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-   -   540 bbc build advice (https://www.offshoreonly.com/forums/general-q/263708-540-bbc-build-advice.html)

Scott Foxwell 10-14-2011 11:35 PM
Originally Posted by Zone 5 (Post 3527892)
If you would like the correct info on which heads AFR says you should use on what engine size, go to their web site and read everything that they tell you about which heads to use on which engine size. Just as a little bit of advance info, they will tell you that 305's are to be used on 396-502 BB's. In fact they actually tell you that their 315's are for the same size (396-502). So either AFR is wrong, and some guy you never heard of is right, or AFR is right. As AFR has been doing heads since 1970 for people like Grumpy Jenkins and Junior Johnson, I'd stick with what they recommend.
So what's the difference between a 305 and a 315 and why would you run one over the other if AFR recommends them both for the same range of engine? Answer: you don't know.
You really shouldn't give advice on something you know absolutely nothing about.

shaun harrington 10-15-2011 07:51 AM
Originally Posted by articfriends (Post 3522826)
Somewhat similar to yours is my base motor my blower motor is built around, 540 with billet rods, 4340 crank, Dart 9.80 block, afr 315 cnc heads and a modified mpi fuel injection. My cam is very close to your 1st cam choice, my motor made 657 hp and 660 something tq but my compression is only 8.2-1. With more compression, a better manifold as long as you pick the right cam and heads 675 hp will be fairly easy. A few guys have built 675-700 hp n/a motors out of 540's on here, a friend of Bob Maderas made 700 plus hp with a fairly large cam BUT in retrospect he has said he wishes he would have went just slightly smaller and had better driveabiility. If you want your cam perfect give Bob a call 585-654-8583, in the end his price for a hyd roller custom spec'd is about the same as what you would pay for a out of a catalog cam anyways plus he is a AFR dealer and can get you your heads for what you'll pay for them most places too unless you are buying used ones, Smitty
One stop shopping,can't get any better than that.
For reference,my 540's make 650hp,canfield heads,crane 240,248 double swap cam.3yrs of beating the snot out of it.sutph30 and group built it.They just did the same for scarab28tomr on this site too.77-78mph,single engine, up to 84mph.So its not hard at all.

jeffswav 10-15-2011 10:10 AM
Originally Posted by Zone 5 (Post 3527892)
If you would like the correct info on which heads AFR says you should use on what engine size, go to their web site and read everything that they tell you about which heads to use on which engine size. Just as a little bit of advance info, they will tell you that 305's are to be used on 396-502 BB's. In fact they actually tell you that their 315's are for the same size (396-502). So either AFR is wrong, and some guy you never heard of is right, or AFR is right. As AFR has been doing heads since 1970 for people like Grumpy Jenkins and Junior Johnson, I'd stick with what they recommend.
AFR is assuming you are going to spool it up to 6500RPM, in a car engine, this would require bigger heads. Most marine engines are going to run 5500-6k max RPM, so a bigger runner is not needed. I am not a expert, this is what I have been told by the pro's.

jeffswav 10-15-2011 10:13 AM
Originally Posted by Scott Foxwell (Post 3527906)
So what's the difference between a 305 and a 315 and why would you run one over the other if AFR recommends them both for the same range of engine? Answer: you don't know.
You really shouldn't give advice on something you know absolutely nothing about.
From what I have read the only difference between the 305 & 315's are CNC porting, same casting. Of course the flow numbers, more important than runner size.

Scott Foxwell 10-15-2011 11:49 AM
Originally Posted by jeffswav (Post 3528053)
From what I have read the only difference between the 305 & 315's are CNC porting, same casting. Of course the flow numbers, more important than runner size.
That's an unfortunate misconception that the cyl head manufacturers want you to believe...that runner size isn't as important as flow numbers. It's the exact opposite. I do my ports strictly based on velocity and shape, then get the airflow I need. Usually, if the shape is right the airflow will be there. I would NOT pick a bigger head simply because of more airflow, which was my point above with the 305 vs. 315.

Zone 5 10-15-2011 11:56 AM
Originally Posted by jeffswav (Post 3528045)
AFR is assuming you are going to spool it up to 6500RPM, in a car engine, this would require bigger heads. Most marine engines are going to run 5500-6k max RPM, so a bigger runner is not needed. I am not a expert, this is what I have been told by the pro's.
Check the AFR site. See what Range they give for what heads. Notice how low they start that range. The word here is range. AFR knows that they are not selling heads only to people turning in excess of 6000 RPM.

Zone 5 10-15-2011 12:00 PM
Originally Posted by jeffswav (Post 3528053)
From what I have read the only difference between the 305 & 315's are CNC porting, same casting. Of course the flow numbers, more important than runner size.
If you take a look at some heads that really respond well to porting, (and that someone spend big bucks to have ported) you will many times see that material is also added to shape them to make max flow. But that flow is not just raw flow. Some of it is gainned by the velocity of the flow. Anyone could just hog out ports, and then pop them on a flow bench and say that flow "x" flow numbers off a bench are not the be all end all.

MILD THUNDER 10-15-2011 12:08 PM
I kinda think the 305 Vs. 315 runner size is splitting hairs. There are a bunch of variables. CNC or not, cam choice, etc.

What Im saying is a properly cammed 305cc can outperform a poorly cammed 315 with CNC. Have a guy like Bob Madera spec it out and be done!

Zone 5 10-15-2011 12:18 PM
Originally Posted by MILD THUNDER (Post 3528111)
I kinda think the 305 Vs. 315 runner size is splitting hairs. There are a bunch of variables. CNC or not, cam choice, etc.

What Im saying is a properly cammed 305cc can outperform a poorly cammed 315 with CNC. Have a guy like Bob Madera spec it out and be done!
You have just said the magic words. If you are used to someone specing your cams that doesn't know what they are doing, you are never going to take advantage of the heads. If a cam is too small, or wrong all around, smaller heads in many cases will hide this. But then when you put the correct heads on, the motor is a dog because its the wrong cam. Then you can't figure out why your engine won't perform to where it should. On a lot of basic builds, you can be very very close out of the catalog. Once you start getting beyond a certain HP level, you need to talk to someone who knows what they are doing. Bob would be on my very short list of people to talk to.

Scott Foxwell 10-15-2011 12:45 PM
Originally Posted by MILD THUNDER (Post 3528111)
I kinda think the 305 Vs. 315 runner size is splitting hairs. There are a bunch of variables. CNC or not, cam choice, etc.

What Im saying is a properly cammed 305cc can outperform a poorly cammed 315 with CNC. Have a guy like Bob Madera spec it out and be done!
Depends on how critical you're being with your build and where the volume difference actually is. Is it in the bowl, is it in the short turn area, or is it a bigger runner? Bigger runner means bigger cross section...that could be detremental on a small engine. True a good cam designer could probably help make up for that, but if you could get the same performance from a smaller port (or better), why spend the money on an expensive cnc port when it gets you nothing? Now the CNC chamber option, I will always recommend. As-cast chambers can vary a ton, and effect flow numbers by 10-15% from head to head. As-cast ports, not so bad. If someone is on a strict budget and aren't depending on flow numbers for a specific combination or result, fine, but if you need to know flow numbers and are looking for consistency, then definitley cnc chambers. AFR is probably going to give you the best out of the box performance on something lke this.


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