Porting intake

I just got done reading all the posts in this thread. The 'tent" seems to be a good idea, however it is accomplished. The "turtle" post got my gears working. I'm thinking of making this out of billet aluminum and using the "bolt through the bottom" method of mounting it. Thoughts?

After reading this post I decided to give it a go here. I machined out a Tent from solid aluminum and radiused it to match my manifold, one of the old types. I used to 1/4 inch screws to secure it permanently and then used lab metal to fill in the gaps. I've used lab metal in the past as a filler for aluminum gas tanks to be powercoated. It's rated to 1000 degrees. After the filler hardened I used 40 grit rolls to blend and rough everything. This should help until I can get my FI project started. In the last picture you can see a hole drilled in the treads of the brake vacuum outlet. That hole reconnects with the lower vacuum line which was blocked by the tent.

Ultimate Torker Manifold?

I’ve been trying to figure out the best way to modify a manifold after thoroughly reading and looking at all of the pictures I could find. I don’t own a machine shop and don’t weld Al so I’m at other’s mercy. Costs which might become prohibitive are somewhat of a concern. I don’t want $200 to $300 in a manifold that will net me 10 or 12 hp, maybe. With that being said, I’ve contacted a local machine shop about how to proceed. It was suggested that the bottom be milled off and a window cut open so the welder could weld the raised (tent) floor in. The initial machine work was estimated at near $100 but that was to make a jig to hold the manifold for milling and to write the program to cut the window in the floor. I still have to carry the manifold to the welder and don’t have an estimate from him. My job is to communicate what I want, do the leg work and porting.

My engine will be a 2.0L and I will use a mild hyd. cam grind from Cam Techniques (probably 212 @ .050 - .246’ lift). I haven’t settled on the valves yet. The engine I did last year for a friend is identical up to this point, we used 2.0L Opel intake valves with 1.9L exhaust valves.

Now that the background is kind of out of the way. I’m planning on using a Weber 38 DGES. Since I don’t race I would prefer a good tractable engine that pulls strongly all the way to say 7 grand. I’m toying with installing a divider to separate the two barrels of the carburetor in the intake. If I do this it will effect the characteristics of the engine drastically I would think. Do the divider or not? Height of the divider? Will there be a need to jet the carb differently for each barrel? Can someone come up with a good idea on how to make an adjustable divider so I can try different heights without making a new manifold each time.

The engine I put together last year may very well be the test mule for this set up. Hope the owner doesn’t notice this thread since I haven’t mentioned it to him yet. ;-)

TIA,

Harold

Some answers maybe . . .

hrcollinsjr said:

I’ve been trying to figure out the best way to modify a manifold . . . 1. I don’t want $200 to $300 in a manifold that will net me 10 or 12 hp, maybe. With that being said, . . . that the bottom be milled off and a window cut open so the welder could weld the raised (tent) floor in. The initial machine work was estimated at near $100 but that was to make a jig to hold the manifold for milling and 2. to write the program to cut the window in the floor. . . .

My engine will be a 2.0L and I will use a mild hyd. cam grind from Cam Techniques (probably 212 @ .050 - .246’ lift). . . . we used 2.0L Opel intake valves with 1.9L exhaust valves.

. . . I’m planning on using a Weber 38 DGES. . . . I’m toying with installing a divider to separate the two barrels of the carburetor in the intake. If I do this it will effect the characteristics of the engine drastically I would think. 3. Do the divider or not? Height of the divider? Will there be a need to jet the carb differently for each barrel? Can someone come up with a good idea on how to make an adjustable divider so I can try different heights without making a new manifold each time.

The engine I put together last year may very well be the test mule. . . ;-)

TIA,

Harold

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1. Everything's relative, Harold, $200-300 for 10-12HP doesn't sound so good taken by itself. It's a different story entirely when looked at relative to your particular engine, however. 10-12HP gain for a ~120HP engine is a "horse" (pun intended) of a different color entirely, 9-10% HP gain.

2. I'd check at a machine shop with a manual vertical mill, using a CNC machine for a "one-off" seems overkill and probably affects the end pricing too. My local guy would do the machining AND weld it . . . just a thought.

3. I'd say "NO", the cylinder pairing (1/4, 2/3) which would result from this divider is "unbalanced" . . . all wrong. Based on the firing order (1-3-4-2), you'd end up with the left barrel feeding its cylinder pair (1/4) during one revolution and the right barrel feeding its cylinder pair (2/3) during the next . . . . . . CRAP!! . . . senior moment . . . thinking about SSD manifold! This manifold would feed from the two carb throats alternately (180° apart), thus "balanced" . . . turning over to RBob . . .

hrcollinsjr said:

I don’t want $200 to $300 in a manifold that will net me 10 or 12 hp, maybe.

