Midrange and low RPM grunt. Discuss please.
11-08-2014, 08:35 AM
#1
Midrange and low RPM grunt. Discuss please.
I see alot of posts lately stating things like
I want a better cruising speed, so I care more about midrange.
I rarely go top speed, so I prefer a bit more power down low
My engines make more torque in the midrange, so I will cruise better
Heres my thoughts on that topic, which some may disagree, or agree with when it comes to building a high performance offshore style marine engine. Disregard this, if you have a ski boat.
Whether your engine makes 350HP at 3500, and 500HP at 5500, or 375FTlbs at 3500, and 500HP at 5500, you will use the same prop. Just because you're making a little more power at your cruise speed, your boat will not cruise faster. More efficiently, possible. But, to cruise faster, you simply need more pitch, more blades, reduced slip, and so on. We prop the boat for a proper wot rpm, which is determined by the engine build.
Now, if you come across a debacle in your engine build, on whether to choose components that will give you more power at 5500, for a slight loss in power at 3500, you may find your boat to run a faster WOT number, and a faster cruising speed, simply because you will be utilizing a taller pitch prop. But choosing the components that may allow a bit more power in the midrange, for a loss of power at wot, you will then find yourself cruising slower, with a slower top speed as well, again, because you wont be able to pull the higher pitch prop at wot.
We've all learned about the effect of port velocity with small oval port heads, dual plane intakes, that aid in low speed cylinder filling. You are not really bringing any new information when you come to oso, and start talking about a 454 build with peanut port heads, a dual plane intake, 650 carb, and try to sell everyone on that technology. It's nothing new, its 40+ year old concepts.
Now don't get me wrong, I am not suggesting taking your stock 454, and slapping on some 345 Dart heads on it, and creating an absolute turd. But technology has came a long way. Camshaft profiles, cylinder head technology, and induction systems have vastly changed since 1975. Things we can do today, with a simple 454 or 502 based engine, are so much further. There is much more to selecting components than simply port shape/size of a cylinder head.
You take a look at say an oval AFR 265 head, or say the 290 CNC version. What makes that head perform so well, isnt just the small runner idea. Its the whole package from the intake flange, to the exhaust flange. What they have designed, is a head that simply flows very well, in the application its to be used in. You simply cannot compare those two heads, to say a stock GM peanut port head, or a GM oval vortec head. Not even in the same league. Just like you cannot compare a GM rectangle port head, to a AFR 325 head, or a Dart 325 head, just because they share similar port CC's on the intake runners. We must remember that we are building marine engines. Most of us operate in an RPM range from say, 2800-6000RPM. The window of 1000RPM-2800RPM, is of little concern for most boaters. We just don't spend much time there. Now, a guy building a saturday night cruiser engine for his chevelle, may want something totally different.
Not long ago, cylinder heads and camshaft choices were somewhat limited. We sent our Chevy iron, to a head guy, and spent lots of money rebuilding them, and modding them in search of airflow, which in some cases, may still be a viable option. But, before you do so, I feel its very important, to determine whether you want to invest the money into those old iron heads, when the aftermarket has much better options, which can provide much greater returns in performance. I'd be willing to bet the single most popular cylinder head, here on oso, is the GM HI-Perf rectangle port casting. Not a bad cylinder head in its day. However, they simply do not hold a candle to whats out there on the shelves today.
There has probably been millions of dollars spent on bigger bore blocks, rotating assemblies, and things in search of more displacement to meet particular goals, when in fact the problem wasnt in the bore size, stroke, etc. We were all limited by cylinder head design, and camshaft design, to a particular HP per CI scenerio. Well, at least to stay within the realms of reliability, octane level, etc years back.
The same guys I see on oso, telling everyone to ditch their 454 for a 502, or ditch their 502 for a 540, are the same guys praising the LS series GM small blocks. The LS line of engines are ultimately impressive on what they can deliver, from a small package. We have technology to thank for that. While the rule "theres no substitute for cubic inches" still holds true, that line just isnt as clear as it was 25 years ago. Back then, some guys had a hard time making a 1hp per cubic inch mill stay together. Jacking up compression ratios, installing stupid cams, and what not, was just the way it had to be done. Lets say back then you had a 420HP 454 merc. You wanted to make 550-575HP. Out came the big dome pistons, a radical solid tappet cam, and it was off to the launch ramp with your poor idle quality, stalling in gear, reverting water, and so on. Today, you can easily hit that number, with a 9:1 hyd roller setup, that will idle very nice, and provide a long service life, by choosing the right induction components.
