small block mods
 

well . . got my new boat a few weeks ago an i was thinkin about do'n a few performance mods this winter. :cool: its a 26 foot chris craft stinger with a pair of 260 small blocks. anyway they have only 400 hrs on them and are very solid and in stock trim. i would like to get them up to about 300 to 325 HP. was thinkin about cams/intake/carbs. any thoughts on combos. i would like to do this without getting into the bottom end. (is that OK stock) thanks all :cool:

small blocks! small blocks! . Im pretty sure you can get 300 with a camshaft change alone. check Dennis Moore's book, you could probably get another20 or 25 with some port work

And you could certainly keep the Q Jets at that power level. Dennis Moore's Book........

Hey Dave- 400 hours? how are the rings? Did you do a leakdown/compression test?

As for the bottom end, IMHO, the stock forged stuff will be OK up to 325HP. I think you could get there with cams/intake/carbs, but a set of heads w/2.02 valves would make it alot easier. What kind of exhaust do you have?

Stock forged stuff?? Last time I looked at a stock 260 it had cast pistons and a cast crank. A 260 is nothing more an assembly line truck engine; same as found in your 1/2-3/4 ton Chevy/GM pickup.

With that said... cam and intake will get you there. Again, check out Dennis Moore's book. A lot of good information!

holy crap . . i keep forgetin i have that book :rolleyes: i'm just so used to askin the board. actually Havasu you told me to get it about two years ago when i got my daycruiser ( its the yellow 23 mirage i posted on hotboat askin "help me identify" similar boat to yours) hated to see that go but i got a smokin deal an this one. rigth now the boat has stock exhaust to the prop but i picked up a set of 4 inch risers and trhu hull tips. i was thinking about an edelbrock performer intake and cam set. maybe the air gap intake .

TomZ is correct- you have 2-bolt mains, cast crank, and cast pistons in a 260. Not to worry, these are up to the task for what you are asking. As far as 400 hours on a SBC? That may have worn out most BBC's, but is nothing to a small block. Do a compression/leak-down check. The only concern may be the valve keepers and retainers. I have seen them fail on stock 260's that have spent their time in a performance environment. That = dropped valves! Been there, done that.

I think a cam and intake manifold change will help, but you probably should do something about your heads. Vortec or World Products won't break the bank, and give great performance increases. CompCams make great marine cams (TomZ has experience with them)- I used a dual- pattern Isky, and am happy. A full roller set-up is not necessary for what you want, and is very expensive, especially when doing 2 engines!

I used Edelbrock's Performer RPM Q-Jet intakes- you can use your existing carbs that way, which are Dennis' choice anyway. Tune it per his book. Same with the Thunderbolt IV.
Obviously, any increases made to incoming air flow can only be utilized with a corresponding ability to get rid of it. That = aftermarket exhaust. Changing just the manifolds on a SBC will yield little or no results (but weight loss), but new manifolds or headers will give you benefit with head, ,cam, and intake mods. I used EMI Thunders, and am happy with them as well.

Have fun!

Hey Dave,can you say bye bye Alpha drives:D

Sorry...I meant cast...maybe my brain is cast, too.

I have same motor in my 21' Donzi. Mine needs head work. I know a guy that works in a machine shop doing there marine applications. I asked about better perf. since he will be pulling the heads anyway. He sugg. he could add approx 30 hp just doing valve job.

Just port up the heads you have aftermarket would be way overboard for what you are asking.

if your goal is 300 hp.. you might as well go for 400 :p :p You might look into vortec heads for around $400 a set they are pretty decent. Dennis's book has alot of valuable information. I used alot of it for referance. And you won't have to worry about your alpha's they will be fine with that kinda hp even less stress with twins. I have over 410 hp in my alpha, always reaming the **** outta of it :D and have had zero problems. Come spring about 490-500 hp will be going through it :D :D

good luck bro, keep us updated



Travis

What is Dennis Moores book that I have seen refferenced here?

BOAT ENGINE BIBLE
 

A must read for any performance boater. (which pretty well means all of us)

Dennis Moore's book is called "Small Block Chevy Marine Performance" (HP Books, 2000). I got my copy from Amazon right after it was published, but I think Dennis has said on this forum you can order it directly from him.
As far as rebuilding/machining/porting the original heads used on the 260 engine, you will find more often than not that these "light-cast" heads either have hair-line cracks or are warped too badly to resurface. These heads were a weight-saving (bad idea) from Chevy, and were not made with performance in mind. You will miles ahead by using the Vortec or World Products.

Very simple mods.....Ive seen several tests that report (Moores book seems to agree) that state stock Vortec heads w a 4 bbl will net 307hp @5000rps. You can get COMPLETE Vortec heads for about $400 per pair. I got mine from Salee performance (A GM dealer in Oregon)It wouldn't hurt that you would get the springs,valves and stuff all new and included either with 400hrs on the motor It wouldn't hurt to replace those anyways.....

For about 800 you can get a set of ported vortex heads

Stock port Vortec heads will support a 400+ horse 383 SBC. If using a cam with over .480 or .490 lift the heads must be modified or the retainers will hit the valve giudes. Stock springs should be replaced too, spring pockets will have to be opened up to acommodate.
Scoggin-Dickey Chevrolet has a kit that includes an Edelbrock RPM Air-gap intake, modified Vortec iron heads for .550 lift, rocker arms, springs, retainers, head bolts and gaskets for $949.95.
Same kit for .570 lift roller cams is $940.95.

I have a 350 mag 1992 what does it have for internals
and what kind of reliable power could be had for $1500 in work?
same here 400 hours I like the weight savings of the smallblock

I have a package I’ve been doing to the 5.7 Vortec engines that is working out very well. I port the Vortec heads and install 2.02/1.6 valves, small Crane hydraulic roller cam
(p/n 104224), Edelbrock RPM Air Gap intake and 600 CFM carb. This results in 340+ PSHP. I’ve seen a minimum of 5 MPH gain and as much as 8 MPH over the base 250 PSHP Vortec engine. The HP peak is about 5200 RPM. The Vortec engine has a stronger bottom end than the earlier 5.7 engines. If adding this package to a pre-Vortec engine the compression will be higher since they usually have flat top pistons. The Vortecs have a dished piston. I would limit the RPM to 5000 and run 93 octane gas. Timing should be set at 32 degrees total. I’ve also done this on a 350 Magnum. The gains weren’t as great since it already has a good intake system. I installed an adjustable fuel pressure regulator and raised the pressure about 5 lbs to compensate for the added air flow. It worked very well although the gain was only about 3 MPH. It would be something good to do if the engine had to come out anyway, but I’m not sure it would be worth the expense otherwise.

30 hp just doing a valve job? Or did you mean a port job? I am building a 355 with a lunati Voodoo 262 cam, vortec heads and stock aluminum Volvo Vortec intake. I have bumped the compression to 9.35:1 and am expecting to see 350ish horsepower. Remember to be nice to the alpha because it cant take much more than 350 horsepower.

I just realized this was an old thread... I just saw Dave 2 hours ago and he said nothing about a new boat... Started reading the first post and was like WTF???