David DeCan

Carb Question for my mild .060 455 build. Edelbrock 2151 Performer Intake, .500 lift cam to be chosen. 3.23 posi, TH400, Stock G heads to be changed to Edelbrock Aluminum Performer box stock heads in future

Can someone enlighten us on the distinction between down leg boosters versus annular boosters on a Holley Carb. Looking at 950 HP Holley.

Thanks.

cutlassefi

Down leg boosters are just that, angle down word. They typically effect throttle response etc. Your best bet would be to buy a Quick Fuel 850. Either the black diamond or the super Street series.

wr1970

X2 for your combo.

David DeCan

Thank you for your input guys. Please explain why you are partial to the Quick Fuel 850 Black Diamond or Super Street? I keep hearing about the Quick Fuel Carbs...

On the surface they look like dressed up Holleys. No?

wr1970

I just think cfm for your combo is my opinion and i think quick fuel is a good carb. Hell i could be all wrong. You asked and this is my opinion. Good luck with what ever you choose.

cutlassefi

No, QF's have replaceable air bleeds, both high and low speed, replaceable power valve circuits, three different rates in which to operate the secondaries and so on. They're not your basic Holley.

EightballZ

what would be the difference between SS and diamond Q-series? just choke and vac secondaries?

cutlassefi

Carbs are the same except for the black coating on the Black Diamond series.

EightballZ

got ya. but is there a difference between SS and Q series? (except choke)

lets say BD-850 and BDQ-850...looks like they differ in jetting

David DeCan

I know I am being redundant Mark, so thanks for your patience.

For my stop light to stop light, freeway cruiser 455 convertible, 450 TQ, you would buy the 850 Super Street Quick Fuel--out of the box carb, over an out of the box Holley 950 HP?

Let me add to the equation a bit--I am a lousy carb tuner. I really need to bolt it on, set the idle, max mixture screws, and have a carb that won't bog like i just threw a can of carb cleaner down the throat when I light em up.

Maybe I am asking too much. If the Quick Fuel Super Street 850 gets me there easier, I am in. Also...

I need a cam, lifters, timing gears too. We talked about this before. Hydraulic, flat tappet. Iron G heads. Stock. Rebuilt. Springs closed installed height 110lbs@1.720 inches. Open 280 lbs @1.250 inches. Coil bind at 1.145 inches. Hooker 3202's, Edel 2151, TH400, Posi 3.23's. Credit card ready...

And I need a distributor. Don't really want to run an MSD box. I have an old Olds HEI I was going to have upgraded. What's the ticket here?

Again, thanks for your help again.

cutlassefi

QF SS would be my first choice for sure.
The regular HEI is fine, just change the module to a better one.
Just let me know when you're ready for the cam etc.

Firewalker

How about the triple stack booster on the Street Demon 625 or 750?? One of the simplest carbs around and cheapest.

madmax442

This is my Black Diamond QF 950 that Mark installed on my build!

olds 307 and 403

I think they need a 800 or 850 cfm for these larger motors. The 750 cfm might be borderline from what 455+ Olds motors seem to want. Otherwise, there is a ton of good feedback on these. I must resist the urge of throwing dual 625's Street Demon on an Offy intake.

madmax442

To be honest I think 850 is the minimum these need! These 455s love big carbs!

Firewalker

I disagree big time. These carbs have produced on Dynos more power than most 455s will ever make. Then you have the Qjets,, with only 750-800 rating going down into the 10s in class racing. Or the Thermoquads rated similarly. Then I have seen a 350 Omega low 12s, with a 2 barrel at over 3000 feet altitude, in the 70s.

Now, if you factor in also the fact this is for street with a mild cam, without trick heads and not all out race....

cutlassefi

An 850 on a 500hp big block will pull about 1.5" of vacuum at peak wot. That's not too big.
Just sayin'.

madmax442

Isn't that depending on how good things are flowing up top into the heads? As an example Torker vs Performer. Too much restriction and it's a bigger number!

Firewalker

In a sense, not too big at all, but does it produce anymore meaningful power and is it the best or optimum, for the street?? Where the plastic center section keeps the fuel in the carb cooler under the hot hoods. Then there is the ease of tuning where the rods or springs can be changed in a just a few minutes, from outside the carb. So you could go from the leanest the motor likes on the street to the richest for the strip in minutes, or for changes in altitude. Then there is the price difference, with the Street Demon 750 at $340 or less delivered.

I don't really subscribe to the too big or too small theory, within limits. The carb ratings, in some ways are rather meaningless on airflow, since any rise or fall in vac changes it flow. Or one reason to rate the 2 barrels, at a slightly higher vacuum giving much higher air flow and almost doubling the cfms, if needed and on demand.

I have run 1050 3 barrels, and currently have a 900 CFM Holley injection system, and had 3 CFM sizes I could have ordered on it, at the same general price. I ordered the 900 because I knew it would be the favorite, if I went to sell it, and knew it wouldn't be too big. I also have the 750 Street Demon to replace the injection, if it gives me anymore problems like frying the ancient Holley CPU again. Just saying

olds 307 and 403

Actually the big Thermoquad is 850 cfm or more with mods. The later Qjets are 800 cfm or more with mods, that's what mine is. No denying the Street Demon is a great carb but about as small as someone should go even with a street 455, I hope they make one more size. I would much rather see everyone buy the Street Demon and enjoy their cars instead of buying an Edelbrock and having another thread on how terrible their car runs.

Firewalker

Actually the Thermoquads as rated by Carter were not the same as Holley's old ratings and for example never flowed 1000, but 900 CFMs when tested. So what was the actual flow of the 750 Thermoquads or 800s??

http://www.v8buick.com/showthread.ph...900-thermoquad

http://www.thecarburetorshop.com/Car...arburetors.htm

http://www.pontiaczone.com/forum/showthread.php?t=30099

DW's 455 is running 11s, with a 750 QJet. The Chevy L78s and other 500+ horsepower BBC ran 780 Holleys to obtain those number, with only headers added.

Then I have seen 350 Olds class cars running low 12 high 11s, with the two barrel Holleys early 70s. No ported heads, or roller cams, or big CFM carb or MSD.

I think the 750 Street Demon is plenty for what he has and 99% of the other Olds. I wouldn't be afraid of losing anything important with the 625. I think some with them might even pop off the hair pin clip on the secondary linkage, and see how fast it runs just on the smaller primaries alone.

As far as more CFMs from the ones that offered from what I see it looks like as easy change, to bore the primaries out even more, and put larger throttle blades in it, but there is probably no gain there in ET. I doubt Holley would cut its own throat, with an even larger one.

The smallest Demon shooter is bigger than what the standard ones Edelbrock is using I think, but they will sell you bigger ones LOL That and the float setting is causing most of the grief I think on them. That, and the inability to change the secondary air flow.

My point is the the street Demon is cheaper, with advantages such as metering rods for tuning and won't be such a problem under hot hoods, with the plastic bowls.

Now, what if they were heat rejecting white, instead of black, would they run even cooler. Now where did I put my rattle can LOL The carb he got looks like a fine carb.