The 454ci big block chevy is hardly a "small" engine to work with, neither is the oso common 502. So before you throw it in the trash bin, take a second look at investing in a modern induction package, whether it be from RMBuilder, or any of the pro's on this site. Lets just calm down with the dual plane and peanut port stuff, and look further into building a great performing modern big block engine. For most of the oso tech guys, you already know this stuff, and can even enlighten further than myself. Just thought I'd throw this out there, as there seems to be quite a few Newbies around lately, who might be able to pick up something from this.
I want a better cruising speed, so I care more about midrange.
I rarely go top speed, so I prefer a bit more power down low
My engines make more torque in the midrange, so I will cruise better
Heres my thoughts on that topic, which some may disagree, or agree with when it comes to building a high performance offshore style marine engine. Disregard this, if you have a ski boat.
Whether your engine makes 350HP at 3500, and 500HP at 5500, or 375FTlbs at 3500, and 500HP at 5500, you will use the same prop. Just because you're making a little more power at your cruise speed, your boat will not cruise faster. More efficiently, possible. But, to cruise faster, you simply need more pitch, more blades, reduced slip, and so on. We prop the boat for a proper wot rpm, which is determined by the engine build.
Now, if you come across a debacle in your engine build, on whether to choose components that will give you more power at 5500, for a slight loss in power at 3500, you may find your boat to run a faster WOT number, and a faster cruising speed, simply because you will be utilizing a taller pitch prop. But choosing the components that may allow a bit more power in the midrange, for a loss of power at wot, you will then find yourself cruising slower, with a slower top speed as well, again, because you wont be able to pull the higher pitch prop at wot.
We've all learned about the effect of port velocity with small oval port heads, dual plane intakes, that aid in low speed cylinder filling. You are not really bringing any new information when you come to oso, and start talking about a 454 build with peanut port heads, a dual plane intake, 650 carb, and try to sell everyone on that technology. It's nothing new, its 40+ year old concepts.
Now don't get me wrong, I am not suggesting taking your stock 454, and slapping on some 345 Dart heads on it, and creating an absolute turd. But technology has came a long way. Camshaft profiles, cylinder head technology, and induction systems have vastly changed since 1975. Things we can do today, with a simple 454 or 502 based engine, are so much further. There is much more to selecting components than simply port shape/size of a cylinder head.
You take a look at say an oval AFR 265 head, or say the 290 CNC version. What makes that head perform so well, isnt just the small runner idea. Its the whole package from the intake flange, to the exhaust flange. What they have designed, is a head that simply flows very well, in the application its to be used in. You simply cannot compare those two heads, to say a stock GM peanut port head, or a GM oval vortec head. Not even in the same league. Just like you cannot compare a GM rectangle port head, to a AFR 325 head, or a Dart 325 head, just because they share similar port CC's on the intake runners. We must remember that we are building marine engines. Most of us operate in an RPM range from say, 2800-6000RPM. The window of 1000RPM-2800RPM, is of little concern for most boaters. We just don't spend much time there. Now, a guy building a saturday night cruiser engine for his chevelle, may want something totally different.
Not long ago, cylinder heads and camshaft choices were somewhat limited. We sent our Chevy iron, to a head guy, and spent lots of money rebuilding them, and modding them in search of airflow, which in some cases, may still be a viable option. But, before you do so, I feel its very important, to determine whether you want to invest the money into those old iron heads, when the aftermarket has much better options, which can provide much greater returns in performance. I'd be willing to bet the single most popular cylinder head, here on oso, is the GM HI-Perf rectangle port casting. Not a bad cylinder head in its day. However, they simply do not hold a candle to whats out there on the shelves today.
There has probably been millions of dollars spent on bigger bore blocks, rotating assemblies, and things in search of more displacement to meet particular goals, when in fact the problem wasnt in the bore size, stroke, etc. We were all limited by cylinder head design, and camshaft design, to a particular HP per CI scenerio. Well, at least to stay within the realms of reliability, octane level, etc years back.
