Gen 6 454 build in Formula 242ls
 

Hey all, I'm finally pullin the trigger on the engine build on my 1989 Formula 242ls. I have found this site the most imformative and technical related, so maybe someone can answer a few questions? I will give you the tech sheet first. It will be a stock displacement gen6 454, stock oval port open chamber 100cc heads (casting #10141279) with some good port work, and possibly some bigger valves if budget permits. It has flat-top pistons, and should be right at 9.62:1 compression ratio. I have decided on the Comp Xtreme Marine hydraulic roller cam (XM284hr) with 112 lobe separation, 110 intake centerline, 0.547 lift, and 230/236 duration @ 0.050. I will be re-using stock roller lifters, getting roller rockers, using a Edlebrock performer RPM air gap intake, 850 carb, and CMI long tube headers w/ dry tailpipes. The question I have it on the cam, is that they say it requires machining of the cylinder heads, but doesn't specify what I'm machining? And the other question I have is about the headers... One of them is leaking, if I pinpoint which tube, can it be separated at the bad spot, fixed, and then the outer sleeve re-welded back on? They are soo damn high $$$ so I really wanna fix em instead of goin with manifolds!!! Any and all help is greatly appreciated guys, this has been a wonderful site and look forward to some responces. I figure if all this should put me around 450-475 horse, 500-525 ft/lb torque, so if I can hit 65ish I'll be happy, I know they are heavy boats... (btw, I'm thinking a 4-blade 23 or 24p to start? I used to have a 22p 4 blade and it ran at 4500 at WOT and got up nice and cruised at a nice speed too. Not doin a 3 blade, makes the boat drive like ****. lol)

Anybody? C'mon now, I know I'm not the first person out there to build a gen6, and who also has a slight hesitation to throwing away a $5,000 set of headers!? lol

The header fix will depend on how bad the corrosion is. If they stainless inner and outer your probably in good shape. Some are stainless inner and mild steel outer. Lots of factors involved, but 99% of the time not a problem to fix them.

A friend of mine has a 88 formula 357 with 454's that are close to what you are planning except for the heads. He is running ported GM 990 rectangle port heads the same comp. XM284hr and weiand 8018 intakes. His motors dynoed at 475 and 495. I have never messed with the GM vortec heads but with the right port work I would expect similar results. If you have the work done professionally you will be real close to the cost of new aluminum castings and if they need guides too than you might exceed the cost of new castings. Also 9.62 comp. ratio is pushing it with iron heads, most guys stay around 9.2

Well the engine has VERY low hours on it, and was babied, so everything is in really good shape... I will be doing the port work myself (have ported many many heads with great results, so that will save $$ there), and from what I am reading, these are actually really good design heads, so hopefully they preform well. As far as the compression ratio goes, that was what it came up with using a pretty thin gasket, so maybe I can throw a thick head gasket on there and drop it a few 1/10ths?? I was planning on running premium anyway as I trailor my boat everywhere anyway, so I gas up on land. Think I'm in the right ballpark with starting with a 23 or 24p 4-blade?

Ditch the air gap intake. Run a big single pane. The intake air temps in a boat are higher in a boat and you need more plenum volume. Cam looks good for your goal, heads are decent but can easily exceed the cost of a new set going through them. Save yourself the aggravation and don't plan on using the headers. Sell them for what they are and buy a new set of stainless marine manifolds. Unless your willing to take a gamble on ruining your fresh heads when they pop another leak.

If you can port the heads yourself than go for it. I am contemplating the same thing right now but I am leaning towards new aluminum castings. The last set of heads I did took about 20hrs so the 40hrs of grinder time to do two sets is not exciting me very much.

I'm a single plane intake fan too. You will have plenty of torque in the 2500-4500rpm range with the oval port heads either way so why not take advantage of the top end the single plane will produce. That cam will make power up to 5500+ rpm. I have had excellent results with the Dart single plane oval port intake #41214000 at higher rpm but a victor jr. or team g might be a better choice.

I would not worry about the prop until later. If you can spin your 22p at 5500rpm you will meet your speed goal.

Adding thicker head gaskets is fine to increase combustion volume but quench clearance is just as important. If the thicker gasket gets you much above .050 quench clearance there are better ways of increasing combustion volume.

I'm glad to hear positive feedback about the various single plane intakes... I was wanting to run one anyway, but was just worried about makin as much torque as possible because of how heavy and underpowered this boat feels as is, not a big fan of takin all day to get on plane, lol. I think I'll be able to get these heads prepped and worked over pretty cheap, so I'm definitely gonna give it a shot using them. I work in a shop myself, and have basically unlimited access to machine shops and any tooling I need, so I should be good to go. I'm glad to hear that your buddy did the same build and made right around 475-500hp, gives me some hope! lol

I'm building a similar gen 6 454 right now as a backup to my 548. I am retaining the vortec heads, doing some cleanup work in the runners, .620 lift cam, Edelbrock Pro Flo XT intake with 102mm throttle body, and will use the Holley HP ECU that I can use on my 548 when it gets back together. I am hoping to get close to 475-500 hp. We will see what a bunch of assembled spare parts can accomplish here. This project started life as a running take out truck engine for $450.

