JROC

Yeah when I thought of the engine internals mass adding to extra grunt it made me think of adding a heavier flywheel to a dirt bike to give it a more tractable, lugging style of power delivery instead of a freer revving, more aggressive style of power delivery. Popular with bikes like a YZ250 if you ride in conditions that don't offer a lot of traction.

LLLosingit

iTrader: (4)

This is false, A heavy mass will absorb a small momentary increase in load but a sustained load like pulling up a hill or just plain cruising while towing a heavier mass is not helping at all.

bammax

The reason big blocks have so much weight and size is because they were designed and built at a time when manufacturers had supplies of heavy iron and worked it on big equipment operated by big people. There just wasn't a need or the desire for lightweight components. Once the technology became cheap and easy and people started to worry about how heavy a car was the engines became alot lighter and smaller. Just look at the LS7 which was a big block in a lightweight small block package.

If this was a Mopar board people would be mentioning the big block 350 or the 383 being available as a B block or a RB block depending on the year. Sometimes things are the way they are because it's just the best option at the moment.

LetsTurboSomething

I literally said that. It was the last sentence, I even gave multiple real world examples of why engineers increased rotating mass on purpose to gain an advantage. They would make flywheels out of aluminum and paper light materials for everything if it didn't help where it needs to help. This is easy stuff, light flywheels on race cars make for **** poor street cars because you cant get into traffic without high rev engagement or you'll stall it. Put a heavier wheel on it and it stores rotational energy and uses it where the engine doesn't make good torque so you don't have to rev it up to where it does...

"But it's advantage is basically limited to engaging the clutch, once you're locked in and accelerating it's a disadvantage. Think of it like this, that weight resists bogging(slowing down) the same amount that it resists accelerating but also requires more outside force to drain off the momentum. It's a kinetic energy storage device."

QwkTrip

iTrader: (23)

A heavier rotating assembly accelerates slower. It also decelerates slower. Basically it resists change of speed more than a lightweight rotating assembly would.

But a heavier rotating assembly also carries more momentum when at speed, so it helps to impart more energy to move the vehicle during roll out with clutch engagement. After the momentum is transferred, then it's slower to accelerate again.

QwkTrip

iTrader: (23)

Ya, unfortunately his theory was wrong. If his theory was right then eventually an engine would start running on it's own if you just made it heavy enough.

Remember, torque is produced by the engine because of the combustion cycle. The reason why big block is different than small block comes down to same reasons why any engine is different from another - different air flow and different mechanics. Big block will usually have a larger bore diameter than a small block of same displacement, different valves, heads, intake, & valve lift. It comes down to how the engine moves air and uses the power stroke.

JROC

I disagree. I mean I agree with some of what you're saying but not everything. First an engine will not run on it's own. Energy isn't free. The flywheel weight/material used to achieve a particular style of powerband is the simplest way to view this. Why do most of your truck based BB's weigh a ton, have a very low RPM range, and produce enough torque to make you not want to use 1st gear for anything other than dealing with a decent to heavy load? (Some of it's gearing, but not really the kind of lowend power I'm talking about) I've never experienced a large displacement SB to make the kind of torque at ultra low engine speeds as a 400+ ci BB truck motor.

I sort of agree with what you're saying about how it flows, but not totally. First IDK if even a LS7 has as large an intake runners and exhaust/intake ports etc. True a 4.25" bore isn't uncommon for a BB, but there are BB motors that will turn some pretty high RPM's and make their best power up top, and there have been some pretty long stroke, and even small displacement BB motors. For example a 428 Cobra Jet is more of a torquey lugger compared to an old 427 FE BBF which is more of an RPM/topend motor. A 351C's basically a SBF with a topend suitable for a 400ci BB. As such it wants to rev to make good power. Unfortunately it's oiling system doesn't let it.

I've ridden in some old BB trucks who's lowend power resembles a diesel trucks (at least a 15+ year old diesel) power. Even my GEN2 L with its 4.165" stroke having, crappy flowing 2V PI heads that make decent lowend power before falling off early in N/A state, and use a huge torque curve to make speed with its blower doesn't make the kinds of lowend power that many BB's make at the bottom of it's RPM range. The closest SB gas motor I've felt to replicating the torque at the bottom of it's RPM range as most BB truck motors is a modded GT500. Even my old Terminator wouldn't compete at the bottom of it's RPM range. (Say under 2,500 RPM's)

Hell that new 7.3L Ford SD gas motor is supposed to be BB based. It also seems to be better suited for the job of being a 3/4 and 1 ton truck motor than the 6.6L GEN5 SBC or the 6.4L Hemi. So there much be some merits to using a BB instead of just designing a large displacement SB. And the GEN5 motors and the 6.4L Hemi both make very good lowend power for a factory N/A SB IMO.

