427Hotrod

Isn't this fun?

First, the strangling it part was to address using the smaller carb vs the 750..not DP vs Vacuum. With the heads in question it's not going to be a high RPM screamer anyway, but still a 750 is going to work fine.


I don't see how a vacuum carb will give better throttle response. Unhook the secondaries of either one and they will both act fine. As mentioned the DP's are a little fatter on a mild application...but the 4779 versions work fine on the avg hot rod. Nothing to getting 20mpg out of one on a 12 sec small block. I've done it too many times. It also ran fine bolted onto a stock '82 Mustang GT. Got better mileage than the 2BBL it came with and ran great.

In fact if you want to have fun, leave secondaries unhooked on either carb and see how well they run at WOT. I used to do it in my street racing days. If someone thought I had too much motor for them, I'd remove secondary linkage and race. 2bbls can run within a tenth or two of 4 bbls quite often!

The vacuum carbs are recommended frankly because they are *idiot proof*. Seriously, no offense...but you can bolt one on a lawnmower and it will run fine. You can bolt it on a 600 HP 454...and it will run fine.

But I can guarantee you that if we bolt a DP on the above combo..it will walk all over a similar vacuum combo....and will idle away from a redlight just fine...it will get good gas mileage etc. Yes....maybe it would accelerate better from 20 mph in high gear at WOT with a vacuum carb....I will concede that...and that's exactly what the Holley tech has to worry about. They have to lean to the conservative side if they hear just one tidbit of info suggesting a less than optimum combo or driving style. Same with cam mfgs.

I love to race the folks that listen to them!!

JIM

billla

The context of your response is drag racing, which as I noted is the RIGHT place for a DP carb. On the street, for a daily driver...no.

I didn't see anything else that needed a direct response

Little Mouse

427 hot rod is right about idiot proof on the vacuum carb. Every 3310 I had on 302,327,350 the spring in the secondary was way to stiff to make sure anything it was put on it would not bog. Lot of people talk about the LT1 or even the 302 with a 780 vacuum carb, chevy could get away with way to big a carb for any street carb on that size engine buy using vacuum. Take the 302 Z/28 in 67 the first yr chevy entered trans am racing they had to use a production carb, the big carb made more power with an engine kept in the 4500 to 7200 rpm range all the time, in 68 they changed rules to allow two fours so the cross ram showed up developed by smokey yunick. The big carb was kept on the production 68/69 Z/28, why because by still using the big carb it could be used in super stock drag racing where any cam the racer wanted could be used and they were turning serious rpm, if chevy did not use the big carb on the production car they would be stuck with a small carb for racing competition. Best way to really make a 780 carb work on the 302 or even the 350 Lt1 was to use vacuum not because vacuum is the only thing that needs to be used on a street car. Vacuum carb is the safer carb if you don't know how or want to tune but the dp is the better performance carb. You can use a dp on your daily driver a performance car or a race car, you rarley see a vacuum carb on a race car unless the rules mandate it, kind of like a Q-jet lol.

DRIVESHAFT

If you were able to test drive your car with a double pumper and with a vac secondary carb,
I can just about guarantee you that you would want to stick with the double pumper.
Either type of carb will work, but mechanical secondaries are more fun.

billla

It's kinda funny how completely opposed the two "sides" are. I look at the DP as being an "idiot proof" carb since any tuning issues are covered up by gobs of fuel and air Every time I've put my Innovate on one (even one that's "tuned") it's been a complete pig.

In the end I think the real aspect we're debating is throttle response. The OP just needs to decide if they want to give up some level of fuel economy and driveability for better WOT performance.

427Hotrod

Ok Billa....everyone to their own of course. That's why they make both versions.

But if someone is having trouble getting razor throttle response off idle with a DP, they just need to look at little closer at the tune. You've got the same 30cc pumps on the primary of each carb, often same boosters, same PV's, same throttle bore...maybe different emulsion circuits and idle circuits...but that usually just gives an even fatter TQ curve at the low end. But yes...THAT part can use a little more fuel. Of course you gotta burn fuel to make power with all other efficiencies the same.


Jim

Les

I have to put in a vote for the DPs. I've had both types of carbs on my bigblock & my smallblock. I know how to tune a Holley carb & have had a 3310 set up nicely for each engine at various times in past years- the smallblock (70 Z28) came w/ one from the factory. They no doubt get better milage when the car is driven aggressively but I've chosen & stayed w/ the DP for many years for both cars. Performance is simply better.

I figure we drive performance cars & I've always leaned towards favoring better engine performance over economy if the difference isn't too dramatic. If my cars were daily drivers I might take another look at it but since they aren't, it's a no-brainer for me.

TWINRAY

Barry's70LT1

Not trying to influence you one way or another. Just my experience.
In 1971 I installed a Holley 750 DP on my LT-1. It did require some metering/jet changes due to being on a 350.

That carb is still on the same engine today. Works great and has 90,000 + miles on it. Not worn out yet.

Gas mileage is no different from a DP to a VS. (When both are tuned) The driver typically makes the difference, not the carb.

I would never go back to a Vacuum Secondary carb.

Jebbysan

With that setup I would go DP but I would purchase the 750HP series or equivalent from AED........you will be glad you did......
I have a fairly hot 406 with the HP carb and it is just perfect for it....

Jebby

PAmotorman

DP carbs use a larger jet and a smaller PVCR than vacuum secondary carbs so in down the road cruising they will run richer and use more fuel. you can convert the primary metering block to a vacuum secondary specification metering block and have better fuel mileage and still run the same at WOT

cv67

Happy w/mine
value was it was precalibrated for my cars weight gear cam etc etc
I hate the smell of gas
The after sale service from Jeff over there is simply over the top that counts for something to me.

With gears cam stick definitely DP...if you get a reg ol Holley get an HP where the air bleeds etc are adjustable so you can really fine tune it.
Talk to Chris Straub about one may be plesantly surprised.

Kacyc3

way to bring back an 8 year old thread and noone notice.

TWINRAY

Just so I could mark it to look it up later. Sorry to get your panties all knotted up

Robert Thomas

😳😖😴

Pop Chevy

I'm glad he did , I found that very interesting. I have a VS carb on my 60 (that is all dialed in) and have a 750 DP on the bench that I was going to sell. Now I'm going to bolt it on and try it !!

Jebbysan

And intrinsically....why does it matter?
Information is information....
Unlike the eight dead threads a day that happen here due to forum know it alls and stupid rhetoric...

Jebby

TWINRAY

And make sure to report the results, thanks

suprspooky

Do yourself a big favor, tune it yourself with an AFR Gauge/Data logger (I use an Innovate Motorsports Dual wideband O2). Lots of good step by step info on the WEB for perfomance Carb tuning, much simpler than FI tuning imo.

Pop Chevy

Are you talking about the LM 2 ? I think I need one !!!