The same guys I see on oso, telling everyone to ditch their 454 for a 502, or ditch their 502 for a 540, are the same guys praising the LS series GM small blocks. The LS line of engines are ultimately impressive on what they can deliver, from a small package. We have technology to thank for that. While the rule "theres no substitute for cubic inches" still holds true, that line just isnt as clear as it was 25 years ago. Back then, some guys had a hard time making a 1hp per cubic inch mill stay together. Jacking up compression ratios, installing stupid cams, and what not, was just the way it had to be done. Lets say back then you had a 420HP 454 merc. You wanted to make 550-575HP. Out came the big dome pistons, a radical solid tappet cam, and it was off to the launch ramp with your poor idle quality, stalling in gear, reverting water, and so on. Today, you can easily hit that number, with a 9:1 hyd roller setup, that will idle very nice, and provide a long service life, by choosing the right induction components.
The 454ci big block chevy is hardly a "small" engine to work with, neither is the oso common 502. So before you throw it in the trash bin, take a second look at investing in a modern induction package, whether it be from RMBuilder, or any of the pro's on this site. Lets just calm down with the dual plane and peanut port stuff, and look further into building a great performing modern big block engine. For most of the oso tech guys, you already know this stuff, and can even enlighten further than myself. Just thought I'd throw this out there, as there seems to be quite a few Newbies around lately, who might be able to pick up something from this.
11-08-2014, 08:47 AM
#2
One might say, well MT, thats all great, but what really would I gain by upgrading heads? Prob not even worth it right?
Well, only you can answer that.
Heres a good article. You look at this 496 stroker build. With the GM rectangles, it made 630HP. If they just did that single pull on that combo, one might say, "Eh, 630HP, thats a pretty good deal".
But, look at what happens when they bolt on some aftermarket castings.
Simply bolting on a set of Dart 308 Iron eagles (summit head in this article), they went from 630HP, to 688HP. 58HP just from bolting on a basic set of aftermarket iron heads. No cam changes, no induction changes, just the heads. Stepping up to some AFR's, Dart CNC's, were talking nearly a 100HP gain here.
Now, does that mean your stock 454 is gonna gain those numbers, probably not so much. But, the great thing about making the investment in a quality set of cylinder heads, is that it will allow you to meet you're particular goals, but in a safer, more reliable, less octane needed, better idling and performing package. Just some things to chew on, before sending those old iron heads in for repairs and major rebuilds.
http://www.superchevy.com/how-to/pro...r/viewall.html
Well, only you can answer that.
Heres a good article. You look at this 496 stroker build. With the GM rectangles, it made 630HP. If they just did that single pull on that combo, one might say, "Eh, 630HP, thats a pretty good deal".
But, look at what happens when they bolt on some aftermarket castings.
Simply bolting on a set of Dart 308 Iron eagles (summit head in this article), they went from 630HP, to 688HP. 58HP just from bolting on a basic set of aftermarket iron heads. No cam changes, no induction changes, just the heads. Stepping up to some AFR's, Dart CNC's, were talking nearly a 100HP gain here.
Now, does that mean your stock 454 is gonna gain those numbers, probably not so much. But, the great thing about making the investment in a quality set of cylinder heads, is that it will allow you to meet you're particular goals, but in a safer, more reliable, less octane needed, better idling and performing package. Just some things to chew on, before sending those old iron heads in for repairs and major rebuilds.
http://www.superchevy.com/how-to/pro...r/viewall.html
11-08-2014, 10:01 AM
#3
Registered
Interesting thread. Seems to me, and I think we are of the same thought, that when building from scratch using a modern HR cam and quality heads you will get both midrange and top end. Most of the torque curves I have seen on recent builds are pretty flat so a gain of x horsepower on top usually gives a corresponding gain above 3000 RPM give or take. I do think middle RPM torque is important both for acceleration and the ability to cruise without lugging the engine.
I will say that in some circumstances a higher HP engine can be more efficient at cruise, a friend of mine with bigger displacement/higher horsepower engines in the same boat as mine used less fuel than I did while running together at similar speeds.
It would be interesting to hear from someone like RM if it would be possible or feasible to design a cam and build an engine around it that would make huge torque in the mid band. If someone was building an endurance race boat for instance. And would fuel consumption at x RPM be lower than the standard build or could a much bigger prop be turned to negate the extra consumption?
Sorry for the lack of technical detail, still trying to learn this stuff. I do enjoy these threads and find them very interesting and informative.
I will say that in some circumstances a higher HP engine can be more efficient at cruise, a friend of mine with bigger displacement/higher horsepower engines in the same boat as mine used less fuel than I did while running together at similar speeds.
