Thread:

Engine/ horsepower/ manifold question

IMO, torque in a v drive is less important than say, a jetboat, or a heavy cruiser. If properly set up, your boat should dry out fairly quickly and hopefully be skimming across the water on the "flat" part in the back... Also, one of the luxuries of the v drive is being able to change gears and props to "dial in" your usage to the engine's "happy spot" of the RPM curve... In reality, boat speed is based on prop speed, which is based on engine RPMs out the final drive ratio... If I were you, I would be very cautious about your cylinder head choice. All the camshaft planing in the world is useless if the heads won't flow... IMO, look around, find some used aftermarket, or factory 990s, that were designed to be used on the added cubic inches the 454 will give you, or the added flow the camshaft is designed for. That said, if your 396 crank is a steel factory unit, you might consider using it. With the larger 4.250/4.280/4.310 (+.030-.060), bore, and the short stroke 396 crank, (3.760 vs 4.000 454) you can build a cool 427/433/440 with plenty of torque to dry the boat out, and plenty of RPM potential to see some pretty scary speeds... Dual plane intakes seem to make a pleasure boat more forgiving in the "drive-ability" areas, but the open plane should RPM up top a little better if comparing apples to apples....IMO, there is a fine line between a "fun" boat, and a heavy "rump rump" cammed screamer.. Yes, you can have both, but it takes an awful lot of homework to achieve that "right outa the box".....If you really want to have a "fun" boat, design it as that when choosing engine parts, and start collecting additional stuff for another "monster" motor for the "need for speed" we all seem to have.... Enjoy your boat for a few years while you assemble a totally different engine. Remove the "sensible" engine and stick it under the bench, install the screamer, and if it fails you still have "old reliable" to fall back on and continue your "fun" on the water..... Believe me, there is nothing worse than having your boat in the shop, covered up, because the "big" motor ate up your boating budget, and then windowed the pan. Always plan for the worse case, and keep that back up complete, ready to go back in.....Good luck..
Ray

Originally Posted by Eddie

...they are oval port semi closed chamber heads...

Sounds like they may be 049 heads. If this is the case and you are set on using them, the dual plane manifold will suit well with a cam aimed at creating max hp at around 5000rpm. 049 heads flow OK in stock form but nose over at about .500" lift, so no need to go crazy with the cam. There is much to be gained with 990 (style) heads in the way of more potential rpm and flow, hence more horse power overall.

I am fond of 427s, myself. Drove a few as a kid and just loved the way they had plenty of TQ, but would also wind out on top.

So, that being said, I personally would use the 396 crank in the 454 block - as mentioned - to make a 427. If you can buy rods and pistons, make it a long-rod motor for better dwell and less angle. Not mandatory to do so, though. It will run just fine with stock rods.

The happy-medium for a V-drive boat comes with a transmission. Put a T400 or Powerglide into the mix and it gives you the best of all worlds. You can gear the the V-drive for all your motor can push on top (high gear), but still have TQ multiplication and slow/idle drivability with 1st, and 2nd gear. I am fond of the usefulness of three gears instead of two. Again, this would allow a heavy rump-rump cam (top end motor) but still have docking manners. Plus, you get reverse.

Originally Posted by Eddie

Thanks for all the help!!! I really appreciate the info, I was looking for some 990 heads but have not been able to find any around here. The 427 ci is a great idea, I just have to check out some of my cranks, I have a few 396 motors, parts, not sure whats good or bad, been sitting for about 30 yrs... I was asking about the airgap, mainly because of its claim to be good down low and up high, performance wise, I have never used one so I dont know, I will probly try using both and see what works, or just go with the open plane, THANK YOU ALL FOR THE RESPONSE,,THATS WHY I POST ON THIS SITE<,,,,,,,,,

I have a pair of 990 heads, but hanging on to them for a future build. Just put some 290 oval ports on the 427 for my '65 Impala SS, which work real well. Way more motor than I expected.

The AirGap will treat your motor well, although it will knock down the top end a bit. Depending on how much you are going to WOT the boat, you may also consider a tunnel ram. Once again, especially if you put in a T400 trans. Regardless of boat-speed, you could keep the motor in a happy RPM powerband. Yes, you gain some weight and give up some HP to drive the trans, but personally I see the benefits out weighing all of the negatives.

