12 mpg 383.....help!

[Sparks280zt]

I think I am going to order this regulator http://www.jegs.com/i/Holley/510/12-803BP/10002/-1

 

Thoughts?

[nullbound]

That's fine as long as you have a return line. Otherwise go with their $25 regulator that's usually available behind the counter at advance/autozone.

 

I completely agree that holley's are pig rich out of the box. Went down a few jet sizes front and rear on both of my 750's.

 

Do you know if the previous owner did anything to the carb? Can you describe more on how it runs under 2k rpms? Does it idle ok? Does it have a good inline fuel filter?

[Sparks280zt]

That's fine as long as you have a return line. Otherwise go with their $25 regulator that's usually available behind the counter at advance/autozone.

 

I completely agree that holley's are pig rich out of the box. Went down a few jet sizes front and rear on both of my 750's.

 

Do you know if the previous owner did anything to the carb? Can you describe more on how it runs under 2k rpms? Does it idle ok? Does it have a good inline fuel filter?

 

I plan on routing a return line. It seems to be bogged down under 2000rpm, very labored. It idles great. There is an inline filter back near the pump, not sure of the brand.

[grumpyvette]

http://www.jegs.com/i/Holley/510/12-803BP/10002/-1

 

thats a dead head style regulator and its FAR FROM IDEAL, all QUALITY return style regulators that Ive seen, have THREE PORTS

 

(1)FEED from tank

(1)CARB feed line

(1)RETURN to tank

and a pressure adjustment screw, and a vacuum line connection to the plenum

 

 

http://forum.grumpysperformance.com/viewtopic.php?f=55&t=635

 

http://forum.grumpysperformance.com/viewtopic.php?f=55&t=211

 

if your running a carb, you need to have a correctly set up fuel system, one of the more common complaints is related to fuel pressure at the carb inlet port, many fuel pumps produce 6-12 psi of fuel pressure at higher rpm levels , some even provide that at idle speeds, that much pressure tends to flood carbs and make float adjustment difficult or useless, only 7-9 psi will almost always overcome the needle & seat and constantly flood the carb, that is probably the source of your major problem, install a RETURN STYLE fuel pressure regulator, and a line back to the tank or at least back to a TEE thats located before the pump intake point

 

http://www.jegs.com/webapp/wcs/stores/servlet/category_10001_10002_10019_-1_10267?sendroicid=bbef8492-2d00-41d6-b158-38db0de2603c&sendroiad=3824188001&sendroikwd=Fuel+Line&gclid=CNrLsez3opkCFQudnAodtC_cpQ

 

yes the diagram says 8PSI your far better off with 5 psi in most street car applications

 

these cheap ones, that are dead head style seldom work well

 

http://www.jegs.com/p/Holley/745059/10002/-1

 

much better

http://www.jegs.com/i/Mallory/650/4307M/10002/-1

 

http://www.jegs.com/InstallationInstructions/600/650/650-4307M.pdf

 

http://www.summitracing.com/parts/MAA-4309/

 

High-flow for your fuel system.

 

When using high-pressure fuel pumps, a fuel pressure regulator must be installed to prevent carburetor flooding. These Mallory fuel pressure regulators feature housings fully machined from 6061-T6 billet aluminum, and specially designed high-flow fuel passages. These features, combined with a quick-acting diaphragm assembly, make them extremely efficient. A mounting bracket is provided to allow quick and easy mounting.

 

 

http://www.summitracing.com/parts/MAA-4307M/

 

http://www.summitracing.com/parts/AEI-13351/

 

http://forum.grumpysperformance.com/viewtopic.php?f=55&t=635

Edited January 20, 2010 by grumpyvette

[Sparks280zt]

Thanks Grump, I will go with that Mallory from Summit.

[dr_hunt]

Actually with Holley carbs, any pressure between 4 and 7psi is within spec. Having to run 5 or 5.5 psi is simply not true. Chevy ford and chrysler put holley carbs on sbc's in the 70's and absolutely none had fuel pressure regulators or return fuel systems. All they had was a simple mechanical stock pump and a 3/8's line.

 

A little bit about holley DP's is contained in the following. You'll have to jet down then open up PVCR's to make it get mpg. Anything else is a complete waste of money and time.

 

Double Pumpers and Gas Mileage (or lack thereof...)

 

Have you heard people complain about the gas mileage they get with performance-type double pumper carbs? There is a reason that the 0-4776 through 0-4781 double pumpers get bad gas mileage. It's the jets! Surprised? Holley sizes the jets and air bleeds on these carbs so that they run on the rich side at cruise speeds. They make more power this way, at the detriment of gas mileage. These are competition carbs, and they are supposed to work this way. Why don't we just put leaner jets in them to get mileage? Because the PVCR's are small, and under power conditions, the carb will supply an overall lean condition. What you can do is lean the jets out, then enlarge the PVCR's to compensate for power situations.

