Carb tuning help

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DP carbs make more mid range power, its a proven fact.

As for which carb is faster, it comes down to gearing and converter stall speeds.

Yeah you put a 750 DP carb on a 2.73 gear car, the Edelbrock 750 might even be faster out of the hole..but place both those carbs on a 4.10 gear car--better yet 4.56 gears--and the DP carb will outperform the Edelbrock.

DP carbs can ram more A/F in the cylinders..like force feeding the motors..if the motor can rev quickly. A more powerful ignition system to burn all the fuel is sometimes needed too.

Why MSD makes 7, 8 and 10 spark boxes. (I have a 7al box right now)
 
I had a race 650 Demon..sold on Ebay for $200 also last week (but I paid $300 for it 2 years ago so) it had the removable boosters and look like an mighty Demon. I did say my carbs all had no choke.

Not sure why DP make more power but they do over vacuum carbs..but running two Carters I get 4 bbls at any time--not as flowing as the 650 DP but then the dual secondaries start to open.

I was worry I lose power but don't think I did..if anything its 10-15 hp and like pulling in top 3rd gear 70mph to red line its better, I know it...have nice 4 lane 70 mph zones here.

I haven't tried open spacers yet either.

Now would an 800-850 DP outperform my two 500 Carters...on the Edelbrock RPM intake, never tried it but most likely.
 
1 wild, I give up no power by running Edelbrocks on an engine like this. The Holleys and the holley based clones are for race engines. They were never designed for milder applications first. They were changed to make them streetable over time. Double pumpers DO force feed fuel. That is how they overcome the slow airspeeds through the secondaries and it's why they feel faster, but on an engine and package that cannot make use of that specific carb size at WOT from idle usually show otherwise. It comes down to knowledge and tuning. Holleys hide a lot of issues Edelbrocks/Carters dont by dumping more fuel.
 
moper said:
So going back to the OP's question.... You wil want to get eh strip kit if you dont have it, and more than likely the ping is a combination of the wrong step up spring and both primary jet and rod and secondary jetting. Also, the AFB uses the counterweighted air door and these can be slightly reduced in mass to get the secondaries to open faster, provided the fuell mix is correct. For what you have, I agree the Holley is not the best carb, and I'd wager it feels faster with it, but on the track isnt any faster. I also am a firm believer in timing first, and timing means the three prts: initial; centrifical; and total. You want at least 15° initial, and no more than 36° total. I'll add that if I had built it, it would have a 750 Thunder AVS on it.
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The initial timing is set at 15* with total at 34*. The reason I have the 600 on it right now is I had it from a previous project. I'm looking to see if I can tune this carb to last me til next summer or so when I can afford a better carb like one of the Thunder series, or maybe just tune the 650 DP I have a little better.

dodge freak said:
DP carbs make more mid range power, its a proven fact.

As for which carb is faster, it comes down to gearing and converter stall speeds.

Yeah you put a 750 DP carb on a 2.73 gear car, the Edelbrock 750 might even be faster out of the hole..but place both those carbs on a 4.10 gear car--better yet 4.56 gears--and the DP carb will outperform the Edelbrock.

DP carbs can ram more A/F in the cylinders..like force feeding the motors..if the motor can rev quickly. A more powerful ignition system to burn all the fuel is sometimes needed too.

Why MSD makes 7, 8 and 10 spark boxes. (I have a 7al box right now)
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I should have filled in these boxes earlier. My Duster is a 4-speed car with 3.91 gears, which is why I had originally tried the DP. I actually really liked the power and response I got with that carb even in factory calibration. I tend to find that when sizing carburetors, you need more CFM with a Carter than you do with a Holley.
 
