Being a novice, I like the long winded videos and see them as a positive because it gives you time to explain all scenarios and helps me understand better. However, I can understand where experts may already know or may surmise half of the things you explain. I appreciate everyone’s patience with us novices and appreciate Eric can reach all of his wide range of audience’s levels of experience. Thank you!
Properly tuned carbs make more power. Too many people just want to bolt a carb on and maybe at the most change jets. There's more to it than that. great video Eric!
I'll say this: on the '86 K2500, switching over from an edelbrock AVS2 650 to a Holley 390 CFM. For anything less than 4,000 rpm, thing works great. Better, quicker part-throttle response, and doesn't run out of power while towing and/or hauling. Also gives a bump to fuel mileage as well. My working theory is that smaller carbs have greater part-throttle resolution and can more accurately meter fuel delivery under lighter loads than larger ones.
I noticed the same thing. I have a 69 F100 with a healthy 347 stroker that I pull my jet boat with. The truck runs great with the 750 double pumper it was first set up with, but pulling the boat it wasn't great. Changed to a 600 vaccum secondary and the performance from idle to 2500rpm is much better. Especially coming up a steep boat ramp. The power from 4000rpm to 6500 is definitely down though
What you are doing is starving it for air so leaner on air creates good vacume at throttle so better reponse you should have some one else drive and gun it while you watch what comes out tail pipe then pull a plug Black and sooty is not good But thats only about 100 horse out of 350 Your kidding your self if you think your going to out pull anything like that
@@alonzahanks1182 if I was going WOT to redline, yeah. I would be starving it. However, I'm not. I don't need all 400 HP and 370 lbs-ft to tow. Transmission and rear gets to do most of that work for me.
The way you analyze data reminds me a lot of my friend and mentor who passed away a few years ago. He used to say give it what it wants, if you pay attention to the output and the condition of the plugs and pistons and rod bearing uppers, it will tell you. He hated “Gospel thinking when it came to cams and induction and liked what he liked based on how it worked.
To be totally fair you either needed to install a choke plate in the 650 DP or remove the choke plate from the 750 VS because the choke plate affects flow. Moreover, the 750 VS is controlled by the spring in the diaphragm. It comes stock with a plain spring. Look up on the chart and you can see to fully open for a 400 cubic inch engine is 7130 RPM. So anything below that RPM won’t be fully open. You have to play with the springs on a VS carb in the same way you play with squirters & pump cams on a DP. I have always had the best performance with the purple spring. I will add that I don’t know how different the dyno loads the engine VS being in a car so possibly the lightest spring being the white one may need to be installed for the dyno. So in summary the comparison between the 650 DP and the 750 VS is not accurate until you can get both carbs to fully open both with or without choke plates. Much appreciate your efforts to educate us.
Big carbs work with big torque converters. Put that 350/1000 CFM carb with a 2200 stall and it won't be happy unless the driver modulates the throttle. Mash it from a stand still and it will stall, or at least bog substantially. I have a Holley 950 UXP that bests pretty much anything else in terms of peak numbers, but you could never use that in something other than a street/strip carb because the part throttle cruise is miserably rich. I've tried various setups to cure it, but most of the time you can bolt on a Holley Brawler for about 2/3 the price and it works great, albeit making a few less numbers. I've had lots of carbs on the dyno, some are old crusty Qjets/modified Chrysler 6 packs/Holley 4 bbls that surprised me how well they worked. I've also dealt with misery such as new out of the box carbs that should be flawless but had drivability woes or unexplainable jetting requirements to make them work. My least favorite is the customer's old carb that immediately squirts out of the bowl vent when you turn on the fuel pump, I can't tell you how many times that's happened.
