gkull

Somebody ask me this the other day? Can I run a Edelbrock RPM dual plane on AFR 195 heads? I said NO, because when you go from small manifold 2.09" x 1.25" head ports are 2.11" x 1.265" According to Bernoulli's principle going small to large decreases port velocity. Which in turn allows atomized fuel to combine together and form bigger slow burning droplets. You also can't just hog out the manifold exit for port matching because the smallest area is still up inside the manifold. You are actually destroying the intake manifolds tuned runner design.

Anyway here is lots of informative reading:

http://garage.grumpysperformance.com...-and-area.333/

jim2527

firstgenaddict

We had a rectangle intake with oval heads on a 60 over 396... with a 710 lift solid roller and in a 69 nova with 5:13's ran a 6.80 in the 1/8 at 110 on ET streets. I don't know what HP but you would have thought it was perfect... I think the turbulence helped immensely in those HUGE intake tracs.

gkull

Both of these above posts are just a perpetuation of circulated myths by the uniformed masses. Either of these above posts could be disproved by installing their setups on a flow bench. first example small manifold port to bigger head claims that it helps. Doesn't understand that turbulence decreases port flow and refers to the sharp edge anti reversion as a good thing. The sharp edge anti reversion is something used on the exhaust port side to work with positive and negative pressure waves in the exhaust primary tubes.

Second post: Larger manifold and smaller heads. Well it is not as bad as the opposite because you would be increasing the head port velocity compared to the manifold, but again not idea because turbulence will decrease the total possible port flow CFM.

gkull

Ideally you want heads with the least cross sectional area for the highest port velocity and then CFM of flow to match the requirements of your motor build. So the major companies like AFR, Brodix, Dart, RHS...….. Spend a lot of time on chamber and port design and then people ruin the heads potential with mismatched ports.

v2racing

Turbulence is a flow and power killer. You can see and hear turbulence on a flow bench, and the higher the pressure differential, the more it shows up. In other words intake tracts may look good on a Superflow 110 flow bench pulled at 10" of pressure differential but when put on a bigger bench and pulled at 28" severe turbulence may show up and the flow would suffer. I saw this a lot when I was doing a lot of customer headwork. You could hear the turbulence and the monometers would be jumping around. I had a lot of other so called porters heads on the flow bench and it was a common problem.

The old myth that you need turbulence in the intake tract to keep the fuel in suspension is a misunderstanding of surface air flow boundary. A mirror polished surface will not create the surface boundary to keep fuel from falling out of atomization along the intake tract walls. A rougher surface will create this boundary and this swirling airflow along the surface keeps fuel from puddling on the walls. Here is where people get it wrong. It only takes a surface as rough as what an 80 grit sanding roll leaves to create the surface boundary. Any more turbulence beyond this is not needed and going way beyond this starts hurting flow and performance.

To address George's comments on destroying the manifold design by only opening up the manifold at the head end, he is talking about the intake tract taper designed into it. The taper is an important part of the intake tract. An intake tracts taper is part of the tuning for the rpm range it will run in. When you compare a tapered intake tract to a perfectly straight one of the same length, the tapered tract will act like a shorter tract than the straight one, the more taper, the shorter it acts. I am talking about the negative and positive pressure waves that travel up and down the intake tract. Time these waves properly and you increase the volumetric efficiency of the engine, meaning, more power. The taper also makes the airflow increase in velocity as it travels towards the valve, which is also a positive result.

Manifold designers know that their intakes will be used on an assortment of engine and head combos, so they are usually undersized at the head end so they can be port matched without ruining the manifold, but that only goes so far. My own engine is a good example of that. I have a Victor Jr. intake. The port dimensions at the head end of the manifold are 1.9 x 1.1 inches stock. The ports in my heads are sized to a Felpro 1207 gasket that measures 2.28 x 1.38. That is a huge increase in area. I had to do a lot of work from the plenum side of the intake to maintain the taper in the manifold.

Mike

naramlee

Any thoughts on dimple porting?

v2racing

I experimented with dimples back in the 90's. This is again addressing boundary layer. What I found was it helped air follow the short side radius better and picked up flow slightly. It had no effect I could see anywhere else. By making a boundary layer it makes air able to follow around the short side radius better, much in the same way it allows air to follow around farther to the backside of a golf ball making the air less turbulent on the back side creating less of a wake, so to say.

It was way too much work to do by hand for the meager improvements I saw.

Mike

naramlee

was curious, i saw some of the prices for cnc dimpling and about had a heart attack

cv67

Id think it would work better with the dimples facing up to stop puddling..the simple waffle pattern on other intakes makes sense
Tried dimpling a set in the 90s couldnt tell anything. Sometimes what may work on the bench does nothing in the car.
Look at a BB Edelbrock roval if you wanna see ahuge mismatch!

