Biggest problems with Qjet are float level, secondary air valve adjustments, and vacuum pull downs leaking. I've never had to epoxy the well plugs on one.
Quadrajets are great carburetors, unparalleled driveability....the one thing the dyno won't show. Anyone wants to know all there is to know on them, pick up Cliff Ruggles Quadrajet book, the literal Bible.
A friend had issues with his Q-jet on his Pontiac T/A.. I offered to let him borrow my Thermoquad which i newly refreshed with a carb kit, full pump travel, new jets and proper air valve adjust. Bolted right on(same bolt patterns). He was floored by how well it performed!!
joe mondello used to work miracles with quadrajets i put a bushing into the throttle shaft to stop the howl and do a few small mods and they wake right up
I've ran quadrajets for years, have one on my 76 Vette. Bigest problem with them is nothing's set right on them. Worked on one in mid 70's on a 3 month old Chevy truck for a guy I worked with. Test drove it and asked what the hell did you do to my truck? I've had it back to the dealer 3 times and it never ran that good. Told him nothing was set right on it. Never had a Thermoquad to play with cause every one I ever looked at had been on fire and were junk.
@@Sabe53 I had a Holley on my big block that had terrible flat spots so I yanked that off and threw on an old TQ I'd saved off a dump truck, purrs like a kitten ever since with perfect throttle response. They are a little weird, I make sure not to crank down hard on any carb screws and many TQ kits have the wrong rubber well seals (too thick), maybe that's how the bowls crack.
The best thing about Quadrajets are 1. The sound when the four barrels open. And most importantly 2. They will start easily and stay running on bad side hill angles and many other carbs will die easier and hard to get started.
I run 1.7/1 full roller rockers in my 350 Chevy. The cam timing stays the same but the lift goes from .486 - .512. It will pull from 1,000 in high gear, and has a Comp Cams cam in it. I did the Riggles modifications to my Quadrajet, new plug wires and now it runs like a bat out of hell. This is in a 1969 Chevy G10 van. It amazes people as to how fast without revving the motor I can leave a stop light without burning rubber or such. If you run a flat tappet cam always run DIAMOND COATED LIFTERS (DLC). The plasma coating is almost as hard as a diamond and since out of carbon is slippery. They do not wear the lifters or cam. No more flat cams and destroyed tappets as I went through 4 times until DLC lifters. You can get them through Comp Cams and Summit Racing.
With 1.7:1 rockers your .486" cam would go to .550" lift, not .512".🤷 Also for every .1:1 increase in rocker arm ratio you get 2° more duration at .050". So going from the factory ratio of 1.5:1 to 1.7:1 you increase the duration at .050" by 4°.😎👍
2° - 3° more duration per every whole number in rocker ratio is what a lot of people say but it really depends on the cam profile and the exact point of measurement in the valve events. When your cutting it close for quench, etc you'd better measure it. A 1.6 rocker might actually be a 1.65. A 1.7 could actually be 1.75 . They can actually vary. Doesn't sound too close until you hit that 7° & 10° BTDC & 7° & 10° ATDC. That's the main places you need to check. If you're not going close, don't worry about it i guess but if your trying to keep it tight and just figure it's 2° extra duration per ratio change, you won't know how close you are until your valve train crashes.
I tried several quadrajets, I actually drove out to Oshawa and had my q jet rebuilt by Donny Oakes. They have the nicest idle and they sound great but it would continually run lean up top. Nothing against them but the lack of parts support and the difficulty as justing them correctly made me decide to switch to the Holley street avenger 670. Great video!
Thanks Micheal, I like your Camaro, I had an 87 IROC 5.7 a few years ago. Pretty sure Bill or another of my carburetor guys would have the solution to that. AG
Thankyou for these video's im from the uk 🇬🇧 we dont get these kind of engine's here, Im learning lot's thanks to youtube. I will own an old American car one day!
