Carb recommendation SBC 383

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Tom68
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Re: Carb recommendation SBC 383

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FC-Pilot wrote: Mon Feb 12, 2024 10:04 am
Tom68 wrote: Mon Feb 12, 2024 4:23 am

What revs was the 480 HP at ?
6600 was its peak. That’s where it made 480. Just a basic iron headed, hydraulic roller pump gas boat engine.

Paul
Cool, was checking to see if it was a candidate for the 470 @ 6000 from a 350 thread. But 480 @ 6600 means it agrees with the theory in the thread.
Ignorance leads to confidence more often than knowledge does.
Nah, I'm not leaving myself out of the ignorant brigade....at times.
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Re: Carb recommendation SBC 383

Post by smokie »

AED got back with me, his recommendation is a 950ho which he says flows 820cfm.i believe he said it was a 750 body in a 850 throttle body. That's a $750 carb. I can get a Brawler 750dp for a little over $400 . My question is, will that almost twice as expensive carb make 30 more horsepower over the Brawler? The Brawler does have an electric choke that I will remove all of it and machine the choke horn off. This is mainly a street car that will see the track a few times a year .

If this was a dedicated race car I wouldn't mind spending the extra for all I could get without question, but being a serious street car and seeing little track time, I'm not worried about 10 horsepower. However 25-30 horsepower is a different story. That's power that I can feel.
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Re: Carb recommendation SBC 383

Post by HQM383 »

smokie wrote: Mon Feb 12, 2024 5:51 pm AED got back with me, his recommendation is a 950ho which he says flows 820cfm.i believe he said it was a 750 body in a 850 throttle body. That's a $750 carb. I can get a Brawler 750dp for a little over $400 . My question is, will that almost twice as expensive carb make 30 more horsepower over the Brawler? The Brawler does have an electric choke that I will remove all of it and machine the choke horn off. This is mainly a street car that will see the track a few times a year .

If this was a dedicated race car I wouldn't mind spending the extra for all I could get without question, but being a serious street car and seeing little track time, I'm not worried about 10 horsepower. However 25-30 horsepower is a different story. That's power that I can feel.
You will find on the street its not just about cfm and horsepower for how it feels to drive. For every degree throttle opening rotation the 1.75" is allowing more air/fuel charge in to the engine. Engines run off density of charge, not cfm. Every degree of throttle opening with the larger throttle bore is more density of charge and therefore better acceleration when rolling into the throttle. Its each to their own though on how certain aspects of driving rank to justify the initial cost.

Edit: a few years ago I did a lot of testing of various cfm Demon brand carbs on my 383 sbc from 650cfm through to 1000cfm. Part of the testing was using a Dragy and timing acceleration from one constant speed up to another speed. I'll dig around later to see if I can find the results. From memory a 1.500" venturi X 1.75" throttle bore was the best response and acceleration. They were not otb calibrations. I carefully calibrated them one at a time.
I’m a Street/Strip guy..... like to think outside the quadrilateral parallelogram.
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Re: Carb recommendation SBC 383

Post by HQM383 »

Testing carb cfm on 383 sbc April 2022. Posted on another forum.
Nothing on for the weekend so I thought I’d bolt the Mickey Thompson’s on and throw the dragy on the dash and do some part throttle to WOT testing. As I’m into street/strip tuning of carbs I thought this type of test had some relevance for the street aspect.

What I did was set some custom parameters on dragy - 60-100kp/h (37.3-62.1mp/h), 70-110kp/h (43.5-68.3mp/h), 100-120kp/h (62.1-74.5mp/h). I went on the same route in the same direction each time performing the same test at the same area in the same street....you get the idea. Four carbies were tested: 650 Race Demon, 750 Mighty Demon with Quickfuel 4 hole metering blocks, 850 annular Mighty Demon fitted with BLP 16 hole boosters and 975 Race Demon (1.500” gold sleeve venturi). For each of the three speed test I held speed steady 1kp/h below test speed ie 69 kp/h for the 70-100kp/h test, then mashed as quick as I could to WOT.

There was no fine tuning to find best possible results, just threw each carb on as they are tuned to date to get baseline. A couple need pvcr enlargement. The 750 I tried two different emulsion/mab combinations.