 

The way to do this scientifically is to measure the diameters of the openings of stock jets and PVCR's using drill bit diameters. Then calculate the total area of all the openings, and add them up.

 

A = 3.1415 x dia x dia / 4

 

Decrease the main jets for proper cruise mixture, and enlarge the PVCR's until you get back to the original area of all the openings. This way, your cruise mixture will give you good gas mileage, and under power, the engine will have proper mixture.

 

BTW PVCR's are power valve channel restrictions and are the two little holes under the power valve.

 

It really is just that simple!

Edited January 19, 2010 by dr_hunt

[Sparks280zt]

Thanks Dr. Hunt

 

Here is the exact Holley I have: http://www.holley.com/0-82751.asp

[dr_hunt]

If you will do what I have outlined above it will give you all the mpg's your going to get out of that carb. PERIOD! If people really don't have a clue about how to answer a question then don't answer it. I have a pet peeve about ridiculous answers that are completely wrong and lead people down the wrong path which directs them to spend money needlessly.

 

You can't change boosters without special tools and knowhow, besides, you'll screw up the fuel metering circuit anyway, which are balanced by holley engineers. Why anyone would attempt to do that is a real Squirters have absolutely zero effect on cruise mpg and so do secondary springs.

 

And don't waste your time on any fuel pressure regulator and return fuel line as it's fixable for probably less than $20 and about an hour's time pulling the bowls, jetting and following the procedure above.

 

IMO what separates he really good enigne builders from the rest are the ones that can tune their engines and those of others. Cause if you build it and it's tuned all wrong, your customer is not going to be satisfied and probably won't come back. But if you tune someone elses engine and get it working right, they will be at your door the next time they need a motor.

Edited January 19, 2010 by dr_hunt

[Sparks280zt]

Thanks Dr. Hunt

[dr_hunt]

Here is how you work on getting it right. Play with jets and once you have the main jets set, it is time to play with power valves. Install a vacuum guage, you can get a cheap hand held one from any parts store like autozone. You can put it face down to the windshield under a wiper, just make sure the hood doesn't pinch the line. Watch when your driving, like going up a slight incline at highway speeds, or accelerating slowly at highway speeds, you will notice the vacuum reading falling. As it falls, it will come to the opening point of your power valve, then pick up a little. If you have a wideband you can tell when the power valve opens because the meter will go lean for a while, then the valve opens, and the meter begins to show rich. You'll probably notice the power increase right when the power valve opens, but maybe not. It's hard to tell with a higher hp motor than with a stocker, like a 6 or 4 banger.

 

If your PVCR's are too small, the meter won't go up high enough, and power will suffer because the engine is still too lean. You can drill out the PVCR's with a small drill bit in a fingertip drill bit holder. If the PVCR's are too big, you will see a big jump in the meter readings, and maybe a puff of black smoke when accelerating. You see that alot in turbo cars that are blowthrough.

 

Now that you have the power valve mixture correct, try some different power valves to see what drives the best with your combination.

 

You should use a power valve that is about 2 inches of mercury below the LOWEST manifold vacuum reading you get on cruise and idle (in gear for automatics). If the power valve flutters open at idle, it can act as a pump, and push extra fuel into the main well, causing a drip from the booster venturis. If the power valve opens a lot while you're driving down the road, your gas mileage will suffer.

 

Hope that this helps you get it tuned right. I'd bet you have several things going on, all of which are covered.

Edited January 19, 2010 by dr_hunt

[long240project]

"60 over 350, squared, line honed and torque plate honed Keith Black hypereutectic pistons. Speed pro rings. 6" Elgin 5140 rods with ARP bolts. Internaly balanced, clevite bearings, ARP bolts used throughout engine, Dart Pro 1 200cc heads, cast crank, crane cam 228@.05 480 lift. 140 amp alternator, weiand water pump, AZC radiator and taurus two speed fan"

 

NOT 383 from this description....

[Sparks280zt]

"60 over 350, squared, line honed and torque plate honed Keith Black hypereutectic pistons. Speed pro rings. 6" Elgin 5140 rods with ARP bolts. Internaly balanced, clevite bearings, ARP bolts used throughout engine, Dart Pro 1 200cc heads, cast crank, crane cam 228@.05 480 lift. 140 amp alternator, weiand water pump, AZC radiator and taurus two speed fan"

 

NOT 383 from this description....

 

It has the 400 crank, just didn't list it. It is in the other paper work I have.

 

Is that what you were thinking I was missing?

