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need your help!!


CrazyDavey

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Alright, step right up guys, I need your ideas and input....

 

1. mechanical vs vaccum secondaries... Holley 850, most of you know the set up..ZZ502, th400, 3500 convt, short tire (26" tall 10" wide Hoosier slicks), 3:42's (turning 5100 in the traps on a 5200 hp peak) and Doug's 2" headers...Holley says double pumper is good for lighter stick cars or cars with a high stall.

 

What do you guys think? mechanical too much down low for a 400?

2. for the same setup what about timing...initial...total...when should it be all in?

 

3. in my most recent outing the 1/8th was new best time and speed, my 1/4 was new best time and speed yet 60' remained the same....no noticable tire spin (prepared track)..it doesn't really bog but takes a moment to gather itself up (if you want to hear it you can on the youtube link in my Fontana Highlights post)....I'm guessing it's related to the 2 above but would like your thoughts....thanks, Dave grin

 

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Dave i brought a 750hp double pumper for my Monte two years ago. I never got it adjust right for my set up. My big block ain't as big as yours, as my comes in at a 404 with 390hp. Cam wise it has one of crane cams old blazer series cam, a 700r4 trans and a 2.73 rear. Rear tire I'm about the same size as yours with a 255/50/16.

I would say stick with the vacuum secondary carb as Holley like to see a double pumper on a a 4sp car with at aleast a 3.73 or better rear end.

 

As for your timing around 38 total should put you in the ball park rather its a double pumper or a vacuum carb.

 

Dave have you tried changing the pump cams and adjusting the pump arm? Also changing the power valve might help some

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850DP with mechanical secondaries with your combo. I can't tell you how to tune it, but I do know it is the right carb. Once tuned correctly by either yourself, or a guru you won't be able to wipe the smile off your face when you mash the throttle. Sometimes I wish I still had my AED 850DP with my old hydraulic roller cam. It was snapier down low. With my setup now I sacrifice a little down low, but my top end is through the roof.

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1.70 60' time is pretty good with your package.... what rpm's are you launching your car at?

 

Robyn right now it seems to like just a little foot brake to take the slack out (about 12-1500) and then let it flash. This is also what Coan recommemded.....

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Guest 72yellowmc
Originally Posted By: 72yellowmc
1.70 60' time is pretty good with your package.... what rpm's are you launching your car at?

 

Robyn right now it seems to like just a little foot brake to take the slack out (about 12-1500) and then let it flash. This is also what Coan recommemded.....

 

Coan makes awesome converters .... try a larger squirter.

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Originally Posted By: Reds72WMonte
Originally Posted By: 72yellowmc
1.70 60' time is pretty good with your package.... what rpm's are you launching your car at?

 

Robyn right now it seems to like just a little foot brake to take the slack out (about 12-1500) and then let it flash. This is also what Coan recommemded.....

 

Coan makes awesome converters .... try a larger squirter.

 

??

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Hey Dave,

 

How much intial do you have dialed in? What is your total intital/mechanical and when is it all in? IMHO you do have the correct carb.

 

David

 

gotta get that info Dave, last time I looked the initial was at 16 but I got to get it on a degreed timing light. Got one coming from Summit....what do you think would be idea for a big block???

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On a B/B I don't know. On a s/b with a performance cam it can be from 16-18 degrees or more if it's real radical. I have mine locked out at 36 with 10 degrees of retard dialed in on start up (MSD E-curve dizzy). Idles clean and no dead spot when I wack the throttle at the track. You might try bumping up your initial 2 degrees to see if that might help. I'm sure some B/B guys will chim in. BTW my carb is a Prosystems 4150 d/p that wet flows 780 cfm on a mild s/b. grin

 

David

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If you end up keeping your vacuum secondary carb maybe you can install one of Holly's quick change secondary spring kits. I put one on my Holly 750 vs carb and changing to the lighter springs really makes a difference. But I also want to try a 4150 dp someday. Tom

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My vote is for a Holley 950 DP. From what I remember, it has a smaller venturi like a 750, but a larger base plate and throttle blades. This way you keep the signal good and also have higher overall flow than the 750 because of the larger base plate. I've heard that 850's can be a little more sluggish because they actually use a larger venturi bore.

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thanks Tom and Scott..I do have a quick change kit I haven't installed yet....been looking at the 950 dp....lot of money for "it could work" but I know there's only one way to find out....I'm concerned my motor doesn't rev enough to take advastage of the higher cfm... grin

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Like David mentioned, Steve, Al and myself all have DP's from ProSystems. They were right on the money out of the box, just had to adjust the float and idle and off you go. I recommend calling a couple of carb companies for recommendations as they are or should be the experts. Speak with Patrick at ProSystems

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Like David mentioned, Steve, Al and myself all have DP's from ProSystems. They were right on the money out of the box, just had to adjust the float and idle and off you go. I recommend calling a couple of carb companies for recommendations as they are or should be the experts. Speak with Patrick at ProSystems

 

X2 for Prosystems http://www.prosystemsracing.com/index1.html

 

Give Patrick a call and he can give you some great advice and build you a custom carb for not much more than an off the shelf. Mine shipped to the door was about 500.00 and was spot on This was about 3 years ago. His customer service is awesome. I don't think the guy ever sleeps! laugh

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thanks Tom and Scott..I do have a quick change kit I haven't installed yet....been looking at the 950 dp....lot of money for "it could work" but I know there's only one way to find out....I'm concerned my motor doesn't rev enough to take advantage of the higher cfm... grin

 

That is a common mis-perception Dave. A 950 Holley actually flows about 830 cfm. I'm not sure why they called it a 950. It uses the smaller main body than the 850 which limits it's flow a little but gives the boosters much better signals. It flows more than the 750 because of the larger diameter base plate bores. Talk to some of the carb companies, they will put you on the right track.

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thanks Scott, I just talked to Patrick at Prosystems, very cool guy. We talked about my setup, he gave me his advice and said there is no question I can improve by 2 to 3 tenths with just a carb......sooooo....16 Visa numbers later mine will be shipped on Monday. He's going to build a custom dp carb for my application that will end up around 920 cfm. He told me put it on the car as it arrives and then stay in touch with him, he will be my newest best buddy.

 

Anybody know where to get a good cage???? grin

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Like David mentioned, Steve, Al and myself all have DP's from ProSystems. They were right on the money out of the box, just had to adjust the float and idle and off you go. I recommend calling a couple of carb companies for recommendations as they are or should be the experts. Speak with Patrick at ProSystems

 

 

dittodittoditto

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I think you would be right with many of the montes on the forum Tim, but since his is using a 26" tire, and also has a 3500 stall, that will make those 3.42's much more workable with the initial shot of the DP and at 3500 rpms, the venturi velocity of all 4 holes is much better than say off idle in a heavy car with highway gears and an 1800 stall. I think people dis the DP more than it needs to be dissed. VS carbs are also very good though, I ran one for many years on my car and it ran great too!

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