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?

doug, it is definately a aftermarket part. the cast is of a finer design and good quality. i will check and see if they designed it for use with a divided head. tom

Thanks.

Even if a complete head is not available, some company there may have commercialized an add-in kit to split the intake; otherwise it wouldn't seem reasonable to sell the split manifold.

If you guys can buy a 12 port head from Brazil,SPA sells a turbo exhaust manifold for that cylinder head also,,,,from what I have been told.

The 12 port intake will work with a throttle body & F.I.,but I have been also told it is restrictive.


MBHD

if that is the case, i am a dealer for spa and can get it. i'll check and see if they can also supply used heads. it would be helpful to get the motor model and years of production. tom

Hi

I have also wondering this situation of siamesed ports and try to find more information of inliners one heads and tried to find also about v8 head to inliners.
But if somebody find used heads I would be intrested.

Brazilian GM 250 Engine, 4.1L, 12 Port Head

1995 to 1998 Silverado, 138 Hp, V8 bell housing pattern
1995 to 1998 Omega, 168 Hp, Opel 3.0L bell housing pattern

12 port engine, 6" rods, lighter piston with shorter compression height
Multi-port fuel injection, one piece rear main seal, cast dual exhaust manifold

Cylinder Head GM Part Numbers
93216528 Cylinder Head
93.238.389 Cylinder Head Complete
93.205.909 Cylinder Head Bare

Pistons, GM Part Numbers ('95 - '98)
93225129 Piston, 0.030 overbore
93225130 Piston, 0.040 overbore

Connecting Rods, 6", GM Part Numbers ('95 - '98)
93205918 Connecting Rod, 6"

The above is information I have collected over a period, some from this forum. Please confirm before ordering. The Brazilian parts are expensive, for whatever reason. The general tariff is supposedly approximately 30%. The Brazilian engine parts are 3 to 5 times more expensive than similar US engine parts. A pipeline to get Brazilian parts at reasonable price is an idea.

I'm personally interested in a real flat top cast piston, preferably hypereutectic. I searched the web and called Federal Mogul and others with no luck yet. The 307 "flat top piston", Federal Mogul 295AP, has very large chamfer around the top edge. This negates some of the effects of a proper quench. I assume this large chamfer was one measure to help reduce unburned hydrocarbons before the use of catalytic converters.

The 1968 and 1969 Pontiac OHC 6 250 had a real flat top piston, GM P/N 9784340,(a standard bore set is currently on sale on e:bay). The piston had deep valve reliefs, for a non-interfernce engine, incase the OHC belt failed. This piston is no longer available.

A 3 7/8" version of the 4" Federal Mogul H660P piston, flat top hypereutectic, for the Chevrolet 327 would be great (5.7" rod).

Path to photos of Brazilian Chevrolet 250 Cylinder Head:
http://www.goravenswood.com/links.htm / Engine / Entre / Cabecotes

Pontiac OHC 6 250 Flat top piston
e:bay Item Number 120320658687

Good info! Just for curiousity's sake, have you ever gotten any price quotes for a Brazilian 12 port head, either bare or complete! Thanks....

In the photos on the Ravenswood site, the differences between the 9 port and the 12 port are certainly obvious and interesting. I assume that the 12 port is compatible with the earlier 194/250/292 blocks? I tried the GM parts listings to no avail, so this is apparently not available domestically. One would think that GM would offer it in the performance catalog...

CNC-Dude, sorry, no prices for the Brazilian cylinder head.

DougE, neither GM or Federal Mogul in the USA will help concerning the Brazilian engine parts, neither technical information or part numbers. I contacted both companies in the USA.

GM of Brazil no longer makes or stocks the 12 port head you have to find one at a dealer to get one, this is what I was told.
I paid about $800.00 for a new bare head as I remember. A new USA siamesed head costs about $500.00 now. Will post the casting number of the Brazil 12 port head.

Harry

Found the info. on the Brazil 12 port head:

Casting number- 93 216 528

PN - 93 205 909 bare/machined
PN - 93 238 389 complete about

Harry

What kind of #'s are you seeing with what you are doing?

This fool is still ranting,he says his flows 240 CFM @ .500
I will deleat my previous statement here on this post as he has cleaned up his auction BS.
It appears to have a broken stud & or studs,& there is no stament in the auction about that.
http://cgi.ebay.com/ebaymotors/Chevy-Inl...sQ5fAccessories

Looks like he took off all the BS from his auction.
So it seems he is still lurking :-)

That flow number of 240 is about correct for a nicely done cylinder head it seems,still don't know how you get 330 CFM.