I had 4 Holleys that I was testing on my 81 camaro, 383 stroker, super t10, 3.42 gears. I had an 850dp, a few 3310s, and a 650dp. The 650dp always outperformed all of them on the street and strip. That being said, I never gave the 850dp much of a chance, I bolted it up and ran a 12.55 @115, but the 650dp ran 12.33 @117. The 3310 carbs would not breach 110mph. That was 20 years ago.. I am now bulding an 1986 IROC z28 with a 327, and my first choice is 650dp. The brawler 650 looks like a great choice!!
It's the annular boosters that make all the difference. Fuel distribution is more important than max cfm. I used to run an annular booster mighty demon 850 on a 452 cu. in. FE. It made the same horsepower as the 8V Weber 48IDA setup.
First car in HS 306SBF with a 3310, 1"open spacer, on a Torker II. Super responsive throttle, excellent driveability. Didn't have access to Widebands in late 1980's only a vacuum gauge. Everyone told me it was way too big. Soft secondary spring and the bigger pump gave it enough of a shot to get the fuel moving off idle. Would do again LOL.
Great info! This solved a 40 year old mystery for me. I replaced a 4777 with a new 3310 looking for more power out of a 302 Ci Chevy in 1984 (327 block, 283 crank). The 3310 made less power than the 4777 (slower ET). I never considered that the vacuum secondaries could have been the problem. I put the 650 back on and a few months later replaced it with a swap meet 4781. The power increase was noticeable between the 650 and the 850. Nothing but double pumpers for me after that. Now I know why the 750 vacuum secondary carb didn't work out for me. Thanks Eric!
Makes sense to me. I used to put a screw in the linkage to make sure the secondary's were opening all the time! I know it would have been better to have a double pumper, but hey, that was 40 years ago!
The 650 made more power from the extra fuel discharged from the secondary squirter nozzles under WOT. Believe it or not, extra fuel is pulled out of the squirters due to the pressure differential across the top of the carb at high engine speeds. Engine Masters encountered this same phenomenon while conducting similar carb tests. A Vac Secondary carb only has one set of primary squirters, where the DP has two sets, primary and secondary. More fuel = more power. Awesome video Eric. Thanks. 🍻
I have done carb comparisons several times on various engines. On the road and on engines that are flat out @ 6000 rpm. Maybe. 289 auto Ford,, 750 dp v 600 v 750 vacc. 600 was by far the best, the 750 really struggled @ under 3000. The 750 Vacc did a better job but still dead down low. 327 Chev with 4 speed. Tried 600, Q jet, and Thermoquad. Q jet best at 2000, TQ best all round and 600 was well ok. These were all carbs off the shelf. The TQ was a near new 340 Mopar carb. 355 Chev race engine. Used a 650 DP. then a 750dp. Same track and it made aprox 250 rpm more on a long straight. Since the engine was 4000-7200 throttle response on slow corners was similar. Lap times with the 750 were a little better. Same engine, 750dp V 830 annular.Very wet meeting but the 830 was actually more driveable and I could use a gear up to normal and it was faster than most. Top end was a little better as well. Compared that with a 750HP and the annular was better more so at 4000-5000 rpm range. 400 Ford,, 780Vacc v 670 street Avenger. 670 was better everywhere except top end. And used a lot less fuel. 351C mild race engine,, Used 750 Vacc that worked extremely well and made the same top end power as a 750DP. DP however was a little faster. Better response off slow corners [4000 rpm] 750 HP was marginally better and seemed to use less fuel. Tried a [brand new] 750 E85 Quik Fuel on the dyno only, Made no more power than on petrol and was harder to start. No driveability under 2000 rpm. As a performance carb the 830 annular was by far the best, a pity Holley do not still sell them. The race engine results were on 100 Avgas. Street engine results on premium 98 unleaded.
i had a 1000 on a CT 350 , it ran perfect and nobody could touch it. the number one reason people struggle with big carbs on small motors is the set up. it’s a compressor and will only pull so much air, therefore you have to reduce the amount of fuel getting dumped in from the accelerator pumps/ nozzles and usually run bigger jets than it had on a big motor. reason for that is the big motor pulls more volume of air through which in turn will pull more fuel. on a small motor it has less pull and cannot draw enough fuel from the same jets. for example the 1000 on my super late model has 80 mains and the same carb on my CT 350 has 84
I have always answered the question of vacuum or double pumper , is it depends on how you drive. If you floor the pedal, use vacuum. If you drive into the carb, go double pumper, and make more power. I had other's try to drive my car and floor it, and it would stumble and quit, and I could drive it and lay two solid stripes for quite a ways. big difference in driving style.
