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A unique BBC application

29K views 70 replies 15 participants last post by  TRBenj 
#1 · (Edited)
This is my first post on Hotrodders- so I should first say thanks to all the helpful info that Ive been able to gather from searching these past few months. Ive been doing a lot of reading since my father and I bought an inboard ski boat with a 454 in July. For those familiar, its a '79 Barefoot Nautique, which was the first year that Correct Craft made this barefoot-specific model. I realize this is a pretty unique application compared to most here, so I figured Id throw a few questions out there that I couldnt find answers to.



First of all, here's what I know. Most Barefoot Nautiques came with 330 hp 454's, which were typical marine longblocks with peanut port heads. These boats typically topped out around 48-49mph. We first suspected that this one had been previously worked on when some carb and ignition tuning produced a much stronger 56mph on the gps. We started pulling casting numbers and here's what we've got (from Mortec):

Block: 14015445, 454 2 or 4 bolt ’75 – 87
Intake: 3933163, fits 68-69 396 375 hp, 427 425 hp
heads: 6272990, 70-up...rect...OPEN...454 service replacement, used on some MKIV crate engines, 118cc chamber

The engine is running great, but we will be pulling it over the winter since we are doing some structural repairs to the boat. We're considering tinkering with the engine to some degree if there are easy ways to add hp. I do not know anything about the pistons (I assume the block has been apart at some point), is there any way to determine my CR without pulling the heads? I also dont know anything about the cam- though I plan to measure at least the lift before doing anything. I suspect that it may be a stock-ish cam (peak hp on the 330hp engine occurs at ~4400), for 2 reasons. 1) We did not pick up any extra speed when we changed props that gave us 300 extra RPM at wide open throttle (5200rpm vs. 4900rpm). 2)This is a reverse rotation motor, so the availability of reverse rotation BBC blanks is and was an area that no one seems to know much about- including the Correct Craft forum, which has a lot of reverse rotation knowledge.

Based on the boats performance, my guess is that the engine is putting out somewhere in the neighborhood of 400hp, right around 5000 RPM. We would like more, obviously, without any adverse affects- namely low end power. We get an instant 2500 RPM or so from a standstill now, and while the holeshot is OK, its not great. Without propping down, we'd like to at least keep what we've got. I know the rectangle port heads are likely to be called overkill for our application, but it does run strong once the boat gets on plane, so Im hesitant to change them (though if building from a stock 330hp engine in the future, Id probably pick 781's or 049's as are commonly suggested).

I am not sure if a stroker is in the cards, but if I can convince Dad, whats the optimal size we should consider going up to? Ideally, Id like to see a powerband of 2500-5500 or so with the 990 heads, with a max RPM of 5500 or so (we can play with the prop to dial this in). Reliability is also key. What should we be looking at for a compression ratio- ~9:1? We run 93 octane now and dont mind doing so. What about cam? How big can we go on 454ci and not harm the bottom end power? Comp tells me they do reverse rotation BBC cams, though Im not super confident in the info I was given.

We do a fair amount of barefooting (39-45mph), so we need useable power, but we also would love to have the bragging rights that a 60mph ski boat would afford! I think another 50hp would get us there. If it matters, we're running a Performance Distributors DUI (HEI) with 24 degrees of advance (initial is set to ~12 deg) and a 750cfm 4160/4150 marine carb with the choke horn milled off. It starts and idles great right now.

Thanks in advance for any input!
 
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#29 ·
Personally, I'd find a set of passenger car oval ports and do some porting, you can get nearly as much flow on top with MUCH better torque/low end. Couple that with the right choice of cam, intake and carb and you could add at least 25~50 ft.lbs. of torque right where you need it, and still have more top end as well. The Edelbrock Performer would be the ideal intake, IMHO, maybe add a 1" open spacer for a little more top end if you have the room. I'd look for an 800DP carb. Big blocks LOVE free flowing exhaust, so anything better you can do there above what you have now will be a worthwhile improvement. If you can add enough torque in the mid range, you may be able to prop up a little as well. :cool:
 
#30 · (Edited)
Cool... looks like the LS6 crate motor was rated at 425hp?