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Believe it or not, it's still probably the best thing going for HP/dollar ratio. If you had an honest 100 hp you could get as much as 10-12 hp from the intake mods. But going from a Solex to a 38 DGAS will only net you 7-8 hp, and the 38 DGAS costs more than the intake (especially if you port it yourself).
A header and exhaust cost a lot more, and you'd be lucky to see 10 HP from this combined upgrade. Ignition? Maybe 2-3 hp on most engines (but better response and driveability).

Easiest way to open up the bottom of the intake is with a hole-saw. Like this.

More recently, I use a vertical bandsaw (woodworking blade) and cut the lower plenum off flush with the intake bottom, then notch it in a 'V' shape with the bandsaw to emulate the peaked floor I will later weld in. I generally notch vertically to halfway between the brake booster fitting hole and the EGR fitting hole. Then you make the sheetmetal 'peak', and weld it in from underneath. Much easier and faster this way.

Here's the previous info I posted on custom valves from Manley.

HTH,
Bob

hrcollinsjr said:

I’m toying with installing a divider to separate the two barrels of the carburetor in the intake. If I do this it will effect the characteristics of the engine drastically I would think. Do the divider or not? Height of the divider?

Click to expand...

If I am reading correctly, you are looking at pairing cylinders #1 and #4 together, being fed only by the outward throttle plate, and #2 and #3 will be paired, feeding off the inward throttle plate.

I would tend not to do this, as you are defeating a lot of the advantages of a plenum style intake. For example you are only drawing air/fuel from one barrel per cylinder. Normally you can store a 'charge' of air/fuel in the plenum, fed by both barrels, and when the next cylinder-in-line opens the intake valve, that 'charge' from both barrels is ready to feed that one cylinder. With a divider, you will only get the 'charge' volume of one throttle plate. It would probably have better low end torque, but I suspect that from 4500 rpms>up it would be severely flow impaired. Unless you used a much larger carburetor. With the full-height divider the engine 'thinks' you have a much smaller carb on there than you actually do. This is essentially the theory of a single sidedraft carburetor as well.

That said, I have experimented with partial dividers, in conjunction with the 'tented' plenum floor. I basically extended the existing central runner dividers to the middle of the plenum, and at a height of approximately 1/2 the overall plenum height. It seemed to help the response without seriously affecting top end power. But, I also spent about 10 hours fitting and shaping the dividers to get them to distribute the fuel evenly. That was a lot of work on the flowbench and the grinding bench for little gain!

Bob

Paul said:

On a more serious note... By this, I presume you form up a sheet of Aluminum into the peak shape and height you desire... What works better a sharp or rounded peak? What thickness is the material you weld back in? And, how carefully do you blend in the peak's material with that of the floor and adjoining walls...

Thanks....

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Well, just like everything else in life, there's no set answer. I'm constantly evolving my intakes, so they are ever changing. Most recently, I make the 'tent' from two separate pieces of aluminum, and weld them at the peak. This leaves a blunted top edge, rather than a sharp edge. I make them from .080" material these days, although I've tried both .063" and .125" thick.

The .063" is a bit tougher to weld to the thicker intake material, while the .125" is easier to weld but tougher to cut and shape to fit. The .080" is a nice compromise.

I weld the material from the underside, so there is no blending inside the plenum at all really. When I used to pay to have someone weld the 'tents' in place, it was from the inside. But this was time consuming and very costly, although it made the inside look nicer. Performance wise? I have seen no difference.

My next intake project (for me, not for sale!) is a fully fabricated intake from scratch, with hammer-formed runners that are .063" thick, and with a fully hand-shaped plenum. I suspect it will weigh about 1/2 what a stock intake weighs, and I can finally remove the OEM tight curves of the stock intake, as well as enlarge the runners consistently. It will have to sit a bit higher than stock too, so it won't fit under a GT hood. I'm guessing about 12 hours of labor to actually fabricate it, but I've already started making my hardwood hammerforms for it.

Bob

This is again a bit off-tangent, but it shows my priorities regardless.:banghead:

No, I won't buy myself a new computer unless I have the cash for it. But, I did just order a new Garrett ball bearing GT2554 turbocharger on my credit card. I am going to build that Opel turbo 'kit' after all, and will prototype on my own car. Basically I will just build a manifold that fits the Manta/Ascona chassis, and will create an instruction sheet to build the rest of the system yourself. Opel owners are, uh, frugal, and wouldn't spend the necessary $3500-4000 up front to built a kit correctly, so if I supply the hardest part (the manifold) the rest of the components can be built up over time without breaking the bank. This project holds more value to me than buying a computer.

A GT chassis is too difficult to fit unless you do some cutting to the engine crossmember and relocate the engine mount. Not enough room to fit it efficiently, and without 'cooking' adjacent components. Not that it couldn't be done, but it wouldn't be 'bolt on'.

Bob