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View Full Version : Speed Demon or Street Avenger ????



67 455 Bird ragtop
12-17-2004, 02:36 AM
Does anyone have any experience with any of the BG Speed Demon or Street Avenger products ?? I'm considering using one of these on my 455 for my 67 'Bird. Would like to hear from anyone who has used one of these carbs. Especially the 870 cfm vacuum Street Avenger or the 850 Speed Demon.

Tom Welch
12-17-2004, 03:04 PM
These seem to be modified Holley carbs. I'm sure there is more to it than just looks, but I don't know. I do know that a good Q-jet or Carter Thermoquad is the best for all around performance on a Poncho. Look up Jim Hand and Cliff Ruggles on the Pontiac Street Performance site. Here you will find a wealth of information.

sporter
12-19-2004, 07:50 AM
No experience with the Demons but I ran the 870 SA on my 455 in my 67 Firebird conv for several years. It ran great except the choke high idle tended to stick. The biggest headache was the stalling under braking. As soon as I hit my 13" Baer brakes hard, it would flood and stall. You can not tune this away with float settings or jet extensions no matter how many suggestions the Holley tech guys give you. Its just a side effect of having a direct forward fuel path between the rear bowls and the downleg boosters. My 850 DP, 750 DP and Proform/Holley 820 all did it. Only the Holley 600/750s with regular boosters would not stall (kinda stumble but keep running). The one Holley I had with annular boosters was the worst of all for stalling. I replaced them all with an 840 Q-jet and no more problems. If you rarely have to hit the brakes hard (no tourists in your area) then the 870 is fine. However, I really did not notice much difference in mpg between my 870 and my 750/850 DPs.

JAY67CHEVELLE
01-04-2005, 05:13 AM
I used a Speed Demon 750 double pumper on my 406 SBC, worked great, even in the dead of NJ winter it idled with no choke. The only suggestion I can make is after you put it on and run it, tigheten all the bolts on the fuel bowls. They loosen up. i tightened mine after the first day out with it and they stayed perfect after that. I will be getting another one for my 67 chevelle.

andrewb70
01-04-2005, 06:22 AM
YOu may also look into a 770 Truck Avenger:

http://www.holley.com/HiOctn/ProdLine/Products/FMS/FMSC/0-90770.html

It should be just right for a 455 and should help with the stalling issue under hard braking.

Andrew

WELTERRACER
02-03-2005, 11:31 AM
Both are good carbs... Ive had a holley 850, 750, 650 and now a Speed demon 750DP. and Now im selling the demon to go back to a Holley(cant use demon with blow threw setup)