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Single 44 idf weber on chevy inline six

General engine tech -- Drag Racing to Circle Track

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modok
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Re: Single 44 idf weber on chevy inline six

Post by modok » Sat Nov 30, 2019 3:30 am

Yes you can get 28mm vents, from empi
But 28 vs 36 that's huge difference.
like 160hp VS 260hp
Do you have a ballpark idea what kind of HP it's supposed to make?

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Re: Single 44 idf weber on chevy inline six

Post by enigma57 » Sat Nov 30, 2019 3:50 am

Adriaan, as you have already there your 44 IDF with 36mm chokes and are working up a manifold for it...... I have an idea which should help with fuel distribution. Not easy to draw using keyboard and my computer skills are limited, but I will see if I can get the concept across.

Background...... In the early 1950s, a modified 2-stage intake was hand built for the Hudson 308 inline 6 engine. This involved 2 log manifolds run parallel one to the other and joined so that a primary set of carburettors could be used for low to midrange (the log positioned inboard or closest to the head) and a set of secondary carburettors were positioned on the outboard log and brought in on progressive linkage. The principle (and function) was the same as that of a modern dual plane 4bbl intake except that it was done on an inline 6 with single throat carburettors.

So here is my idea...... Either create or use a modified OEM or aftermarket manifold for the inboard log on your Chevy inline 6, but unlike the modified Hudson intake...... With no carburettors on this part. I have attempted to depict it below (the trident shaped upper piece being close to the head and having 3 siamesed ports connecting to the headports). This piece will serve only as a mechanism to direct air/fuel mixture into the headports, but will have no carburettors mounted directly on it.

Now below it is the outboard U-shaped piece (shorter log) having 2 connections joining it to the longer inboard log. The points of connection to the inboard log being at the midpoints between the siamesed paired ports at each end and the siamesed paired ports in the middle. Position your twin throat carb in the center of this outboard log where I have placed the two o's. This should allow your single 44 IDF twin throat carb with 36mm chokes to distribute fuel more evenly to all 3 sets of siamesed headports. Similar architecture to the modified Hudson intakes only you will have (and need) only the primary carb function......

(please disregard dots (periods)...... I am attempting to use them to align other symbols)

I___I___I
..I_oo_I

FWIW, I did the math and if you take the cross sectional area of a 44mm diameter circle and subtract the area of the 8mm X 44mm throttle shaft, this leaves you with equivalent cross section equal to that of a 38.57mm diameter circle. So if you are building all or only the outboard log from scratch...... Cross section (inner diameter) of your intake logs need be no larger than 38.57mm. But...... If you have vertical clearance underhood...... Raise the flange where you will mount the base of your carburettor so that you have at least 2 inches (50.8mm) from surface carb base will attach down to bottom of your log or horizontal cylinder below. And of course, if you can use mandrel bends for turns and flare the 2 pieces connecting outboad log to inboard log,,,,,, That will help flow as well......

(please disregard dots (periods)...... I am attempting to use them to align other symbols)

I............I............I
\________/\________/
...V_____00____V

Sorry I cannot use keyboard to draw very well, but I hope this description makes sense.

Image

Here is an Offenhauser dual carb intake on a Chevy inline 6. Essentially, you would be doing the same thing only you would make a shorter outboard piece to mount your IDF carb and connect its ends to the sides of the inboard piece where the Offy intake positions the 2 single barrel carbs.

Of course, provide a heated plenum floor for the outboard piece. This will help atomization and drivability noticeably. If you make your outboard piece from tubing, just weld a smaller piece of 3/4 inch OD tubing to the bottom of it (running lengthwise) and bring heater hoses to each end to allow engine coolant to heat plenum.

