#46452 - 12/30/08 10:32 AM
Re: Siamese Intake Question...
[Re: DougE]
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tlowe #1716
12 PORT ADVERTISER
Active BB Member
Registered: 04/01/04
Posts: 2327
Loc: Dysart, Iowa
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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
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#46460 - 12/30/08 03:27 PM
Re: Siamese Intake Question...
[Re: tlowe #1716]
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DougE
Active BB Member
Registered: 12/15/08
Posts: 83
Loc: Springtown, TX
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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.
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#46467 - 12/30/08 06:38 PM
Re: Siamese Intake Question...
[Re: Mean buzzen half dozen A.K.A. Hank]
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tlowe #1716
12 PORT ADVERTISER
Active BB Member
Registered: 04/01/04
Posts: 2327
Loc: Dysart, Iowa
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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
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#46487 - 12/31/08 08:56 AM
Re: Siamese Intake Question...
[Re: tlowe #1716]
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Make_110
Bulletin Board Only Member
Registered: 12/31/08
Posts: 1
Loc: Finland, Scandinavia,Europe
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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.
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#46492 - 12/31/08 10:18 AM
Re: Siamese Intake Question...
[Re: Make_110]
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Winter
Active BB Member
Registered: 08/27/06
Posts: 206
Loc: North Carolina
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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
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#46497 - 12/31/08 03:42 PM
Re: Siamese Intake Question...
[Re: CNC-Dude #5585]
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DougE
Active BB Member
Registered: 12/15/08
Posts: 83
Loc: Springtown, TX
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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...
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#47568 - 02/04/09 10:56 PM
Re: Siamese Intake Question...
[Re: Mean buzzen half dozen A.K.A. Hank]
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CNC-Dude #5585
Active BB Member
Registered: 09/27/08
Posts: 1735
Loc: N. Georgia
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[quote=DougE]I've done many "lump" siamese heads that had the intake ports flow over 330 CFM OK, Larry,,,,,Twisted6,,,,what are we not doing????? Besides breaking into water jackets & a lot of welding & epoxies? MBHD
_________________________
There's no such thing as too much cam....only not enough engine!
12 Port Head Manufacturer
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#47580 - 02/05/09 09:31 AM
Re: Siamese Intake Question...
[Re: Mean buzzen half dozen A.K.A. Hank]
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CNC-Dude #5585
Active BB Member
Registered: 09/27/08
Posts: 1735
Loc: N. Georgia
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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.
_________________________
There's no such thing as too much cam....only not enough engine!
12 Port Head Manufacturer
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#48410 - 03/08/09 10:33 AM
Re: Siamese Intake Question...
[Re: DougE]
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Ed Farrell
Bulletin Board Only Member
Registered: 01/27/05
Posts: 3
Loc: Bonsall, Calif.
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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
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#48445 - 03/09/09 11:49 AM
Re: Siamese Intake Question...
[Re: CNC-Dude #5585]
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panic
Active BB Member
Registered: 01/11/05
Posts: 1340
Loc: Hempstead, Long Island, NY
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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.
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#48616 - 03/14/09 07:57 PM
Re: Siamese Intake Question...
[Re: Turbo-6]
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CNC-Dude #5585
Active BB Member
Registered: 09/27/08
Posts: 1735
Loc: N. Georgia
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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....
_________________________
There's no such thing as too much cam....only not enough engine!
12 Port Head Manufacturer
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#48627 - 03/15/09 12:23 PM
Re: Siamese Intake Question...
[Re: Turbo-6]
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Greybeard
Active BB Member
Registered: 01/27/06
Posts: 75
Loc: Sequim Washington
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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.
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