product Review #1 AED's 1250 Carb - too big for a 350??

[DavidVizard-GFN]

Product Review #1

This is where we look at a promising product and give you a preliminary evaluation prior to any in depth evaluation we may subsequently do in our Product Spotlight Series.

AED's 1250 Dominator

A carb for all occasions (Almost)?

by

David Vizard

As is so often the case our quick test of this 1250 cfm AED Dominator came about by virtue of a number of ‘chance encounters’. The first step in that direction was almost insignificant. During a conversation with AED’s boss John Dickey, he happened to mention that they had got the drivability of their new series of Dominator carbs such that there was almost no such thing as a carb too big for the engine. That stuck in the back of my mind.

The next element of this series of events was that I incorrectly assembled (one of those 1 am deals) our largest dyno AED 4150 series carb (about 930 cfm) and it was sent back to AED for a rebuild. Next day the dyno becomes available to test Dusty’s new 350. This engine, even if it was near the bottom of the ladder in terms of race engines, was Dusty’s first foray into building such. Sure it had a few concessions to street use such as a 10/5/1 CR and a slightly more conservative cam than would otherwise be the case but apart from that it was the real McCoy in terms of a budget race engine build.

So we get on the dyno and as usual it’s all a bit of a rush as we have just one day to break this engine in and test several manifolds and the like. Well we get to test the essentials but, as ever, it takes a little longer than expected. Up to this point we had been testing the dual plane stuff and Dusty was hot to see if his motor could break the 560 hp number that so often cropped up as a target figure from the many hot shot engine builders he so often talks too.

So it’s now late in the day. The two plane intake comes off and the plenum prepped, port matched Super Victor goes on. Since the big 4150 series AED is at AED’s shop we have to make do with the slightly souped up 750 AED carb we have. A great carb but it is probably a little on the small side for those big numbers. Although drivability is still a factor here Dusty was most interested in the 6000 – 8000 rpm range as that, assuming the motor delivers as anticipated, is what it would use on the track.

So the ‘souped up’ AED 750 was installed. At this point the engine is also dumping through two big Flow Masters. I made three pulls on this combo and the result was 451 lbs-ft and 557 hp. At this point we have 30 minutes to do something that might net the 560 horse target.

At this point I recall John Dickey’s comment about ‘no such thing as too big a carb’ with his new Dominator. I also mentally edit out the ‘almost’ that was also in that comment. I see we have an adaptor/spacer that will allow us to bolt the big AED Dominator right on to the Super Victor. So the regular spacer and the 4150 AED were removed and replaced by our monster carb.

Since we had time for one shot and one alone at this 560 hp number Dusty elected to remove the big Flow Masters ( which in previous tests at around this power level had near zero effect on output) and install the right tuned length collectors for this setup (a previously determined length from similarly cammed motors). Unfortunately the precise length could not be had with the extensions available to us at that moment so a little compromise was forced on us here.

With about 10 minutes to go we fired up this now very raucous open exhaust 350. I played with the load and throttle at relatively low rpm to see if I could find any holes in the drivability. None appeared – so far so good. A low speed pull showed the engine made too much torque for the dyno to hold it at 2500 rpm but as it passed through the 2500 mark it did consistently show 320 -340 lbs-ft. At 3000 rpm, which was about the first point the dyno would hold it (dyno was set for high rpm, pulls) a recorded 396 lbs-ft came up. That was just 5 shy of what we saw for the souped up 750. So far so good. At this point there was literally 2 minutes left before it was time to shut shop and go home. I made a pull – just one. This 350 soared around to 8100 rpm like a 150 Decibel watch and cranked out almost 584 hp in the process. The before and after figures are as per below but please remember this is not a true before and after test of just the carb because the tuned length open exhaust also plays in here. What it does show though is that the low speed capability if this AED carb is exceptional.