I dont run DPs on much that isn't spending most of it's life on the track. Have you tried to track test the two carbs back to back? Not a dyno, but at the track?
 
moper said:
1 wild, I give up no power by running Edelbrocks on an engine like this. The Holleys and the holley based clones are for race engines. They were never designed for milder applications first. They were changed to make them streetable over time. Double pumpers DO force feed fuel. That is how they overcome the slow airspeeds through the secondaries and it's why they feel faster, but on an engine and package that cannot make use of that specific carb size at WOT from idle usually show otherwise. It comes down to knowledge and tuning. Holleys hide a lot of issues Edelbrocks/Carters dont by dumping more fuel.
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They both need initiation or use a shooter to initiate the flow, call it what u like.:read2:

I don't wanna argue, it's cool man... we all like what we like... and if we try other things enough and get it right.. we find what really works and what does but maybe not as good.
:cheers:
 
1wild&crazyguy said:
funny how in 2yrs they cost $725, meanwhile you say you bought it new for $300.

BS.
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I got it on Ebay from a racing driving school in NC...forgot the name..oh, Jeff Gordon I believe. Was listed as used one season, they buy new motors and carbs for each new school year I got pictures too but look back at my old threads on here, sure I posted about it before...I loved that little Demon, best carb I ran...but two OK carbs I now like better.

I buy little brand new from Jegs or Summit, not as long as Ebay has better prices, even if used. More money for gas and chicks, lol

Have you ever ran two Carters on a Edelbrock dual plane intake..they do still make them for big block Mopars but I would use two 600 Carters..or maybe two 750.
 
I have to agree with Wild on this one Moper, carb's don't force anything down an engine, the engines vacuum draws the fuel/air, Holleys are just metered "richer" in most areas over the eddys or carters, but there tuneable like any other carb, i just know a couple guys who can 'really" tune Carters for max power, & yes they scream, as good if not better then the adverage holley, i've run my holleys vs. eddys back to back at the track, the holley allways ETs & MPHs better for ME, but i have a nack for tuneing them, am i the best, Hell no, not even close, but i'm better then most i've seen at the track trying to tune theres, i've tried to help (after they ask), but they don't listen, so i've stopped helping, there on there own, i know my **** runs, tuff luck for them, you would be surprised how well a QJ would run, i met a guy who was a master at them. I generally like holleys for there metering.

I preffer DPers, even on the street, but it helps to have at least a 25-3000 stall & some gears, or alot of torque lol. If you really look at any fast street car that run single carbs, you'll very rarely find a carter/eddy on them, i want the best of both worlds, so i tune my holleys to have the best street manners.
 
I know I won't influence the mindsets, and don't worry about debate. I like debate :D. So long as it's based on more than "my car runs this so you should too..."lol I think my reply above is not written clear enough for me to be happy with it. So we'll try this again...sorry for the wordy and redundancies for the ones who know this already but I think the info might help...lol. Also bear ing mind the OPs application... A street car that sometimes races.
The engine is an air pump. The intake side is the suction side. This we agree on. It sucks air through the carb. The air moving thru the carb sucks the fuel out of the idle circuits, the transfer circuits, and the main circuits depending on the movement of the throttle plates. This is true for every carburetor, everywhere, made by everyone. That's the basic premise for how they work. Now, different manufacturers have different ways of skinning the fuel curve cat. All use some sort of bleeds and emulsion passages, and all use a form of booster in the venturi to address issues of signal strength at various rpms and loads. In terms of the secondaries..
Carter uses the airflow thru the secondaries to open a flapper door that is either spring loaded or counterweighted against the air flow. What that means is when you open the carb to WOT, the secondary throttle plates open fully, but the air door will not. As the airflow increases with the engine's need, more fuel is pulled thru and the door opens more, etc, until the door is wide open matching the throttle plates. There is no accelerator pump on the Carter secondaries, not even the race versions. It's not needed when they are matched to the combo and tuned properly. The reason no accelerator pump is needed is the way the main circuit fuel is metered. This is much different and more precise than the Holley design.
Holleys come two ways: vacuum secondary which is a little misleading... and the mechanical secondary or "double pumper". Holleys were designed as a race carb first. As they got a good rep on the track, factories started using them and when that started, they had to be tamed a bit and re-calibrated to work in situations of part throttle and idle.
The vacuum secondary uses airflow in the primary side to pull open the throttle plates of the secondary against a preload (closed)spring. This is why it's misleading. It's not ENGINE vacuum, but it's own signal from the primary venturi to the vacuum pod. If the air speed is not high enough, the secondaries get a weaker signal and the spring holds the blades shut. This balance means the engine never sees more air than it can use when again, the carb is matched and properly tuned. You should never feel a bog when the secondaries open on a VS holley. If you do, they are bogging the engine and you're not as fast as you could be by slowing the secondary opening down with a stiffer preload spring.
The mechanical secondary carb is more similar to a Carter design. Meaning when you floor it, the secondaries open 100%. However in doing so the engine sees an immediate drop in vacuum and signal strength. Think of inhaling thru a straw, and then opening your mouth fully during the same inhale. The problem is, the sucking is caused by fuel burning, and the fuel isnt moving as well or as much as it was at lower throttle. No signal, no airspeed in the rear of 2 barrels. So, the way Holley fixed this was to use a second accelerator pump on the secondary side, that is 20ccs larger than the primary on most carbs. This is specifically to dump a volume of unmetered fuel into the intake when the vacuum signal and airspeed drop with the transition from light to wide open throttle. As this carb dumps fuel instead of reacting to increased airflow... I said it force feeds it. That's not entirely accurrate...lol. But Holleys in general make more use of unmetered fuel than a Carter, and on a street or multi-use engine, metered fuel is where it's at. And when everything is properly done, there is no loss of power. Most gains from simple carb swaps are the result of one or more issues that were addressed by the new carb rather than figured out by the owner with the old carb. Rather than one design being inherantly bad or good over another.
I feel better with that response...lol.
 
