I have a chance to purchase a 289 Cobra 2x4 intake with carbs. Carbs are 3258S and 3259S. Does not have correct fuel log. Carbs likely need rebuilt but recently came off running engine. Any thought on current value much appreciated.
Hi RedGT350,
I'd say between $1500 and $2000. It will be near $1200 to restore. I prefer the Holley high rise dual quad with the Holley Carbs LIST 3360 and 3361.
Best of luck
Cory
I sold same intake for $500 and had to work to get that. It was a couple years ago.
Does it have the original air cleaner assemblies? Those are really tough to find.
The dual Holley set up is a much better way to go. The differences in price reflect that.
Does not have correct air filters .
Agree with others that the set up with the carter carbs is considered undesirable compared to the Holley because they did not run as well. The value reflects that. This is not a setup that you want to invest a lot of money in if buying to flip given the market value and the much smaller buyer pool.You may be holding on to it for a while. If you are wanting for a personal car and if function matters then there are much better set ups out there. Most informed enthusiasts think when they look past the nostalgia aspect of the vintage duel Carter set up is that it is considered "the" duel four setup that didn't work that well. ;) Just my thoughts others may have different.
I had one a while back sold it for $1000 ... the only carbs that fit on it are the afb carters / maybe you could turn holleys sideways ... but i never tried that .
Quote from: gt350shelb on January 31, 2020, 07:16:54 PM
........... maybe you could turn holleys sideways ... but i never tried that .
Setting up linkage for that would be fun ;)
Have the same setup with NOS filters. The intake and carbs came with a car I purchased. Not sure if the owner ran it or just purchased it hoping to get around to it
You can use Dominator linkage for that. Those carbs ares so big you mount them sideways. Linkage works fine.
What makes the 2x4 Holley set up work well is not necessarily the carbs. The vacuum secondaries do work but it is the way that the dual plenums on the intake are designed and the Ford 427 2x4 linkage works progressively.
None of the dual AFB setup has that.
I have been running the small letter COBRA dual quad intake for over 40 years on hot street engines. For all out race engines turning 7500 rpm plus the Holley set up is best. For the street it will outperform any vintage 4 barrel carb set up, it looks good runs good and you will get smiles from anyone that looks at it or anyone driving or riding in your car, just make sure you have an engine that can benefit from multi carburation. ;)
Quote from: shelbydoug on January 31, 2020, 08:24:43 PM
You can use Dominator linkage for that. Those carbs ares so big you mount them sideways. Linkage works fine.
Doug where can you find the duel Dominator linkage? I have that setup and I'm intending to build an engine before too long for the Dual Dominator. I have been running the Dual Holley set up on a factory TA style intake for over 40 years and it runs great. I also have another NOS TA intake and also one of the independent team 2/4 TA intakes. I figured I would have to custom make the linkage for the dominators but if you know where to get it I'd sure like to know.
TIA. Roy Richards
The most impressive sight one will ever behold is the sight of dual DOMMINATORS on a small block Ford. I have never been smart enough or willing enough to drop some major coin, on the use of this set up. The sight and sounds emitted from such engines running this set up will treat your senses to something you will never forget. Think of one of VOGTS engines getting ready for a spin. :) It is the most impressive so over the top setup that you would think its impossible to make it work... OOOOH they make it work all right, you just need the rest of it to go along with the ultimate small block set up. PURE AWESOMENESS.....
"Doug where can you find the duel Dominator linkage? I have that setup and I'm intending to build an engine before too long for the Dual Dominator. I have been running the Dual Holley set up on a factory TA style intake for over 40 years and it runs great. I also have another NOS TA intake and also one of the independent team 2/4 TA intakes. I figured I would have to custom make the linkage for the dominators but if you know where to get it I'd sure like to know."
Most racers are going to make up their own sideways linkage since there is hardly a universal application for dual Dominators at all? It's been over thirty years since I built one for dual Dominators but there are a starter kits that can give you a basis to work with.
Here's one.
https://www.summitracing.com/parts/edl-7077
I agree that multiple carburetion runs much better then you can do with any single 4v carb.
There aren't many that have done side by side comparisons and it isn't necessarily the difference in total horsepower that makes them better. It's the progression of power throughout the rpms from right off of idle, not even just high rpm power.
I think it is also true that in many cases it is difficult enough to deal with only one carb and multiple carbs raise that to a power sometimes of an unknown number complete but they do come with all of the rights and privileges, i.e., frustrations.
