Factory Horsepower ratings

[fraserscrane]

Does anybody know what the factory horsepower rating is for a 1989 ford 460 king cobra?I heard it is 340 h.p..Ijust had my 460 completely rebuilt bored out .030",polished & balanced crank all new bearings,a performance marine camshaft heads were completely rebuilt & cleaned up for better flow all new gaskets etc.I paid the extra $ & put it on the dynometer(more just to make sure everything was in proper running order)The motor peaked at 325.5 h.p.@4600 rpm.The torque peaked at 430.8 ftlbs@2800rpms.WHAT HAPPENED TO MY H.P.??Is the factory exagerating with their ratings?The boat is a 22' larson senza,which I have not yet had in the water,so I'm hoping this motor will move the boat past 60mph.Any info will be greatly appreciated.Does anyone know actual factory specs Thank's Fraser

 

[paulie0735]

Re: Factory Horsepower ratings

Well, I hate to burst your bubble but this is a very good lesson for all those who expect big changes from relatively minor engine work. When you break it down, all you have really done is add the cam and all that’s done is move your peak HP up the rev range a touch. These engines were never all that powerful but they made nice fat torque at low rpm and that’s why they used them for boat screws. Your dyno sheet tells you the entire story...... 430 ftlbs at 2,800 rpm!!! That’s 230hp at a ‘very low’ rpm. That's up on the factory spec and I would think mostly due to the over size bore. Compare those numbers with most new engines today and you will see what I mean. The stock 460 heads flow more than adequately and won't benefit from any clean up work unless your gunna run a supercharger or your going to spin the thing past 5,500 rpm. The rest of the money you spent really just freshened it up back to the original factory specs. What you have now is a healthy 460 that will launch your boat out of the hole as well as it did when it was new. As for your top speed being higher than when it was new!! No, but you should feel a bit more mid range push via the bigger cam. Just make sure it’s propped for 4,700rpm (peak hp) at WOT. Should sound nice too with that bigger cam but the down side will likely be a bigger gas bill……….. for the record if you want big hp gains from these engines you need to do extensive work to both the exhaust and inlet sides for fuel and air, spark advance curve will need to be reworked, compression needs to come up into the 10’s and cam needs 500th lift at least. Than you need to spin the thing into the high 5’s or 6. Getting that much rotating mass to hold together at those speeds means a ‘big money’ investment in the bottom end and also the valve components will all need to be the good stuff……….. Good luck with rebuild no2.

 

[lilmandavis]

Re: Factory Horsepower ratings

ive got the factory omc 460 and it blew a cam on me so i rebuilt it with h beams 10-1 pistons threw out the main bolts and put in studs. forged crrank, reconditioned h beams, v series bearings, melling oil pump. cc'd the intake and exaust chambers to match each other hogged the intake to match the ports on the heads. i dont like to polish the intake ports cause it eliminates the turbulence to get the mixture good. i figure i can get about 52-5500 rpms out of her. but does it ever suck gas man. i should of built a roller 350 with just as much power for ALOT cheaper. wouldnt have that low end torque though. iv e got like 6 grand in the thing. i should of had it dynoed its bored 30 over. anything else and its goin in my truck!! screw the boat!! heres a pic of it almost done

http://i78.photobucket.com/albums/j91/joshuaj_33909/100_30341.jpg
im just scared of the cobra blowing apart on me now so i cant really push it!!!!

 

[fraserscrane]

Re: Factory Horsepower ratings

Well, I hate to burst your bubble but this is a very good lesson for all those who expect big changes from relatively minor engine work. When you break it down, all you have really done is add the cam and all that’s done is move your peak HP up the rev range a touch. These engines were never all that powerful but they made nice fat torque at low rpm and that’s why they used them for boat screws. Your dyno sheet tells you the entire story...... 430 ftlbs at 2,800 rpm!!! That’s 230hp at a ‘very low’ rpm. That's up on the factory spec and I would think mostly due to the over size bore. Compare those numbers with most new engines today and you will see what I mean. The stock 460 heads flow more than adequately and won't benefit from any clean up work unless your gunna run a supercharger or your going to spin the thing past 5,500 rpm. The rest of the money you spent really just freshened it up back to the original factory specs. What you have now is a healthy 460 that will launch your boat out of the hole as well as it did when it was new. As for your top speed being higher than when it was new!! No, but you should feel a bit more mid range push via the bigger cam. Just make sure it’s propped for 4,700rpm (peak hp) at WOT. Should sound nice too with that bigger cam but the down side will likely be a bigger gas bill……….. for the record if you want big hp gains from these engines you need to do extensive work to both the exhaust and inlet sides for fuel and air, spark advance curve will need to be reworked, compression needs to come up into the 10’s and cam needs 500th lift at least. Than you need to spin the thing into the high 5’s or 6. Getting that much rotating mass to hold together at those speeds means a ‘big money’ investment in the bottom end and also the valve components will all need to be the good stuff……….. Good luck with rebuild no2.

 

[ron7000]

Re: Factory Horsepower ratings

hey post your dyno sheet !