Just a reminder- this motor was set up for reverse rotation, which would have been original on the boat. I dont know what the specs are on the existing cam, but I wouldnt be surprised to find out that its pretty tame. Im still being told by Comp that they can custom grind any RH cam I want- so if you guys could give me an idea of what would work best for this combo with an intended powerband of 2500-5800, that would be a huge help! Ill be sticking with hydraulic flat tappet for cost and availability reasons.

The plan right now is to put a Performer RPM on instead of the GM intake. I'm also considering roller rockers- Ive had good luck with Crane in the past and have heard good things about Scorpion as well. Any BBC-specific info I should be aware of here?

Edit: Rickracer, thanks for chiming in! We're still keeping an eye open for some 781's or 049's for a reasonable amount, but I wouldnt be disappointed if we stick with the 990's. The holeshot wasnt terrible last year, and the boat will be 400lbs lighter now due to all the waterlogged foam we removed- so that should provide a nice improvement all by itself. I forgot to mention that we're actively searching for a new set of exhaust manifolds, and we plan to upsize the 3" hoses to 4". The cam is really the piece of the puzzle I need the most help with.

As far as the carb goes, we put a newish 750cfm Holley Marine on there last year. Its a 4160 (vaccuum secondaries) with a rear metering block conversion kit and a milled off choke horn. According to the CFM calculators Ive used, that should be sufficient to turn the 454 up to 6000rpm at 95% VE, so I expect that to be OK for the time being. We have a short angled carb spacer on there now- if I remember correctly, its an open one. We were maxed out on headroom last year, but with the floor rebuild we should be picking up at least a 1/2", so we'll likely go as tall as we can.
 
#31 ·
Big blocks are rather hard on the valve train, especially with the more radical profiles, and the fact that most of today's oil don't have the necessary extreme pressure lubricants for flat tappets, plus the fact that rollers can make SO much more power than flat tappets with similar specs. With that in mind, I'd strongly consider going roller. When I was building/rebuilding a 427 for my Vega, I talked to every major cam manufacturer, and they were ALL trying to talk me into a smaller roller than the flat tappet I was already running. I finally called Herbert Cams and talked to somebody who was speaking my language ( I think it was Doug Herbert, but I'm not sure, he mentioned his Dad, Chet, in our conversation). Their first suggestion was EXACTLY what I had in my own mind that I was looking for, and the price was GREAT. I installed it with a set of used rollers I picked up at the track pretty cheap, and after a few thousand miles, one of the lifters wiped out. Herbert had me send the cam back to them for repair, cost was like $50 or $75, I don't remember now for sure, but when I got it back, it looked like BRAND NEW, I don't know for sure if they fixed it or just sent me another one, but either way, I was so pleased with them that I ordered a new set of rollers, along with matching springs, retainers and locks. Best money I ever spent on that motor, and I highly recommend emailing or better yet, giving them a call, and just see how affordable it would be to go roller. :thumbup:
 
#32 ·
Rickracer said:
Big blocks are rather hard on the valve train, especially with the more radical profiles, and the fact that most of today's oil don't have the necessary extreme pressure lubricants for flat tappets, plus the fact that rollers can make SO much more power than flat tappets with similar specs. With that in mind, I'd strongly consider going roller. When I was building/rebuilding a 427 for my Vega, I talked to every major cam manufacturer, and they were ALL trying to talk me into a smaller roller than the flat tappet I was already running. I finally called Herbert Cams and talked to somebody who was speaking my language ( I think it was Doug Herbert, but I'm not sure, he mentioned his Dad, Chet, in our conversation). Their first suggestion was EXACTLY what I had in my own mind that I was looking for, and the price was GREAT. I installed it with a set of used rollers I picked up at the track pretty cheap, and after a few thousand miles, one of the lifters wiped out. Herbert had me send the cam back to them for repair, cost was like $50 or $75, I don't remember now for sure, but when I got it back, it looked like BRAND NEW, I don't know for sure if they fixed it or just sent me another one, but either way, I was so pleased with them that I ordered a new set of rollers, along with matching springs, retainers and locks. Best money I ever spent on that motor, and I highly recommend emailing or better yet, giving them a call, and just see how affordable it would be to go roller. :thumbup:
I totally understand the advantages to the rollers and would love to go that way. I may give Herbert a call regardless to see what they can recommend. I should have mentioned though that, to my knowledge, reverse rotation roller cam blanks dont exist for a BBC. A buddy of mine looked into the costs associated with going roller on his RH 454 and it would have been north of $2k. Thats not an option Im considering at this time, as $2k could buy a lot of flat tappets! Im well aware of the issues with modern oils, but Ive had good luck with Valvoline VR1 on my flat tappet Fords to date. If thats one reason I cant go super aggressive, so be it- but a sub 6000 rpm cam shouldnt be TOO crazy, should it?
 
