CiCiC3

I have a BB that I have running with a Holley double pumper. I like it except that keeping the output of excess hydro-carbons at a minimum is too much of a battle. I think that by switching to like an EZ-EFI I will be able to take care of that problem for good and probably a few others as well. Is this correct or are there still some issues with that on 500HP engine.? Thanks

fleming23

You can certainly have the tuner set to call for a certain air/fuel at different RPMs but it will only go so far as to reducing "excess hydro-carbons." This is why catalytic converters came into play and their main role.

If the carb is super rich at idle, having a self-learning EFI system can and will help clean it up a bit. Depending on what you are working with now, swapping to a system like EZ-EFI can definitely improve driveability and things like cold start. However, these are all things that can be addressed on your carb by someone who knows how to tune them properly as well. That being said, I am about to swap a 950 cfm 4150 out on my 496 to put on an EZ-EFI 2.0 system....

CiCiC3

Ok thanks, it sounds like from what you say it won't entirely clean that up. I have had the carb worked on about 3 times in the last year but they have concluded that to get it dialed in correctly it's going to need to be dyno-tuned otherwise it's like shooting in the dark mostly for adjsutment. So maybe a dyno tune would do for me.

billla

Is this a required emissions thing, or is it just running consistently too rich? A DP carb is never going to win an emissions contest ;-)


A dyno tune will certainly cost far less than a new EFI system. What carb specifically do you have on there now?


And...if you're taking the car to a shop that doesn't even have an A/F meter....then it's the wrong shop.

CiCiC3

It's a Holley 850 double pumper 4781-6 on a duel plane Edlebrock performer. The only dyno place I can find so far around town is a VW racing shop. They said they could do it, but I have a few concerns it may not be the right place to go to.
In Kentucky emissions are not regulated so shops don't mess with measuring devises unless it's for racing. And there is not much racing going on except for horses.

billla

They're for sure not the right place. You didn't answer about what the "hydrocarbon" thing is about, but again a DP isn't really a fuel economy or emissions carb - and that one's an "old skool" street/strip model vs the newer HPs and Ultras.


I'd post in your regional forum for a dyno shop that knows American muscle. I'd have every confidence that a good tune will address whatever you're facing.

CiCiC3

That's what I was hoping to hear more or less. So maybe Cincinnati has a shop I can take it to, to get a more efficient setting. At the same time I realize it's not going to be all that clean but should pretty well match a fuel injection system in that respect?

billla

Willing to be the Forum folks in your area will know the right shop.


I doubt that a DP can match an EFI system given it's natural proclivities to put performance against all else - a vacuum-secondary carb would be better in all respects EXCEPT zero-to-WOT.

CiCiC3

Racing is important, but I don't want people to pass out from fumes either. Not into competitive racing, just fast for fun.

billla

Honestly, if you're not going zero-to-WOT on a regular basis, I'd think hard about a vacuum secondary carb in the future. That said, I'm 100% confident that a good dyno shop is going to get that DB working pretty well.

roscobbc

Surely tuning of that DP as far as ever day emissions and 'exhaust fumes' are concerned will be little different to tuning a two barrel carb. Secondaries will not be used in every day use - if the DP is higher spec unit it will have 4 corner idle so in real terms could be more efficient if tuned properly than an off the shelf vac secondary carb.

billla

Agreed for the most part - but with a 500 HP engine it's likely seeing the secondaries more than occasionally The problem comes in with the mechanical transition to the secondaries based solely on throttle position, and that big fuel shot to cover up the associated bog. It's pretty darn tough to beat a properly calibrated vacuum secondary carb for efficiency.

roscobbc

#

As you say a Vac Sec carb is without doubt more 'efficient' in terms of only ever operating secondaries when there is a 'real' engine demand rather than a 'driver' demand. The 'tip-in' transition point from idle to main jet etc is tunable to a degree if the DP carb has idle bleed adjustment but its all a bit 'seat of the pants' and 'old school' in terms of setting up accurately unless done with AF meter. Will the tuning shop go as far as 'stagger' jetting if there are variations cylinder to cylinder? The OP if concerned about the 'smell of raw gas' etc sounds to me like a 'sensible' driver and the issue here should certainly not be secondary tuning as these only ever going to operate at higher speeds where the OP would not himself notice any excess gas issues. Unless of course the OP enjoys 'nailing' the gas pedal when stationary or 'lighting the rugs' on a regular basis. I have a 950DP on mine and, yes if driving 'energetically' and have have buddies following me they do complain about the smell - but with 500+ HP the secondaries do not operate that often in normal suburban usage. I would have thought that if the OP just concentrates initially on the primary side of things and perhaps optimising primary squirter jets and cam operation he may find his answer. Question for the OP - what size are the primary jets? - what sort of tune is the engine in? - what is the vacumn reading at idle?

pauldana

EZ-EFI 1.0 to 550hp
EZ-EFI 2.0 to 1200hp…. I'm running this one

billla

Of course, this depends on the CFM of the carb - a 750 CFM carb is going to see the secondaries if it needs more than 325 CFM, your 950 is going to see them if the engine needs more than 475 CFM.

I didn't catch the size of the engine, but let's look at a 454 making 500 HP - it's going to need more than 325 CFM at around 3,000 RPM, and more than 475 CFM at 4,500 or so...so it's hard to imagine keeping a foot out of it that much. The RPMs are higher for less CID, but still well under 5K RPM.

CiCiC3

It's a .030 over 454 1974. 2.05 and 1.89 valve sizes if I remember. It was leaned on jets from stock at sea level. Now in July we will be moving to Denver so maybe I should hold my horses until we get there because that will be about 4000 ft higher. Maybe an EZ EFI would make things easier.

jarrettslee

I have a 1973 corvette the an 1st gen HEI distributor (red and black wire) and the coil was the stock gm coil with a Resistor wire and the cloth sleeved wire. The coil was labeled “use with external resister”. during installation of a Holley sniper quadrojet I damaged the stock coil and replaced it with a msd master blaster 2. I used the the same wiring as before.



I have the sniper negative coil lead hooked up but can not get rpm to register. Or the vehicle to start. The hand held remains at stalled. I feel like the new is not hooked up correctly? I send the sniper back to Holley for diagnostics and they said nothing is wrong. So the problem is on my side. Does anyone have any thoughts on a way forward?

4-vettes

jumping on the back of a 7 year old thread is no way to get your question answered. which by the way has nothing to do with the old thread you attached to. START A NEW THREAD! Ask your question properly.

jarrettslee

it was a relevant threat for my problem. But I’ll take your advice and start a new one and maybe reference this one. Thank you.