View Full Version : Holly jetting
11-12-2007, 01:56 AM
I'm running a 670CFM on a 350 with a T/A dual plane, mild cam. (22in vacuum)
The 670 Advenger came with 65/68 jets out of the box.
I'm up to 74/78 and just starting to get color in the plugs(they are white, not ash, not tan).
T/A and Holly say "you sould be good out of the box, maybe one size larger but not more, That is the right carb for your 350."
How can you argue with the pros?
How can you argue with the color of the plugs.
I'm looking for some experience, anyone else running the same 670?
Sean Buick 76
11-13-2007, 08:44 PM
Too bad you have already bought that carb. The stock 350 loves 800 cfm so a healthy 350 really likes 850 plus cfm. Dyno testing and track testig prove this. For lower rpm the smaller carb is ok but the larger carb will destroy the performance over 4000 rpm. I had a 650 Edelbrock on one of my 350s and it was a step down in performance vs the old 20 yr old Q jet stocker. I cant help with the jetting though, I use the Q-jet 800 cfm carbs.
11-13-2007, 09:34 PM
Thanks for sharing-
Yeah too bad is right.
The learning curve can be rough.$$$
I spoke with Holly again today and they assure me it's the right carb, with no real answers and i'm up 10 sizes on the jets. He did say check the timing *%@#.
I run the 1/8 mile at Irwindale Speedway in So Cal.
I'll ask around, maybe some one has an 850 they can lend me for a few runs. Hey I might have a 670 to lend out soon.
PS- Dig your cars...:YA:
7 skylark 1
11-14-2007, 05:46 PM
if your running pump gas you will not see much color on the plug. i tuned my carb with a wideband and mph at the track. my plugs are white. try jetting it at the track for best mph. race fuel will color the plug.
11-14-2007, 09:58 PM
why do you say there won't be much color?
I've changed hundeds of plugs, most with color, why not now?
11-15-2007, 02:27 PM
This is the color i'm shooting for, so far i'm not even close with 74/78 jets.
7 skylark 1
11-15-2007, 08:28 PM
this is a good info on plug reading. hope it helps.
Sean Buick 76
11-17-2007, 02:16 AM
its plain and simple. If my a stock low comp 350 loves a 800 cfm Q-jet over the 750 cfm stocker than you need a bigger carb forsure. There is both dyno and 1/4 mile proof that even without mods the Buick 350 needs a big carb to make power. A build up 350 wants a 850 cfm for sure, and can handle 1000 cfm for racing.
The problem here is that no dealer wants to sell a carb thats too big and so they lowball on the suggested cfm because it will not overcarb the engine and make it run like crap it will at worst just leave some performance on the table which is where you are with that little carb. Add the that the basic theory of cid to CFM sizing that works great with almost all engines but Buicks. A stock 455 just LOVES a 1000 cfm carb, try that on a cheby 454!
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