I'm so excited to see the arguments
So here it goes... My carb guy (an 85 year old master gm tech grad) convinced me to let him take my q-jet 4 barrel 650 cfm and turn it in to a 2 barrel by not allowing the two big barrels open anymore. He showed me a chart that shows how much cfm's my 350 needs at all rpm's.....and not until the very highest of rpm's does it actually need the full 650 cfm's. He said the two small barrels alone carry you all the way from 0 to 90 of nothing but raw power!?!?!
We will see what happens! I'm on the fence.
Oh and he explained the top end performance to but he lost me... But he said that's still there as well it just evens out after 90 mph.

 

Then these pics will blow your mind, they made some like that, kinda.

[Thats no photo chop]

 

Wow! So is he right?

 

Maybe, kinda, sorta

I can say since I put a built TH350 in my V8 car with a kit n a higher stall, I don't open all 4 as often. I don't need to stomp it a after a turn, Just flash the TC and smile. Getting the power to the ground better has meant less throttle input is needed for the same ammount of fun just toolin around.

But id never get ride of the big gulp back two.

 

I guess I'm gonna try it out and then try out a nice 4 barrel and see the diff for my self... I'm really curious to know how it will work!
He said if I don't like it he'll take it on a trade for a junk (his words) holly or edelbrock he's got on the shelf.

 

what did gm put these on? what years? I've never seen one before

 

no clue, or forgot

 

Gumby, what pics?

K88-79, any q-jet can be made into a 2-bbl without spending a dime. They have a lock-out for the secondary throttle blade shaft that is engaged when the choke is not fully open. All you have to do is wire that lock so that it is always engaged.

 

My answer is no.

First off, that chart about how much CFM an engine needs has been proven time and time again to be way off. Doesn't it assume 100% VE too?

Secondly, a Qjet is 750 or 800 CFM. There are no 650 Qjets unless you include the fact that some have a tang which limits how far the air valve opens ( but they're still either 750 or 800 cfm castings )-*.

Thirdly, a Qjet only flows what your engine needs up to it's full CFM rating. How on Earth will rendering the secondary side inoperable improve performance? If your engine doesn't need the extra flow of the secondaries, it just won't open them.

Fourth, why did GM put 4 barrels on small CID engines if it didn't have any effect? You think GM would spend more money than it needed?

Lastly, there's a video on youtube that shows a Qjet on a smogger 350 Chevy truck in action while being driven at WOT ( camera mounted above the carb ). It shows the secondaries opening up just fine. How would your friend explain this?

Me thinks your friend is going a bit senile. Does he even know what CFM the primaries flow at?

 

Just so were clear...I'm not on either side... Because I simply no nothing about motors or carbs. So with that said, he is of sound mind and thinks as clearly and quickly as anybody else around.... He is very smart and remember he's a carburetor master(if that's what you call em) who was trained in the beginning of his career by GM. He's been all over the united states to different schools teaching people about carbs...and has all the pic's and news paper article's to prove what he's achieved.......so to say does he even know what this or that means is just silly! This guy really knows carbs...expecialy q-jets! But like I said, is he right about it performing better.. Idk? He says when you floor the gas (even a q-jet) all 4 barrels open and it then has to try to digest all the extra air and catch up versus only getting what it needs. Yes it is a 650! He has a tool you stick in there and measures this...and sure enough it's a 650. Remember he specializes in q-jets.

 

I had to go find that video lol http://www.youtube.com/watch?v=nRK9n4NQvOA#t=1m2s

 

turn on images dude

They are [img] code links

not attachments

 

I looked at the video... I couldn't tell if it did or not? Anybody else?

 

Which is it? Does he REALLY know carbs and what he says should be taken without question OR is he 'right' about it performing better? Your logic is off. You can't support part of what he says based on his experience and knowledge ('Yes it is a 650!/...digest all that air/etc.) yet question the other part (about it performing better). You've already argued both sides of the issue without any help from us.

Aside from that, I suspect you've misunderstood some of what he's told you...your interpretation of some of these 'facts' doesn't agree with the actual workings of a q-jet.

 

How'd you miss those big suckers opening at 1:05 in the video?

 

My logic is off??? I'm arguing the fact that he's not an idiot or just some guy. So Which is it? I don't know? I'm confused.. I've never heard of such a thing. That's why there's sites like thirdgen... For people like me who didn't come out of there mother working on a sbc's

 

On the video... I thought we were looking inside or something for the two big barrels to open? See I know nothing!lol

 

Slow down and think about it. I can see how you could be confused.

