383 volvo upgrade?

[pine island fred]

Re: 383 volvo upgrade?

Hi guys. Been eavse dropping on your conversation, always wanting to learn something. Question came to my mind. Have not paid much attention to engine size and related HP. for what seems a life time ago. Saw reference to a 383, ( CHRYSLER ? ) rated at 350 hp. Thinking that is a lot of HP for a marine engine that size.
Went to my YAMAHA book and sure enough my engine is rated 115 HP. at 5500 RPM from about 108 cu., respectable output for an engine that size although I never turn that fast, most people do. Now I picture a 383 flayling away under the deck at 5200 RPM, 60 miles off shore, continuous power setting. Can that engine be that reliable to ask it to do that? Considered that is the rating of the engine but the prop will not allow it to turn that fast, lots of metal turning. In a boat, what would be the max RPM when firewalled and HP output at that setting? Is this a normally asperated engine with marine manifolds?
Understand, my experience with an engine under the deck goes back to a 327 ( RAMBLER) rated at 220 hp. back in the 60s so I have been out of touch with these for quite some time. Might explain my dumb question. regards FRED

 

[Maclin]

Re: 383 volvo upgrade?

Thanks for the elegant and factful post there Reo.

This has been discussed here before, someone posted a HP and Torque graph where the torque was in one scale and the HP was in an other and claimed this proved that they do not intersect "there", but in all realities where graph scaling is equal they HAVE to. And as Reo re-iterated, it has nothing to do with peak torque, volumetric efficiency , BMEP or anything else.

 

[Maclin]

Re: 383 volvo upgrade?

Hi guys. Been eavse dropping on your conversation, always wanting to learn something. Question came to my mind. Have not paid much attention to engine size and related HP. for what seems a life time ago. Saw reference to a 383, ( CHRYSLER ? ) rated at 350 hp. Thinking that is a lot of HP for a marine engine that size.

The 383 being discussed is a Chevy small block stroker, not a Chrysler.

As to the other question about maximums, in general drives are designed for 5,000rpm action and below. Some can handle more torque than others., The drive ratio and prop pitch combination determine the final load placed on the engine.

In auto racing in general more RPM means more power, so raising the peak HP by camming appropriately works well there especially since a transmission is part of the equation. In boats there is only one "gear". Also the exhaust system is used for more than just efficient expelling of the exhaust. It also expels the spent cooling water. It also must itself stay cooler than in an auto due to the small enclosure it is in. Water is right at the end of the exhaust manifold ready to get sucked back in due to the phenemon called Reversion whereby a small negative pulse draws the moisture back up the exhaust path. Putting a race type cam in farly stock marine I/O configurations is a good recipe for reversion and hydrolock problems at some point.

There are different exhaust options. Water jacketed headers that exit thru-hull can eliminate the reversions problems from large cams. You still have the problem with drives wanting to stay around 5,000 rpm, and again drive ratio and prop pitch are the ultimate limiter there regarding the balance between holeshot and top speed.

Low end torque improvements are one path to more satisfying performance in marine applications where the stock exhaust will be maintained. Again prop pitch and drive ratio are major parts of any equation. Increasing the engine's low end torque in a large enough amount may mean you can go the next lower numeric ratio and still maintain the desired holeshot and also get more top speed.

 

[mylesm260]

Re: 383 volvo upgrade?

Um... I'm pretty sure that's not entirely correct

Example:
http://www.nsxprime.com/FAQ/Technical/images/97nsxpowercurve.gif

You're right that many auto engine torque/hp graphs are that way, but not all of 'em, and not all marine engines either. FYI it's not some kind of universal engine law that they intersect there, it's due to the desired power range of those engines which are made to be coupled to auto transmissions driving auto wheels.

Erik

Uhhh

HP = Torque @ rpms / 5252


so at 5252 RPMS, an engine will have the same HP as TQ. Always.

You're graph doesn't count because your'e TQ and HP scales are different.

 

[pine island fred]

Re: 383 volvo upgrade?

Thank you for your reply. Reminds me of reading the tech articles in ROD & CUSTOM or HOT ROD to many years ago. What caught my eye was the poster mentioned going 60 to 80 miles off shore and I was wondering about reliability. Would you normally run an engine of that size at 5200 continuous? Have always assumed that the longer the stroke the peak torque came in at a lower RPM. High speed diesels use to torque out at 600 to even 800 RPM but they were BALDWIN or ALCO units, different animals. My experience is very limited with inboards or I/O, few time I have operated one I have found them best at what at least use to be called ON THE CAM. Everything is just right and the throttle is back off the firewall. Never wanted to bring a trashed engine back to the owner. Once operated a friends ISLAND GYPSY with twin diesels. They would spin up to 2400 rpm but anything over 2100 was of no consequence to performance.
While I have your attention ( maby) could you give me another heads up on a theory? What is the maximum bore for an engine in relation to the stroke ? Does manifold pressure or compression ratio have anything to do with it? Saw mention of it somewhere but it was only a very brief statement. Thanks! regards FRED

 

[Reo Baird]

Re: 383 volvo upgrade?

Thank you for your reply. Reminds me of reading the tech articles in ROD & CUSTOM or HOT ROD to many years ago. What caught my eye was the poster mentioned going 60 to 80 miles off shore and I was wondering about reliability. Would you normally run an engine of that size at 5200 continuous? Have always assumed that the longer the stroke the peak torque came in at a lower RPM. High speed diesels use to torque out at 600 to even 800 RPM but they were BALDWIN or ALCO units, different animals. My experience is very limited with inboards or I/O, few time I have operated one I have found them best at what at least use to be called ON THE CAM. Everything is just right and the throttle is back off the firewall. Never wanted to bring a trashed engine back to the owner. Once operated a friends ISLAND GYPSY with twin diesels. They would spin up to 2400 rpm but anything over 2100 was of no consequence to performance.
While I have your attention ( maby) could you give me another heads up on a theory? What is the maximum bore for an engine in relation to the stroke ? Does manifold pressure or compression ratio have anything to do with it? Saw mention of it somewhere but it was only a very brief statement. Thanks! regards FRED

As far as maximum bore vs stroke, its more a matter of maximum stroke vs bore. Bore is limited by block design. Too much bore = thin cylinder walls = block failure.

Ideally, you want a square bore to stroke ratio for least stress and most power output. Many high performance engines aim to meet this square bore to stroke ratio. Too much stroke means less RPM. RPM is what makes power. for example, to make 400 hp at 3000 rpm, you'd need twice as much torque (thus twice as much cylinder pressure and therefore stress on engine components) as you would to make 400hp at 6000rpm. That said, in marine applications, you need that big ton of low end torque as generally you are operating in the 0-5000rpm range, so using a high output high reving motor doesn't really make sense (therefore, extra stroke beyond what would be reasonable in a high reving motor would make sense).

 

[Ridemywideglide]

Re: 383 volvo upgrade?

Just because the numbers intersect at this number does not mean this is peak torque. It simply means that before 5252rpm, torque will be less than horsepower, and after 5252rpm, horsepower will be greater than torque.

I think this should read, before 5252 torque will be greater than horsepower, and after 5252, horsepower will be greater than torque.

Elsewise, very good, informative post.

 

[Reo Baird]

Re: 383 volvo upgrade?

I think this should read, before 5252 torque will be greater than horsepower, and after 5252, horsepower will be greater than torque.

Elsewise, very good, informative post.

Yes thats right... thanks for the correction.