I'll tell you something Eric. I'll start by saying I love all of your content. You can never win an argument with these internet mechanics LMAO😂. I mean look you're an expert in your field with years of experience, dyno pulls and I'm sure the list goes on. I know that you are a humble man and you will say that " I'm no expert ". The truth is that the internet is a terrible place. At least to me it is. The truth is I never selected a carburetor by doing a mathematical formula. I actually took the car to the track during test and tune nights at the drag strip and swapped carbs around until I was happy with the performance. GUESS WHAT HAPPENED? The bigger carb always ran better. Of course I'm talking about a drag race street/strip combination. We're not talking about grandma's 1978 Impala. Man oh man..... Keep up the good work sir
An annular booster carb will always make more power than down leg boosters. Although, some will say, the larger boosters restrict some air flow. But being created equal the annular booster will out perform. Also for drivability the annular booster atomizes the fuel better even at lower engine RPM'S than down leg boosters.
@@tomhowe1510 Because the fuel is atomized more efficiently compared to down leg boosters. More fuel is able to be completely burned which in turn creates more energy. Annular boosters also help to reduce fuel deposits within the intake manifold and cylinder heads where they could potentially drop out. That is why fuel injection is so popular regardless of its tuning capabilities. Ford in the 80's took advantage when using Holley carbs and installed annular boosters on the primary side only which helped with throttle response, drivability, better fuel economy and emissions.
Your 406 really needs that 1000 cfm carb, and the dyno verifies that. At 100% VE and 7000 rpm it needs 822 cfm by my calculation. As you say, getting intake vacuum down, or really getting the manifold pressure up, allows the engine to make power. Driveability comes from knowing how to tune part throttle, too, not just full throttle. Great video, thanks Eric
So you told us the way to add more information to your data is the record manifold vacuum along with speed and torque. Even if you had vacuum recored for all configurations at the same high engine speed it would be an interesrting datapoint ... just saying.
People who say certain carbs drive bad, & carb is too big, probably built one engine if that! They definitely don’t know what does what inside a carb! Most hear double pumper & they think the fuel is pumped into the engine 🙄🙄🙄🙄! (Yes there’s the pump shot!) When you have done it hundreds of times, you know the truth! Let them keep losing to the guy who has the bigger carb, on a similar engine! Going from a 1050 dominator to a 750-4150 we have seen a tenth to two tenths lost! Lots of times! Good video!
the 11 to 1/Pump gas street comment,......... I think a lot of that depends on multiple factors ( heads/Chambers/pistons top and Local altitude) here on the east coast , Old school Mopar 440s , 915 heads, flat top pistons and 80% humidity 110+ LSA cams will ping around 32degrees total timing , same engine same with KB quench dome , you can run as much as 40 degrees. now on the other side of it , alum head SBC @ 11 on 93..they'll run pump 93 no mater the time of year here in Eastern PA. I do G3 Hemi(s) , my personal 04 Ram runs Eagle heads on a stock 04 Short block, roughly 11.80s to 1 comp, I run 93 oct and 24 degrees total timing(G3 hemi in general doesn't need a lot of timing) I've done tuning for similar combo's for a few people who live Denver and Phoenix ,In Denver that combo can't run more than 16 degrees with out the knock sensors going Nuts, Phoenix roughly 20 degrees.......Eric, I love the Videos , lots a respect .
I’ve always run 1000 + cfm low profile dual plane, dual quad intakes on the street with my high performance small blocks. You have to know how to set them up and how to tune them, but they always made more power, better throttle response, and improved fuel economy over single 850cfm and smaller carbs.
