Inliners International Forums General Discussion Hi Performance Siamese Intake Question...

I started on a 292 project which I was planning to turbocharge. I've bought a MegaSquirt for same, and was planning to use multiport fuel injection. Because I haven't found any intakes that meet my needs, I've pretty much resigned myself to fabricating my own intake.

My question is as follows: I've always wondered about constructing the siamese intake port with a full length splitter so that it becomes two individual ports on the manifold side. The port splitter would protrude from the intake, and be shaped to form with the head bolt boss and so provide a properly tapered and smoothed passage at least all the way past the boss.

Even though a 'window' to the other side of the inner port would exist, it seems like a satisfactory enough passage to create some ram effect would result. Has this been tried?

tlowe did something similar, except his divider was actually inserted full depth into the port, and his head also had the lumps installed. So his port didn't have the bolt boss in it to obstruct the airflow. There as some pics not to far back in one of these topics that shows it, and he said it made a noticeable difference even over what he got from the lumps themself. Maybe he will be watching this post and can direct you to it.

Douge
also search "siamesed port" July 01,2007 and newer.

It may not be as important with FI as with carbs.

doug,
i have some intakes from brazil , that are made like you are describing. i will get some pics on wed and post them. they also have efi bungs installed.

i think if doing this, you need to take it all the way to the valve to kill the siamesed robbing effect. tom

turbo-6, glad to see you post on the brd again.

Tom
I have a problem with my computer and can not login, thats why I have not been posting. Just looking in when at another computer.

Harry

Doug I saw the intake that I think Tom is talking about at the midwest convention this past summer if so it is a fantastic looking intake and if it is the one that he had then and if memory serves me correctly you could even run dual injectors. I was very impressed with the entire intake. He had just gotten the one he showed me and didn't even have a price yet but if it is with in your budget I would give it serious consideration.

Guys:

I'm probably off in "left field" on this but I'm wondering if all the port work (lumps and dividers, etc.) beyond some basic port 'n polish work is really so much of an issue with a turbocharged application? Is there a "ram effect" in play with a pressurized intake charge or does that only apply to naturally aspirated engines? Just curious . . .

Having a good flowing head is not as critical when you are sending pressurized air into your cyl head.
That being said,your engine will still make more power when you do all the tricks of the trade to your cylinder head.

But when you divide your cylinder head like Tlowe did & making your intake port window too small you are losing some power.

Turbo6 did that with his cylinder head(divided intake port),but he had to turn up the boost more to make the same power as a undivided cyl head.


Turbo6 seems to have fuel distribution problems (running lean in a few cyl's? IIRC) w/the siamessed port so he divided the intake ports,but this made the intake port window too small.
He now has a Brazilian made GM 12 port cyl head to try out.

From people I talk to from Brazil,that particular 12 port cylinder head will crack @ the 500 HP range,casting is too thin,& that is why the heavy hitters in Brazil with there fast inline Chevy 6's use the siamessed port cyl head.

Just some info I have gattered from a few guys I talk to in Brazil,could be right,could be wrong????

MBHD

FWIW, I agree with Hank.

Ron

I agree with everyone the better the air flow the more HP you will make.

A turbo charger increases the density of the air not the air speed, therefore the air speed of a small port is greater than that of a large port and a larger port will flow more air. You just have to be carefull that the air speed does not get too fast. All that said, with FI you can somewhat put the fuel where you want it with a carb you have to control the wet flow if you want the engine to live, with the larger fuel demand of higher HP this becomes a problem.

The talk is the Brazilian head cracks, the thickness of both heads are the same, if you port it out to were is flows good air I believe it would crack easier so I just cleaned my head up and kept the walls as thick as possible and put smaller valves than normal to keep it strong. Since the port enters higher than a stock US head the low lift flow is a little better which will not hurt. Time will tell!

As for as bump ports , stock ports, divided ports, or whatever air flow is air flow. If you know the air flow you know the biggest part of the VE of the engine and the HP potential of the head just multiply the air flow number by the increase in density of the turbo (not the pressure ratio) and you get the max potential of your setup.

