Close



Results 1 to 11 of 11
  1. #1

    Default Carb sizing or 351 build age old question

    I would appreciate advise to carb size. I would prefer to run Manual secondaries. Vehicle intent: Some Pro touring, long "fast hauls".

    I know this is one of the oldest asked question of man kind... Please see attached specs for the motor I built. It is based on a 351 roller motor. All the engine, cam and head spec are include so I will not do the run down of the build, but let my fellow members evaluate the data. Additionally, this is going into the 86 GT fast back, Weiand Stealth, Millings oil pump prepped by Professional oil pumps, Canton t-sump pan, T5, 3:73 gears (?)no power adders, just right foot and hard turns. We've discussed the IFS suspension on other threads.

    I appreciate the honest and serious advise

    cam card.pdfUCF 351W SpecSheet.pdfRHS HEAD pg2.pdf

  2. #2
    FEP Senior Member 83gt351w's Avatar
    Join Date
    Nov 2014
    Location
    Grand Rapids, Mi
    Posts
    654

    Default

    Your cam is very similar to mine, and I run a 650 dp with mechanical secondaries. I installed larger squirters to get rid of the hiccup upon take off. My 351 has edelbrock rpm heads. But, if I had a 650 vacuum secondaries, non dp, I’d love to try it.

  3. #3
    FEP Senior Member droopie85gt's Avatar
    Join Date
    Jan 2005
    Location
    Cordova, TN
    Posts
    994

    Default

    I would say a 650DP would work as would a 750. I think anything larger would be on the big side. One of the best tools you can get is an 02 sensor/gauge setup. When I was running an edelbrock carb, I put the gauge on and I could drive around and monitor the gauge. I could check WOT, fast starts and cruise and I got that thing pretty well dialed in. It got decent mileage and pulled hard in all gears with no hesitation.
    1985 GT, Sunroof, 5 Lug, Rear Discs, 01 Graphite Bullets, 88 forged piston shortblock, 2.02/1.60 Alum heads, Weiand Stealth, Holley C950 TBI, BBK Long tubes

  4. #4
    FEP Super Member erratic50's Avatar
    Join Date
    Dec 2016
    Location
    Nebraska
    Posts
    4,575

    Default

    My 85 is getting a Dart based 353 big bore here soon. Similar CID so I’m paying attention to the discussion.

  5. #5

    Default

    Sure swung hard for the fence with the heads and camshaft... don't choke it off with a carburetor too small. The combo might have less than 10"Hg manifold vacuum at idle. The Windsor torque and the T5 and 3.73's take good care of the brief bottom end, so it'd be a single plane like a Victor Jr and an 800 double pumper if it were mine (the results below will speak (loudly) for themselves). A classic 800 double pumper (before all of the "that's too big" guys go nuts... an 800 double pumper has the same bores (1-11/16") and venturi (1-3/8" primary & 1-7/16" secondary) as a 750/780 vacuum secondary)) that is, with (adjustable) 0.033" primary idle feed restrictions and (adjustable) 0.070" primary idle air bleeds for a good starting spot. If the manifold vacuum ends up nearer to 5"Hg than 10"Hg or so at idle, and off-idle and cruise manifold vacuum no doubt quite higher, like ~15"Hg or better (which will "pull" harder on the idle/transition circuits, veering richer, instead of leaner like ~16:1 like a good working carburetor should), adjustable transfer slot restrictions added can really dial in best light part throttle acceleration and cruise (still no doubt with overdrive, operating on the primary transfer slots, not yet the main jets) fuel mileage, without affecting best idle adjustment with the mixture screws. That's right, wilder than mild, or more radical built engines and "hot rods", even with good big carburetors, do not automatically have to equal the stereotypical pig on gas. I did some simulations... stereotype-bustin' data



    I'll take the rather small penalties at less than 2000rpm, for the (no changes in peak rpm tq and hp) nice large increases of torque and horsepower, and no penalty at all but also increases in averages of both torque and horsepower across the board "area under the curve" baby... woot!
    Last edited by Walking-Tall; 03-25-2019 at 02:03 AM.
    Mike
    1986 Mustang convertible ---> BUILD THREAD
    Past Fox-chassis "four eyes":
    1983 Mercury Cougar LS
    1986 Ford Thunderbird ELAN
    1980 Capri RS Turbo

    Work in progress website ---> http://carb-rebuilds-plus.boards.net/

  6. #6
    FEP Super Member xctasy's Avatar
    Join Date
    Jun 2012
    Location
    Dunedin 9011, New Zealand, South Pacific
    Posts
    3,961

    Default

    In my (almost life-long) research on the 1969 to 1982 FoMoCo 351C, the advent of the 4150 or 4160 versions of the originally 396 Mystery Motor 4-bbl Holley 750 to 780 cfm Vac Sec was to make those 390 FE engines get up and beg.

