small block vs big block

[likwidsukr]

Since you have a boat with a BBC in it already,put a SBC in the other. My Tahiti does 60mph at 4900rpms with a 350[.060 over] spinning a Panther and I'm totally happy with that from a 9.0 to1 motor. Especially since it cost me only 1600 bucks for a COMPLETE rebuild.
valve job with new valves,seats and springs-550.00
motor work and assembly-850.00
timing set and oil pump-200.00
Included in the motor work and assembly are-
bore job,replace crank,replace rods,new pistons,new cam,new lifters,new bearings,complete gasket set,freeze plugs,install rotating assembly.
I say go for it. I'll give you a set of logs if you pay for my camp site and slip at Tower Park V.
Steve that sounds like a real deal Bro.!! I say go for it.
WTF not.

[LVjetboy]

"After that pump characteristics which suck HP gonna load that SBC up and drag it down."
Hi Mike :smile:
I'm assuming you're talking impeller matching not speed? An interesting thing about i/o's. We have a 27' cruiser (6500+ lb) with dual prop. On launch, if you could call it that, rpm ever so slowly climbs to 3k, once on-plane continues slowly to 3.8k maximum. Just a wag but maybe 20-30 seconds to reach max rpm and power. That's with a 454. Nothing like a jet where rpm goes to max very quick...less than a second? I think that's a key point overlooked by some who insist low-end torque is more important than peak hp. Two different applications.
"Dont matter what you do the SBC got to turn RPM to get HP. This makes your impeller small and therefore your pump ineffecient."
Pump efficiency's the big unknown there. I think your right about trends, but without pump efficiency curves who knows how much? Depends on impeller cut and rpm. For example, what's the efficiency trade-off going from an A to a C, or from 5k to 7k? Without curves or data, it's hard to draw specific conclusions about SB vs BB based on pump efficiency and impeller matching. Although it'd be easy to calculate what that efficiency difference would have to be for the SB to equal the BB using typical engine power curves, those numbers wouldn't help much in real life.
jer

[miketsouth]

Hey Jer
Upon pump efficiency (mikeT estimate of the situation).
While we dont seem to have pump efficiency curves, we do have a fairly accurate HP/RPM curve.
And that is 'internal' or static pump efficiency, exclusive of intake setup, but inclusive of RPM.
I suppose this could only be measured in thrust, tied to the dock. Some might call it 'launch'. If i only have 300hp is it better to put it in with a AA impeller(4300rpm) or an E impeller(5900rpm)?. I know what my cheep engine thinks. Keep the RPM down and mikeys pocket and gas tank full
http://www.cpperformance.com/TechTip...r-curve-lg.jpg
I say the AA. Why (you ask)? Look at the cut, or the way that the impellers are different:
http://www.cpperformance.com/TechTip...mpeller-lg.jpg
To make the smaller impeller, you are shaving off the 'centrifugal' part of the pump, and leaving more of the 'axial' part. (the mixed flow pump gains efficiency by using some of the centripital charactistics of the water being thrown by the vanes?)
The the outlets of the impeller vanes are now further from the bowl vanes, and the speed of the impeller vs the water is increased. Yes, less impeller surface to cause friction but far more turbulence but methinks that the AA would give more thrust/HP.
Can i quanitfy it (you ask)? no :frown: do i have any personal experience(you inject)? no :redface:
It does sound plausible, though; one cut change may be small indeed.
For my wallet, more than ~350hp means BBC. Oh, yeah. I WILL get 80mph from an almost stock SBC next year, God willing.
One more think. Pressure differential. No (other than positive displacement) pumps that i see (boiler feedwater, chemical feed, deionizer, process etc) use one stage to get more than 100psid. They will always use more than one stage. About one stage per 100psid.... Efficiency.
He said 'positive displacement'...yeah Jer, i toyed with it. Too heavy, too big, to do the pressures and flows. Clearances to tight to run river water.

[Cas]

I think that's a key point overlooked by some who insist low-end torque is more important than peak hp.
jer
jer,
After all the discussions about tq v hp, I'm surprised (kind of) that you mention low end torque. I don't recall too many, if any, that were talking about low end tq. Most everyone, including myself have said the peak tq needs to be higher in the rpm curve....above 4500.
Low end tq is bypassed quickly.