It would be interesting to hear from someone like RM if it would be possible or feasible to design a cam and build an engine around it that would make huge torque in the mid band. If someone was building an endurance race boat for instance. And would fuel consumption at x RPM be lower than the standard build or could a much bigger prop be turned to negate the extra consumption?
Sorry for the lack of technical detail, still trying to learn this stuff. I do enjoy these threads and find them very interesting and informative.
Last edited by hotjava66; 11-08-2014 at 10:45 AM.
11-08-2014, 11:08 AM
#5
The stock truck cam was a measly 194/203 duration with around .400 lift. Couple that to a wimpy 2 barrel throttle body, and you have a severely rpm and power limited big block.
The cam used in the old 330s was an old GM cam i believe used in the LS5 454. 214/218 with about 480 lift.
I can see where taking that truck engine, installing a bigger cam, 4 barrel carb, could net around that power gain. That truck 454 was anemic.
The cam used in the old 330s was an old GM cam i believe used in the LS5 454. 214/218 with about 480 lift.
I can see where taking that truck engine, installing a bigger cam, 4 barrel carb, could net around that power gain. That truck 454 was anemic.
11-08-2014, 03:45 PM
#7
Gold Member
Stimleck. Everything works as a unit. There is no one "magic" part that can yield results without complimenting hardware.
Cam without proper valvetrain= no good
Heads with no cam= no good
Huge cam with wrong compression= no good
Killer engine package with log manifolds= no good
You get the idea.
Cam without proper valvetrain= no good
Heads with no cam= no good
Huge cam with wrong compression= no good
Killer engine package with log manifolds= no good
You get the idea.
11-08-2014, 07:15 PM
#8
Mt , I usually agree with what you have to say but in the first post of this thread you talk about people who are looking for cruise speed and power, I'm certainly not an expert, but if this is the goal why would you prop for wot?
not my goal for sure but a little confusing nonetheless. Cary on.
my stock 502 is always interested in threads like this!
not my goal for sure but a little confusing nonetheless. Cary on.
my stock 502 is always interested in threads like this!
Now, you can install a 28P prop, and only turn 5100RPM WOT. This will give you a better cruising speed at 3500RPM, than the 26P. However, at wot, you will likely see a speed loss. The other downside to "overpropping", is that at WOT you can "LUG" the engine. Which is not good for either the engine, outdrive, etc.
There seems to be alot of confusion on whats considered a good cruising scenerio. Most guys simply look at engine RPM. They feel, that because they are at 3500RPM, thats an excellent cruise setup. However, just because your RPM is lower, doesnt necessarily mean you will get better economy. The load on the engines is what really matters, in my opinion.
Like in my boat, I have superchargers. I mainly try to cruise on long distances, around 0" of vacuum/boost. Whether I am light on fuel, in calm water with the drives kicked out, that may be 3500RPM. If I have a full tanks of fuel, people on board, some rough water where the drives are tucked, that may be 3000RPM.
Pretty much all boat builders, pick a mercury engine package. They install props that simply operate within the engines specified WOT range. Of course you change change prop "STYLES", like say going from a 4 blade to a 5 blade, or things of that nature. But I personally, think a boat needs to be propped according to the dyno sheet. Otherwise, why not just put a huge prop on the boat that only allows 3500RPM at full throttle.
11-08-2014, 07:16 PM
#9
Registered
Mt , I usually agree with what you have to say but in the first post of this thread you talk about people who are looking for cruise speed and power, I'm certainly not an expert, but if this is the goal why would you prop for wot?
not my goal for sure but a little confusing nonetheless. Cary on.
my stock 502 is always interested in threads like this!
not my goal for sure but a little confusing nonetheless. Cary on.
my stock 502 is always interested in threads like this!
11-08-2014, 07:18 PM
#10
If my description of cruise/load scenerio doesnt make sense, think of it this way.
Look at your tow rig. Lets say going down the road at 65mph, the engine is turning 2000RPM, and getting 18mpg. Then you hook your boat to the hitch. At 65mph, you are still turning 2000RPM. However, the engine is much more loaded, and now you get 10mpg.
Reducing cruise RPM, by adding more load at that given RPM (with a higher pitch prop), will not really save you gas money.
Look at your tow rig. Lets say going down the road at 65mph, the engine is turning 2000RPM, and getting 18mpg. Then you hook your boat to the hitch. At 65mph, you are still turning 2000RPM. However, the engine is much more loaded, and now you get 10mpg.
Reducing cruise RPM, by adding more load at that given RPM (with a higher pitch prop), will not really save you gas money.
