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-   -   750 double pumper or vacuum secondary (http://www.hotrodders.com/forum/750-double-pumper-vacuum-secondary-187506.html)

stroker444 11-12-2010 02:21 AM

750 double pumper or vacuum secondary
 
Im seriously thinking about putting fuel injection on my 383 because its my daily driver and has a 6 speed behind it. I really want efi, but its just going to cost so damn much mainly because of the harness and injectors. Right now I have a holley 750 double pumper with a proform mainbody w/ adjustable air bleeds. Its only 8 months old and its set up pretty well for my engine, but I get a bog if i just punch it at low rpms (WOT). One of my friends offered me 250 bucks for it (just cost over 600 a few months ago), with the money I could buy a holley 750 vacuum secondary and tune it, but am i really saving that much money buy selling my double pumper for the vacuum secondary? I get pretty decent mileage with the carb i have now, but If the vacuum secondary will be just as decent for performance and mpg, i wouldnt mind selling it and having the extra cash around.

lg1969 11-12-2010 08:07 AM

What's the gear ratio on the rear end?

sqzbox 11-12-2010 08:15 AM

Auto or manual tranny? You'd probably get better mileage with the vacuum secondary and the bog would go away. :D

ap72 11-12-2010 08:48 AM

If properly tuned you'll probably get worse mileage with the vacuum secondary carb.

As for EFI, you can use the intake system from an LT1 along with megasquirt to put together a poorman's ramjet system. Works pretty well up to about 450hp.

kleen56 11-12-2010 09:00 AM

It's a matter of preference. I personally like the double pumper carbs because they come on when you want them to. Vacuum secondaries are OK but there's nothing better than depressing the pedal and manually giving the engine that squirt of fuel. I also run low gears which helps with carb performance. It's hard to recommend a carb because everyone has their opinions. Just like this one :welcome:

F-BIRD'88 11-12-2010 09:26 AM

Tune the carb you got.

A vacuum secondary carb will need just as much tunng.
EFI will need $$$more$$$$.

Get yourself a AFR meter/gauge, manifold vacuum gauge some numbered pin drill bits , a soldering gun and electronics solder (to create and dial in the jets sizes etc). Start by correcting the idle and off idle circuit transition (idle air bleeds idle feed restriction) and then work on the accelerator pump circuits. Correct the ignition timing curve.
These are the areas that need work to sharpen up the throttle response.

even a simple cheap narrow band AFR gauge/(heated) 02 sensor will show you 99% of what you need.

cliff tate 11-12-2010 09:39 AM

double pumper
 
my vote would be 650 vacume secondarys,you can change springs in the 2dary diafram to have them come on sooner,tune it re prev. post. i have a 302 in my32ford that has a mild cam andported heads with biger valves the 600 holley works well,no bog. ther ar some deals on e bayfrom holley thes carbs ar returns with minor isues,i bought a newish 1 for 150 including frt,it is on another 5ltrworks great,they had larger carbs for more $ ,it is a make a offer type of auction. double pumpers will never be good on fuel relitive to vacume 2nds and sensible driveing. my opinion cliff

F-BIRD'88 11-12-2010 09:50 AM

Just quickly review some of your old posts I can see a few things.
The cam you have is way too big for how you actually drive your car.

And it is most likely a mis match for your exhaust system.
That cam is not in the game below 2500 rpm.

You are retarding the spark timing to allow running regular gas cause you are too cheap to put good gas in the tank yet want to spend $1000's on EFI.

Retarded timing is going to effect throttle response.
Especially if it was never right in the first place. Just checking your posts,
it is not near right for that cam. Needs a lot lot of work.

stroker444 11-12-2010 10:06 AM

Quote:

Originally Posted by F-BIRD'88
Just quickly review some of your old posts I can see a few things.
The cam you have is way too big for how you actually drive your car.

And it is most likely a mis match for your exhaust system.
That cam is not in the game below 2500 rpm.

You are retarding the spark timing to allow running regular gas cause you are too cheap to put good gas in the tank yet want to spend $1000's on EFI.

Retarded timing is going to effect throttle response.
Especially if it was never right in the first place. Just checking your posts,
it is not near right for that cam. Needs a lot lot of work.

Ive noticed that you find a way to be a dick just about everytime you reply.

65 Imp SS 11-12-2010 11:09 AM

Every combination is different, the performance cams like more initial timing. Also sounds like you need more fine tuning on the carb's accelerator pump circuit here is vid kinda basic but informative.
http://www.youtube.com/watch?v=k-Nx5HEzvlY

ap72 11-12-2010 11:55 AM

Quote:

Originally Posted by stroker444
Ive noticed that you find a way to be a dick just about everytime you reply.

Whether or not you like the comments they do carry merit. It's not about the original post but often people will attempt to change a part that works in an effort to compensate for one that isn't. Its like changing the water pump to fix a leaking heater core...

cobalt327 11-12-2010 12:14 PM

Quote:

Originally Posted by stroker444
its set up pretty well for my engine, but I get a bog if i just punch it at low rpms (WOT).

This is either/both the accelerator pump circuit and initial timing. There is no reason the carb shouldn't work on your engine- providing it's in tune and you modulate the throttle using your brain and right foot as opposed to just matting it, like can be done w/a vacuum secondary carb.

IF you have too much cam, this will manifest itself by being lazy down low in the rev band- but that's a whole 'nuther thing from a bog. Maybe a more in depth description of what's happening will help.

brucer69 11-12-2010 12:34 PM

an lt1 setup would work, but the optispark distributor is crap, and actually wouldnt be worth messing with....


heres a junkyard parts list for an LS based fuel injection setup

any ls1 based pcm will work, you'll just have to get it reflashed, many reflash for like $50.00

heres the list

12200411 PCM (LS1, Truck, S-10, Blazer, Express, others)
Wiring Harness for 12200411 (must follow Vortec L31 schematics for the 18436572 firing order)
Vortec 305/350 Distributor (has camshaft sensor in it)
Vortec 305/350 Harmonic Balancer (if your 383 is internally balanced, if not, retain your balancer and cut the thickness of the reluctor wheel from the hub)
Vortec 305/350 Timing Cover(crank position sensor provision)
Vortec Timing Reluctor Ring (goes behind timing cover)
Vortec Crank Position Sensor
Vortec Ignition Module
Vortec Coil
Knock Sensor (2001 Express Van w/ 5.7 engine)

injection intake and rails, professional products makes a decent setup...

injectors, ford 30lb redtops would be minimum, can be found on ebay very reasonable..


i have always made it a point to run a dbl pumper with a manual transmission..

if you have a bog off idle go to a larger discharge nozzle.. if you cant get the dbl pumper adjusted correctly you'll never get a vacuum secondary carb to work correct..

68NovaSS 11-12-2010 01:27 PM

Quote:

Originally Posted by stroker444
Ive noticed that you find a way to be a dick just about everytime you reply.


Name calling won't be tolerated on this board. Reading the post you refer to, I don't see anything out of line, just the member's opinion.

ericnova72 11-12-2010 01:34 PM

Quote:

Originally Posted by stroker444
Ive noticed that you find a way to be a dick just about everytime you reply.

F-Bird's post is spot on, but you just don't want to hear it. I feel the same way as he does, you're trying to crutch what you have rather than make it right, complain about cost but want to blow $$$ on EFI that won't even earn a return on its investment for something like 70,000 miles of driving cost.

The DP can get as good a mileage as anything, if you set it up right and keep your foot out of it.


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