Best regards,

Harry

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Re: Single 44 idf weber on chevy inline six

Post by chevyfreak » Sat Nov 30, 2019 4:51 am

modok wrote:
Sat Nov 30, 2019 3:30 am
Yes you can get 28mm vents, from empi
But 28 vs 36 that's huge difference.
like 160hp VS 260hp
Do you have a ballpark idea what kind of HP it's supposed to make?
Not really. Didnt intend for it to be max hp. Just wanted to to a big bore inline six. But guessing from a stock 150hp from the 250 maybe with what i did in here by 185 to 195hp range.
Actually wanted to take the 230 crank with 3.25 stroke, but 302 chevy pistons were way beyond the budget. So took the 250 crank and went 308 holden pistons, had them anyway, just took off 020 from the tops so it sits flush with the deck.
Was a budget build so getting everything done and some parts took me a year, went along as they money were availible. Didnt do it with all the math involved. More the old skool way, using what you have to build a weird creation.
the guy that did the cam went on details i gave him on the motor, he was helpfull in regards to cam size, there im happy. Just playing with different carb setups to see what works for the engine.
But with bigger cubes i suspect the 38dgv (27mm fixed chokes) cant keep up. On the 230 it's a wonderfull setup. On a stock 250 its good as well but change to a build setup and its on the limit.
Hence the idf, easier to get the correct setup as the chokes is changeable.

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Re: Single 44 idf weber on chevy inline six

Post by chevyfreak » Sat Nov 30, 2019 5:09 am

Harry i see what you mean. Sadly i have the problem with space to the side, cant even fit dcoe sidedrafts. Same situation as what you got but less space.
Reason i went idf , design basically same as dcoe just in downdraft form.
With building an intake i can however move the carb a bit away from the engine, so middel runner a bit longer. Maybe someting weird like a divider inside to direct it so it goes to space between the port spacing similar to your drawing
I did look into going 2 x 1bbls but getting 2 used monojets thats the same is a nightmare and even then in building them up , gaskets i can get at the carb shop but needles and jets not readilly availible. And about 80% of them i have seen the base were cracket due to over tightning.
2 new units (chinese copies) is more than double from what the idf costed me. They work quite good as i have one on my 230. No issues there only the buying part and then still the intake for it. Sadly no used intakes around so its either importing a new intake or building one.

Thanks for your input.
Regards.
Adriaan.
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Re: Single 44 idf weber on chevy inline six

Post by modok » Sat Nov 30, 2019 5:35 am

perhaps 32mm would be a good size.

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Re: Single 44 idf weber on chevy inline six

Post by chevyfreak » Sat Nov 30, 2019 6:13 am

modok wrote:
Sat Nov 30, 2019 5:35 am
perhaps 32mm would be a good size.
Likewise thinking, had that idea as well. Will check on that later.
That 40dfa has 28mm venturi where the 38dgv has 27mm.
The 40 carb were more responsive above 3000rpm.
So i think the 32mm venturi could be a workable size given my foundings with the 38 and 40 carbs.
One of those cases where it comes to seeing what the engine wants.
With harry's help in jet sizing i have a ballpark to begin off.
Luckily i did get a mini jet assortment kit so at least a couple of sizes for mains and air correctors. And some idle jets as well.
But will do some checking on venturi sizes in meantime.

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Re: Single 44 idf weber on chevy inline six

Post by enigma57 » Sat Nov 30, 2019 6:24 am

chevyfreak wrote:
Sat Nov 30, 2019 5:09 am
...... With building an intake i can however move the carb a bit away from the engine, so middel runner a bit longer. Maybe someting weird like a divider inside to direct it so it goes to space between the port spacing similar to your drawing......
That may be a good way to do it, Adriaan. May I ask what sort of vehicle you will put this engine into and how much vertical hood clearance do you have? If its an older vehicle with narrow side clearance, but lots of space above the engine and you are building your intake from mild steel plate and tubing......

Buy 3 J-bends (180 degree bends). 1 for each siamesed pair of runners. Bring middle runner over rocker cover and allow 1/4 inch clearance between bottom of tube and top of rocker cover. Do the same for the front and rear runners, but add a small amount of tubing in center of 180 degree bends so that you can roll (lay) both end runner tubes over towards the center runner and have all 3 intersect just to the drivers side of rocker cover (I am assuming RHD car as you are in South Africa?). Build small plenum box to join all 3 runners and mount your carburettor to it. If hood clearance is an issue, you can change from IDF downdraught to DCOE sidedraught. And as before, heat bottom of plenum using engine coolant plumbed through tube welded to bottom of plenum.

