Carb(s) and manifold question- OPINIONS WANTED!

[Captainkirk]

OK, here we go.
First off, I've always been a Holley guy. My last current setup on my Duster was a Holley 650 douple-pumper perched on top of a Edelbrock Torker 340 (X-type) manifold. I was really surprised to hear so many here reflect negatively on the Torker, and there seems to be a large group of anti-Holley guys here as well. In the interest of being well-informed, I'd like to hear what you guys prefer, and most importantly, WHY. First, a little about the setup.
*'72 Duster (stock chassis)
* 8 3/4 Sure Grip
* A833 four speed
* stock rear springs and shackles and torsion bars (at this point)
* 340 std bore, should be running about 11:1 compression
* mildly ported stock heads, 1.88 intakes
* cam undecided yet. Might reuse the former cam as it had less than 5000 since new, as follows: .450/.475 lift, 298/308 duration. The cam grind is another subject for debate.
* Forged crank, stock rods
* TRW domed pistons with Speed Pro rings
* at present, Chrysler electronic ignition with Mr. Gasket quick advance curve springs, no vacuum advance, total advance set to 32 BTDC
* headers (to be determined) with duals and crossover

I know I could bolt on the Torker and the Holley and it would run very well. It did before. But I'd love to have a little exotica perched on top. The six pack setup I always dreamed about will set me back about 1800 bucks, which in my book is outrageous for the miniscule performance advantage I would gain. If I had money to burn it would be no contest. But I don't.
A 2X4 setup running an Offy manifold and two Edelbrock Performers or Thunder AVS's would set me back about 1200 bucks. That's still outrageous.
Fuel injection is worse yet, in the three grand arena. No thanks.
So; here's what I have to work with. I have three carbs available at present; the Holley 650 DP, a Carter AVS, and a TQ. I've all but eliminated the TQ from the mix due to the really goofy choke arrangement. I need a simple mechanical cable operated choke...period. (unless someone knows of a good mod for this).
I really haven't explored any other carb options. I love the tri-power idea, but unless there is a cheap aftermarket alternative, it may have to wait.
Now, as for manifolds; I saw in a thread recently many of you favored the Weiand Stealth over the Xcellerator, the Eddy RPM Air Gap, the Eddy Victor and the Mopar M1. Surprise! I never woulda thunk it, but that's why I'm asking. So, given what I have to work with, I'd appreciate any and all comments on my forthcoming build and will take all comments and suggestions under serious consideration. If you have a "favorite son", convince me!

 

[rumblefish360]

How big is the AVS?

The Torker II is an intake that wold work best in a serious streets tripper. The Mild HI-PO days of this intake are over when the RPM came out. The RPM has beter torque and HP across the board over the TorkerII. But if your skipping 4,000 RPM, the Torker II will do.
It will be fine for anyone building on the cheap. And sometimes, thats just the way it is.

I have never seen a dyno dual between the Stealth and RPM. I did come across a berb writin, by Steve D of Mopar Muscle I think, that made a mention to this when the question was posed to him about the performance between the 2 intakes. It was a "Don't be worried about it. It's to small to worry about."

The difference between a Carter and Holley in there performance has been noted that the Carter seems to make more torque and the Holley more HP. This was noted at a trach test and tune. (Carter 60 footed better and the Holley had better top end.)
I can show you how to add an electric choke to an OE Carter.

Chose the carb by whatever reason suites you.
Chose the intake to fit the style driving in the rpm range of the cars operation and intended use.

You don't need to be convinced. You need to think it out and be a tad logical about it. Do what you can with what you have or do what you can with your wallet.

 

[flyboy01]

Torker - old technology, good peake HP & TQ, poor average performance.
Performer RPM - Great average HP & TQ, outflows most single-plane intakes
Mopar M1 - Best top end power, good race intake.

My choice would be the Demon carb, the Holley is a good carb, there are upgrade Proform parts available to make the 650 flow better, check Summit. Fuel injecton will not give you more power, just better driveability. You might want to consider a large 750-800 cfm Vac secondary carb for street drivability. The RPM intake will help tremendously with that too.

The TQ and AVS are good design, but they are hard to find parts for. Most auto parts stores worldwde have holley parts, easy to tune and understand too.

