Autolite 2100, what size venturi?

[jahearne]

About to buy an Autolite 2100 for my 250/AOD project. As you well know a good one isn't cheap and neither is time on a dyno, so what do you think I should start out with? and if you got one, what are you running? Here's the details: 250, 40 over 255 pistons, Classic Inline's 2V Performance conversion, 1.75" intake and 1.50" exhaust valves, approx. 9.3 to 1 compression, 277 hyd cam w/ 112 degrees lobe separation, headers, AOD with 3.50 Truetrac posi. It's going to be a daily driver with a lot of freeway time.

I'm thinking 1.14 venturi that are common on 289 because the 250 is modified. Mike suggets a 1.02 and thinks a 1.08 is too big yet alone a 1.14 and he forwarded some links, which I shared below. CFM calcutor suggest around 300 cfm @ 5000 rpm 80% efficiency 255 cu in. Subsitute 289 for 255, we get about 340 cfm.

http://www.4secondsflat.com/Carb_CFM_Calculator.html
http://falconperformance.sundog.net/compcalculator.asp
bore 3.72 (.040 over)
stroke 3.912
cc volume 66
head gasket .050
dished 4
80% @ 5000 rpm = 295 cfm

Food for thought ( Thanks Mike! ):
Read our tech article, "A Day at Pony Carbs"
http://classicinlines.com/PCdyno.asp
And on 2V Carb Swaps http://classicinlines.com/DynoSwap.asp and
http://classicinlines.com/Dyno3.asp
Part 1 & 2 viewtopic.php?t=52903
Part 3 & 4 viewtopic.php?t=54061
http://classicinlines.com/dyno3A.asp

Somthing I found:
"Now is a good time to understand carb flow ratings. 2 barrel carbs are rated at 3 inches of vacuum and 4 bbl carbs are rated at 1.5 inches. A 650 carb on a 358 cubic inch engine will seldom see 1.5 inches but a 350 carb on the same engine will frequently see 5 to 8 inches. At 7 inches of vacuum the 350 carb is really flowing about 430-440 cfm."
http://www.camcraft-cams.com/index.php? ... rrel-carbs

So, what do you all think? 1.02, 1.08, 1.14, 1.23 or Holley 350!?

 

[351 celi]

I love all my motorcraft/autolites! I currently run a 1.08 but it is on a 250 turbo. I previously ran it with a 1v adapter when it was NA and it had decent response, but lost some bottom end compared to the Carter RBS. The RBS, by the way, was a huge improvement over the YF. At first I had a 1.21 on the car NA, way too big, on a 1v adapter, I only had rockers, full ignition and full exhaust upgrades, not built like you are. I have another 1.21 on my bronco II V6, and to get steady a/f ratio across the RPM range, I had to block off the power valve (this was tuned with a wideband), so a 1.21 really is a lot of carb for our small displacement motors. I would suggest a 1.08 for improved bottom end, and they are much easier to source vs. a 1.14, but either sounds like a good choice for your set-up. Good luck, autolites are great!

 

[CZLN6]

Howdy John:

What a nice dillema. You're right. Dyno time is expensive and scarce. And what you would likely find is that one size does not fit all situations. I've run a 1.08 on my 250. Then tried a Holley 4412 @500cfm. I never got it tuned right. I needed a jet block with tuneable air bleeds and went on to a 1.14 instead, then a 1.33 (scarce), and next will try a 1.23. All Autolites seemed to have better throttle response than the Holley- probably due to the annular discharge ventri. The 1.08 and 1.14 were very comparable. The noticeable difference was that the 1.14 appeared richer at an idle and off idle, for slightly better throttle response. All of my observations were plug color and vacuum readings as well as driving. Both gave good mileage.

The Autolite 1.33 and the Holley were less crisp off the line, but definitely pulled stronger on the top end of the rpm range, 4,500 - 5,500. Both offered very low vacuum readings at highway cruise speeds and mileage suffered.

I'm about to sort out the 1.23 and hope for an Indian summer for a few month to get it done.

I'm running a 260 comp cam (pre CI) so I'm guessing your engine will be able to handle a higher rpm range than mine. In general-
*Bigger is better for top end- to a point.
*Earlier carbs seem to have a richer idle and cruise circuit, which seemed to be better for my engine. So I'd recommend a 1.14 from 1964 - '67, on 289s and 302s, or a 1.23 from a 1967 - 70 from a 351 or a 390 engine.
*VE changes with rpm. VE at idle will be as low as 60%. At peak HP/Torque, I'd guess your engines VE will be 90% or more. Ideally, you will need to find a carb that will work well at both the lower and higher VE for a street driven engine. I tend to favor the smaller side of that balancing act.
*Electric chokes from later engines are easily adapted to earlier hot air/water chokes and work much better. They also allow you to seal of the hot air intake which is a source for contaminants.

