Afternoon team, how ya doin'?
I have a query regarding my 1985 305 Z28, vin code "H" (Carb, non-HO engine).
I have over the last year fitted the '85 HO chip (helped a little), then an Edelbrock 2101 cam (helped even more), then a Performance Products Power Plus intake (helped even more). All of these were done separately and the
(seat of pants) performance rose each time, with a month or so in between to shake them down.
So far, so good. By the way, all this involved removing the AIR & EGR systems (yes I blanked off the relevant vac tubes!). The air con pump belt is off, too (not required in chilly old England!).
I have just fitted a set of Hedman 68470 headers & matching 17470 y-pipe and a large-bore cat-back (the cat has been replaced by a straight pipe before I got the car). Also, the EFE valve is now history too.
Since doing this last bit, what I find now is that the low-down torque is dramatically better (I've had to radically alter my driving style 'cos the back end now steps out on exiting a tight corner with the hammer down), but whereas before (before I put the headers on) she pulled really hard from 3,500 revs and hit 4,500 easy from 30 or so mph up, she now bogs and seems asthmatic and the 50-80 mph time is slower.
Any clues? She ticks over real smooth at 600rpm or so, and I have fitted new plugs (champions), HT leads and caps.
Do I need to mod the Carb (Standard CC Qjet) or the distro (also standard HEI CC model)?
Many thanks
Mal

 

I would do a full carb rebuild.

Notice your in the UK, so I will try and make it simple parts wise.

Rebuild the carb following the correct procedures.

I heartily recommend the Rochester Quadrajet book by Doug Roe.

Best one out there period, should be able to turn it up on ebay or amazon.com easy.

Get a rebuild kit, and a new float and set it up properly. Also, any junkyards near you that might have older american cars? If there is, you can take the secondary rods and hangers from them for your carb to experement.

Your bog your describing sounds like a possible lean issue or secondary air door problem from the description.

Do some reading over on the carb board for the info your looking for. Some good stuff there to find too

later
Jeremy

 

hmmmmm - I can get a Qjet manual & rebuild kit without too much difficulty.
Just thought it odd that it's only since I changed the headers this came up. When I say it 'bogs', the symptoms I mean are a general lack of punch above 3,000 or so when pulling, and it doesn't really recover, just feels lacking and a little 'chuggy'. Is it due to the better exhaust breathing and it can't suck enough air in - i.e. would a dual-snorkel/open air filter help?
Lots of variables to think about, I guess!

 

Im guessing that with the increased flow of the headers you current calibration on the carb cant keep up and your going lean.

 

try taking your air cleaner out, and driving down the street and back, and note if the power is any better in those RPMs. I know my single snorkel intake chokes the crappenstien out of my 350, and did so on my LG4 too.

 

Find you some DR or DA rods for the secondary side as well as a F-Hanger. Those will give you a richer A/F mixture, but only when you hammer it. The rods can be found on early 80s Monte Carlo SS and Vans. The hangers can be found under the hoods of mid-80s 307 olds equiped engines.