When you have them running right though the rewards are worth it.
Just the sound of the "whomp" when they open is awe inspiring alone but not for everyone. It's a very ancient analog thing vs. a computer digital thing, like running from a Tyrannosaurus Rex for you life! ;D
GM used Carter AFB two fours on many combinations and so did Mopar but the Holleys seem to work much, much better.
There are also more then just a couple of 289 Cobras with the Carter 2x4s on them and I can't ever recall the dual Holleys on a 289 Cobra that I can think of.
These seem to originate around the time of the Shelby 289 T/A coupes?
I personally can attest to more then just a little finagling with the Ford linkages to get these things to work right.
On the street, I'd say use the 427 dual for linkage that mounts the carbs backwards with the primary carb (with the choke) in the front. It can be a little finicky and time consuming to get just right.
The later T/A cars (intended for racing) wisely mount the carbs the other way. From what I see that is simply for race simplification of the throttle linkages, since there it matters little where the choke is and what if they pull smoothly off of idle. Those cars were just virtually run at WOT all of the time.
I don't like The proximity of the carb bowl to the distributor cap with the carbs mounting forward. I consider that inherently/significantly dangerous. I have already lost two cars due to carb fires and I don't want another.
Mounting the carbs backwards gives more than an additional 1/2" clearance to the cap. Call me finicky if you like?
I am pretty sure vs. very sure that the original Shelby Boss 302 Trans-Am car had dual Dominators mounted sideways on a unique intake manifold.
I believe it was Randy who posted pictures of it on the crashed forum? Inquire there.
Quote from: REDGT350 on January 31, 2020, 11:25:38 AM
I have a chance to purchase a 289 Cobra 2x4 intake with carbs. Carbs are 3258S and 3259S. Does not have correct fuel log. Carbs likely need rebuilt but recently came off running engine. Any thought on current value much appreciated.
The T/A style with rounded runners is the most desirable and best performing of the small block 2x4 intakes. The TA intake commands much more money than the other versions. If this lead you have is the same one I saw recently out there in internet land, then it seems IMHO to be alittle steep on price for what it is.
Here is the C60A T/A manifold on my car with a matched pair of 427 Ford Holleys, 3300 and 3301.
I never actually tried to see if Dominators would fit but I'm not sure there is much point at all to that as a solution to anything?
On the surface one would think that what I have here is drastically over carbed? I can tell you that it isn't at all but I think that it being a 347 based on the original 302 block has a lot to do with that?
It's also very responsive to throttle input and so far I can't tell you how high is up yet.
I'm not even sure Dominators would fit in the engine compartment. Notice the secondary carb is already up against the firewall?
It's going to take me a long time to find this setup boring...and yes it is factory air conditioning.
These Webers are on my Pantera. Boring they are not either but are a bit different to the 2x4 Holley small block.
The linkage for them is actually simpler, believe it or not, then the backwards Holley's.
I won't show you the 2x4's on my 67 GT500. Those are rather run of the mill.
I hope there is no one here from "Green Peace"? I wouldn't want to seem to upset the ecological balance of this planet?
Oh. I by no means profess to be an expert on anything but I do have some experience with these setups, burnt knuckles, head bumps, pillaged wallets and probably can save you some wasted time, money and effort in pointing you in the right direction?
Just like age and cunning (cheating) overcomes youth and exuberance every time, highly experienced often overcomes highly intelligent? It could save you a divorce also? ;)
Forget about the Carters. If you want multiple carbs go with the Holleys or the Webers.
Here are pics of the Ford "high rise" 2x4. This one is a Blue Thunder and is probably more then anyone could need? (top pic)
The other pic is of the T/A. You can clearly see the shape of the runners. It's really a little bit of a strange duck. I immediately lost 4 inches of vacuum installing it.
It isn't so much that the T/A runners are rounded, they just plain have a larger cross section with greater volume.
When you examine it you will clearly notice that the runner lengths are close to equal, each runner acts as an isolated individual port runner and idling with connected plenums is kind of a hookie-dookie dance.
The regular hi-rise set up probably got more of a "Holy Shitskies" reaction then the T/A simply because VERY few have any kind of idea what they are looking at. If they did, they would just realize what a sick puppy I really am I suppose? Ah...TS to them (tell Superman)? ;)
They both have some similarities to an individual runner manifold at WOT. The T/A has more and you could consider it a mini-tunnel ram with an idle plenum?