650 Race Demon:
60-100 kp/h - 2.10 sec
70-110kp/h - 2.03 sec
100-120kp/h - 1.23sec

750 Mighty (.028” mab, emulsion .028” x .028” x):
60-100kp/h - 2.34 sec*
70-110kp/h - 2.01 sec
100-120kp/h - 1.23 sec

750 Mighty# (.033” mab, emulsion.031” .028” x .025”):
60-100kp/h - 2.15 sec*
70-110kp/h - 2.00 sec
100-120kp/h - 1.26 sec

850 annular Mighty#:
60-100kp/h - 2.14 sec
70-110kp/h - 2.02 sec
100-120kp/h - 1.23sec

975 Race Demon:
60-100kp/h - 2.00 sec*
70-110kp/h - 2.00 sec
100-120kp/h - 1.20 sec

* had some wheel spin so not 100% accurate.
# lean from .91 to .94 lambda.

I was surprised how close the results were. Two of them I’ll open up the pvcr to get .87 lambda @ WOT or below and test again. The 750 has .055” and 850 has .059” pvcr’s. The remainder were already at that lambda area. And no, none of the carbs had any hesitation.

To come is the 825 Race Demon with several test including mini annulars and std downlegs. I’ll also mix up mab/emulsion on that one too.

Quarter mile test will have to wait until done on the track. Pointless with the dragy on public roads as I would not get traction and I do not want to be doing around 190kp/h on public roads.

For reference car is 3350lbs, 383 sbc, 26” tire, 3.89:1 gears.
(I later learned the 16 hole boosters were over atomizing with the emulsion set up at the time. Emulsion was reduced and subjectively performance increased but didn’t test.)


And
I’ve done some more testing but unfortunately a bit inconclusive as temperatures have dropped coming into winter here compromising traction. Previous test listed were on the same day with ambient temps ranging 21c to 24c. Today and last weekend cooler. Today as low as 13c. I think this is the main cause of traction issues with the same M/T tyres previously used. Despite traction issues what I can report is this;

825 Race Demon:
(downleg .160” boosters)
60-100kp/h - 2.01 sec (had wheelspin so promising combo. Ambient 19c)
70-110kp/h - 2.02 sec (as above)
100-120kp/h 1.23 sec

850 annular after opening up pvcr from previous testing:
70-110kp/h - 2.05 sec (wheelspin again as only 13c ambient. Only test saved on that drive. Other two are videos below that don’t capture custom parameter data).

As it’s panning out various cfm carbs from 650cfm (1.28” v X 1.688” t) to 975cfm (1.500” v X 1.75” t) downlegs and an 850cfm annular (1.56” v X 1.75” t) are all performing quite similar under street driving conditions when tuned for similar AFR windows. However, they do feel slightly different during the test from smallest to largest cfm making the data a little surprising. Most would choose the 650 for its instant response feel but it appears throttle response has two factors. One, the obvious of time it takes for the engine to respond to the rapid throttle angle change and two - acceleration rate after engine responds. These two factors are balancing out over the cfm spread to be in the same ballpark under the test I am performing.
Not sure how many more of these test I’ll do now temps have dropped making them inaccurate and price of fuel gone through the roof (paying upwards of $2.20 a litre in Aus at the moment) and M/T tyre price and availability like rocking horse poop as well. I may move on to quarter mile testing.

Below is 60-100kp/h test with the 850 annular Mighty Demon with 16 hole BLP annular boosters and modified from stock emulsion and mab. Took a while to steady at 59kp/h.



Below is 99kp/h WOT (100 - 120kp/h test). Time under acceleration gets to 128kp/h as gps display lags.



*The two above test did not capture data
I’m a Street/Strip guy..... like to think outside the quadrilateral parallelogram.
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Re: Carb recommendation SBC 383

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750 all day long
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Re: Carb recommendation SBC 383

Post by turbo camino »

bigcam406 wrote: Tue Feb 13, 2024 12:51 am 750 all day long
If there were only one version of a "750" that would be really helpful.
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Re: Carb recommendation SBC 383

Post by cgarb »

smokie wrote: Mon Feb 12, 2024 5:51 pm AED got back with me, his recommendation is a 950ho which he says flows 820cfm.i believe he said it was a 750 body in a 850 throttle body. That's a $750 carb. I can get a Brawler 750dp for a little over $400 . My question is, will that almost twice as expensive carb make 30 more horsepower over the Brawler? The Brawler does have an electric choke that I will remove all of it and machine the choke horn off. This is mainly a street car that will see the track a few times a year .

