19' jet boat that will run an Aluminum impeller, so rpm limit for an aluminum is around 5500 tops. Impeller will be selected based on motors torque curve.
I have the block torn apart at the machine shop. Trying to decide on compression ratio and cam for my setup to get it close to 500hp as possible.
850 dp carb
Ford racing manifold
Currently 2.5" log manifolds, might switch to thru transom headers
D3ve heads intake and exhaust ported per Scotty tech index
Stock sized valves
Needs to run on 89 octane at sea level
Keeping flat tappet cam style
Had .030 taken off block decks
What compression and cam would some of you run? I have my own idea, but want to hear others. Thanks!
19' jet boat that will run an Aluminum impeller, so rpm limit for an aluminum is around 5500 tops...Trying to decide on compression ratio and cam for my setup to get it close to 500hp as possible.
850 dp carb
Ford racing manifold
Currently 2.5" log manifolds, might switch to thru transom headers
D3ve heads intake and exhaust ported per Scotty tech index
Stock sized valves
Needs to run on 89 octane at sea level
Keeping flat tappet cam style
Had .030 taken off block decks
What compression and cam would some of you run? I have my own idea, but want to hear others. Thanks!
500 hp@5500 rpm or less with a stock stroke 460, D3 heads, a single 850 cfm carb, thru transom logs, a flat tappet cam, and on 89 octane pump gas is a reatlively tall order. Adding thru-transom tubular headers helps but that upgrade alone is not a guarantee. The heads must breathe well, and the carb big enough to allow the well prepped heads to breathe, for staters.
im not trying to hit 500, merely saying the most out of my setup with what is listed. So I can figure out what pistons i need to order and let the machine shop know how much to cut off of the heads and such.
Get a set of Federal Mogul, Speed-Pro Pistons. Flat top #H535P +oversize and mill the block decks .030".
Buy a custom cam & kit, do a good performance valve job and put it together with a Performer RPM intake manifold.
BTW, an aluminum impeller is only rated for around 425ish horse. After that a bronze piece is recomended, or a stainless piece if you want to spend the money. I'm not saying that you can't run more (I've put 600+ through mine) but you're poking the sleeping bear and at some point it will let go, and in a jet......it won't be pretty.
Impellers are rated for HP, not necessarily RPM because a certin amount of HP will only let the engine spin only so fast with a given cut on the impeller. Jets are like a water brake (like on a dyno). Engine RPM will be pretty predictable with a given HP and impeller cut.
After you get past a certain HP number it gets expensive for the jet to keep up, you start needing inducers and loaders to keep it fed out of the hole and at speed. Build your engine according to your wallet in that respect. A 550 horse engine will sound good and get you at around mid 60 MPH and be quite a hoot to drive and the whole shebang won't be as expensive to build and maintain as an ego tickling 650 horse set up that gulps $15/gallon 110 race fuel.
Rob
right, however I'm going to build and dyno this motor and select an impeller to match the torque curve best.
Im getting a set of flat top pistons with 4.2 cc dish, the block deck already has .030 taken off. I roughly cc'd my ported d3 heads and they came out to around 98cc. I know where my dynamic compression needs to be for 89 octane at sea level at 140 degree water temp. But cam and compression dictate dynamic. I don't know how much cam is too much for this setup, I need a good cam to match and i planned to make compression what it needs to be pending cam so my dynamic compression comes out right.
I just don't know how else to do so, last thing i want is to build it and be like well it could have made more power if it had a bigger cam but compression is to low for a bigger one. you know?
Adhering to a DYNAMIC compression for detonation control in anything other than a mild engine is a bunch of crap ... to many other things, like temperature and internal EGR and air velocity and quality past the intake seat and chamber swirl or tumble and quench, (both heat wise and combustion chamber activity wise, WILL make the REQUIRED dynamic compression different in every instance; static compression will always remain the same no matter what other circumstances are involved.
