Holden red6 siamese-port head

[johno]

Hi there guys im just chasing any information on porting siamese intake-port heads. Im a 6cyl red motor freak, first motor i ever fell in love with, and from what iv seen these are about the only engine that uses a siamese port. Does anyone have any experience with porting these heads? I developed this particular head over many years and thousands of dollars (it started life as a Bathurst 6000 YT head!!) but i still feel there could be more flow gains hidden in the port as it is quite an odd shape! It flows 115.7cfm @ 10" / 0.520" with the webber manifold & carb set-up fitted. Any ideas?

[johno]

Heres a pic of the chambers with valves removed.

[200cfm]

Very interesting design. My stude has siamese exhaust ports on 3 & 5, 4 & 6. Have always wondered what would happen if I cut out the wall between the intake valve ports on the head. What about the air speed on those ports? Has to be way down except perhaps at the throat of the valve. Does it make power for you? What would be the design on the manifold attachment? Curious how it could make power with slow air speeds. Area looks big so the air speed has to be slow I would think.

[edgey43]

It looks very much like a classic A series Mini head. I have ported many over the years and race a classic Mini. The inlet ports look too large based upon what i have found with the Mini. Normally on the Mini heads I run a blade configuration between the two inlet branches and fill the ports back in. I am currently getting 132cfm @ 28" / 0.425" not bad for an old cast iron 1293cc Mini engine.

[johno]

I'm running a triple-webber intake set-up on the motor, three speed auto with 2800 stall, B/W 4:11 gears with full-spool and 13" wheels. It has a stage 6 solid cam and idles at 750rpm with EFI level emissions. I fitted it to my street driven LH torana that weighs 1260kg with me in it! No-one , including myself, expected it to go so hard, it cuts high 12's!! We built a copy of the motor for my brother, to drag race in his LC torana with methanol , it pulled a 12.4sec at Townsville drag-strip. If you look inside the intake mouth you'll see 2 big holes, one in the roof, one in the floor. Standard heads have a 'huge' boss here and the head-bolt used to run down inside it. We mill the boss out entirely and recess an allen-key head head-bolt into the hole you see in the port floor. The hole in the roof, which was the old head-bolt hole, is then plugged. Unfortunately the guy i used to go to for flow-bench testing never had any velocity probes so i don,t know what the port speeds are, but i am going to buy my own soon!!

[Greg]

Johnno, when you buy probes, buy a pair of Bruces ones. Mine arrived last week and they are beautifully made and the U probe is tiny, you can squeeze it in anywhere. The price is very good too.

Have you tried raising the intake port roof? I used to do a lot and the higher, the better. you can weld a little on the top edge of the manifold face so you still have somewhere for the manifold to seal and you just need to move the manifold up to suit.From memory I used a blue manifold because it had taller ports.

[200cfm]

Are the intake runners also equivalent CSA as the port? What length did you set the intake runner? This design is working and making good power.

[coulterracn]

Johno

I'm not familiar with the head you are running but it looks alot like the old Chevy in line six. Kay Sissel built some killer heads by adding a "Lump" at the short side radius. The Chevy inline six did not have much of a short side radius so Sissel would braze the head to add 'the Lump'.

Looking at the photo of your head it looks like you heads has a good lump for the short side radius. The recess where the head bolt boss was is a trick Sissel used to open up the port. A few years later Sissel made a divider to separate the ports. The divider can be made of mild steel or aluminum plate with a thin wall tubing where the head bolt boss was originally. Then use epoxy to blend the corners, etc...

Ray

[johno]

I think you might be right about lifting the roof more Greg, as it seems to be very busy in that area when i jam my flow-balls in there, youv also sold me on a set of Bruces pitot probes. The webber manifold I'm using is identical to the 12port blue/black head version, Redline only change the bolt pattern to suit the two heads. It has 2 straight runners which are seperated by a dividing wall right up to the port mouth, they call them a 'Branch manifold' as the two runners join at the port and provide a nice boost/ram effect. I spent alot of time chasing a manifold and carb set-up which would give me the right intake tract length to hit the "second harmonic pressure wave" which, after much flow-bench time and calculations, we settled on 18" from intake valve to .5 diameter past the end of the carb ram tubes (this calculation is from David Vizard). Yella Terra , when they were still doing exchange heads, offered this head in three stages. First was your basic stage 3, second was Bathurst 6000 (mine) and third was Bathurst 12000 which had an aluminium port divider fitted to the intake port. Unfortunately, to this date, iv never been lucky enough to see a Bathurst 12000 version, and probably never will as they stopped modifing them due to castings failing from age.The holden L6 engine was built, as far as I am aware, as an Australian version/copy of the chevy L6.

[Greg]

Johnno, a few years back I bought the port dividers from Yella Terra, I'm not sure if they still sell them. I started with a fresh head as they're not tall enough for the port I had or that you have there. They were cast aluminium and I epoxied them in. It makes for a much nicer looking port but I had to roll pin them in place as when you fit the head, the head bolt squashes the port and will squeeze them out a little and make it difficult for the manifold to seal.

For all the work, it made no real difference to lap times (was a group NC car). I also changed to a smaller stem valve (VS V6) which did make a difference. The main problem was the head kept cracking spring seats due to the springs to suit a roller cam, there isn't a lot of metal under them.

[johno]

Was the aluminium port divider YT supplied meant to fit ports with the 'sleeved head-bolt' boss or with the boss removed like mine? Do you have any pics of them?

[Greg]

With the boss removed, I'd say it would have fitted spot on into a YT head with the head bolt tube removed. I don't have any photos, it was about 8 years ago and have had a couple of computer crashed since then!

[200cfm]

So the manifold port that feeds the entry shared port is still divided. And the performance on the track show it works. Wonder if the air speeds through the throat and through the curtain area of the valve are different or the same if it had a divider wall?

[jakesportingservice]

Lookin at the pics i was wondering if you put a divider in between the valves like on a import honda or similar would be of benefit ?
Not that it would have to come clear out to the end of the runner where the head bolt hole is i would think that it would help if the valve were seperated and you would be able to make more of a bowl and shape the short side like on a normal head .

Jake

[johno]

Yeah the manifold has two seperate ports up until it meets the port mouth, then its one big hole to the two intake valves, this set-up means both barrels of the 45mm DCOE webbers feed each intake valve pair! Yella Terra designed an aluminium divider, which ,as GREG mentioned above, did'nt seem to do squat for his track times!! Heres the set-up in the car, the manifold is painted black, as is the rest of the engine to help it run cooler. :;):