#36 ·
The 1970 LS-6 had closed chamber heads,the 1971 passenger car and later crate engines all used the open chamber variety,although IIRC they all used the same pistons.The car versions had a different intake,it was a low rise version,to provide hood clearance,whereas the crate's came with the high rise model.
Guy
 
#37 ·
Blazin, dont knock that 351w! This is my first BBC- all of my other boats have SBF's. Its pretty easy to take that 351w and add about 75hp. The holeshot and midrange power are pretty sweet! This is how I set up my Ski Nautique. The cubes of the BBC allow it to swing a pretty serious prop though...

So no recommendations on a cam? Ive yet to call Herbert- Id like to have a basis for comparison before I do. Here are a few Comp bumpsticks that fall within the RPM ranges Im shooting for. A few are from the Marine Energy Line, the others from the Extreme Energy Line. Should I look at other cams? Would another line serve me better? Comments welcome!

XM270H

XM278H

XM288H

XE268H

XE274H

Again, the set up in question involves a 454ci with 10:1 CR, 990 rectangle port heads and a Performer RPM intake. For comparison purposes, I'm assuming we'll be able to put out hands on a decent flowing set of shorty header style wet exhaust manifolds with 4" outlets (straight piped all the way back). I'm looking for the best powerband in the 2500-5800 RPM range.
 
#38 ·
Well, I had a friend of mine plug my numbers into his desktop dyno along with the 990 flow data from Stan Weiss and the cams listed above. Looks like the XM278H and the XE274H work the best. The 274 has about a 10hp and 15ft-lb advantage down low, and the 2 cross paths around 5000rpm. The XE274 peaks at 450hp@5000, but is still making 447hp@5500. The XM278 pulls a little longer and peaks at 455hp@5500.

Both make decent power down low 240/247hp and 520/505 ft-lb at 2500, so I dont think I can go wrong with either. If I had to pick one, Id likely go with the 274 for the slight power advantage everywhere but at my intended WOT, and it doesnt give much up there. Not sure if Ill end up with either- but at least I have a baseline now. Ive had good luck with Cam Research (Ford only) in the past, so Id like to find a similar outfit for the BBC... next step is to call Herbert.

Thanks again for your help, guys!
 
#39 ·
Hey Trb

Hey Man, Sounds like you've got a serious project going on now. I've been to busy too post some info for you. But I have it now. Sounds like you have a 454 that may have been assembled with a grab bag of parts(not uncommon w/marine engine builders). They used whatever GM had available that suited their needs. I don't know if a rebuild is in your plans, but its going to be hard to determine just what you have without a complete teardown. Here is what I found in my books; While the pistons and heads make it appear to be an LS6 engine, the block and intake say it isn't. Your block appears to be a later light duty truck block(14015445)produced~'75-'90. LS6 is 3963569. Your heads are the LS6 real McCoy(6272990)('71 open chamber)(probably old style valve seats,not hardened). The LS6 heads with hardened seats is the 14096188. Your intake is from '68-'69 396/427(3933163). LS6 intake is 3963512. Your pistons are the early closed chamber LS6 design, because they are std. bore, it makes me think it was a purpose built engine. Also drops the compression about a point using the closed chamber piston with open chamber heads. L2349 specs; 10:1 with 119cc heads,.265 dome, 5/64,5/64,3/16 rings,press fit pins,4.25 bore,comp. dist 1.645,658 grams weight, dome volume 30.6, bore clearance .004. As far as the cam is concerned, you may want to pull the original and see whats in there before deciding on where you want to go. From my experiences with boat cams, don't get too greedy with the duration, use generous lift(check piston to valve clearance) Use a wide LSA for idle quality. If it were me, I'd have the original reground to whatever you want, because it gonna be a special order anyway, you'd just as soon save the cost of the reverse cam blank and only pay for a repair/regrind. Hope the info helps. olnolan
 
