Now lets assume I was able to change some parts. How much of a difference would it make powerwise to optimize everything based on 305s vs say 315- 320- 335?

About the same as me changing a few things to find 30-40 hp that in the end won't make much if any difference in speed... I very well know engine builder here told me to stick with my combo even though I am not too happy because te cost to change certain things at this point are not worth the gains..

You really keep missing the point don't you. Your expertise is in name calling and stupid picture posting. I don't know or care if you know them or not. These clowns that you seem to think can make good HP use dyno numbers @ 20% or more correction, and they use them in CARS. You do understand that a high HP CAR engine is not going to work in a boat don't you? If its wet its gonna revert, and the part specs that are needed to get a boat on plane and running are not even close to what you need to run a drag car or a street car.

305's will support a 540 but you are at the edge of where you want to be. If you have the money, the 315cnc's are going to be a much better choice. Assuming of course that you have the airflow from the carb or efi and the cam to take advantage of the heads. AFR can do some additions to the 305's to make them a bit better than the basic ones, again depending on the dollars you have to spend. You can call AFR and ask them for specifics. I'd tell you who else to call, but then some people on this thread will get into name calling which won't help you.

How would you explain, all the guys on yellow bullet, chevelles .com, performance boats, etc, that have bought parts from these guys, and dyno'ed at THEIR OWN facility, in various parts of the country? I could probably post up about 50 links to threads of their customers who have good feedback.

Get over yourself with this "marine" thing, as if its some secret society of how to build a "marine" engine. Sure, you run a little wider ring gaps, little more piston to wall, maybe a little more bearing clearance, maybe a little more guide clearance, wider valve seats, possibly a very mild low overlap cam if running "wet manifolds" and a little more conservative tune up. Some of the BEST marine engine builders, started out building drag race engines many decades ago. And I'm not talking about 637hp 509s'. Guys who daily put together 1000 plus HP builds and idle like stock 525's. The fundamentals still apply, whether its airflow, induction, chamber design, boost, stroke, etc

You keep talking about REVERSION. Is that all you have any knowledge about? Why, because straub sold a cam for guys boat engine years back , and it reverted water? Get over it already. When you do get another boat someday, look into dry tailpipes, so you don't have to crutch your engine with the fear of "reverting" with a lame azz camshaft. They came out in the 70's, and just about every company selling marine performance exhaust, will extend the risers for a reasonable fee, or any good tig welder with some stainless tubing.

Here's a build Alex Haxby did a few years back, with AFR 305's, on a 540ci. Keep in mind, this was a 9:1 engine on 87 octane, dyno'd in full marine trim, with all accessories and marine manifolds. Dyno headers, no accessories, a little more camshaft, another point of compression, I could easily see 700hp.

Are you really this thirsty to keep drinking the kool aid? How many times are you going to list CAR sites. This is NOT a car site. Can a car guy learn to build marine engines? Sometimes. Sometimes not. If they want to understand and not think they are smarter than the guys that have been doing it for 30 years.

You just listed 5 simple things that need to be changed in a marine engine. you skipped the hard stuff, but hey sorry if you don't understand it so you can't post it. Call straub. he can tell you. Ooops wait a minute I forgot. He doesn't know how to put a carb on an engine so you better pick someone else.

You do understand that in todays world that building a 1000 HP engine that will idle is not an "oh my god" event don't you? The days of the 900SC are long gone. The marine guys that know what they are doing are doing 1500-2000 today. and they idle too.

Why reversion? do some more homework. there are dozens of straub crap cams that reverted and trashed engines. again, stop believing them and do some of your own research on a MARINE site. If you want trashed car stuff go to the Vette forum and do some searched. the trail is long and expensive.

Wet exhaust? You ever hear about noise? you may be an inconsiderate jerk with dry exhaust, but the lakes I use don't put up with that stuff. Dry exhaust sounds great till you piss off every person around you and then wonder why performance boats got kicked off yet an other lake.

As to HP, sorry that you don't like 637. How about you go to a big poker run and tell all the guys running twin 525/600/700 that their engines suck because you don't think it means anything to build/run engines in that range.

Its called mufflers. I have dry stellings headers , and with gaffrig mufflers closed , they sounded like 330's with wet exhaust. They have plenty of options out there for that.

Please, I don't need a "lesson" from a guy, who doesn't have a boat, and had to have someone else build and spec his engines, about building "marine" engines. I am doing just fine in that department.

what makes you so fukking great? you are not engine builder, your posts are no different then any others.... many different factors in many different builds...Gellner built his name off CAR ENGINES.... now has a HUGE marine backing.... yep... cars.... endurance is endurance... yes there are differences but it's not things that are secrets...

Somehow, this guy isn't getting what I am saying. He keeps talking about foxwell/straub's "correction factors" being bullchit. What I was trying to say, is they have many customers who buy parts from them, or take advice, and go dyno their OWN engines, at their OWN choice of dyno, and post the results on public forums. If I bought a cam from straub, bob, mike jones, whomever, and go dyno my engine at my local shop, how in the fuk, does straub, bob, mike jones, have any influence on what the numbers are? Its not their dyno, nor are they even there!

Again, he keep saying "those are car guys", this is "offshoreonly".

He's gonna tell BCK, that going to the 315 AFR's would be a "much better choice". I've seen many times on forums, where Tony Mamo, has advised guys, to stick with the as cast head with CNC chamber version, as their isn't much to be gained by going full CNC port for the money, unless going for every little ounce of power.

I wonder how many guys have wasted THOUSANDS of dollars, because their salesman, or internet warrior, told them their parts were sub par, to what they can purchase. Only to find minimal gains, if any.

Last year, there was a huge argument, over some 454 builds, with 177 baby blowers, and AFR heads. I was beat up by the internet warriors and parts salesman, because I suggested the 305 head for that build, when they said the 265 heads would have been a better way to go. I then got yelled at by them, for contacting AFR directly with my inquiry! lmao. Anyhow, two different oso members built these combos, nearly identical , except for the heads. You know what the 305s gave up in low speed torque to the 265s? ZERO. You know what the 265's gave up to the 305's at 6000RPM? Very very little. One thing that should be considered, IF, there ever was a need or want to upgrade from a 454, to a 502, or even 540, those 305's still would have worked just fine with a blower, and be willing to bet, those 305's would stomp those 265 ovals, had it been a 502/540, with a whipple, or 10-71 on top. Neither one was a bad choice, and since the guy buying the 265's, was in need of static compression, with the smaller chambers, it made sense to go that route. Point is, neither choice was a make or break. Wanna know where the real power lie in those builds? The blower. A swap to a better blower, would be a change worth talking about, and certainly make changes on the speedo.

My general advice to BCK, would be, save your money buddy. Focus on the combination of the build, not only to make a good dyno number, but a reliable package that you could ABSOLUTELY stand on ALL DAY LONG in that killer old school larry smith scarab with #5's. Why? Because at that power level, in that hull, there is no reason you would need to let off the throttles for much. Sticking a camshaft in that is going to beat up the valvetrain, to try and make 20 extra hp, is not worth it in my opinion, and dropping the coin for the FULL CNC port versions of those heads, would be better spent on prop work, valvetrain component upgrades, or other things, that at the end of the day, make more of a difference, than what a little CFM is going to do for you at that level, in that boat. Thats just my opinion.