If this was a dedicated race car I wouldn't mind spending the extra for all I could get without question, but being a serious street car and seeing little track time, I'm not worried about 10 horsepower. However 25-30 horsepower is a different story. That's power that I can feel.
AED makes fine carburators. I'm sure whatever they recommend will perform well. I have an 850 Methanol carb from AED and I am extremely happy with it.
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Re: Carb recommendation SBC 383

Post by steve cowan »

smokie wrote: Mon Feb 12, 2024 5:51 pm AED got back with me, his recommendation is a 950ho which he says flows 820cfm.i believe he said it was a 750 body in a 850 throttle body. That's a $750 carb. I can get a Brawler 750dp for a little over $400 . My question is, will that almost twice as expensive carb make 30 more horsepower over the Brawler? The Brawler does have an electric choke that I will remove all of it and machine the choke horn off. This is mainly a street car that will see the track a few times a year .

If this was a dedicated race car I wouldn't mind spending the extra for all I could get without question, but being a serious street car and seeing little track time, I'm not worried about 10 horsepower. However 25-30 horsepower is a different story. That's power that I can feel.
You won't see 25 - 30 hp in a carb unless something is wrong, I dynoed my spare 383 over Xmas and between my 950 hp carb and my 1050 carb 4150QFT with annular boosters was 5 ft lbs and 10 ish hp average all the way to peak at 6800 rpm.
I done some work on a friend's AED 950HO carb last year,they have billet metering blocks but not adjustable emulsion so I blocked 2 of the 4 emulsion jets and fitted transfer slot jets to the main body, I tested carb on my 3500 lb streeter and ran consistently 10.48 - 10.50s all day and the best mph to date with the AED carb 126.85mph.
The carb owner was at track with me and was impressed with carb operation, fitted to his 509 BBC as it was off my engine and runs very nice.
If you buy the better carb the parameters are wider if you upgrade your combo later on.
steve c
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Re: Carb recommendation SBC 383

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smokie wrote: Mon Feb 12, 2024 5:51 pm AED got back with me, his recommendation is a 950ho which he says flows 820cfm.i believe he said it was a 750 body in a 850 throttle body. That's a $750 carb. I can get a Brawler 750dp for a little over $400 . My question is, will that almost twice as expensive carb make 30 more horsepower over the Brawler? The Brawler does have an electric choke that I will remove all of it and machine the choke horn off. This is mainly a street car that will see the track a few times a year .

If this was a dedicated race car I wouldn't mind spending the extra for all I could get without question, but being a serious street car and seeing little track time, I'm not worried about 10 horsepower. However 25-30 horsepower is a different story. That's power that I can feel.
i would do an HP body AED. it will run good right out of the box. I think a 750 HP HO would be fine. I can tell you that John wanted me to run a 1050 dom on my sbf. I asked him what out of the box carb would work best, he said the 1000H0. He was right. the 1000 works great and I think I paid $500 for it at the time. I think his recommendations are what he thinks would work absolutely best. I like the HP body stuff because of the screw in air bleeds, I also like the AEDs because their emulsion package is usually spot on and runs really crisp compared to other stuff.
"Anyone who thinks the low RPM engine will be faster just does not have as much experience as the rest of us" -The late, great Joe Sherman.
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Re: Carb recommendation SBC 383

Post by rfoll »

Time for a reality check. A 383 with Chinese heads. Street-strip 6500 rpm. Discussions of 850-100 cfm, etc. Cutting off the choke horn on a new $700.00 carburetor. With an automatic transmission on a street driven car I will always choose a vacuum secondary, especially if that "3500" rpm converter doesn't get there. Maybe on it's best day behind a big block. Assuming you can clean and assemble a carb, this will get you where you want to go. https://www.ebay.com/itm/225998461432?i ... R6662rC0Yw
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Re: Carb recommendation SBC 383

Post by skinny z »

What is it about the annular boosters that might contribute to diminished top end output as opposed to a down leg style?
Case in point albeit 25 years dated and the numbers are a little fuzzy.
A 750 BG VS annular booster carb ( the same one I have now on my 357) that was on a street/strip 350, 288/294, 236/242 hydraulic roller, AFR 195's and an RPM Air Gap. While it tracked well enough for a 3600 lb streeter, somewhere in the mid-low 12's at 111, the owner commented on the "finicky" nature of carb tuning.
It did get excellent highway mileage though. Somewhere north of 20 US MPG/24 Imp.
Now a switch to another 750, this one an AED VS (IIRC) with down leg boosters and it netted another couple of tenths quicker (I don't recall the trap speed improvement but there was some I think). Nothing else was changed other than the air of the day. At the same time, the highway economy dropped off some.
The BG had been modified with screw-in air bleeds, the IFR was addressed. The usual suspects of carb tuning. The emulsion side of things was left as in was made.
Always struck me as a curious thing. Even more so now that I'll be drag racing this 357 (emphasis on track performance) and that BG carb is my jumping off point.
Last edited by skinny z on Tue Feb 13, 2024 11:28 am, edited 1 time in total.
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Re: Carb recommendation SBC 383

Post by rgalajda »

Since you have decided to use a Victor Jr single plane intake manifold the answer is easy. 750 cfm.

