How much hp can a quadrajet support?

[WESTOF7]

I want to build a stock appearing(to the average person) n/a 400 sbc based off a dart block with ported afr heads I'm going for as much power I can get out of it and still stay streetable. I'd really like to keep a quadrajet on it and an hei maybe with an aftermarket box. The cars a 86 z28 with full suspension coilovers completely stripped r spec bfgs built t56 and a ford 9 inch baer 6 pistons all around. Its built more for open road track and autocross but will be making alot of trips down the 1/4. Can a quadrajet be made to work? I know the guys in s/s run pretty fast with these but havent been able to find any information on their setups. 

[omaha]

   That is a very good question and one that I have not heard yet!  (at least not that I can remember).
I will take a guess. If you could get a true 800 cfm, at 400 cubic inches I would guess 600 HP would be feasible.
Would probably require alot of rpms (7000?) aluminum rods, ultra light pistons/pins / serious crankshaft.
That 400 rod stroke ratio is not the best,  but of you have a tall block....maybe 600+ (just a guess here).
I am not knowledgable of the Q-jets  functioning at high rpm or what modifications would be needed. I know those ss racers can be pretty secretive about stuff. (and sneaky!)

[Cliff Ruggles]

One of our customers uses a later model large cfm unit at 750hp.  His car runs high 9's in the 1/4 mile at 136mph.  He has at his disposal a Quick Fuel 1000cfm Holley, it runs no faster anyplace than the q-jet.

We have a Super Stock customer running mid-9's with a small block Chevy using a smaller "750" cfm unit, built from an early 1970's Chevy divorced choke truck carb.

My own engine uses a 1977 Pontiac carb, it makes close to 600hp, and powers my daily driven 73 Ventura to low 11's at over 120mph.....Cliff

[WESTOF7]

guess I was on to something when I started collecting these after all and all my friends thought I was crazy  . Do you do any additional work to the higher hp cars that you wouldnt do in a normal performance rebuild? Like porting anything like that? Any problems from running the fuel bowl dry if I held it to the floor?

[omaha]

Yes, I think "keeping the fuel bowl full" is a majpr factor for a HP Q-jet application. Just concentrate on fuel delivery. Design a system from the start.
       There are some "porting" things that can be done. Just obvious minor stuff like casting flash smoothing, throttle shaft trimming (careful here...), matching up the top/main/base etc. Another mod involves removing the  outer ring (in the primary bore). Not sure if this mod is right for everyone. Maybe on a "race only" deal. 
    I always wondered about removing the  "bump" in the large bore primaries. Have never tried it but maybe will experiment with that............GOOD LUCK!!

[Toronado]

If you want a daily driver (not race) stay Q-jet!

(BUT) I was thinking there has to be a limit.
Theres no way a Q-jet could work on a 572 BB
blown or turbo, it would run out of fuel just idling, right?

So is there a limit with the Q-jet, Im sure there is a limit.
I love the Q-jet but just watching many drag races they
are not the best drag race carb. I have heard if its all
out competition. just look at the design differences between a race
carb and a Q-jet the race carb flows better if set up
with the correct engine combination (not stock)
for smaller combo's ya the Q-jet is one of the best hands down but to a certain point.

There are larger carbs for good reason they are
definite situation were more air and fuel are required
. So I figure over 800hp or torque you will need
bigger carb. than Q-jet makes, because GPH fuel requirements.

I would bye this one for my imaginary 572 BB block build,
C & S Aerosol 1000CFM Billet Dominator Alky Carburetor (incredible design)
http://compare.ebay.com/like/150560900686?ltyp=AllFixedPriceItemTypes&var=sbar&rvr_id=218160508287&crlp=1_263602_304662&UA=WXO%3F&GUID=c983571d1250a06459b0f160ffdb8a2d&itemid=150560900686&ff4=263602_304662

[Cliff Ruggles]

I love the Q-jet but just watching many drag races they
are not the best drag race carb.

Actually, they are an EXCELLENT full race carb. 

My current unit has been in service for over 15 years on 4 different engines.  455.4hp, 494hp, 514hp, and currently over 550hp.

I've made over 1200 documented track runs with this carb, never once stumbled, hesitated, bogged or gave any troubles anyplace.

It's been good enough to win the Pontiac Nationals 3 times, the APEX Musclecar/Import Challenge, and quite a few finals at local bracket races and fast street car events, etc.

The best thing about using a Q-jet for racing, is that tuning changes take seconds, and all external, carb doesn't have to come apart.  The adjustable airdoor makes for perfect lauches with any track conditions.

Once you get around the fuel delivery deal, the rest is easy.

