If you want to build a 700hp 540 you don't need 315's. If you want to build an 800 hp 540 you don't need 315's.

If I design a 540 to run with 305's and slap on a set of 315's, what's going to happen?

Here's your quote:
I simply asked WHY the 315's will be better.
Answer: they won't. There is no advantage to throwing a set of 315's on a 540 that's trying to make power at 5600 rpm, or even 6000 for that matter. I don't care what cam, what carb, what EFI you have to provide "enough airflow"...just because the 315's flow more air doesn't make them a better choice. Heck, why not a set of 357's? The 305's already flow more than enough air and have enough cross section for 7000 rpm. Honestly, a set of 290 ovals would be a better choice. Much more appropriately sized for a 540 peaking @ 5600 rpm.

If you want to build a 540 that is going to spin over 6000 which is what you are going to need to get 800 HP, and you want to put 305's on it, have at it. The restrictions that the 305 is going to cause are huge. Not to mention, we are talking boats here, not cars. a totally different world.


well duh, you designed it to turn lower rpm's. why would you put 315's on it?


Well sure they do if you want to leave HP on the table.


you just dropped RPM from 7000 to 5600. Which is it? one size doesn't fit all. Or maybe you should sell AFR on this and they can't stop making all different sizes of heads, because you said they don't need to.

and yes, I know what I typed. which to anyone but you means that the engine is going to be spun and make HP. Last I looked the same cam that makes 650 HP in a 540 won't work to make 750 or 800 HP.

You know, you can get good look at a T-bone by stickin your head up a bulls ass, but wouldn't you rather take the butchers word for it

What restrictions?
Please explain. What do you know about cross section, velocity and port/valve area vs. engine displacement and rpm, and what the engine wants or needs? What do you know about any of that regarding hp/tq production? Tell me how much experience you have in induction and engine design and what it takes to make X amount of power for a given combination?
For ideal velocities in the port and valve for a 540 turning 6000 rpm, the areas need to be about 2.64 sq. in. of minimum cross section in the port and about 3.03 sq in. of valve area. The AFR 305 has a min. cross section of 2.99 sq. in and a valve area of about 3.79 sq in. With a 240* @ .05 cam, a 540 turning 6000 rpm needs about 351cfm @ 100% VE. The 305 intake port flows that much somewhere between .550 and .600" lift. I just don't see a restriction but maybe you can point it out to me.
If you want, lets look at 7000rpm. Minimum cross section 3.08 sq. in., valve area 3.54 sq. in. and lets say with a 270* @ .05 cam, needs about 364 cfm. The 305 still has enough cross section (-.09 sq in. is insignificant as far as a restriction), still has enough valve area and still flows plenty of air. Yes, we are talking boats not cars, but I don't think the cylinder heads know that...do they??
And FWIW I would not tell someone to choose a set of 305's over 315's to make 800hp but by the numbers, you can see if you HAD the 305's, it could be done.

YOU said the 315's would be a better choice. Answer the question. If I design a 540 to use 305's and slapped a set of 315's on it, what would happen? Rhetorical question. Answer...nothing.


Answered above. If there was a slight increase from the 315's over the 305's due to being CNC ported and more consistent from cyl to cyl, it wouldn't be enough to justify the cost and not enough power to even notice on an off shore boat. That's the biggest point here. Waste of money, but at the OP's target of 5600 there would be no improvement.

I have no idea what the rest of this nonsense means. You obviously can't answer the simple question of WHY the 315's are a better choice or how the 305's on a 540 are "on the edge ", but you dance very well.
I really don't have any more to say here.

I was told 325's were best for 540....

and thats the correct answer after I cropped all the stuff that no one except a few of us understand.


Nothing would happen if you designed it for 305's and then bolted on 315's? so now you changed your answer from the prior post.



you don't understand the difference in a WOT of 5600 or 7000? If thats the case, something is really wrong with your engine parts choices.

Mine? 30+ years worth of race cars and boat engines. What is yours besides being a former drywaller and now you chose to be a head "expert" Oh yea, I forgot you worked at Dart doing who knows what for a while. So that makes you the expert? I don't think so. I don't post on 20 different forums saying I'm an expert and thinking that the more times I lie and say I'm an expert, that sooner or later people will believe the lie. and I certainly have never said I was an expert on anything. You OTOH seem to have it tatooed to every post. Hey Hey look at me. I'm the best, everyone else is wrong but me. Do you not understand that experts earn that title from OTHER people saying it, not because you think you are the be all end all

And yet, you still haven't answered the question. Typical of you to shift to the personal attack, though. That's when you KNOW the discussion is over.

Youre wasting your breath with this goof. 30 years experience in racing and marine engines, and yet, needed sutphen 30 to build his 600hp 509s ? He cant grasp the concept of jacketed tailpipes, and youre talking cross section widths, port velocities vs duration, etc ?

Maybe he'll answer back with some more "correction factor " lessons.

Ya know, if you had to pay .10 for every google search you did, you would be bankrupt

I missed the personal attack. You and your buddies are experts at that. If you don't like facts posted about you, I'm sorry. You asked about me and I told you. I also posted background about you. The fact that you worked at Dart and did drywall is not a personal attack as far as I can see.

I've answered the questions about the AFR's. Just because they don't agree with your thought process is not my problem.