So, in theory a 1.01 or 1.02 would be ideal at idle and street speeds and would run out of breath as the rpms climb to 5,000 and beyond. A 1.23 would be slightly less crisp at lower VE, but capable of taking the engine strongly to 5,500 and beyond. Obviously, a 1.14 makes for a very decent compromise.

FYI- The "Ford Carburetor Guide" by Pony Carburetor is an excellent guide book. Holley has several good reference guide books as well. There is also a useful website, I can't recall the title. I'll get back with it.

Lastly, Autolites are relatively cheap and easy to find. They may be the world easiest carb to rebuild and to work on. All of mine are gi-mes or $5.00 swap meet picks. Some carb cleaner and a Motorcraft CT-499D (for '58 - '74) kit and all have worked well. I alway start with whatever jet came in the carb and assess from there. So, given that, using a 1.02 as per Mike's suggestion, for everyday use, and keeping a ready 1.23 for going to the races is very doable. Once you're setup for the Autolite changing to another is a breeze.

So, after all that, I'd suggest that you start with a 1.14 or a 1.23 and assess from there. (I'm saving the 1.33 and the Holley for Bonneville.) I'll be watching for what you choose and how it works for you so keep us posted.

So, that's my two cents, for what it's worth.

Adios, David

 

[jahearne]

Thanks 351 celi and especially you, Dave. That's great information. Some real world experience and Mike's dyno results are extremely helpful. Awesome, at first I had six to chose from now I'm down to two and I'll post my results as I go.

I'll look for a used or rebuilt 1.08 and 1.14 to start out with because I'm running an automatic. Mike suggests to start low, Dave a bit larger & 351 C right in the middle. If it was a T-5 & not an auto then I bump it up a notch with a 1.14 & 1.23 cause I like to rev manual trannies.

Can't help but wonder if a Pony Carb 1.02 or 1.08 would out perform a used 1.14 or 1.23.

 

[AzCoupe]

If you want to try a few different sizes, I'll let you borrow a couple carbs. I have two used carbs (1.01 & 1.02), and a couple rebuilt carbs (1.06 & 1.23). I might even have a used 350 laying around? Then all you'd need to do, is find the 1.08 and 1.14 for a dyno session. I'd even be willing to pitch in a few bucks for the dyno time, as it would make a great tech article. You could probably test five or six carbs in two to three hours, depending on how many pulls you needed for each carb (to get the jetting dialed in). You might hit the A/F ratio on the first pull, or it could take two or three pulls, hard to say.... just have a good variety of jets on hand. Most shops charge $100-150 for the first hour (minimum charge), then an extra $40-60 for each additional half hour.

The smaller carbs will give you better throttle response and drivability, more bottom end torque, higher manifold vacuum (smoother idle), and more velocity (which helps to overcome the different runner lengths on the log manifold). The bigger carbs will give you more horse power on the top end.

With your set-up the 1.01/1.02 would be good to about 4000 rpm, while the 1.08 would rev to roughly 5000 rpm before running out of air. Question is, how often to you rev over 4000 rpm's? Are you willing to give up a little throttle response, low end torque, drivability, and fuel economy, for a little more top end power?

While I'd really like to see the numbers from a dyno session, I'd be more interested in knowing how each carb performs on the road. After the dyno session, you could run each carb for a week or two, making note of the gas mileage, idle quality, drivability, and so on.....

BTW, here's the CFM ratings for the Autolite's.
1.01 = 240
1.02 = 245
1.08 = 287
1.14 = 300
1.21 = 351
1.23 = 356
1.33 = 424

 

[falcon1963]

jahearne from what i have seen at dyno tests, there is more than just changing main jets.

You may get the WOT ratio ok. but there is still other aspects of the air fuel concerning cruise & idle.

You need an experienced dyno operator to advise you.

 

[CZLN6]

Howdy Back John and All:

Wow!!!! Mike's offer is very generous. If you can do the Dyno testing I'd suggest that you focus on two, maybe three carbs. Do at least three WOT tests, for comparison and averaging, then three tests at a steady, cruising engine speed. Don't forget to refine ignition advance for each carb. Ideal advance settings will not be the same for all carbs. Mike's suggestion of driving each carb for a week or so will be valuable also. The carb that achieves the highest HP my not be the most fun to drive around with, especially with an AOD.

