So what’s your recommendation then? Also what are you saying no too?Apologies No, but like anything else buy the one from the supplier who will give you the most support and carries the full range of parts. if you buy one that is just too damn unique you will never get a straight answer out of anyone when you need help. Make sure they know what you intend to do with the motor, if they are going to put in a baseline calibration for you.
most carb problems are solved with a better ignition , correct curve and the right plugs
Nice fancy carb producing superlative mixture increases pressure in the cylinder and that will highlight failings in the ignition system. i've been there and done that ...wasted loads of time
Dave
Sizing carburetor
- Thread starter rymor92
- Start date
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Dave999
Well-Known Member
i'm admitting i have no experience with either
and hence i don't know which
they seem to be the right size so buying one with good support from the dealer makes sense
buying one with no support doesn't
i could buy a holley or derivative in the UK and get support
if i buy a edelbrock/carter my support is limited to guys who put 500s on 3.5 litre rover buick V8s.I'm never gonna meet them... they like Rovers
this is my point,
you already have an example.
Asking for carb assistance resulted in being questioned/criticised about your cam even though you provided detail and explanation for its purchase.
so if you are going to have to ask questions having something that is relatively common helps,
turn up with something a bit different (your cam) and look what happens
i'm sure someone who owns one of those carbs will be along shortly
i'm only here now due to the time difference i'm much further west its 2pm here 9 am in NY
dunno where your location 43551 is
Dave
and hence i don't know which
they seem to be the right size so buying one with good support from the dealer makes sense
buying one with no support doesn't
i could buy a holley or derivative in the UK and get support
if i buy a edelbrock/carter my support is limited to guys who put 500s on 3.5 litre rover buick V8s.I'm never gonna meet them... they like Rovers
this is my point,
you already have an example.
Asking for carb assistance resulted in being questioned/criticised about your cam even though you provided detail and explanation for its purchase.
so if you are going to have to ask questions having something that is relatively common helps,
turn up with something a bit different (your cam) and look what happens
i'm sure someone who owns one of those carbs will be along shortly
i'm only here now due to the time difference i'm much further west its 2pm here 9 am in NY
dunno where your location 43551 is
Dave
I would look more into the avs2 carb but to me it feels at only offering a 650 or 800 is a big difference and they need a middle man as I think that’s where my engine would be the happiest.i'm admitting i have no experience with either
and hence i don't know which
they seem to be the right size so buying one with good support from the dealer makes sense
buying one with no support doesn't
i could buy a holley or derivative in the UK and get support
if i buy a edelbrock/carter my support is limited to guys who put 500s on 3.5 litre rover buick V8s.I'm never gonna meet them... they like Rovers
this is my point,
you already have an example.
Asking for carb assistance resulted in being questioned/criticised about your cam even though you provided detail and explanation for its purchase.
so if you are going to have to ask questions having something that is relatively common helps,
turn up with something a bit different (your cam) and look what happens
i'm sure someone who owns one of those carbs will be along shortly
i'm only here now due to the time difference i'm much further west its 2pm here 9 am in NY
dunno where your location 43551 is
Dave
Newbomb Turk
Well-Known Member
You are way too caught up in CFM ratings. That's a poor way to size a carb.
You need something with a 1.375 venturi and a 1.687 throttle blade.
That just happens to be a 750. You can run a much bigger carb than most on here think and lose nothing if you get the timing curve correct (that's not locked out or all in by 2500...you need a real curve) and then you tune from there. Most lack of bottom end and drivability issues stem from poor cam choices. That's why several of us mentioned the cam.
Many a carb has been blasted from improper timing and a bad cam choice.
junkyardhero
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street/strip 800
toruring/cruising 650
unless you're looking for 10ths and a few more mph in the 1/4 it's going to run no different on the street between a 650 and 750
I would buy the street demon, I have used them since they came out they are good carbs.
In fact the last one I bought, I removed an 700 DP and replaced it with the 625 street demon on my 340 Duster.
I am running about the same combo as you, with a little more cam and the same gears, but a manual trans.
It it very responsive and easy starting.
How do you think the 750 would run on my setup. Sounds like it should be a good fit for mine.
It would be a good choice.
I don't have experience with the 750 Slayer, but I do with the 450 Slayer. Same carburetor, just smaller. I have it on the slant 6 in Vixen. I love it and it runs fantastic. The tuneability is great, with the idle and high speed air bleeds on top, idle fuel restrictors in both metering blocks and it even has bleeds under the power valve. That's some real adjustability.
I've also run a 625 Street Demon on the 400 in my Ford truck. I like it. It ran great. My only one complaint was that the primaries ran out too soon and I was into the secondaries a lot. It was because the primaries were so small and this engine has a high demand for fuel in this heavy truck. I now have a 650 DP Brawler on it and it's a beast. I'm sure it could take a 750 Street Demon and I may put one on it eventually, but I already had the 650 Brawler.
I looked hard at the brawlers too. Looked identical to slayer in specs and adjustments but with billet throttle plate and metering block
The 650 AVS2 would be the best carb for your combination. Forget about the brawler, crawler BS carbs. Some just don't get it.....
I posted the page below on another thread on this forum. It is very informative about carb size. 383 Dodge v 428 Ford. Dodge was 3.3% lighter but was down 45 cubes, or 11.7%. Both had 3.5 axles & both ran 14.04 for the quarter. The Dodge was 1 mph slower at 99 mph. The Dodge had the 625 Carter AVS, Ford had a 700+ cfm Holley [ pretty sure 735 cfm ].