I will also need to machine the valve guides down, install spring rotator eliminators, and machine for 7/16 rocker studs. I will be using stock sized valves. I have read that installing larger valves only worsens the valve shrouding in the chamber due to the fast burn protrusion.

While you are in there, How's your transom?

Glad to hear about the valve shrouding before I bought new valves! Lol, well that will save some money. I've built dozens and dozens of engines before, but this is my first Vortec BBC, so I'm still gathering info. And as far as the transom goes, I pulled the engine last weekend, and it was suprising clean and solid. Looks like someone had already been in there and painted it too, unless Formulas were painted grey inside from the factory

The chevelle forums have more info about making something out of these heads than on here. Most will say they are junk on here. Exhaust runners flow great so just some clean up is needed. Intakes have ski jump "vortec design" and causes swirl into the chamber but hinders flow. Be careful porting too much as the castings are thin. If you want to run premium pump gas, they will make good power around 34° timing but you will find many tell you that is too much. Depends on source as always here on internets. I have found a few articles about porting them but they dont go into deep detail and are scarce or are not backed up with flow results being as most applications for them are very budget oriented so the expense of flow tests is forgone.

The small chambers are a bonus and are hard to achive a budget minded replacement casting to maintain close to the same CR. I was going to ditch them for 781 castings but didnt want to loose all that compression or have to change pistons and rebalance. Trying to just do simple rebuild with good bearings and gaskets so I decided to run the vortecs.. I have one money pit of a motor that gets best of best. This one just has to work as a spare to get on the water and hopefully be able to reach what my hull used to do when it had a stock 502 mpi.

It will be interesting to see how our motors end up performing. These heads can make very good torque on a 454 i understand. Keep us posted!

As far as the timing and compression you will find that boat motors are run more conservative because of the excessive heat generated by the longer duration under high load that a marine engine has to deal with.

Here is some good reading for you.

http://www.chevelles.com/forums/show...highlight=l-29

http://www.hotrodders.com/forum/bbc-...cs-171714.html

http://www.fullsizechevy.com/forum/g...g-results.html

This seems to be about the best porting information I can find on these heads. With a little work they can flow close to stock 781's Worth a shot if you have time on your hands to hold a die grinder.

That was a great article! Its nice to see some actual data and results from the exact head I plan on using. The way those were ported look IDENTICAL to how I've always done my heads, and how I planned on doin these: smoothing and shaping the valve guides, opening up the bowl and smoothing out really good (especially the first inch of the valve seats, and smoothing out and shaping the short turn radius). Ill gasket match it, but not take much out in that area as that's not where heads get choked up. Ill re-use the stock valves after reading this too. Dyno tuning was an idea I was kicking around too, but we'll just have to wait and see what accesable dynos and cost permits. I figure if I can get this anywhere close to 500 horse, I will at least be able to keep up with the majority of what's out here on the rivers. (Not tryin to be a LOTO hero... that will never happen, lol)

I would do some research around these forums before sticking with the stock valves. Im not sure what valves GM put in the vortec motors but I do know that performance marine engines are very hard on valves. Most builders spare no expense in that area. Consider that merc uses inconel exhaust valves in their motors starting at the hp500 on up.

Most of the late model GM truck engines came with Inconel valves due to towing/emissions compensation exhaust temps. The 96 7.4 I just took apart has them and except for some carbon buildup that has been removed, they look good.

I did this....... Rebuilt my gen 6 7.4 with 279 vortec heads. Put in 2.19/1.88 valves and ported and blended as much as I dared. Don't mess with the ski ramp. Used the GM .510/.540 lift hyd roller cam from the 7.4 magnum... Got it cheap....... Excellent cam with great torque. Uses all stock valvetrain........ I don't think I gained that much with porting and the larger valves. Dont even think about using a single plane intake. You will be giving up power right where you need it. Air gap will outpower any intake with your combo. Oval port heads make lots of torque so add parts that build on that..... Motor will be out of breath by 4,500..... Single plane does not start making better power unil about 5,400pm on up. I cruise my 26ft wellcraft at 3,700 rpm at 40 mph all day long effortlessly.... 3,000 Rpm is 32 mph with a bravo 3 24P...... Gets up on plane quick and easy and has torque out the wazoo!

I built a 242 a few years ago and I would say that if you make the power you think you will make, you should hit 63-65 MPH. I had around 530 hp in my 242 and I would hit 68 mph. Honestly though I don't think you will make over 425 hp I think with your combo you will will hit 61 MPH on the GPS. In order to make the power you want you are going to need to spin it to 5100-5300. As for props get a Mirage plus 21 pitch. There is no need for a 4 blade on a 242, yes you MAY gain a little in the midrange but it will kill your top end. My experience with props is that as long as your going to build the same cubic inch engine you will typically spin the same prop, only now it will spin more.

