Intakes designed to be smaller than heads??

[SmockDoiley]

I've been doing some research on a better intake choice to go with my TrickFlow heads and it always seems that intakes have smaller runners than the runners on the heads. Example: TrickFlow lists 2.00 X 1.200 for the Trackheats, but an Edelbrock RPM which is the same RPM range has 1.86 X 1.05. So I started looking to see the closest matching intake and its the Super Victor Jr. 8.2. It has 2.00 X 1.96 which is super close, but this thing is designed for 3500 to 8500 rpms. I thought it would be optimal if the runner from the carb to the valve was the exact same size with no breaks and as few bends as possible, but I guess Im wrong if intakes with the same power band have smaller runners, and everybody just seems to port match. Just an observation, but I would think that the Super Vic would be a great bolt on because its the exact same runner size, but obviously not with that rpm range and that its only for racing.

 

[sleeper89]

good thread smockdoiley. i've noticed this too but never bothered to inquire further. i could be WAY off but i think it's done to promote mid-range power, also it could give room for the air to "compress" just behind the valve when it closes. ie. air rushing through intake, reaches the head which opens up a little and thereby decreases velocity of intake charge as it hits the valve. this could have something to do with pressure waves bouncing back as well just some thoughts to get things moving

-steve

BTW, i noticed the #'s you posted for the super vic jr. were substantially larger than those for the intake: 2.00 x 1.20 vs 2.00 x 1.96. notice 1.96 vs 1.20....this would be why the vic is for high rpm, that's a HUGE port.

 

[SmockDoiley]

Woops, where did I get those numbers. Its 2.00X1.18, and the trickflow head intake runner is 2.00X1.20. Thats why I was saying that they match almost perfectly, but an intake this size with an rpm range of 3500-8500 obviously means my idea is wrong. Sorry about the screwy numbers.

 

[SmockDoiley]

It just doesnt seem to make sense to me because people port intakes or port match them to get them to line up with the intake runner of the head. Why not just buy an intake that matches it already. I know intake length and design makes a difference too, but if you could set that aside for a moment and take 2 intakes with the exact same design but with different size runners what would be the power difference. I would think that an intake that doesnt properly line up with the heads would cost power. I know smaller runners on an intake generates better low and mid range but if the runners were the same size as the heads which also make good low and mid range, I dont see how it would affect anything. Plus I cant see how an intake with small runners supports 1500-6500 rpm range, and a head with large runners supports the same power band.

 

[bluevenom867]

if the runners are smaller than the openings on the heads they act like a venturi on a carb and speed up the air flow. larger runners increas total flow but the air slows down.think of it this way,scients actually consider air a liqued so its comparable to water.would it be easier to dump water from a smaller bucket to a bigger bucket?(small runner to a bigger port) or same size buckets (matching runner and port)?
also the runners need to be a little rough a the bottom to mix the fuel/air better
if you can make a smaller runner flow more air with out porting it (because porting makes it smooth) and still keep the velocity,it will make large power AND torque
if your runing EFI then move the injectors higher in to the manifold to boost high rpm hp and flow the most air possible.

 

[SmockDoiley]

I'm not talking about porting though. I know a rough floor will help mix the A/F. I understand that larger runners promotes higher rpm horsepower, but I dont get how smaller runners on intakes support the same power and rpm range as a same range head that has larger runners.

 

[SmockDoiley]

I guess the small intake runners are used to accelerate the air, but by the time it gets to the head, the head doesnt have to worry about speeding up the flow so the runners can be larger; just make sure it gets to the chamber efficiently. The only point that it would create unwanted turbulence and backswirl is when the smaller intake runners meet the larger hard runners, and thats why people port match.

 

[Blk91stang]

Smock, If the bigger ports in the head dont affect the air speed, than why not just make the ports smaller in the head to match the intake? I dont know the theory behind it but im all for portmatching the intake to the head.. In my own theory.

 

[SmockDoiley]

They do affect velocity, but I'm trying to figure out why intake runners are smaller than head intake runners yet they support the same power band. The only thing I can think is that the smaller intake runners help accelerate the air into the larger slower head runners. By the time it gets to the head it doesnt need to accelerate much because its already moving; it just needs to move quickly. Hence large head intake runners, but obviously not too large are you'll lose that velocity. And obviously port matching allows a smooth transition from the intake to the head. I guess a large opening(the head) sucking from a small opening(the beginning of the intake) will create good air velocity and vacuum. Though you can buy an intake with the same runner sizes as the head like I was talking about above, its going to kill bottom end because its just sitting there in that large opening and it takes a lot to draw that into the chamber(high rpm). But a narrow passage that opens up gradually(port matching) into a large opening accelerates quickly and grows as it reaches the combustion chamber. It can open up because its already moving so it doesnt need the narrow passage to accelerate. In affect, like coasting once its reached speed.

 

[331 cobra]

here are a few ideas:

If the intake is the same size as the head and there is any misallignment, you have no chance of getting a decent port match without welding or epoxy unless you grind on the heads also.

Aerodynamics have shown that the air will create a boundary layer in the area of the step. The boundary layer is like a port wall that is made of air. So your engine will act like it has heads that are port matched to the smaller size.

You are either going to port match it, or skip it, the difference in power is probably small.

 

[Blk91stang]

I have seen an intake and heads being not portmatched and produce very similar flow #'s and 1/4 times than being portmatched. 331 Cobra, I'd like to hope what you say is correct. This would save a lot of porting and headaches..