So how come every Holley Dominator Carburetors are DP carbs and none are vacuum? Cause they make the most power being mechanical secondaries.

I will agree many street cars would be as fast with a vacuum carb--maybe faster even but race cars with 5,500 stall converters don't need a vacuum carb and every .1 second matters, maybe every .001 seconds. Vacuum secondaries don't open as fast as mechanical s and they don't open all the way super fast.

Go on Speed Talk dot com and post how vacuum carbs make as much power as DP and see what the pro racers who use dynos to test stuff have to say.
 
freak, You've completely missed the point. Following your ligic I should respond with "How come we're not all running injected nitro?" This is a street car. How many dominators are oin cars idling in city traffic or driving over slowly rolling hills in the mountains? Or are driven in the rain or snow? STREET CAR. not racer. Once the carbs reach full throttle and either the air door is wide open, or the accelerator pumps are fully discharged, the carb brand makes no difference assuming they are well tuned. The cars that need DPs are ones that have gearing or convertor or cam that requires more rpm to work. That's when they shine. Like a race car with a 5K convertor will need the DP carb to get moving from 1/5 throttle opening to full. Aks why guys run a two step rpm chip when they bracket race over there... Because the carb can be held at WOT until the brake is released. A tthat point, no squirtor is needed because the engine has the airspeed thru the carb already. They get to WOT much better and that's where they are designed to work at. It's the times they are not at full throttle that matter on a street car. That was my point.
 
Cool, gotcha you.

Believe of not a few guys on speedtalk are running dominators on the street. The is many threads about how to convert the 3 circuit to 2 circuit for better street manners.

One guy car runs in the high 9's in the Q and for a joke he has a trailer hitch on the back and pulls a small trailer, lol.

get it...instead of the trailer pulling his car to the track, he pulls a trailer on the street, ha ha


But us "normal people" can't afford to play their game.
 
All this is opinion......

No one here has done it all, most haven't done or know 1/10 of this.

It's all about power, you think funky mix fuel dumping is why there raced and winning more?????
It's called tune ability & better metering the Holley does it better PERIOD!

What makes power....it ain't poor tune/metering, thats for sure.


Now,
All this crap that deviates from the OP's question needs to be erased.....
yes this too.
Otherwise you're gonna have the same suspects pressing there opinions over and over till it's the last post/word or a real argument breaks out.

You can put your opinion in a sentence or 10 paragraphs, but it's still says the same thing.
 
Ha ha ha you know what if you go to moprchat.com you'll see a post by a guy whos run carters since the dawn of time.... Well guess what he decided to do on a whim.....RUN A HOLLEY, And guess what? he ran faster by 3 tenths, multiple passes, right out of the box!!!!!! and even had not so favorable weather/elevation. He even admitted he didn't believe it at 1st and felt like a trader to the edy/cater community, as did the rest of the carter loving forum... cause next thing you know, all the usual suspects were calling him a liar and saying that he just didn't tune his carter right.