What this tells you is that the 383 with the smaller carb accelerated quicker but lost out at the top end. Because the trap speeds were so close, it indicates the 428 was slower for most of the quarter & only picked up at the top end. I would rather have a car that is quicker from 0-90 with a small carb......than 90 -120 with a big carb. And this is what many do not seem to get....
I posted the page below on another thread on this forum. It is very informative about carb size. 383 Dodge v 428 Ford. Dodge was 3.3% lighter but was down 45 cubes, or 11.7%. Both had 3.5 axles & both ran 14.04 for the quarter. The Dodge was 1 mph slower at 99 mph. The Dodge had the 625 Carter AVS, Ford had a 700+ cfm Holley [ pretty sure 735 cfm ].
What this tells you is that the 383 with the smaller carb accelerated quicker but lost out at the top end. Because the trap speeds were so close, it indicates the 428 was slower for most of the quarter & only picked up at the top end. I would rather have a car that is quicker from 0-90 with a small carb......than 90 -120 with a big carb. And this is what many do not seem to get....
MyD750
'71 Duster 340 TX9
This is a decent article that talks about the baseline carb sizing. There's a lot of grey area, but it provides a formula for guidance. https://www.motortrend.com/how-to/much-carburetor-need-application/ Perhaps the most 'arguable' variable is Volumetric Efficiency (VE). If anyone knows of a solid reference in determining (somewhat accurately) the VE, it would be a great post.
Mike
Mike
Good n/a motors are higher then 100 % VE
Boosted motors are higher then 100% VE
Thats why just using the cfm calc is foolish
Better to be a lil bigger then to small
340=750 all day every day
If you ant to split hairs 4778 700 dp works great on a 340
The newer carbs then that have the better adjustability
Boosted motors are higher then 100% VE
Thats why just using the cfm calc is foolish
Better to be a lil bigger then to small
340=750 all day every day
If you ant to split hairs 4778 700 dp works great on a 340
The newer carbs then that have the better adjustability
Dale Davies
Well-Known Member
Being a street driver and an Air Gap intake, I would choose the Edelbrock AVS2 650 CFM carb. An Air Gap does not have the heat transfer a conventional manifold has, so the annular boosters aid fuel atomization for better driveability.
Dale Davies
Well-Known Member
On a boosted engine you ate stuffing more air in which expands greatly in the combustion process. You need more exhaust port and valve along with lift and timing to get the exhaust out.
TT5.9mag
Two atmospheres are better than one
Trust me, I know exactly what’s going on in a boosted engine. I have many. And have built MANY. You don’t “NEED” more port, valve, lift, or timing to make em work. Boost acts like a multiplier of what the NA engine will do. Anything you do to make the NA combo better will make the boosted combo better, just when it’s on boost it’s more better. Yes I said more better.
junkyardhero
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i believe the preferred terminology is: more better-er.
please refer to the FABO style guide that was sent out via email, some traditional vernacular has been updated and abridged.
The AVS 800 flows less than advertised. Something to do with the annular boosters restricting flow. Not an issue unless you really need the CFM
Dale Davies
Well-Known Member
OK captain.
So what I *think* you are trying to tell us is that you are looking for a carb that will be pretty close out of the box.
* You will not be taking it to the track or a dyno to tune in the full load WOT.
* You will use it at least three seasons of the year.
* Tuning will be somewhat limited.
With those goals, the rest becomes easier. Carb with choke tower. Automatic choke if it has a pull-off will be a plus. You call on whether choke (auto or manual) is important to you).
Carb that is decently calibrated as purchased and doesn't have known issues (like the Eddy 750 and many of the newer Holley 4150 types with excess emulsion etc)
Smaller primary venturis will be easier to dial in than larger ones.
A secondary that is actuated by demand can be a benefit in this situation.
Go with the carb system you think you'll be most comfortable tuning. Off-idle is the most difficult to adjust if it can't be corrected with throttle-transfer slot rlationship. The Carter low speed circuit is more sophisticated, but if a Holley type is off - its more accessible if you are willing to put in the time and effort. These are the trade offs. High speed and full power is jets and rods/springs or jets and power valve restrictions/PV.
Nothing will be entirely plug and chug - just some will require only the basics: Timing, Fuel level, throttle position, idle trim. Then adjust high speed cruise restriction, and wide open throttle - full load as much or as little as you want.
What the all-knowing Bewy does not "seem to get" is that a fifty plus year old magazine road test involving three cars from different manufacturers tells us very little (IMO) about optimum carb sizing. And that 383 Super Bee ? That's the fastest stock one I've ever seen road tested in a magazine. It makes me suspect that it's been tweaked/supertuned. The 428 CJs were typically faster than 383 SBs and RRs. Then there is that Carter vs Holley dyno test from fifty years ago that you referenced multiple times. It could simply be the result of the Holley having a secondary spring that was too stiff. Easily corrected. We know you hate Holleys. If you want to prove their inferiority, maybe you should post up more evidence than the same two sources. Here's a dyno test involving multiple carbs on a 383: Moparts on the Web - Main Index
65Val
Average Length Member
From the "Articles" section...
How to choose the right size carburetor for your engine
Bad-*** Racing Engines specializes in building some of the baddest street and race engines around!
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