    I was born in 1970. In 1972, the European Pantera got an M code hydraulic cam engine with R code Boss parts, including its 750 cfm 4350 Spread bore. It was a great carb, it allowed a 330 hp net with 280 degree special cam, closed chamber 11:1 compression and the later 1973 GTS 310 hp derated open chamber 9.4:1 engine a seamless 600 rpm to 6300 rpm performer, from 20-40 mph in top in 6.4 seconds, to a 167 mph top speed. So other 4-bbls can do that too. The only thing with some four barrels are the mechanical secondary stiffnness, and the inabilty to take corners with out fuel surge. The Boss 351 had surge, and secondary shaft failures due to the linkage, and the Pantera, no fuel surge anywhere, and an excellent linkage, but with a stiff action when going deep into the secondaries. Any 3200 pound car that does 14 second quarters with stock Ansa mufflers and Tri Y headers is an exceptinally fun thing to pilot.


    The Chrylser 340 LA's, both the 275 and 290, were clear proof of how much development work Mopar put into detonation resistance, and small primary barreling.

    Exactly when Chrysler was backing off from the Hemi and polysperic to the Wedge engines, the Ford head guys discovered polyspheric, canted valve engines, Hemis, Cammers and 427 GT40's, and then the 302 Boss and......the 1970-1972 export 351 4V HO Phase II and II engines, just M code export engines with R code 1971 parts like you found in Panteras,

    For 1971-1972, the now illegal for Clean Air Speed Kills 1971 Holley 390/Boss 302 780 cfm carb was a very good one.


    I think that the reason for Mopar and GM and Fords drive into the Thermoquad, Qjet and 4350 SpreadBore was that the primary and secondary booster carbs were in theory able to match the lower air speed and fine atomisation of a good 780cfm Holley vac sec, without the emissions issues. Mech secondary's, I really like a whole lot better, and metering rod spreadbores, well, they can work too. Although never liked, the 4165 and 4175 were exceptinal carbs.

    The key point is that however you do it, a one barrel per two cylinder carb to engine configuration that sits in about 750-800 cfm absolutely can make a sensational job of delivering seamless performance from a Cadillac like 600 rpm idle to a Ferrari like 7000+ rpm frenzy. Spreadboring was a transitional response to the needs to make MPG and BHP.

    A Square Bore is such a lot of fun to tune, and there is depth to its composition that can be hidden under a Dominator style air cleaner, and still deliver over 450 hp to the street.The tall 351w block gets noticed! People will know its not a 302 HO 4V, For James, its the same...a thick bulkhead, siamese bore 8.2 with internally neutral balance is probably the nicest engine option you could wish for.

    Wish Ford had done the 353W siamese block at the factory....


    What Ford did do in the factory was make the 6 bbl Holley 6 pack . It quickly got scraped, and thats what sits on the 340 6 pack....Fords brace of Holley carbs. The order was reprocessed under Mopars 340 carbs.

    366 6V intake built by
    Ford to race in Nascar was intended to use a set of sleeved Holley
    List 4782, 4783s (sleeved in order to reduce the cfm from 1350) which
    at this point were originally vacuum secondary....when Nascar told
    Ford no after they built 500 complete motors each with 6V intake and
    carbs ready to go so they could use the motor in Nacar racing, Ford
    physically smashed each motor and the intakes and carbs over a week,
    so the very few intakes which survived were bare intakes on shelves
    in offices or with the engineers........


    The center carb (part No. 0-4792) has 1.50-inch diameter throttle blades and is rated at 350 cfm. The twin 500cfm outboard carbs (part No. 0-4790) are vacuum operated 1.6875".

  7. #7
    New User
    Join Date
    Apr 2017
    Location
    Wenatchee, Washington
    Posts
    34

    Default

    How does the single plane perform in street driving at partial throttle vs the dual plane? I'm tempted to get the Victor Jr for my 351 but I'm concerned about streetability.