#40 · (Edited)
Olnolan already suggested a blower but you have way to much compression for that. Dreaming a little, it would however give you an instant almost 100 hp at the start and probably 150 to 175 top end with no rpm change. You probably aren't going to go 10 mph faster but you will be in the rarified field of fastest Natuque's around. The starting blast would be great. I doubt a person could hang on to the handles on a barefoot start!!!

You could probably put on the larger high pitch prop and go a little faster with no change of your top rpm but you already know that boat drag is exponential.

Reality says that the RPM manifold and about an 800 vacuum sec carb with a yellow spring would be the way to go. In this case the Air Gap would work too as the outside air is usually balmy and your under hood air temp can get pretty high. You won't really need the heat passage.

Keep the rect heads. They are helping you.

I'd just freshen the motor and do your cam what ever you decide. I think you have a pretty good idea of what the boat needs.

Once again I'd suggest an AFR gage to get the tuning exact. You will need the data logging feature too as your runs will be longer. You will need a good Holley book to understand exactly how the carb sections work with each other. You will be amazed how much you get by just getting the carb really tweaked to your operation. You can make adjustable air bleed with brass set screws. See the book.
AFR stuff;
http://www.innovatemotorsports.com/


I'm not a big nitrous fan but for the relatively short bursts and for just wasting fuel and blowing rooster tails and general screwing off it would be hard to beat. Even a 50 or 100 hp shot would be just plain fun. With a boat weight isn't a real big issue so you might even consider getting the whole bottle instead of just a couple 20# ones. Hard to beat $$$ per hp.

Don Hampton blowers is really big in boats if you still want to go after a blower. I think you can just flip the front cover around on a 6-71 and drive from the right side instead of the left for rev rotation. The rotors would still turn the same direction. Install the idler system on the left side of the motor. I haven't done this however.
 
#41 · (Edited)
A couple of things to consider...the first of which is to remedy the soggy foam. That in itself will get you a NOTICEABLE improvement in perceived power. We had a 21' Thunderbird Formula with a soggy deck. Tore it out and replaced it...WOW, what a difference. Second is hull design. Adding a bunch more speed on a hull not designed for it MIGHT lead to stability issues. Trim Tabs on a shaft drive will help your hole shot, but they won't get any more of the wetted surface out of the water when the hull is up on plane. Are you going to use the boat for skiing? If so, replacing the soaked foam will get you into great skiing range....without spending unnecessary money on the engine. If it ain't broke, don't fix it...however, you MIGHT consider a roller cam/lifters. You'll get more of what you're looking for with a roller. As far as top end, I guess you don't HAVE to run it full (6,500 RPM) throttle if stability becomes an issue... :thumbup:
 
#42 · (Edited)
desoto, the soggy foam is being remedied... its out! We're about to start rebuilding the structure (all composite, no foam). It should be a tad lighter than it was from the factory, not to mention all the water weight the foam was holding last year. Im hopeful we'll see a noticeable improvement in holeshot just with the weight loss... any top speed gains will be a bonus. I have to say that the boat didnt slow down much, even with a boat full of people!







Yes, we're planning to use the boat to ski- well, barefoot, actually. The top speed is a bonus, as we dont 'foot over 45mph. Being able to pull multiple barefooters comfortably is a requirement, though.

