PDA

View Full Version : SBC Cost / Performance Mods



tailwind
07-25-2002, 08:29 PM
As learned from alot of previous posts, Donzi owners have to go faster!

Here is my question: By going with an alum block/head setup how much additional HP
can we achieve, and at what weight savings potential? For sake of argument, let us all assume
a smooth idle, and constant torque thru say 5,000 rpm.

Additionally, let us assume current vortec manifold etc. Would indeed it be possible to achieve
400 Prop shaft hp? and if so how much weight reduction 200-250 lbs?

I guess what I am asking is the most dependable HP versus weight.

Best regards,
Randy

Murphy
07-25-2002, 10:40 PM
Tailwind,

Not sure how exactly to respond to your questions. Weight reductions is only a small part of the equation. Otherwise, the component combo's you suggest are way too vague to allow anyone to make a reasonable statement about performance. Suggest you pick-up Dennis Moore's book on Small Block Marine Performance Engines. It will give you a good general idea of what modifications can be made to a SBC to improve performance. Asking for a smooth idle, constant torque curve, and 400hp in a small block are like saying you want to marry double-D stripper from Crazy Horse II who also has a Phd and teaches Sunday School. If you want 400 from a mouse you'd better team up with somebody who knows exactly what they're doing and bring your wallet. Incidentally, I'd make sure I saved enough for a Bravo drive in the process.

Murph

Rootsy
07-26-2002, 07:31 AM
you can probably squeeze 400 @ crank out of a 350 in "kinda sorta" mild form for not a bust the wallet amount.... 375 is very doable... with the camshaft selection you will have to use to avoid reversion you're likely going to see your torque curve begin to fall off around 4000 rpm and your hp peak in the 5000 - 5500 range. don't forget the exhaust... it'll be your restriction in the whole equation at those power levels...

i'm sure a few others will have their twists on this topic... you might consider going the stroker route too for a bit more punch...

Rodger
07-26-2002, 07:58 AM
Jamie is right, more displacement will make your goal much more feasable. I had a 350 in a 16 footer and wanted similar user friendly performance such as you do. I ended up building a small block 406 for it and pretty much met my goal.

MOP
07-26-2002, 07:59 AM
Why not go with a 4 bolt 350 mild cam and a 671 blower running about 5psi boost that should get you where you want to go with great torque. Yeah the up start will not be cheap but look at it this way, if you puke a really nice expensive mill sometimes there is not much to salvage. But a fairly inexpensive standard marine block 150 dollar cam and a blower setup will get decent time if you don't hammer it alot. Blowers produce torque from the bottom up, and when it blows up unbolt your goodies and bolt to another block. I feel in the long run it will be a cheaper route and it will be way cool looking.

TORYSMINX
07-26-2002, 10:50 AM
I just had built a 385 cu in stroker for my minx and I wanted exactly what you wanted. You have to pay big money for these things. Forged crack 4340, forged rods,Pro Action heads,Roller everything.

You have to weigh how much you want to put into the boat? I went overboard and yes I am pleased but to do it again I would have gone with a mild big block and used the extra money for the drive.
I have a little under 500hp in this thing but it costed me like 8k roughly. The exhaust is a big thing too at like 1800 bucks and you NEED THESE!

Too get the desired HP I think you would have to use a high lift CAm with a lower duration.2.02 heads at the least and roller everything. Figure on at least 600 for Cam,rockers and lifters. OH I forgot that you need all MSD stuff(Billet Dist,7al box etc) too figure in also.

about 7k I think will get this done but I could be way off. Just my two cents

Good luck
Tory

Rootsy
07-26-2002, 12:11 PM
one large consideration... are you going to be or ever going to be running in saltwater? if so the aluminum motor is probably not so good an idea...

my 350 is now in the neighborhood of 360 - 370 hp @ crank... i started with a 250 hp 2V mercruiser and about 3000 +/- dollars later here i am... that 3K includes a completely new roller valvetrain, cylinder head castings, gaskets, intake manifold, ignition work, carburation, odds and ends and some exhaust parts... not full blown stainless marine or anything. the lifters and the stainless valves were free... so taht saved me a good 500 bucks... my motor is very docile you can hardly tell there is a performance based camshaft inside of it... i had zero labor costs since i do all of my own work...

guess what i am gettin at is if you want to make a lotta HP and have it stay together and be reliable it will cost a fair penny... if you want to go stroking things or blowing things it'll get considerably more expensive... i am sure i could have cheapened things up a bit here and there but that wouldn't give me peace of mind when i am WOT...

BigGrizzly
07-26-2002, 02:02 PM
You will save only 163 pounds total. as fot even torque there is only one way with that engine and the word is Procharger. To get a tracable engine from 2600 to 5000 is easy with or without a supercharger. It is the total package is the key. There isn't any reason to go all aluminum unless yoyu have it already. If it were me and I had the choice I would go iron an closed cooling system. You will never be the fastest, so strive for the longest living engine. Just remember even with the best stuff engines can break.

Randy

tmdog
07-26-2002, 04:31 PM
Grizz---- good advice but, why the closed cooling system?

MOP
07-26-2002, 05:05 PM
From what I have read closed cooling lets you run hotter giving a little more power. But as I have posted before, if I had ten over heats a month at my place nine were fresh water cooled. I at one point worked on the boat owned by the owner of Sendure. I had a talk with him and he admitted to me that he had an agreement with the OEM's for a 15% margin on cooling tubes. That is about the only thing not coverd by Warentee, its like an anuity for the OEM boys. If you do go that way I would most asuredly use a big block cooler on a small block or go custom. Make damn sure you have alot more tubes than a stock SB setup. Me I will keep on Flushing and not worry! The darn thing will either wear out or blow up before it rots through.

mattyboy
07-26-2002, 07:37 PM
then you get to a point you lighten the engine, and get some big hp, that you gotta change the alpha to a bravo then your adding weight again
the quest for speed ain't easy or cheap!!!!

Matt