C3 Stroker

I ran the Edelbrock RPM Air Gap with AFR 195 heads on my former 383 sbc, as I'm sure many others do. This is a very popular combo.There was not a difference you could see unless you really looked close. AFR recommend a Fel Pro 1205 gasket (2.09") and instructs not to gasket match their head to it, just bolt it on. The car ran mid 11's, and I don't believe I had any problems or lost horsepower. BTW, I did match the intake to the #1205.

v2racing

My flow bench and dyno testing showed me that a slight mismatch with intake slightly smaller than the port didn't lose any flow or power, but a large mismatch did. It didn't take much mismatch with the intake bigger than the port to hurt flow and power.

Mike

v2racing

As I said in my first post, it doesn't take much of a surface roughness to create a boundary layer. An 80 grit sanding roll does the job. That is all you need to keep fuel in suspension. Of course, the longer the port and the more turns in it, the more chance of fuel falling out of suspension, so on something with a really short intake tract like a Y-manifold Harley, the surface of the port means almost nothing because the air fuel mixture just doesn't have time in it's short travel to have fuel fall out of suspension. Chevy's have a much longer intake tract so the surface is more important. Of course this is all on carbed applications. With port fuel injection or direct injection it's not critical. Also as air speeds increase like at WOT, it becomes less of an issue for carbed applications also. Part throttles are more critical.

Mike

cv67

Id think with a well tuned carb'd engine using an 02 sensor how bad could it really be? Sure is a lot different than the old school tuning methods

v2racing

I'm not sure I'm understanding your point. Tuning isn't going to fix a mismatched intake tract, it's airflow or fuel falling out of suspension. They are just basic physic you have to deal with. It's all the details like this that make the difference in how much performance one gets out of combination, and there are huge amount of little details to work with. It's why two people can build the same combination and one of the engines will just plain thrash the other.

Mike

C3 Stroker

You are correct.......my correction, I matched the intake to the head, not the larger gasket, so no flow or power was lost.

naramlee

you mean like the black magic art of reading spark plugs? :P

suprspooky

If someone asked me the original question, I'd say sure you can but you'll likely be leaving HP and VE on the table. If a person uses a specific Manifold that isn't a perfect match to their Head it may be because they need the under hood room or like me they just love their Tri-power. Some folks don't care about a small loss and are really asking if they will have major problems having a mis-match. I tested a very close port match Dart S/P oval on the Dyno against my rectangular Tri-power and lost 20ish HP but no other problems (drive-ability, idle, etc.). So to me it's really, can you? yes. Should you? maybe depending on your goals.

Jebbysan

Let me just first say that a Rec port intake on an Oval port head is a huge no-no. Period.
I port match everything as far as I can up into the port as it improves the lead in of air and fuel. That said.....almost nobody flows heads with an intake installed on the head and even then nobody wet flows in this manner. Dart is the only one I know of so far. That said....some intakes (Edelbrock Victor Jr. for example), require a LOT of work around the port entrance area......it really depends on how the intake is cast. The RPM is pretty good in this regard out of the box.....so seeing much improvement would be less than hopeful......but then again, how does it fit on your heads? Port matching as a tool to improve flow is directly proportional to how mismatched your setup is.
When I say I port match everything....that is after mocking up the intake on the engine and heads to be used and see where you are at. I have yet to see a real nice deal out of the box. Some intakes require a lot of work....some very little.
Now moving on to higher end stuff.......I have used the Dart single plane oval intake on a rec port head......because the runners are smaller in cross section....this improves velocity......Dart even makes a CNC program that takes the oval intake and machines it back to rec about three inches up the port.....these are awesome on heavy cars and boats.......so there is benefits, just where do you stand?
As for the RPM on AFR heads......check it and bolt it on......the RPM is a cork after 525 horsepower on a small block anyway.......too many curves. On the RPM, milling the divider clean out is the key to flow on the upper end.....and then the 180 degree deal becomes redundant. If it was the only intake you had or could use.....then yes, mill the divider and port match up as far as you can....otherwise, move on to a single plane.....there are so many good ones out there now.......AFR should cast the Titan in aluminum until they fix their sealing issues........
FYI....most high end builders scribe their port match .030 smaller than the host cylinder head port to attribute for shift upon install and to prevent reversion.

Jebby

cv67

I was referring to the dimple finish vs reply
I dont see a problem giving an intake a little work thats off .1 myself. Most times theres little or nothing to be gained but I go after every little bit, why not..but also flow them every time too.Even then it doesnt mean it will improve. Theres better places to go after power