454 merc build recommendations
 

Hello,

This year I picked up my first boat. A garetta 24 with 454 carb with thunderbolt v and bravo 1 drive. At the moment it doesn't really run that well. Have been diagnosing an issue where it doesn't rev out all summer (it stops at 3500 rpm and starts missing, sounds like a rev limiter). Runs about 50 mph at 3500. Have noticed that it also uses a lot of oil, about a quart every hour.

The seller I bought it from swapped engine because when he was about to sell it to me he test started it and noticed it pushed water through the crank ventilation. Have been talking with a machine shop owner that thinks the oil issue could happen if the previous owner only swapped blocks and used the same internals from the previous engine.

The oil issue is the main reason I'm planning on rebuilding the engine and since it's already out of the boat I might as well upgrade the parts I'm replacing anyways. Also might swap out the complete ignition system for an aftermarket one (been thinking daytona sensors since the machine shop sells those). Thinking this will be a nice winter project.

Now to the questions I have. My budget is about 10k and I (obviously) want to make as much power as possible to pick up some mphs. Goal is 70mph but more is better of course. What road do you guys recommend? Most of the labor will be free except for the bore and hone. From the research I've done it seems like a 489 stroker build might fit my budget best. Looking for recommendations for parts as well.

Is running stock rods possible with this build or is it best to swap all internals?
Is porting the stock heads for this application possible? Or completely out of the question and new heads are needed? In that case which ones?
Carb and cam recommendations?
From what I've read it seems like exhaust upgrade is always needed. What exhaust does people run?

Or is it better to go the forced induction route? Anyone tried turbos?

Pretty new to engine building but I like researching and are surrounded with people that has a lot of experience. But not with boats. Only engines in other applications. Therefore I'm asking here! Replies to any or all questions is greatly appreciated!

Tried attaching some pictures of the boat (because everyone likes pictures:D) and engine cover but couldn't yet because of the post limit. But the engine serial 0F810432 and it says it's and MCM 7.4 bravo if that is to any help. Not sure if it's still correct after the swap but I think so.

Thanks in advance!

I’m looking to discuss and learn!

The SWAP renders all serial numbers irrelevant.
with that said, your engine block has a serial number (rear deck surface) and the heads have casting numbers (under the valve covers).
in order to START giving advice we need to know at LEAST those numbers.

The original MCM454 had an iron 2 plane spreadbore intake (not good for performance), low compression cast pistons and cast crankshaft (neither the hot ticket for hp), and peanut port heads (also not great for performance).
If you get your block ID then we can tell you whether you have provisions for factory style roller cam. The head ID numbers will help us advise you depending on your hp goals.

X 2 :thumbs
Whatcha’ got Willis ?

How about if his motor is the 454 365 mag, aren't those supposed to be aluminum intakes. Are the mags much better for upgrades?

If its labeled as a 7.4 then its most likely the lower hp 310/330 with a 2 bolt main block and peanut port heads.

Here are some old threads on building 330's
My 330 on Roids - Final Results - Offshoreonly.com

330 on steroids? - Offshoreonly.com

454-330 build up help - Offshoreonly.com

Aha! I'm not able to look at those right away. Let's say that's the case. Is it better to just find another block then? Too bad they are a bit harder to source over here in scandinavia.

I'll post the numbers in a day or two

Thanks for the tips Griff!! Will make sure to read those!

Look for "Crazyhorse" (Dave) and "Dyno" (Don) in those 454/330's on steroids threads....Crazyhorse is very smart and he worked as a machinist in a speed shop for several years and builds his own stuff. He's a friend of mine and lives close by and I see him and talk to him periodically. I haven't seen Dyno/Don for several years.

Dave and I were just talking about "SuperV's 454cid engines that he built back around 2006 pr so...cast cranks, 2-bolt mains, 3/8" rods reconditioned and ARP rod bolts, hypereutectic pistons, flat tappet hydraulic cam, made 505hp @5500-5600rpm on Tom Earhart's dyno back then.

SuperV put about 400-500 hours on those engines and just sold the boat---they're still running fine over all these years. I will call Crazyhorse/Dave and talk to him more about it just to make sure what I am saying is accurate info from those engines he built

Did that dyno don have a red boat with a radar arch?

I've read through those and that's about the same horsepower I'm hoping to make. But do you ever rev a boat engine that high?

Jocke,

If I'm spending your money, Molnar rods and crank and JE pistons. You can't go wrong with this foundation.

It might not be applicable, as I'm not familiar with all the blocks out there, let alone which one you've got, but there are kits out there that allow you to convert your 2-bolt (assuming....) main block to 4-bolt. The kits allow one to do the "machine" work with a hand drill and taps, using bushings and a drilling jig, but you might be able to get your machine shop to do this work for you while they've got it in house.

