Re: Still up in the air about heads
If i had a choice between a 400 smallblock and 383,it would be the 400,i'd punch it out .030. bore to stroke ratio is better on a 400 then a 383,it would have everything 383 would have in torque + the extra hp that the cubic inches would give you. Now,if i had your boat w/stock 350 smallblocks and had crankshaft/bottom end problems,i'd rebuild them using your good blocks and turn them into 383's. If i had your boat and motors were rebuildable,good factory steel cranks etc,then i would just bore them enough during rebuild to have fresh bores,polish cranks,etc and use my money for killer top end parts(cylinder heads,exhaust,BLOWERS,etc!After putting a blower on my boat 4 years ago,other than maybe a 525efi (because they bare supposed to be ultra reliable),i couldn't have a boat normally aspirated(boost is like drug!!!).
Wouldn't that fountain be cool with a little pair of matching superchargers on lt!!!I have known alot of guys w/boats who piss around with various mods in their quest for speed and after working hard to modify a n/a motor they see 2.5-5mph and still want more. Look at how fast your boat goes right now and decide how fast you want it to go then figure out the cheapest way to achieve it,if you want to gain 15 mph then your going to need some serious mods . |
Re: Still up in the air about heads
1 Attachment(s)
Originally Posted by articfriends
Twin 29,i don't have any personnel experience with a 383 or 400 in a boat but i have built both for street and strip motors,mud boggers & circle track. They will last just as long as any other small block,just a few things you don't want to do that i'm going to list (you might already know these but i'll throw them ought there for you or anyone else that it may help).
1. Never use the stock 400 rods (they are too short which gives you a less than ideal rod to crank angle, causing high stress over 5500 rpm's) 2.Don't jump thru hoops to find a stock 4 bolt 400 block(they only made them in 1970 anyways),the 2nd set of main cap bolts weaken the main bearing webbing,(you can actually see where the bolts protrude thru casting),if your building stock 400 block arp studs on a 2 bolt block are fine or splayed caps if your going to buzz it to the moon(or aftermarket block) 3. DO NOT bore stock 400 block past 40 thous MAX,Cylinders are already too thin,can crack easily, run too hot and you get crappy ring seal due to cylinder distortion. 4.Eagle makes a ok 3.75 stroke crank with 350 chevy main journal diameter for guys who want to build 383 without searching for hard to find 400 crank + the associated work on the mains to get it to fit. 5. Always drill the steam riser holes in your heads if running a stock 400 block,you can open the holes up to the size of the gasket on block too to prevent debris or corrosion from plugging them in a marine application. 6. You will be balancing any stroker combination you build anyways,you should have it zero balanced so you can reuse your original 350 flywheel (if replacing a 350). If you choose to use the external off-balance a 400 crank has built into it you will have to find a 400 only flywheel (harder and more exspensive to find). Most you guys out there know all this anyways but i posted it for some of the guys who might not to help them avoid unforseen problems,Smitty Roby |
Re: Still up in the air about heads
Originally Posted by robyw1
You seem to forget that the fuel needs the velocity normally associated with a small port to stay properly atomized and suspended. Plus we need more than just peak horsepower here. His engine has to be able to carry his boat to that peak horsepower. If it can't then his engine will have a loud bark but no teeth. Also I want to see this engine you got 100% VE. The baddest of the bad normally aspirated engines are getting about 88 to 90% volumetric efficiency. The N/A formula 1 engines are getting mid-90s. Are you sure about your numbers?
No offense here, Just want to know. Roby we sat the SS/IA class record in montgomery last spring @ 9.79... not running so well right now at indy though.. we are qualified 94th @ 10.03... the car has been 9.68... class eliminations coming up and two IA cars are qualified just a skosh quicker @ 10.00 and 9.95... |
Re: Still up in the air about heads
Hey guys, not to get "off the subject" but, Have we decided what heads I'm going to use? :p
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Re: Still up in the air about heads
I have but I don't know about anyone else. :D
Roby |
Re: Still up in the air about heads
Robyw1,i edited the steam hole reccommendation,your right,in the past ive run a drill in them that just fits to clean them up(iv'e seen them partially plugged and rough where crud builds up and catches in the hole.
I'm on board with robyw1 on the 180 heads too. With what liberator21 says he's trying to achieve i feel they are right size. jaroot,i'm sure if your turning a drag motor 9000,your buzzing up a nascar engine that is trying to make max power under the given rules (with hundreds of thousands of dolllars of R&D in head flow/vs cam profile vs limited carburation) or your building a 6000 rpm small block for a boat with radical exhaust,intake etc bigger would be better,Smitty |
Re: Still up in the air about heads
Liberator21
Much of the conventional wisdom regarding small block heads and port volume vs. velocity is shifting due to the fact that many of the newer design heads are increasing volume incrementally without any resulting loss in velocity due to the port dimensions and cross sectional area. Today’s 200cc intake port is vastly different than the hogged out ports modified in the past. Add to that this build is a 383 cid with 6.0 rod and the requirements are significantly different than your basic 350. First the stats: A 383 w/ 6.0 rods vs. 350 w/5.7 rods 383 has 9.4% more displacement 383 has 7.8% higher mean piston speed 383 has 8.4% greater piston acceleration The above increase the flow velocity per the given dimension of the port 200 cc intake runners have 11% more volume than 180 cc The 383 will have more torque than the stock 350 engine @ every rpm point, reducing time to get on plane. Most recreational/performance boating is @ 3000+ rpm (try and keep a 21 footer on plane under 2500) where port velocity (to a degree, very important not to go to far) is not an issue. High port velocities are most effective at or below peak torque. A marine engine should cruise @ near peak torque and WOT should be near peak HP. The SportsmanII heads sometimes get bad press on their out of the box flow #’s (on the exhaust side) with an I/E ratio of 67%, however, some basic bowl blending really wakes up the exhaust side and will yield upward of 72% I/E. I have personally used 3 sets of Sportsman II’s (1) 350cid & (2) 383 cid. in marine applications. Cammed correctly, they have all performed extremely well and given very satisfying performance throughout the power curve and very substantial WOT increases. It bears noting that the 2 latest performance small block cylinder heads released by GMPP are the 210 cc Fast Burn aluminum http://www.sdpc2000.com/cart.asp?act...d=3129&pid=144 and the new 206 cc large port Vortec iron http://www.sdpc2000.com/cart.asp?act...129&pid=229034 Equally important is the selection of carburetor, intake, cam, and valve curtain area. More is not always better, but the 200cc threshold that was once thought of as too big for anything but high rpm race applications is now finding that volume and velocity (to a degree!) can work with the correct cross section. I would be happy to answer any questions regarding the specifics of these builds. Bob |
Re: Still up in the air about heads
bob,
Dido on cross section...200cc heads for the 383 will be a nice match. chris |
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