Again people have been using different flywheel weights for years to adjust a powerband whether it be in cars, dirt bikes, chainsaws, etc. I see no reason why you couldn't get the same effect from a heavier crank/rods/pistons. I could agree that they should not necessarily make more torque or lowend power per say, but they should change the way it gets transferred to the ground IMO. If you took a LS7, swapped out the titanium rods with some forged steel rods and put a steel flywheel on it you'd probably have to drop it's capable RPM's even with a stock topend, but it will probably feel a little more luggy, or torque. That's an assumption on my part, but it seems sound, especially when you consider that you have a factory motor with a 4" stroke turning over 7000 RPM's.

QwkTrip

iTrader: (23)

Engine makes torque via the "fire in the hole" kinda stuff inside the cylinders. The flywheel is there to smooth engine speed during load transients.

A few practical examples:

* Applications with greater load transients (like towing) need heavier flywheels to maintain drivability. Different engine and drivetrain combinations need different flywheel moment of inertia, so you can expect to see heavier flywheels paired with bigger & heavier engines that have bigger & heavier drivetrains that haul around bigger & heavier things.

* A heavier flywheel kills engine throttle response and torque. You won't see heavy flywheels in road race cars that accelerate and decelerate hundreds of times in a track session because it slows them down.

* A heavier flywheel can improve street drivability and even drag racing times by limiting engine speed transients. The drag racer is trying to get down a short little stretch of road in as little time as possible. If the time gained with a heavier flywheel (more aggressive launch, and higher rpm at clutch lockup) is better than the time lost down the track due to less engine torque and power, then it's a good tradeoff.

LLLosingit

iTrader: (4)

This is the part that not true, A heavier rotating mass does store energy to an extent but so does the rest of the driveline and the vehicle itself (when moving) but rotating weight is only good at initial acceleration on a vehicle and it only helps for a couple seconds after that it robs torque that could otherwise be used to accelerate, The difference in a BBC and SBC is in the bore and stroke combinations available. A long stroke will make more low end torque where a short stroke will usually make power with RPMS.

But the examples you used do not apply to towing power or sustained use. The snow blower example, It helps if you shove it into a pile of wet snow but the energy stored in the heavy mass will be used up in a very short time but then takes time to replenish, It's not like you can have a 10lb flywheel on it and make any long lasting gains. It all comes down to work required to move an object, If you need a short burst of energy then stored energy is great but if you need energy to last and be as efficient as possible (towing) then you want the rotating mass as light as possible.

The reason a BBC is used in heavy trucks was durability, It makes the same power output as a smaller engine but will last longer because it turns less rpms and therefore wears slower, The added size is also beneficial not because of the weight but because they are stronger because of their size.

LLLosingit

iTrader: (4)

[QUOTE=QwkTrip;20245853

* Applications with greater load transients (like towing) need heavier flywheels to maintain drivability.[/QUOTE] This isn't exactly true, A heavy truck once moving doesn't need rotating mass to maintain drivability, It's sheer weight alone is enough and once the clutch or converter is 1:1 with the engine the heavier rotating mass is a disadvantage when it comes to acceleration. I drive heavy trucks for a living, Lighter is always better.

QwkTrip

iTrader: (23)

Thanks, good point of clarity.

HioSSilver

iTrader: (8)

Finally someone else understands this.

BrendanC

I called Duraburb. 28k without getting it to Florida and back. Seems like 30k to me.

Otherwise, I magically know how to put one in - 12-15k to find a good Duramax engine out of a doner. Then, I rebuild it. Why would I put it in dirty? I'm not an animal.

BrendanC

Yes, the 2007 I have is the 4l80e and I have a hard-core built unit to go in with this new engine. If I want more gears, I can get a gear-bender. I mean Vendor.

BrendanC

I have to upgrade that too, but relatively simple, and gives me an opportunity to put a hardened LSD in. I want to put a real 1150 AAM in as it has a non-FF axle now.

4.10 (or is it 4.11? I always get confused).

BrendanC

So update: I have the short block. Dart head I had for 4 years in a box was cracked (check your parts on delivery damnit). So had to buy a whole 'nuther head.

Short block built is 632. 4.610 x 4.750.
Heads are being machined. NEED TO FIND A CAM.

Gen 7 BBC was intended for LS and LT firing order. Luckily or unluckily as the case may be, the LS based trucks use the E38 ECU which also will do that firing order.

So basically, it is a 4/7 and 2/3 swap cam when referencing it in a BBC cam core.

So I will attempt to turn this into a Cam convo.

BIG engine. NOT high RPMS, but also not needing all torque at 1800rpm. I need it starting at about 2250 or so up to 6k rpm.

Pulling on a road that goes UP, the truck will shift down, and I will end up at 3500 rpm. If that is past my peak, I am missing out.

I believe the lift should be over .600 But how much? And what duration and LSA? I have asked Jones cams for some ideas.

Steven Hunt