Image

https://www.holley.com/products/exhaust ... rel_bends/

Just a thought,

Harry

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Re: Single 44 idf weber on chevy inline six

Post by naukkis79 » Sat Nov 30, 2019 6:36 am

Single two-barrel carb with 36mm venturis is still awfully small carb for 250cid engine. And using IDF for plenum installation isn't beneficial, even Quadrajet would be huge improvement.

Even BMW and Mercedes used Quadrajet for their six-cylinder engines.

Using IDF or some other non-staged carb is pretty much same as using single-barrel carb - staged two barrel is huge improvement for tuning possibilities.

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Re: Single 44 idf weber on chevy inline six

Post by chevyfreak » Sat Nov 30, 2019 7:43 am

naukkis79 wrote:
Sat Nov 30, 2019 6:36 am
Single two-barrel carb with 36mm venturis is still awfully small carb for 250cid engine. And using IDF for plenum installation isn't beneficial, even Quadrajet would be huge improvement.

Even BMW and Mercedes used Quadrajet for their six-cylinder engines.

Using IDF or some other non-staged carb is pretty much same as using single-barrel carb - staged two barrel is huge improvement for tuning possibilities.
Idf on plenum intake not ideal but is possible. Grant somewhere there will be compromises but at least its bigger and more tuneable than the 38 or 40 2bbls i tried currently.
I did try a qjet. Even with some tuning im not getting it right. Idling is okay and full throttle its ok but off idle it goes mega rich. So cruising its not ideal, Played with jets and needles but need to get a weaker spring and some other size jets and needles. Not a stock cam so even my weakest spring on power piston is too much , lifts almost directly when opening throttle.
Will look at that later on. Maybe on one of my other engines,
As for the mercs , bmw and opel they used a solex 4a which looks like a qjet but is a tad smaller. I had one. Worst carb i ever had.

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Re: Single 44 idf weber on chevy inline six

Post by Truckedup » Sat Nov 30, 2019 7:45 am

Last inline I built about 10 years ago was a 261 Chevy (larger truck version of the 235)...A mild cam, Ross flat top pistons with tight quench,9-1 compression, home made tube headers and a Rochester 2GC on a modified stock intake with water heat...This was a large base carb off a 71 Chevy 350 truck, I think they are about 325 CFM..Had to drill out the low speed jet to .048 and increase the main jet a few sizes. I t ran very well with good throttle response.I believe it had about 170 HP at 4500 rpm. On a motorcycle, a 36 MM slide valve carb will support about 50 or so HP...
Motorcycle land speed racing... wearing animal hides and clinging to vibrating oily machines propelled by fire

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Re: Single 44 idf weber on chevy inline six

Post by chevyfreak » Sat Nov 30, 2019 8:02 am

enigma57 wrote:
Sat Nov 30, 2019 6:24 am
chevyfreak wrote:
Sat Nov 30, 2019 5:09 am
...... With building an intake i can however move the carb a bit away from the engine, so middel runner a bit longer. Maybe someting weird like a divider inside to direct it so it goes to space between the port spacing similar to your drawing......
That may be a good way to do it, Adriaan. May I ask what sort of vehicle you will put this engine into and how much vertical hood clearance do you have? If its an older vehicle with narrow side clearance, but lots of space above the engine and you are building your intake from mild steel plate and tubing......

Buy 3 J-bends (180 degree bends). 1 for each siamesed pair of runners. Bring middle runner over rocker cover and allow 1/4 inch clearance between bottom of tube and top of rocker cover. Do the same for the front and rear runners, but add a small amount of tubing in center of 180 degree bends so that you can roll (lay) both end runner tubes over towards the center runner and have all 3 intersect just to the drivers side of rocker cover (I am assuming RHD car as you are in South Africa?). Build small plenum box to join all 3 runners and mount your carburettor to it. If hood clearance is an issue, you can change from IDF downdraught to DCOE sidedraught. And as before, heat bottom of plenum using engine coolant plumbed through tube welded to bottom of plenum.