    Quote Originally Posted by Walking-Tall View Post
    Sure swung hard for the fence with the heads and camshaft... don't choke it off with a carburetor too small. The combo might have less than 10"Hg manifold vacuum at idle. The Windsor torque and the T5 and 3.73's take good care of the brief bottom end, so it'd be a single plane like a Victor Jr and an 800 double pumper if it were mine (the results below will speak (loudly) for themselves). A classic 800 double pumper (before all of the "that's too big" guys go nuts... an 800 double pumper has the same bores (1-11/16") and venturi (1-3/8" primary & 1-7/16" secondary) as a 750/780 vacuum secondary)) that is, with (adjustable) 0.033" primary idle feed restrictions and (adjustable) 0.070" primary idle air bleeds for a good starting spot. If the manifold vacuum ends up nearer to 5"Hg than 10"Hg or so at idle, and off-idle and cruise manifold vacuum no doubt quite higher, like ~15"Hg or better (which will "pull" harder on the idle/transition circuits, veering richer, instead of leaner like ~16:1 like a good working carburetor should), adjustable transfer slot restrictions added can really dial in best light part throttle acceleration and cruise (still no doubt with overdrive, operating on the primary transfer slots, not yet the main jets) fuel mileage, without affecting best idle adjustment with the mixture screws. That's right, wilder than mild, or more radical built engines and "hot rods", even with good big carburetors, do not automatically have to equal the stereotypical pig on gas. I did some simulations... stereotype-bustin' data



    I'll take the rather small penalties at less than 2000rpm, for the (no changes in peak rpm tq and hp) nice large increases of torque and horsepower, and no penalty at all but also increases in averages of both torque and horsepower across the board "area under the curve" baby... woot!

  8. #8
    FEP Super Member mmb617's Avatar
    Join Date
    May 2005
    Location
    Altoona, PA
    Posts
    4,249

    Default

    Quote Originally Posted by Jmac509 View Post
    How does the single plane perform in street driving at partial throttle vs the dual plane? I'm tempted to get the Victor Jr for my 351 but I'm concerned about streetability.
    I have a Vic Jr on my engine and haven't noticed any problems in street use. I have a 408 under the hood now but there was a time when I ran a 351 with that same intake and I didn't notice any particularly soft spots at low rpm, which I believe is what the concern is with a single plane intake on the street.

    I think the increased torque of the 351 over a 302 coupled with the light weight of a fox body car adequately covers the soft low end problem.

    Just my opinion, but based on real world experience.
    408/T5/3.73's

    We're not fast racers, we're more what's known as half fast racers.

  9. #9
    New User
    Join Date
    Apr 2017
    Location
    Wenatchee, Washington
    Posts
    34

    Default

    Awesome, thanks for the input I think I'm going to give the single plane a shot.

    Quote Originally Posted by mmb617 View Post
    I have a Vic Jr on my engine and haven't noticed any problems in street use. I have a 408 under the hood now but there was a time when I ran a 351 with that same intake and I didn't notice any particularly soft spots at low rpm, which I believe is what the concern is with a single plane intake on the street.

    I think the increased torque of the 351 over a 302 coupled with the light weight of a fox body car adequately covers the soft low end problem.

    Just my opinion, but based on real world experience.

  10. #10
    FEP Super Member erratic50's Avatar
    Join Date
    Dec 2016
    Location
    Nebraska
    Posts
    4,575

    Default

    Going with an RPM AirGap on my 353. Traded my Edelbrock 600 for a 750– now it will be to rebuild it an dial it in after the motor is assembled.

  11. #11
    FEP Senior Member
    Join Date
    Jan 2011
    Location
    Vancouver BC Canada
    Posts
    784

    Default

    I don`t think a 650 Holley DP is too small so a 351. My 331 SBF is a little smaller, but it makes 485 HP, and runs 10.2 second 1/4 mile ETs with a plain old Holley 4777 650 DP, pulling 7000 RPM. I don`t drive it on the street, but the 650 works great. And my same Fairmont has gone 9.9 ETs at over 132 MPH with a Holley 780 vacuum secondary carb, which is quicker than it ran with several larger double pumper carbs. (800, 850, and 950"HP", 950 3 barrel, and a 1050 Dominator. Many guys run bigger carbs than their engine actually needs, kinda like feeding a baby with a firehose!
    1978 Fairmont 2 door sedan, 428CJ 4speed. 9.972ET@132.54mph. 1.29 60 foot
    Replaced the FE big block with my 331/4 speed in my Fairmont, best 10.24ET @128 MPH.
    1985 Mustang LX hatchback NHRA Stock Eliminator 302 4 speed best in legal trim 12.31@107 mph, but has gone 11.42@115 with aftermarket intake, carb, and iron Windsor Jr. heads.New for 2012! 331 cube SB Ford, AFR 185 heads, solid flat tappet cam, pump gas; 10.296ET@128.71 mph, 1.37 60 foot.
    1979 Zephyr Z7, all original 302 auto, 2nd owner.

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •