Re: Oval port or rectangular port intake???
 

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.

Re: Oval port or rectangular port intake???
 

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.

Re: Oval port or rectangular port intake???
 

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

Chris

Re: Oval port or rectangular port intake???
 

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

Re: Oval port or rectangular port intake???
 

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.

Re: Oval port or rectangular port intake???
 

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

Re: Oval port or rectangular port intake???
 

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.

Re: Oval port or rectangular port intake???
 

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

Re: Oval port or rectangular port intake???
 

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??

Re: Oval port or rectangular port intake???
 

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.

Re: Oval port or rectangular port intake???
 

I am not one of "those guys that know a lot more" but leave them alone,,they'll be fine. I have run several motors with huge heads and smaller intakes with very good results. You simply have a faster "charge" to the head. I'm sure it's not optimal, but if you match you won't do much other than slow the charge down earlier in it's path to the valve.

Re: Oval port or rectangular port intake???
 

Thanks guys. But, I just can't see myself leaving it like this. It just goes against my grain. I am leaning toward leaving the width alone and just raising the top of the intake port to come close to matching the head. I plan on just going in about 1 1/2" into the port to blend.

Re: Oval port or rectangular port intake???
 

If the Mfg says not to,why. One thing to think about is if you ever go to a oval port head,you will then have a problem.

Re: Oval port or rectangular port intake???
 

I been looking at the pic of your oval ports and how small they look compared to the head port and i know the dyno doesn't lie but what if you had a few individual ports flowed on the intake? If they flow equal or better than your intake ports on the heads,leave them alone and run them.If they flow less than the head ports do than why would you want excellent flowing cnc'd heads that are restricted by the intake,seems like a logical thing to check,Smitty

Re: Oval port or rectangular port intake???
 

Those "steps" in the picture? Like they said, they are machining marks from the CNC mill. They use a ball-end cutter and when you step over for the next cut it leaves a little "cusp" or peak sticking up. They could reduce the stepover to a smaller value which would reduce the cusp to darn near nothing. But no need to do this. Intake likes a little texture to keep from wetting the port sides. Exhaust, in my opinion, needs nothing, but the gain you get is minimal unless you go to full polish (and that doesn't stay that way long unless you repolish every three hours or so...).

I thnk I understand the step CStr was talking about where the intake runner leads into the head port. Roby was seeing the "brick wall" as an impediment to flow (which it is). But since it is on the bottom side, where fuel tries to fall out of the stream, the step "launches" the fuel back into the center of the stream where centerline flow rates re-atomize it. Kind of a trade-off: lose a fraction of total flow rate, gain better fuel atomization and burn-ability. At least that's how I see it.

My "eye" hates any mismatches anywhere. But I've watched flow numbers do really weird things with teeny changes that you'd swear would hurt it.

Re: Oval port or rectangular port intake???
 

Cooltoys,

In the box with the manifold was a paper from Dart saying that you should match port the manifold if you are using it on a rectangular head. It just seems like alot.

Re: Oval port or rectangular port intake???
 

Oh.
It would be a nice trial (although your $22 in gaskets) to do a before and after. Bet you won't see a change. What do you think Mcollinstn?

Re: Oval port or rectangular port intake???
 

If you have decided to try to gasket match THAT intake (shown in the picture), then you might as well start over and get the rect port intake.

It's kind of EITHER OR.

Re: Oval port or rectangular port intake???
 

Exactly what I was thinking as well. I know it's not an easy choice when trying to make the right selection of components when power is concerned, but why go to all the expense of paying someone to do all that grinding to match them up when you can just buy a rectangle port intake manifold? That's why I was saying that I wouldn't touch a thing and just leave them as they are.

Re: Oval port or rectangular port intake???
 

I plan on doing the porting work myself. So cost isn't a factor, time is the only cost. While I don't have a rectangular port manifold here to inspect, I was under the impression that an oval port intake has smaller runners than its' rectangular countepart. That is where the extra power comes from at relatively low rpm's. But, a gasket match should be done just to smooth the transition from intake to head.

Re: Oval port or rectangular port intake???
 

If you can rough the match porting in using a bridgeport and cone cutter it will save you many hours of grinding. Then just finish it with the hand grinder.

Re: Oval port or rectangular port intake???
 

I roughed in all the ports today. I may be finished by tomorrow. I'll post a picture when done.

Re: Oval port or rectangular port intake???
 

. . .But transition is not and inch in. . . an intake runner to be effective needs gradual transistion to maintain port velocity. Random expansions in straight areas of the port are not good ideas.

