yet? Will you be making it down to peoria this summer?

[QUOTE=MILD THUNDER;
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.[/QUOTE]

Great Scott! Do you see some serious ****!

Have lots of parts,Just trying to get the best most reliable combo single engine application.

Nice pics and impressive numbers.

How do you post pics, Am I limited by the type of member I am?

I helped out OSO member Wayne272 on something similar. We talked over the phone a bunch regarding cam selection and parts to use, etc. He had a pair of stock 365HP 454 Mags. With a cam upgrade (stayed flat tappet due to budget reasons), the 177 Blower, GM rect port heads, few other odd's and ends, stock shortblocks, he made 590HP at 5400RPM, and over 600FT lbs from a very low rpm, with a peak boost psi around 4.5psi. I think he's VERY happy with how his boat performs compared to with the stock 365 mags.

Real nice power from a basic setup, with no fancy parts. Just GM iron heads and crane flat tappet cams.

Went with that cr mostly because if it was good enough for merc, its good enough for me. But also because i plan on different heads, a 110cc head will put me at 8 flat. The efi cams i had upgraded last year when it was still na. Didn't see much reason for another custom grind with plans of different heads and exhaust in the near future. Im quite happy even with this setup as they push my bathtub 87mph on just 6psi and stock merc/gil manifolds!

In the boat ready to go once mother nature starts cooperating. Couple hours on them already to get my first couple oil changes out of the way so were ready to boat. I think the first trip to Peoria is going to be for the 4th. Most likely stay at EPBC. What do you run? Ill have to keep an eye out!

If you go with a small blower and want to make efficient power, you need more compression and NOT more blower speed. With aluminum heads 8.25 :1 is no problem. Huffers look good and are fun but cost money and are somewhat high maintenance...kinda like a stripper.

Boat sold. Buying a biz. Hopefully something nice once some debt is payed down!

I'll probably be on a 18' sea ray with a tower and blue tribal decal, an old maroon 21' regal, or maybe dr. Bobs big 46 sea ray.

Thanks for the advice I will keep boost the same Pulley's seem to be an issue to change, and I will go with aluminum heads that should help with possible detination.
Any idea what size runners would be best, dart heads are usually what I use. also I usually put in the 2.3'' intake valves , Anyone know why merc put in smaller intake valves on th e525's?

[QUOTE=MILD THUNDER;4123250]I helped out OSO member Wayne272 on something similar. We talked over the phone a bunch regarding cam selection and parts to use, etc. He had a pair of stock 365HP 454 Mags. With a cam upgrade (stayed flat tappet due to budget reasons), the 177 Blower, GM rect port heads, few other odd's and ends, stock shortblocks, he made 590HP at 5400RPM, and over 600FT lbs from a very low rpm, with a peak boost psi around 4.5psi. I think he's VERY happy with how his boat performs compared to with the stock 365 mags.

Thanks, this looks like exactly what I want to do . I have a new roller cam sitting around will post the specs to see what you think if it is a good match or not.

The stock GM rect port heads, normally had 2.19 intake valves. They used a 2.25" intake valve on the HP engines like the 525, HP500, etc. 2.3 intake valve is pretty large if your using a 4.250 bore block.


Smallest rect port dart head in aluminum, would be the 310cc runner. Your 525sc intake will be for a rect port. You'll need to watch the port match, as the GM style rect port openings, are slightly different than the Dart's . They are actually a bit larger. Port matching them would be a good idea.

I have only built N/A engines, The merc specs for the 525 and 600sc engine used a 2.190 intake, I was just puzzled by why this was done.

Also the cam I have is a roller 587lift intake and 610exh. Intake open@ 33btdc closes75atdc .Exhaust opens@82btdc closes36atdc
Will this work or is it too much for this application.

Strippers are also known as huffers right? Seems fitting they are much alike. Lol

I know this is a bit of an older thread but... the 2.19 intake works better on the smaller 454 bore.

Interesting thread. I'm contemplating a lot of the same for my 242LS. A 540 NA would be great, but I'm weighing the costs all around.

I know this thread is older, but MildThunder, i am about to do the exact builds you were just describing here. I have 365 mag motors, stock except for Crane gold roller rockers & MSD distributers. Im about to get a set of 525sc blowers, and they come with a set of fresh 1050 Williams carbs, but i was wanting to at least throw a cam in them while i have them apart, and was also gonna stay flat tappet for cost purposes.... I have always had good luck with Comp so i was gonna either do a grind from their Xtreme Marine line, or one of their Blower cams. Both are right around 0.570ish lift, but the Blower cam is on a 114lsa versus the Xtreme Marine 112, would either of these be similar to the Crane that your buddy used? I'm running stock manifolds for the time being so I'm thinking 114lsa may be better? (Do NOT want any reversion issues). Didn't think i could get as highs 590hp but after reading your post I'm awfully impressed and kinda pumped to try it out!

Stock exhaust is going to hurt you. I am assuming you mean stock 365 cast iron exhaust.

,I currently run a flat tappet Comp cams CB 280AH-14 (.050 232 in/237ex, LS 114, lift .547 in/ex) in my .060 over 525SC with 8.5:1. It pulls much better than the HP500 carb motor I had as a spare wihile rebuilding the 525SC.
Agree, exhaust should be looked at, I have CMI E-tops.

Believe me, it's next on the list for sure, but it may just have to wait a little bit till funds recoop.

ANY cam upgrade worth doing will require an exhaust upgrade with long risers.
The stock 454mag exhaust will have reversion issues.

I might have exhaust that could work for you.... fairly cheap, too.

Whatcha got TomZ???

Merc 496 aluminum manifolds and risers. If you're going with a reasonable cam, the risers will work well. I'm using a 525 EFI cam in my blown 454, and I don't trust the risers in regard to reversion for my setup.

I picked up a set of Stainless Marines so these will be going up for sale. Anyway, just putting this all out there in case you could use it.

You could always extend the risers, to fully dry tails all the way thru the transom. We've done that a few times. I see no reason to run wet exhaust unless silent choice these days. Fully jacketed tails, with water dumping at the very end, works great, and if too loud, clamp on mufflers work as well with that setup.

That was my plan originally (I had about a foot of stainless welded to the risers), but the angles wouldn't work right with regard to the transom. The Stainless Marine exhaust fixes that. The risers will run dry to the tips.