Doug, have you tried the Blue Thunder 2x4 & compared the performance against the T/A intake ??
I am pretty sure there's an old thread from last year where Randy said has done a side by side comparison with the blue thunder and the T/A and there was significant difference. Here is the C6OA that I have with 1850's on it.
Quote from: Wedgeman on February 01, 2020, 02:58:38 PM
Doug, have you tried the Blue Thunder 2x4 & compared the performance against the T/A intake ??
Yes. There is a noticible difference.
Consider though that the Blue Thunder ran with 2/1850's. The T/A handles the two 715's.
If you think about it, that isn't out of line? It's like a 700dp with vacuum secondary "afterburners", so a 700dp mated to around a 350 ci engine is about right.
The vacuum secondaries only open when the engine can handle it.
I was told that the reason the race cars went to the mechanical carbs with center squirters is that the drivers complained that the vacuum secondaries had issues closing when necessary?
The Blue Thunder idled better with more idle vacuum. 14 inches. The T/A immediately dropped to 10.
I'm still looking for a vacuum leak but may be resigned that the manifold is just a strange "Alien" device and that's all it provides and to install a vacuum pump?
Consider that the idle quality was never a serious consideration as it was to my knowledge never intended to be on a street engine. I would describe it as VERY streetable (except for this lack of idle vacuum).
There are remnants in the design of the manifold from something that would have a street application such as a heated exhaust cross over and what apparently was intended to have the primary carb primaries centered in the manifold?
Randy thought that it is worth another 20hp and would loose 20 lb-ft but you can't prove that by me. I presume he was thinking of a 289?
Neither was he surprised when I asked him about the vacuum drop. He expects some loss of idle vacuum because of the larger runners. I just didn't expect a 4 inch loss?
For a race car, that's not any kind of issue. A street car with power steering, power brakes and air conditioning (and a tilt-pop steering column) needs vacuum.
It would be great to have a dyno in my garage but my impression is that I just went from a 450hp engine to a 500hp engine?
It may be a little much for an average enthusiast to deal with because of these "quirks"? I can't speak to that other then I'm not sure I'm done with setting the engine up again from just the intake swap?
Quote from: JMobley on February 01, 2020, 03:21:42 PM
I am pretty sure Randy has done a side by side comparison with the blue thunder and the T/A and said there was significant difference. Here is the C6OA that I have with 1850's on it.
He's about as knowledgeable as anyone is going to find on that subject.
Doug, you would be far better off running 390's or 465's over running a 600 or larger carburetor. You would pick up performance overall. I have Run 390's and 465's on my 302 Windsor like I said for over 40 years. They have run great all the way to 8200 RPM. I used to run the car quite a bit at Willow Springs back in the day. Here is the best article I've ever seen on 2x4 setups and they have a lot of pictures including the Dual Dominator setup on a couple of Trans-Am cars. They also have a picture of the Cobra 2x4 Carter intake. The Duel Dominator setup uses an IR intake which I have along with a pair of NOS carburetors and the offset distributor that it requires. Randy and I have known each other for over 40 years and he is one of the most knowledgeable people on Ford engines especially small blocks that I know
https://www.hotrod.com/articles/5-tips-dual-quad-carburetion-success/
Sincerely, Roy Richards
Quote from: TA Coupe on February 02, 2020, 05:01:28 AM
Doug, you would be far better off running 390's or 465's over running a 600 or larger carburetor. You would pick up performance overall. I have Run 390's and 465's on my 302 Windsor like I said for over 40 years. They have run great all the way to 8200 RPM. I used to run the car quite a bit at Willow Springs back in the day. Here is the best article I've ever seen on 2x4 setups and they have a lot of pictures including the Dual Dominator setup on a couple of Trans-Am cars. They also have a picture of the Cobra 2x4 Carter intake. The Duel Dominator setup uses an IR intake which I have along with a pair of NOS carburetors and the offset distributor that it requires. Randy and I have known each other for over 40 years and he is one of the most knowledgeable people on Ford engines especially small blocks that I know
https://www.hotrod.com/articles/5-tips-dual-quad-carburetion-success/
Sincerely, Roy Richards
One of the nice things with this setup is that there are so many possible combinations.
Most likely for me, I'm not done experimenting?
