Best intake charge flow for an NA head?

Ok, this is my amazing paint work.... Top is the bigport 4ag head, the bottom is the small port. What do you think? which would flow better and make more power?

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Welcome to the cult of JVL drink the koolaid or be banned.

Hmmn, I think this becomes one of those "what do want it to do" questions.

The lower port appears to have a straighter shot, which is usually good everywhere, and the smaller ports will probably help with port velocity, for better low-end and midrange.

Top is bigger, might give you more joy at a gajillion RPM -- might not.

Bigger question -- which one is currently sitting in your car or on your garage floor? That one will go fastest for least dough...

Nice Paint artwork BTW.

Cheers, Ted

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Pure mathematics is the enemy of every truly creative man -- Sir Alec

More airflow doesn't always equate to more power. Port velocity is also critical, especially when dealing with low compression engines and/or big camshafts.

What else is being done to the engine? If you're striving for 200 hp then the big port head makes sense, but I suspect you'll probably have 12 or 13:1 compression and radical cams, etc.

However if you're looking to bump the power from 115 hp to 130 hp then the small port head might make more sense...especially for rallying. You don't need a Formula Atlantic powerband in a rallycar.

Bob

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Opel is a 4-letter word...
http://www.flickr.com/photos/10498579@N07/sets/

10.5-11:1 pistons (not sure of brand yet)
ITB's
Stand alone programmable ECU
264 cams (or 264 in/ 256 ex.... possibly both 272s... )
Ferrea low profile valves
Toda/TRD/Paradise Valve springs
Balanced bottom end
3 angle valve job

thats pretty much it, that I remember.

And I have no idea which ports are more direct, I just needed to show the small port being small then the big port, and it sorta happened. Which I guess means it could be a more direct shot.

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Welcome to the cult of JVL drink the koolaid or be banned.

Dazed_Driver Wrote:
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> 10.5-11:1 pistons (not sure of brand yet)

Go for at least 11.5:1
and talk to me about CP pistons
> ITB's
> Stand alone programmable ECU

Good.
> 264 cams (or 264 in/ 256 ex.... possibly both
> 272s... )
That's pretty mild-damn near street cams.
If you get your staticcompression up then the real or corrected compression will still be good when you take into consideration the critical INTAKE VALVE CLOSING. Remember you're not amking compression until intake valve closes, so you need to know that.
Standard street cams may close the valve at 55-65 degrees crank rotation AFTER bottom dead center or ABDC. A "longer" duration cam will close them later, and if you visulize where the piston is (again rtemeber it only goes half a turn from botton to top or 180 degrees, and if the valve isn't closed till 1/3 the way up, you really don't have "10.5:1", you have substantially less)
Good thread on Turbobricks.com/forums with pretty pictures.
Here's one:
http://www.turbobricks.com/forums/showthread.php?t=102526&highlight=intake+valve+closing+ABDC

> Ferrea low profile valves

Why? Only reason to do that is if the standard valve fail at high revs.

> Toda/TRD/Paradise Valve springs

Good.
> Balanced bottom end

In a 4 cylinder inline motor if all the rods weigh the same+- 1 gram and all the pistons weigh the same you're golden, save money get the flywheel (STEEL) balanced but don't sweat the pistons/rods.
> 3 angle valve job
>
> thats pretty much it, that I remember.
>
> And I have no idea which ports are more direct, I
> just needed to show the small port being small
> then the big port, and it sorta happened. Which I
> guess means it could be a more direct shot.

You could do well to look at the port dimensions for Ford's BDA which is a classic rally motor. I would suspect the smaller ports will flow all you need for a rally motor with cams of 295-300 degrees.
>
>
> Fiesty Peacock?
>
> audio heartline: how does suspension cost so much?

Cause there is a lot of stuff and it's expensive materials and a lot of machine time.

> AE86Driver85: its hella bad ass super awesome
> RALLY gravel spec beastily dampers of doom
> audio heartline: ...

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John Vanlandingham
Sleezattle, WA, USA

Vive le Prole-le-ralliat

www.rallyrace.net/jvab
CALL +1 206 431-9696
Remember! Pacific Standard Time
is 3 hours behind Eastern Standard Time.

Will there be a step-down in port diameter at the head? That can only reduce ariflow and cause a lot of extra flow resistance.

A step up in port diameter has been used to reduce pulse reversions, so it stands to reason that a step down will reduce desired forward airflow. A lot of work is spent on matching head port diamaters to intake ports, not creating step-downs in diamater.

Regards,
Mark B.

starion887 Wrote:
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> Will there be a step-down in port diameter at the
> head? That can only reduce ariflow and cause a lot
> of extra flow resistance.
>
> A step up in port diameter has been used to reduce
> pulse reversions, so it stands to reason that a
> step down will reduce desired forward airflow. A
> lot of work is spent on matching head port
> diamaters to intake ports, not creating step-downs
> in diamater.
>
> Regards,
> Mark B.

No Mark, if the flow runs into the step, ie port smaller than manifold runner, it bumps over and flows over that step somewhent smoothly.
If the flow encounters a sudden step UP in diameter ie port larger than mainfold runner, there WILL BE eddies and those eddies will big of unknown size but those eddies will cause flow disturbances and restrictions.
I had a real live gen-u-whine thermo-dynamic flow injur-near type dood 'splain it to me. And if one thinks of water in a river (add sediment) think of where the sediment gets deposited, and how sand bars are built.

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John Vanlandingham
Sleezattle, WA, USA

Vive le Prole-le-ralliat

www.rallyrace.net/jvab
CALL +1 206 431-9696
Remember! Pacific Standard Time
is 3 hours behind Eastern Standard Time.

Here's an interesting link I ran across doing some research on my own corolla... some interesting comments involving the Cosworth BDA motor and the toyota 4AGE...

To quote:

-------snip-------
The twin cam 4AGE is basically a road going, mass produced version of the Ford Cosworth BDA twin cam racing engine. They share the same bore and stroke (81mm x 77mm), the same size valves (29.5mm & 25.5mm), and in some versions of the 4AGE very similar port shapes & sizes. When fully prepared for racing, they both produce similar hp figures at similar revs, so it would seem that Toyota has done an excellent job with them.

The parallels continue - The 4AGE is the first twin cam that Toyota made with a rubber drive belt for the camshafts, as was the BDA. The 4AGE was a development of the single cam 2A, 3A. & 4A engines, but I guess Toyota must have planned to make the 'A' series engine into a twin cam, perhaps again following the 'A' series Cosworth engines.
-----------End snip-----------------

plus some cross-section pictures of the big-port vs. small-port heads and such.

http://www.billzilla.org/4agstock.htm

also, if looking for donor heads, the Geo Prizm GSI also had the smallport head.

--sarge

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---** To be in compliance with the Anarchy **---
Jorden R. Kleier
Baraboo, Wisconsin, USA
1990 Mazdog Protege 4WD
1973



Edited 1 time(s). Last edit at 10/05/2007 01:04PM by SgtRauksauff.