Mike Kirby has a Hendric (SP) cylinder head @ his shop that flows 330 CFM,,,but they ported into water jackets,rebrazed or epoxied all back up. It has the bowls really widened up,but into water jackets.

Well, at the 330 cfm level, it definately isn't a street head! It is very thin all over. "Huge" intake valves, very tiny combustion chambers, this also unshrouds the intake valves unbelievably well because the chamber is so shallow,you will see a big jump in flow by doing this. But compression will sky rocket. Also, keep in mind, to achieve this level of flow and HP, you need to make the bowl area at least 85% of the size of the valve you are using, and this should be machined and not ground with a grinder. Also,a 2.02 valve will still be too small to see those kind of #'s. And finally, if you do all the above mods, this last step is the most critical and very important, and if you don't do it,not only will you loose valuable flow and HP, but potential engine damage can occur. Because you have now made the head so thin and flimsy, by decking it so much and removing so much material from the ports, and removing the head bolt bosses, and heating to apply brazing material, you absolutely have to do the valve job with a torque plate bolted to the head. It distorts so much when you torque the head to the block if you dont, that the valves wont seat. Even pulling the head between rounds at Indy and other races, I had to put the torque plate on it just to lap the valves, its that critical. Much of the epoxy and chamber brazing you saw with the head Kirby has is most likely a repair. We were constantly having to replace the entire combustion chambers on several ports, because the head was milled so much and the deck was so thin, the compression so high, the chamber would seperate from the head entirely. I've often wondered what the practical limit would be for those heads as far as flow goes for the street, having a good reliable good flowing head and not having a time bomb. 280...300 CFM, I've been thinking about doing another one on the conservative side, just to see, since there seems to be a lot of interest in these engines growing.

Think about this in relation to siamese intake ports. As no. 1 piston is on the intake stroke the cylinder is filling with the intake charge. Due to the crankshaft design of 120 degrees between throws the ajoining cyl, no.2 intake vale breaks off its seat and the no.1 cyl stops filling. The cure, have the crank throws come up together and change the firing order, buy a 12 port head, or divide the intake port. Each has its drawback. I had this discussion with nonother than Bruce Crower many years ago. Ed Farrell

Well, the siamese port cofiguration has never really been an issue until more recently, when fuel injection has been adapted to these engines, and the intake valve overlap of adjoining cylinders begins to play its part. Many very high HP engines have been built using these heads for over 30 years and have been very effecient with carburetors and reliably as well. Its just trying to figure out how to make one injector feed 2 cylinder that share the same intake port that has shown a need to try and develop other solutions, that were never really a problem otherwise.... It would be very easy to swap #2 with #5 cylinder on the cam,as a possible solution, since they are at the same position on the crankshaft at the same time for a timing swap. That might be something to consider for the fuel injection guys that still want to use the siamese head possibly. tlowe has encountered leaning conditions in his engine with fuel injection, and has found that dividing the intake port has shown to be a considerable improvement and possible remedy for this problem altogether. And quite possibly, the simplest cure for siamese port issues.

As no. 1 piston is on the intake stroke the cylinder is filling with the intake charge. Due to the crankshaft design of 120 degrees between throws the ajoining cyl, no.2 intake vale breaks off its seat and the no.1 cyl stops filling.

The adjacent pairs are as separated as they can be.
The center #3-4 pair have symmetrical 360° - 360° - 360° interval of separation.

The #1-2 and #5-6 pairs have an irregular interval: 240° - 480° - 240°, etc.
If the intake duration exceeds 240°, the later cylinder will cause a minor leak as its valve begins to open, but since this is BTDC vacuum is minimal, and no actual flow will occur until the piston moves down ATDC a bit and the lift reach perhaps .020". The earlier cylinder is already coming up to compression in any case.
In addition, #1 & 6 do not have this problem, since their complementary cylinders (#2 & 5) are 480° later and cannot interfere.

Swapping the lobes to substitute 2 for 5 will subject the crank to higher torsional loads. Development of L6 engine blocks and cranks dates to before WW1; everything you can think of has been tried, patented, and in most cases failed. I can't find an L6 with a firing order that places 3 power strokes at one end of the crank, then 3 at the other.
Dividing the ports will certainly cure the EFI distribution problem, but will reduce peak power as all the racing head prep has show. There's just not enough port area.