HA HA


Why are people like this?
 
Don't think this is a street car but its a cool Mopar at the bottom of the page.
69"satellite,3900lbs,8-71,14lbs boost,I/C,998HP/980ft.lbs 446cu.in W/gas
http://www.speedtalk.com/forum/viewtopic.php?t=18169

Sorry, can't seem to find that picture I was thinking about...only seen it once and can't recall the thread. Most of those boys are out in California thou.
 
Cause just like everything else..what they have is the "best"...

I hear from the pro carb shop guys its a myth to run a small carb for better power..I mean some claim a 1050 Dom modified by them, will work great on a street 350 Chevy. But whos got $2,000 for a carb, lol.
 
1wild&crazyguy said:
Ha ha ha you know what if you go to moprchat.com you'll see a post by a guy whos run carters since the dawn of time.... Well guess what he decided to do on a whim.....RUN A HOLLEY, And guess what? he ran faster by 3 tenths, multiple passes, right out of the box!!!!!! and even had not so favorable weather/elevation. He even admitted he didn't believe it at 1st and felt like a trader to the edy/cater community, as did the rest of the carter loving forum... cause next thing you know, all the usual suspects were calling him a liar and saying that he just didn't tune his carter right.

HA HA


Why are people like this?
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Thats NO surprise, this debate can go on & on & on & on, well you get the point lol. I KNOW what runs faster, they can talk till there "blue" in the face.
 
I disagree on teh value of these debates. No arguements here. If these guys were pitted next to me and spouting this we'd be barbequing, havin' beers and doing this all night without fighting...lol. I still want to hear the facts on why the DP is a better carb on a street car other than "it runs better because I said so...". I admit in a racing package the Holleys will run better. Mainly due to ease of tuneability that Carters and Edelbrocks lack. Again I stress with the OP's issues his car is not a race car or race setup. There is a point wher it just is not feasible to try and make an Edelbrock or Carter run stronger where a Holley or Holley clone you simply buy the parts and make the minor chagnes... Well, unless you're a FAST or Stock Eliminator car and have to run whatever it came with...lol
 
Maybe i agree, tough,. in theory its an easy equation to select carb cfm by engine displacement. no it aint that easy, it also depends on the air speed, runner lenght, plenum, camshaft, head and ofc the engine volume.. i wont even try to coment what carb, only thing i could add is that the design on the carter/edelbrock carter copy venturie tend to mix fuel better at low cfm (idle speed) results in a more even air/fuel mix then agen the engine sound "milder". typical Holley issue is overcarbing.. u buy a 850 carb on ur 273.. it runs lean.. u compensate with 84 jets and maybe a 50cc pump.. it idles like a race car.. air/fuel mix is like mommy's tea can, due to the low airspeed in the venturie/boosters.. dont do this..

mopar btw recommended 750 vacum sec for theyr 472 crate engine..

when it comes to vacum sec... any street driven car wit automatic trans should use it, it helps controlling the airspeed/cfm in different engine vacum and engine loads u will have in street driving. this helps u to have better air/fuel ratio over the spectre..

I say this only cus i made every all of this experiences by failing.. lol i had a Holley 750 dp on a 340.. had 50cc pumps just to keep the engine going after launch cus of no airspeed.. and i had 80 sec jets and 76 pimary.. lol Hell yea it sounded like a real race car.. 8)8)
 
