mdricken

I've got a ZZ4 motor with a Comp cam with around 224/230 duration, otherwise a stock setup with headers and a open element air intake.

I want to go to a double pumper carb but was worried that a 750cfm would be too big for this motor. Right now I can squeeze out 13.5s @100 on street tires and a 670cfm vacuum carb.

sprojam

i think this is to much carb if it is seeing street an strip duty my budy is running pretty much the same setup with a kieth dorton 670 carb an cheater slicks an is in the 12s good luck

mdricken

I guess I should have said that I will only race with this carb. ie put it on on race day and swap the old carb back on when it gets home. I'm mainly looking at a 750 because they are so common vs oddballs like a 670DP.

Thanks for the input. 12s is pretty fast.

xpndbl3

iTrader: (5)

on a track only vehicle no carb it too "large" realistically speaking. A 750dp would be fine for track duty or daily driver duty even.

zz4monte

On a stock zz4 I tried it and it was always rich but with the bigger comp cam I would say it might be good to go. I would say 700-750 DP would be good. You have alot more duration with that comp cam.You could use a little more carb for the top end.

zz4monte

A very common thing people do is over carb. Especially in double pumpers!!!

five7kid

iTrader: (14)

With 3000 stall, a 750 DP will be just fine.

sprojam

i was always told big is good to big for the application slows you down but i also understand that by rejetting youd prolly be alright and for the street not what i use but im a street driver that wishes i got to spend as much time on the track. truelly i wouldnt run that card on that motor good motor but not big enough for that carb

sprojam

truethfully i have never had good luck with holley carbs and double pumpers are out of my rage everytime ive tried one it killed my performance truethfully im best with a vacume secondary carb everything else ive tried has been a major pain in my but why this is i dont know so i guess if you have good luck with that type of carb go for it for along time i ran qaudra jet an a ocasional holley now i found my new baby in the edelbrock thunder series carbs i love um

five7kid

iTrader: (14)

I don't know why you two have had so much trouble with Holley carbs, but they aren't all that mysterious.

If you're running 13.5's with a 670 Street Avenger, you'd probably run 13.3's with a 650 double pumper. Assuming traction was available and consistent. Street tires is the biggest problem I see with that combo.

750 DP, traction, all other things being equal, you should be seeing low-13's, high-12's, without question. With less stall, lower # gears, and q-jet, I'm at 13.3's sea level with my car - you should be much quicker than that (although your car is probably a little heavier than mine).

sprojam

well i was just replyin not my car no holley here but anyway i think they are depermental and dont hold a tune probally just me but id rather run a 13.3 then a12.8 an the next time down a 14 flat this is the kinda experience i have had with them an if you let them set a week good luck

zz4monte

Got nothing against double pumpers. I love my 650DP. Just that a lot of people think that a 750 is perfect for every 350. I was just trying to say that every 350 does not need a 750DP but if you run a stout cam like his I see no problem with a 750.

five7kid

iTrader: (14)

It would be fine with the ZZ4 cam and that stall as well.

Now that I look this over some more, I'm thinking the ZZ4 intake will probably become the limiting factor. That much cam should have a different intake to match.

zz4monte

I know a guy with a monte ss that had a zz4 and did the same cam swap. He upgraded to the Performer RPM. Made a big difference in the top end with that cam.The zz4 intake is just a performer built by edelbrock for gm.Performer RPM is a 10hp gain according to sallee chevy on a stock zz4.

mdricken

I could look into that, but my car is a street car before a race car, so I wouldn't want to compromise my already tiny hood clearance or make the car act funny at low rpms. Ist the performer RPM a single plane intake?

five7kid

iTrader: (14)

No, it's a dual-plane. 1500-6500 RPM powerband. P/N 7101. You shouldn't have hood clearance problems. With a 3000 RPM stall converter, you aren't going to notice any low-RPM torque reduction.

zz4monte

Yep.Performer RPM is a high rise dual plane.If I was changing to that cam I would go Performer RPM all the way.It is a very streetable intake.

