Intake Manifold/Porting, No-log head.(long)

['68falconohio]

I've been working on my cylinder head. E0 casting, bye bye log.
1.75/1.5 portflow valves(CI), 30* backcut on intake...have not ordered yet. I'm going to unshroud valves enough that they clear but want to keep the combustion chambers close to stock size prior to shaving due to CR goal of 9.3:1.

Need some advice and insight on the intake manifold and porting. Here's what I'm seeing and a little confused as to which direction to go.





The surface in red on the second picture is at nearly a 45* angle to the general direction of the intake port. I'm contemplating making the runner of my intake manifold the size of the cardboard tube in the second picture and 'filling' the area in red some how. With zero experience with porting or desigining intakes, this 45* degree angle looks like it's going to kill airflow.

The other option instead of making the intake runner the size of the cardboard tube is to make it the full size of the port at the mating surface and to have it come off of the head at the same angle as the cardboard tube is shown. Am I worrying too much about the angle of the area in red???

I'm looking for a way to fill the area in red if I so choose. Is there a high-temp epoxy that can be used to fill this area? Or a better idea?

I realize that these pictures don't really tell the story but it's extremely hard to take meaningful pictures of an intake port, even with lighting from the combustion chamber side.

On another note, I think I'm going to step the primaries on my headers also. When I milled the exhaust mounting flanges off, I found the exhaust ports have an even smaller cross sectional area now. I'm going to run 1 3/8" primaries for (unknown length as of now) and then 'step-up' to 1 1/2" in an effort to keep the velocity from dropping a lot when the exhaust goes from the small port in the head to the primaries.

Note, I have 'The Scientific Design of Intake and Exhaust Systems' and am nearly through it. I need to read it again, and possibly another time.

Any advice or voodoo magic tricks with fluids is always greatly appreciated.

 

['68falconohio]

Had an epiphany, if I choose to fill in the red area I'll use some sort of bolt in piece like the guys on the other side of the fence use for 'lumps'.

 

[gb500]

admire your courage to start the log mods - but i'd spend some timing researching port sizing etc.
spend some time at :
www.speedtalk.com


i'm no expert but 'generally' the more down draught (steeper) an intake port is the better it flows


and the inlet port should be in the region of 86% to 90% of the valve diameter-depends on applications etc etc etc but trawl through speed talk - inc registering to read 'advanced engine tech'

re expoxies for port filling :


http://speedtalk.com/forum/viewtopic.php?t=327

brett

 

[rbohm]

8) you dont want to fill the top of the port, rather you want to use it. as stated the steeper the flow angle, to a point, the better as this will help give the airflow a little extra velocity and these little sixes need all the help they can get.

 

[StrangeRanger]

You also need to have the porting match the application. The porting job which you would want for the street would be different from that you'd want for a track car and different yet from a Bonneville car. Bigger ports flow more at higher RPMs but they lose velocity as RPMs decrease and can lose performance at low to medium revs.

 

['68falconohio]

gb500,
thanks for the tips, I already had an account on speedtalk.com and it's awesome. I've just been lurking and reading there, my biggest problem when researching there is the number of posts and my inability to use the search function adequately. Not that I'm upset that there's that much info out there, just that I have trouble finding what i'm looking for.

I'd read that post on the porting epoxy, my concern with it was if it could be safely used to build up a port wall nearly 3/8" of an inch.

EDIT: accidentally posted before I finished writing...

rbohm,
I've read that a steeper approach angle increases the velocity, which I want for torque in the low rpms. Which means a straighter shot at the valve = higher velocity = higher flow, correct? But, the other pictures I took and didn't post came out blurry and they show that the roof(area in red) point to the floor of the intake port before it gets to the bowl area. That's why I was considering filling it in and making a straighter shot at the bowl area/valve(depicted by the cardboard tube). It will have a smaller CSA at the intake mounting point than if I don't fill the red area but it will be much straighter and looking at my donor head that I cross sectioned, I should be able to make the intake ports 1.450" round ports with a decent percentage of the CSA pointing right at the valve. This will also allow me to use 1.5" tubing for my intake mainfold runners easily.

IF I left the red area unfilled, and made my intake manifold runner the same size as the mounting surface's hole(roughly 1.450" by 1.9" oval), I think I would have too low of velocity at low rpm.

IF the intake manifold's runners went from 1.5" round to 1.450" by 1.9" oval at the manifold mounting surface to 1.5" round in the head port... I would get some strange velocity fluctuactions, correct? Maybe it would help the mix make the turn down from the intake runner into the cylinder head port, or maybe it would stop flow? I really don't know.

IF I'm not making any sense, I apologize. A bit of a newbie.

SR,
I understand that a big port head that flows 'mass' CFM at .600" lift is not going to be a good street head for me. Especially since my max lift is .420".... I need a 'good' velocity at low rpm without starving the engine at higher rpms.

I want this engine to be optimal from 2k-5500 rpm. I'll give up power at 5500 for torque at 2000. I'm not racing this car, yet...

Thanks guys,
Stephen

 

[StrangeRanger]

FWIW Ricardo found that volumetric efficiency was maximized at a mean intake velocity of 140 FPS with the acceptable range being 40-240 FPS. The engine tech in our 300s is not appreciably different from the engines upon which Sir Harry was experimenting in the early 50s so those figures are probably still pretty close. If you have a 2.02 in^2 port (matching the the area of the intake bowl opened up to it's max. 1.64 dia. and subtracting the valve stem area) those velocities occur at 831, 2908 and 4985 RPM.

