IHI

iTrader: (1)

Alright , I've been racing all season with a Holley 750 VS cause VS are supposed to be the **** with an automatic right? WRONG!!! When I built my motor EVERYONE said buy a double pumper, everything I read said a vaccum works best with a auto, so I went from a 600VS on my 355 running consistent consistent 14.3 and 1.95 shorties to the 750 VS which improved to 14.1 and 1.85-1.88 shorties and consistent 14.1's. Called the Bro-in-law as he has DEEP pockets and changes his engine combos on a weekly basis-no ****-asked what he had laying around for a carb that'd work with my 355. He gave me his old Holley race 830 that he drilled the squirters out in and the ole fuel line over the vent tube carb to save it from the dreaded fuel slosh, after installation on Sunday and tuning the mixture screws noticed an immediate seat of the pants and gas gauge difference for the worse. VERY responsive and likes the gas!!! First run off the trailer was a 13.699 and a 1.82 60', WOW, second TT 13.701 and 1.826 shorty; much more consistent and much more powerful to say the least. The rain cell moved through the area and caused delay plus a change with temp and humidity, kept a 13.68 dail, made it to the semi finals, then dialed a 13.70 cause the round before the guy red lit so I had the chance to run it out and it ran a 13.75. Semi finals had to race the female points contender and told her to push the tree or go home, ate my words as she cut a .516 to my lousy .572, she ran a 13.849 on a 13.82 dail to my 13.709 break out on a 13.74 dail-should have kept the 13.68 and it would have been alot closer. Morral of the story-if you want BIG power F... the VS carbs and get the DP, BUT I also used 1/2 tank of fuel in 8 passes (2miles) so if fuel mileage is of concern be warned, but I'm tellin ya, damn what a difference!!!!
Also as a final note, I, as well as others have been bothered by the cobbeled up dual exdhaust set-up that was installed on my car, right out of my Heddman full tube headers with 3" collectors they were bottle necked down to a 2 1/4" reducer then to the 2 1/2" pipe. Then made a multi curve path back to the Super Flow mufflers (Flow master knockoffs) and turn outs before the rear tires. So since this was my last race as my daughters first birthday is Sunday and I'll miss tomorrow, I took off the goofy exhaust and ran open headers- to my dismay it ran the EXACT time as the first run off the trailer, 1.82 shorty and 13.690. Who would have thought?! In conclusion it's nice to know that my car runs the same corked or uncorked for street comp, but I'm still baffled, I guess my set-up might like a little back pressure.

unknown_host

iTrader: (1)

Thats quite a difference, i too had heard that double pumpers are bad on auto cars.

AlkyIROC

Not all double pumpers have bad gas mileage. Buying a DP with progressive linkage such as a Speed Demon isn't as bad as everyone thinks. When the carb has progressive linkage, the secondaries won't open until the throttle is opened more than typical daily driving allows.

Q-jet's are mechanical progressive linkage carbs and nobody complains about them. At least not in the same way as complaints about a DP Holley.

IHI

iTrader: (1)

Unknown, it's now that I fully understand the performance reason for DP vs VS, for a street car that sees alot of street driving a VS is great cause your not dumping all the fuel at once for the trips to the store, it's comes in when demanded, there is probably a better theory as why autos like VS and sticks like DP, but in my case it's rarely street driven so it's not a concern, the Holley I run now Stephen does not have the mechanical progressive linkage, it's both sets of butterflies opening at the same time, it came with 70 jets in both front and rear which originally I thought was odd, but all my plugs are perfect after trips down the 1/4mi., yes they load up in town, but I'd rather have that then a tear down and piston replacement. For performance applications or bad *** street machine the DP is the way to go cause it's all the fuel you need on demand, I've heard alot of people say that barametric pressure can cause a difference in the way the secondaries come in on VS also, whether there's truth to that I don't know, but it sounds feasible.

five7kid

iTrader: (14)

Vacuum secondaries open based on flow through the primaries. Barometric pressure will affect the density of the air going into the carb, which will affect the power it puts out. But, I didn't touch the VS adjustment when I went to Topeka this past weekend, and that's a BIG change in barometric pressure - the secondaries acted the same there as they do here. I did jet up, though.

