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  1. #1
    casual poster LXCHEV's Avatar
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    Default Ultimate street carb choice for warm 383 SBC

    Hey all - long time no post!

    Keen to hear advice from any carb / engine combo gurus as to what would be the perfect 'street focused' carb for my setup (looking at the traditional 4 barrel square bore Holley style range). Looking for both size suggestions (CFM) as well as secondary style (vac versus mechanical)...



    Without revealing what my current carb is, I am trying to address a few issues:



    I have no performance complaints with the current setup, but the car has always been a 'rich' runner (despite professional dyno tuning) - it generally smells a little fuellie, the spark plugs always come out filthy rich and black, and quite often it blows a bit of black smoke out the rear when you really stomp on it and give it a hard time. The current carb also does not have any vac port for either PCV or brake booster connections. And one other 'whinge' - it's never felt like a super 'snappy/responsive' carb (i.e. feels a little doughy) - unless you go straight for WOT.



    We all too often get caught up in the quest for max power and 'racing performance' - but these days for me - to be brutally honest, my car spends 90% of it's life just cruising around at low and mid revs - with the odd blast here and there. After a bit of research, I have a new carb in mind - but once again, I won't comment until I hear a few other opinions first. And no, I don't wish to pursue EFI at this point in time.....



    I want to get the most finely tuned carb with the absolute best street manners possible (yet still be able to attend a drag day once a year if I want to without completely compromising it's performance).



    So clean slate - here's the key info for the current setup:



    381 SBC

    10.5:1 comp

    Comp Cams hydraulic roller (XR288HR) - 236/242 @ 0.050" | 110LSA | .555/.576 valve lift

    Iron 'Pro Lightning' heads (200cc intake runners) - flow numbers aren't exciting:

    LIFT 0.200 0.300 0.400 0.500 0.600 0.700
    IN 131 178 214 233 241 246
    EX 98 133 158 178 191 193

    RPM Air-Gap dual plane intake

    Tri-Y pipes (1.75" -> 2" -> 2.5") with twin 2.5" exhaust

    -----

    TH350 with 3,200 stall

    3.7 rear gears

    -----

    Max revs - I reckon somewhere between 6,200 and 6,500 RPM (from memory peak power is 6,200).

    To cruise on the freeway @ 100KMH, it's pulling a solid 3,000, maybe 3,200 RPM.

    Car weights in around 1,680kg with driver

    On the chassis dyno - makes 230 rwkW (by my maths, that's about 440 flywheel HP).



    Open to any and all feedback!

    Cheers,
    Brett.

  2. #2
    Do you ever leave? EH179's Avatar
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    Mate, have a look at the Pro Systems site and fill out a recommendation form with the details you have provided above.

    Patrick will get back to you quickly with the size/type of carb you are after, where you can compare with what you have now.

    His prices are very reasonable, even after you add in the freight to Aus, it can still be cheaper than buying here.

    If you buy one, you will have a custom carb to suit your engine and it will run great straight out the box.

  3. #3
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    G'day Brett, it's been a while, good to see you're still around !

    I know this is an unpopular opinion but I still like vac sec carbs for street use. The original 3310 750 vac with the down leg boosters was a great carb out of the box. These days I just buy a second hand 750 vac, fit a Proform main body and a secondary block and run it.

    Again.... JMHO.

  4. #4
    casual poster BasicQ's Avatar
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    Like EH said give Pro Systems a go or a Holley 750 Street HP, they have the accessory ports and a better calibration for what you want. Might have to square up the air bleeds pri/sec but that’s easy enough.

    Does the carb you have now have the word Ultra in it’s name?

    Reckon I have seen you around the Geelong area at car meets in the past. Gateway hotel, Meredith car show and others?
    Last edited by BasicQ; 21-09-2020 at 09:47 AM. Reason: Last question.

  5. #5
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    I'd buy a tired old original Holley LOOOOONG before I even looked at a Prosystems let alone hand over a single cent for one.

    I sorted a large CFM unit for a 496BBC for a friend, wouldn't idle properly, had poor mixture screw control, blah blah blah.

    What I found was a disgusting mess inside, 2/3 of the holes in the body associated with the idle and transfer and power valve signal were miss aligned with the gasket and base plate, some were more like as little as .010" showing as being open for business! It honestly looked like one of our asian friends in a sweat shop held the body with their feet and drilled all the holes by hand, honestly, I bet a bunch of the lads over there would do a better job than this carb came with!

    I mentioned this in another thread some time ago and a few people came out of the woodwork agreeing that they had been caught with similar things.

    Do your homework before coughing up for a Prosystems...

  6. #6
    casual poster LXCHEV's Avatar
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    Thanks for the responses so far gents - excellent feedback and I will explore all options.