Dump the cam. No arguments, its old design technology, the ramps are slower than a modern Comp Xtreme Energy or Hughes, either of these cams take advantage of the larger Mopar lifter which allows a much faster "Rate of Lift." Get one of these and they will give you more power and TQ with the same overall duration. New cams and lifters only cost an extra $200 in an engine build, reusing old cams is asking for trouble, unless you kept track exactly which lifter goes to which lobe. My advice, get a fast rate of lift cam with less overall duration and you will be happier, especially considering you are older and wiser, a tempermental, fire spitting engine is not a great weekend cruise engine.

I love the story of the Duke, but nostalgia does not make a great engine. Get some newer technology, and enjoy the engine more.

 

[AdamR]

Best for the street on a 340 would be a RPM or RPM air gap. I think the 650 will be ok. 750 would pull better up top.

 

[rumblefish360]

The TQ and AVS are good design, but they are hard to find parts for. Most auto parts stores worldwde have holley parts, easy to tune and understand too.

Point of view, easy to argue. Though you do have the edge until the word, "Understand" was used.
AVS can use AFB parts. AKA New Edelbrock parts. In most any HP store. Maybe not Autozones.
I'm with ya on the cam. Chuck it. Grab a new one.

 

[Captainkirk]

Best for the street on a 340 would be a RPM or RPM air gap. I think the 650 will be ok. 750 would pull better up top.

Adam;
Just curious as to why you think a 750 would pull better up on top?
Using the CFM formula from "Holley Carbs and Manifolds" (Mike Urich & Bill Fisher), page 6.....
(CID divided by 2) times ( max RPM divided by 1728 ) times (volumetric efficiency).......
(340 divided by 2) times ( 6500 divided by 1728 ) times (85%V.E.)........
(170) times (3.76) times .85= 543 CFM
Seems like a 750 would be overkill for a smallblock?

 

[rumblefish360]

All is dependent on build. With a larger carb on top, the engine will breath easier and eeper through the larger opening instead of pulling it through. (So to speak)
If you tune the carb well, you can actaully get a 1050 Dom to work on a stock 318. But this is not what you would want to do.

 

[flyboy01]

Adam;
Just curious as to why you think a 750 would pull better up on top?
Using the CFM formula from "Holley Carbs and Manifolds" (Mike Urich & Bill Fisher), page 6.....
(CID divided by 2) times ( max RPM divided by 1728 ) times (volumetric efficiency).......
(340 divided by 2) times ( 6500 divided by 1728 ) times (85%V.E.)........
(170) times (3.76) times .85= 543 CFM
Seems like a 750 would be overkill for a smallblock?

Those formulas are supposed to work, but nobody can explain why they dont, but there are theories. Everytime you see a dyno test, the bigger carb tends to work better for HP. A small carb maintains throttle response through velocity, which is how a carb sucks the fuel through. But in reality, modern carb designs like the Demon, have superior velocity and sensitivity because they were designed with aerodynamics in mind. Thus a bigger carb can give you better flow, better HP, even with a small engine. If you are building a high winding engine, then it is even more important to go with a bigger carb.

 

[daves66valiant]

I have tried to come up with a street friendly setup that may see some romping at the track on occasion. I think it is important to get opinions but beware of information regurgitated from a manufacturer's website. I have used FABO and the knowledge of mopar industry experts to help me make an informed choice with no arm twisting or convincing. I think there are plenty of people on FABO that know their stuff and others who spew info they now nothing about personally. You obviously know what has worked on your car in the past. I echo the others that it is time for an upgrade in technology & performance that is suited to your intended performance goals.

My favorite sons once I get it all installed:
I really like the simplicity of the Demon carbs. I traded a Holley 750 DP for a 650 Mighty Demon ($500) for my 340 and really look forward to seeing how it performs. I watched the DVD that came with my carb a couple of times and feel it will be very easy to tune and setup. I got mine from FBO and its been inspected and already setup ($35) according to my car/engine/cam/gears/ignition and intended driving style.
The RPM and Air-Gap get alot of air time on this forum and probably with good reason. Don't think you could go wrong on this one. ~$200 bucks well spent. It may not be exotica but sure is easier on the pocket book.