Distribution in a siamesed port is not just a problem with EFI actually it's less of a problem than with carbs, since you can put the fuel right into the port.

I personally have never had problems with the fuel distribution or reversion issue that many people say plague engines with siamese ports. I assumed their circumstances were unique to what they were or weren't doing compared to what I was experiencing with many of the Comp Eliminator engines i've had my experience with. panic mentioned some guidelines he felt should be observed to help aleviate this "phenomenum", if you want to call it that, in regards to camshaft duration. But i've used camshafts in 292's that have had well over 320 degrees duration @.050, and over .900 lift at the valve, and not had issues that you could say were from reversion or fuel distribution because of having siamese ports. So I, really don't know what problems people are actually having, except what tlowe has shared with us in his port dividers he has made....

you can put the fuel right into the port

But that's not the problem.

mentioned some guidelines he felt should be observed

Sorry - what were those again?

If the intake duration exceeds 240°, the later cylinder will cause a minor leak as its valve begins to open, but since this is BTDC vacuum is minimal, and no actual flow will occur until the piston moves down ATDC a bit and the lift reach perhaps .020". The earlier cylinder is already coming up to compression in any case.
In addition, #1 & 6 do not have this problem, since their complementary cylinders (#2 & 5) are 480° later and cannot interfere.

I believe this is what I was thinking about that you mentioned.

I'm not referring to driveability problems as tom is, but when you need to put in enough fuel to support over 600 HP you start to see the distribution problems in the siamesed ports, especially with carbs.

So if it effects the fuel at high HP it must have some effect on fuel anytime. A divided port on the street would still support over 250 HP (naturally aspirated) and have all the benefits of a small port. If this is not true the V8 guys should cut out their dividers and small blocks will out flow the big blocks.

The 600HP level is well within the range im seeing with the 292's in Comp. We've always used a plenum style sheetmetal intake with(3)500 Holley 2bbls.,(1)carb inline with each intake port.

Yes, but over 600HP you will have problems on siamesed ports that is one reason everyone went to Ford 300's then AJ's aluminum head then 4200's all with divided ports, Nobody runs 250-292 style siamesed ports now.

panic mentioned some guidelines he felt should be observed to help aleviate this "phenomenum", if you want to call it that, in regards to camshaft duration.

Not a guideline at all, obviously no serious engine has a nominal intake duration below 240°.
It's a comment about something that happens, but evidently the results are small enough not to be detectable as a problem.
Vizard wrestled with a problem of similar nature but greater magnitude on the Mini (with different duration and firing order numbers, of course - the point of event overlap is only 180°, so the duration where both valves of a shared port are open is far longer with a given intake cam) to get past an effective ceiling beyond which more intake event wasn't producing the expected results.
His cure was fairly minor changes in the LSA and intake/exhaust bias between cylinders, depending on their position as early or late in the port's function.

Question: What is the highest HP a siamesed port (naturally aspirated) engine has made and can be proven, ie. in a written publication etc.?

My vote is:
Jim Hedrick and Cotton Perry, H/MP Chevy II.
549 HP 1979 Popular Hot Rodding Mag.

Food for thought !

How about Glen Self,any published HP level or track times ?

MBHD

Yes Glen Self held the national record for his class F/EA, but just recently lost the record to Glen Tredwell now it's 7.95 @ 164.83.
I'm not taking anything away from anyone, all the NHRA record holders make unbelievable HP with what they are working with. If you figure the National Records, ET and Speed, for their legal weights none are making more than mid to high 500's by using their ET's and mid to high 400's by the speed numbers, even with todays new style motors. It's common knowledge that the speed number is a better barometer of the HP of an engine.
I'm just trying to show that no siamesed port motor ever made over 600 HP and trying to approach it had the possibility of being a problem.

Well I worked for Jim for 15 years, and Cotton's engine is the one I was referring to that made over 600 HP. It actually made 612 HP the last time it was dynoed just prior to Indy in 1986, when Cotton drove the F/Dragster of Brian Browell. Cotton actually set both ends of the record for that class at that time. Also, many publications are full of misinformation, either mistaken or intentional, so don't ever believe everything you read in them. But, I can assure you, that there have been quite a few since then that have also seen HP levels above 600 as well. The only thing that was changed on the engine the way it was run in Cotton's Chevy II, before it was put into Browell's dragster was the headers and the oil pan, nothing else....I've also seen the references that were used in Leo's book that were quotes where he was asking Jim about certain subjects like camshaft info and head flow. And what Jim told Leo, was very conservative, in reality to what was actually being done at that time. Jim was extremely secretive about any pertinent info regarding his techniques or knowledge about his engines, and would have never divulged any kind of info that wasn't already public knowledge. Not that Jim intentionally mislead Leo, he just told him things that were done 10 years earlier, and not current methods or concepts for that time period....

