maverick2

I'll be running a closed cooling system with wet exhaust. Exhaust manifolds are performance manifolds with high center risers so water reversion back into the exhaust is less of a problem. Planning on using a marine cam to further inhibit reversion and tailor the torque curve to the application. Now back to the heads... Brodix IK 200's vs Canfield 195's???

This 406 will be going into an aluminum jet boat. Pump/impellors will be set up such that torque demand gets too high to turn past 5000 rpm. On plane at 2800 rpm, cruise at 3200 rpm, and play between 3200 and 4800 rpm.

The "good deal" on the Brodix IK 200 is $825 (heads are complete), while the Canfields were about $250 higher. Was originally leaning toward the Canfields, but at that price for the Brodix, they are kind of hard to pass up... As for Dart, my builder had problems with the last 3 sets of heads he got in from them, so he's not a Dart fan right now.

I'm in the acquisition phase of my 406 buildup. Goal is 475-500 ft-lbs peaking at about 4400 rpm, running smooth and strong from idle up thru that rpm range, and topping out at 5000 rpm. I've narrowed my choices on heads to Canfield 195's, or the Brodix IK 200's (I've got great price options on both, so dropped AFR from the mix.) Any recommendations? Pros/cons of each based on experience? Thanks.

Thanks for the different idea. Actually ran across a thread on a jet boat forum from a builder that specializes in builds with those blocks -- their performance characteristics looked great for this application, but if I remember correctly, he was struggling to find an outlet for the various "bolt-ons" it takes to "marinize" an engine for safe use in a boat. It seems like there are multiple options available for any Chev block and a lot of Ford blocks, but it's pretty limited beyond that? Will track that thread down and see where it takes me. Thanks!

Thanks for the detailed response – I’d previously read those (or very similar) articles on rod:stroke ratio. The majority of the published builds I’ve seen to date for the 406 have used the 5.7” rods (rod:stroke ratio of 1.52), while most of the 377 builds have used 6” rods (giving a rod:stroke ratio of 1.72), so the difference between those two (which equates to about 2 ½ degrees difference in rod angle) were the numbers I was playing with. A more accurate comparison is probably one assuming a 6” rod for the 406 and a 6.125” rod for the 377 (gives a pretty comparable piston compression height for each) yielding rod:stroke ratios of 1.6 and 1.76, respectively. Probably a moot point since the general consensus seems to be that the effect on engine durability is nil when comparing the 406 to the 377. (As an aside, the article “The 350 Chevy should have built” was one of the big things that made me take a second look at the 377. Once I saw that the 352 in the article made 440 ft-lbs with a very broad torque curve, it made me think that 475 ft-lbs (my min torque goal) was probably attainable with the same block in a 377 configuration.)

BRAAP. PPARASKA, & Grumpyvette; Thanks for the good feedback – that’s the type of discussion I was looking for. Based on what you’ve seen in the past, here are a couple questions you might be able to help me answer: 1)Is cylinder wall flex with a 400 block a real or imagined problem under sustained high loads? I’ve got no experience to know if this is more rumor (like the over-heating rap the 400 gets labeled with), or a valid concern? 2)If cylinder wall flex IS an issue, is it mainly the result of piston side loads against the cylinder wall, or is it the result of extended operation under high cylinder pressure conditions? Thoughts? Thanks again.

No, I could add a turbo if needed to get to my torque goals, but if I can't get there with a 377 (or find that there's little/no durability benefit to doing it with a 377 rather than a 406) I'll simply build the 406. There are quite a few different recipes for a 406 to get the numbers I want w/o adding the complexity of a turbocharger.

The photos in this website are pretty typical. It's a recreational boat, built for conditions that range from Class 3 and 4 whitewater rivers, to 4-6" of water in shallow streams. My interest in "durability" is do to the fact that VERY, VERY BAD THINGS happen if you lose an engine in a class 4 rapid.... http://www.bentzboats.com/recreational_photo_album.htm