You asked if his performance claims were right than countered another post with statements as to his expertise on carbs and q-jets. My point is you can't question one particular claim he's made in the area of q-jets yet use his credentials to back all the others. If he were 'universally' correct on his knowledge of q-jets he couldn't be wrong about a 'specific' fact.

Irregardless (and I digress). Your car will run fine with the secondaries locked out. No need to do anything other than tie the lock out lever back (it's the lever going from the choke pulloff (vac can) on the pass side to the secondary air horn lever (across the top/behind the choke cover). Try it out and see. You'll lose a good bit of top end power but with the stock 305, maybe not so much. You may force yourself to accept slightly better mileage when you can't open it up all the way.

Please don't permanently modify anything or stick another carb on there in place of the stock computer controlled one. Your computer relies on the carb's feedback to control ignition timing, etc.

I suspect, from some of your (his) statements, he's actually offering assistance in adjusting the air valve tension and choke pull off for improved performance.

 

Hmmm, nothing turned off. Might be blocked by my ISP, though.

 

Could be the extra bits of the url
[I pleaded the 5th]

http://thirdgenchat.org/four%20two%20barrel%20qjet.jpg

http://thirdgenchat.org/four%20two%2...20qjet%201.jpg

 

I'd find a new carb guy. Why did my motor pickup .3 going from a 750cfm to a 950cfm if I didn't "need" the air flow. At wot you could have a 2000 cfm throttle body on there and it would perform fine, you want the least restrictive flow at WOT that can still meter fuel properly. I wouldn't go back to that guy again and find someone who isn't an idiot

Other than a circle track car that is restricted to a 2 barrel there is NO REASON to dump them.

 

Sorry, but there are no 650 cfm Qjets. What exactly did he measure and what did he use?

This guy reminds me of some of the 'oldtimers' I have dealt with in the past. The kind of guys who have forgotten more than you'll ever know but at the same time has some of their facts completely wrong.

It's like the old GM certified mechanic from the 60's who tells you things like 'Yeah those 442 cubic inch engines were great in those old Oldsmobiles'. You try to correct him without sounding like a know-it-all, but in the end they swear they're right, so you just nod and say 'OK, whatever you say'.

A properly tuned Qjet ( on an engine that needs to breath ), will always be faster than if you took that same carb and locked out the secondaries. Just like $10 will always be worth more than $5.

 

You could've doubled your improvement with a 650 cfm Q-jet modded into a 300 cfm Bi-jet! Just messing with ya K88-79.

 

Lmao... Yea the thing that kept going through my mind was... really?? All these car guys and engine builders and this fact eluded all of them?? Your the only one who ever figured this out? But like you said you can't argue with an old timer! Lol
Thanks guys it was fun.

 

I have to laugh, there's always someone out there trying to re-invent the wheel! Newsflash, the wheel works, and has been refined , downsizing it is going in the wrong direction...

 

Any suggestion's on a carb for my setup?
Sbc 350 standard bore
Flat top pistons
Edelbrock performer intake...if there's more than one type of performer this one is a high rise dual plain... I'm pretty sure.
Comp cam 281 advertised dur and 484 lift
291 stock camel hump heads
Headers.. Not sure what kind
Dual exhaust not true.
I think that's about it.. Not sure on the rear end gears. And I haven't decided on a torque converter yet.

 

[ the main body casting was only made in 750 and 800 CMF ]

here is one link, just search qjet on google

http://home.earthlink.net/~quadrajet...ow_ratings.htm

 

Yes. The stock qjet.

OUCH.

 

Those heads are gonna hurt my performance?

 

They make a great door stop, there are better options out there for not much money.

 

there are betr opt out there but i hvn seen ant tht wasnt ridiculously expensive (3917291 casting camel hump small block chevy heads. 2.02in intake valves and 1.6in) take this into consideration GM Fastburn Heads 2.00" Intake/1.55" Exhaust ( bare ) will cost round 5-6 hundred each but u need 2 so double that... myself i would stic with the humps u got a set of big heads there PLUS they also came on the Duntov 327 built in the 60s producing over 375 hp and that my friends was b4 the fuel crisis of the 70s where they decided to stop making all out muscle cars and make economy cars myself i would keep the heads but hve a shop clean n install new parts then slap this in the block its the same cam that was in the 65 corvette with the Duntov 327 anyone who does not see this as tru look up the info ....
Nostalgia Plus™, N+30-30H
GM 30-30 Cam w/ Increased Power
Part Number: 12-672-4

 

I remember in the 70's if you had a 30/30 cam you were somebody!

 

Cool. An old thread raised from the dead by texting from a cell phone. Thumbs up to you nightstalker!

 

Thanks I was about to search for it!