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.

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

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.

Would like to see a dyno of a pp gen 4 with merc manifolds ,its hard to believe the truck motor gains 100 hp and makes power to 5000rpm with just a cam swap from merc.

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.

do heads make the cam or does the cam make the head?
essentially can heads work well without stepping up the cam?

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.

Well, thats pretty much how it works. Lets say you build an engine, and it makes peak HP at 5500, and peak torque at 4500RPM. Lets say in a particular boat, using a 26P prop, nets you a WOT RPM of 5500. That would be the correct prop for the boat/engine combo.

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.

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!

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.

Good explanation, just curious, and you have an answer that makes sense.
Thanks, Ken
How did you know what I was wondering, lol! I hope they get the post order straightened out soon.

Most of you know I come from a desert racing background, so I am much more in tune with susppension than motors.

THereis an old saying in my world that still rings true,

Good shocks can make up for bad springs, but good springs can never make up for bad shocks...

How would that translate to motors?

Bad ju ju I'm guessing, but hey, moters definitely not my game. My job is to make engineers bad ideas a reality lol.

Now that takes a LOT of alcohol.....

You don't know the half of it! :ernaehrung004:

Someone get this back on track. Sorry for the derail.

Depends on what you are starting out with for each.

If You have a cam that allows jack in for air, adding better heads won't help a ton.

Put a set of AFR's on a 330 454 and you won't see as much as you'd think.

Put a set of AFR's on a 260hp 5.7 Mag, and again, you won't see as much as you'd think.

Your biggest bang for the buck is always getting rid of your biggest restrictionn1st. If your motor has 2,3, or 4 restrictions as bad as each other, well, then you need to address all of those.

BTW:

This is easy to remember.

Nothing beats good head. Nothing !

Is there a way to "view" fuel consumption? Boost is an easy reference, but my 454 mags are not boosted.
I had same issue with overpropped when I brought my boat down from Va. to South La.

25p M+ ran fine in Va. and close to 5k. They cruised at 3500 @50 in flat water, 52 in a lil choppy (2ftrs)
Then it heated up and got humid. Still cruised the same, but could only turn just over 41-4200 lugging motors at WOT. Yes, that was a oddly high amount of rpms to loose in the heat/humidity. Lost 200 rpms the next weekend I ran in la. with same temps, though we have a lot more humidity. (ended up with labbed 24b1s)

I also searched for torque curve dyno results and "boattest" fuel consumption tests, but like MT said, its all relative. Boat, weight, pitch, WOT vs correct WOT range.

Always thought that being able to hit at least bottom range of WOT would be your best cruise possible and hitting top would net best WOT speed but smaller pitch to get the extra rpm at WOT would hurt cruise.... then again, we are only talking about 2-3 mph difference at same cruise rpm...

very interesting thread MT!

Prop for max engine rpm. That's all.

Fuel flow meter.

Boats that go on long trips have these for a reason and not just $$$ for gas.

Newer boats have that on smart craft, how do they work on older motors? sorry, never really have seen them.
Assume they read flow on fuel rails? Gauge on dash or just on motors? I am really more interested in finding my sweet spot for efficiency.. I normally just run 3800 @ 50.....

Type in Fuel Flow Meter into a search engine.

Oh, if you have a return fuel line (All EFi...some people do with performance carb set up) you'll need two meters and do a meter A minus Meter B set up, as Meter B will be measuring return flow which of course is being returned ie: not being used by the motor.

Oh, if you have a return fuel line (Most All EFi...some people do with performance carb set up also) you'll need two meters and do a meter A minus Meter B set up - some Guages can be progeammed to show net reult vs having to get two guages), as Meter B will be measuring return flow which of course is being returned ie: not being used by the motor.

Check flo scans website. All the info is there with diagrams on how to install. A little pricy but one of the better ones in my opinion. You can get 1 gauge that will monitor both motors. In my formula I installed it. It had 2 switches and 1 button installed with the gauge. The switches were one from port to stbd and one from rpm to fuel flow. The button was basically a reset for total fuel burned. You run te boat and test total fuel burned. When you fill back up you do the calculation and adjust dip switches on the back of the gauge until you are damn near perfect. You will then end up with accurate burn rates.