Bentwings, great tips- thanks. Yes, Id love to install an A/F meter to tune this thing... but it does get a little tricky with the wet exhaust. My buddy had a piece machined with a port that installed between the manifold and riser, so that may be something I can emulate, depending on what type of manifolds I end up with. Until then, Ill have to rely on plug chopping... I did convert the secondaries to a block with replaceable jets in anticipation of dialing it in though.

A blower would be very cool if I could make it work with the reverse rotation- that may something Ill be researching in the future. Its out of the budget this year, though. Ive heard nitrous is an easy way to make gains, but Im not crazy about the idea. All motor would be a cooler way to go, IMHO. Everything we've discovered about the motor so far indicates that its too fresh to justify tearing into- but eventually Id love to put together a 496 stroker for it. This year, Im just trying to optimize what Ive got with a few select parts!

Olnolan, great feedback- thank you! Are you suggesting that my CR is about 10:1 like I think, or is it lower? The plan now is to at least measure the valve lift on the cam and proceed from there. If I were to pull it, would a shop be able to measure it up and tell me what Ive got? It sure would be nice to have a baseline. A regrind is certainly an option, but Comp says they have the reverse rotation blanks and can custom grind whatever I want for ~$300... so thats my back up plan. Id prefer to find a smaller outfit that really knows BBC's and how to make them work in a boat application like mine.

Many thanks to all!
 
#43 · (Edited)
Yep

Yep, Its zackly what you thought according to my piston book,says 9.99:1.
It should go a bit quicker without the extra baggage. Properly chosen exhaust and camshaft should wake her up. Something gives me a feeling that its got a tiny cam in it, does it have any lope in the idle? For best performance the exhaust should push out water for the shortest distance possible with the least restriction. All the big offshore powerboats use real short tailpipes for this reason. 10:1 may need premium w/octane booster added. If you indeed have the old style valve seats, lead substitute additive may be needed also. As far as propping goes, you understand that pretty good already. The only difference in your prop theory and mine is the fact sterndrives are limited to 5000rpms input or they go caa-boom. With your 1:1 box that can handle about anything you throw at it, your only limit is when your engine goes caa-boom. I have learned a bunch of top speed tricks from an old outboard drag guy and a few more from my buddy that is a propeller specialist, but I'll save them until you get it going again. olnolan

oh, yep, any automotive machine shop should be able to set the cam up in v-blocks, check and chart it for duration and lift.
 
#44 ·
10:1, good good. That means my desktop dyno numbers were based on the right info. From what Ive read on here, the BBC needs some compression to respond to a cam, so while its definitely on the high side, thats not all bad. We ran 93 octane all summer and it wasnt pinging with the new HEI (DUI) distributor. Total timing was right around 36-37 degrees (initial was 12 or so).

Im not a believer in "lead substitute"... I think its a marketing scheme. Im running non-leaded gas on all of my boats, even the old ones (1971) that supposedly require the lead. Im putting the money Im saving on the substitute away to pay for a valve job someday. ;)

Im guessing it has a tiny cam in it too. We didnt gain any top speed with the smaller prop that let it turn up to 5200 (the other one only turned 4900), so it wasnt making any more power higher in the RPM band. The stock 330hp cam would have peaked around 4400-4500 with the peanut ports- maybe a bit higher with the 990's... so a cam making power up to 5500 should hopefully wake this thing up. I cant say that it had any lope at idle- it was pretty smooth, idled down to 600-700 rpm just fine and started very easily. My fingers are crossed that it still has the original cam in it- that would give us a good opportunity for more easy power! Great info on having a machine shop measure the cam... Ill add that to the list of things to do ASAP.

We cant change the length of the exhaust, obviously, but we're eliminating the mufflers and going from 3" hose to 4". Even if we go with some classic aluminum log manifolds, they should flow better than the cast iron pyramids... plus save 50-80 lbs. True headers would be nice and we're keeping our eyes open, but they may not be in the budget.

Youre correct- the Borg Warner 72C is a stout tranny and will handle all the power we can throw at it. It doesnt care how many RPM's we turn either- it would see more strain if we tried to turn a steeper prop... which we're not.

