is my carb too small??

[Anonymous]

is it possible that my carb is too small for my engine??? ive got a 200ci 3spd manual with hooker header, msd 2,000 miles on re-build all the rest is stock. however when i push on the gass from a stop, and try to go slow it shakes violently. and when i try to let her rip its like the engine makes alot of noise for not really going that fast but then catches up with its self. i know it sounds weird but its like if you were to make a movie and the sound was always ahead of the video. the other thing is that at about 2100-3200 rpms in second gear it boggs down. now is this because it is too small.....oh wait i didnt tell you what the carb was. it is a holly 1940 it came with the car. but anyways i just put it on with no equipment (rpm, dwell) gages so the fuel/air mixture is probably wrong and i will fix it. but do you think it needs to be tuned or is it too small cause i heard they only move like 140 cfms.

 

[Anonymous]

Sounds more like tranz clutch problems but I don't know shiz.

What I do know is - is that that carb doesn't work properly with the stock points style distributor. Either get rid of the carb and go back to an autolite/motorcraft (dumb idea) or get rid of the distributor and replace it with an electronic one - Duraspark II.

Either way though, yes that carb is probably too small for the engine. If you don't want a 2bbl then try a Carter YF or Carter RBS.

 

[Anonymous]

size does matter...

but make sure they can take it. cant shove too much in there. Might end up hurting things

 

[Anonymous]

What I do know is - is that that carb doesn't work properly with the stock points style distributor.

Actually, it does work properly with that distributor. He said that he has the Holley 1940, which was offered as a replacement carb. (at that time) for the 1100. Don't confuse it with the Holley 1946, which was used almost 20 years later on Fairmonts in conjunction with the Duraspark II.

 

[Anonymous]

Oh, I c, well I'd still go with the Duraspark II and some more carb, maybe the 1946 as I've heard its not too bad or something by Carter, or a 2 bbl of some sort.

 

[67 Falcon]

Install the Duraspark and a Carter YF from a 250 or a Holley 350 CFM 2 bbl. Rusell

 

[Anonymous]

Hi P66,

I agree with kcstanger, what you discribe sounds very much like a bad clutch. Have it checked B4 you do anything else.

As for the carb, the air flow required by any piston engine is related to the amount of air the the engine requires, i.e., internal cumbustion engines are air pumps. The air requirement is calculated as follows:

((CID x rpm/2) / 1728) x VE

In the case of our 200ci I6's, the factory NET HP rating is 91 @ 4000rpm. So, if the engine were 100% efficient (a VE of 100% - not a chance) the cfm requirement would be 231. While I don't mean to offend you (I have one also), the stock log head is very inefficient. My analysis says 75% is the correct number. So, 231 x 75% = 174cfm. Bottom line, you need a carb with a minimun flow of 174cfm on your car. The stock 1940 flows approx. 180cfm. Marginal at best. Since you have a header and upgraded ignition you have probably improved the efficiency of you pump enough to be too much for the 1940. Having said that, do not rush to the bigger is better side (the dark side in my opinion). Both carb volume and velocity need be considered.

Simply stated, HP requires intake volume (high rpm, big flow, - head and cam to match). Torque rsponds better to intake velocity. As produced, our cars are built for low end torque. Why? As an old saying goes ...you race HP, but you drive torque... So, when you are ready for your carb upgrade I think it hard to beat a progressive 2V like the Holley 5200 or the Weber 32/36 on a street car. The progressive design helps to keep velocity up as it runs on one venturi until the rpms come up enough to handle the extra volume. The 5200 flows 270 cfm (will support 5000 rpm @ 90% VE - probably never see 90%) and has a total venturi volume of 1.77" vs. the carb bore volume of 1.77 for the stock 1.5" head (through 1969),and 2.40 for the stock 1.75" head (1969 "M" and up). The 32/36 Weber flows 320 cfm and has total venturi volume of 2.9 sq. in. So, I wouldn't use this one on the early head. Actually, I have a hard time justifying the 320 cfm on a car that is used on the street. On the other hand, if you are building a car that is going to be expected to come out of the hole at 3000 rpm and shift at 6000, volmue will be king. A 500cfm Holley 2300 would probably work well on such a car, but only if prepared like Mustang Gezeers.

No doubt more than you ever wanted, or cared, to know. But, I have been seeing a lot of bigger is better mind set on the forum lately. Thought I'd throw in my 2 cents.

Steve

 

[Anonymous]

hey steve how much torque and HP do you think your getting out of your car???

 

[Anonymous]

Hi P66,

Below is a copy of a response I posted to a HP discussion a while back. Although I have not dyno'ed my car as yet (soon), I think the following analysis is defendable. As for torque, I use 1972 numbers as a base because they are developed on the same criteria as todays numbers, apples-to-apples if you will. So, the stock 200 I6 base is 91HP @ 4000 and 154 @ 1600 (very flat curve by the way).

__________________________________________________________

Hi all,

For the record, a stock 1967 200 I6 Mustang was dyno'ed at 67 rear wheel HP by AK Miller a number of years ago as a baseline for mods developed by AK. As noted earlier, Ford stated the net HP of this engine as 91 @ 4000rpm. This appears to be support the common view that the drive train will absorb 25hp. Mustangaroo's 105 rear wheel hp was obtained with a Holley 5200, header, upgraded ignition, 1.6 adjustable rockers AND a 2V head. Add the 25 back and you have 130 at the flywheel (net HP) without a cam. How much of this increase you can allocate to the head is yet to be determined. Someone will have to dyno a car with a 5200, header, ignition, and 1.6 rockers before the value of the 2V head can be stated. However, if you want a guess, Clifford has advertised for years that their carb, header, and ignition upgrade is worth 25% at the rear wheels. I can state from personal experience that the 1.6 rockers make a difference. So, for the sake of discussion, let's say 30% total. 67 x 130% = 87. Add back the 25HP and you have 112 at the flywheel (net HP). So what is my point, I don't think it rational to assume that a 2V will add 35HP to a stock car. 18 to 20 is a more reasonable expectation. However, we will not know until a vehicle with the appropriate mods is dyno'ed.

Torque vs HP. I agree. The way I heard it was ...you race HP, but you drive torque... I like a strong bottom end. Torque has been high on my list of priorities with all of my mods. Second is weight control. Lite weight and lots of torque is fun to drive. It leaps across wide intersection in a single bound. Sorry, couldn't help myself.

My 2 cents - Steve

 

[Anonymous]

Small error in above info. Should learn not to quote numbers from memory. The 1972 200 I6 is rated as 91 HP @ 4000and 154#/ft @ 2200. While I really don't have any idea what my corrent torque curve is, it is much stronger than stock.

Steve