Heads and cam make the engine the best match will make best results... I am firm believer in custom cams... I have always ground my own for the combo...

You may have big tq numbers but them numbers under full throttle not part throttle so it really don't matter... Of course you want a strong solid tq curve especially to get old heavy boats moving....

Tim when did you get a cam grinder??? Lol

Haha he's called Cam Motion! Bob does grinds for his boat cams I guess also...I don't believe in off the shelf cams unless you are doing simple combos... All my car stuff has been custom with great results boat engines were custom but going bigger this year so either grinding new or buying a set mild thunder kjows if that sound perfect for my combo

Back in the 70's, they used to install "Economy" meters in cars. I remember as a kid our family car was a 1975 Bonneville. In the instrument cluster, it had the "economy" gauge. It started out in the green while cruising down the highway. Upon acceleration, it would swing towards the red. Harder you accelerated, further into the red it got. lol, all it was, was a vacuum gauge.

High vacuum=low load
low vacuum= high load

To get back on topic though, there is something to be said about having an engine package that operates efficiently in your cruise range. Like I stated earlier, you wouldnt want to slap some huge 345/360cc port heads on a mild 454 engine, with a cam that would make peak power at 7000RPM, in an engine you don't plan on spinning past say 5400RPM.

There are alot of options though nowdays, as far as engine combinations, that give you a bit more flexibility. We have great valvetrain components available, that will allow you to safely turn that smaller CID engine, a bit faster to make up for its lack of CID.

I'll use my friend Joey's engines we recently built up as an example here. He had 522ci shortblocks to work with. Really nice components in them. He had Lunati Signature series blower crankshafts, oliver connecting rods...He like any of us, wanted to make good power. He had his sights on 1000HP.

Him and I talked alot about his build options. At the time, he had Edelbrock marine performer heads, and was purchasing 1071 blowers and intercoolers. I just knew, his edelbrock heads were not going to allow him to meet his goals, at least without an insane amount of boost that is.

A couple of his buddy's told him he really needs to go to a 4.25 stroke, to make them 555ci. I disagreed, and thought he could hit his goal, but it would take the right cylinder head/cam/boost/rpm combo.

Thats when I recommended he get in touch with Bob Madera, and look into some AFR heads, cam, etc. After working with Bob, Joe decided to go with the AFR 315 cylinder head, Bob did a cam for him, and the right valvetrain components to go with the setup.

When it came down to dyno day, the results were what we hoped for. The engines made their target number, within the target RPM/BOOST levels. The torque was outstanding as well.

Now just for comparison purposes, or to go deeper into all this. Our other buddy had recently dyno'ed his blown combo. His was a 540ci, 345 Dart heads, also a 10-71 blower (its what he had to work with). While this build had the cubic inch advantage, it made less power. With both engines at 8lbs of boost, the smaller 522ci, made 37 more HP at 6200RPM, and quite a bit more torque thru the rpm band. Same dyno, same dyno headers.

One would think that the larger engine would have made more torque, along with more power. I was really surprised at the torque production from this 522, not only was it a very flat curve, the numbers were really great for what it was. The key was the 522 simply had a better package. With that being said, the iron headed 540ci making 893Hp at 8lbs of boost, is/was nothing to turn you're nose to. Its just a comparison. But if they were both 540ci, Joey's engines, would have made around about 70HP more lb for lb of boost. Keep in mind those 345 Darts, are tremendously better at moving air, than a GM rectangle port casting. So, if that 540ci deal had a set of GM heads, that 37HP gap, probably would have been closer to a 137HP gap. Point, theres more to building a good package, than simply throwing cubic inches at it. Same goes for N/A engines as well.

It's all about how much air get's in the combustion chamber.

More cid's has more demand and room for more air. It doesn't necessarily get you more air.

especially when cslob grinds ones.most air left out in any cam he specs.<lol>

Couple key things there. Key word, fully ported. lol.