I don't think you can ram tune a siamessed port unless the cam is very mild or the valve timming is different for each cyl. or both. Too much for my small brain (just turn up the boost).

Just my thoughts,
Harry

As once said before I beleive if your going to divid the ports and still want the lump port speed (CFMs) you have to widen the
port to get back some of what the divider has taken away.

Harry,
what kind of intake manifold are you going to use?


Custom I would think.

Rick

I'm trying something different it's sheetmetal manifold with each individual port drawing from one venturi only then each jet will control each cly.

Harry

I think way too much is made of "Siamese" ports as it was of the original twins! Those guys got married to two different women and raised families. There must have been some strange times but function ruled! It's not like any adjoining ports are firing in secession or even on the same revolution. Much has been said about the ports acting as a plenum. That could be a + in a turbo/supercharge application. In a NA engine it seems that port shape and size would make more difference than how often a port was called on to perform. Yes 12 port cross flow with perfect ports, valves, rockers, and chambers would be nice, but in reality just how much better is it?

I agree with Beater, I think too much is being made from the siamese port issue. In a Flathead V-style engine with siamese exhaust ports, it has been shown and proven that dividing the ports helps dilution and reversion of neighboring cylinders that have firing sequences closer together in those type of engines(90 degree firing)! In the 6 cylinders, the firing is farther apart(120 degrees), and doesn't create the same dilution and reversion issues,even on adjoining cylinders! There have been many high horsepower siamese port engines built and raced,both N/A(over 600 HP) and Forced induction(over 1000 HP), that haven't had the ports divided. Not to say there might not be some gains to be achieved from dividing the ports. But as already has been said, you make the port window smaller, which will diminish the flow to some degree and possibly create other issues as well. Also, by design, the siamese port has a very poor short side radius, and adding a "lump" to even a stock engine, will yield a very noticable increase in performance. Like Beater said,a 12 port would be nice, but i've seen a "lump" siamese head flow over 330 CFM on the intake on quite a few heads.In comparison,I doubt a 12 port could obtain that because of their thin casting design.

Yes it looks like a firing order of 153624 would give you even distribution to all cyl. But you have to look at the valve timming not the firing order. If you plot the valve timming events you would notice that only the center port has equal time between events. In the front port when #2 intake is closing #1 is starting to open and the rear port is a mirror of this. It doesn't seem to matter until you try and make a lot of HP, and #1 or #6 goes lean
The guys in Brazil use FI or carbs with injectors as an auxiliary fuel systen on siamese ports. They have even said on dynos you can see the exhaust pipes are different colors because of the fuel difference.
I think what is happening is that when #2 valve is closing and #1 is starting to open the air stops until #1 can start to pull air in but the fuel falls out of supension.
In the old days guys with siamesed ports used different valve timming on different ports because of this problem.
I divided my head and have not had a problem since.

Harry

Were you able to determine any before and after changes on a engine or chassis dyno or see any changes at the track. Just curious if it made any measurable increases that you could see.

That is a closer look than I had taken. Like you say it would mostly show on high horsepower engines, the ones we want to build. The cam grind would certainly play a part. A good place for a roller cam and some forced induction! Didn't one of the Wayne heads employ different timing? Did I read that in the Twelve Port Story?

Has ran the fastest run ever, only because it made it down the track without melting something!

Really I divided the head only to prove to myself that at a point the siamesed port will not work. Not to try and make more HP.I have had more manifold designs to try and get it to work, some were so bad in wet flow that would artificially wet the end cyl but hurt the overall picture.

I was talking to a guy and he said years ago many people had tried to remove the center divider in a small block head for a supercharged motor and it would hardly run. And if you chart their valve events they are not as bad as an inlines.