Good luck with your build. I'm still harboring a fantasy of building a 565 from the block up. Someday.....

Thanks. Brad.

Yup, if that’s where it makes it’s most power.

Why would you build a motor that makes most power at a certain rpm and never run it there….ever ?

I understand that but just assumed that you usually build boat engines to make most power at lower rpms. Don't know where I got that assumption from though

Jocke,

The boat I grew up on had a 482 blower motor that regularly saw 6200 RPM. I will tell you, though, that a backfire at 6500 RPM wreaks havoc on a blower input shaft.

Thanks. Brad.

Jocke,

From what I can gather from reading the many threads on the topic, the key difference between a street engine and a marine engine is in the clearances in the main and rod bearings. There are always differences in how we establish torque and power curves, but that is the same as with street engines in that we build to and “gear” them to a specific purpose. But the fact that a marine engine will spend extended periods of time at WOT, or even at something short of it, mandates that we build more clearance for all those parts to spin their guts out that whole time. We also (typically) use considerably heavier oil and make more effort to keep that oil cool.

Thanks. Brad.

Jeez Brad!! What props and drives did that boat run?

Aha, alright. But do you use different ratios in the drives or lower pitch props to be able to rev them out that high then? Or is it possible to rev out a 24p prop with standard ratio drive?

a last post to be able to post pictures

Here are the pictures I tried to post in the original post!


https://cimg5.ibsrv.net/gimg/www.off...7023fcab1.jpeg
https://cimg7.ibsrv.net/gimg/www.off...f128ce28a.jpeg
https://cimg8.ibsrv.net/gimg/www.off...4f52cb1a6.jpeg

Actually not sure if it is a garetta since I've found no model plate in the hull. That's just what the previous owner told me. But he said garetta 28 and when it arrived it was only 24 feet so not sure what to belive.

Jocke,

It was a 21' Nordic daycruiser V-drive that my dad built from a bare hull in '76. If I remember correctly, it was a 15% overdrive to the prop, turning a 13X13 prop. It would run ~85 on a good day: sucking fumes, two people, no gear/cooler, etc... Not at all comparable to what you're working on, but the comment was directly in response to your question about "high" revving engines. The 496HO that's in our PowerQuest regularly turns 5100 or so at WOT, and the 496 is a relatively low revving engine.


https://cimg6.ibsrv.net/gimg/www.off...61da559d2.jpeg
Yes. That little guy in the copilot seat is me. A looOOOoong time ago.

Thanks. Brad.

Cool boat! I was looking at those kinds of boats (mostly with jets though) before I bought mine as well. Decided to buy this instead because I thought those were a little too impractical with little space and not being able to run as well in rougher seas. They are and sound cool though.

Jocke,

FWIW.... You can call Merc tech and they can run your serial number and tell you just about everything there is to know about your engine. Forged/cast parts, 2/4-bolt mains, heads, whatever. But there are undoubtedly several here on OSO that can tell you that just from the model. There are a great number of very knowledgeable guys on here, of which I am NOT one of. Most of my knowledge comes from reading what THEY have to say. If they correct anything I've said, go with THEIR commentary, not mine. :ernaehrung004:

Thanks. Brad.

Yes! That's what I've gathered from here as well (not that you are unknowledgeable but that there are a lot of knowledge in this forum). That's why I posted. But since the engine was swapped (or at least block) I'm going to be looking for numbers on the block and heads later on this week and post as soon as I find them.

Thanks for sharing Brad...the old school family boats are a lot of fun. Back when a lot of guys built their own.

Tartilla,

Yup. I was 5yo when he built it. Good times. While I’m sure the plan was always to build a boat, it all started with a rough cast 6-71 blower, off a semi, (he had it polished) out of the TradingPost, and then it was like…. “Now what?” It had a Holley 1150 3bbl carb. Dad had a lot of the hardware made at local machine shops and designed/built the interior himself. The hull was originally designed for a jet drive, so they glassed in extra stringers and gussets to stiffen it. You could still feel it twist when dad stood on it. It had massive torque. We pulled five slaloms out one day. I was not one of them. It took about a dozen pulls for them all to come up without knocking each other over.

https://cimg0.ibsrv.net/gimg/www.off...d4c8fce37.jpeg

I can still remember the night they fired the engine up in the boat the first time, in my grandparents residential driveway, at about 1AM. They apparently couldn't wait until morning to give the key a twist.

Sorry for the hijack…… 🤷‍♀️

Thanks. Brad.

What Brad says about crank rods and pistons is spot on. Get a good foundation for your budget, and you'll have something to build on.

4 bolt main is obviously a better choice, but at a higher cost for your location. Splayed caps are an expensive option.

Figure out what you have...and the health of the bore/block.

489 @4.25" or 496 @4.375" stroke would both give you more power for the investment.

