454/425hp mercruiser
 

Hi everyone,

Have 1990 Baja 370es from 2012 with twin Mercruiser 454/425hp ''performance series'' for this year,
this week need refresh engine but i think both engine have already been redone but don't think with original parts !bore .020, have head casting 14096188, roller rocker 1.7, hydraulic lifter, intake is not original seems like air gap because clear 3'' under (carb), carb holley 850 dp, camshaft B&M 3646 ( unable to find specs for this camshaft !) but when i bought this boat there were 2 gauges as if he had already had blowers !!

Question : this is the right set up ? beacause need to replace camshaft and lifter (broken)

Thx for reply !

Engines may have had blowers at one time and that cam might have been purchased as package from B&M.
Heads and roller rockers are correct. Stock carb was a Holley 800cfm.
Stock cam for the Merc 420/425hp engine was a Crane 132561.
Crane is out of business, but here are the cam specs Crane Cams 132561 H-228/312-2S-14 T1.2 Camshaft
I would upgrade to roller cams though. Flat tappet cam's of today are junk and 50/50 if they break in correctly. This would be a good choice Teague Custom Marine | BBC Mark IV Billet Camshaft - Stage 1

This!!

And even if they do break in correctly, the risk of failure later is still a factor.

OP, you said a lifter was broken? Depending on what you mean, you could be looking at a bigger issue (a worn lifter/wiped cam lobe means a full rebuild… metal will be everywhere).

All engine disassembly and all cylinders are perfect, crankshaft perfect, pistons set perfect, no issue other just 1 lifter and lobe camshaft,

as i refresh, bearings, seals, rings set, oil pump, new lifters, and cam, would there be a possibility to increase some HP with a hotter cam?,
i have a HI-Rise aluminum intake manifold, head 14096188,

If you don’t use a roller camshaft, you’ll be rebuilding it again.

Griff already recommended a cam.

The cam I recommended is the same spec as the old Crane 168731 and is very similar to the 500efi cam. I wouldn't go much bigger for your boat. You need the low end/mid range torque.

So I would have no advantage in installing roller lifter?

That is a roller cam that he suggested.

There is always an advantage to going with a roller lifter over a flat tappet.

Originally, the idea was that there would be more power for the given lift and duration compared to a flat tappet, but these days, the primary advantage is around keeping the engine together.

The cam that Griff referenced is close copy of the Crane 168731 used in the Merc HP500 502. The 168731 cam did have some issues with reversion so if you go that way, make sure your exhaust is up to the task.

I installed 500 EFI cams in my Merc Gen V 454's a few years ago. I don't regret it. Didn't gain much performance, but the roller piece of mind was worth it.
https://cimg8.ibsrv.net/gimg/www.off...2be411fbb.jpeg

The 168731 cam is close a 500efi cam and they didn't have any reversion issues. The HP500 carb engine cams were different and they had reversion issues at idle.
The 168731 is a roller cam

I thought the 731-ish cam that Merc used caused some reversion issues. Maybe I got that one a little wrong?

Had to dig around for the HP 500 specs... courtesy of RMBuilder a way's back:

284*/292* @ .004"
222*/230* @ .050"
.576"/.598" valve
110* LSA
105* ICL
115* ECL

That 110* LSA probably didn't help much with the Gils that they originally came with.

Have the 169621 500 EFI cams in the Bullet - 060 and 080 over 454s with B&M 250s. 188 heads, nothing special just super reliable and really strong. They really like the 500 EFI cams. Anyway, supercharging isn't the subject here. :drink:

Yeah and Merc actually changed the Gil tailpipes from this style to the ones that are taller and have more swoop
https://cimg9.ibsrv.net/gimg/www.off...c9c26d3b5b.jpg

Have same exhaust Rookie Pic engine but not same intake ,

Mine is more elevate

I agree with installing new hydraulic roller cam and lifters as Griff has suggested, but just make sure that those Gill Marine exhaust manifolds and tailpipes are a completely dry system especially with that cam being on a 110 or a 112 LSA otherwise you're going to have reversion problems.
If you have a "wet" exhaust system, then you most likely will need a lobe separation angle (LSA) of 114° within the cam specs of the camshaft so as not to revert or have reversion of water back up into the engine.

Also I would stick with the Air-Gap dual plane intake manifolds that you said you already have... They will give you better lower and midrange performance on those 454's especially with a heavier boat like the 37 ft Baja that you have. They would provide great throttle response and work great for your application.
You could even add a phenolic 1" OPEN carburetor spacer to keep the carburetor from getting heat soaked.
and for a hair more performance.
Just my .02 but I think you're on the right track with the advice given by the others.

A 168731 won't have reversion issues with full length wet exhaust tails like the ones in the pic on my 525SC. The water mixed into the exhaust about 2" before the rubber hose connection to the exhaust tips.

Griff, would you happen to know/recall what RPM the 500 HP peeked out at with that 731 cam in it?
Thanks

I put one in my 525SC (pictured above) but only did the top end and never dyno'd it. I gained about 150-200 rpms over the stock flat tappet and would touch the 5400rpm rev limiter with light fuel.
The 731 is nearly identical to a 500EFI cam, so I'd guess peak hp around 5300-5400.

Thanks Griff... With my pair of baby 482cid sized engines both making exactly 510hp each on the dyno at only 5000rpm, then I can only conclude that it's probably because of the Merc Thunderbolt distributors and the Rev Limiter chip it has in it. 🧐

Similar ?
 

don’t know how much similarity there is to the 500 to 525 cams but I have been happy with performance on mine all the way around

What Thunderbolts??? TB IV's don't have rev limiters, but TB V's do and are built into the module.
You would know if its hitting a rev limiter. RPM's would bounce 200 rpms or so back and forth at WOT.

The Hp500 cam is the ‘721 cam. Merc never used the 731. The 500efi cam is not same as 731.
i have listings here, old speedwake, bf’s, and others ??? With all the crane marine hr’s cams. If one can’t find i’ try.

Heres is 1 of’m

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Thanks Griff, I am NOT exactly sure which of the Merc Thunderbolt distributor setups that are on my 482's, but they have that flat looking module with ID numbers on it and I will definitely take a look at it when I get my boat out of Winter storage.
My 482's were built and dyno tested back in 2008 and have not been run since that time until last Fall. I will have to try to find the dyno sheets but I specifically remember them both being Dyno'd @ EXACTLY 5000rpm each... but I don't recall how the RPM's reacted etc after 5000rpm on the dyno sheets.