Harry

Okay... Here is another brain-dead newbie question: Since it is possible to furnace-braze parts of heads together, as demonstrated by the small-block head conversions, would it be possible/desireable to saw three small blocks out of the head and and braze into place a new casting which includes longer radius port bends, individual ports, and more optimized port shapes?

For reliability and sealing, it might be better to mill out the top of the head and leave the head floor and valve seats, and just replace the ports and valve guides. It seems like such a replacement port casting would be relatively easy to develop as the casting would be open at the sides, and so not need elaborate self-supporting cores. Obviously, the new port walls could be left somewhat thicker to allow for porting without hitting the water jacket.

Its not a brain dead question. Its been done before. I have some pictures, if I can find them I will post it. But from talking to the guy it was a lot of welding. A LOT OF WELDING!

Yeah, I remember seeing on the Wayne Mfg. Company website before it was removed from the internet, and the 235 12 port head had a different valve arrangement than an OEM siamese 235 head, and required a specially ground camshaft to go along with the 12 port head.

It would be much easier to take sections from several different aluminum heads and just Tig(heliarc) them, than trying to furnace braze cast iron heads, and probably a lot cheaper. Thats what Leo did with his engines, and seems to have had good results from those heads instead of cast iron....plus, I dont think there are any cast iron heads that would provide that much of an improvement over a professionally ported siamese head with "lumps". I've done many "lump" siamese heads that had the intake ports flow over 330 CFM, its doubtful that even the best Dart or World Products cast iron head could even be made to flow close to 300 CFM. Very few aluminum heads can even do it either. Very few people have ever had a really good "lump" head to truly know and see their potential.

OK, Larry,,,,,Twisted6,,,,what are we not doing?????
Besides breaking into water jackets & a lot of welding & epoxies?


MBHD

I have seen one on a flow bench that did 320 with lumps. But the port was also raised 1/2" on the roof and the floor was also raised 1/2". The intake seat also had a parabolic cut instead of a 5 or 7 angle job. Lots of welding and work.

All of the "Wayne" 12-port heads made for the Chevy 216-235-261 engines by Wayne Horning, Harry Warner, Bob Toros, and the recent Wayne MFG. Co. had the the same valve arrangement as the the stock engines. The 12-port head that Wayne Horning made for the GMC after he and Harry Warner separated did have a different valve arrangement (I-E-I-E-I-E-E-I-E-I-E-I) in an attempt to eliminate hot spots. This, of course, requires a custom camshaft. I believe that this is explained in Part 2 of the 12-Port story in the "Historical' link and in the April 1951 HRM. Pat Swanson also described the various Chevy and GMC 12-port heads at the Denver convention in 2006. Several members brought in examples of most of the heads for "show and tell."

I've been off the board for a long time, but this post caught my interest. Back in 2002 I tried port EFI on a stock 250 (no turbocharging). Made a custom manifold to hold the injectors, etc. Sure it ran, but there were always dead spots in the range where it would falter. Examination of the exhaust ports and manifold, plus the plugs led to the conclusion that #1 and #6 were running lean. At the time I wasn't thinking about valve timing, but more intake manifold geometry and was it ramming more air in to 1 and 6...

Anyway, to try something different I went to a TBI on a 4-bbl Offy manifold and that cleaned it right up!

This always puzzled me, and a few years back I found this link:
http://www.starchak.ca/efi/siamese.htm
which explains why the whole problem of charge robbing occurs. Makes so much sense when you look at it, and I wish I'd found this back in 2002.

So, given this reality, I think the only options (untried by me) are the "port divider" proposed above, or perhaps the clifford manifold for the three side-draught webers. I wanted to try three small TBIs, mounted on their sides and flowing directly to the head. At the least, this should provide a few even air/fuel distribution, because the geometry of each siamese pair will be identical.

