What is the best carb for me?

[mikepmcs]

one box came with the msd today, so i'm just drinkin beer and mocking it up.  you said you ran your box by the can? are you talking right next to the battery then on the core support.
ordered the comp wires yesterday as well cause i just noticed my brand new accel's have little razor blade cuts all over them,     can't even imagined how that happened, they are brand new for pete's sake.  i did have my hood open all day at the last car show but i can't think anyone would do that here in maine.
oh well, now i got the right stuff and am ready to wqire it up.  i have no points so i'm guessing i will be running the purple and green wire setup.
now i just need to figure out what to disconnect??? The red wire on the new msd box if i read the instructions right, says i can use the existing + side wire on the old coil to tap that power, is that right??
ok well here's some pics of my setup  in the house and i'm gonna try and take pics as i go.  before and after stuff so in the future we can reference that and if i have any lessons learned sort of thing.

[dodge freak]

First I have Mut of a Mopar, its in really nice shape but its a St Regis-you might have seen them on the A-Team taxi cab wars or T J Hooker anyways I ripped everything out, lean burn, vapor canister, etc. That does take some room, I put my where the vapor can was, it was right where the battery is but the other side, it can go even in the trunk but its more work. MSD saids to wire the heavy positive and negative Right to the battery. Thats what I did, use 12 gauge wire or 10 if its a long ways. Fine a 12 volt lead that is 12 volts only when the key is on the run postion that goes to ING. The coil leads go to the top 2 C+ and C- with the red positive lead going to C+ and the black negative lead going to C- . The pick up wires from the dist go to M+ and M- what I did was to take a old pick up coil and snip the lead off 5 " from the plug it go either way on to the dist, this way you don't have to cut yours and its nice if you need to pull the dist. there is a male and a female post on that rubber boot I call the post thats bare metal male and the one in the boot thats in the rubber female . Hope you follow me-I am using 2 boots 1 coming out of the dist and the 2nd is the one I snip off my old pick up coil . The male post coming out of the dist is + and goes to M+ the female post thats in the rubber part of the boot goes to M- . This is the only "hard" part, like I said I messed up the first time and had them backwards so if they are not right the motor will run poor and just switch them- no harm- but I just look at mine and thats how it is. Thats is it, to mount it I got a 15" by 3/4" board of wood and screw the wood down with long sheet metal screws, I then screw the box to the wood with wood screw and used rubber washers under the box-no mounts too hard to use but it looks like you have a nice area to work so its up to you, I drive hard and its been fine that way. ON the coil I used 2 small prices of wood like 1" by 5" and screw it to the sheet metal by the dist, I then used wood screws again and screw the coil to the wood.

I hope this helps- you spent good money so I don't mind helping you. This is good-get that box running and then put the carb on. This way if someting is wrong you know its the box and not the carb.

[mikepmcs]

Hey, i started another thread called msd install.
http://www.dodgecharger.com/forum/index.php/topic,15845.msg176982.html#msg176982

i'm posting up pics.  I really appreciate your help so far, please stay in on the other thread cause i will probably need any tips i can get
i got you on this one.  c+/- you are talking coil and m+/- you are talking magnetic pickup, right?

ok my batt is on the drivers side and i'm gonna have to install on the pass side, just no room on a 69 and plenty of room on the pass side.  i'll put it around where the orange box is and the coil near by.  i'm gonna half to get some 10awg cause i'll be running wires straight to the battery  + and -.  the red wire is the only one right now that i can see i'm gonna have a little trouble finding the right ignition on power feed to. ok i'm just lazy but i was thinking the existing setup might have that already done for me.  i'll be mounting with the mounts provided but i do like your wood idea. i have a lot of room on that side to mess around(yeah i don't like drilling in to the inner fender but hey, it's all about performance right.

ok enough for now, i need a beer.
thanks so much for your instruction so far, it's PRICELESS!!!

v/r
Mike

[hewi]

G'day.

My DC is running a pretty standard 383 Big Block.

Is this carb too big?

http://www.trademe.co.nz/Browse/Listing.aspx?id=63531613

Also, is a year a bit long just to be sitting?

