Brcarz28

Are there any gains that anybody has had by removing the runner wall between the siamesed intake ports on both intake and head. I read about this in Dave Vizards' small block chevy head porting book. He says in the book that he is not sure what the theory behind it was, but it was hard for him to determine what kind of power it made because the motor maxed his dyno out. I am recently porting and polishing my heads for a twin turbo application for an LT1. If anybody knows someone or has done this, some info would be greatly appreciated.

MaxRaceSoftware

i did this +20 years ago

removed the common wall all the way to headbolt hole
which i then had installed a tube
to seal water/headbolt hole, and for aerodynamics

gave up after doing just 1 head of the pair
never finished the other head
never got a chance to dragstrip or dyno test that idea

theory would be very similiar to designs on current
4 valve heads with 2 siamesed intake ports

and why pushrod area was widened on Professional type
heads like SB2, 18 deg, 15 deg, Canted-Valve SBC, etc
and like heads that require offset rockers/lifters

Damon

I would think that would actually make things worse, overall. The main restriction in a head is the valve and the stuff within about 1/2 inch of it. I would bet that siamesing them would create odd/detrimental flow problems in the upper RPMs. Obviously, I've never done this.

The factory HAS done this on some 2 valve heads. The rather crappy Pontiac 301 V8 comes to mind.

SStrokerAce

thinking about that puts some interesting things on the table.

Airflow wise it could be done just like a 4 valve head, that should have some benefits to the higher lift numbers of the head and hopefully the casting would have enough room in the casting to put a big enough valve and venturi in there.

Now the real problem with this is that on a NA engine you are going to have all sorts of problems since you will completely wipe out the tuning effects of the motor since the intake runner length will effectively be cut down to 1-2" from the standard of about 8" in the LT1 which is already short.

On a blown motor, it might be a good idea. I'm saying MIGHT, not probably. The sad thing is that you would need two sets of junk heads to try it out.

The problem I see is a mixture distribution issue. The motor is going to need a port that looks like a 4V port but the wall that splits the two cylinders is going to need to be rounded off rather than have a sharp leading edge. Still it's ugly and the motor will never give you huge flow gains like a 4V head might do.

Bret

Steve in Seattle

Does David V. give any examples on which runner walls to remove?

I understand that it may help shorter the runners for high rpm use... but on an LTx intake I doubt there's many gains to be seen for so much work. Might be interesting to play with, but I imagine cylinder's 5 and 7 would have problems in this design.

I guess the idea is that vacume from one of the two cylinders pulls air into the "macro runner" initially and finally starts to pull it up to speed before hitting the valve pocket. My understanding is that most modern head porter's try to limit the amount of crossection changes in the runner length... this seems like a bad idea that way... but using a vacume signal from an adjacent cylinder to get air moving down the runner initially sounds like a cool concept (especially with surface fouling and such).

Ideally I'd imagine you'd want a custom crank/timing to get siamesed runners evenly split. With the standard 1-8-4-3-6-5-7-2 firing order you get some interesting stuff happening in th 5/7 area.

MaxRaceSoftware

Does David V. give any examples on which runner walls to remove?
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its the "common wall" between the siamezed intake ports

example=> the wall divider between intake ports on cylinders #1 and #3 , or #5 and #7, or #2 and #4, or #6 and #8

the cyl head i did this on was a #462 double-camel-hump head
milled common wall with vertical mill till i broke thru into headbolt hole, finished with hand porting, then pressed in tube for headbolt to go inside of and seal water at same time

20+ years ago, didn't have hardly any selection of heads or offset rockers/lifters, or easy means to weld pushrod sides of heads
so milling that common wall was an easier fix to effectively widened or increase the pushrod location "Port Limiting Velocity Choke" that David Vizard and Alan Lockheed were referring to
(Sonic Choke)

with Blower, the blower would overwhelm any wave tuning effects lost to removing common wall while increasing the cross-sectional area at the crictical choke point

might even be possible to catch wave tuning at 1st harmonic with such as short port

the mid-port length on SBC # 462 casting is approx 5.200" +
inches

(the mid-port length on SBC #034 casting is approx 5.400"+ in.)

so David was probably trying that idea out without having to resort to offset rockers and lifters to be able to widen choke point at pushrod in the cylinder head he was using in that dyno test

if it were a 4-valve head with siamesed intake ports, there would be no choke point there, thats why many MotorCycle tuners
are able to use epoxy and reshape factory ports.

The very short siamesed intake port section seems to work very well in MotorCycles and Race Car engines with 4 or 5 valve chambers, it effectively removes the sonic choke point out of port
and still responds to wave tuning overall lengths

Steve in Seattle

hmmm... interesting idea. Never porting a head myself, I'll pass on this project But I'd love to hear if anyone else tries this out.

It seems like removing the 5/7 wall may be a problem, but I don't know either way.

Think it's possible to see results without messing with the 5/7? probably a really bad idea from a harmonics outlook... but who knows.

Brcarz28

Well, I decided to go ahead and remove the walls on all of them, including between 5 and 7. I don't think that I am going to remove the wall as far as MaxRaceSoftware said that he did(down to the bolt hole,) but I am going to stop about 3/4" away from it. I am trying to be as radical with this kit as possible. This kit is eventually going to be a high boost application. If it doesn't work out, there are usually used heads and intakes on e-bay for pretty cheap. Once I have finished, I plan on having them bench tested for flow. Since there is only one way to know what kind of gains I can really get for my particular application. I will go ahead and be the "guinea pig" and let you guys know what I get out of this modification, if anything at all. Thanks for all of the ideas and theory.

Steve in Seattle

Sounds like fun. Let us know how it comes along, and make sure you take pictures before, during, and after.

Sounds like a whole lot of grinding about to take place.

LT4orbust

Well ....it's 10 years later, are you done grinding the intake wall out? I'm porting mine and I broke through the divider, after looking at it for awhile I'm thinking about cutting the intake gasket divider out and making the whole divider length just thin enough to hold together. Possibly remove all of it about 1 inch into the head and all of it in the intake, 1997 LT1 engine.
I'll see if anybody has tried this first , idk...just a thought at this time

TGGodfrey

Removing the devider is going to affect port velocity in the lower rpm range negatively. On a racing engine(higher RPM stroker) that is going to spend most of its time in the 4500+ rpm range, it might help but i doubt it.