Removing common wall between intake runners

[redc4]

I have read in the past about removing a portion of the common wall between intake ports on heads like a small block chevy, etc. From what I gather, the main advantage is to gain cross section area. Are there any other advantages/disadvantages to doing this on a head with limited cross section area?

[bill jones]

-I want to hear the answers to this one myself.

[LilRacr]

I am also very curious about this one.

I am a novice compared to most of you guys, but I would like to think futher into this about making the runners of the head one also, and splitting the ports at the bolt of the SBC?

The pushrod restriction would definatly be removed!

[Guest]

Not sure if this helps but anyway, the early Australian Holden straight six head shared the same intake runner in pairs, the later model straight six head didn't, the early straight six head actually flowed better with all the usual porting techniques

with the early head it had a pillar at the intake entrance which the head bolt was located, after the pillar it opened into a common area for both intake valves to share, modification technique involved cutting this pillar away & installing a sleeve for the bolt to run through to increase flow

thought I would mention this because it seems to be a similar theory to the topic

[redc4]

Timewarden, this is exactly the type of head I am looking at. It is off a chevy inline 6.

[redc4]

Timewarden, this is exactly the type of head I am looking at. It is off a chevy inline 6.

[Dave Koehler]

Long while back the practice used to be to remove the pillar on the chevy 6, spot face the floor and use a short stud or allen bolt and in some cases a flat head bolt (tapered). The original top bolt/head face was machined for a plug.

Dave Koehler
www.koehlerinjection.com

[Grocerius Maximus]

http://www.selfracing.com/portintruder.htm

[ChrisU]

I must be misunderstanding the question. Are you talking about making the 2 ports 'one' for a particular length? Can you elaborate?

[redc4]

Yes, for example, cutting out the common wall between 2 intake ports on a sbc head. At least up to the head bolt near the bowl area.

I got a look at a comp eliminator I6 head, and it is basically one runner for 2 valves. Looks interesting. But that head was pretty much designed that way from the factory. This head flowed pretty good on the intake side for the valve size. 317cfm for a 1.94 intake valve = 106cfm/sq in.

[bill jones]

-are you trying to compare the intake runner of a 4 valve head where all of the air is going into the same cylinder----to a SBC head where there is two different cylinders that would be sharing the same port with the divider removed?

[redc4]

Bill, I am comparing a sbc head to an Inline 6 chevy head, whereone large runner feeds 2 valves, with one of each going to a different cylinder.

[hwp123]

I took a chevy 6 250 cid head over to friends shop to flow it on his 110 superflow. I had carefully ported it ,left the head bolt support in but slimmed it down. It had the original 1.72 intake and 1.5 exhaust valve with the original factory valve job with who knows how many miles on it.It just so happened that another friend of mine that had won a bunch of dirt track races showed up to flow one of his heads he had won some races with. It had 1.92 and 1.6 valves with the bowls just hogged out big time,the head bolt support cut out and a tapered allen bolt for a head bolt. It also had the latest secret trick of the year which was a center divider that extended from the back wall of the bowl to about half way to the intake manifold face tacked in place and as this was twenty years ago I dont remember the flow rate but it was not too good. We knocked the divider out cleaned it up and it flowed 80 percent on what flow range i don't know. The friend that owned this head wanted to experiment so we started to add clay to the port trying to make a ski slope to the bottom floor starting from nothing and building up to maybe a half an inch higher at the short side radius and blending in with the ssr. As we keep experminting with this we got the flow up to 100 percent of that scale. Then we flowed my head and we were surprised but it flowed 79 percent of this same scale even with the much smaller valves.(Intake) The flowbench owner said that it was evident that I had spent a lot of time on the porting . I hope this helps.