Thanks for sticking with this thread – I know it’s gotta be frustrating the hell out of you. Actually, options for pump, impellor, and nozzle are pretty limited. (There are really only 2 pump mfrs suitable for whitewater jetboats, and both offer similar performance/characteristics to one another.) In each case, you CAN re-size your impellor and/or nozzle to drop the rpm at Wide Open Throttle and take advantage of the 406’ inherent ability to make more torque at lower rpms, but it comes with serious tradeoffs. Both pumps seem to be most efficient above 3000 rpm, such that changes to an impellor or nozzle have a noticeable effect on performance characteristics above 3000 rpm, but make little difference to thrust and operation below 3000 rpm (which is generally lousy). As a result, if you set up a pump to run WOT at 4000 (which is most typical in order to match the peak torque of most commercially built marine engines of 3700-3900 rpm), you are still stuck with a cruising speed between 3000 and 3200 rpm. With a 600-800 rpm split between cruise and WOT, most boats leave a lot to be desired as far as “fun factor” and drivability. About the only way to increase the number of options you have for impellors and nozzles is to increase the point at which peak torque occurs on your powerplant. My desire to get peak torque at around 4500 rpm should allow me to achieve around 4700-4800 rpm at WOT and cruise at 3200-3300. These splits are a lot more fun to drive – the boat is more responsive to throttle changes, and mid-range acceleration and handling takes a big step forward. It’s pretty hard to attain that with a whitewater jet boat by decreasing the engine speed at which peak torque occurs... When I started this process of building a boat, I figured out the most limiting factor of the boat build (which is the pump), determined what kind of performance and rpm range I wanted with the pump, and then started shopping for engines which met the needs of the pump for that kind of performance. (There are a lot more commercial engine options available than pump options, and the options for custom built engine performance is nearly unlimited in comparison…) The answer I walked away with was the sbc 406 – it has the potential to meet and exceed my torque needs across the desired rpm range while coming in at the least weight. As I started looking at the torque potential of the 406, the question came up about the value of sacrificing some of that torque potential in order to improve upon engine durability/longevity for THIS APPLICATION. (I won’t even consider building a 377 over a 406 IF I don’t think I can get to the torque numbers I want, but right now I think I can, as does my engine builder). Assuming for a moment that I CAN get there, my question is whether or not it’s worthwhile in terms of durability – does the 377 (with it’s superior rod:stroke ration, longer dwell, and better quench conditions) offer some inherent durability/longevity advantages over the 406 GIVEN THE OPERATING PARAMETERS/SCENARIO I’ve laid out? I think it does – and that’s what I’m trying to pick people’s brain about. Bottom line is that if I can’t go into an engine build thinking the 377 will make the torque I want AND thinking the 377 doesn’t have some durability advantages, then I’ll simply build the 406. With all that said, I’ll ask the durability question again: Assume each engine (a 377 and a 406) is going to spend a lot of time running at 4000 rpm. Mated to identical pumps, both engines will have to make 375 ft-lbs, which is the Tq demanded by the pump at that rpm. Which engine will live longer, and why? What problems would you expect to show up first?

Actually my mind is not made up -- I'm trying to determine if downsizing to a 377 effectively addresses a potential weakness of the 400 block for this type of application. When my builder threw the concept of a 377 on the table, I immediately discounted it because I didn't think it could/would get the torque I want. After doing some looking, I think that 480 ft-lbs is attainable with 10.5:1 CR IF the components are well matched. I'm not expecting (nor needing) to get torque comparable to a 406 out of it, so if a 377 buys me some durability/longevity AND meets my torque goals, WHY NOT build it?

I understand what you're trying to say, but I don't think this line of logic works in this application. Consider these two options: build a 377 capable of a peak torque of 480 ft-lbs at 4500 rpm, or build a 406 capable of a peak torque of 520 ft-lbs at 4500 rpm. With the impellors that I want to use (selected to give me the performance I want from the 2500 - 4000 rpm operating range where the boat spends 95% of its time) the pump will limit the top speed of the 377 to about 4700 rpm, while the top speed of the 406 will be about 4900 rpm. (The pump will prevent both engines from turning any faster, so the references to additional wear and stresses by turning higher rpms with the 377 is moot.) Assume each engine is going to spend a lot of time running at 4000 rpm. Mated to the same pump, both engines will have to make 375 ft-lbs, which is the Tq demanded by the pump at that rpm. Which engine will live longer? I believe the 377 will live longer which is why I'm considering this route. The 377 will have to generate a little higher cylinder pressures to make 375 ft-lbs at the same rpm as the 406 (making up for its shorter stroke), but at these engine speeds, that additional pressure should not be a big factor on rotating assembly stresses, and makes no difference on valve train stresses. Where I think the 377 excells over the 406, is in the lateral stresses on the cylinder walls. With a significantly better rod:stroke ratio, the 377 is going to have a lot less side thrust into the cylinder wall, meaning less friction loss, cylinder wear, and cylinder wall flex in a block that already has relatively thin walls. In a marine application, I think this can be a very real scenario because of the sustained high loads that are typical of boat operation. Does that help to explain my line of logic? Thoughts?

The basic question I'm asking is whether or not there's an engine longevity/durability advantage in de-stroking to a 377 in this particular application... If so, the sacrifice of torque doesn't bother me a bit, since the only thing it will buy me is 200 rpm (roughly 5 mph) on the top end, where the boat spends almost no time. (In order to take advantage of that torque increase within the normal operating zone, I'd have to move up to the next larger pump size, which is an additional $3-5k, and not yet in production...) On the other hand, if there is no durability/longevity advantage, it's a no-brainer to stay with the 406...