Also I would stick with your original Performer RPM. You are not going to gain anything by going to a single plane, you are simply not turning enough RPM's to take advantage of the upper RPM power they make.

I don't have a problem spinning the engine to 5500 rpms... as it would only be for short bursts, so if I have to go down in pitch to make a 4-blade work, I am willing to do that. I have tried literally over a dozen 3 blade props this past summer, and I just don't like how the boat runs with them. I usually always have 6 adults, plus coolers/gear with me, so its ususally loaded down pretty good, and being able to cruise at a medium speed is a must. Every 3 blade made it pourpose its ass off, the one 4 blade I had made it jump up on plane, cavitate just a tad for a second, and then cruise nice and flat at around 2,900 rpms @ 30mph GPS and only lost 1 mph top speed. Top speed is important to me still, as I participate in poker runs, but losing 1 or 2 mph is something I am willing to sacrifice to make the boat driveable. And I know the engine specs aren't anything crazy, but I've built some 500hp engines before, and I think with some good head work, 9 1/2 compression, and it being a decent size roller cam, close to 500hp should be attainable with a good intake and 850 carb with open exhaust I would think...? 65mph would make me happy as hell

I hate to say it but your not going to get anywhere near 500 hp with vortec heads, not in a boat at least. I'm running a slightly bigger cam than you are going to be running, with the 8.9 compression ratio, performer RPM intake and a holley 800 (the engines were 454 mags) and I'm not making over 430 hp. I know that based on what other formula 292's get for speed. I'm no better than stock 502's, maybe even a little slower. When it had stock 330's in it mine was on the fast side for stock engines (63 MPH now I'm at 68 MPH) so I know it's not that I have a heavy boat. Yes on a desktop dyno the engine should be making close to 480 hp, but this is not the case. I also know what I had to do to make 530 hp and that was far more than what you are planning on. It takes a lot of hp to make a Formula go fast and 65 MPH in a 242 take some power. If you haven't bought your cam yet I would really suggest to you talk to Bob at Marine Kinetics. The price will be close to the same if not the same as the off the shelf Comp but it will be customized to your set up. Bob will also tell you the realistic HP you will be making. If you would like his number let me know, I'll post it. Not trying to be Negative Nancy here, but the posts from the Chevelle site are not really relevant for building a boat engine. If looked back at some of my original posts I wanted to do something similar to what you are describing for my 242. However the more I learned the more I figured out it isn't really possible. Many here have tried on here only to be disappointed in the end.

As for props- did you ever try a Mirage Plus? If not I would try one, for the 242 that is the best prop out there, I'd be willing to bet that is what 90% of the 242 guys are running. Not all three blades are the same but on the same hand not all 242's are the same.

Vortec head 454 build with dyno results

http://www.offshoreonly.com/forums/g...l-results.html

Thanks for posting that Dandercam1! I know my build is on the mild side, and I'm well aware of the Formula 242 being a heavy ass boat. Well lets be real, it's like pushing a fat ***** on roller skates through a gravel parking lot. But either way, I know I can make it run a whole hell of a lot better then it is stock (51mph), and to be honest, yeah it won't be the fastest thing in the world, but until I can get into something newer and a little bigger and speed effient years down the road, I don't really like anything else out there for the money I got into my Formula. Yeah I know I could go fast for cheap in a Baja, but I like the quality and ride of my boat. Plus, if that motor is making 460/500 with the same exact build as me, how can I not match that or pass it with a single plane, roller rockers, and long tubes? Just sayin... I think I can get close

My experience with single plane vs dual plane comes from two back to back dyno comparisons. The first of which was a 9.5-1 comp. 468 with Merlin oval port heads a short duration solid flat tappet cam (270* s-s)and a Holley hp750 carb. The Victor jr. made an extra 23hp at 5300rpm over a performer rpm air gap. Torque was the major factor on that motor which was the reason for the test but surprisingly the air gap only made significantly more torque below 3000rpm. From 3500 - 4500 the torque curve was almost the same and from 4500 up the victor jr. started to make more torque. End result 514hp at 5300rpm with the victor jr.

Second experience was a far different combination than anything you would run in a boat but a 12.5-1 comp. 447ci motor with a 296*/304* s-s .714 lift cam and ported 781 oval port heads picked up 41hp with a Dart single plane over a performer rpm air gap. That motor made 652hp and 587tq on 110 octane

There are tons of variables and every motor is different but the dyno is the only way to know what the motor will respond to.
I'm not trying to argue my point but just sharing the experience from which my opinion is based. I would be more interested than anyone to see a back to back comparison on a marine motor with wet exhaust.

I wonder what your motor would make on that dyno ....... :party-smiley-004:

Even dyno numbers can be subject to scrutiny