What carb are you Big Block boys running on your 500-600 h.p. street engine?

 

Demon 850 DP annualar discharge

 

500 or 600? There’s a difference.

 

More information needed. Street engine can mean different things to different people.

 

Mark is correct on that. I'm at 500. 600 will take more.

 

I'm at 543 h.p. 1970 Cutlass, 4030 lbs with driver, hydraulic roller, A/C, idle with16inches of vacuum with power brakes.

 

Not knowing about gearing or transmission but knowing the car is 4000+ lbs. If it's a true street car and if you are more concerned about drivability over absolute HP. I would recommend for a double pumper a traditional 750. If your willing to go vacuum secondary you can step up to an 850. The reason is on the double pumper with the smaller venturi you will have better low speed part throttle torque response even when tipping into the secondary. Also at higher rpm cruise you will start to draw from the main circuit sooner once again giving better fuel atomization that makes better power. Moving to a vacuum secondary leaves the secondaries closed when not needed. This allows for a stronger booster signal to the primaries. This again makes better torque.

 

Sorry.. left out that info. 3.90 gear with a 200r4. Thanks for all the advice.

 

Hmmmm yes and no. QF mech secondary carbs have three stages of secondary engagement, you can have them come in fairly late if you want to.
And atomization will also be determined by the ability of the metering blocks to do their job. Adjustable air bleeds and power valve circuits will help this too.
On most of my over 500hp builds I use the QF SS850, they still pull over an inch of vacuum at WOT. But, great carb and very tunable. For 600 or so HP however I’d be inclined to go to a true 950.

 

And once again you missed the target. Yes the larger carburetor can make more peek HP. But your dyno is not 4000+ lbs with AC driving around at part throttle running of the T slots going to get ice cream. Pluss with that much idle vacuum on a 1.75 tb your throttle blades will be closed passed the t slots. That leads to poor fuel management at low speed. If you switch to a 1.688 tb you can open the throttle blades further and have better low speed fuel management. This goes back to don't pick your carburetor strictly by CFM, its by application.

 

This was interesting when I called Holley. Any comments?

 

The 950 HP only flows a bit over 820. It's a good carburetor but probably not the best choice for your combo. Out of the box it's suited for a more radical motor. Would most likely run way rich at idle part throttle out of the box. They also can run rich at WOT due to a very active booster venturi set up. If you spend the time it's an excellent carburetor. I currently run one on my car. It's just as fast as the 850 Warrior and 60 foots almost as fast as the 750 Brawler. I can't comment on the other 950 as I have no experience with that one.

 

You might want to look at this. I made over 530/550 on a brand X motor with it. Very street friendly.
https://www.holley.com/products/fuel...arts/SS-780-VS

 

That’s pretty much all I use, Quick Fuels.
Just that in my experience, the larger carbs seem to do just fine when adjusted properly.
Thanks.

 

Are you referring to the "Classic " or the "Street " 950 that flows 820 cfm.

 

List 80496. I think they call it classic now. It's 1.375 venturi (same as 750) with 1.75 throttle. The booster is a step down with back cut thin profile.

 

Good information.. Thank you. Thats the opposite that I have read. I read the Street version was the one that flowed 830ish cfm. Not the Classic.

 

I realized I used the wrong terminology, long day yesterday. I should have wrote Down leg, double step. Some of the flow numbers from all the brands are off. The 850 warrior is more like the old 1000 HP. I did not know this untill I received it. From what I have heard the dry flow is somewhere between 920 to 960. I have not confirmed this. I do know it took a massive amount of jet (86/94) to get it to run correct on my 437. I didn't feel comfortable with it so I put the more restrictive 950 back on. Same performance, more consistent with way smaller jet (77/85) and squirter. What alot of people think is if there is vacuum at WOT it means the carburetor won't flow the required air. It's only partially true. Sometimes the restriction allows the carburetor to work better and that can compensate with a better power curve.

 

Wow! Those a deadly consistent runs!!! Congrats. Seems you have your ride dialed in. The reason I started this thread was because I currently have a Street 950hp on the car And I saw a Classic for sale for a descent price. I heard that there was a difference in cfms between the two. Like I said, with the information that I was told, the street version wasn't a " true" 950. Like most of us.. I am always looking for improvement. I do have the street carb dialed in pretty good. The wideband says 14.3 at idle, cruising at 14.8 and 12.9 WOT. Im pretty confident i get the car into the high 11's. My PB now is 12.02 with some traction issues. Do you guys think its a waste of time and money to try the other carb?

 

586 hp with a 800 cfm Quadrajet (level 2), 590 hp with a modified 850 cfm Thermoquad (primary bowl venturi removed), and 595 hp with a Holley 950 HP Ultra (0-80805, with 1.6" venturi).

Dyno test results, Qjet vs Tquad Vs 950 Holley

 

Thanks. Still some funny stuff going on on the first half but I'm thinking it's more in the launch procedure and suspension. In my opinion you should hit your goals with the HP you stated. Can you post a time slip? If I were you leave the carburetor alone and work on your traction first. No good to try and tune the motor for ET if the car is not working, you will be chasing your tail.

 

#236. Couldn't get to the track more recently. Anyways, agreed. Need to work on my 60' . But i was just curious about the carb. Thanks again for everyone's input.

 

Great comparison.. Nice curves 👌

 

Very cool dyno comparison. Interesting the Holley leads top to bottom, the Thermoquad only beats the Qjet past 5000 rpm. Interesting.

 

X2 for the quickFuel. I know Holley bought them but I still think they’re better carbs.

And btw…I’ve called their tech line and have gotten geniuses…and I’ve also called and gotten idiots.
-peter

 

I must have called on idiot day!

 

I agree with your thought about the 60's. Do you think it's traction or tune up?

FYI the picture below shows the difference between the (left) 950HP "classic" and an (right) 850 Warrior. This 850 has the same high flow down leg double step boosters as the 950 , the same set up as the discontinued 1000HP with down leg.