Greg

That is interesting! I wonder about using a roller cam with a profile that could open and close valves faster to get full lift but be open a shorter time to eliminate the over lap. With forced induction you could still fill the cylinders.

greg,
here are a few pics of a intake from brazil. it is split right up to the carb hole. i also have a clifford type intake from them that is split the same way, with injector bungs.




tom

Wow!,
looks like for some top end power for sure.
Are the runners a little bit smaller than a Clifford?
Here are a couple other types,no, dividers,but just some other choices w/intakes from Brazil I believe?
http://cgi.ebay.com/ebaymotors/Chevrolet...A1%7C240%3A1318
http://cgi.ebay.com/ebaymotors/Chevrolet...A1%7C240%3A1318

MBHD

hank,
the two you listed from ebay do not split the siamese intake runners as we have been discussing.

the runners on the black intake i supplied pics for are in total alittle smaller than a clifford port. i think with head port dividers and a turbo, this would be a kickin intake. tom

Tom ,
the intake pic you posted looks sorta like the PES manifold in Leo's book on pg 114.


I know it's not split & it is not a flat design,it rasies the carb up high.

But just a note from Leo's book on the PES manifold.
Strickly competition use.
The PES runners appear to be much smaller than the one you showed.

I am not sure how that manifold you have pictured in this thread,would give you any low end or mid range power,even with the deviders,volume appears to be way too big to be practicle.

I devided my Clifferd intake manifold,it helped,but I made more practicle street power w/my Offy intake manifold.

Sure, w/a turbo it will make top end power,but on the street,it will cause the turbo to spool slow.
Just my two cents thrown.
I do not know for sure,but that manifold looks like a hardcore race only unit.

Guys in Brazil do not seem to be using it,@ least I have not seen it on any of the fast cars or street cars.

Is the manifold fresh off the press? Just introduced to the market?
Do you have any info on that manifold from the manufacture?

MBHD

I'm a new guy here. Just been reading and trying to learn. I'll have to say this is a very informative site. Tom, can you post pics of the intake with the injector bungs?

Bob

Tom,

On closer inspection, it seems you already did, if I'm seeing things right. What about the Clifford type. Is that a 4 barrel type or the Weber type with FI bungs?

I went back and searched TLowe's split port post; Tom fabricated siamese port splitters much along the lines that I was considering after rejecting the notion of splitting the port only up the head bolt boss.

Version 2.0... I'm now thinking of removing the head bolt boss as is done for the lump port. The vertical port splitter can be formed around a new head bolt boss tube which is inserted in the opening where the original boss was located. When the splitter is properly located in the port, the head bolt hole and the splitter can be overbored and a steel sleeve pressed in to secure all parts. I'm sure that an appropriate epoxy would be needed to seal the waterjacket.

Like Tom's splitters, I don't think that an airtight division between the halves of the ports is critical; just trying to get the bulk of the airflow and the injected fuel into the correct opening.

The big advantage that I can envision for this approach is that curved horizontal blades could attached to the convenient splitter to serve as turning vanes. Very often in both aerospace and in powerplant airflow applications, turning vanes can make a short radius turn act equivalently to a much longer radius turn. Could this provide the benefit of a lump port without reducing the port runner volume as much?

Welded-in turning vanes would also seem to provide increased resistance to vibration/metal fatigue of the splitter tongue.

DougE,
if you are considering running normally aspirated & run a port devider in the cylinder head, it will hurt your airflow & therefore lose power.

If turbo or supercharging & uses the deviders you can get away with it running OK because it is forceing air/fuel mixture into the cylinder head.

MBHD

bobbristow, here are pics of the clifford type intake with fuel rails and divided runners.





anyone interested in them please PM me.

hank, the 1st intake(black) has smaller runners than a clifford. i think it would be a good low/midrange intake. tom

Tom,
I still say you should install injector bungs on a devided Offy intake & try it on your Elky.
If it does not work to your likeing, you can always sell it on Ebay.

4 injectors per port on the Clifford intake,,,,for running alky?


MBHD

Thanks, Tom

Bob

A question for TLowe...

The "Brazilian" intake pictured above in black appears to be regular production. Does that imply that there are regular production heads (or modification kits) that are designed to work with the split intake?