I initially set up the high rise with two converted 4180 ('85 Ford GT) carbs. Those are generically a "600 cfm" carb but with the annular discharge boosters probably closer to 565 or so.
I had tried a pair of 1850s with the high rise and the 4180s were much better.
The article is very interesting but doesn't deal with a small block application at all. There is much specific cross over information that does apply.
Don't forget that on the T/A manifold, the carb application eventually arrived at 660 center pumpers with mechanical linkages. On a 289, if that isn't over carburation for the street, I'm not sure what is?
It doesn't touch why the dual dominators work on a 302 either. That simply is because the manifold is an IR design and that is as close to running Weber 48 IDA's as anything.
The Holley "carb size demand chart" is for a 180 manifold with a center plenum. IR manifolds need to be dealt with by the individual flow of the port.
Interestingly enough, I am having the same issue of getting the engine to idle down from 1250 and I haven't looked at the secondary settings. A great reminder!
When I switched over to the T/A, I also had some technical maintenance issues and wound up switching to 1.7 shaft rockers, and AFR 185 heads (which immediately bent all the push rods).
I had the 3300 and 3301 here restored by Holley and they needed to be wet checked and run in so...guess what?
Now all I can do is in an attempt to maintain some semblance of sanity, which probably went out the window for me 30 or 40 years ago, and drive the thing enough to get an idea of where to go with this set up?
Don't forget that I am also screwing around with the advance, both the initial, rate of advance and total? The aluminum heads are throwing some major curve balls and I'm still searching for cause and effect in several cases.
Not to change the subject and compare t-bone steaks with apples but I learned from my Audi TT turbo that running lower boost at 20 psi with a different curve makes much more power then it did at 28 psi and it doesn't blow up the intercooler!
I don't doubt that there may be better carb combinations and that the much smaller carbs yield more area under the curve but my impression was that the smaller carbs (so far) made TOO MUCH torque for my gearing with the Doug Nash 4+1.
So so far I have gone through the 4180's, the 1850's, and the 3300's. I have not tried the 465's and I just looked at my electric bill for the month and it is clear that I won't be for some time.
VERY fortunately for me, I don't have to run a head to head match up against you and Randy. I'd probably screw it up anyway and blow out the clutch or blow a tire?
Strangely enough but probably predictably, I've run into a scenario where my 2.5 mile test circuit is just too short to accurately test these combinations. I really need probably days or weeks of time on a road course like VIR to accurately make decisions on which is the best combination. I'm probably way over my head with driving ability since the car is really at a T/A level already and I need someone like Miles, Donahue or maybe Possi to drive the car and tell me what it needs?
I guess since these "issues" aren't likely to happen with "standard improvements" and I suppose that indicates some level of success on my part? It probably also indicates the accuracy of the adage of "be careful of what you wish for because sometimes you get it!" ;)
You see, for me, these solutions just create issues in other areas? Adult diapers aren't cheap and my friendly local cops don't argue, they just stare and back away. The NYS troopers however are the "Gestapo".;D
I do appreciate these types of discussions since it benefits me as well as others with information that only insane folks would be able to obtain in a nut house if we were all locked up together?
However, there are others here that are also hopelessly infected and this info could help prevent nurses chasing them with big hypos filled with sedatives, so carry on.
The true answer is something that I really heard from Randy, "I just got you into the game, you need to figure out the details".
It's now like Force complaining to Coyle that the car doesn't make enough power and Coyle shooting back, "hey, sometimes you need to get the monkey to pedal the car". In my case it's only me. 8)
Also, I acknowledge that ultimately I may be forced to decide which carbs are best simply for simple "streetability" of the entire car, and simply put, I just don't know where that is yet, but inevitably I will... eventually. Check. Acknowledged!
Quote from: shelbydoug on February 01, 2020, 02:31:58 PM
It's really a little bit of a strange duck. I immediately lost 4 inches of vacuum installing it.
It isn't so much that the T/A runners are rounded, they just plain have a larger cross section with greater volume.
Quote from: shelbydoug on February 01, 2020, 03:22:41 PM
I'm still looking for a vacuum leak but may be resigned that the manifold is just a strange "Alien" device and that's all it provides............