As you said you can pretty much count on the chance that the secondaries did not open all the way on the 750. Not only due to the spring in the pod but also if it does not have the little brass tube that protrudes slightly into the venturi to help it open that will hurt the opening as well
Love your videos Eric and they keep getting better. Don’t ever bend brother, people have stupid theories that defy logic like there’s ghosts in the engine.
You're exactly right and if you look at where the vacuum is being drawn for the second barrels it's usually from the first Barrel the air flowing through the Venturi where the vacuum is being created
Power is a broad term, but sure a small carb can make more torque and maybe a better average hp. Lost almost a second off drag car time, going from a 750 to a 650. Both were jetted well.
there is nothing wrong with a 3310, I have one of the older one s that has Metering blocks at both ends, so the jetting can be set proper. I have been running it on my Drag car for 40 years, I have tested a 750 double pumper Demon, With no gain in MPH or ET.. The problem with most carbs is they are not set up right.
@@justinadams1360 Get a good race 750 "ATM. Don't use any of that choke tower stuff. I have done back to back runs same AFR race ran a 1-1.5 faster in very close air with a 850 to a 750 not all cfm is the same.
@TPVPRO Same here! On a 383 sbc tried 650cfm, 750cfm, 825cfm, 850cfm downleg (also called a 1000cfm depending if its sold as a race or street carb) 850cfm annular, 975cfm. All can be and were calibrated via emulsion and emulsion bleeds to drive very similar but my favorite go to was the 850cfm annular. The 975cfm had just as crazy throttle response as the 750cfm. 650cfm great throttle response but ran out of puff after the initial kick in the pants. It's all about tailoring the calibration to the specific engine and carb size.
The 750 dp and and 750 vac flow the same cfm the difference is how the secondaries open dp opens mechanically vac uses vac drop to open they still flow the same
I have always said go up in carb size unless your performance falls off, comparing carbs of different types alters your test results. Test carbs of the same type against themselves, you'll still get similar results, but it will not have any bias towards one type over another.
The larger carb makes more power before noon, the smaller carb makes more power after noon 👍🏻 I give up on the carburetor rules of thumb and such. What works best in one situation might work worse in another.
I don't think that you can have a carburetor that's too big, only boosters that atomize incorrectly for what the engine needs for optimum power. An interesting test would be two carbs of the same flow rate with different booster types.
I agree to a point. But... A 1350 Dominator on a 283 with iron heads and highway gears will be extremely difficult to tune compared to 650 while driving on the street. I believe in this scenario, even Eric would agree the 650 is the better carb for the application mentioned above.
I disagree, to prove a point I took a completely stock 273 and adapted a 1450 C&S aresol Dominator I tuned for a car cruise weekend. It worked great and I was averaging 22 mpg in hilly country!
@@MAXIMUMWEDGE yes, the Dommie was tuned for that application. Out of the box, tuning the 650 to meet those requirements will require less effort, probably none really. I didn't say it was impossible, just that the 650 will be easier to tune.
Personally I like smaller better for anything street/strip. To me feeels better in the seat. If I'm like strip only, big stall, very low gears etc then yes big carb
Wouldn't the drivability be drastically changed if the big carb is on a mild 355 rather than whatever power level it was supplying in your s10? Say you have a 350hp 355, won't a big carb be harder to get dialed and behave correctly? Asking for my friend who is converting a Mercedes V8 to a carb who I'm recommending a 650 over the 750 or 850 he wants. It's 350hp on a good day(I'd guess more like 250 wheel). 5.6 ltr.
Yep that more correct than not. A 650 is probably big enough a 650 vacuum secondary at that not a double pumper That engine would hate a 750 double pumper
@@KingJT80 yeah basically what I told him. It is going to get its brains kicked in at higher RPM in a drift car but I still don't think a 750 is necessary, and there's nothing available to make it a really nasty naturally aspirated motor without spending a shitload of money.
