what carb do you use

[Dave-R]

Let me state again what i am saying and what seems to conflict with what you usually tell people. Although in your last post you seem to have changed position slightly.

I would use a 750 on a hot but streetable 340-383 sized engine or a stock 440. I would use a 850 on a hot but streetable 440. I am not talking about stock or very near stock engines here. I am talking about engines with decent street/strip camshafts fitted.

You are right that the six packs rating is divided between 3 carbs and it is only 960cfm at WOT. But it is at WOT off the line at idle. Nothing progressive about that.
You also forget that a 4bbl is divided into two halves and an 850 is also only an 850 at WOT. True that a spread bore carb of that sort of size would work better. Smaller primaries and bigger secondaries make a lot of sense for a street strip car. which is what the six pack gives you.

Your theory about lack of vacuum with the bigger carbs is correct.

However the lack of metering signal (suck) is a low rpm thing only right? No way can you convince me that a 440 at high rpm is not drawing enough air for a 850 or even a 1000cfm carb to supply the correct amount of fuel.

So the lack of metering is a low rpm effect.

Now. There are several things you seem to have forgotten.

The cars we are talking about will (should!) have lower than stock rear gears and higher than stock torque converters. So really the rpms are higher anyway.

Another thing you have forgotten is that the accelerator pumps are there to compensate for any lean condition as the carb opens until the rpms are high enough for the metering to work.

But the biggest thing you have forgotten is the power valve or fuel enrichment system. That is there for exactly this sort of problem where you have a carb opened quite wide (so large cfm) on a car with tall gears (low rpm) and large mass going up a hill (high engine load).
In these conditions even a small carb would lean out without the fuel enrichment system. It is that very same low vacuum signal you are talking about that brings the system into operation.

Sure a 750 on a 440 will work great on the street. Been there and done that. But in my opinion on the track with lower than stock gears you need a 850 to flow enough air at the top end of the rpm range. And you can't argue with that when a 960cfm six pack is doing that just fine.

[Anonymous]

Several things I seem to have forgotten????

It's all basic tech advice from BG and Don Gould, now forget the latter just for a moment, are you actually saying Barry Grant doesn't know what he's talking about.

My Motor will make around 550/600HP 362 CI Race Demon 795 RS the removeable sleeves because it will be a little big so there's some experimenting to do. This is not a street motor, so how does a 750 on a 340 work thats streetable, never in a month of sundays and that's from BG not me, go take a look at the BG site

What actual cam specs come under the heading "hot but streetable"

[Dave-R]

Forget it. I don't want to get into an argument over it. I can't argue with corporate advertising.

I think those Demons might flow better than Holley claims for its own carbs. So what goes for a Holley might not for a Demon. Maybe. There may be other things about the Demons that change things.

But you didn't say anything about the other systems in the carb that are there specifically to get over any lean spots. I just thought I would point those out.

[Anonymous]

I'm gonna vouch for Demon's backed up with the service offered by USAimports.

The spec sheet thing is definatly the way to go, my Demon was set up to my inlet/cam/headers etc before it left the states then fine tuned by Neil(Wil) on the car.

The car runs without fault, the fuel system looks the dogs, Neils at the end of the phone or best bet once the Demon arrives is take yer car to USAimports.

No doubt you would be happy with any well set up carb of the right size but its the service from Neil that I'm especally pleased with.



Since becoming a Demon owner I have noticed the Demon stickers on the wall in the background whilst watching dwane spit his dummy on American Hotrod, I didn't see any other makes!
Whatever you think about that lot Boyd himself is no fool!

Russ

[Anonymous]

neither is Barry Grant, or Don Gould for that matter, horse to water and all that, carry on Dave i'm sure you know best, when faced with such seperior knowledge I wonder why Barry Grant ever bothered

[Anonymous]

750 on any street driven 340 wake up man, not on this [planet

[Anonymous]

come on over to our forum Dave, no holds barded there, not the place to do this here

[Blue]

I'm not getting into an argument here either but I can say from what I have tried personally that big blocks like a big carb for maximum performance. A smaller (750) carb might be great for general use under 5000rpm but it runs out of breath big time above that. Here's an example, 383 4 speed duster with a 750 holley, it was really all done by 5000rpm but the cam I had in it made power to 6500. Bolted on a tunnel ram with a pair of 660 centre squirters expecting to see all my bottom end power dissapeer at the expense of top end rpm, well not a bit of it, I could even light up the tyres pulling away in 2nd and the thing pulled hard to 6500. It was appalling on fuel but a hell of a blast to drive, it still idled at 900 rpm and had blinding throttle response. Having said all of that I would still advise anyone to use a 750 carb on a big block for 'normal' use, but in certain circumstances you can run faster with a far bigger carb than would seem to be suitable for the application.

[Alex]

Enough. you both stated a case lets not Bananarama! any further or it gets locked.

[Anonymous]

Lock it if you want Alex, i'm cool, basic BG tech, Bulldog and wasps and all that

[Alex]

Yeah but 'basic BG tech' may not stand up all the time, I had a problem with a 340 just before the nats a few years back so in desperation lobbed a 750 on it just to get me there, never missed a beat, ran faster then ever etc, granted 4.10:1 rear but you said never, well I am here to tell you I am the exception to the rule! also I reckon my Road Runner needs more carb, 100 mph terminals for a low 13's car seems slow to me?

Anyway, we should all remember there are guys on here who have worked these motors for years and have good experience and learnt the hard way through trial and error with no outside help, and I have lots of respect for them and the set ups they run, hell I fix these cars for a living and still call some of the forum users for a second opinion as they have to me.

[Cannonball]

very mild 440 e body 3,7001bs with driver turns 6,000 rpms holley 600 vac sec 12.84 no argument there,
all out iron headed 440 roller cam ported to max heads , 37001bs with driver 1050 dominater loves it 11.00s horses for courses
a nice useable 440 only needs a 600 vac sec good gas mileage good performance

[Blue]

Had a 750 on my 340 as well, loved it! We are having a discussion here, not a row so no need to to lock it, a lot of what is being stated here is opinion not fact, I'm not clever enough to discuss the science bit, I can only say what I've tried!

[Alex]

Blue I won't lock it unless it gets personal mate. I am enjoying listening to both sides of the coin, I know what I have tried over the years and the results that came of it, remember us trying to get the Duster to launch? that was a ain huh??!! drat those plug leads!!!!

BTW what do you tink about trying bigger carb to up the MPH on the Runner? wondering about trying Neils FBO ECU for a start but I am sure it is lying down from lack of fuel or air ??

[Dave-R]

Well I am not going to enter into a battle of wits with an unarmed man but you would be hard pushed to find a 340 or 360 anywhere running 13s or better that didn't have a 750. You might find the odd example but on the whole it is pretty universal. Or at least used to be. Maybe things have changed.

Going back to my earlier comments about how well Demons flow. I wouldn't be suprised if they did indeed flow more. That way in any direct comparison they would come out on top.
If that was the case a 750 Demon might well be too big for a small block.

Just a thought.