Thanks for a great educational video guys, I'm pretty sure Austin knows as much as I do, he's been hanging around me for 30 years, as for the rocker deal, if the ramp speed was too slow the rocker would increase it basically getting it open faster, and helping blow down and scavenging, I doubt it was the actual lift.....a more modern cam like an XE series wouldn't have liked the 1.6 as much...... the stronger the initial exhaust pulse the more velocity in the exh pipe early on, that's why it helps in the early phases of overlap, I would bet one of Dave's trick 650 Holley's would have been a bit better possibly, I know they accelerate like crazy from my experience, again great video, Austin's race carb would have been better,but not streetable,nice job on the build Alan, that's a decent little powerplant!
I would have preferred a test that had used an intake manifold that was specifically designed and optimized for the quadrajet. Using a quadrajet adapter on a non quadrajet manifold I hypothesize would result in poorer performance for the quadrajet. Test the quadrajet on a quadrajet manifold and prove me wrong if you dare.
Those are some impressive torque numbers for a 355 💪🏻 Those Promaxx heads ain’t no joke! They are probably the best of the budget heads, along with the AFR Enforcers. When you can get brand new aluminum heads for around $1,000 it’s a no brainer. To correctly recondition factory heads would be way up there.
the hp gain would not show on a time slip nor the TQ for the money spent I did the same on track test made no improvments in time or mph in a dragster ,SBC. thanks for the information always.
Hey AG, Tim here, ANOTHER great Sun morn vid!!......that little SB makes GREAT hp/tq.....the cam and heads like each other!!....as the tq curve is nice......which shows VE......i didnt expect to see 420 lb ft.....and the carb exercise was SO neat to watch....(yes i'm a holley guy) but showed a Q-jet can hang.....TY sir for another enjoyable Sun morn coffee vid!!!....i ENJOYED!!
I was one of those asking about qjet comparison. I find with modern pump gas most qjets need a little more jet than stock. With most mild to moderate street builds the qjet works better for frequent use. I’ve used several qjets rebuilt by Lars grimsrud and they work flawlessly. I don’t think anyone would debate for a more aggressive build then the Holly is a more popular choice and for good reason. The bowl in the qjet isn’t big enough to provide the fuel volume for a more aggressive build.
A Quadrajet will flow 850 CFM. It's a set it and forget it carburetor. Holly's are great race carburetors. To enjoy a Holley you have to get a brand new one out of the box that nobody else has played with because a lot of times you have to figure out what the last monkey did and that can be very frustrating.
It appears that the engine was happy with everything Those Quadrajets work pretty awesome , 1 issue with the Quadrajet is they have a small fuel bowl They are pretty much equal to anything out there , they work very good on the street Thank You for the Video
Billlittle: Thanks for your response. Looks like the 1.6 is an easy & cost effective 10 HP or better gain. The cam lift on the video's 355 is almost identical to mine.
This is a great video! The quadrajet is a great carb to run on the street if you take the time to learn how to adjust them.. AG, your cam selection is great! I've been picking up on the open and close time and the relationships with CR.. this is very interesting stuff.. keep them coming!
See, I told you the 1.6:1 rockers on the exhaust would make more power. With .1:1 more rocker ratio not only does it give you slightly more lift it also increases the duration at .050" by 2°. That extra exhaust duration is going to pull slightly harder during the overlap cycle helping to fill the cylinders slightly better. It would be interesting to see if the 1.6:1 on the exhaust only makes more power? Summit offers a performance flat tappet 4/7 swap line of camshafts that work very well. The part numbers start at 1200 and IIRC go all the way up to 1208. Cutters Performance on this sight used the 1205(stage6) 4/7 swap Summit cam on a budget 350 build with Vortec heads and made just over 500 HP! Take a look at those if you get a minute, I think you'll like at least one of them? A friend asked me what parts should he get to spice up his sbc 307 and I recommend a set of the Bay of e new sbc Vortec 305 heads, a genuine imitation RPM Airgap dual plane intake and the stage 4(1203) Summit 4/7swap cam. He just got it running and so far he has went from 15.9 seconds in the QM to his best 13.9 seconds. A whole 2 second off of his QM times. I believe he has more in it too, he's still figuring out where to shift and it needs a bit of tuning as well. There might be mid to low 13s when he gets it sorted out? Or even high 12s with different gearing? Not bad for a little sbc 307. It's a low mileage engine from I think he said a 72 Chevelle that was removed for something bigger. It's in a '70 Nova now.😎👍
@@thisisyourcaptainspeaking2259 Yes, that's why they work so good on a sbc 307 with it's smaller bore size. Even though they have 1.84" intake valves, they only flow about 10 to 15 CFM less than the Vortec 350 heads. But on the exhaust side they actually flow around 10 to 15 CFM more than the 350 version. The smaller chambers of the Vortec 305 heads help raise the compression ratio from 8:1 to 9.88:1 for the 307 as well. The 350 Vortec heads have a 64cc chamber vs 58cc for the 305 version. There is room to grow with the 305 Vortec heads for him as well if he wanted to use them on a 350 he could have bigger valves installed and with a little bowl blending and chamber unshrouding it would be an easy 30 to 50 more CFM on both sides. Plus it will be easier to get the compression up with the smaller chambers if that's what one wants. If not it's just as easy to pick an inverted dome piston to get the compression down. So many piston choices now for a 350, not so much for a 307 trust me I have searched. The Stan Weiss sight has the flow numbers for the Vortec heads is what I am referencing to.😎👍
@@itseithergonnaworkoritaint7852 Also, I believe the 307 can be bored considerably, so he's got a lot of cylinder wall to work with in case he manages to wear it out somehow.