I don't know factory specs, google might return some info on 460's. It wouldn't be the first time ratings were exaggerated, especially from Ford.

hp = (tq * rpm ) / 5252

horsepower is a calculated number from torque and rpm, so don't get all bent out of shape over it. A given torque at higher rpm equals a higher horsepower number than at a lower rpm. Torque is the unit of measurement of what the engine produces, so you want as much of it as you can get bu t have to decide at rpm is most practical.
If you're goal is to go as fast as possible then you'd want to get as much torque as high a rpm as possible, since the faster you spin the prop the faster you go. The only limitation is you need enough low end power to get the boat on plane for the given prop and not lug the motor too bad.

I don't put too much stock in the saying a boat has to be propped so you hit w.o.t. rpm range. It's taken out of context. What dictates the w.o.t. range? my best guess is it's the point where the tq curve starts dropping significantly and you stop making hp. For smallblocks that's always in the range of 4000-5000 rpm but for a big block where torque can peak at such a lower rpm, or if you mod the motor different from what the factory rated everything at, then your wot range is going to be lower. Going by your dyno sheet, I would think you could have wot rpm at 3000-3500 rpm and be ok. I would just prop the hell out of it and see how fast it'll go as long as the motor isn't bogged down and lugging when getting on plane. I'm guessing on your dyno sheet that torque falls off pretty good from 430 lb-ft at 2800 rpm, we already know you have 370 lb-ft at 4600 rpm. You can use excel to play with the affects rpm has on power.

 

[QC]

Re: Factory Horsepower ratings

I just want to add a little to this as I am on a personal crusade to clarify the torque discussion as it relates to engine performance; the media and advertisers have done a great job of confusing 99% of the public on this topic. paulie0735c has done an excellent job of explaining things here, but I wanted to emphasize a good point he makes. There is no top end performance improvement to a marine application by increasing low RPM torque (peak torque). The ONLY benefit of low RPM torque increases is hole shot improvement (time to plane). Whenever evaluating marine performance improvements it needs to be understood that the low end torque increases will NOT translate to higher top speeds unless you also increase the high end horsepower and prop accordingly.

lilmandavis also displays an excellent understanding of this with his 350 roller comment . . .

Edit: I was typing as ron7000 posted. I believe what he describes is a good way to burn valves and blow up outdrives . . . and to decrease hole shot.

 

[ron7000]

Re: Factory Horsepower ratings

i dont like to polish the intake ports cause it eliminates the turbulence to get the mixture good.

if it works for you then more power to you, but you'll find info widely available contrary to that idea. The purpose of doing anything to the intake is to increase flow especially at high rpm for power. Turbulence as in mixing the air and fuel so that every fuel molecule hooks up with an O2 molecule happens in the cylinder. If you slow down incoming air you're losing power that would otherwise be available.

 

[Tail_Gunner]

Re: Factory Horsepower ratings

:/ ok i might be missing something here, but ron7000 the prop is the final component in the boat's preformance. If you have a lot of tourqe @ lower rpm that indeed will help with a hole shot and if the right prop (type) is used it will increase fuel effeincy. However when going to WOT it is critical to have a prop that will run on the edge of the engine's rpm band, over propping will lug a engine and under propping will .............well just defeat the purpose.



If your engine is running @ it's peak preformance id suggest you take measurements aka speed @ wot go to prop forums and post your preformance and what type result's you are looking for. It will save you a lot of guess work and money.

From my limited understanding of prop's youd try to find a prop that has the most cup and rake (= bite) then go to A pitch that will run your motor @ its peak rpm range, From there you will have to decide if a 4 blade is in order for good midrange boating or a 3 blade higher top end @ less of a hole shot.............Umm maybe trim tabs or a combination of both.

:devil: Opp's a bit off topic there, but did you recarb for your new cam and increased bore?

Edit: ok dont know if this helps much but i did some research and what i found was a orignal truck engine only had 215hp @ 370lbs of tourqe, and thinking back i can remeber the 460 alway's had breathing problems. (carbration) You might want to look into a 850-900 cfm carbif you havnt already. Looking @ your spec's that 460 is a beast (tourqe) you might want to regear trying to take advantage of all the tourqe, see if you get Don or a few with his knowledge of your sterndrive and see if you can spin one up taller gears........... aka Overdrive.

 

[ron7000]

Re: Factory Horsepower ratings

I understand and agree with you that you don't want to be overpropped where the engine is overworked, to the point your hurting the engine. Coming up with the criteria defining when the engine is overworked is a whole other topic as well. What I'm asking is what defines "the edge of the engine's rpm band" ?
What determines what rpm you should hit at w.o.t. ?
I think I know the answer but I'm asking as well.

 

[QC]

Re: Factory Horsepower ratings

What determines what rpm you should hit at w.o.t. ?

Cost, manufacturers, design, engineers, cost, valve train components, airflow, warranty, engine life, cost, input components speed capability, metallurgy, cost, volumetric efficiency, physics, compromises, lack of transmission, etc. etc. etc. oh, did I mention cost?

 

[Tail_Gunner]

Re: Factory Horsepower ratings

What determines what rpm you should hit at w.o.t. ?