fastcar06

if this is primarily a street car than why would you not consider a vac secondary carb. i have seen too many guys over carb on the street with double pumpers and wipe out bearings. look down your carb sometime and see just how soon double pumpers start to open the secondaries. fouling plugs and fuel in the crankcase are common. vac secondaries if adjusted right should be the norm for most street cars.
i too am a big fan of the rpm intake. my motor has a torker currently but will prob. get switched to the dual plane rpm.

sprojam

that way when us true street strip guys pull up to um its a race cause they are all loaded up thats usually good for two to three lenghths an the other guys smilin just cause your set for the strip. and i dont think theres any detuning thats quick an easy that will work

five7kid

iTrader: (14)

You tune the primaries of a double pumper and vac sec in the same manner. If you're washing out bearings, it's because of improper tuning, not because it's a double pumper. I never open the secondaries on the street unless I really want to. And, if you think about it, you're going to get into the secondaries of an undersized carb sooner than you will an oversized carb.

Personally, I find the fact that the secondaries will stay open momentarily when you back off of a VS carb rather unnerving, something I can do without, and does not happen with a DP carb.

It's a simple matter to properly size and tune a double pumper for the street, and it's the double pumper car that's going to put 2-3 lengths on the VS car before he knows it.

mdricken

The double pumper is something I'll swap on on race day. Otherwise I'll stick with the 670cfm VS for gas mileage and drivability.

Hopefully I can get away without fouling too many plugs or washing bearings during the weekend.

xpndbl3

iTrader: (5)

if you know how to tune a carb you won't wash bearings or foul out plugs. a double pumper could be used on a daily driver without any issues at all. vacuum secondaries are great for motor homes or tow vehicles but have no place on a performance motor.

sofakingdom

iTrader: (1)

That's the type of carb that its HP is "rated" with.

I'd say it's just near about perfect.

sprojam

yeah i here ya on the 2 tenths 3 is pushing it but anyhow my biggest complaint is they dont hold a tune and my experience says not consistant i guess to make along story short it depends alot on preference. but i am running my best times with this new thunder series carb 850cfm verse 650cfm double an its there every weekend when i pull her out not near the tuning that is required with a holley and when you do tune its much easier.

mdricken

I'd be happy to move away from a holley, but I paid $100 for my 700r4 linkage setup. I hear that edelbrocks are easier to tune. Any other options besides a holley for all out racing?

bluegrassz

iTrader: (3)

I am running a Holley 3310 750vs on my setup. Check out my sig for my engine/trans combo. I also have a good carb in my sig for sale. Its is a 750 VS Speed Demon.

five7kid

iTrader: (14)

Where does this stuff come from? I've had to adjust my carb for a "tune" issue exactly once in the last 2 years, not including the conversion from gasoline to E-85; and the "problem" involved readjusting the secondary float level, probably from something being in the needle/seat upon initial adjustment (which probably occurred during the E-85 conversion and inlet filter replacement), which later flushed out necessitating the readjustment.

Consistency when converting from q-jet to Holley in 2001 was a big improvement, and going from VS to DP in 2003 was another step improvement in consistency.

On the other hand, a fellow racer with an Edelbrock/Carter/AFB carb would change the rods when arriving at and before leaving the track, but doesn't touch a thing now that he runs a Demon DS.

We really need to get a hand on all of the wive's tales being presented as fact around here.

fastcar06

hasn't telling tales always been involved in racing. i guess the thing to consider here is finding a carb that he could use on the street and track without swithcing. while it is true that some combinations could benefit from a dp carb, not all will given the type of driving they do. if you look at the carb selector on the holley site they will advise you that most street cars should be using a vs carb. of course there are always exceptions. but with a mildly modified 350 engine in a 3500lb car mainly driven on the street, my personal opinion is that a vac. secondary carb would give him the best drivability. sure it is just an opinion, but were all aloud to have one. if the only goal here is et's than sure put on the double pumper. i think we all would agree with that.
just my two cents.