I know what you mean about publications with misinformation also now the internet is the same, you have to prove everything to yourself. That's why I always go by the numbers, what was the record of F/D in 1896 and what was the weight to cubic inch factor. E/D is now the old F/D, and the record now for E/D is 7.44 @ 176.81 at 4.50 lbs per cu in that makes about 450 to 500 hp for that ET and speed.

Jim Hedrick has always been my six cly God. He took the Sissel-Kirby bump port head (an ingenious design) and took it to the next level. We are all at a loss without him.

Back in the mid to late seventies, I was just a kid and couldn't hang with my brothers older gang as much as I would have liked. One of his friends built the chassis on the ChevyII and another designed the 3 Holley intake manifold and my brother help build the manifold. Jim and Cotton used our trailer to campaign the Chevy II. Anyway Jim told my brother about changing the cam timming for better mixture control. Do you remember anything on this?

No, I don't recall the actual weight/cid factor for that class that long ago. But the ET was 8.04 and I cant recall the MPH. Cotton and I are actually working on a book similar to Leo's, but it will chronicle his and Jim's accomplishments and contributions to advancing the 6 cylinder. I agree with your earlier comments about the ceiling on the siamese head being in that HP level as a cap. But considering what has been able to be obtained with these heads, despite their shortcomings is pretty amazing to say the least. We had one of Sissell's 12 port aluminum heads to go to the next level with, but NHRA never would make a decision to allow it to be used. The Fords were granted the Billet head to be legal, therefore taking the lead in the inline battle,with a much better cylinder head,unfortunately. Im also doing some "lump" heads for some guys in Brazil, as these engines are experiencing a boom in popularity there, and giving me an opportunity to sort of carry on with the Perry & Headrick legacy in a small way.

Amazing is an understatment, Good luck in your endeavors,keep us posted.

Have you ever done any R&D with a bump port and a divider, bringing the bump out into the manifold. The area at the head surface is similar to the pushrod area on a small block if you make the manifold similar to a chevy port it make work.

Just dreaming!

I don't know NHRA rules for today, but when I was active in the '60s, weight breaks did not include the driver. In a small digger or altered, the driver can contribute an extra 10% in weight, which throws off computation of horsepower by just using the class weight break for the computation. Another aspect in calculating power is that not all cars can make the min. weight break, but fall into the class anyway.

In 1965, my Chevelle 300DX 2dr sedan with a 350hp 327 fell into the bottom of the A Stock class. A/Stock was the home of the Mopar 426, 427 Fords including the '66 Fairlane, and 427 Chevy Biscaynes. I was not allowed to add ballast to make B/Stock so I taught my wife to run it. The 70 lbs difference made for nearly a tenth, and many sorry looking faces after getting beat by a "girl". Anyway, if one is to calculate power from performance #s, you need to know the actual weight of the car and driver.

Today driver weight is included in total weight of car, don't think anyone in Comp will give up anything not to have an edge.

But went back and added 200 lbs to total weights and recalculated HP
ET--650 HP
MPH--525 HP

I have rule books from the 60's will look it up, just to know.

Half of "the Danica Patrick story"...

I agree, the speed number is a better barometer of the HP because it removes the chassis and most of the gearing effect from the equation.

Re: "Not that Jim intentionally mislead Leo"

There's a line in a movie where someone is bragging about what a good pool player he is. He points to the acknowledged old master, and says "he taught me everything I know".
The master pauses and says "but... I didn't teach you everything I know".

I think your calculations are pretty close. The hybrid headed E/D and J/AA Fords are getting over 650 on the dyno, and subtracting about 10% for drivetrain losses puts you back around 600 to the ground. I think e.t. is a better predictor of power-to-the-ground than mph as converter slip or clutch slip can adversely affect mph by a few mph.

By the way the Ford hybrid head was made legal when FoMoCo cooperated with some of their racers and assigned a Ford part number to the head and put it in their Performance Parts Catalog for sale.

6RE6

I'm building one, with custom intake and exhaust running a 500 CFM holley, flat top ross pistons, eagle rods, a crane 272 cam, and roller rockers