Without going inot great detail, Wide Open Throtle reaching the maxium rpm the mfg states. With that said putting a prop on that will run @ wot and reach a certain speed, It can vary greatly from one prop to the next (speed that is) The trick is to find a prop that will grab the water, lift the boat (whether the stern need's lifting or the bow) and still run right @ wot, In this case the motor has a tremendous amount of touqe so by increaseing the gear ratio you can turn the prop faster, and here comes the catch 22 can you gear a stern drive up and will it hang together............Im damm sure that motor has enough tourqe to pull about anything............. lol its almost the same as a 7.3 liter powerstroke diesel

 

[ron7000]

Re: Factory Horsepower ratings

am i close?
yes, I have nothing better to do :=

 

[QC]

Re: Factory Horsepower ratings

Well your graph is right. Yes theoretically, fuel economy would be better if you propped to run that boat at 2800 RPM wot, but it wouldn't plane unless you had a transmission. Also there is an addition to the "C" word . . . and the "W" word (cost and weight).

Yes, it would cruise very efficiently, but it would suck is another way to put it

 

[Tail_Gunner]

Re: Factory Horsepower ratings

What your graph show is the engine @ its peak tourqe and while its realative its only half of the answer and theroy ( this is a real engine)

If that graph holds true 8) it should crusie and plane very nicely Id suggest a 4 blade stilleto or it would really compliment that system, but he wants speed lol its not a barge and am i assuming here that is what your trying to acheive just proping for maxium thurst @ such a low rpm? Edit :er tourqe

 

[QC]

Re: Factory Horsepower ratings

Maximum thrust is acheived at maximum horsepower . . .

 

[fraserscrane]

Re: Factory Horsepower ratings

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[whywhyzed]

Re: Factory Horsepower ratings

Eddy the Jack russell typed that...

 

[ron7000]

Re: Factory Horsepower ratings

> Maximum thrust is acheived at maximum horsepower

I disagree, max thrust is at max torque because torque is the unit of turning force coming out the crank which is turning the prop. Thrust can be independent of rpm, just increase the prop pitch.

on the tq/hp chart, since hp is calculated from tq you can almost always back out the graph given the two numbers at their rpm. This one is rather easy because you know they are peak values and tq is so much lower in rpm than hp. I basically kept tq as high as possible till max hp was hit at 4600 and also maintain a reasonable curve. The curves between 2800 and 4600 have to be darn close, I could be off a few hundred lb-ft < 2000 rpm, there I just guessed.

my opinion is prop it as high as you can so that the boat doesn't struggle getting on plane from 1000-2000 rpm and gives adequate performance, and w.o.t. is no less than 2800 rpm which is based off the dyno value. Propping less than this and your just going easier on the motor, which isn't a bad thing but you're giving up max thrust which is max speed.

 

[fraserscrane]

Re: Factory Horsepower ratings

Hey!!.Great info.- Thank's for everyones time!!.I do have the dyno sheet & am trying to copy to this site.This sheet show's fuel consumption at pounds per hour,which I'm sure will interest you.I belive that 1 gallon of fuel weigh's approx.8 pounds.The fuel levels are at the 9th from the left of the chart(or the 2nd from the the right).The chart shows rpms first,then torque,h.p.,etc.oil temp,water temp..I hope this helps .A LITTLE MORE INFO ON THIS BOAT-.The original prop is aluminum,14 1./4x21.It now a stainless prop but not sure of size.I know i'ts a 3 blade,the boat is at the marina waiting for the motor.I bought this this boat from the widow of the original owner.He died last may,and until then the boat ,was hardly used(31 hours on engine meter)not sure how many actual hours,but does not have 1 single scratch,no damage at all & It's a 1989!!!.The block had a nasty crack at the front,& 1 frost plug was gone,from not being winterized,hence the rebuild.I did opt for a new block,but learned that the original block had been bored in the past.The pistons were in brand new condition,so I had the new block bored(good move???)I hope so.Like I said ,I HAVE NOT YET HAD IN THE WATER!!!!.& I hope I do not have any issues.The outdrive has been gone over & ok(I hope).New seals,impellor etc.I have very little previous history of this boat,but The hull is super clean,no stress cracks whatsoever,original interior is like new,roller trailer is as new!!.I paid $ 6000.00 for package as is .The motor cost $ 5000.00 including the dyno,($750.00 for dyno).Another $1000bucks to remove & reinstall the motor).I was talking to a guy that has this same boat listed at$22500.00 up here in Canada,so I hope I'm not to far off with all the extra bullshit I've gone through!!!.I will post my gps results,including different props etc.What a great site!!! awesome info ,I'll try to repay what I' m in the mist of learning Thank's Fraser P.S KEEP SENDING YOUR FEEDBACK!!!!

 

[QC]

Re: Factory Horsepower ratings

ron7000,

Thrust is work, Horsepower is work. Torque is twisting effort. You can make 300 lb/ft torque with yiur bare hands. I guarantee you cannot make as much thrust as a 300 bhp engine . . . Think of thrust as a jet drive. Pushing effort out the snout . . . Ya gotta have bhp . . .