Mike Tkach has done a few 502 Builds using the edelbrocks and had similar power number results. Around 600ish, but the heads had no port work.

I think the edelbrock heads are a decent bargain, but they are simply not that great of a head for moving air. Their new E CNC heads look impressive though.

Heres a nice article with a 502 with AFR 315 heads. It does have a fairly aggressive solid roller, , but 740HP from a 9.6:1 502 engine is pretty good!

http://www.sporttruck.com/techarticl...ylinder_heads/

If you are going to discuss low and mid range and how it relates to performance and economy it would be interesting to see what the actual load is on the prop roughly per RPM and relate it to the HP/torque of the engine at that RPM.

A buddy of mine just did 502 CI engines with fully ported Edelbrock oval ports, 9.5:1 compression Cams from Bob M. and 850 CFM carbs, did 621HP and 644Tq, I forget rpm, but those are good numbers for N?A 502's... its all in matching parts up good...

It would be interesting to see if my 540`s would close that gap vs. Joey with:

1. Wedges to increase velocity
2. Same (bigger carbs)
3. intercooler or matching intake temps
4. same compression
5. Bob cam

Last day today before I put the winter cover on Joe, sure you don`t want me to pull it so we can experiment?

502ci stock crate GM. 245/250 112LSA cam, with .650/.650 lift. Not a small cam, but not a rediculous cam either. For those who don't want to read the full article, I'll sum it up here

AFR as cast 325cc with CNC chamber option. 665HP/593FT lbs 3500RPM=540 ft lbs

Brodix 294cc Race Rites. 634HP/582 FT lbs 3500RPM=531 Ft lbs

Dart 335 Full CNC . 660HP/589FT lbs 3500RPM=534 FT lbs

Edelbrock performer RPM 315cc. 616HP, 566 FT lbs . 3500RPM 523FT lbs

RHS 320cc .638HP, 584 FT lbs. 3500RPM=531 Ft lbs

Trick Flow 320CC. 655HP, 587 FT lbs. 3500RPM=527 FTlbs

Merlin 310cc. 631HP, 581 FT lbs. 3500RPM=531FTlbs

As we can see here, the torque production, at 3500RPM, is very similar. Highest number of 540FT lbs, and lowest number 523FT lbs. 17ft lb difference. But, lets look at the HP. 665HP, vs 616HP. Lets call that 50HP. In a boat engine, 50HP peak, is not peanuts. Lets say we installed this combo in a boat, let say a 35 Fountain. with the edelbrocks, and it ran 80MPH top speed. Going with say the AFR 325, it wouldnt be a stretch to pick up 200RPM per engine by doing so, with the same props. Possibly a solid 2-4 MPH gain, simply by choosing a better cylinder head. An 80mph boat, vs and 83mph boat. The gains would prob be even higher if we were talking going from a stock GM 502 mag head. Now, of course theirs a cost comparison to consider. If you have a perfectly good set of heads now, upgrading may not be worth it to you. But, if youre building from scratch, going from the cost of an Edelbrock performer head, to say a as cast AFR head with CNC chamber option, is really a no brainer, in my opinion. The Dart CNC head is an excellent cylinder head, but they are not cheap. The Trick flow 320 appears to be a good bargain as well.

Its very easy to get caught up the port sizes and shapes, and how we've always been taught that small ports = more torque, big ports =more upper HP. As you can see in this test, the larger port heads, just happened to make the same, or more, torque at 3500 than the smaller port heads, and the largest port head, did not make the most upper RPM HP.

http://airflowresearch.com/articles/article131/A-P1.htm

This posting time stuff is getting annoying!

oh yes for the edelbrock are good fully ported, out of the box I hear good things about AFR, never used them yet but many buddys have with great results, I had to do lots to the pro comps that came on my engines to kae them right, you know that story though...

ever hear anything on those cams your buddy has?

Go for it! Yank them fukers out.

Theres no doubt making the right changes can improve or make more power on your setup. The purpose of my example, was to show its the combination of parts, can be of more benefit than simply cubic inch displacement.