Feel free to clue me on on any speed secrets you know- not all will translate to a direct drive inboard but some may help. We're still using the boat to ski, so prop options are limited- but any info helps! Luckily the hull seems to get up out of the water pretty nice for a ski boat, which is certainly helping us. My other Nautique wont even break 50mph, even with a 350hp 351w pushing it! A few guys I run with have tweaked their hulls to get the bow up more at speed- this involves grinding the "hook" out of the last few feet of the hull... but those were flat bottomed boats. Not sure how that would affect this v-hull. The flat bottomed boats tend to run faster with a bit more weight in the back seat (people, lead, coolers, etc), but this boat didnt respond in the same way. Im still learning!
 
#45 ·
I forgot about the wet manifolds but doesn't the water that cools the manifold get dumped into the pipes a ways aft of the manifolds. I had a humps on my my old boat and the water entered the pipes aft of that then out the transom. If so you could inatall the 02 sensor between the manifold and the humps. It can not get wet however. You could even run a temporary one into a check port for it then remove it for running after you get it set up.
 
#46 ·
bentwings said:
I forgot about the wet manifolds but doesn't the water that cools the manifold get dumped into the pipes a ways aft of the manifolds. I had a humps on my my old boat and the water entered the pipes aft of that then out the transom. If so you could inatall the 02 sensor between the manifold and the humps. It can not get wet however. You could even run a temporary one into a check port for it then remove it for running after you get it set up.
It depends on the style of manifold. Some have seperate manifolds and risers. Of the ones that do, some are gasketed to allow water to pass between the 2, and some transfer the water via an external hose. The latter is easier to add an O2 port, but but both are possible. If we end up with one piece manifolds (manifold and riser are one piece), it wouldnt be possible.
 
#47 ·
I finally called Herbert this week and was disappointed. They dont have reverse rotation blanks, claim they couldnt grind one if I got them one, and they dont sell anything tame enough for my application (all 6500+ rpm cams). I guess theyre out!

Can anyone else recommend a smaller outfit that really knows their stuff and might be able to help me? Maybe Comp is better with BBC's than they are with SBF's... I have not been very impressed with their Ford cams. With similar lift and duration numbers, they were about 30hp down on the desktop dyno compared to my Cam Research piece. Id rather not leave free horsepower on the table!

If there are no other places worth pursuing, any input on whether Id like the XM278H (from their Xtreme Marine line) vs. the XE274H (from their Xtreme Energy line)?
 
#50 ·
Thanks for the leads guys! I will call Bullet tomorrow if I get a chance. Im not sure who I spoke to at Cam Motion, but whoever it was sure knew their stuff. I would love to have them build something for me- very knowledgable. It sounds like they cant get the reverse rotation flat tappet blanks either- though he could grind me one if I were to source one. He makes his own billet (roller) blanks, but cant make a reverse rotation version since the snout for the gear drive is different. Going to a chain drive would be possible, but then Id be swapping gears on the distributor and oil pump... and Im not sure if reverse cut gears are available for those. He said he could regrind my existing cam, but was limited with what he could do since he wouldnt have a ton of material to work with...

...so I will keep searching for a blank! Comp didnt want to sell their blanks last time I spoke with them, unfortunately.
 
#51 ·
Camotion

Hey TRB, Pull your cam and have it built into anything you want. I mentioned this before. If you spoke to the owner, his name is Kip. He's a good ol home town boy that will sit down and talk about what you want. I had the pleasure of talking with him on cam eating issues in a 468. I ain't sure about it, but he might be able to rework the lobes into a low lash solid roller design. Solid roller with low maintenance. You're gonna need to keep it moderate on the cam if you don't upgrade the exhaust, else its gonna run like a shack of schit. If you do a serious enough exhaust system, then you can throw some more cam at it. Just trying to help you out. Been there, done that. :D olnolan

Oh, I forgot to mention Kip grinds the top secret cams for alot of NHRA record holders and circle track guys as well. He might be the best kept secret in alot of venues.
 
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