    Firstly - yes, current carb does have Ultra in the name - it's a Holley 750 Ultra HP aluminium jobbie (double pumper). Over the years I've gone from a Quaddie, to an 825 Mighty Demon (d/p) and then on to the current 750 Holley Ultra HP.

    Generally speaking, are the 'Ultra' series carbs considered street friendly at all, or more race inspired?

    BasicQ - I used to get to the Geelong All Holden Days, but not those other shows you mention. Sounds like another similar torrie down your way!

    Andrew, good to hear from you too mate! I am seriously tempted to try a vac-sec - even something as small as a 650 or 670 (when you run the calcs, that shows as the optimum size). The Street Avenger or Brawler series had got my attention. But to be honest, I don't care too much what my starting point is, so long as my tuner will be able to customise and fine-tune it accordingly. What is it about the ProForm bits that you like so much? I would prefer to simply get an 'off-the-shelf' complete carb, but I love the way you tackle your builds with practical methods to generate results...

    Cheers.

  7. #7
    Do you ever leave? EH179's Avatar
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    There was one other person in that thread that had a bad experience with Pro systems, Mick.

    Any company can have a bad batch of materials come through, or a disgruntled employee can cause havoc.

    The OP hasn't stated what brand/model carb he has now, but if he had of, I'm sure the collective here could sort the carb out for him, saving the purchase price of a newie.

    I did mention in my previous post to fill a spec sheet out and at least get a recommendation, which will allow him to compare the calibrations of the two.

  8. #8
    Do you ever leave? TRIKHQ's Avatar
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    Another good carb is Quick Fuel , thats what I am running currently. 950 on 406, 642HP. Alot of my friends have swapped from Pro Systems to QFT as they are great out of the box, good reponse, better fuel metering. We had a 406 on the dyno , 601HP. we tried 3 carbies back to back. First was Holley 950 Ultra ( in reality they were 830. always ran very rich) , then a ProSystem 4150 1000cfm that I had built for my engine and a QFT 950. The QFT made 10 more HP and 12 more Ftlbs. than the other 2. In your case a 850 probably the go.

  9. #9
    casual poster BasicQ's Avatar
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    Maybe there is a blue LHCHEV getting around my part of the world!

    With the amount of adjustment in the carb you have you could get it right but if the lack of vacuum ports is a deal breaker then there are other options to start from. I am sure you can appreciate no matter what you start with some tuning will need to be done for your unique engine, that said in the context that all engines are unique. Ultra are race inspired but again, with the amount of adjustment they can be made to mimic a street HP.

    On US forums the Yanks either love or hate Pro Systems. Like EH179 I put them up as a suggestion to give their recommendation a crack and also part of the cost is them taking some of the guesswork out for you. You will need to do your own research as far as reputation/quality goes as I have had nothing to do with them.

    Quickfuel have a big range and their version of a Street HP would be worth looking at. Also their HR Series.

    The formula widely used is a good guide and returns good information on a minimum size carby ie if you go smaller than the equation result it would be a restriction. Having a dual plane manifold would have a stronger signal to allow good metering with a 750 or even an 850 to avoid pumping losses and still provide good manners. If you have a mate with a 650 see if you can borrow it. Stick it on, connect a vacuum gauge and go somewhere you can go WOT. If the gauge gets to 1.5 or below a 650 will do the trick. If it can’t get that low it’s a restriction on your engine and go a 750. Holleys get their cfm rating from that 1.5 in/hg.

    All that said don't tell the missus your about to spend $800-$1000 AUD on a carby just yet as I believe your 750 can be tweaked for better street manners and still have the cache of an Ultra HP!
    Last edited by BasicQ; 21-09-2020 at 02:10 PM.

  10. #10
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    EH179, it wasn't a case of "sorting it out" with a little help from his friends... It had the holes in the wrong places, the china copy body was very poorly cast, putting the holes in the wrong places, I set it up in my Milling Machine and repositioned most of the holes, I also had to re-tap the Mixture Screw threads, like it say, it was an expensive POS, I'd hate for anyone to cough up $1000 at others recommendations and end up with such an awful mess posing as a brand new performance carb.

    I've not experienced any poor quality Quickfuel stuff, or older genuine Holley stuff.

  11. #11
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    Ultra metering blocks are fully tapped?

    Should be reasonably easy to get right but the main requirement to be a dyno tuner is getting the finance.

