WetWilly

I recently purchased a '95 Scarab 31 with twin HP 450's and "Performance" Bravo's. They have Gil Exhaust with switchable mufflers on the transom. The props are Mirage with the following numbers 48-13247-25 and 48-13248-25 which seem to be 25 Pitch but what diameter? Also, the edges are rough and tips have some dings which I will get fixed this winter. Boat ran mid 70's with this combo but I think we were hitting the limiter @ 5200. I don't know a lot about these engines, any concerns? Valves or springs like the 500? Any mods to get more HP out of them? They already seem to have good hard parts. What would anyone estimate top speed to be?

KAAMA

Yes, those are decent baseline engines with the exhaust system they come with. I believe they have the GM rectangle port heads which are really a little too large for a 454. You could have some wedges installed in the intake runners and do some short side radius work and clean up pocket/bowl areas and unshroud the valves. Another thing that would unshroud the valves is to "bore notch" the cylinders bores---you have to know what the hey your doing to make sure this is done correctly. I'm not sure if the HP450's have a hydraulic roller cam or not. If they don't it would be a good thing to have and make even more power. With the correct headwork and cam. You could see maybe another 50-75hp gain. "JimV" does a pretty good job with installing wedges.

JaayTeee

HP450's were made, 1995, and 1996,
they do have hyd. roller cam's.
a friend of mine just bought a boat
with these engines and was wondering
about some of the same issue's.
so i checked on mercruiser parts.com,
valve springs ARE the same as HP500'S
it seems to me, that, the older {pre 98"}
HP500'S didn't have the spring breakage
problems, you may be ok, depending on
hours.
friends 31' profile with these engines
ran 79 mph on gps, running 27 pitch
mirages.
hope this helps.
jt

Griff

Here are the some specs for an HP450:

454CID
8.8 comp ratio GM forged pistons
Rect port heads with 2.225int/1.88exh
Dart Aluminum Single plane intake
Hyd roller cam .576/.598 lift with 284/292 duration @.050
Dart Aluminum Single plane intake
Holley 800cfm carb
TB IV ignition with rev limiter
Timing in my manual shows 2 different things.
In the specs section it shows 18*@ idle and 32*@3800rpms
In the timing curves section it shows 18*@ idle and 38*@ 3000rpms. Not sure which is right.

KAAMA

Griff, Do you think those might be more like advertised duration numbers on the cam vs. @ .050 numbers? I could be wrong, but it sure sounds to be unless it's perhaps a "typo".

WetWilly, with the specs that have been listed that engine is actually pretty good right out of the box for 454 cubes. With the wedges installed and some bore notching on the cylinder bores I would say you'd be between 500-525hp. Then later if you went to bigger cubes like a 502 or 509 those heads with wedges installed would still be awesome. In fact, you could still use all the other parts you have from the HP450 like; intakes, cams, heads, carbs, cranks, rods, exhaust manifolds and install them in/on a 502 cube block and be about 50hp ahead of the 454. With the 502, you'd only need to buy larger pistons ---and the bare 502" blocks themselves of course. But if you want to give those engines more of a "KICK" the wedges installed in those GM heads whether it's a 454 or a 502 is a real good way to go. Have fun.

WetWilly

Thanks all for answers so far, KAAMA how to get in touch with "JimV" on wedges - that sounds interesting. Also, any other ideas of speed? I think that Profile is a lighter boat than the 31' Scarab @7,900 dry weight out of the catalog. I may try a set of 27" to see if overall performance improves. This boat seem less efficent than my last one at lower RPM.

KAAMA

WetWilly, It all depends on how much $$$ you're willing to spend! There isn't much more you can do to those 454's unless you put blowers on them but you'll really have to lay down the SMACK for those! But if you really want to save a good chunk of cash and stay with what you have (naturally aspirated 454's) have the blocks "bore notched" and then you can get a quote for some wedged heads from JimV 616-735-0800. He also does bore notching. Like I have said; the HP450's are pretty good right out of the box with exhaust system they come with (GIL). The only RELIABLE way to enhance them for any further gain without supercharging them are the wedges and the bore notch job. I would say even those hydraulic roller cams that come stock in those HP450's are even good enough and you'll save BIG money there as well. At this point the wedges and the bore notch will give it the best kick in the pants you're looking for with those particular engines. Just my .02

You might think of having your props lab finished as well. York propeller does an excellent job 714-773-5444 California

Ratchet

Wet Willy ....here's some food for thought (speed). These are some 31 scarabs I know of & their speeds

Mine - 1994, fully loaded thunder package (as heavy as they come) -70 - 71 on GPS with 355 small blocks . I estimate 430 or so hp

My friends - 1991 (I think) - 502's carbed - 70-71
this one used to run 84-85 with 620 HP 555's

My other friends 1992 (I think) - 502 efi's, Imco exhaust - 72-73

My other Friends - 1994, I dentical to mine.........approx 500-525 HP 509's - 78 - 80

Just tryin to give you an idea of the different power we have & the speeds.

I'd be willing to bet with the mods talked about, you'd see 76-78 or so ?

Good luck.....let us know whatcha end up with.

Griff

I'm sure you are right and they are advertised durations. I was just copying specs out my Merc HP Manual without really thinking about them. It does say those #'s at .050, but that would be about the 5th mistake I found in the manual. No wonder why Merc service is AFU'd

Dennis Moore

Griff
You got that right! Don't trust the Merc engine specs, you wouldn't believe how little the Mercruiser people actually know about engines! GM engineers do all of the engine work for Mercruiser (except for the High Performance engines).

Sincerely
Dennis Moore
Family and Performance Boating Magazine