[LVjetboy]

"I'm surprised (kind of) that you mention low end torque. I don't recall too many, if any, that were talking about low end tq. Most everyone, including myself have said the peak tq needs to be higher in the rpm curve....above 4500. Low end tq is bypassed quickly."
Both low-end torque and low-end power are bypassed quickly with a jet. That's why low-end engine characteristics (whether you focus on power or torque) are not important like they are for cars or maybe even props. I mentioned "low-end" because that's a common carry-over from the car guy way of thinking...maybe not mentioned in this thread but certainly in others.
On peak torque and where it's located? This maybe key to the Q vs Hp confusion.
Because power and torque are related by definition, moving peak torque up the rpm's without changing the magnitude of that peak torque WILL cause peak power to increase. Performance goes up. So some may conclude we're all saying the same thing.
Nope.
That's because those who focus on peak torque typically mean low-end torque or quote peak torque magnitude as a measure of performance. From that they conclude a big block with gobs of low-end torque rules. Because they got more torque right? Or since torque rules, then matching impeller to peak torque gives best performance? But for jets, peak power not torque rules.
Let me illustrate.
Here's a big block Chevy 454 with gobs of torque...some may say low end torque...but gobs of it none the less:
Peak Torque: 480@3000
In a car that low-end power comes in handy. For a jet maybe not. To match that engine to impeller power you'd choose an AT 9.25+ and apply 325 hp to the impeller. If you tried to match impeller to peak torque you'd end up applying even less power to the impeller.
Let's compare that to a small block Chevy 350 with the same peak torque but at a higher rpm:
Peak Torque: 480@5000
Btw, this small block only puts out 380 ft-lbs at 3000 rpm. A whopping 100 less ft-lbs than the BB. To match engine peak power to impeller you'd choose a Berk C/D- and apply 550 hp to the impeller. That's 225 more hp than the big block! Even though both peak torques are the same magnitude.
Impeller cut and pump rpm efficiency aside, applying 225 more hp to the impeller based on engine power curve matching can be a significant performance advantage. Even for that low-end torque challenged small block.
So is that 225 more peak hp of the small block cancelled out performance-wise by the efficiency of a bigger impeller cut operating at a lower rpm?
Don't know. We have no pump efficiency curves. Only trial and error and limited test combos under certain conditions. But I'd doubt it. Especially once you figure in the weight loss of that small block and corresponding reduction in hull drag.
My point is, lacking pump efficiency data, focus on how much power's applied to the impeller for best performance. Even if we had pump efficiency data, that would just modify impeller cut size based on the engine power curve (not torque) to determine performance.
Pump efficiency's based on Powerout/Powerin not Torqueout/Torquein...that would be more along the lines of gear ratio.
MikeT, pump efficiency curves have more info than just pump power vs rpm curves. Even if those power vs rpm curves are accurate, they don't tell the whole story. Like how effectively your chosen impeller converts engine power to pump thrust. That's the question.
jer

[Havasu Hangin']

My last (mildly built) small block had over 460 ft-lbs at 3,000 RPMs, and peaked over 450 HP at 5,200 RPMs on the dyno.
Needing high revs to make power with a SBC is a myth.

[miketsouth]

spill it. what was the combo. CID? (i suspect +400cid), Compression(suspect 10.5/1). Roller valvetrain?
I am looking at something like this right now. I figure 406 cid, fair heads, cheep pistons, hydraulic cam, 9:1 should get me a regular gas 400hp@5200rpm reliable cheep engine.

[Havasu Hangin']

spill it. what was the combo. CID? (i suspect +400cid), Compression(suspect 10.5/1). Roller valvetrain?
I am looking at something like this right now. I figure 406 cid, fair heads, cheep pistons, hydraulic cam, 9:1 should get me a regular gas 400hp@5200rpm reliable cheep engine.
383- hydraulic roller (222/230 .509/.528 112 LSA)...Ported Edelbrock RPM heads (70cc chambers)...10-1 pistons; Holley Steet Dominator manifold w/Holley 830 carb; MSD ignition (36 total timing); 91 gas.
When I started it up in the driveway...it sure sounded like a big block (and it sure fooled alot of people on the water). Not bad $/HP for around $5K.
I read Dennis Moore's book on SBC performance, and he was almost dead on with this recipe. With a little bigger cam, Brodix heads, 500+ HP is very doable. Phaff builds a pump gas 383 that is over 500HP with that combo- I think it makes peak power closer to 6,000 RPMs, though.
450HP with a 406 is very doable. If you have some decent heads, spring for the hydraulic roller- the motor will love the extra lift.

