How much RPM will it handle?

[BlueLightSpecial]

Kind of a crazy question, but does anyone know if an AQ280 will handle a Small Block Chevy that safely turns 6000rpm? An engine builder friend of mine is trying to convince me to build a motor with him, for my boat. He has built many marine engines, but they were all backed by a mercruiser. It would be a low torque motor, but my concern isnt the torque, it is the additional 2000 rpm that is possible. Will the upper and lower gear boxes handle it? Im thinking they wont, and I am still happy with the performance of the stock 305, but then again, there is no such thing as a car or boat too fast!

 

[Bondo]

Re: How much RPM will it handle?

Kind of a crazy question, but does anyone know if an AQ280 will handle a Small Block Chevy that safely turns 6000rpm? An engine builder friend of mine is trying to convince me to build a motor with him, for my boat. He has built many marine engines, but they were all backed by a mercruiser. It would be a low torque motor, but my concern isnt the torque, it is the additional 2000 rpm that is possible. Will the upper and lower gear boxes handle it? Im thinking they wont, and I am still happy with the performance of the stock 305, but then again, there is no such thing as a car or boat too fast!

Ayuh,.... You, 'n especially, yer Bud don't seem to understand a Boat motor,....

If ya build a High spinnin', No low end, Torque-less motor,....

It'll Never get to 6 Grand, 'cause it'll never get outa the hole....

Build yerself a motor, that is All in, by 4 Grand, 'n peaks out at 4800 rpms...

That's the WHY of Marine cams,... yer Power's gotta be made from Idle, to 'bout 5 Grand....

 

[aerobat]

Re: How much RPM will it handle?

bond, fully respectfully, but rubbish.

power is torque x rpm. when you have an engine which cannot offer you much torque but much rpm you have to use a lower gearing in the drive to get good results or you holeshot sucks and the engine struggels to rev out.

when you have an engine which offers you much torque but low rpm,s you have to choose higher gearing or you will have a very good hole shot but the engine will overrev and the topseed sucks.


what you are right is the thing that they may get dissapointed when they use a drive ratio designed fora a low rpm high torque engine.

basicly torque and rpm,s are tradeable against each other and for this we have a gearing to meet the engine characteristic. engine torque alone as a number without looking at the reving capability of the engine as well the gearing means virtually nothing.

cheers

 

[Bondo]

Re: How much RPM will it handle?

bond, fully respectfully, but rubbish.

power is torque x rpm. when you have an engine which cannot offer you much torque but much rpm you have to use a lower gearing in the drive to get good results or you holeshot sucks and the engine struggels to rev out.

when you have an engine which offers you much torque but low rpm,s you have to choose higher gearing or you will have a very good hole shot but the engine will overrev and the topseed sucks.


what you are right is the thing that they may get dissapointed when they use a drive ratio designed fora a low rpm high torque engine.

basicly torque and rpm,s are tradeable against each other and for this we have a gearing to meet the engine characteristic. engine torque alone as a number without looking at the reving capability of the engine as well the gearing means virtually nothing.

cheers

Ayuh,.... Let me Guess,... Yer a Hotrod Car guy,... I know what power is,.... 'n how to make it....

Put a big enough cam in a SBC to spin 6 Grand, 'n the boat will never break over onto plane....
Especially in a 305....

Put it in with a jetdrive, 'n you'll Fly.... but this ain't no jetdrive...

Why do ya think all the Hotrod guys go to Hi-stall converters,..??

 

[aerobat]

Re: How much RPM will it handle?

Put a big enough cam in a SBC to spin 6 Grand, 'n the boat will never break over onto plane....

our cam results in a higher output at high revs and weaker low end torque right ? sooo... like said just use a gear of lets say 2.0 :1 and not 1.5:1 and i assure you you will get onto plane ,with a higher topspeed, since the engine simply pushes more horses into the water.

this mercury racing V8 revs 6000-6500 rpm,s- with a big cam- and i assure you it will get on plane here as well.

http://www.mercuryracing.com/sterndrives/hp1100/specs.php

further-i also assure you a 150hp honda outboard with lower displacement but 6000rpm is not weaker than a 150hp inboard with much higher displacement and torque but just 4200rpm. ( excluding the factor of mass outboard vs I/O) -the honda has a lower gearing and trades torque vs rpm to get the same output at the prop.

cheers

 

[Bondo]

Re: How much RPM will it handle?

our cam results in a higher output at high revs and weaker low end torque right ? sooo... like said just use a gear of lets say 2.0 :1 and not 1.5:1 and i assure you you will get onto plane ,with a higher topspeed, since the engine simply pushes more horses into the water.

this mercury racing V8 revs 6000-6500 rpm,s- with a big cam- and i assure you it will get on plane here as well.

http://www.mercuryracing.com/sterndrives/hp1100/specs.php

further-i also assure you a 150hp honda outboard with lower displacement but 6000rpm is not weaker than a 150hp inboard with much higher displacement and torque but just 4200rpm. ( excluding the factor of mass outboard vs I/O) -the honda has a lower gearing and trades torque vs rpm to get the same output at the prop.

cheers

Ayuh,.... He said 6 Grand,.... not 16 Grand.... The OP is also not Mercury Racing....