If you are interested extra opinions then I would check out FBO at http://www.4secondsflat.com/ I know this is a shameless plug but I really like talking to the guy(Don) and he is super duper helpful and educational based on physics and engine dynamics. Fill out a spec sheet and email it to him. It may be helpful as it was for me in addition to FABO.

Originally Posted by AdamR
Best for the street on a 340 would be a RPM or RPM air gap. I think the 650 will be ok. 750 would pull better up top.

I dumped my older Holley 750 DP and M1 for the setup the above. I'm sure it would have worked well but I think my new combo will be better suited for my intended performance goals. I will be hanging onto the M1 just in case I want to race in the future.

 

[340mopar]

Adam;
Just curious as to why you think a 750 would pull better up on top?
Using the CFM formula from "Holley Carbs and Manifolds" (Mike Urich & Bill Fisher), page 6.....
(CID divided by 2) times ( max RPM divided by 1728 ) times (volumetric efficiency).......
(340 divided by 2) times ( 6500 divided by 1728 ) times (85%V.E.)........
(170) times (3.76) times .85= 543 CFM
Seems like a 750 would be overkill for a smallblock?

The 85% VE is for a stock style motor, with the items he is going to add his VE good easily be 100%. At 100% VE the formula shows a 639cfm so a 650. You want to have some cushion being this formula is just a best guess so I add 10% to the total cfm. 10% of 639 is 63.9 which equals basically 704. Just 5% more over 100% puts him at 671cfm + 10% = 738cfm. If it were my car I would run the 750.


Chuck

 

[daves66valiant]

Those formulas are supposed to work, but nobody can explain why they dont, but there are theories. Everytime you see a dyno test, the bigger carb tends to work better for HP. A small carb maintains throttle response through velocity, which is how a carb sucks the fuel through. But in reality, modern carb designs like the Demon, have superior velocity and sensitivity because they were designed with aerodynamics in mind. Thus a bigger carb can give you better flow, better HP, even with a small engine. If you are building a high winding engine, then it is even more important to go with a bigger carb.

What do you think dyno testers do half the time? They wind out the motor, use the biggest carb possible and jet it to get peak HP. People get hung up on the max HP numbers and bigger carbs. It all seems bogus if you are not racing and want a nice driving street car. Especially after you try to drive away from the dyno shop and you car runs like crap. But those dyno numbers and big carbs sure look cool. :blah5: Give me a chassis dyno tuning that incorporates crisp throttle response, idle quality, and peak HP and I'll be happy. I can't think of many times that a street car will run at 6500 on a regular basis other then at a track. Believer that bigger is not always better. Gotta go with what you are build the engine for.

There is info out there. Obviously, there is a constant battle in understanding A/F ratio and diluted air velocity and reduced air speed with bigger carbs. That is why bigger carbs on small blocks have to be highly jetted to get anywhere close the A/F ratio needed.

 

[daves66valiant]

The 85% VE is for a stock style motor, with the items he is going to add his VE good easily be 100%. At 100% VE the formula shows a 639cfm so a 650. You want to have some cushion being this formula is just a best guess so I add 10% to the total cfm. 10% of 639 is 63.9 which equals basically 704. Just 5% more over 100% puts him at 671cfm + 10% = 738cfm. If it were my car I would run the 750.


Chuck

yes yes yes. The VE of 85% is for stock. For an engine that has more efficient combustion and better atomization of the fuel from a newer carb will get better HP and TQ numbers. The 639cfm requirement with 100% VE is for WOT at max RPM. I don't know why you would need to go 15% over that if the newer carbs are better at increasing atomization at WOT. Unless that 15% extra is because the engine was built for racing. Also, when are you going to be at WOT and at 6500 rpm for very long? This is why a high performance 650 seems like it should work okay for a street car. For a race car a 750 would be my choice.

 

[Captainkirk]

According to the Holley book, 75% VE is for a stock engine, 80-85% for a modified street/strip motor, 90-95% for a full-blown race motor, and 100% only for supercharged/turbocharged motors. That's what I based my computations on.

