SoCal Jet Boats
Tech Talk => Engine Mechanical / Electrical => Topic started by: bbfsouthwind on October 04, 2010, 06:52:48 PM
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I was looking at overlap drawings of crankshafts and noticed the 4.5" crank I was wanting to run has a very small overlap and seems kind of weak looking to me. If someone could shed some light on what would be the best compromise between stroke length and crankshaft strength. I want as many c.I. like anyone else but I don't want a crank that I am afraid of breaking when I put nitrous on the motor. I plan on making around 700hp n/a then some nitrous once everything is sorted out.
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what heads are you going to use and what kind of comp do you want
700hp is easy with a 4.150
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Ported dove heads and 10-10.5/1 ce. Will be running a custom camshaft, haven't decided weather to go solid roller or flat tapped solid. Cleaned up tunnel ram with 2 660 center squirters.
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I was looking at overlap drawings of crankshafts and noticed the 4.5" crank I was wanting to run has a very small overlap and seems kind of weak looking to me. If someone could shed some light on what would be the best compromise between stroke length and crankshaft strength. I want as many c.I. like anyone else but I don't want a crank that I am afraid of breaking when I put nitrous on the motor. I plan on making around 700hp n/a then some nitrous once everything is sorted out.
Technically speaking, the less rod/main journal overlap the less stuctural integrity of the crankshaft, yes. But this does not mean in-and-of-itself that a crankshaft "isn't strong" per se....regardless of manufacturer and/or brand application. But...one may indeed deduce that a crankshaft with less journal overlap is likely not as strong as an equivalent crankshaft with more journal overlap. That much is obvious.
Most offshore cast stroker cranks for the BBF that are 4.500 stroke are "rated" to 700+ hp. That being said, I have seen more broken crankshafts, more windowed cylinders, more burnt valves, more blown head gaskets, etc, from nitrous oxide than any other form of power adder. Therefore, if you want to have 700 hp + nitrous oxide then I would insist on a forged crankshaft,....I don't care how much or how little journal overlap there is.
LO
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So let's say that I choose not to run nitrous down the road and I just upgrade cylinder heads later instead. Would a good cast scat crank fit the bill? 1k for a crank is a little out of my budget at the moment but I want a strong setup.
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So let's say that I choose not to run nitrous down the road and I just upgrade cylinder heads later instead. Would a good cast scat crank fit the bill? 1k for a crank is a little out of my budget at the moment but I want a strong setup.
yes
700hp with dove heads is a tall order in a jet boat
lakes built a 521 (ithink) for dan hurcules and it makes over 700hp on pump gas but, it has good heads
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So let's say that I choose not to run nitrous down the road and I just upgrade cylinder heads later instead. Would a good cast scat crank fit the bill?
Yes, ported D0VE heads can get you to 700 hp, and the addition of better heads could get you more horsepower down the road.....but you will still be exceeding the rating of that cast 4.500 crankshaft when you add the better heads. They've been known to hold in excess of 700 hp but I won't recommend it.
1k for a crank is a little out of my budget at the moment but I want a strong setup.
1K ought to get you a brand name forged crankshaft, not just a cast one. And depending where you go you may have money left over. If you're worried about spending $700-$900 on the crankshaft alone, then you probably shouldn't be looking at building a 700+ hp engine as a properly outfitted one can run you well into the 5 figures. If you want just a 4.500 stroke shortblock that will hold well over 700 hp (onto which you can install your ported D0VE heads), you're still looking at several thousand.
LO
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lakes, the amount of port work that is needed to get to 700 hp with the dove heads is a lot $$ wise dont you think ???
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lakes, the amount of port work that is needed to get to 700 hp with the dove heads is a lot $$ wise dont you think ???
Lol, it sure can be. :)
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On my next engine, I want to go forged 4.3 stroke and run P51 heads. I will give you a call Paul when I get ready to do that.
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I have been thinking and I will just set aside 1k for the crank and balancing. There is no need to do this twice. I will be getting a 5 angle valve job cut on the heads and will be porting them myself the rest of the way. I bought brad's dove a heads a while back. I think that the power I am asking for is reasonable. I build an iron head 347 smallblock Ford that ran on pump gas and made just under 525hp, and I know what I am really looking for here in this motor is torque. I just want my boat to run in the high 80s.
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Port the heads before you do the valve job.
