Hi All.

I'm (still) keen to find a Speed Demon 575 or 750 (annular) user, their thoughts on it, and a brief desription of their engine spec.
I have a mildly rebuilt 350 in my 75 with auto trans. Forged pistons, roller rockers from Summit and an Edelbrock manifold and cam, -surely a popular combo.
I had a new Holley 600 but it turned out to have internal problems but it was dicovered far to late to return. I currently have a beaten up Holley that I originally borrowed from fellow UK Corvette Club member which I bought cheaply to keep me going.
The car and engine bay are pretty clean and I though a BG carb would look good in there, plus it's newer technology.
I was going for a 575 Speed Demon but the BG techies reccomended a 750 Annular which seems huge to me. Interestingly, Jegs, with the same info, reccommend the 575. The thing I'm really after is low end torque, and reasonable gas mileage would help too with UK prices!
Cheers, Rob.

 

Would a 650 annular booster, electric choke split the difference for you.Part # QFT-SS-650-AN www.summitracing.com
It has all the modern adjustment capability.

 

750 is my choice.....

 

put it this way,
the tech at barry grant also recommended the 750 annular for my 454.
i dont know how much stock you put in math but there are formulas out there that will give you a good idea on what carb size you need.

 

Love the look of the Quickfuel, but I think they're mechanical secondaries. I've an auto so I'd go with vac's.
Rob.

 

I don't see any mention of annular boosters on speed demon carbs?? mechanical or vacuum. down leg booster.

Looks like there chokeless 820 race demon is there smallest carb with annular boosters.

650 cfm should be good for a mild 350, fuel milage there is only so much you can do without an overdrive trans.

Small DP carbs are not a problem on auto cars, I had a 4500 pound
pickup 350, auto trans, 307 rear end, 650 cfm holley DP it was a daily driver.

from a performance stand point that 650 annular booster after what your used to bet you would be shocked.

 

the part # is not listed on their website.
however
http://www.jegs.com/p/Barry-Grant/De...43583/10002/-1

has all of them
vacuum and mechanical

 

personly I would stay below a 750 unless you plan on running big time at the track....650 is my choice for you on a street driven vette. Then I would pick a vac secondary...again if 85% street driven for good power and good gas millage...if you do not care about gas millage and only car about power then go with a mech secondary.


If you can wait...

comming soon.......Ultra Street Avengers and Ultra Double Pumpers are made totally from aluminum, which allows them to be 5 lbs. lighter than their zinc predecessors. The aluminum construction allows them to hold their shine much longer as well. They come tumble polished from the factory, but can easily be hand polished. The metering blocks and base plates are made of 6061-T6 billet aluminum for added strength, mating surface integrity as well as good looks. The metering blocks and base plates come on the carbs in Red™, Blue™ or Black™ anodizing.
Also new, is a built-in, clear fuel level sight window which makes for easy float adjustments. The Ultra Street Avengers come with vacuum secondaries, are available in 670 and 770 CFM and have all of the bolt-on-and-go features that made the original Street Avengers popular. The Ultra Double Pumpers are available in 650 and 750 CFM and come with mechanical secondaries and electric chokes. Both feature four corner idle circuits for precise tuning and both have enhanced fuel curves for optimum performance.

 

CFM = ((CI x RPM)/3456) x VE

Estimate VE based on HP/CID:

HP/CID / VE
<1 / 75.00%
1 / 85.00%
1.2 / 95.00%
1.4 / 100.00%

I take "mildly built" to mean < 350HP at the crank, so....

RPM/CFM
1000/76
2000/152
2500/190
3000/228
4000/304
5000/380
6000/456
7000/532
7500/570
8000/608
8500/646

We look to see that on a square-bore we're not using more than 1/2 the carb capacity at cruise RPM to be sure we're not into the secondaries.

That mild 355 will need to turn 9800 RPM to use 750 CFM

The 575 will give you the best throttle response and all-around driveability. A vacuum secondary 650 would be fine. The 750 is just too big.

 

if your above 400 hp go the 750
if your below it go the 575 - 650
i like demons too and have the 750 Dp
those holleys look nice 76 sting
im with billa, a 750 will make a nice cruising motor a slug

 

And Chevy used how big of a carb on DZs & LT1s?

 

Do a search on a few performance sites, most don't care for BG's shelf carbs. Stick with a Holley, IMHO.

 

Around 650 is a good choice.
CARBS Tests TQ/HP
http://www.corvettefaq.com/c3/carbcomparo.htm

 

A Holley 3310 750CFM vacuum secondary carb. This was with an engine making > 1 HP/CID (if you believe the stock specs, which were conservative) and a high-revving engine not REALLY intended for the street.

DZs and LT-1s (not LT1s) apply to a mildly built 350 how, exactly? IMHO, this is where folks get into trouble - racing parts used on the street.

 

 

Thanks for all your replies so far. Pretty much what I expected and I think I'll go for the Speed Demon 575. Still would love to hear from someone actually using one.
YOU MUST BE OUT THERE!!!!!
Cheers, Rob.

 

I've been running a Speed Demon 575 on my warmed over Hyd Roller- Brodix headed 327 w/ a 4 speed for a couple years now.

I could not get the car to idle good w/out being too rich w/ a 600cfm Holley. I was reading the articles about drilling holes-when I found the Barry Grant article.

I bolted on the Demon and was able to get it to idle great and not too rich- in minutes. Plus my gas mileage went up a 3-4 MPG. I've been really happy w/ it.

Richard

 

My turn.....

I have a 400+hp/tq at the wheels on my 383. I have been running a Edelbrock 750, and have ordered a BG 750 Mighty Demon Annular yesterday. It should be in this week; I will put it on, run another dyno and post the results to you. The techs over at BG claim I will be gaining somewhere around 20-30HP....Hmmm... we will see. I will also post the drivability comparison between the two...

 

I JUST pulled the trigger on a Speed Demon for my '75. Should have it by Wed.