 

[340mopar]

According to the Holley book, 75% VE is for a stock engine, 80-85% for a modified street/strip motor, 90-95% for a full-blown race motor, and 100% only for supercharged/turbocharged motors. That's what I based my computations on.

How old is that book? In a supercharged/turbocharged application you can have over 100% easily.


Chuck

 

[Captainkirk]

How old is that book? In a supercharged/turbocharged application you can have over 100% easily.


Chuck

Let's just say Carter was in the White House...

But then the engine was born when Nixon was in the White House. Things don't change as much as we think.

 

[340mopar]

yes yes yes. The VE of 85% is for stock. For an engine that has more efficient combustion and better atomization of the fuel from a newer carb will get better HP and TQ numbers. The 639cfm requirement with 100% VE is for WOT at max RPM. I don't know why you would need to go 15% over that if the newer carbs are better at increasing atomization at WOT. Unless that 15% extra is because the engine was built for racing. Also, when are you going to be at WOT and at 6500 rpm for very long? This is why a high performance 650 seems like it should work okay for a street car. For a race car a 750 would be my choice.

The CFM rating does not directly effect atomization, meaning just because a newer carb has less cfm than an older one it won't automatically atomize fuel better. It is advantagous, as far as power is concerned to have the carburator cfm match or be higher than the cfm of the engine at it's highest rpm. If you don't then you will create a vacuum in the intake. If this happens you will lose power. Nextel Cup cars experience this problem when they run with restrictor plates. One thing also to remember is that a 4 barrel carb has secondaries so at part throttle cruise you are only running on the primaries so the total cfm of the carb really doesn't come into play. Carter AFB / AVS carbs have smaller primaries than the secondaries while Holley has the same basic size on both. This is why the AFB / AVS has better response at low engine speed compared to the Holley. This small primary high level of throttle response is why I like Q-jets / Thermoquads for the street, you have the throttle response of a small cfm carb with the punch of a large cfm carb at higher rpms.

It sounds like you like the crisp throttle response more than the extra little bit of power that you would receive if you spooled up your motor with a larger carb. If this is the case then by picking a carb on the smaller side would be the right choice.


Chuck

 

[flyboy01]

Its really the quality of fuel atomization, not CFM. The last several years I have been dealing with V8 fuel injected engines, and they don't really have any penalties for too big a throttle body. It really is all about modern flow dynamics. In theory, you could go with a 1000 cfm carb on a 318 if the fuel atomization is good enough, the engine will take all the air it needs, which is why fuel injection works so well. With a carb, it is the air flow through the carb that creates a suction that pulls the fuel into the airstream, then the airstream atomizes the fuel. If that flow is too low, like a dominator carb on a 318, then the flow will slow down so much, that fuel will no longer be pulled into the airsteam, and it will lean, or puddle in the intake, causing a Hiroshima sized backfire through the carb. Of course this is an exxageration, but you get the idea. Try sucking a cup of water through a straw, then try the same thing with a 2" piece of PVC pipe. Different experience.

Everyone here seems to be right on many levels, the best thing you can do is talk to the pros, call Holley or Demor and ask them, give them your engine specifics and they will recommend what is best. I would hate to say, "you need this", then have it not work. But I would recommend any NEW carb design, newer than 10 years. Computers have made a huge difference in figuring out flow dynamics.

Remember opinions are like A**holes, everyone has one, and they all stink.

 

[daves66valiant]

The CFM rating does not directly effect atomization, meaning just because a newer carb has less cfm than an older one it won't automatically atomize fuel better. It is advantagous, as far as power is concerned to have the carburator cfm match or be higher than the cfm of the engine at it's highest rpm. If you don't then you will create a vacuum in the intake. If this happens you will lose power. Nextel Cup cars experience this problem when they run with restrictor plates. One thing also to remember is that a 4 barrel carb has secondaries so at part throttle cruise you are only running on the primaries so the total cfm of the carb really doesn't come into play. Carter AFB / AVS carbs have smaller primaries than the secondaries while Holley has the same basic size on both. This is why the AFB / AVS has better response at low engine speed compared to the Holley. This small primary high level of throttle response is why I like Q-jets / Thermoquads for the street, you have the throttle response of a small cfm carb with the punch of a large cfm carb at higher rpms.