Chris

Re: Oval port or rectangular port intake???
 

While I was working on the ports, I made what i believe to be a smooth transition. I had to go into the port a good 3" to achieve it.

Re: Oval port or rectangular port intake???
 

My eyes don't like mismatches either mcollinstn. Truth is we don't know what exactly happens to the fuel when it hits that obstacle. When you trip up the flow like that I see it as waves crashing over a seawall during a hurricane. In my opinion there will always be a wet spot there no matter the RPM. That not withstanding the biggest disruption of fuel atomization if the sudden opening of the throttle blades. All of the fuel that once was suspended is now on the floor of the intake trying to get pulled in every direction. With the injector atomizing fuel it is already in the port where velocity is high being rushed in ONE direction to the combustion chamber.

Roby

Re: Oval port or rectangular port intake???
 

God bless injectors...

Re: Oval port or rectangular port intake???
 

I finished the manifold today. Thats as far in the runner as I can reach to smooth the transition. It feels real smooth, I hope it works.

Re: Oval port or rectangular port intake???
 

Checkmate, as Paul Harvey used to say... let's hear The Rest of the Story.
How did your work end up on the dyno? What result did this intake work have on your torque curve? Do you have and before/after comparison numbers?

I've read this thread a couple of times and discussed the topic with my engine builder yesterday. There are some interesting ideas here, ones that I'm also trying to accomplish. Torque (long and flat) is my goal.

First, some background: I started with a pair of HP500's, and last winter I had the lower end freshened up,(now 509's) and added a set of Pro Action 320 aluminum heads with 119cc chambers. I stayed with 2mm dome pistons, so my CR is still right around 9:1, maybe slightly lower. We did some mild port work on the heads, they now flow 365 @.600 intake, and 255 @.600 exhaust. Running Ferea 2.25 intake and 1.88 exhaust valves. For the most part, the rest is stock HP500 (cams, carbs, Dart rect port intake). They currently dyno at 523hp @5250, and 562lbs @4500.

My focus for this winter is cams and carbs, and I'm trying to get my torque numbers to come in high under 4000, and stay flat as possible through 5500. I'm having custom cams ground, and the numbers aren't set yet, but ballpark is .600 lift on intake and .615 on exhaust, hydraulic roller lifters. I'll be going with a pair of Pro Systems 4150 carbs @950 cfm, with custom fuel curves based on flow numbers and cam data.

So now this thread is making me question what to do with my intake. My Dart rect port manifold is a decent piece, with good torque performance, and I could possibly benefit with the added runner length of a Brodix. But this oval port concept flared to match rect head ports has me intrigued.

Net, net, $350 or so x2 for the intakes, plus $200 or so x2 for port work puts me at $1200 for an end result that I haven't seen yet. If I gain 10-15lbs, it might not be worth the return on my investment, but if I'm looking at 30-40lbs, it's a different story.

Overall, I'm running a relatively small displacement motor (as compared to the Big Iron on this board), so port velocity of smaller intake runners might get me the torque numbers I'm looking for. In the end, I'd like to see peak torque around 625.

What's the scoop? I'd like to hear some "real world" data.

Thanks,
Brian

Re: Oval port or rectangular port intake???
 

Brian,

I wish I could answer the question about rectangular port vs oval port with real data for both manifolds. But, I can't. I only dynoed the blended and port matched oval manifold.
I dug up this old thread I started with my dyno results. I hope it can help you answer a few questions.

http://www.offshoreonly.com/forums/s...540+dyno+today

Re: Oval port or rectangular port intake???
 

Those are indeed some impressive dyno results.

Other than cubes, we're close on a number of things... yet even with the smaller oval port intake sizes, you're still feeding it with a 1050. Hmmm. And your cam numbers are smaller than I was thinking, but I'm leaving that equation up to Sterling. Good information, thanks.

So... can we attribute your torque numbers to velocity on the intake side? Did you do anything else out of the ordinary? Did you message the heads any more than the cnc work? I'm sure the work Nickerson did on your Dominators helped a lot.

Just trying to decide on whether to dive in to the intakes on my project.

Thanks again,
Brian

Re: Oval port or rectangular port intake???
 

Brian,
I would be very interested in hearing what Sterling would say about the oval vs rectangular port intake. Please post what they say.
I didn't do anything else unusual to the ports. I left the heads just as they came from AFR. I really don't know for sure what to attribute the torque #'s to. I am hoping that I made the right choice but without real dyno #'s with the different manifolds, it is just an educated guess.