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I have a bbf 508 with dove heads that are ported-cobra jet size valves, just dynoed at just over 650hp, on pump gas. It is full roller and crank is 4.140. If that helps any.
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That's some good power. What kind of camshaft and intake?
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On my next engine, I want to go forged 4.3 stroke and run P51 heads. I will give you a call Paul when I get ready to do that.
No prob.
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If someone could shed some light on what would be the best compromise between stroke length and crankshaft strength.
This depends on application, combination, etc. Generally speaking, I reallly like the 4.3 stroke/6.8 rod combo for several reasons, including pin placemernt at BDC, rod ratio, power producing capabilities, etc. It's an "overall" winning combo and works great in a jet boat.
I have been thinking and I will just set aside 1k for the crank and balancing. There is no need to do this twice.
bbfsounthwind, are you aware that you cannot just purchase a crankshaft and re-use your 460 rods and pistons? If you use a stroker crank, then you also need stroker-specific connecting rods and stroker-specific pistons. Quality, brand name complete stroker kits (crank/rods/pistons/rings/bearings) run about $1699, and $400-$500 more for the 4340 forged crankshaft. Then add the balancing, mallory metal, boring the block, etc.
LO
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Yes l.o. I am completely aware, you must have just misunderstood me. Anyways.. how many cubes can you get out of a 4.3" stroke with a 6.8" rod? And I had planned on spending around 2k for my rotating assembly, give or take a few hundred. I want to stay at a .030 overbore or as close as possible.
Ps this isn't my first rodeo with stroker motors, just with a bbf. And I appreciate everyone's input, thank you.
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copied from 460ford.com
For(d) easy reference;(formula......Bore X Bore X Stroke X .7854 X 8 )
Stroke (in.) Bore (in.) Overbore (in.) Displacement (cu. in.)
3.590 4.360 stock 429
3.850 4.360 stock 460
3.850 4.390 0.030 466
3.850 4.400 0.040 468
3.850 4.420 0.060 473
3.850 4.440 0.080 477
4.140 4.360 stock 494
4.140 4.390 0.030 501
4.140 4.400 0.040 503
4.140 4.420 0.060 508
4.140 4.440 0.080 513
4.300 4.360 stock 514
4.300 4.390 0.030 521
4.300 4.400 0.040 523
4.300 4.420 0.060 528
4.300 4.440 0.080 533
4.500 4.360 stock 537
4.500 4.390 0.030 545
4.400 4.400 0.040 547
4.500 4.420 0.060 552
4.500 4.440 0.080 557
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I've had several BBf stroker motors.
The 4.3stk/6.800 rod technically is a great setup. Had this setup also.
The difference in strength between the 4.3&4.5" stroke is nill.
The last engine I built was an all aluminum 604cid. I ran the crap out of that engine in a sand car. 4.500 stk x 4.625 bore w/6.800 rod, 930hp.
Honestly even a cast crank would be fine. But for a few hundred dollars more, why not get the forged crank.
I am currently just starting a new BBF build. Boss hemi heads, 4.5"stroke w/6.800 rods.
I thought about doing the 4.3 stroke, but only for a millisecond.
-Gordon
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Shitcan the nitrous and the heads, and buy a set of aluminum heads.
Save the money from porting and the nitrous, and have a better all around engine longterm :)
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I'll be keeping my heads I have for now. I've already paid for them and the porting will be free. I just don't have room in the budget for alum heads :-[X :P
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the intake is a weiand tunnel ram, 2-750 holly double pumpers. Cam is a comp-cam solid roller lift is 726, duration is 268 intake, 276 exhaust, 108 lobe separation.
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I am about to pull the trigger on the rotating assembly, I want the extra cubes from the 4.5" crank but I.don't want to sacrifice durability in the stock block with the long stroke. I.just need a good push either way 4.3 or 4.5
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I went with the 4.500 and bored the block .030 over and ended up with a 545 cid. I could not be happier! Right now as it sits it is @ 11.23:1 compression and this winter I am going to 14:1. As it sits now I pull a detailed bronze B impellor to anywhere between 6300 to 6500 rpm. Make sure you get a dished piston or your compression will be through the roof!
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Will be running a 22cc dish probe piston for now until I switch to p-51 heads later down the road.
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Same piston I was running! I am swapping them out for JE next week.