Probably a better title for this video would be "how much power is my vacuum secondary carb choosing me?" . Also a trick I bet would close some but certainly not all of the disparity between the 650 and 1050 would be if you could add a significant amount of plenum volume with a tall spacer or something but if your not restricted to a certain size then just get a bigger one.
I'm very surprised you didn't mention using a vacuum gaugeto work out best carb size... isn't pressure drop what it's all based off? Joe Sherman told me many years ago he likes 1 to 1.5" at wot. I can't think of a better way of knowing, rather than guessing. Would've picked up what was really happening with the vac secondaries on the 780. Joe also said in most cases putting a larger carb makes more hp, but doesn't mean it'll be faster on race day.
I used a Holley 650 double pumper on my '69 GTO {400} worked great and I am using same on my '64 Ford 390FE, mind you I don't usually go beyond 4,000RPM, bottom line though LOVE your explanations
exactly used to knock a weight off carter afb in 68 javelin to open secondaries of line i must have been only one to say a 750 was to small lol But i did forget about the Double pumper
And that question begs another: how come Holley hasn't come out with a tps sensor for vacuum secondaries? I know where my foot is while driving [which settles primary for me], but what I don't know while I'm driving is... where are the secondaries?. A little 10 segment led bar that tucks somewhere would be wonderful - I have a cowl hood, and I'd stick it right inside. How fast and how far secondaries respond is important.
Its not engine vacuum, theres a port in the primary side under the venturi but yes. Pretty obvious the 750 wasnt opening, dozens of DP vs VS dynos out there where they make more or less the same power. Ive done this exact same test myself and made some money doing it.... still have a 680 vs on my 450hp 351. 750dp was boggy down low, lost a couple hundreths and almost 2mph. Small price to pay for way better drivability, the 500cfm only lost a tenth and was snappier still. Granted if i had more converter or a single plane or a manual would probably be a different story. 500 nosed over at 6k, 680 will pull to 7k, no noticible difference on the top end with the 750, just annoying at cruise and downshifting.
That proves bigger is better. The vacuum secondary didn't catch up until until it was fully open and the 650 was running out of flow. Double pumpers rule if you can use it. A big heavy car or truck might drive better overall with the vacuum secondary carb. Lighten the spring until it bogs then back up one.
So far I’ve seen three or four test with that new Edelbrock 4150 Holley looking carburetor and so far it’s been 15 to 20+ horsepower better than everything else but I have not seen it versus a dominator I’d like to see you test one of those!
I dont think people realize thst cylinder head & carburetor technologybhas improved tremendously since the Holley cfm chart days of the late 60's early 70's. Yes I dont belive a 1000cfm carb is a good choice for my 77 Monte Carlo with its stock SBC that produces less than 200 HP at the crank. Its all combination specific. I've seen engines under 350 CID running two dominators & shifting @10.8K rpm. Combination specific. You want zero air restrictions, and proper A/F mixture over the entire operating range.
Which comes from engine vacuum. Without engine vacuum it will not open. The vacuum has a direct relation to motor size and rpm. That’s why you need different springs for different combos.
thats correct, but it depends on the flow through the primaries. If you floor the pedal with a larger carb , it takes a while for the engine to get up to the point of the correct vacuum signal. Too large a carb on a street car , not properly setup and geared, can cause signal delay.Thats why on a street car I would recommend a smaller carb, which usually gets you a better signal earlier. It also gets into your driving style, do you just floor it , or carefully drive into it. If you carefully drive into the carb, I always recommend a larger double pumper.
It should be this one weingartnerracing.braveshop.com/#!/SBC-Dyno-Session-8-5-29-2024-Print-Book-Dimpled-Spacer-test-and-Intake-Tests/p/669950810/category=0
Mostly, things seem to come down to droplet size, given the same afr. And every combo is just a little bit different. Interesting how much improvement has been obtained vs the old standard 3310... boosters do indeed matter.