Does de-stroking a 400 sbc to a 377 have the potential to significantly improve on the engine’s durability if used to run relatively high sustained loads? I’m building an aluminum jet boat, and picked up a good 400 block (2 bolt mains, casting #330817) with the intent of boring it .030†over and making a 406. With a goal of 475-500 ft-lbs around 4500 rpm, I started looking around for build recipes, and quickly found (thru grumpyvette and multiple other places) that the torque potential of a 406 far exceeds what I need (sounds like 530-550 ft-lbs is pretty attainable with a good builder). At the same time, I’ve also had quite a few boat gurus caution me that high sustained loads typical of a marine application can be tough on a 400 block because of the lousy rod:stroke ratio coupled with the thinner cylinder walls. One of the things I’ve contemplated is de-stroking the block to a 377 to address that potential weakness, and not worry about trying to wring every last drop of torque out of the block. I know reducing displacement tends to fly in the face of conventional wisdom, but if I can still meet my torque goals (based on the performance of a comparably sized 383, I believe this is very do-able) and improve the potential durability of the engine, what would be the downside? Keep in mind, there is no benefit for me to build an engine with any more torque than 500 ft-lbs, as the additional torque is essentially un-usable unless I jump up to a bigger, significantly more expensive pump. In order to eliminate a few questions/confusion up front, here’s a little background on the application. A jet-drive for a boat is basically a direct-drive pump bolted to the back of the engine – no gearing, no clutch, no transmission. There are a handful of different jet pump manufacturers out there, but really only two that make a good pump for whitewater applications (must be able to handle aerated water well). As you can see below, the power demand rises exponentially with engine speed, and it becomes difficult (as well as counterproductive) to turn one of these pumps past the 4500 to 5000 rpm range if they are equipped with the whitewater-capable impellors I want. Top speed (both boat speed and engine speed) is dictated by the point on the engine’s TQ/HP curve where the TQ/HP demand of the pump surpasses the output of the engine. Pump loads are dependent upon the particular impellors chosen, and are pretty well known for any given engine speed. As an example, TQ and HP demands by the pump would be pretty typical of the following for the pump/impellor combination I’m looking at: Jetboat Pump TQ and HP Demands RPM TQ HP 2000 118 45 2500 147 70 3000 219 125 3500 285 190 4000 374 285 4250 432 350 4500 466 400 4750 500 452 What this means as far as operation for a boat of the size that I’m building, is that it will hop onto plane at about 2800 rpm (absorbing approx 200 ft-lbs and 100 hp from the pump) cruise at 3200 rpm (absorbing about 250 ft-lbs and 155 hp), and top out at whichever engine speed the engine hp/torque curve crosses the pump power absorption curve. My goal is to build an engine that will spin the pump between 4500 and 4800 rpm. As a result, I’d like to build an engine with a peak torque between 475 and 500 ft-lbs, and have that peak torque hit right around 4500 rpm. This would give me an 1800-2000 rpm split between planing speed and top speed, and a 1400-1600 rpm split between cruising speed and top speed. These splits are head and shoulders above what the commercially available marine engines can do with these pumps/impellors, and are a lot more fun to drive. As a side note, it’s very difficult to over-rev one of these engines, since the pump loads gets extremely high once you get above 5000 rpm. As you can see, this application is a bit different from that of a performance engine for a street car: I’m looking to achieve strong torque in the mid-range engine speeds (rather than the lower rpm range that street cars often shoot for) with very smooth operation from idle to peak torque. I really don’t need/want a big rpm split between peak torque and peak Hp since the engine will not ever see speeds that are more than 500 rpm above the peak torque once I get the right impellors on board. Most street engines seem to sacrifice some torque in order to achieve a relatively large rpm split between peak torque and peak HP – I don’t need to worry about that… Engine durability needs to be an important consideration. Boats tend to operate for relatively long periods at constant loads between 3000 and 4000 rpm (skiing, climbs thru a long set of rapids,…) while street engines tend to fluctuate engine speed and load pretty regularly. I need to build this engine with that “sustained load†in mind, hence my consideration to de-stroke the 400… What are your thoughts – is my logic flawed, or am I heading in the right direction? As a follow-on question, as I look at build recipes for the 377, would it make sense to consider a head, manifold, and cam combination used in a 383 buildup? (Basically adopt those components from one of many 383 builds that makes the torque/performance characteristics I’m looking for…) Or is the airflow thru a 377 different enough that this approach doesn’t make sense? (I am NOT having much luck in finding published info and torque/hp curves for a 377 except for those that are built to rev thru the roof…) Thoughts?