Porting intake

[BQS4]

Originally Posted by Tru-Craft Those turtle inserts are clever, they guide the air towards the runners and twist it a little. BQS4, I agree with "your" idea (twisted minds think alike), bolting in the insert is the easiest way. I just didn't want to make a steel plate to hold the manifold during welding, to keep it from warping the manifold. But I like the tent insert idea! Hopefully it stays bolted in place!!!!!!! Best insert design????? If its an insert it can be machined any shape we want?

Lyle;
You don't have to make a steel holding fixture to weld the intakes, just use a junk cylinder head. Just about everyone has one.

[Tru-Craft]

Originally Posted by Paul Lyle, What is the thickness of the spacer you made? 1/8, 1/4, 3/8? Also, shouldn't the spacer holes be radiused on the exit edge? Just a thought.

I made a 1/4 spacer. Don't know about the radius! Are we trying to keep the mixture together as long as possible, for better torque?
If not, why 2 holes in the spacer? just open up the plate to a large oval tapered towards the runners?
Better get Bob in on this!

[bq97]

Opening up the spacer into a single oval increases the volume of the intake manifold, not good for low end torque.

Brian

[Tru-Craft]

bq97 that makes sense! Everthing I have read says if the manifold and runners are smaller in volume that will increase air velocity and low speed power. If we open the runners up, we gain top end power, if the engine can turn fast enough to use the added air. On our 2-cycle go-kart race motors we open everything up to the max allowed, but we turn 14,000 to 15,000rpm!
OK, if we follow this thought, the insert I have should be better for low end power! Its mass is larger which equals less manifold volume.
Any thoughts?
Lyle
Hey if we make a rotating insert, hooked up to an electric DC servo motor, computer controlled..........variable intake volume

[BQS4]

Lyle;
If you go back and read Bob's comments on the spacers, he specifically states that the spacer has to have 2 oles, not one big oval, to work properly.

[Paul]

Lyle,

Sorry I was in a hurry when I made my last comment.

But my thought was this: ... you've just ported the manifold and blended the bottom edge of the carb mounting surface so that the air from the carb turns around the radius toward the runners...

Now with the Spacer... If the holes in the spacer are smaller than the hole in the intrance to the intake then the bottom edge of the holes in the spacer might need to be raidused to help the air flow begin its turn...

Now, if the holes in the spacer are the exact same size as the hole in the intake... (except for the web of the spacer).... then no radius is needed.....

Hope I didn't confuse things too much...

[Tru-Craft]

Paul, I bored the spacer and the manifold together so they match, no step at all. So like you said no radius is needed.
Carb is rebuilt and manifold is on!
The throttle linkage shaft on the 38 is shorter than the 32-36 something wrong here!? Working on that next.
Here is a picture of the manifold with spacer and insert.
Hopefully it will run!
Lyle

[hrcollinsjr]

Lyle,

Your manifold looks like it has a step under the primary side. Is that the early style restrictive manifold?

Harold

[RallyBob]

Yes, that is certainly an 'early' style intake, it is more restrictive in terms of airflow.

In regards to Paul's comments, it is best to retain two separate holes on the spacer, and even better results can be had by grinding a radius at the underside of the spacer at the center 'divider' between the two holes. Remember that with a DGAS especially, both barrels will be feeding each cylinder momentarily during the engine's operation, so putting a radius here helps the 'far' barrel feed each runner. So you nailed it right on the head Paul!

Bob

[Tru-Craft]

Yep, the early style! Good one to chop up and experiment with!
I put everything on tonight, manifold, rebuilt 38 carb.
Idle screws set at 1-1/2, cranked until fuel got to it and it fired right up
Adjusted the idle, a little tricky with two screws!
Took it out for a run to check the plugs, too lean!
Pulled the 142's and put in 150's, still looks a little lean but will drive it work and see how they look.
The 38 actually idles as good as the 32-36 did, kind of amazed.
It does feel quicker than the 32-36.
Will put the watch to it when I get the jets right!
By the way I removed the choke assembly. Shafts,butterfly's, everything! Don't need it here, and it should flow better!
Lyle

[asdasc]

I have a question that maybe only RallyBob can answer, but if others of you know, please help me out. I am grinding away at an intake manifold. All I have access to is the 1970 version that has the restricted plenum. According to Bob's article, the best one to port is from a 1973 or later 1.9 intake.

My plan was to use this as practice while I looked for an ideal doner.

This is so much work, I don't want to do it again!

So the question is, how much of a difference is there between a ported version of each - early versus later model of the intake? Is the difference significant between them, or is it just a 'little' better?

I am just using it for street use, and don't have a 'full race' motor, but it will have 2.0L pistons, etc. My whole goal is to improve 0-70MPH performance. I won't probabaly ever have the chance to run it for extended periods at high RPM, other than cruising on the highway.

Thanks,

[nobody]

Jeff try 1-800-447-2886 and get spooked, says he has 10 of them.

[turbocon86]

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?

http://www.ricdidonato.com/Intaketent.jpg

[Geek]

Is the effort worth the gain over the simple tent?

[asdasc]

TurboCon,

Yes, my imagination tells me that if it is blended into the existing manifold properly that this would be the best design. Please let us know how it turns out.

From what I understand, this tent makes a big difference in the torque when done properly.

[Washout]

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.

[hrcollinsjr]

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

[tekenaar]

Originally Posted by hrcollinsjr 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

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 . . .

[Paul]

Originally Posted by hrcollinsjr I haven’t settled on the valves yet.

Harold, I just finished a head for my daughter's 71 GT. I bought Manley RaceFlow valves... using the same part numbers Bob has listed in the past. The cost of the valves, from a Manley distributor, was $140.90, shipping included. These valves are the perfect addition to any Opel head when ported to Bob's street porting article.

[RallyBob]

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

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