There are many possible effects which may cause the vacuum pressure loss (often defined as a manifold pressure gain), but in limiting responses to the above, I would expound upon this suggesting that one is correct in stating that the larger intake port runner at fault, but also, in that a reduction in the carburetor signal is experienced, the carburetor being say somewhat deafened, losing it's responsiveness in fueling reaction, and requiring an increase in the throttle area, even if only for idle control; therefore the same engine is displacing the same area (R.P.M.), but with an increased leakage rate (reduction in throttling), hence loss in the pressure drop. ;)
Scott.
Quote from: pbf777 on February 03, 2020, 12:07:39 PM
Quote from: shelbydoug on February 01, 2020, 02:31:58 PM
It's really a little bit of a strange duck. I immediately lost 4 inches of vacuum installing it.
It isn't so much that the T/A runners are rounded, they just plain have a larger cross section with greater volume.
Quote from: shelbydoug on February 01, 2020, 03:22:41 PM
I'm still looking for a vacuum leak but may be resigned that the manifold is just a strange "Alien" device and that's all it provides............
There are many possible effects which may cause the vacuum pressure loss (often defined as a manifold pressure gain), but in limiting responses to the above, I would expound upon this suggesting that one is correct in stating that the larger intake port runner at fault, but also, in that a reduction in the carburetor signal is experienced, the carburetor being say somewhat deafened, losing it's responsiveness in fueling reaction, and requiring an increase in the throttle area, even if only for idle control; therefore the same engine is displacing the same area (R.P.M.), but with an increased leakage rate (reduction in throttling), hence loss in the pressure drop. ;)
Scott.
"Throttle area"? Are you saying that it could be larger carb throttle plates could be part of it?
Well, it's a little different but consider this scenario: The tuning of your engine is approximately correct, but you choose to richen the fuel mixture "some" to the point of idle speed loss, so to offset this, you open the throttle "some" (idle screw-stop) in relation to its' previous sum to raise the R.P.M.'s back to where it was, but I'll bet you'll loose some of the vacuum value in the process. Or say your initial ignition timing is somewhat conservative, so you increase it's value, now the idle speed has increased, so you decrease the throttle opening to reduce the R.P.M.'s back to where it was before, and I'll bet you'll increase the vacuum value.
Now, different engine states of tune will respond more readily to this effect than others, but generally this is what one can expect to experience. There have been many classes of racing in which a manifold vacuum value has been incorporated into the rules, and these participants will learn all the tricks to creating more than the typically expected manifold vacuum values considering the camshaft and induction. ;)
Scott.
Here's a link to part one and part two of an article that directly relates 331 stroker small block Ford. The results may surprise you.
http://www.mustangandfords.com/project-vehicles/mdmp-1206-dual-quad-carburetors-testing-part-1
http://www.mustangandfords.com/how-to/engine/mdmp-1207-dual-quads-twin-win-or-double-trouble-part-2
Roy
Quote from: TA Coupe on February 03, 2020, 08:53:48 PM
Here's a link to part one and part two of an article that directly relates 331 stroker small block Ford. The results may surprise you.
http://www.mustangandfords.com/project-vehicles/mdmp-1206-dual-quad-carburetors-testing-part-1
http://www.mustangandfords.com/how-to/engine/mdmp-1207-dual-quads-twin-win-or-double-trouble-part-2
Roy
Thank you Roy.
As I recall, the general consensus of that test was that the engine was under cammed substantially and as a consequence the results are questionable.
I suppose the results are proportional but considering an engine like that should produce documented results in the 425 to 450 hp area, and they are showing half throws in my mind questionable competency in the test itself?
I suppose you could blame that on the dyno but showing half would even question the rationale of even building a 331 when a 289 4v A code should show more?
To me, that was an absolutely terrible test and really shows little. It isn't worth the paper it was printed on.
Quote from: pbf777 on February 03, 2020, 08:04:34 PM
Well, it's a little different but consider this scenario: The tuning of your engine is approximately correct, but you choose to richen the fuel mixture "some" to the point of idle speed loss, so to offset this, you open the throttle "some" (idle screw-stop) in relation to its' previous sum to raise the R.P.M.'s back to where it was, but I'll bet you'll loose some of the vacuum value in the process. Or say your initial ignition timing is somewhat conservative, so you increase it's value, now the idle speed has increased, so you decrease the throttle opening to reduce the R.P.M.'s back to where it was before, and I'll bet you'll increase the vacuum value.
Now, different engine states of tune will respond more readily to this effect than others, but generally this is what one can expect to experience. There have been many classes of racing in which a manifold vacuum value has been incorporated into the rules, and these participants will learn all the tricks to creating more than the typically expected manifold vacuum values considering the camshaft and induction. ;)
Scott.
Here's the thing though Scott. Running smaller carbs on a t/a manifold is just going to run the engine lean at some point, if not at every data point.
I'm at 16 degrees initial and searching for the right combination of timing and throttle opening.
I am actually showing a hair lean with the 3300/3301 combination right now at idle.
A 700cfm dp Holley is about right for a a 347ci engine. I did run a 4779 on my Cleveland and that was just a hair to much.
Here with two 715 vacuum secondaries, if the engine doesn't need it, then the secondaries will compensate for that. Those are also tuneable with opening points.
Where I THINK this is going, is less initial advance. Maybe 10 to 12. Less total advance. Maybe 32 to 34. A larger initial throttle opening?
I DID have 14 inches with the t/a and the 4180's initially but had problems with those carbs trying to enrichen the idle. They were so lean they were dulling the ceramic on the headers.
I do have a pair of old 1848's here that aren't ready to run yet. Those are a possibility to at least test in the future?
As far as testing 2x4's on FE's, I just want to point out how Ford itself ran the gammet going from 652, to 715, to 780's.
They, just like the car magazines had dynos also. Wow! Imagine that?
So the only thing I can determine for sure right now is, testing in progress, final results to be determined...AND the t/a is somewhat of a different beast then the high riser and maybe just a little steep learning curve at the moment?
After reading the which is best, it became clear that there is only a handful of people interested in vintage performance pieces. The sad fact is that very few of us want to feel the way it was or is. Very few tinker around with their toys or are worried about even driving their cars anymore. To those that can and do, it is the most awesome feeling experiencing what our for fathers concocted for some good times. ;)
Quote from: shelbydoug on February 04, 2020, 10:41:08 AM
Here's the thing though Scott. Running smaller carbs on a t/a manifold is just going to run the engine lean at some point, if not at every data point.
Not to be stickler for details but, your description of anticipated lean event is not fully accurate, although commonly stated, and my intention is solely to aid. ???
It's probably better to understand that the carburetor first and greatest function is that of an air-valve, controlling the total sum of atmosphere being allowed to enter into the engine's cylinder(s), and remember that the volume is constant, within the pumping efficiency of the device, only the density changes with the throttling effect, so often this sum is defined in weight measurements. And this is the only effect one has as one operates the throttle, with the exception of the accelerator pump function on the transitional throttle motion.
The responsibility of fuel application should be considered as a secondary function of the carburetor, as it is a reaction to the first. It is the air motion thru the carburetors' venturi(s) which syphons the fuel from the reservoir within the fuel bowl(s), perhaps also understood as being forced out into the created lower pressure within the venturi by the higher pressure of the nominal atmosphere acting upon the fuel within the bowl(s).
So, in the example of the carburetor(s) being "too small", what most often actually happens is that as the engine capacity requirements encroach upon the the carburetors' throttle capacity one encounters the effect of throttling, the density is reduced (and so is the fueling requirement) with a pressure reduction experienced within the induction system, even though the volume passing the venturi(s) is still increasing with R.P.M., and with this increase in the pressure differential the fuel is more effectively syphoned, and in reality the performance drop-off from carburetor restriction will be yes, the lack of available air delivery, but the greater offender will be a fueling mixture going to rich! ;)
As an example, perhaps, one recalls the old adage in drag racing of tuning a rich mixture for best E.T., and a lean mixture for M.P.H.? And that kinda sums it up short & sweet! ::)
Scott.
I have a 67 mustang with a 347 and it has the T/A intake with the 390 cfm carbs and I can't say enough about how great it runs and has a decent idle even with a big comp roller cam. With the AFR 185 heads it certainly has 400+ hp and does not bog or hesitate at all, very satisfied with it. Just to mention The carbs are backwards as on big blocks.
Quote from: pbf777 on February 04, 2020, 08:25:59 PM
Quote from: shelbydoug on February 04, 2020, 10:41:08 AM
Here's the thing though Scott. Running smaller carbs on a t/a manifold is just going to run the engine lean at some point, if not at every data point.
Not to be stickler for details but, your description of anticipated lean event is not fully accurate, although commonly stated, and my intention is solely to aid. ???
It's probably better to understand that the carburetor first and greatest function is that of an air-valve, controlling the total sum of atmosphere being allowed to enter into the engine's cylinder(s), and remember that the volume is constant, within the pumping efficiency of the device, only the density changes with the throttling effect, so often this sum is defined in weight measurements. And this is the only effect one has as one operates the throttle, with the exception of the accelerator pump function on the transitional throttle motion.
The responsibility of fuel application should be considered as a secondary function of the carburetor, as it is a reaction to the first. It is the air motion thru the carburetors' venturi(s) which syphons the fuel from the reservoir within the fuel bowl(s), perhaps also understood as being forced out into the created lower pressure within the venturi by the higher pressure of the nominal atmosphere acting upon the fuel within the bowl(s).
So, in the example of the carburetor(s) being "too small", what most often actually happens is that as the engine capacity requirements encroach upon the the carburetors' throttle capacity one encounters the effect of throttling, the density is reduced (and so is the fueling requirement) with a pressure reduction experienced within the induction system, even though the volume passing the venturi(s) is still increasing with R.P.M., and with this increase in the pressure differential the fuel is more effectively syphoned, and in reality the performance drop-off from carburetor restriction will be yes, the lack of available air delivery, but the greater offender will be a fueling mixture going to rich! ;)
As an example, perhaps, one recalls the old adage in drag racing of tuning a rich mixture for best E.T., and a lean mixture for M.P.H.? And that kinda sums it up short & sweet! ::)
Scott.
Semantics.
A 450 cfm carb with 75 jets tells me something about fuel delivery and the timing of it in specific rpm ranges. When compared to a 750 running 65 jets on the exact same engine.
Most likely the engine demand for fuel is being restricted by too small of a venturi in the case of the 450.
The runners on the T/A out of the box are 250cfm. The high rise, 220 worked. That right there explains a lot.
The flow of the heads at 297 at .500 complicates things in a nice way, but the flow at mid lift is better then the race heads of the day were.
Horsepower is also a function of engine torque delivered in a faster, i.e., shorter time. The shorter the time, the higher the number.
The amount of time to deliver the fuel to the engine is really what is being tuned here.
The variables cannot be tuned infinitely and instantaneously. Two 715 carbs may be too large. Two 390 carbs may be too small BUT they may not be.
They both could be perfect in a certain rpm range.
It depends on the time period each is allowed to deliver. The 390 needs more time. The 715s don't.
Gearing here is also significant. There are 2v carb'd 351 station wagons running 11 seconds.
It all depends on what you get and when.
The tuning can stand as it is now. I learned something with the Webers a long time ago. After a period of time they seem to be flat and lacking. Pull them off and go back to the single 4v and wow! You just gave away conservatively 100hp! Now they don't seem so flat do they? ;)
Ultimately it depends on the person deciding. What's good? What's not?
In this case, my case, only actual testing can illuminate a choice of performance characteristics, that is unless there is a dyno that can simulate a run available. An actual and variable loading.
Then the best combination can be selected and maybe for each segment of the run.
That generally can not be done with an analog system (carburetors) but is possible with a digital system, electronic fuel injection which can plot each rpm.
Of course I did see that done by Bob Ingles with carb'd BB Chevy Pro Stock engines in the late '80s but that was the early days of that type of tuning to non multi-billionaire types that I had any introduction to. So I suppose my statement isn't completely true just not easy or cheap to accomplish.
It is said that Ford actually built a computerized dyno like that in 65 or 66 to run the MKII 427 GT40's through a LeMans cycle (simulated race) to determine the best operation of the engines for the greatest probability of success and dependability.
Mine is the school of hard knocks method. The grey hair at this point counts for something? Lots and lots of grey hair. You just need to keep it short enough to keep out of your eyes so it doesn't blind you to what is going on. Not so easy sometimes?
Quote from: shelbydoug on February 04, 2020, 10:40:32 PM
Most likely the engine demand for fuel is being restricted by too small of a venturi in the case of the 450.
Remember, the engines' demand for fuel, within a relatively narrow ratio range, is commensurate with the volume of air. ;)
Scott.
I was looking for an old post and ran across this one and thought I would show a couple of pictures of the dual dominator on 1 of my engines. I was just setting it up so I could take a few measurements. Also a couple of pictures of a dual dominator set up in a car and also on an engine stand.
Roy
A couple more
I do realize that the dual Dominators is intended to run with somewhat of a radical cam profile but how "streetable" is that set up?