Sounds like your DP carb has been set up "square" - no power valves, all four venturi acting equally (except for idle circuits - probably doesn't have them in the secondaries). Without power valves, it won't drive very nicely on the street; but on the track, where there are only two modes (three if you count staging), it will work fine.

As Jester argues on the Carb forum, the secondaries on a VS never completely open, unless the carb is undersized. Just getting all of the flow should allow the DP to outperform the same size-rated VS every time. In your case, you increased the flow as well.

IHI

iTrader: (1)

If you want to see the carb I got it's in Jegs listed as Chokless Race Carb, then the bro-in-law had the choke tower milled off also. Lists as : 830 CFM, features dual 30cc accelerator pumps & annular boosters. When I orginally picked it up, he had the 2.5 power valves both front and rear, he said he runs them with all his carbs, I wanted 6.5's as that's what my engine vaccum called for so he dug up 2 new 6.5's that I installed, then he was gonna buy bigger squirters, but drilled the stock on's out to the diameter he was gonna buy and it worked so well, he never bought the new ones, I thought for sure it'd drown out my motor, but it takes it and loves it, so I'm not gonna play with it either. This carb also has the 4 corner idle circuit and center hung float bowls. After I bolted it down, the bowls where right where they needed to be, I adjusted all the idle/mixture screws and away I went. Everyone at the track was telling me the VS would make it harder to have consistent ET's on account of atmospheric changes, it did run fairly consistent, naturally as the night cooled off night racing, or the sun got hotter day racing car would speed up or slow down, but that's to be expected, but it was usually only .1-.2 off it's normal dail, now with the DP the runs did seem more consistent, 13.69, 13.709, 13.70, 13.69, so it was even more consistent I think, so for out at the drags lookin back a DP might have made me more money this year as I lost alot of races by .007-.05, we won't talk about the red eyes though.
I always psyce myself out during actual bracket races, during TT's I'm usually .500-.515, then I seem to get nervous and start cutting .550-.600 and you can't win races that way. BUT, when I'm in the gambler races, it's like a switch goes off in my head cause I know I have to push the tree to beat the Super Pro and Pro guys, so in reality I've made most of this years money in the Gamblers, cause I go back to cutting great lights-because I have too. I still finished 6th this year in my class and that was missing 5 races-almost half-13 races in a season down here, if I would've had my head outta my *** I would have as least bought in and got my 10 points, cause that would have raised me up to 4th. Lesson learned for a rookie year I guess.

five7kid

iTrader: (14)

Ah, I should have said "no power valves or two power valves". With jets that small, two power valves does make sense. Should run fine on the street, too.

I'd like to get a DP as well, but have to consider which would lead to winning more races - a new $430 carb, or a new $430 weather station. Is it really even a contest?

IHI

iTrader: (1)

To tell you the truth most guys at our track, even some of the rail cars still use the simple wood weather stations like you'd buy at Wal-Mart, next year that's what we're gonna try and document and see how it works, we're planning on it this year but never happened and I wish we would have, might have been more consistent, but until you get as many things on the car to be as consistent as can be, I don't think the weather station could be fully utilized to it's potential. Like I said I noticed with the DP my times were much closer together, all things being equal, I always tried to keep the tranny temp and motor temp the same before each pass, and when we had races that drove in circles from return lane to staging again, I always had to dail up a little cause once the tranny get hot, convertor acts a little differently, and it doesn't cool down as quickly as the motor, so I'd slow down about .05-.10. I just installed the tranny temp gauge a few weeks ago and it's always at 100 when I'm staged and the motor at 160. Hottest tranny has been yet is 125, but I'm not running an 8" race convertor either-those guys range anywhere from 150-180 between rounds.
I'm hoping now that most the things that could vary are unvariable now as far as the drivetrain, so next season we're gonna try the Wal-Mart weather staion and documentation, might not look as cool, but if ours cars are dailed in to that particular gauge then it should be consistent.