355
9.3-1 ( iron heads)
dart ironeagles 180CC int. runner
224-234 @.050 112LSA 495-510 ( LPE 213)
weiand stealth intake
Summit HEI...hi po coil
turbo 350
10" midwest converter 2800 stall
currently 3.08 gears 3.45's on the way
26" tall tire.
3440 lbs with driver

200 plate kit.

6K max RPM


I currently have a 750 VS on it and i'm thinking it's too big.

I'm going to borrow my friends 650 DP tomorrow, i think it'll work better.

My question is, if it does which carb is preferred the 650 DP or the 650 speed demon VS or a 650 mech. Demon ?

thanks

 

It's basically impossible to go "too big" with a vacuum secondary carb. With a double pumper you can over do it but you have to go WAY bigger than most people would consider "too big" in reality. I've run 850 double pumpers on engines similar to that and never had a problem.

The double pumper WILL have an advantage over a vacuum secondary carb, assuming both are set up correctly. With a double pumper you get IMMEDIATE WOT from both side of the carb. A vacuum secondary carb, by it's nature, has to open the secondaries slowly and gradually to avoid a bog.

I think a double pumper might get you better performance than a vacuum secondary on your setup (you use an automatic with a relatively high stall that can take all 4 barrels opening up quickly- the engine is never "lugging" at low RPMs like a manual trans car might).

However, I wouldn't be at all afraid of putting on a double pumper carb with as much as 800 CFM on that engine. If you're going double pumper, don't feel like you have to drop the CFM rating to make it work well. You don't.

Brand of carb is up to you. I usually use home-tweaked swap meet Holleys built to my own specs (I'm cheap and I've been doing this for a long time) but I understand the new "tuner" Holleys are very nice. Demon, Barry Grant, even the Holley Street/Strip Avenger series carbs.

 

thanks. I'll see how the testing goes tomorrow.

 

well after testing there is almost no difference between the carbs. I already have the 750 so i'll stick with it.

 

What kind of "testing" did you do?

My 396 picked up 2 tenths in the quarter going from a 750VS to 650DP. That was when I had a 2200 stall converter.

Admittedly, I haven't put the VS back on since going to the higher stall.

 

i tested 0-60 and 1/4 mile test.

 

Last Friday afternoon, my car ran a 14.20 in the afternoon time trial. Later that evening, it ran a 14.15.

Saturday morning in time trials it ran another 14.15. Early afternoon 14.13. 1st round of elmination 14.123, then 14.09, then 14.06, and finally a 14.045 late afternoon.

I didn't change a thing between Friday afternoon and Saturday afternoon.

That 2-tenths I talked about earlier were based on extensive database recording under similar conditions. The DP has never run as slow as the VS did at its best

My point: Your data might not be as accurate as you might think. With the stall you have the DP will never give you bog problems, and will give you more consistent performance.

The only "advantage" I can see of the VS is it will operate the secondaries w/o WOT. If you consider that an advantage.

 

It actually did bog down low, below 2500. The converter is a 10" but the guy made it tight because on the nitrous. it stalls around 2800 with 3.08 geras ( will be changed) i tested with my speedo which can calculate all the #'s and there wasn't enough differenct to warrant buying a new DP since i already have a VS carb.

Anyway i'll post track times next month.

 

Then that was tuning, not the fact that it was DP.