@@thisisyourcaptainspeaking2259 That is correct, they used one pattern to cast the 350 and 307 blocks. Most 307 blocks are thick enough to bore to 4.00" or more. But would be better to leave thick and use it with lots of boost. Add splayed main caps and a halo girdle and all forged internals and some block fill to the bottom of the water pump holes and you're ready for 1,000 + HP.😎👍
@@itseithergonnaworkoritaint7852 I'm going with a similar setup for my 307. Bored 0.04 over with the 305 Vortecs and an air gap intake. But I'm putting in KB165.040 283 pistons and reconditioned 400 (5.565") connecting rods with ARP bolts. I also had the block decked to 9" puts the piston 0.005" in the hole. I'm going with a Howard's CL110305-08 Retro-Fit hydraulic roller. You could use the 350 Vortecs with the KB166 pistons (w/5.565" rods) for some more CR.
Thank you for making and sharing this video!!! I would have loved to see the VE throughout the rpm range on both carbs!!! Is it accurate to say a 1.6 rocker ( vs a 1.5) will "make" the engine see the cam as having a little bit more lift and also a bit more overlap?? It seems as though using a different rocker ratio may be a way to "fine tune" the cam to what the owner is looking for?? Thanks again!!!
13:32 That carb is quite lean in the first 500 RPM of the pull. If you were to run the air turbine it would have shown 14 maybe 15 to 1 air/fuel with the brake specifics. This could be a secondary metering rod shape and/or air door spring adjustment issue, however it's leaning towards rich at the end of the pull. Edit 15:01 The air door is pretty much wide open even at the start of the pull. I didn't see the adapter, but given it's height, the transition for the secondaries is going to be very abrupt. Doing this test on a spreadbore capable intake that you can use just the tin adapter plate for the square bore would have been a more accurate comparison, and I suspect the results would have been somewhat closer.
Very good numbers for the displacement. Holley definitely has it's advantages, but on a build like this on the street it's hard to beat the Qjet. I really like the Qjet and bought many years ago a bushing kit to keep the throttle blades from hanging up and control vacuum leaks. They are a great,.......how the heck, carburetor.
Stock for stock, i don't think there is a carburetor that will beat a Quadrajet off road. That center float design is damn good off camber. I would imagine it's pretty good on the track too. BTW, i am a Mopar guy but enjoy all brands.
would be a neat segment doing a test with a few people trying their guess at setting mixture by ear and checking against the O2 gauge. and how accurate "using a vacuum gauge " will get you .
It's clear the lift is higher with the 1.6 rockers, but what about the duration? The total duration would not change but the .050 lift would because of the faster lift off the seat. Question is, by how much? I've heard 4 degrees and even more with higher ratio. Do you have any ideas? Thanks.