Cheers,
Hewi

Ps. Price is in NZ dollars

[mikepmcs]

Hewi
I'm gonna say yes to the 1150 holley, too much for a stock motor, but people much smarter than me will chime in.
i'm running a holley 750 hp right out of the box and it does fine, i have a moderate cam(mp 484), msd 7al ignition, 8251 coil and msd super comp 8.5's just like was suggested in this thread.  it runs like a champ.  no stumble but a little rich(my eyes are burning right now).  now i just need to learn how to tune it.
I hope i don't blow my motor.  i just dialed in the timing again at about 37* at 2800 rpm.  no vac advance hooked up to the dist.  took it down the road and it seemed to do ok.  i have 2.7's in the rear so no holeshots but it didn't stumble when i romped on it.  my only concern is that it stays revved up now when i let off the gas at idle, still haven't figured that one out yet, maybe i need a stronger return spring but i thought mine was plenty strong.  it seems like it's sticking or something. who knows??
anyways to answer your question, i think that would be good on a race application with a built motor.
v/r
Mike

[dodge freak]

I use two springs on mine-one from the throttle bracket on the bottom and the other in front from the throttle level to a post on the intake. Its hard to get the right springs some are strong enough but you can't open the throttle all the way. Bet you don't even know what jets are in it, maybe 73 or 72 -what ever they are go down in the front side 1-2 sizes. Holley says always move 2 jet sizes at a time but I can feel one size. You won't hurt anything by it a Little to rich-too lean yes, thats why I go just a little smaller on the jet. NO rods like the eddy carbs-yea - the power valve opening you can change but its most likely at 6.5" which is fine. I doubt if its opening, some people run a 5" or even 4 or 3" but thats for very hot cams. When the vacuum goes under the power valve rating-like 6.5" thats when it opens. They go as high as 10.5, 8.5 is good for stock motors but all holleys come with 6.5" .Have you try the idle screws, thats all it might be, it should be jetted very close to what you need. The float level too matters ,take the little screw off the side of the bowl and see if the fuel comes out, it really should not motor freshly turn off until you push on the fender to rock the car. You need to get a Holley repair and tune book. Too much to cover but its easy. I use those gloves the dentist uses, gas stinks.

[hemigeno]

I know a lot of guys swear by the C.I. x 2 = CFM for carburetor sizing, but I disagree with that calculation.  Hewi, the Holley tech you were talking to earlier was giving you the same advice I would give you if I were calculating the optimal CFM for your engine.  Here is the formula that an OLD-time carburetor guy gave me, and it's been backed up by a couple of engine gurus that I deal with every now and then:


       [Engine CID]  x   [Expected RPM Maximum]
---------------------------------------------------------------      =    Optimal Carburetor CFM
                               3456


So, for your 383 engine, with maximum 6,000 RPM, the calculation goes like this:

         383  x  6,000                    2,298,000
-----------------------------   =    ---------------    =   664.93  CFM optimal
              3456                             3456

Based on that formula, anything larger than the 670 carb that the Tech recommended is wasted potential CFM.  Your engine is only going to pull so much air through the venturi, and putting a larger carburetor on only slows down the air going through it.  When that happens, your carb is harder to tune, more prone to bogging down, etc.

I'm nowhere near the engine expert that Chryco, Ron and some of you other guys are, and I'll leave the Vacuum vs. mechanical secondaries debate for others.  However... I have heard over and over from some very savvy engine and carburetor guys that the biggest mistake most people make when working on their engine (especially street engines) is oversizing the carburetor.

Do what you want to, but I agree with the 670 cfm recommendation you were given.



Geno

[Ghoste]

There is a factor for volumetric efficiency but that depends on cam, heads, exhaust and so forth.

[hemigeno]

There is a factor for volumetric efficiency but that depends on cam, heads, exhaust and so forth.

I agree, but I was told that the same formula I posted would handle most of the cam/head/manifold combinations seen on anything but a race motor.

[dodge freak]

On a vacuum secondary carb it only runs on the primary until the engine needs more. On a 750 carb thats only a 500 until the secondaries open. Thats why the factory went with those, Chevy had them on the 327 motors and 302.

[firefighter3931]

I know a lot of guys swear by the C.I. x 2 = CFM for carburetor sizing, but I disagree with that calculation.  Hewi, the Holley tech you were talking to earlier was giving you the same advice I would give you if I were calculating the optimal CFM for your engine.  Here is the formula that an OLD-time carburetor guy gave me, and it's been backed up by a couple of engine gurus that I deal with every now and then:


       [Engine CID]  x   [Expected RPM Maximum]
---------------------------------------------------------------      =    Optimal Carburetor CFM
                               3456


So, for your 383 engine, with maximum 6,000 RPM, the calculation goes like this:

         383  x  6,000                    2,298,000
-----------------------------   =    ---------------    =   664.93  CFM optimal
              3456                             3456

Based on that formula, anything larger than the 670 carb that the Tech recommended is wasted potential CFM.  Your engine is only going to pull so much air through the venturi, and putting a larger carburetor on only slows down the air going through it.  When that happens, your carb is harder to tune, more prone to bogging down, etc.