[miketsouth]

383- hydraulic roller (222/230 .509/.528 112 LSA)...Ported Edelbrock RPM heads (70cc chambers)...10-1 pistons; Holley Steet Dominator manifold w/Holley 830 carb; MSD ignition (36 total timing); 91 gas.
When I started it up in the driveway...it sure sounded like a big block (and it sure fooled alot of people on the water). Not bad $/HP for around $5K.
I read Dennis Moore's book on SBC performance, and he was almost dead on with this recipe. With a little bigger cam, Brodix heads, 500+ HP is very doable. Phaff builds a pump gas 383 that is over 500HP with that combo- I think it makes peak power closer to 6,000 RPMs, though.
450HP with a 406 is very doable. If you have some decent heads, spring for the hydraulic roller- the motor will love the extra lift.
Many thanks HH
Someone still believes! I had to keep the cost down last year because the boat itself kind of emptied my wallet. I have rebounded (somewhat) but got the opportunity to see what the SBC did for the driveability of the little cheyenne tunnel:
Good acceleration, thanks to the light weight but somewhat lacking in topend for lack of HP, [should read lack of money spent in the SBC] (some BBC eat rooster)
At the low RPM targeted i can stand on it till the oil pressure drops and still have a motor. I stood on it all summer (got passed by some BBC all summer too)
The low RPM targeted also appeared to give me good fuel economy.
The low compression (9:1) allowed me to use 87octane river gas. Used a lot of it.
The lightweight also made the boat feel pretty good in rough water which would have rattled my teeth and backbone out in my previous jet. (tunnels are nice, too)
The hydraulic cam, while not offering as high of lift or aggressive profile(dirt cheep) made the combination hands off. Get in and go and go and go. I supposed lift was not as important at the lower RPM targeted, and lower lift should mean longer engine reliability and lifetime.
The 406 builds are getting more and more affordable (uh, for me that means cheep) . I suppose as long as i target lower rpm (5000 or so) i can have a little more HP with good reliability. Cam match to RPM/impeller a must.
I'm stikcking SBC. I am going to concentrate on the pump setup, too. I am convinced on any jet, that is where the most advantage will be had, above 55mph. How do you say loader, rideplate, shoe and wedge.
http://mywebpages.comcast.net/katiejet/teriblast2.gif

[Havasu Hangin']

The 406 builds are getting more and more affordable (uh, for me that means cheep) . I suppose as long as i target lower rpm (5000 or so) i can have a little more HP with good reliability. Cam match to RPM/impeller a must.
I'm stikcking SBC. I am going to concentrate on the pump setup, too. I am convinced on any jet, that is where the most advantage will be had, above 55mph. How do you say loader, rideplate, shoe and wedge.[/IMG]
Mike- the SBC non-believers will probably never be converted. My personal opinion is that if you have no long-term goals past 500HP, then the cost and weight savings with a SBC cannot be beat.
Keep in mind that I am not a head expert (so consider the source), but to keep the low-end torque on a 406, I probably would go around 180-190cc on the intake runners. SBC's love flow (or hate restriction), so some port-matching and bowl blending will probably be a wise couple hundred bucks. Cam and heads can make or break a SBC recipe.
That Crane cam I used would probably make peak HP on a 406 around 5,000 RPMs. Don't fear the hydraulic roller...the ramp steepness and lift are not that of a solid roller. It is truely a "fire and forget" option, with no adjusting necessary. You are correct, the extra lift will not really move around the power band, but will definately help the HP numbers. Crane has a kit that includes retrofit lifters, springs, pushrods, etc. for a couple hundred bucks. I'm gonna guess that the hydraulic roller is probably good for 40HP or so over a flat tappet.
Also, if you go with a bigger cam, don't be afraid to bump up the compression (you'll bleed off a little more pressure). With aluminum heads and how cool our engines run, most builders cheat by adding a little more static compression (knowing it won't detonate).
Good luck...and don't let the BBC cult brainwash you!