Now before you all go installing one of these monster carbs on your 350 lets fill you in on John Dickey’s comments when we spoke to him about this test. Quote “Really – I knew we were on to something here but I would hesitate to recommend that much carburetion on a 350. We know that they work well on engines as small as 400 inches and drive like an electric motor at low speed”.

At this point we were outside the boundaries of what AED conceived, at that time, to be a viable deal. However this test adds to the bank on data they have to work with. What we have proved here is that this carb is very drivable even on an engine considered too small for it’s flow capacity. On this occasion we got it to work and who knows - we may get it to work equally well on our next high output 350 (and you can bet we will be looking into testing it more rigorously) What we have shown here is that this big carb at least, to a sizable degree, resets the standard when considering what the maximum flow needs to be if the drivability and low speed is not to be negatively impacted past a certain minor degree.

Here, from the data from one pull, is the before and after when the carb was changed out to the AED 1250 Dominator and the exhaust opened up with near optimal tuned length collectors.

I am now sufficiently confident that if we are doing a high effort engine of more than say 390 cubes, this is the carb we will give most serious consideration too.

David Vizard

[MAP]

Greetings David,

If the mechanical and packaging difficulties could be surmounted, would adding some vacuum-controlled valving on the secondaries let this carburetor offer possibly near the very best of the low-speed and high-speed worlds?

Best,
Mark

[Bryce Mulvey]

Mr Vizard Do you have any intake manifold vacuum data before and after the carbs were changed? I'm also curious to know if there was difference in the amount CFM the engine took in when the carb was changed.

[DavidVizard-GFN]

Originally Posted by Bryce Mulvey

Mr Vizard Do you have any intake manifold vacuum data before and after the carbs were changed? I'm also curious to know if there was difference in the amount CFM the engine took in when the carb was changed.

Bruce,

In our haste to get this done before T&L closed down for the evening I did not get as much info as maybe i should have done. I remember the air flow into the engine being up measuably starting from about 5500 or so rpm. The idle was good but I do not remember what the vacuum was compared to the 4150 carb this Dominator replaced. Also I remember the intake vacuum at WOT being less with the 4500 carb compared to the smaller one but I can't recall just how much. There was a lot of pulls made that day and since then I have done a lot more. At my age things start to blur somewhat!

As of now Dusty is building an upgraded version of the 350 that this carb was tested on. We intend to use the Dominator right out of the gate on this engine.

The target on this engine is to crack the 600 hp mark on hopefully pump gas. We'll see.
DV

[red65mustang]

your article is not a test of over-carbing a 350 at all....

what your test proved is that particular motor parts combo does want more than the 750cfm carb will/can supply at best possible WOT Hg for A/F mix above 6500!

(you gave no details for the build except the intake so I plugged in RPM heads/10.5CR/294 cam/Victor intake/350 chevy into my Desktop Dyno to get just roughly close to your chart HP results and find the motor total cfm for this example)

EX:
750cfm Holley carb
6500rpms=735cfm thru the motor/520HP
7500rpms=782cfm thru the motor/456HP

1150cfm Holley only change
6500rpms=752cfm thru the motor/535HP
7500rpms=807cfm thru the motor/478HP

my $.02
what your article and my example do prove is a particular parts combo may indeed "need" more than 750cfm to make max HP possible

[rookie]

This may give you a little more insite on the engine Product Review #4 AFR 195 Comp Eliminator Heads, but I think the good's or held back for a future article.

[red65mustang]

rookie,
thanks for the link....
(with only 195cc's the flow effiency on those AFR's is darn good to produce those dyno numbers!)


but do note:
the stock Edelbrock RPM heads in my example are only 171cc's (!!!).....
as small as they are they even indicate a larger carb may be needed due to the performance parts combo....

LOL,
he mentioned in the heads article, there were some Sprint Cup car 350 heads laying around (about 280cc's)....
use a Cup car 8,000rpms HP peak cam.....
"fair chance",,,, with those heads and cam mounted.....
the 1250 AED carb isn't even big enough for max HP possible!!!