I'm nowhere near the engine expert that Chryco, Ron and some of you other guys are, and I'll leave the Vacuum vs. mechanical secondaries debate for others.  However... I have heard over and over from some very savvy engine and carburetor guys that the biggest mistake most people make when working on their engine (especially street engines) is oversizing the carburetor.

Do what you want to, but I agree with the 670 cfm recommendation you were given.



Geno

Geno is bang on the money here.  The 2 x cid works well for a race type build that spends most of it's time at high engine speeds and low speed operation isn't a consideration. Too big of a carb is difficult to tune and often results in poor throttle response/bogging etc.... on the street.

Fwiw, if you want to use VE (volumetric efficiency) in your calculations the correct factor is .80 unless the heads are heavily ported.


Ron

[dodge freak]

Well I think the factory's knew what they were doing when they had a 273 dodge motor with 2 - 500 cfm 4 bbl carbs as a high performance option. Or all the GM motors that had a 750 Q-jet on them-the Q-jet went on everything from the small 305 motors up to the 454 motors. It was able to do that cause the primary's were so small that even a low power 305 motor would run ok cause the secondaries would not open up much if at all. The 454 motors ran ok too because the secondaries would kick in fast cause the primary's were too small for it.

Maybe it is better to have to small of a carb compare to having too big of a one , but if you use that chart a 500 cid motor that spins to 5000 rpms would need only 723cfm carb. So a 750 would be too big for it. No way! Thats why they make vacuum secondaries carbs. The primary's stay close until the motor needs more air. Just cause it says 750 does not mean it flows 750 all the time. A 750 flows no more than 500 on just the primary's and thats without a choke, a 750 Q-jet flows about 250-300 on just the primary's.

There is good reasons racing motors have 1100-1200 cfm carbs and they only rev to 7500 or so . I am not saying any street motor should run those carbs, but a 750 vacuum secondary carb can work well on most motors if it has the right spring in the secondaries, might not give the best gas milage and be harder to tune than a 600 but it would not be crazy to run a 750 instead.

[hewi]

Hey guys (and girls  )

What do you think of this carb for a 383 BB?

http://www.trademe.co.nz/Browse/Listing.aspx?id=63116836

Would this be a good carb for me?

Cheers
Hewi

[dodge freak]

Thats one of those "phony" hp carbs. Well if he got the right metering blocks for it and base plate , yeah it be ok, but I bet he didn't , just the blocks is all you need. I would also stay with a vacuum secondary one. DP are for 4.1 gear cars and still they needed headers and a hotter than stock cam, the vacuum carbs are a better choice unless you know what you are doing and have the right set up for them.

[mikepmcs]

Hewi
what's the price on that carb, it wouldn't show it when i pulled up the ad.
v/r
Mike

[Rubberduck]

here´s a calculator for the  cfm:

http://www.4secondsflat.com/Carb_CFM_Calculator.html

I think 600cfm or 650cfm would be fine.
A bigger carb just needs mor gas.

Mario

[Beer]

I was shocked with my Stroker Smallblock when I saw the dyno and what the airflow used was on the 402.
I put had an edelbrock 800 on it, and it dyno'ed at 414 HP on 580 CFM IIRC. I will double check those figures when I am home, but I was expecting it to be high 600 to low 700's in the CFM. I may swap the carb out to a smaller one when it gets into the car.

[hemigeno]

here´s a calculator for the  cfm:

http://www.4secondsflat.com/Carb_CFM_Calculator.html

I think 600cfm or 650cfm would be fine.
A bigger carb just needs mor gas.

Mario

Thanks for that link, Mario...  already added it to the Favorites

Incidentally, I ran the same engine parameters that Hewi is using (383, 6,000rpm), and it kicked out the exact same 664.93 CFM figure.  More importantly, that number was listed as the 100% Volumetric Efficiency value, and if Ron/firefighter's 0.80 VE figure is used, the carb sizing is knocked down to 532 CFM.

I also don't take the factory's installation of a particluar size of carburetor as a cancellation of Bournelli's Principle.  Tom Hoover will quickly tell anyone who will listen that the Hemi would have performed better with a single 4bbl, but the public's perception of the motor would have suffered.  You can get OK performance from multi- and large-carb setups, mostly by utilizing progressive or stepped linkages, or finding some other way to limit how the throttle plates open up.