The big elephant in the room...is the exhaust. A Stainless Marine system runs about $3900-4000 US for the short length risers.

Used Stainless Marine BBC manifolds can be found here and the usual places.

I saw that EMI exhausts are a bit cheaper. Are they worse than stainless marine? I was also looking and saw that the ones with the taller risers aren't that much more expensive. Isn't it worth it to get those in order to be able to run a more agressive cam?

Based on your engine's serial number.

https://www.mercruiserparts.com/7-4l...v-8-1996-199-1

Hmm not sure how to tell what kind of engine I have from that

Buy a crate 550HP 502 and not spend it on the 454.

And this is coming from someone that runs 600HP 454's

Jocke,

As much as I love building my own stuff (never have done and engine), there is some validity to this. Just sayin'....

Thanks. Brad.

Remember, we're talking about a stock/factory Merc 454cid/330hp engine and how to modify it from its original stock/factory build form while retaining most of the parts from the same engine. This is basically a LOW BUDGET UPGRADE that will work/survive within certain parameters---that's basically why we called it a "Merc 330hp on steroids" It's for the guy who would like a little more power without breaking the bank or his wallet while basically using the Merc 330hp engine as a base platform.

From what I can remember from back in the day (early 1980's) guys looking to get 400-475hp from the 330hp engine was what they wanted and my friend's 1978 30' Scarab had a pair of Merc 454"/330hp engines in his boat back then with the old Merc heavy, crude, cast iron "log" style 2.5-3" exhaust manifolds.

The legendary Ray Baker and his engine building shop (Baker Engineering) I lived close by just outside of Grand Rapids, Michigan... I would see him at some of the Offshore boat racing events in Grand Haven in the tent areas near the pits---I specifically discussing the Merc 454"/330hp engine and he told me he had dyno tested some factory new Merc ones that he said usually made way less than even 300hp---like anywhere as low as 240-280hp (and I remember Ray saying "some even lower than that") with Merc's cast iron junk exhaust manifolds.

That was back in the mid 1980's or so and cannot remember all the small details but Ray's dyno tests revealed HP figures shockingly way below the adverstised "330hp" from the factory I remember thinking no wonder people wanted more power from the pitiful Merc so called "330hp"...and Ray was beginning to sell a lot of upgrade packages for the Merc 330's to customers back then.

Ray also told me that those Merc engines really needed a better breathing exhaust system just to wake them up much beyond 375hp. The first thing my friend did (with his 30' Scarab) was bought some used Hardin Marine P-1000 exhaust manifolds with dry tailpipes. Just by adding those alone woke his bone STOCK Merc 330's up from about 4200rpm before,---- all the way uo to 5000rpm afterwards.
If you are looking to approach the 400hp mark with a 454cid engine, then you have to begin looking at an aftermarket free breathing exhaust system and a DRY system where the discharge water does NOT mix anywhere within the collector/tailpipe, then the more and better potential for making power. Anyway, that was our starting point.

You have a Gen VI 7.4L 454, non-Mag engine assuming the info on the flame arrestor cover is valid to the engine beneath it.

You will hear 101 different opinions on here including my own.... and I am not saying my opinion is the right one either. I'm just giving you some testimony on what I have witnessed and expeienced over the many years when the Merc 454"/330hp engine was what guys wanted to upgrade way back then. Technology has certainly come a long way since the 1980's...with tons of more parts options, etc...so yes, you can go out and lay down the smack for a new 502 crate engine or other options.

The thing you will want and need to make sure of is, accurate machining process---even on a new factory crate that was/is not designed for marine usage especially when it comes to all the bearing, valve guide, piston/ring clearances, etc. .... unless you trust the factory. Because you would have to have all that stuff checked out and properly clearanced if you rebuild your 454"/330hp engine===or any engine destined for marine hi-perf use.....even a new from the factory crate engine would still be a wise thing to do.

Perhaps a factory crate engine would be a better choice these days if you have the money--- but you are the one who has to determine all the machine work costs and other costs involved, but you were specifically asking about the engine you currently have now. It's your money and your decision. You have to weigh it all out and do your own due diligence.

I will post again later of what we had to do with the 454'/330hp engines we had back in the early 1980's and others that I have seen built back in those days... we did not have the options that we have these days.

Kaama,

What is your opinion on the dry exhaust 1/8" weep holes at the tips of the pipes to cool the mufflers?

One of the issues I've seen on my dry to tip system is the pipe outlets discharge inside the hull...plumbed to the transom dedicated water outlet. All great, except the last 15" of pipe has no water flow for cooling without the weep holes...even without clamp on mufflers.


800 rpm on the top end is a massive airflow increase with no other changes. Best money spent on good exhaust.

Wasn't there some info and threads that good open but short style exh manifolds performed just as well or better than full length tube style?