I think the engineers who laid out the 300 had read their Ricardo

 

['68falconohio]

SR,
I tried to duplicate your calculations and did not get the same results. Here's what I came up with @1150 RPM with a 300-6 cyl.
I used Bore of 4.00" and Stroke of 3.980" to get swept volume of 50.01 in^3 per cylinder.

50.01 in.^3 *1150 RPM=57516.3 in.^3 per minute.

57516.3 in.^3 per minute / 60 seconds = 958.6 in.^3 per second.

958.6 in.^3 per second / 2.02 in^2(intake tract CSA) = 474.6 in. intake tract per second.

474.6 in. intake tract per second / 12 in. = 39.55 feet of intake tract per second.

I made assumption that the using the RPM and swept volume of the cylinder would be a suitable way to get the mean volume / time. I'm well aware what assumptions do and thinking that could be what messed me up?


Multiplying my FPS of intake tract by ~1.38 gets my RPMs for 40, 140, and 240FPS to line up with your numbers pretty closely in my excel sheet.

What did I miss? Or did I just mess up my calculations in general.

Thanks for your help,
Stephen

 

[StrangeRanger]

I assumed a volumetric efficiency of 70% to get my numbers.
The whole thing is built into a spreadsheet so I can play with the numbers

 

['68falconohio]

SR,
Bingo! now my spreadsheet gives same data as yours. (save for fact that I made my RPMs go up in increments of 50)
I was thinking that the correction factor was volumetric efficiency, but wasn't completely sure.

Is there any way to get a good assumption for volumetric efficiency without actual flow data of the ports. Even knowing the cam timing of my engine I'm thinking no.

With that being said, from what I've read it would be better for me to assume a higher volumetric efficiency than what will actually occur with my engine for a torque build, correct? By assuming a volumetric efficiency that is too high I'll error the port CSA to the small side, giving a higher velocity at lower rpms rather than making them too big in CSA, causing a lower velocity and moving my usable rpm range up.

My ports aren't going to have the same CSA for the entire length, which I've read can be extremely useful. When the ports open up in the bowl area, the charge slows causing a low pressure area in the bowl. The high pressure area in the port above the bowl should help prevent reversion, correct? Taking this principle to the exhaust side, it's part of the reason I intend to step-up my header primaries after a certain length.

Also, increasing the CSA before a turn will slow the charge and help it make the turn, correct?
If so I need to research if there's a velocity range where the charge likes to turn the most and try to size my ports in those areas accordingly.

I'm not naive enough to think that this head is going to work out perfectly as designed, or that my design is going to be remotely close to perfect. BUT, I'm going to try my best to educate myself on the basic principles of designing an intake/exhaust system and build on what I learn this go around for future endeavors.

Thanks Again,
Stephen

 

[StrangeRanger]

70% is actually a pretty good estimation of a bone stock 300.
The combination of long stroke, poorly-flowing head, low CR, strangler intake and exhaust and conservative cam events don't give you much.

The limiting factor is the OD of the intake bowl which is limited to the ID of the valve seat. That's intake valve diameter minus at least .140" (2 x .070 seat width.) Larger valves increase the diameter to which the bowls can be opened and because they increase the flow potential they allow you to open up the rest of the intake tract without necessarily losing intake velocity. This obviously increases the VE potential of the engine as well. Larger valves are a good thing if you're looking for power.

The RPM numbers I quoted are for a stock intake valve. Go to a 1.94 intake valve and modify the intake and exhaust systems to increase VE to 75% and the RPM for 40/140 and 240 FPS become 941 / 3295 / 5648. If the VE goes to 80% they become: 883 / 3089 / 5295. Increased VE is always a good thing.

BTW on stepped headers think about Prof. Smith's reflected wave and imagine that the step-up transition occurs at a header length which promotes power production at some RPM in the middle of your powerband for the street or at your HP peak for the strip. Nothing to do with reversion, you want that sonic pulse where it's going to do you some real good

 

['68falconohio]

BTW on stepped headers think about Prof. Smith's reflected wave and imagine that the step-up transition occurs at a header length which promotes power production at some RPM in the middle of your powerband for the street or at your HP peak for the strip. Nothing to do with reversion, you want that sonic pulse where it's going to do you some real good

I started re-reading Smith and Morrison.

Negotiations with Santa Claus and my wallet came to an end. I'm not getting a copy of Ricardo, but instead both volumes of "The Internal Combustion Engine in Theory and Practice" by Charles Taylor. 1/3 of the price.

Thanks again SR.

 

[gb500]

this is another good book:by david vizard
http://www.amazon.com/Theory-Practice-C ... B000KJ19BK

written in the late 60's/early 70's- has a lot on theory of valve sizing-both inlet and exhaust , inlet port (runner) sizing , inlet port shapes,etc etc .
has a lot of practical examples - but all for british 60's cars .

i picked mine up from ebay for about $15 (australian)
brett

 

[mugsy]

I tried to duplicate your calculations and did not get the same results. Here's what I came up with @1150 RPM with a 300-6 cyl.
I used Bore of 4.00" and Stroke of 3.980" to get swept volume of 50.01 in^3 per cylinder.

50.01 in.^3 *1150 RPM=57516.3 in.^3 per minute.

Remember we are dealing with a 4 stoke cycle: so its Suck, Squish, Bang, Blow. So its only "suck" every two revolutions. I think your numbers are off because you assumed the 50.01in**3 working volume was used every revolution. It ain't. It's used every OTHER revolution.

 

['68falconohio]

Good point, It's going to take me a quick minute to get back up to speed. Punny, I know.