Run the numbers,... yer full of it,....

Ever notice ya don't see millions of German hi-revin', Hi-horsepower motors, pushin' millions of Boats, all over the world,....

There's a reason for that....

 

[aerobat]

Re: How much RPM will it handle?

Ever notice ya don't see millions of German hi-revin', Hi-horsepower motors, pushin' millions of Boats, all over the world,....

There's a reason for that....

the reason are the production costs vs benefits of the "old" GM blocks used by mercruiser and volvo as well marketing strategy of succesfully selling proven and working "old" engines vs the development and purchase costs of new designs.

it has nothing to do with the physics of torque and power.

you can install a 200 bhp 80 lb/ft 15000rpm japanese motorcycle engine in a boat and it will with a proper gearing outperform a 150 hp 180 lb/ft 4200 rpm GM block in top speed and hole shot since it pushes more force ( power) on the prop -but there is no market for having such a screamer in the back .

i VERY much appreciate your knowledge and help with real issues , its not to pay, but in this particular case you are fundamental wrong about what torque and power is.

torque is the turning force of the engine , power the product how strong and how fast the engine can do it. the low torque high rev engine cannot turn the flywheel very strong, but it can turn the flywheel very fast so a lower gearing can be used to convert the low force high spin input in a high force low speed output at the prop - and the prop finally pushes our boat, not the engine torque by itself !

 

[Maclin]

Re: How much RPM will it handle?

The thing about "proper gearing" for a high-winder with no torque to speak of off idle is, you end up at about the same top speed by the time you gear it down to multiply the missing torque enough to come out of the hole. On a car "out of the hole" is figurative speech. On a boat it literally has a hole to climb out of.

 

[jimmbo]

Re: How much RPM will it handle?

Many a hot rodder has failed to make a good marine engine.

 

[Scott Danforth]

Re: How much RPM will it handle?

if you want a killer small block in a boat, build a 383 stroker, or even use a tall deck block and build a 434. the 305 wont cut it. set up a drag race motor or a hot rod motor to climb a 10 mile long drag strip at a 45 degree angle and you get the idea of building a boat motor. Think more tow truck than high reving small block.

 

[BlueLightSpecial]

Re: How much RPM will it handle?

First off, he is a reputable engine builder. He builds engines for a local marine shop, as they race formula 1. He has built his reputation by building marine engines, and. Circle track engines. 2nd, he is building a 383, not my ho hum 305. My question was, would my 280 handle 6000 rpm. I did not ask, how to build a hot rod marine engine, I have an EXPERT doing that for me. He has never built one for the old volvos, so he wasn't 100% sure if they would handle the rpm. I appreciate some of the responses, but, mr bondo, with all due respect, I am not a freaking idiot.

 

[Scott Danforth]

Re: How much RPM will it handle?

your boat and exhaust choice will determine your cam. that in turn will limit your RPM. if your using thru-drive exhaust, your limited to a 268/270 cam to prevent reversion - which will run out of steam between 5000 and 5500 RPM. can the VP drive handle 6000 RPM, maybe - however it will handle 5000 RPM all day long

 

[aerobat]

Re: How much RPM will it handle?

I did not ask, how to build a hot rod marine engine, I have an EXPERT doing that for me. He has never built one for the old volvos, so he wasn't 100% sure if they would handle the rpm.

to come to this particular question i,m afraid nobody can tell you for sure. not a single volvo penta revs in that region so the leg is not designed or tested for that rpm,s . it also depends how much juice your tuned engine will put into this leg at 6000 , its not only the rpm,s by itself.

on the other hand i do not see a solid reason why it should in every case not handle 6000rpm.

remember also that when you use the original gearing the prop may turn at 6000 engine rpm that fast that you get severe cavitation problems and finally have no use of it . further , but that depends on setup, when your engine develops high power at high rpms but low end is weak you may be indeed dissapointed on getting out of the hole when you leave the gearing in the drive as it is.

just try it out and report the results !

 

[Maclin]

Re: How much RPM will it handle?

The whole idea of a 383 stroker is more torque down low and midrange so I do not understand your "It would be a low torque motor" comment.

I am sure you have all confidence in the builder, but it sounds like he builds for racing. If you are racing, then ok, but for a recreational boat I think that rpm "goal" will be troublesome and cause drivability issues from a dead stop.