I have a mildly built 383 small block with stock but slightly ported heads and a 262 Voodoo cam. When shopping for roller rockers, sticking with the 1.5 ratio was recommended to not chance pulling out the pressed in studs I unfortunately retained. Has that been a problem with a 1.6 upgrade? I was recommended to keep
To help the viewers see the difference why not overlay the graphs? I never look at average numbers but always overlay 1 run from the next, as a visual representation eliminates odd peaks and dips and shows trends much better. It also shows how timing can positively affect peak HP but negatively affect torque early in the pull, something that needs to be considered with the intended application.
Good point, it definitely makes a difference but i don't know if it is that much. Maybe i should get an electric pump?. Thanks for your comment Billy. AG
I like quite exhaust but I sure did love the sound of a Chevy truck with the air cleaner flipped, my dad wasn't to impressed with that cheap performance hack.
Great results, thats going to be an excellent strong street engine. What Intake centerline did you end up installing that 1105 camshaft on. What intake vacuum did it make at idle? Cheers 👍
Thanks Craig, i installed the cam IVCL at 109 degrees ATDC. Idle vacuum on my test stand was 15-19" depending on idle speed. It was a bit lower on the dyno, not sure why? The Summit cam has very soft ramps. AG
@@goldsgarage8236 great intake vacuum! Maybe a little less on the dyno due to the small load just being hooked to the dyno. I always prefer soft ramp lobes when doing flat tappet stuff, they last and work great. Get greedy and flat tappet cam bite!
Mike's Carburetor Parts online has a variety of secondary metering rods but call first to be positive. You won't be able to get every one GM made without a lot of work looking and spending.
why would you go with the 650 did the engine only use 700 CFM or less? what we are actual airflow numbers?? from my experience the average 350 with a good cam. Decent heads intake runs just fine on a 650 but with the 650 the vacuum increases way too high to be comfortable with that and it won’t make peak horsepower or torque I think you’re much better off with the 750 and depending on the AFR, you’re gonna have to do some jetting and air bleed work and you’re most definitely gonna want a four corner circuit carburetor. A stock 350 runs absolutely perfect or as perfect as a carburetor can be on AF hours with a Holley 650 Dufy double pumper with a 68 primary jets and a 72 jets in the secondary. in a 7.5 on the power valve, and I prefer to use the red cam piece for the 30cc Excelerator pump.
Good idea. actually I have an Edelbrock shop carburetor that i use for start ups on my test stand. I will bring it to the dyno next time. I also have 2 Carter AFB carbs that i will be using on a dual quad 409 build. AG
Holley vs Q-Jet doesn't really matter, that matters is what the engine wants/needs. then engine can only suck a given amount of air and fuel through the intake track over the period of time the intake opens until the time it closes. that is what really matters. as only and the carburetor can provide all those needs, then the horse power will remail similar. so Holley vs Q-het at this point it boils down to which one mixes the air and fuel better. so which one would i choose? if it were a street driven car where it gets me from point a to point b and a daily basis, then its Q-Jet all day long. once you get a q-jet dialed in you never have to mess with them. same goes if i took it to the track one or twice a year. Q-Jet all the way. now if it were a dedicated track car and spent all its life at the track, then i high end Holley like an XP or a Holley clone would be my choice. it is easier to fine tune air bleeds and primary jets on a Holley than on a Q-get. have to take the top of to change jets or primary rods is a PITA. also having to use adapters probably hut the Q-jet, if intake was designed for a q-jet then i would have helped the Q-Jet more. example the non RPM version of the Edelbrock Performer with the Q-Jet flange may have made more power and torque the Q-Jet but would have hurt the Holley. I would have loved to have seen this test with an old school Holley 4175 vacuumed secondary spread Bore carb vs the Q-Jet. on a q-jet style manifold.
Thanks for the comment. The Holley gave up good BSFC numbers with the 68 jets and 6.5PV in the front and 79 without PV in the back so we did not make any changes other than timing. AG
A flat tappet cam? I don’t know why an engine builder as educated as you would even chance it with a flat tappet. How much extra $$ to go hydraulic roller and have no worries? Cheap insurance in my opinion, but to each his own.
Thanks for the comment. About 25 or so flat tappet installs in the last five years with zero failures. I have videos on this topic on my channel. A roller can add $1,000-2,000 to the cost of a build. AG
