Good stuff guys. I remember reading years ago that peak torque and volumetric efficiency was produced when port air velocity was around 240 feet per second. If I assume that significant flow only occurs for 200 degrees every 720 degrees, Bob's numbers work out to 220 feet per second. Port area varies according to CID and RPM.

Since I am working on the HP500EFI engine right now, I have measured the port area in the intake manifold. At the flange between the upper and lower sections it is 3.63 in2. It is the almost the same at the flange between the intake and the head. According to the rule of thumb about port velocity, this area should only be about 3.00 in2, in other words oval port, but since there is no wet flow I guess slower velocities (and the resulting lower pressure losses) are OK.

The other thing is the runners in this intake are at least 12 inches long from plenum to cylinder head. I don't know how to calculate this but the longer runners have to resonate at a lower RPM and the cam must be picked with this "tuned port" in mind. In another thread about the HP525EFI it was reported that a cam with 236 duration is being used with this same intake to make over 540 HP stock. So that much duration is OK.

Good info rmbulder/Bob, I am very humbled by the input and info some of you guys offer---thanks!

The intake runner cc/size of the 357 cnc ported AFR's to my cubic inch ratio (565 cubes, short deck block, 4.25" stroke and 6.385" rod) is .63----is that good or bad or what? What are the perameters or boundry lines with this ratio that makes a good comination? Cams (Reed) I will be running are (at .050" lift) 232*/238* on 112* lobes (284*/290* adv) .578"/.578" lift. I run with Stellings full length tubular headers. Thanks.

Kaama,
You did get my e-mail back didn't you?

Chris

Chris, No I haven't---sorry, and I was really looking forward to your response. I have just found out that for some reason I am NOT getting most of my e-mails lately. I have a couple friends that I spoke to on the phone say that they sent me e-mails recently and I have not recieved them! I'll have to check into it---thanks.

Mark/KAAMA

WOW, thats alot of information.. Just for the record, I went with a Dart oval port.

Next is the carb. I have been talking to PRC carbs, they want to cut down their 1050 dominator to a 750 by using larger boosters. Effectively, putting a cork in the carb. They claim that will be just what I need. The next chance I get, I will call Dean Nickerson to get his views.

Checkmate454,did you have the 315 cnc's flowed? I was curious how they compared to what afr claims(plus i ordered the same set bare a few wks ago to replace my merlin vrs)Smitty

No, I have not had them flowed. I have heard that AFR's flow numbers are a little on the low side. Meaning that the heads actually flow a bit more than they claim.

Kaama,
Sent it back to you the day after of reciept. If you want to call and discuss, that's fine. 423 854 0007 Thats good from 8:30 to 7pm. But I don't have a problem with the size camshaft you are using. You just may want to add 1.8's to the intake.

Chris

Below is a picture of a Dart oval port single plane intake that just arrived here today. I ordered it because of Darts' recommendations and some board members success with oval port intakes. I made a quick template of the head ports, ( I know it is not very good ) I didn't have the right gasket, but it is close enough to see what I am talking about. Some guys here have said that they have raised the top of the intake runner to match the head port. As you can see from the picture, if I am to do this, I have ALOT of grinding to do!!!! Should I do this, or send the manifold back and get a rectangular port??

Checkmate454Mag,

From the looks of your picture in Post #49, I don't think you really need to touch a thing! I felt like I had to open mine up a bit because mine ran into a wall on the high end of the port of my Dart Pro-1's that I originally had---I now have the AFR's, but please understand that just because I had to do that certainly doesn't make me an expert on this stuff.

This is a hobby and sport of mine that I really enjoy. I suppose some stuff I can be very dogmatic about---that I know works for sure, but I usually try to help guys out like you by telling them what I have experienced in my 30 years of being around these offshore boats and the engines that make them go, but my experiences don't necessarily make me right. There are a handful of guys on this board who are WAY more qualified than me (some have already posted within this thread) that can offer up some input on this stuff. That being said, I suppose you could open them up a little more or a lot more if you desired, but by the looks of it you certainly don't have to do either or.

Mark/KAAMA

Perhaps some of the other guys more knowledgable than I can chime in here again.