Let's say this was a Performer or a Performer RPM or Performer Air Gap which have a true divided plenum , then more cfm would be beneficial.
That's because the divided intake does not communicate with all four barrels of the carb the same way as a single plane intake.
As the divider gets cut down in a dual plane intake manifold such as the RPM Air Gap, the effect is improved output at the top end. Carb cfm required becomes less.
If there was no plenum cutout on a dual plane intake, carb cfm required for improved output at top end rpm range would be in the 850 to 950 cfm or more.

The 850 which has 1.57 Venturi size and down leg boosters. This carb will not show low speed performance as well as the 750 unless a high gain booster is used such as an annular booster. At very minimum the dog leg boosters would need to be machined with a step.

Dyno and track performance are much different than street performance where low speed drivability and torque come into play.
At the track if you are launching at 3,000 rpm or above, you are not dealing with low speed drivability or lower airflow rates.

My preference would be the BR67258 Brawler 770 cfm vacuum secondary carb. I have used this on a 500hp BBC street car with a Victor Jr and the secondary operation was impressive.
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Re: Carb recommendation SBC 383

Post by cab0154 »

years ago I had a stock jy 302 in my fox, converted it to carb and ran a too big AED 750 HO modified on it. it was too big, but the engine didnt seem to care. a carb with good emulsion has a lot bigger window of what it will tolerate vs a lot of the lesser off the shelf stuff that claim all kinds of tuneability. we actually used that same AED 750 on a cleveland when a good known 830 annular we had, had a dead sport off the brake no matter what we did. put that AED on it, and the cleveland went from running high 7.20s/low 7.30s (1/8th) to high 6.80s/low 6.90s. there is a lot more to this stuff than CFM ratings.
"Anyone who thinks the low RPM engine will be faster just does not have as much experience as the rest of us" -The late, great Joe Sherman.
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Re: Carb recommendation SBC 383

Post by HQM383 »

cab0154 wrote: Tue Feb 13, 2024 4:00 pm years ago I had a stock jy 302 in my fox, converted it to carb and ran a too big AED 750 HO modified on it. it was too big, but the engine didnt seem to care. a carb with good emulsion has a lot bigger window of what it will tolerate vs a lot of the lesser off the shelf stuff that claim all kinds of tuneability.
That's right. If anyone read the test i did with the Dragy then they will see how close in responsiveness a 650cfm through to 1000cfm carbs can be made to be. Saying xxxcfm in this day and age is like saying "a 3/4 race cam is too big for that engjne". It lacks a whole lot of detail as to what the 3/4 race cam is.
I’m a Street/Strip guy..... like to think outside the quadrilateral parallelogram.
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Re: Carb recommendation SBC 383

Post by skinny z »

skinny z wrote: Tue Feb 13, 2024 11:26 am What is it about the annular boosters that might contribute to diminished top end output as opposed to a down leg style?
cab0154 wrote: Tue Feb 13, 2024 4:00 pm ...a carb with good emulsion has a lot bigger window of what it will tolerate vs a lot of the lesser off the shelf stuff that claim all kinds of tuneability.
HQM383 wrote: Tue Feb 13, 2024 5:30 pm That's right. If anyone read the test i did with the Dragy then they will see how close in responsiveness a 650cfm through to 1000cfm carbs can be made to be. Saying xxxcfm in this day and age is like saying "a 3/4 race cam is too big for that engjne". It lacks a whole lot of detail as to what the 3/4 race cam is.
So, how does this work? What's the relationship between the booster style, the atomization and the emulsion?
I've experienced what appeared to be a top end deficit when comparing 2 carbs of different manufacture (BG vs AED) and booster style (annular vs down leg respectively). FWIW, both were "750 CFM" although butterfly and venturi size are only verifiable with the BG. The AED was track faster. The BG, better highway mileage.
Kevin
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