I thought of getting a crate engine as well, but since I'm getting the labor for free (except bore and hone which seems to be around 500-800 USD) that just seems like a way more expensive option. The cheapest 502 I can seem to find is about 10k and then I would still have to get an exhaust on top of that. Of course I get some money from selling my old engine but in order to sell that with a good conscience I would still need rebuild it since it's consuming oil. Unless I'm missing something.

The only advantage I can see with a 502 crate is that it's more susceptible to future upgrades. But I think if I'm ever going to go beyond this build I'd replace the hull as well with a more proven hull and I suppose it's easier to sell the whole boat as is and get a whole boat with engine. Is this train of thought wrong?

Tearing into the engine and solving the oil consumption issue and running it is a valid COA. If you have any inclination of getting a more suitably sized hull, then minimize your mods...clean it up....enjoy it...and keep your eye out for what you want. Then make the investment into the good parts on something you want to keep, and suits your needs/wants.

As many can attest here on OSO...if you build up a good engine with exhaust etc...you likely won't get the money out of it when you sell it.

A quart/hr oil consumption is pretty rough. Intake gasket leak? Rings would have to be rough for that level of use. Compression test and or leakdown test would give you a lot of info.

By the way friends, I am not trying to steal anyone else's thunder here---if any of you other guys lurking out there have some input, then don't let me stop you---and if I need correction on something then correct me on it---I am not claiming to be a "know it all" ...it's just that I have some witness experience with these old Merc 454's---especially the 330's just trying to give some good feedback---and I usually enjoyed my high school Creative Writing English Class and writing gives me something to do. I enjoy writing. even though I do have some bad writing habits---and besides that, I am retired now also. So if I am making any of you sick or disillusioned, then just ignore my posts.

Anyway Tart, I highly doubt a 1/8" weep hole would hurt performance as long as you're not dumping the entire water cooling charge into the tailpipe.

I should note on those P-1000 exhaust systems we had that the water dumped at the very tip on the inside of the jacketed tailpipe---2 holes at the top and 1-hole at the bottom---we latter installed a pair of Merc's 440hp cams on a 110* LSA (they were actually made by Ultradyne Cams), but we never experienced any water reversion with that P-1000 exhaust set-up.

Yeah, it was something like 4200-4400rpm (almost laughable on a boat like that these days) on my friend's 30' Scarab---so, adding those dry P-1000 exhaust manifolds really woke up those 330's...we already knew we would see an increase, but were very surprised with the RPM increase/difference.

Keep in mind, you don't need a full length tubular header exhaust system----those P-1000 exhausts were a jacketed aluminum Manifold design with dry jacketed stainless steel tailpipes that worked well enough for what we wanted to do back then at that time.

Try not too laugh, but back then we always thought we'd be "one of the boys" .if we could just make 440hp with our own home-made recipe on a budget 440hp engine as compared to Merc's 440hp engine. Mercs 454"/440hp engines came stock from Merc with GIL exhaust manifolds and stainless steel dry pipes back then as well---they were comparable to the P-1000's. Another manifold style exhaust system that would work well is a Stainless Marine system.

A good breathing exhaust system is going to take a good little chunk of the of the money out of the budget for a warm up on a 454"/330hp on steroids project though--- it's one of those things guys may tend to forget about when doing these kinds of upgrades. Anyway, back then we thought if we could make a true 440hp from our pitiful Merc 330's using the same 454cid from a stock factory Merc 330hp we would be very happy. We were just guys who barely had enough money to scrape up and be able to dump in these boats/engines back then.

Another thing I forgot to mention when talking to Ray Baker back in the mid-80's about the Merc 454"/330hp engine was that I remember him telling me that the best Merc 454"/330hp engine that he ever dyno tested only made 313hp---and it was new out of some guy's boat---but he said some of the better ones dyno'd at about only 280hp-----and usually much lower than that and I remember one of his employees telling me that too. .

I do NOT know exactly where to split the hair exactly when making power using various stock Merc cast iron crude breathing exhaust systems that you can try get away with to obtain a certain amount of horsepower. Merc used to produce the old 454"/370hp and the 454"/400hp engines back then and they only had the stock Merc cast iron heavy log style very crude breathing exhaust systems on them and I am sure they most likely did not make the advertised HP with those engines either---soon, one of the options Merc offered the GIL exhaust manifolds with stainless tailpipes with their 454"/400hp engines and I think they called it their 400hp Cyclone High Performance package---I am sure it made closer to the 400hp mark than the one's with the cast iron exhaust system ...,

.....but remember if you are on a budget with a 454cid or any engine with the old heavy cast iron exhaust system, then keep in mind the more power you want to make---then the more you will need to lean towards a good, aftermarket free breathing exhaust system.