Scott D's description of what a boat engine "sees" compared to a dragracing car is perfect. If the low end is "ignored" it will not be much fun out on the water in my best "bench boating" opinion.

 

[Scott Danforth]

Re: How much RPM will it handle?

Thanks Maclin

 

[BlueLightSpecial]

Re: How much RPM will it handle?

Ok, he was out on the boat with me today. I asked him about the low torque motor. He said from idle. He meant lower in the rpm range. I am partially deaf in the left ear, so I didn't hear " low RPM torque". He said he could build a reliable 383, or 406, that would give the the torque I need, and spin 5500+ all day long. All on pump gas. I just have to pay his cost for parts. All machine work will be done by him, and free of charge. He is planning on using the 64cc vortec heads that he will massage over, a marine cam (can't remember which one he said). My apologies for stirring up a debate, I need to remember to turn my head to the good ear, so as not to miss important details. Oh, and sorry bond-o for getting pi$$y. I know you know your stuff, and you have helped me in the past.

 

[muc]

Re: How much RPM will it handle?

1983 Galaxy 19' B/R with a V/P AQ225D/280

Will a AQ280 handle 6,000 RPM ---- probably ----- but why would you care?

You got to get that power to the water.

1. most 280 drives don’t have trim – if yours does great, but if it doesn’t most of the horsepower gain won’t be useable.
2. where will you find a prop that will work? It’s all good to talk about gearing but outdrives only have ONE gear. To get a high RPM motor to work in a boat you must use controlled slip of the prop to overcome the lack of low RPM torque. This is done by directing some of the exhaust gasses over the prop to allow the engine to spin up enough RPM’s to get into it’s power band --- something I don’t think you will be able to do with a 280 drive.

Aerobat ---- I love your idea of a 200 HP motorcylce engine in a boat. Did you plan on slipping the clutch or using the 6 speed transmission to make up for the fact that engine has no usable power until 4,000 RPM?

BlueLightSpecial --- If your looking to go a little faster you will be happy but if your looking to go a lot faster I’m afraid your hull/drive combination will be a big dissapointment.

After 30 years in the boat business I have found that 95% of the time the saying “if you want a faster boat – sell your boat and buy a faster boat” is very true.

 

[BlueLightSpecial]

Re: How much RPM will it handle?

Tell this to my wife:

After 30 years in the boat business I have found that 95% of the time the saying “if you want a faster boat – sell your boat and buy a faster boat” is very true.[/QUOTE]
T

 

[aerobat]

Re: How much RPM will it handle?

Aerobat ---- I love your idea of a 200 HP motorcylce engine in a boat. Did you plan on slipping the clutch or using the 6 speed transmission to make up for the fact that engine has no usable power until 4,000 RPM?

lets take for even numbers a 3.0 150HP I/O with a 2:1 transmisson. when the engine revs 4200rpm the prop turns 2100rpm and absorbes 150 horses , right? gunning the engine will result in about 3000engine rpm and 1500 prop rpm until out of the hole and the engine can rev further due to lower resistance when on gliding speed, correct?

now take a 1.0 200 hp 15000rpm motorcycle engine , install the same prop and aim for the same 2100 prop rpm at rated engine speed. that calls for a more than 7:1 gear ratio . with this ratio and about the same 1500prop rpm to get out of the hole the engine will rev 10500 rpm and not 4000. in this region you can bet it has power.

of course its purely theoretical, but hopefully helps to understand what i mean.

the smaller high rev engine just trades massive rpm for lack of engine torque to get finally more torque and power on the final prop shaft .



nevertheless such things are not practicable in boats for mainly two reasons.

1) its far more costly to develop a very high rev high tech small displacement engine for a given power than a low tech high displacement low rev engine when space and mass in a boat is not that critical like in a motorcycle.

2)bigger displacement low rev engines tend to have a more flat torque curve than smaller high rev engines which is all in all more practicable for multiple recreational use like trolling, planing, tubing , skiing and more.

cheers !

 

[Bondo]

Re: How much RPM will it handle?

Ok, he was out on the boat with me today. I asked him about the low torque motor. He said from idle. He meant lower in the rpm range. I am partially deaf in the left ear, so I didn't hear " low RPM torque". He said he could build a reliable 383, or 406, that would give the the torque I need, and spin 5500+ all day long. All on pump gas. I just have to pay his cost for parts. All machine work will be done by him, and free of charge. He is planning on using the 64cc vortec heads that he will massage over, a marine cam (can't remember which one he said). My apologies for stirring up a debate, I need to remember to turn my head to the good ear, so as not to miss important details. Oh, and sorry bond-o for getting pi$$y. I know you know your stuff, and you have helped me in the past.

Ayuh,.... Reread the thread,.... It's the points raised by aerobat that I was goin' after anyways...

'n yer 1st post lead me to believe you were thinkin' of the 305,...
You said Nothin' of a 383...