1.75 carb inlet

Georgia200

Well-known member
So the area of a 1.75in circle is 2.4in, increase the circle to 2in and the area is 3.14in.

A 30% increase.

Is there enough meat to increase the carb hole on a C9 head from 1.75in to 2.0in and still have a reasonable chance of it sealing?

It seems like that would make a 2V carb adapter more worthwhile in cramming as much air into the engine as possible.
 
It's only an 1/8" of an inch at the edge of the hole. I've been thinking the same thing.
 
also we makem 'cone' or funnel shaped anyway which helps...
 
Are we pushing air into the engine or pulling the air in?

If we bored it an additional .125in that is still a 22% increase.

There is also some room between the mount holes and the opening to make the inlet oblong.

I will not know what carb I can use until the engine is in the car and I see how much room I have to the hood.

Im still looking for a set of 65/66 6 cyl engine frame mounts. Of all the 6s swapped to 8s, I would think someone has a set.
 
Howdy Georgia and All:

Which C9xx head casting are you using? I'm assuming one with a "M" suffix. If so, then "yes". Also note that the increase in area is a very positive effect when designing exhaust pipes.

To take full advantage of the larger diameter inlet hole spend some time tapering the bottom of the new holes sharp edges toward each end of the log. Tapering, or rounding the bottom edge of the inlet hole is worth doing to increase air flow. And yes, inlet air and fuel is drawn in by engine vacuum. We did some experimenting with "turtles" or "lumps" placed on the inside bottom of the log to direct flow to each end of the log. That wasn't very successful. It was an idea stolen from Chevy six head work.

We did inlet tapering both with the head on and off. To do it with the head on stuff oily rags into each end of the log to catch the grindings. Later we varified the positive effects of tapering the sharp edges on a dyno. Isolating to amount of improvement was difficult, but tapering did help vacuum drawn flow. The effect is similar to back-cutting the intake valves and blending and shaping intake ports.

Keep us updated on your progress and what you find.

Adios, David
 
Im trying to keep the induction simple and trouble free.

In my area, there are not many shops that will be anything other than a basic valve job on a log head.

Milling the log flat and brazing in additional metal is not going to happen around here unless its in my own garage.

So Im interested in how much I can increase the 1.75in carb hole, without going outside the machined carb mounting surface.

I like the Classic Inlines 2V carb adapter because of the insert. I have this fear that somehow an adapter mounting bolt ends up wedged in an intake valve. Sure, there is little chance of this happening, but stranger things do happen.

I had not really considered a 2V adapter, but the 1100 is so restrictive that I think a 2100 is a better carb for my 250 as long as I can get it to fit under the hood with a drop base aircleaner.
 
Howdy Back:

I can tell you that I put a 2100,1.14 on my 250 in my '65 Ranchero. I did a direct mount with a thinned phenolic spacer and it was very close for hood clearance. No adapter. Direct to a modified D8xx head. Used an air cleaner from an early 80s LTD with a V8.

Prior to that and since we did alot of experimenting with one barrels- 1100, 1101, Carter YF and RBS. All worked quite well. All with a curved Dura Spark II ignition. All better than Holley 1940 and 1946. The 1101 was a slam dunk easiest bolt-on and go. All others required adaption of fuel line and linkage. The Carter RBS was a close second and the shortest.

We built home-made engine mounts to get the engine to set as low and as far back as possible. That helped hood clearance.

What carbs do you have on hand to work with? What ignition are you using?

Adios, David
 
David'n Mike W sure have the experience!
"...The Carter RBS was a close second and the shortest...."
I'd just use the adjective "lowest" 4 shortest (along w/yer 1100/1101) it has a lill more cfm tho.
My YF is just great too -but- too hi'n less cfm.
(Like offered B4 - 6 or 7 "low hood' options" if interested, David's #8 post has many of them).
The DIY mounts'n towers R far'n away the best option but fab skills/equp R often limited.
U R NOT reinventin the wheel, many have gone B4 U...
 
Currently on my 200 I have a reman 1101. Its a MT carb on my 200/C4 but seems to perform well.

I also have a 1.08 2100 that needs a rebuild but is in nice shape.

My block is out of the tank, it cleaned up really nice, looks like a 030 overbore. Crank just needs polishing.

The shop should know by Friday how far down the pistons sit.

Once I get that info, I can figure out my pistons, rods, CR, cam specs and cfm requirement.

My current thought is that I will use a 2V adapter and run a 2100 if it will fit under the hood. I will save my 200 head which is also a C9-M casting in case I ever decide to try my hand at direct mounting a 2100.

My car is a 67 coupe.

I have a pair of 69 Mustang 250 frame mounts. They are useless without the insulators. The 69 insulators have an offset stud that attaches to the frame mounts. Without that offset insulator, the engine will sit about an inch closer to the firewall, in turn the tranny mount and driveshaft do not work.

My current plan is to find a set of 65/66 frame brackets. The 65/66 brackets are narrower than the 67 brackets, maybe enough to let the 250 slide down far enough to clear the hood.
 
"... on my 200 ..."
"...to let the 250 slide down..."
the 200 will havea 1 inch lower deck. I thought U hada 250.
David's mentioned several of the 6 or 7 'raise the hood' methods.

The direct mount is 1, I'm not sure what the adapter adds but if
1/4 to 1/2 inch I would need to eliminate on the bronk - its that tight.

I would not C the frame side 1/2 as useless. It can B 1/2 the solution.
The 'late Mav' frame side is almost identical & the engine side will fit a 250.
I wish to avoid custom/DIY for time element'n replaceability (frm the shelf) but
is something I may do in April. I think the late Mav is pretty close tho (avoid frnt chunk,
mate to dodge 5 speed, fit under the hood).
 
Howdy Back:

Georgia- what adapter are you talking about? A two barrel to one, or a two barrel plate to mount to a modified log? The two into one will add too much height.

What did you decide on enlarging the carb inlet hole?

The RBS was the stock carb on 250 engines starting in 1970 I believe- followed the 1101. FoMoCo chose it for shortness, linkage and vacuum signal. The Autolite 2100 is slightly shorter. By the way, the 2100 may be the all-time easiest carb ever to rebuild. both the 1101 and the RBS have 1.75" throttle bores. Both are rated at 210 cfm.

Keep it coming.

Adios, David
 
Still gathering info.

ive got three projects going on at once.

5 lug swap - Axle bearings go on tomorrow, then I will start assembly on the car.

Block - As soon as I know specs, I will order parts.

Head - Im only keeping the bare casting, everything else is being replaced. I will talk to my guy about milling the log, but I dont think he will do it. Maybe an RBS is the easy way to go for now.
 
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