Keep in mind too that ANY water cooled exhaust system will sacrifice power when compared to a conventional style header at least in the testing I've done on my dyno. I've seen an engine drop about 100 horsepower when comparing a cheap set of chassis headers to a set of water cooled manifold and about 75 horsepower when running a set of water jacketed Lightning headers. The 454 small block Chevy that I built last year with jet boat in mind dropped 50 horsepower when going from a normal header to a set of Kodiak water cooled manifolds. That was on an engine that made 630 horsepower at 5700rpm in back to back testing.
After much debate I am going to use the 2.5" log manifolds that are each 2.5" to 3" outlets on the transom. Its a 1973 Taylor SS Im restoring and i want to keep the original look.
Water temp will be around 140 for the motor, quench will be whatever this .050 head gasket compresses is(not listed online, blue material), 4.2cc relieved flat tops, being a boat it will likely only be used during the summer so hot temps here in north texas.
140* engine temp is not enough. There's a reason that automotive engines are set up to run 180* or 190*. Depending on the type of cooling control you have for that set up IMO you need to be at at least 160* at full song. The set up that I run is a gate valve inside the transom that I adjust for the varying lake temperature and I generally run right at 180* at idle and about 20* cooler wide open. As a matter of fact the oil temp in a marine set up is what you want to pay attention first. Jets are constantly under load when they are running. The only time they are not is when they are idling or shut off. And even when idling they are somewhat loaded. Oil temp is a critical factor in a jet motor.
Rob
About 140 degrees is about what most off the shelf marine thermostats ARE.
The hotter it gets the better fuel you need to run in order to stay detonation. With 87 octane gasoline you will then NEED less compression ratio and therefore less power.
There's the key word, "power". You'll get better atomization, distribution, a more complete burn and better flame front with the optimal cylinder temperature. IMO, if detonation is a concern then the engine set up hasn't been addressed in the design stage correctly and using a lower temperature as a crutch is just that.....a crutch.
IMO.
Rob
any jet boat i know of runs about 140, in order to get warmer you have to limit flow to a point where you could possibly have boiling occur around the heat sources. Its not really a crutch because there is no way around it from what i have found in the jet boating community.
Hell i guess I could probably find a way to run 93 at sea level. Once or twice i might have to load up a few extra tanks of premium for long hauls where we might drive to another place on the water with a marina and restaurant. Its so seldom i could throw in a bladder filled with 93 though.
I've been running my boat at the temperatures I mentioned earlier for 8 years now and I've never had a boiling issue and it's never been a stock horsepower rating either.
Piston to wall clearances, even though a marine engine has larger wall clearances built in because of the colder than "normal" (ie: smaller bore diameter), are happier, and a more efficient burn is attained.
Most boat engines will tell you right on the valve cover to run 93 octane or better.
It's your engine, do as you wish.
Rob
CP has a thermostat kit for a BBC that can be adapted. I have an original Hardin for a BBF on the 460 in my 21 that I'll be using on the 545. Runs 175 all day long.
I didn't mean for that to sound antagonistic. I'm just trying to point out that sometimes general opinion isn't necessarily accurate (thank you internet).
.....But, then again, I've never been accused of always thinking inside the box or following the general consensus with my eyes closed either. lol
Rob
Well i was concerned about the logs being to restrictive but if I'm aiming for upwards of 500 i read logs are just fine. Obviously not as good as longitudes, but in a closed engine compartment and $1200 for headers I'm using logs!
Personally I would opt for a split duration camshaft with a lot more exhaust duration so as to compensate for the thru-transom log exhaust backing up at 5000 rpm (more than would the OT headers). Speculating on a possible 450-500 hp engine combo in my head, that cam might have 15* degrees @ 0.050" more than the intake...possibly more split than that.
On d3ve heads I found .005 removed = roughly 1cc. Is this information I found correct?
Mine measured 96cc today. If i Cut them down to 90cc it puts me right at 10.0x static compression with a .050 uncompressed head gasket.
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