Wanted - Holley Tuning Guru in the UK

[BruceA]

I'll have to agree with Jac on this one. In too many cases it only 'sounds' good to say you have a 'double pumper' carby installed. Most of my friends had them but had no idea why or what they did, it just sounded better than the next guy. It may have the mechanical secondaries but it also has 2 accellerator pumps. They are there to cover up the air 'hole' that is left when you bury your boot at low RPMs, when the vacuum signal vanishes from the main jet.
All my friends had 750 and 850 DPs on their cars and I had a 650 spreadbore with VS on my 350 Chevy. My 1/4 mile times were consistantly lower than theirs, even in a heavier car. As stated above if set up for the correct application VS carbs will work just fine.
Sorry for my 'Chevy" outburst there ...... back to the subject in hand!

 

[Jac Mac]

Doesnt matter what the 'Name' on the rocker covers is. Most if not all the factory Hi Perf cars were fitted with Vac Secondaries- Hi Po 289, Boss 302-351-390-427-428-429-460. Chev Z28 302-327-350-396-454, plus all the others Buick, Poncho etc etc. I cannot think off-hand of a factory USA V8 that came stock with a Holley DP. But Im sure some diehard will sus one example out !

 

[RichardH]

hey guys - chill. I asked because i have been told that vacuum secondaries are prone to going "off". This might be correct or Bllx. I did not intend to stir up a vacuumVmechanical argument, just to find out more. It seems that opinions are well entrenched !
As for fixing the vacuum secondaries - that is, of course, one option. I thought my post was quite precise, obviously not. It boiled down to 3 options - fix vacuum secondary (bearing in mind the "going off" scenario) - change to a "reliable" mechanical secondary carb - or leave it as is until next year. I am partly led to believe that if the car had not been dyno tested, I would not have noticed anything - a case of "look for a problem and you will find it?"
You may agree or disagree with what I have been told. I only post it, so that I can try and draw my own conclusions. I am not stating that it is true - just that it is what I have been told by those that profess to know. Please do not shoot the messenger.

 

[Malcolm]

Hi Richard

Suggestion? Why not grab a lift with me when I go to the rolling road and investigate your options with the chap at Raceshack? Bring your carb with you! Personally I have never heard of anyone with a vacuum carb having any more or less issues than a chap with a double pumper. I choose my double pumper as I had no carb at all at the time and being of competitive bent felt it suited my needs. I also have disconnected the choke and vacuum advance to the dizzy. Fuel econmy be dammed! The carb has not been serviced in over 10 years so feeling sorry for the abuse I give the car I felt guilty enough now to do somethng about it! As to carb size the GTD factory back then felt that on vacuum carbs you needed a 750 cfm but only a 650 cfm double pumper for equivalancy. This assumed a not too radical engine say up to 350 bhp. If you over carb a car, to get it running right you will down size the jets to those you would expect in a smaller carb and on most engines ie not mega high revving engines the air requirement is met by the smaller carb. Maybe it is all to do with willy size after all?

 

[RichardH]

Malcolm - did you ever get to Raceshack?