It sounds like you like the crisp throttle response more than the extra little bit of power that you would receive if you spooled up your motor with a larger carb. If this is the case then by picking a carb on the smaller side would be the right choice.


Chuck

Sorry guys maybe I used the wrong wording or have a misunderstanding of this. Wasn't really thinking that the CFM had anything directly related with the atomization of the fuel. Was thinking that the carbs nowadays like the Demon are more efficient at improving airflow over the older designs and are more efficient by design at atomizing the fuel in high performance camed engines. Newer carbs allow improved tuning/designs to compensate for A/F mixture demands of higher performance engines. I guess it boils down to your build specs and also the engine timing needed. Carburetion is pretty cool stuff.

I don't remember exactly but I dont think the 650 size is an actual cfm rating for the 650 Mighty Demon carbs. Was thinking that the 650 Mighty Demon may be versitile enough for his combo even at 100% VE and still not be under carbed. Right, a 750cfm will make more power but may be less efficient at atomizing the fuel for the best acceleration in normal street driving. Yeah you're right about me 340mopar I like things to be efficient hince the 650 Mighty Demon for my 340.

Some believe the 650 Mighty Demon flows better than a 750 Holley (unless it is majorly tuned and tweaked). Up for debate to I guess. After reading about he Demons and wathing their DVD I'm pretty jazzed about them. The price(bang for your buck) is great, which is what the Captain is thinking about too.

If I'm misguided on this let me now 340mopar. I respect your opinion as well.

 

[daves66valiant]

Its really the quality of fuel atomization, not CFM. The last several years I have been dealing with V8 fuel injected engines, and they don't really have any penalties for too big a throttle body. It really is all about modern flow dynamics. In theory, you could go with a 1000 cfm carb on a 318 if the fuel atomization is good enough, the engine will take all the air it needs, which is why fuel injection works so well. With a carb, it is the air flow through the carb that creates a suction that pulls the fuel into the airstream, then the airstream atomizes the fuel. If that flow is too low, like a dominator carb on a 318, then the flow will slow down so much, that fuel will no longer be pulled into the airsteam, and it will lean, or puddle in the intake, causing a Hiroshima sized backfire through the carb. Of course this is an exxageration, but you get the idea. Try sucking a cup of water through a straw, then try the same thing with a 2" piece of PVC pipe. Different experience.

Everyone here seems to be right on many levels, the best thing you can do is talk to the pros, call Holley or Demor and ask them, give them your engine specifics and they will recommend what is best. I would hate to say, "you need this", then have it not work. But I would recommend any NEW carb design, newer than 10 years. Computers have made a huge difference in figuring out flow dynamics.

Remember opinions are like A**holes, everyone has one, and they all stink.

Your example of the straw and PVC pipe is what I mean by bigger is not always better. I think you are right as far as the newer carbs being designed better to allow larger carbs on smaller engines without the problems of large A/F droplets puddling in the intake but the engine better be setup for it otherwise the full potential will not be realized with the larger carb. I agree also that you should call someone at Barry Grant or Holley. I called Don at FBO because he is a Barry Grant retailer and has lots of experience with them. He has it down to a scientific calculation based on multiple factors and it's not juju theory either.
http://www.4secondsflat.com/Carb_size.html

Dave

 

[rumblefish360]

According to the Holley book, 75% VE is for a stock engine, 80-85% for a modified street/strip motor, 90-95% for a full-blown race motor, and 100% only for supercharged/turbocharged motors. That's what I based my computations on.

By todays standards, you should increase all numbers by 10.
Don is very up on the carbs and a smart fella. He loves them Demons. He can set you up well.

 

[GT340]

Adam;
Just curious as to why you think a 750 would pull better up on top?
Using the CFM formula from "Holley Carbs and Manifolds" (Mike Urich & Bill Fisher), page 6.....
(CID divided by 2) times ( max RPM divided by 1728 ) times (volumetric efficiency).......
(340 divided by 2) times ( 6500 divided by 1728 ) times (85%V.E.)........
(170) times (3.76) times .85= 543 CFM
Seems like a 750 would be overkill for a smallblock?