 

[fordman54935]

This thread reminds me of when I purchased a new Edelbrock intake when I switched to a 4-bbl on the 351C in my 71 Torino. This might not pertain to 5.0 Mustangs directly, but I can remember when I got the manifold and was reading the instruction sheet that came with the new intake it specifically said that the installer should NOT port match the runners on the intake to the heads. I assume this is because of the ideas mentioned before, as a larger opening will lower port velocity, etc. Just an experience I had, and the instructions also said to contact the Edelbrock tech lines for more information pertaining to that. Just figured I'd add my $.02

 

[331 cobra]

I have seen an intake and heads being not portmatched and produce very similar flow #'s and 1/4 times than being portmatched. 331 Cobra, I'd like to hope what you say is correct. This would save a lot of porting and headaches..

I don't think you can hurt yourself by doing a nice port match. You just have to make sure that you maintain the taper of the port and get the angles to match up so the air is flowing as straight as possible.

It's just a way to get an extra 0.1% out of your engine. If you can live with an engine that might have a couple of HP locked up in it, it probably isn't worth the effort.

As for me, I will leave nothing on the table, I want it all.

 

[proxses]

This thread reminds me of when I purchased a new Edelbrock intake when I switched to a 4-bbl on the 351C in my 71 Torino. This might not pertain to 5.0 Mustangs directly, but I can remember when I got the manifold and was reading the instruction sheet that came with the new intake it specifically said that the installer should NOT port match the runners on the intake to the heads. I assume this is because of the ideas mentioned before, as a larger opening will lower port velocity, etc. Just an experience I had, and the instructions also said to contact the Edelbrock tech lines for more information pertaining to that. Just figured I'd add my $.02

This may be due to the wall thickness of the intake. There may not be much room to port, and they don't want you to port a hole in the intake.

As for the general dicussion, the smaller ports may be for manufacturing. You have many companies making heads and intakes for 5.0's. Unless each one measures each component from the exact same place, there will be disparities. So the slightly smaller port may be designed to mate up with just about any head, and prevent the air from hitting a wall, were the ports did not line up. I'm sure the tolerances are slightly different on every single 5.0 out there, and that no two head and intake packages line up exactly the same. Just an idea.

 

[68converted]

I have a buddy that went to school for aero space eng. He bought AFR 165's and the RPM2 specifically because they are ports matched. He said something about "air slip" "mounding" and "velocity" and some other techy lingo to explain that this was the best setup for me. I took his advice. His car flies. Into the low 11's... I don't want that, but it should do well anyway.

Ask a pro race mechanic and they will say port match! I would love to understand it more. I will ask my buddy to go over it with me and I will post when I can. Great thread!

 

[Highbredcloud]

Very interesting...so what happens when the intake runners are bigger than the head runners...? i.e...lets take the stock E7 heads and let just throw in a holley systemax II intake on it...the runner on the intake are much bigger so would that cause some sort of a problem with turbulance when the air in the intake hits the heads? I have always wondered that...although it is always better to have a smaller intake than the heads...smaller opening going into a larger opening even if it is just slightly smaller...but seriously what would happen if it was the other way around? bigger opening on the intake going into a smaller opening on the head even if it is just slightly bigger intake runner than the head runner? any ideas?

 

[Michael Yount]

Smock - remember, flow is impacted not just by cross section but also by shape, length, direction changes and obstructions. Even if the cross section, shape and length were identical between head port and manifold runner, remember, at the end of the head port the flow has to make it past this pesky obstruction called the intake valve. You have no such obstruction in the intake manifold. Also flow numbers on the intake are usually from air inlet (carb base for you) to the manifold outlet; on the heads they can be through the manifold, through the intake port with the valve are various lifts; sometimes just the head without the manifold and the valve at various lifts (usually the case). And, flow benches are just like dynos. Numbers vary depending on the bench, the operator, the ambient conditions, etc. Furthermore some numbers are run at 28", some at 25", and often that detail goes missing when the numbers are passed around. In my opinion it gets more complicated because you're supercharged -- and flow capabilities under boost may be different - typical flow bench numbers mimic a naturally aspirated set up. So trying to do any meaningful comparison based strictly on flow numbers that came from different sources doesn't really tell you much. You're got enough power to split the block at any time anyway - do you really want/need more?

 

[tmoss]

Aerodynamics have shown that the air will create a boundary layer in the area of the step. The boundary layer is like a port wall that is made of air. So your engine will act like it has heads that are port matched to the smaller size.

Yes............and this layer will vary in depth as velocity changes.

No one gas mentioned pushrod pinch in the heads. Remember guys it's the whole flow path, not just the intake. Pushrod pinch exists in some heads and not in others. Push rod pinch exists in Ford heads. Look at the intake runner of the head. The port narrows just inside the flange face because the casting wall has to get around the hole that the pushrod passes through immediately adjacent to the runner. So, the width of the runner at the flangfe face is smaller than the width at the pushrod pinch. Do you port match to the runner flange face or do you port match to the width of the pushrod pinch?

 

[SmockDoiley]

I'm not really looking into port matching though. I just thought it was cool that the race only Super Victor 8.2 had the exact same ports as my trickflow heads. I know they are only for 3500-8500, but I was wondering how they could be for a different rpm range if they have the exact same port size. Unless its true what I was talking about how the air needs to go from small to large so it can accelerate and stuff.

 

[SmockDoiley]

Yes, More power!!!!More power dangit!!!