Note- Not all 1.08s are the same. For instance, 1.08s were used on 302 V8s from 1968 to '73, on engines equiped with Auto or Manual trans, and with a variety of rear-end gearing from vehicle line to models. So the internal tuning, mostly in the K cluster varies considerably. K clusters are usually marked, but I am not aware of any decipher for what the markings mean in terms of tuning. So one 1.08 may be just right, while another will perform differently, but not too bad. Earlier carbs, 1.01, 1.02, 1.14 and 1.23 will have a richer idle and transition circuit as compared to later 1.08 and 1.21s.

FYI- Earlier carbs with hot air/water chokes can be upgraded to later chokes with electric heating elements. The later are better in that the carb is no longer drawing dirty air and contaminents into the carb. Be sure to plug the hot air vacuum draw, or you'll have a big vacuum leak.

Pre-64 2100s will frequently be fitted with Holley main jets making tuning a little easier. Holley jets are volume referenced, while Autolite jets are more like a part number. When changing jets, if you have to go up or down more than two numbers I'd suggest that you look for another carb. Most likely a change greater than two jets sizes will have exceeded the range of internal limits and adjustibility. I always start with the standard settings, based on the carb tag, if available, and vary from that. If the tag is missing look at the foot of the carb, below the carb size casting. It will usually be stamped with year and vehicle line. Tags can be deciphered from Ford Service manuals or from the Pony Carburetor Guide. The Motorcraft rebuild kit CT-499D also list a wide range of applications.

Easy tuning of a 2100 is limited to idle speed, low speed idle screws, accelerator pump timing and amount, and main jet. Float level can vary performance also. FYI- the earlier carbs- 1.14 and 1.23 seem to have a richer idle circuit. The air screws offer some adjustibility, and then the balance is limited to internal oriface restrictions and air bleeds. These are not easy to alter or user friendly. There is also internal channel restrictions and air bleeds for high speed function. In most cases the 2100s we're talking about hear will be within an adjustible range for your purposes. The settings for Mike's carbs in AZ will likely be too lean for the San Fransisco air.

Mike's suggestion about assessing your driving habits as a factor in choosing the "best" carb is right on. The Dolly Parton theory of capacity- you know, "Bigger is better" is not always true with carb and cam selection. Sometimes enough is just right.

I hope you take the time and make the investment in your selection, and share your process and results with us.

Whoa!! I do go on. I hope I'm helping.

Adios, David

 

[CZLN6]

Howdy Back John:

I forgot to mention the power valve (PV) as a tuneable feature of the 2100. The Autolite PV are color coded and are based on elevation- below 5,000 ft.= green and red. With yellow and uncolored for above. Holley power valves can be used in the 2100s and are stamped in a much wider range and easily available. The marked vacuum level is not very accurate, but better than Autolite. Chosing which power valve is more are than science. The PV is opened when the vacuum signal drops below a certian point. It is either open or closed, based on vacuum load. To get you in the ball park, start with what you've got, then drive with a vacuum guage hooked up. Take note of when vacuum drops and how far. You probably don't want the PV to open at light throttle pressure/light acceleration. You do want it to open at spirited acceleration (WOT). Once your determined the lowest vacuum readig in normal driving, choose a PV with one number lower for best economy. So if your daily driving drops vacuum to the 6 to 7 lb range choose a Holley PV with a reading of 4.5.

For Dyno testing the PV should be open at WOT. It should be closed a cruise testing.

Keep us posted.

Adios, David

 

[jahearne]

Thanks agian for the advice. And Mike thank you! I will take you up on your offer. I've started my Autolite collection and have a 1.14 on the way. When the time comes, I'll borrow what I don't have and donate to your collection what ever I don't use, so that others may benefit.

It's a good question... I won't be doing over 4000 rpm hardly at all with a 5000/5500 pull every once in a while when passing\merging, never past 6. A carb topping out a 5000 would be ideal for the street.

Will look for a shop with a dyno but first got to find a machine shop with a torque plate. So far I'm 0 for 3.

I drive 70 miles round trip to work and a good 100 to the marina on weekends, a lot of freeway with daily drive across San Francisco stop n go. That will provide plenty of road testing in a decent amount of time... once I get the bottom rebuilt, throttle linkage figured out, AOD TV hooked up (hope that used tranny is in good shape) & off to a good start so far.

 

[jahearne]

Alright! I finally got her running and now the fun begins.