Go to this site and enter your numbers: http://www.corvetteactioncenter.com/tech/tools/carb.html

 

[Captainkirk]

Go to this site and enter your numbers: http://www.corvetteactioncenter.com/tech/tools/carb.html

I did.....598 to 707 CFM. So I'm right on the money, according to this.
One thing to remember, in our discussion; in choosing carb size, fuel metering is a tangible....adjustable via jetting and/or power valve size (on a Holley). Air flow is a different story. At idle, cruise and light accelleration, the butterflies are partially open, creating a higher vacuum (manifold pressure) and a lower air velocity through the venturis (hence the application of booster venturis on the Holley). At WFO, a vacuum secondary Holley or AVS/Thermoquad, etc has the primaries standing on end....engine demand opens the secondaries as needed. While this makes for a nice metering system, it is not as efficient as four butterflies standing on end (as in the case of a double pumper) due to the restriction of airflow through the venturis caused by partially closed throttle plates. We can all agree, I think, that wide open, unrestricted venturis provide the most efficient air metering device. This is why the Holley DP produces such excellent top-end results. There is a down side, of course; less torque down low at partial-throttle application due to excess air flow caused by throttle plates opened too much at lower power settings and the resulting drop in vacuum (manifold pressure), which we compensate for on a DP by squirting in excess fuel to 'cover' the bog, or sag in the torque curve via the accellerator pumps. You guys are probably right in stating that a spreadbore design such as the TQ with it's small, torquey primaries and vacuum controlled air valve secondaries would be a smarter bet for a street-only motor. I'd like to know how a TQ or AVS would compare to a Holley or AFB on a dyno run or strip test (E.T.). Unfortunately, unless one of you has actually done this, it's all a matter of debate, trial and error.
I will look into the Demon carbs; never had any experience with them. New Holleys are running about $350.00, and Proform and Quick Fuel upgrade parts are available for my 650 DP for around the same dollar amount. I'm not aware of any performance parts for the TQ, but the design is very intriguing and I'm curious if anyone is running one on a street/strip combo with favorable results?
Naturally, I'd like to get the most bang for my buck out of this build. It was extremely quick before running the 'prehistoric' Torker and 650DP, and I wouldn't hesitate to run them again. But if, as many of you seem to suggest, the equipment is leaps and bounds ahead today from what is was back in the day, I owe it to myself and this build to eke the most performance out of it that I can. Thanks for your opinions.

 

[daves66valiant]

No problem Cap. We are all here to help. Barry Grant carbs are an awesome bang for your buck. I looked into the Proform upgrade for my Holley 750 DP also. Just felt more comfortable with the qualities of the Mighty Demon. I haven't really heard anyone really complain about the Barry Grant carbs. Lots of Holley complaints though. Lots of debate to be had here. Goodluck.

Yep Rumble...Don at FBO is one of the good guys.

 

[Captainkirk]

So, as long as we're on the subject, let's hear the pros and cons of the short-lived Carter ThermoQuad. I visited the link posted on this thread....that guy sure seems to like 'em. Other opinions?

 

[rumblefish360]

Well Cap. the T-Q can be hard to tune. Parts are out there for them, but waiting a few days on a pair of jets or linkage part can really suck. Some have complained about warpping fuel bowls. While it is true, I have had none do so on me. I have overheated my engine a few times with no ill effects on the carb.
If you want to run one, I would suggest if your not up to task on a proper rebuild of one, speak with Demonsizzler on the matter. He has done work for me before with excellent results.

I do like the carb alot. It does however IMO have it's place while others will say garbage and others say any application, I yeild at race unless it's built for it.

On the street, if used properly, even with bigger cams, it is IMO an excellent dual purpose carb. You can get good mileage from it. It's wide open throttle (W.O.T.) performance is of ledgendary status known for the sound. That low growning howl.
The Carters seem to make more torque vs. the Holleys high end HP.
The Carters have allways made for an excellent set up on street rides. Be it AFB, AVS or T-Q.

You have to want to run a T-Q. I'll not try to talk anybody into running a T-Q. I can only say how I feel and what I have experianced from them.
I look foward to my next T-Q on a street stripper set up.
I also have an AVS I look foward to use as well.

Bottom line, run what your comfy with. Theres no arguement in that. No matter what they say.