The use of vacuum secondaries does help, but the very fact that airflow through the carburetor is dictated by the engine's demand means that you are not utilizing the carb's full potential.  This can be proven mathematically.  If that's the case, why put it on there if it's not going to be used?  All it does is make the engine harder to tune.  It won't kill a car's performance to slightly oversized its carb, but it does not help it at all to put a huge one on there.  The POTENTIAL airflow is there, but IMHO the downsides far outweigh the bragging rights (and that's all the positives you get) from having a really large carb on your engine.

[dodge freak]

Well all I can say is that I went from a 650 DP carb which I got cause I did not want to over carb then after using it for 5 years put the profrom main body on when they first cam out it noticed a nice improvement. The engine is a 318 bore .030 with headers and 3.91 gears with a 2.74 first gear. Why it ran better if it needs only 450 cfm I have no idea, just sometimes real world works better than mathematically.

Its your money, go do what I did-buy a 650 carb then later on upgraded it to a 750. You may be surprise. I do have a MSD 7 al box and I know if I had the Mopar chrome box it would bog a little, it helps burn the fuel. Even over the 6 box I seen a improvement. I used to have to slowly -like a full second- floor it from a stop , now I can just punch it and it sounds nice and crisp. The closer your motors like stock the smaller the carb should be. With the 750 you have room to grow, if thats what you want.

[firefighter3931]

One other thing to consider is that the factory allways used a dual plane intake manifold. The divided plenum basicly has one side of the carb running 4 cylinders and the other side of the carb running the opposite bank....there is no left to right (venturi) sharing. When using a dual plane manifold the carburator requirement is higher so that's why the factory was often a little on the generous side.....think of it as a pair of 2bbl carbs running a pair of 4cylinder engines. Also with the carbs being vacuum....it was an "on demand" useage as opposed to a mechanical secondary which forces the air/fuel down the engine's throat. Just because a vacuum secondary carb is rated at 850 cfm doesn't mean the engine is using all of it.

Fwiw, mine was dynoed with several different carb and intake manifold combinations. The biggest carb didn't actually make the most power....surprising huh ?  The motor made as much as 560hp in one configuration and was pulling just over 800 cfm at 6500 with a VE reading of 110%....this is a pretty efficient motor that would be hard to duplicate with a factory head, dual plane manifold and running on pump gas.

Some things to think about next time you're considering a carb swap....


Ron

[Ghoste]

And with a single plane...?

[firefighter3931]

And with a single plane...?

Actually three....Victor, TM7 and the Street Dominator which is the one i settled on for a couple of reasons. I will say that this motor did not like the Performer Rpm dual plane....choked the engine off at 6000.

Ron

[Plumcrazy]

here´s a calculator for the  cfm:

http://www.4secondsflat.com/Carb_CFM_Calculator.html

I think 600cfm or 650cfm would be fine.
A bigger carb just needs mor gas.

Mario

Thanks for that link, Mario...  already added it to the Favorites

Incidentally, I ran the same engine parameters that Hewi is using (383, 6,000rpm), and it kicked out the exact same 664.93 CFM figure.  More importantly, that number was listed as the 100% Volumetric Efficiency value, and if Ron/firefighter's 0.80 VE figure is used, the carb sizing is knocked down to 532 CFM.

I also don't take the factory's installation of a particluar size of carburetor as a cancellation of Bournelli's Principle.  Tom Hoover will quickly tell anyone who will listen that the Hemi would have performed better with a single 4bbl, but the public's perception of the motor would have suffered.  You can get OK performance from multi- and large-carb setups, mostly by utilizing progressive or stepped linkages, or finding some other way to limit how the throttle plates open up.

The use of vacuum secondaries does help, but the very fact that airflow through the carburetor is dictated by the engine's demand means that you are not utilizing the carb's full potential.  This can be proven mathematically.  If that's the case, why put it on there if it's not going to be used?  All it does is make the engine harder to tune.  It won't kill a car's performance to slightly oversized its carb, but it does not help it at all to put a huge one on there.  The POTENTIAL airflow is there, but IMHO the downsides far outweigh the bragging rights (and that's all the positives you get) from having a really large carb on your engine.

Edelbrock 1806
Holley Street Avenger 670

[Chryco Psycho]

I don`t use the formula , I have installed 1050 dominators on 3 440s witha minimum gain of 40 hp & as much as 70 over an 850 , + the 6 pack is over 900 CFM rated as a 4 bbl , & it works fine