Image

https://www.holley.com/products/exhaust ... rel_bends/

Just a thought,

Harry
Its in an opel senator a2. Yes rhd, but with mcpherson strutt towers and aircon unit not much space for dcoe setup. Holden used the same sort of body with some changes as a commodore vk.
Low hood line. Had a qjet on with homebuild intake so carb is sideway and blades opening away from engine and biggest airfilter i can get in is 10 inch. 12 inch if i space carb and aircleaner but then i must cut the hood a bit more.
So running 3 dcoe over valve cover will have front carb above hood line and center one about halfway. But have space for the downdrafts. center of intake. Even 2 off them spaced correctly.There were 2 vents in the hood so one side will get a scoop. The vent is broken. Thats where i have space to either lift the carb or run 2 if i want, can get 2 carbs on at least.
Had another idea to go 2 dgv carbs but before i get there i want to try the idf at least and see.

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Re: Single 44 idf weber on chevy inline six

Post by chevyfreak » Sat Nov 30, 2019 8:09 am

Truckedup wrote:
Sat Nov 30, 2019 7:45 am
Last inline I built about 10 years ago was a 261 Chevy (larger truck version of the 235)...A mild cam, Ross flat top pistons with tight quench,9-1 compression, home made tube headers and a Rochester 2GC on a modified stock intake with water heat...This was a large base carb off a 71 Chevy 350 truck, I think they are about 325 CFM..Had to drill out the low speed jet to .048 and increase the main jet a few sizes. I t ran very well with good throttle response.I believe it had about 170 HP at 4500 rpm. On a motorcycle, a 36 MM slide valve carb will support about 50 or so HP...
I have a large 2jet here. Came off a 400. Needs a major clean up and a rebuild kit. And shaft needs to be rebushed. Can always try that later on if need be.

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Re: Single 44 idf weber on chevy inline six

Post by enigma57 » Sat Nov 30, 2019 5:20 pm

:D Wish you weren't so far from here (Texas). I've got a few goodies you could play with as far as carbs and intakes for that engine. Also have a new hecho en Mexico cast-iron exhaust manifold for 292 heavy duty truck and bus with single 2-1/2" outlet. In theory, a single 2-1/2" OD exhaust constructed of tubing having 16 gauge wall thickness will support 200 HP without power loss if your muffler will flow 2.2 CFM (or more) per HP generated (measured at flywheel).

More if need be but beyond that point, you will begin to experience back pressure beginning to build incrementally, resulting in diminishing returns as power level and RPMs exceed appreciably beyond that point. Of course, you could always braze or weld a 2nd 2-1/2" outlet to such a manifold. I have done that before using a gutted big block Chevy heat riser having same 3-bolt flange and bevel for donut gasket as this manifold has. These cast-iron manifolds weigh quite a bit, though. Would cost a fortune to ship something that heavy to S. Africa.

FWIW...... If you bring dual 2-1/2" exhaust pipes together and join them 15" - 18" downstream of exhaust head pipe connection...... A single 3" OD system if built to same parameters as discussed with single 2-1/2" will in theory, support 338 HP priour to back pressure beginning to build as discussed earlier.

BTW...... If you are considering a store bought intake for your 44 IDF...... AussieSpeed make a beautiful manifold base for these engines. Its intended to be used with interchangeable tops (either a dual carb top or a supercharger base). However, you could take one of these bases and add a 3/8' thick machined aluminum top plate of your own to fit your IDF carb to this intake......

Image

http://www.aussiespeedshop.com/product/ ... rrency=USD

Just add an engine coolant tube under plenum to warm plenum floor for better atomization and enhanced drivability and you are good to go.

Best regards,

Harry

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Re: Single 44 idf weber on chevy inline six

Post by modok » Sat Nov 30, 2019 5:28 pm

What direction the throttles open can have a drastic impact on fuel distribution and wet flow.
I would guess having the LOW hanging end of the throttles toward the outside would be preferable for distribution, but worse for wet flow.
At least.....build it so you can try both ways.

The 38/38 the throttles open toward eachother, maybe you don't think much of it but it makes a difference.

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Re: Single 44 idf weber on chevy inline six

Post by enigma57 » Sat Nov 30, 2019 11:19 pm

:D Couldn't agree more, modok! A pair of correctly positioned and oriented 38 DGAS carbs would be very interesting on an AussieSpeed intake. Or as you say, a single IDF with low side of throttle blades positioned outboard. Possibly add a directional vane in plenum to help with fuel distribution?

Best regards,

Harry

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