We have carbs clear up to 897cfm, which can easily support engines over 750hp and cars running into the 9's.  As much success as we have with them, there is still some 1970's mentality still lingering.  The old "get rid of the Q-junk and get a Holley" is regurgitated once in a while, but NEVER when our car is sitting in the staging lanes in the final rounds at a big race!.......Cliff

[Toronado]

What about the differences between a race carb and a street carb (rather bad or good),
the Q-jet is great and I amazed to hear that they can be customized to 890 cfm!.

 I sure do agree the Q-jet can work great as a race carb and often beats
other brands on the track, I have seen the reports. It just seems to me
that the race carb does have improvements for all out performance, like
deleted choke, larger fuel bowl, better air flow.

But a race carb does have less parts & a far
more simple design, and is not built with idle quality in mind.
A Q-jet does have a lot going on as far as parts and
different tunning points for good idle and power, and can be tweaked
in many ways way beyond a race carb so you can idle real smooth.

Also a race carbs design focus is more on getting the most air and fuel
as fast as possible to the hungry race engines that have wild cams and lopy idles
& dont use parts for low rpm operation like a standard street carb with choke towers.

The Q-jet is very powerful I have experienced its performance in my cars, on my 1972 caprice 454, my 1981 corvette 350, & my 1970 toronado 455. i just like the race carbs because of there innovation and
track results not that there the best, but they have there place.

[Cliff Ruggles]

One of our customers has a dedicated 9.90 race car.  He has at his disposal a 1000cfm Quick Fuel Holley, and one of our 897cfm q-jets.

He claims there is no more than .02 seconds between them at any track in any weather.

He uses and prefers the Q-jet because the car idles better, and is easier to "stage" (footbraked car).

I doubt if too many folks reading these threads have 730hp engines in their cars and run into the 9's, "race" car or "street" car.

The biggest downside to using a q-jet for racing is NOT the small float bowl. 

Doesn't matter how big the bowl is.  End hung float bowls are not as good as a center bowl with the jets in the bottom of it.

The q-jet only has ONE needle/seat assembly to feed the HP of the engine.  Fuel delivery in really high HP applications must be up to par to get them to work.

One of our Super Stock customers has an early Camaro powered by a 355 SBC.  He used two 250gph pumps and 10AN lines, with a full bypass system with his q-jet.  He runs mid 9's at over 150mph, and it's a smaller "750" cfm unit!......Cliff

[Toronado]

Great read Cliff those fuel pumps that guy is using
is some serious gas flow way more than I thought
a Q-jet could handle, talk about running like fuel injection.
I figured the likability of the Q-jet is due to
great idle and massive power potential which
is the best of both. I bet the inventors are proud
to see they still have a following and hold up compared
to new designs.

[Cliff Ruggles]

Keep in mind here that the Q-jet got an extremely BAD reputation from the very early models 65-67 that used the plunger-bypass fuel inlet deal.  What  POS.  Didn't work back then, and still HOPELESS today.

In 1967 they started using a threaded in needle/seat set-up, but stuck with the early hinge pin location and HUGE float.  These carbs are better than the first design, but still far inferior to the later set-ups.

By 1969 they figured out the float/fulcrum deal used a much better set-up, which could handle higher fuel pressures with a much smaller float.

By 1971, ever tightening emission standards had most q-jets so lean at idle, they wouldn't work on most applications beyond the pathetically underpowered small cammed low compression engines they were delivered on.

The problem is, or was, that the early units gave them such a bad reputation, folks just kept dumping Q-jets and buying Holley's, Carter AFB's, and Edelbrock AFB clones.

The truth here is, that once you get one dialed in for what you are doing, you can make as just as much power as anything else, and get a LOT better fuel economy for "normal" driving.

A few years ago, while we were dynoing one of my engines for the High Performance Pontiac and Popular Hot Roddings "Engine Masters" edition, the representative from the magazine asked us to do some carburetor comparisons.  He said that he could get more coverage with additional articles on carburetor comparisons, etc.  Available at the dyno shop were several well prepared Holley HP and Demon carbs.

I really didn't want to do the testing, figuring I'd get outran, just to see it in print a few months later, and have to hear about it on every website that supports this hobby for the next 15 to 20 years.

It sort of went like this.  After all the testing was done, the dyno shop staff grabbed up a big fancy HP series Holley and said, "now lets see how much power this engine can really make"!

Well, it LOST right at 2HP and 3ft lbs torque.

We installed the engine back in my car a few days later, and tested the carbs back to back at the dragstrip.

The Q-jet was exactly .02 seconds quicker, and .30mph faster than the Holley.

The magazine representative did NOT follow up with any additional articles about this testing.....wonder why?.......Cliff

[Paul]

Thats very incredible. If they would have posted the results I would guess it could have turned the tables for Holley and Quadrajets!