Originally Posted by Eddie

Thanks , I was also wondering about a single carb tunnel? vs the airgap, not sure how well the single carb tunnel would work compared to the victor jr open plane that I have?, so right now I am considering airgap, victor jr , or single tunnel ram, the tunnel ram only becuase I have a friend that has one, he may let me have it for a good price, but not sure if I should even bother with that? THANKS FOR THE HELP, when I have better info on the parts I have, I will re-post to see what you guys think might be better, but im to busy working right now to even dig my stuff out,,, HAPPY NEW YEAR,, THANKS FOR THE HELP!!!

Most people here will tell you not to bother with single-carb TR. If you want to stick single-carb, go with a Victor Jr., or other well made single-plane. Single-planes are the mid-step between dual plane manifolds and tunnel rams, in essence.

However, anyone here will also tell you that you need to cam the motor for what your END result will be. If you plan on doing a tunnel-ram, either during the build OR later on, you need to cam it for a TR. If you are gonna stick with single-plane, the cam will not be THAT much different, so they can somewhat share a cam profile. Dual plane will like a tamer cam AND will not make use of any high-rpm cam timing. So, you need to know what your combination will be AS you are assembling the short block.

The difference I see between a jet and a flat is, when you mash the loud pedal, the jet basically goes to whatever peak rpm it's going to run and stays there. Because of the limitations of the pump, you're typically stuck with making as much power as possible in the 6500-7000rpm range MAX. Some ultra HP race boats will push more than that, and most weekend "performance" jets will see less than 6000rpm. This is why jets have the reputation for needing lower rpm power rather than higher rpm power and why bigger is always better in a jet. With a V drive, you can gear and prop to run whatever rpm you want so a smaller engine isn't a problem to get some rpm out of. The other difference I see is, a VDrive wants to burn the prop to get some rpm out of then hole, but unllike a jet, when the prop starts really biting it'll pull the engine down and then the engine needs to be able to recover and pull through a range of rpm. 99% of the time, both cases will benefit from the widest rpm range and broadest usable power available. A jet is a drive system that's loaded 100% right off idle and needs good power to keep accelerating the impeller. On a VDrive, once the prop is loaded, the engine will need good power to accelerate and keep accelrating. With peak power under 7000, I'd build both engines about the same. Maybe cam a little different one to the other, but not much.

With some very basic mods, the oval port iron heads will feed the 427 or the 454 just fine up to about 650hp. You can expect about 310cfm @ .600" lift with a 2.19 intake and a good valve job and basic bowl blend, maybe 240-250cfm on the xhaust. I wouldn't waste my time with the airgap since there's very little load on these engines at lower rpm. The Vic Jr with a 750-850 will make as much toqrue and more HP than the 'gap. I also see no need for rect. port heads for either engine- even if you go aftermarket. You can run a set of 990's but the engine/cam won't be quite as user friendly and won't make a single HP more in the 6000rpm range. No matter what you choose, having accurate flow numbers will really help in deciding what direction to go with the cam. A roller will obviously have perfromance advantage over a flat tappet and personally, I wouldn't run a FT these days. Rollers are a good investment for both power and reliability.
The thing about the 427 is, by today's standards it's just an overweight smallblock. You're going to have to turn some rpm to make some power. Not quite as much so with the 454. Unfortunately budget dictates everything, but for a "budget" 427/454 in a flat, I'd be looking at investing in a solid roller valve train, a little head work on the ovals, some decent rods and pistons (longer rods if you have the choice), as much compression as you think you can stand, and the best machinework and as much attention to detail as possible.
Of course, there's no substitute for displacement, and a 489/496 would ba another choice.
JMO

ETA: An Edelbrock Street TR (oval port) and a pair of 650/750's on it would be way cool on either the 427 or 454 with the ovals .

If you are thinking about that 3.76 x 4.250 combo check around for pistons first...seems like availability is kinda limited. And pay attention to the open/closed chamber deal. 396/427 heads should be closed chamber...put them on a 454 short block and the pistons might hit. As long as you have the time it might be a good idea to wait for a deal on 454 stuff to come long. Nothing really the matter with the smaller motors...they seem to work better in lighter boats
and you need to spin them harder to get the most out of them.
And these days with engine oil the way it is, lifters with wheels
are a good investment. Have a flat tappet cam go flat and by the time you tear down and clean all the metal out of the motor, buy another cam/lifters/gaskets you didn't save any money. I swapped a dart/1050 for a t/r and 660's on my deal and i like it much better.