Recap: 250 .040 over, 255 pistons, 9.3 CR, 277/277* 112* cam. 2V conversion, large valves, basic port job. Using a '68 Autolite 1.08 with 48 jets. Had one heck of time with the float level, but got that one figured out. Got to get an oxygen bung installed. But she roadtested okay. AOD transmission shifts well. A bit of hesitation to WOT when rolling 20 mph, but not bad. No hesitation off the line. Some surging under light cruising, so it might be a little lean. Spark plugs a white/grey with a spot of light brown on the cone, Autolite 46 gapped 0.035". Still using points with Blaster coil set to 12* idle 900 rpm in park, 650/700 in drive; idle is rough. Set idle mixture with vacuum gauge and verified with Gunson Colortune. Unfortunately, still using stock converter in the tranny so, city driving is going to suck for a while. And CI header into single 2 1/4" pipe out the back with flowmaster - wow, it roars and it's louder than my last one with a glass pack! but sounds awesome! 3:50 TrueTrak and it does 80 mph no sweat.

Work out a couple bugs and save up for some dyno time!

 

[bubba22349]

Running down the road I think your right on about going richer. From the plug color looks like you need to go up a couple jet sizes

 

[jahearne]

Cool, I have a set of 50's. I'll try those.

Thanks,

 

[bubba22349]

 

[CZLN6]

Howdy John and all:

While the top is off for changing to the #50 main jets, check to verify that the float level is on the high side of what ever the spec are. You might also increase the initial advance another 2 degrees. With you cam you should be able to safely get away with more timing.

Oh ya, and enjoy!!!!

Adios, David

 

[jahearne]

Sounds good. Thanks for the suggestions!

Currently I got the vacuum advance plugged into the carburetor base. I am thinking I should have connected to the manifold port. My vacuum gauge isn't very accurate anymore and have yet to find a local Snap-on tool dealer to repair it. It's a non-SCV distributor. Any thoughts on using that port off the carb base?

 

[CZLN6]

Howdy:

I'd start with a ported vacuum source and add the initial as needed. When you start with a manifold source you are likely to get too much advance at idle and at cruize (high vacuum) and not enough when you want to accelerate. Your cam will have you down some on vacuum anyway so start with a ported source and test from there.

Adios, David

 

[bubba22349]

I will second the ported vacuum to me is the better way for a street driven car. It's not that you can't make it work good with the manifold vac. or even make a locked out one (good for race only cars), just be prepared for more tuning to get it right. It all depends on the use you intend.

 

[jahearne]

Got it. Stay with ported vacuum, bump up the initial timing from 12 to 14 & a little extra fuel in the bowl. Intention is a daily driver with a lot of freeway miles. I'll be able to drive to work in a day or two for its first day out in the real world.

 

[jahearne]

I have yet to make down to the muffler shop for a O2 sensor bung, but I changed the jets to 50 and now the spark plugs are a reddish brown. She's great on the freeway but a chore to drive in the city with a stock AOD made for a Lincoln. I moved the distributor vacuum to the manifold port instead off the carburetor port and running a bit cooler. Prior to moving the vacuum, upon turning it off in the driveway, it backfired so loud it nearly shattered our windows; shattered my ear drums. And the headers were glowing orange and now I got an exhaust leak to fix @ the header flange. Now when I turn it off, it wants to backfire - you can hear it build it in the pipes but no pop just sounds like one big fart in the bathtub; don't ask me how I know. The only hesitation I got was off the line as the engine started to bog in drive waiting for the light to turn green. If it does stall it's hard to start, acts like it's flooded, which it could be. It will only start after a stall by cranking it WOT. I think it's still running hot. The headers are wrapped but no heat shield for the carb or phenolic spacer - not enough room. Still running points. Need gauges; '67 only has idiot lights.

 

[1961 Futura]

Howdy:

I'd start with a ported vacuum source and add the initial as needed. When you start with a manifold source you are likely to get too much advance at idle and at cruize (high vacuum) and not enough when you want to accelerate. Your cam will have you down some on vacuum anyway so start with a ported source and test from there.

Adios, David

Could you explain why being hooked to manifold vacuum would result in insufficient advance during acceleration? I realize vacuum signal drops under load, but does manifold vacuum somehow drop more than ported vacuum? I thought the only difference between ported vacuum signal and manifold vacuum signal was that because ported vacuum was above the throttle plate, there was no vacuum signal at idle.

I've been researching this topic all morning, and most sources are saying to abandon ported vacuum as a '70s emissions gimmick and go for manifold vacuum. But, those are also mostly generic sources aimed at the GM crowd.

Thanks for any help!

-Dave