moper said:
I disagree on teh value of these debates. No arguements here. If these guys were pitted next to me and spouting this we'd be barbequing, havin' beers and doing this all night without fighting...lol. I still want to hear the facts on why the DP is a better carb on a street car other than "it runs better because I said so...". I admit in a racing package the Holleys will run better. Mainly due to ease of tuneability that Carters and Edelbrocks lack. Again I stress with the OP's issues his car is not a race car or race setup. There is a point wher it just is not feasible to try and make an Edelbrock or Carter run stronger where a Holley or Holley clone you simply buy the parts and make the minor chagnes... Well, unless you're a FAST or Stock Eliminator car and have to run whatever it came with...lol
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Moper, i'll shoot, no spouting here, i've grown past that (well sometimes), ok, so now we agree that the holley is faster at the track, its just been proven time after time, i'm not saying there isn't that RARE ocassion of a guy running hard with a carter/TQ or QJ, because it happens, but those carbs do need alot more tooling to make them shine at the track, & most of the adverage carter guys can't get to that level of perf. with them, but THEN, how will they do on the street in that form, prob not good i'll garauntee, just like the holley, they will need to be re-tuned & calmed back down, just need to find that happy "medium", my BIGGEST complaint with the eddy is its dead spot, mainly on the 750 AFBs, because IMO, there Thunder series are alittle pricey, i've heard they don't have those issues, & the metering on them just isn't all what its cracked up to be, my TQ ran stronger then an eddy 750 "on the street", especially WOT but there finicky too & i had to mess with the jetting among other things, especially the rear door, holleys just have a better style metering, they respond better, especially under WOT, they may need a few adjustments here & there, but all the parts are availible, i still think the eddys can be made into a way better perf. carb right OOTB, we have a guy that can build a fairly wicked TQ (demonsizzler), the eddy/carter lovers need a guy who can make them shine, then i'd be more abt to buy one & give it a try on a street, even on the track.
Most of us on these boards are racers, we want power, even in our street cars, if you want to stay very mild, then ok, drop a carter on it, but if your looking (which most of us are) for a street thumper, then you'll need alittle compression/gear/cam/stall yada-yada-yada, then a holley DP is the best choice, with alittle tuneing they can be dialed in, we have good gaskets now, so there WILL be NO MORE leaks, hell i've proven that to myself. Orrrrrrr, PAIR up a couple carters & run a street ram, for some reason, the 500s or 600 eddys work great damn near right OOTB this way, thats a given, & has been proven, the holley 600vs's work great too, but they need some jetting/pump changes, i love my holleys (even on the street), have a soft spot for DPers, that'll most likely never change, but untill someone can produce a wicked OOTB eddy, i'll never buy one again.
 
look what i just found under the coutch .. hmmm we will prolly never agree on this issue.. but that is kinda good cus then we get experience from all sides here in this forumm that from today will be my 2'nd home :) tnx gys.. tough when u read tech books u get alot of "ah haaaa ofc that is why" so, but i havent read any carter book's yet.. maybe i should, there is no magick anyways just a matter of the right air to fuel ratio at all times.. notice that i have on this proform the vacum sec.. (i like the trottle response better on the dp) but this time i will try the dynoproven way of the book hehe..

proform.JPG
 
Just for kicks, I took the 650 DP apart and found two things: a piece of the cork surrounding the idle screw was jammed in the idle needle seat on one side and the secondary Accelerator pump check ball retainer came out of place. So after I go through the rest of the carb, Im going to give the Holley another shot. If it was running just slightly off with the two problems I found, then I bet it will run pretty sweet once I go through it all.
 
Norway, You're missing one. SA Design part number 11-3. Supertuning and Modifying Carter Carburetors..lol. I have that one too. Copyright on my Carter book is 1988...lol.

Joe - For purposes of this discussion, I'm ignoring the prices initially and the parts costs to get them all adjusted properly, or as good as the individual designs allow... That is where the Holley advantages IMO go away. It's the part and mixed throttle driving that shows where Carters/Edelbrocks shine. Holleys have a main metering system consisting of holes drilled up along the main fuel well to the booster. When the carb is level, and float level is good, and wide open throttle is applied, the main jest meter the fuel. But, when the fuel is sloshing, or the floats are a hair off, or the carb is on a sharp angle up or down... The emusion holes become exposed at the wrong times. In the secondaries that means jet extensions. Also for enrichment under load, the power valve is simply an unmetered dump of fuel when the vacuum level begins to drop. Notice there is no difference in the size of that hole that passes fuel from the 390cfm to the 950HP. There could be 30 or more jet numbers difference in the carbs, but the PV is the same size hole?
 
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