  12. #12
    casual poster BasicQ's Avatar
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    I know there hasn’t been any contention over the size (cfm) carby the OP would best be served using but at the same time there has been suggestions of different brands of carby that would best suit the OP as others have had great results and even seen better numbers on the dyno with brand ‘A’ netting higher numbers than brand ‘B’ or ‘C’. I have also lost count of people asking on the big wide world web “what size carb for my engine” and debate ensues as some say “that 950 HP is way too big for your 383!” or “you need something bigger than that 850 double pumper on that 496 you should try 1000cfm”. There are also others that changed from the likes of an 850 Demon to Holley 950 HP and the car goes better and the owner is under the assumption that he needed a bigger carb all along. But what 950 is too big and was that 1000 change really a step up in cfm?
    CFM is regulated by the venturi diameter at its smallest point and throttle bore size. Type and placement of booster has an effect on cfm too but the below list all have down leg boosters. The list shows that quite often the cfm number is nothing more than a designated name or a number assigned to a carby by the advertising dept to differentiate from like cfm carbies. When choosing cfm for performance it’s a good idea to dig deeper and see what constitutes that cfm number.
    To the OP use this list when deciding cfm over several popular brands.

    Venturi is first number - throttle bore second

    750 cfm
    Holley Ultra XP 1.376” - 1.688”
    Street HP 1.376” - 1.688”
    Demon 1.400” - 1.688”
    Quickfuel S/S 1.375” - 1.687”
    Quickfuel Q series 1.390” - 1.687”
    Brawler 67200 1.390” - 1.687”
    Brawler 67257 1.375” - 1.687”

    850 cfm
    Holley Classic HP 1.56” - 1.688” (named 830cfm)
    Holley Double Pumper 1.56” - 1.750” (does have choke horn)
    Holley Ultra and Ultra XP 1.56” - 1.750”
    Holley Street HP 1.56” - 1.688”
    Holley Track Warrior 1.56” - 1.75”
    Demon 850 (any) 1.56” - 1.75”
    Quickfuel S/S 1.56” - 1.75”
    Quickfuel Q series 1.39” - 1.75”
    Brawler 67201 1.39” - 1.75”
    Brawler 67214 1.56”- 1.75”

    950 cfm
    Holley Classic HP 1.376” - 1.75”
    Holley Ultra and Ultra XP 1.60” - 1.75”
    Holley Street HP 1.56” - 1.75”
    Quickfuel Q series 1.450” - 1.75”
    Brawler 67202 1.450” - 1.75”

    1000/1050 cfm
    Holley HP 1.56” - 1.75” (named 1000 cfm)
    Quickfuel Race Q 1.59” - 1.75” (named 1050 cfm)
    Brawler 67209 1.59” - 1.75” (named 1050 cfm)

    You can see that if a range of either 850’s or 950’s were tested on a dyno on the same engine those guys testing would come to the conclusion a certain brand or type of carby was better than another. If all were optimized it may well have been the venturi and throttle bore combination that the engine best responded to despite the brand name on the carby. A Demon 750cfm, Brawler 850cfm 67201 and a Holley 950cfm HP Classic would be closer in actual cfm than their name suggest.

    For CFM 750 and above oils ain’t oils.

    Hope this helps.
    Last edited by BasicQ; 23-09-2020 at 09:51 PM. Reason: Add 850 & 950cfm info

  13. #13
    casual poster BasicQ's Avatar
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    Delete this post please.
    Last edited by BasicQ; 23-09-2020 at 05:40 PM. Reason: Remove text of doubled up post.

  14. #14
    casual poster BasicQ's Avatar
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    Looks like with the site problems when I first hit ‘Post Quick Reply’ and a message popped up to ‘try again in 29 seconds’ it really did publish that first post.

    Smitty2 are you able to remove the double up post 13 and this post?
    Last edited by BasicQ; 23-09-2020 at 01:58 PM.

  15. #15
    casual poster LXCHEV's Avatar
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    Very interesting BasicQ. Thanks for taking the time to post that up.

    Just on the note of site problems - last night there were several other posts in this thread, which have vanished? I hadn't had time to respond yet, but there were some good insights put forward on other ways to liven up my old dinosaur.

    From what I can recall - there was something around the potential of having a poor ignition system. I'm actually using a full ICE setup (Digital Compu-Curve with Bosch dizzy and no vac advance), however I should dig out the original spec sheet and share the curve details - perhaps it needs revisiting (it was originally setup for a previous incarnation - still a 383, but different cam and stall etc). From memory, it's set around 12 degrees initial with a total of maybe 32 degrees. I'll need to check that.

    There was another post talking about the fact my heads and intake are potentially costing 50+ HP, which I agree with whole-heartedly. Long term I do plan to invest in a set of AFR's and whatever intake at the time is best.

    Convertor diameter was also mentioned. Again, pushing the brain cells a bit to recall, but I think mine is a 10".

    All great comments and very appreciated!

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