Eric, I have the 950 I pulled from my S10's 400, which has had a lot of work done on it for 'GAS.' If you want to give it a try for another test, I'd be happy to help. I also have a 950 E85 from ATM.
Buddy of mine had a Big Block Nova with a DP. Ran fantastic. Switched to a VS and magically went about 4-5 tenths faster in the quarter. Why. He couldn’t hook. Switching to the VS and tuning the secondary opening allowed him to leave just soft enough to hook. Would have been a different story with slicks.
Give me a 1000 CFM with annular boosters any day. For years the magazines (before the internet) warned you not to run a double pumper on a street machine. That is a crock, and there is the dyno test to prove it. If you've got a well warmed over small block (pretty easy to do with the proliferation of aftermarket heads and other parts) and you have the converter or a manual box to go with the setup by all means you can run a double pumper. Don't expect to run a larger vacuum secondary (say, 750 cfm as tested her) out of the box and get fantastic results over your old Qjet. It may perform even worse.
Thats because the Edelbrock 750 with oversized pump kicked holleys but under 6500 rpm and got 10 miles per gal and didnt have pop off valves failing unless in all out race car I wouldnt go holley
At this combination, of course. BUT if you take a stock sub 300 small block with stock heads, headers+exhaust, intake and cam, and slap a huge carburetor on that and run from 2000 up, those numbers will be different. I would argue that having a single 1000 cfm carb is too small for a racing engine. As seen in those numbers, it falls on it's face before 8000.
A list 3310 is a 780 vacuum secondary, not a 750! A bigger carb will make more peak h.p. A smaller carb will make more average h.p., thus is the better choice for a street car. I didn't watch your video. But from my experience this is true! You can't drive a Dyno!
I wonder if it’s all things tuned and jetted equally, is it a function of the more area is changing the pulses in the intake. Because if an engine is only capable of moving X amount of air at its volumetric efficiency. The only way I can see without forced induction that stacking is how you would force more air in. X amount plus the pulse. More area changes the tuning and a larger area would offer less impedance to air moving through. Or am I just being high?
oh now I got to read all the comments, just from past tech and people racing ,Giant carb on tiny engines for the street are not as good as matched carb and seeing 600 cfm NHRA Cars run mid 10s makes me wonder about internal mods or such
Carb cfm recommendations are a guideline for selection nothing more so whats the standard use ? Every combo is different most dynos cant replicate what the engine sees on the road anyway your right saying your 1000 felt fine on the 355 seat of the pants counts ! tune up vehicle gearing everything has an effect In " some " way making it all work together is the challenge.
Had a Holley 1050cfm Dominator carb and the little 327 made in the 600hp range Got a 750cfm carb now and smaller Cam shaft , There is a big difference ! So I would give this video a Thumbs down just for talking about it
TO BE FAIR. As far as running 11.3 on 91 pump gas for hundreds of dyno pulls with no problem, an engine on a dyno is NEVER going to get as hot as an engine under a hood when its 100" outside. Just pointing out I wouldn't go to the bank with that statement.
Ok. The s10 old 355 had 11.9 compression 91 octane cruised everywhere even when it was 100. Underhood temps were high. Even now they are 155. No problem but I have a timing controller to lower timing at lower rpm. I wouldn’t try that with straight timing
That is pretty cool now i learn more about carburetors now also i was curious on choke tower vs none what is yiu had 2 of the exact same carburetors just 1 holley xp without choke tower of couse and then another holley with a choke tower to see how it dies on a dyno. I am sure it probably won't do much because it was a curious of mine because i do want to get a Holley xp without the choke tower and on how it compare mine i already have with choke tower which it is now mostly off
No choke tower is good for a couple of hp up high in the rev range from the tests I've seen. Nothing drastic. What does help is no choke tower and contoured venturi entrys. You'll see almost all high performance carbs have some type of smooth and contoured entry into the ventuis.
