I called Holley tech line to ask what carb to buy for my engine.They told me a 670 will be good .So I got the 670,got it on the engine, the float Leve was out to lunch got that fix .Then the car was like dead at the start line and very strong at the top.So i called the tech again.He said change the power valve to half the vac when the car is in gear so my vac was 91/2 so I got a 41/2" and get #68 jets for the primary so I did that.The car is the same nothing changed.Bad at the bottom end and ok at the top.There is no flat spot, it just feels like I'm draging another car behind me.So I called again this morning.They said that the carb is to small for my engine and he gave me a p/o # for the store that I got the carb from so they can give me a new 770 Avenger.My car had the old style 1850-3 holley and it was good from the bottom end all the way and up to 6800rpm and then it feld that the was no more power and the gas mileage was bad like 15mpg. so I thought the new Avenger will do the trick.In my opinion a 770 is to big for my set up for street driving. So what to do? :confused: My engine has a 67 z28 intake a isky 270 280 mega cam with roller rockers 461 original heads flat top forged pistons 700r4 with 3.73 rear and a [heavy foot] :D

[ 05-10-2003, 08:31 PM: Message edited by: MRCOOL_RSSS350 ]

i.m.o. i think a 600cfm would be enough, if u had bigger valves, etc. i would go for the 770

ROBERT Thanks for the reply. Thats what I thought that a 600 or this new 670 avenger will be ok.So today I got a 8"power valve 11/2" less then my idle vac,I changed the pump cam to the second notch I re installed the 65 jets and I installed the black spring on the vac secondarys.Well the car goes like it should.It has a crisp punch and it never stops pulling.I think I will change the power valve to a 71/2 so it will be 2" below the idle vac.in gear.I don't know why the Holley tech guys said to go with what they said, but it was all wrong and good thing I din't get the 770! graemlins/thumbsup.gif

So is that the rule of thumb? Having a power valve 1-2" below idle vac? If that's the case, I need a 4" power valve. :eek:
I don't have an avenger though. I've got the 4150.

Steve 2" is the # If you have a/c maybe 21/2 thats what I found out.Holley said 1/2 of your running vac in gear.I think thats is wrong!Nick

Usually I recommend customers 1/2 vacuum in gear +1. I have a feeling the biggest difference was in your pump cam/jetting.

Thanks. I have a 4-speed though. I'm going to pull this carb apart soon.