What size jets should I put in a Q-jet im rebuilding? Going on a mildly built 350. Tired of foolin with my edelbrock 750.
Good to see you're going back to QJet:TU: They can really scream if you can tune it right. Try a search on this site on quadrajet, qjet, jetting, anything you can think of to find what you need. There are many threads talking about this very subject.
I would probably go with the 74's for the primaries....should deleiver enough fuel for pretty much any SBB build up. Mike
carb jetting I've got a small chart that shows various quadrajet rod/jet combos that was printed in the March/April 1995 GS X-tra. Changing jet sizes gives you more WOT fuel flow, while changing rods helps meter the part throttle fuel flow. I've run everything from .69 to .73 jets on my '69 350. For all around driving I've settled on .70 jets and a 42 rod. I've got another carb set up with .73 jets and 45 rods that I use at the track. Part time throttle fuel flow stays the same at .711 and the WOT fuel flow increases from 1.118 to 1.194. My 350 is .030 over, forged 10:1s, Lunati 220-230 cam, TA headers, stock intake and quadrajet, and mildy ported stock heads. I have a muffler shop (no mandrel bends) 2 1/2" full exhaust with h-pipe and turbo mufflers. It's run a best of 14.15 @ 96 with a 3.23 gear and P215-70-14 radials. Ken McMillan '69 GS California '69 GS 400 convertible (under resto)
What about a stock 401 Nailhead with stock exhaust manifolds and a free flowing dual exhaust? I've currently only modified the secondary rods and hangers with AX rods and a B hanger (large difference in WOT). I used to run a 1 inch spacer but removed it and found a bit more low and midrange throttle response. No adapters as I'm using a 66 Q-Jet intake manifold so the carb sits on the original runners. I was told not to touch the primary side in either the jets or the rods but as many of you know I can never leave well enough alone .
Time to tweak the primary side of that Q-Jet Bill --- I'm surprised you haven't futzed with the primary side of that quadrajet yet. I thought I got this link from one of YOUR posts about 6-9 months ago, maybe I'm wrong. Much good info here, and this tuning procedure makes a lot sense to me; you're running on the primaries most of the time (no matter how you're driving :Brow: ). Q-Jet Tuning Please have a go at that carby and let us know the results you get. :TU:
You're right Kevin, it is one of my old links. I haven't read it for a while and will have a go at some of the suggestions it recommends. I like this part as it explains what I (and probably many others) didn't know... Great stuff. Thanks for reminding me. I think I was afraid to pull the top off and wanted to adjust the secondaries because they are simple to adjust.
It also matters which carb you are jetting, 750 or 800. The 800's had bigger primary venturi and were jetted richer from the factory.
I've read that article, and I have to say I don't agree with him about how much the secondaries actually open, especially on a healthy 350+ cu in motor. Other than that it is pretty good.
What would you say Ron? They open more or they open less? I'd love to set my camera up inside the engine bay (probably impossible) and actually watch to see how much they open. Not to mention it would make awsome footage.
The hood and air cleaner would need to be removed...not an impossible feat...but a pain in the butt to work out. I'd like to see footage like that.
I actually think they open slightly more. I can hear the secondaries on two of my cars start to open b/t 2000 and 2500, and they positively howl at high rpm. The corvette in particular sounds like it wants to eat the hood... Judging by the performance on my 84 Camaro with the secondaries disconnected, I noticed no change in power up to 2000 rpm, a slight change up to 3000, a noticeable change up to 4000 rpm, and a the car felt DOG slow after that (I start to shift at 6k normally). I couldn't tell you exactly how far it opens, but based on the amount of CFM a 350 cu in motor wants at 6000+ rpm, i'd say they are mostly open by 5000 rpm or so.
footage... Ya know... I maybe able to do this... my dads new digital camera is pretty small and takes quite a bit of video. though how would i light the engine bay? (12v christmas lights??) hmm.... i'll see what I can do. hopefully it has a macro setting.... Nate
You wouldn't need christmas lights if the hood was off...the light from outdoors should be enough to catch the butterflies opening.
yea..... yea... but who wants to pull a beautiful hood off of the car? maybe if i have to remove my fender again i'l pull the rest of it out and do it. (i think there is enough clearance under the hood to close the hood on it.) I'm also not sure how the law would like seeing a car cruzin around without a hood and a tripod hangin out of it. (hmm.. speaking of witch.. my dads camera tripod can mount the camera upside down... hmm....... maybe I will have to do it.... though i need to get my 4bbl on first just not as cool with a 2bbl nate
Yeah and the 2bbl doesnt have secondary butterflies to film opening up. You planning on putting the 4bbl on soon??:Brow:
yep yep.. i found a guy on here who had a 70 4bbl for a buick I plan on rebuilding the carb this week while im off for school. I still need to find an intake manifold but i have a source on one in western IL but im going to check my local junkyards to see what they have on my way home there are 2 along I-94. heck I'm only looking for the boat anchor one anyway so nobody wants them. though it still needs new exaust (only have single on it now)and i think the cam is shot... but hey.. Nate
I installed a new set of 9mm spiral core leads today (got a noticeably difference as well) and thought "why not take a video while I'm at it". I warmed her up and gave her a good 'ol workout. Took three films. One from the rear, one showing the Q-Jet secondaries opening (great sound ) and one from inside showing the tach. The movies are quite large and I'm in the process of compressing them but couldn't resist taking a snap of the tach while I was at it.