[rsicard]

Sparks280Z: Use a return type regulator. http://www.summitracing.com/parts/AEI-13301/

[Sparks280zt]

Sparks280Z: Use a return type regulator. www.summitracing.com/parts/AEI-13301/

 

Thanks, I purchased one from Summit. I ordered it Monday night and it was here in less than 24 hours, that was fast!

[John Scott]

Out of box Holleys are safely designed for sea level applications. They're typically pig rich since fouled plugs are a lesser liability than melted pistons. Unfortunately the compromise is driveability and optimum performance levels. Best bet is to go wide band. I have 383, AEM wideband, HP 750 244@ .050, ..613/585 ISKY, Vic Jr, Mallory 140 and return style reg like G-Vette's 1st pic above. T56 (.62 6th) w/ 3.7 rear and get easy mid 20's mpg cruising 75-80.

 

Diddling with the jets and powervalve restrictions is just the tip of the tuning berg.

I got tired of all the compromises I was dealing with my HP carb and started researching, eventually drilling and tapping out my $600+ carb and making my own bleeds, and tuning myself. I'd post my specs for my 750, but its absolutely pointless since I'm at high altitude and every engine combo will be different. Not that you will have to, but as a hint I'm a mile from any Holley rule of thumb spec and have changed every emulsion hole, air bleed and jet. The result has been a carb that performs like FI, no stumbles hiccups, or misses, flat cruise and wot AFR and for the first time my plugs stay clean.

Not for the fainthearted as you can turn your carb or your engine into a pile of junk as well.

 

 

Here's endless reading from here, some good advice, some just big egos,...good luck!:

http://www.innovatemotorsports.com/forums/

[Sparks280zt]

Out of box Holleys are safely designed for sea level applications. They're typically pig rich since fouled plugs are a lesser liability than melted pistons. Unfortunately the compromise is driveability and optimum performance levels. Best bet is to go wide band. I have 383, AEM wideband, HP 750 244@ .050, ..613/585 ISKY, Vic Jr, Mallory 140 and return style reg like G-Vette's 1st pic above. T56 (.62 6th) w/ 3.7 rear and get easy mid 20's mpg cruising 75-80.

 

Diddling with the jets and powervalve restrictions is just the tip of the tuning berg.

I got tired of all the compromises I was dealing with my HP carb and started researching, eventually drilling and tapping out my $600+ carb and making my own bleeds, and tuning myself. I'd post my specs for my 750, but its absolutely pointless since I'm at high altitude and every engine combo will be different. Not that you will have to, but as a hint I'm a mile from any Holley rule of thumb spec and have changed every emulsion hole, air bleed and jet. The result has been a carb that performs like FI, no stumbles hiccups, or misses, flat cruise and wot AFR and for the first time my plugs stay clean.

Not for the fainthearted as you can turn your carb or your engine into a pile of junk as well.

 

 

Here's endless reading from here, some good advice, some just big egos,...good luck!:

http://www.innovatemotorsports.com/forums/

 

 

Thanks John,

 

Looks like I will be moving to Laramie, WY in August, and the elevation there is 8000 ft!

[dr_hunt]

Out of box Holleys are safely designed for sea level applications. They're typically pig rich since fouled plugs are a lesser liability than melted pistons. Unfortunately the compromise is driveability and optimum performance levels. Best bet is to go wide band. I have 383, AEM wideband, HP 750 244@ .050, ..613/585 ISKY, Vic Jr, Mallory 140 and return style reg like G-Vette's 1st pic above. T56 (.62 6th) w/ 3.7 rear and get easy mid 20's mpg cruising 75-80.

 

Diddling with the jets and powervalve restrictions is just the tip of the tuning berg.

I got tired of all the compromises I was dealing with my HP carb and started researching, eventually drilling and tapping out my $600+ carb and making my own bleeds, and tuning myself. I'd post my specs for my 750, but its absolutely pointless since I'm at high altitude and every engine combo will be different. Not that you will have to, but as a hint I'm a mile from any Holley rule of thumb spec and have changed every emulsion hole, air bleed and jet. The result has been a carb that performs like FI, no stumbles hiccups, or misses, flat cruise and wot AFR and for the first time my plugs stay clean.

Not for the fainthearted as you can turn your carb or your engine into a pile of junk as well.

 

 

Here's endless reading from here, some good advice, some just big egos,...good luck!:

http://www.innovatemotorsports.com/forums/

 

LOL, so true, which is why advice on changing your boosters is such misleading information. They all go together, it's not as simple as most people think. Buy a carb with downleg boosters for the best signal and tune from there. Heck, buy the holley carb tuning book, written by the Pro's that built your carb and soon you'll have it all dialed in. My book is sitting on by bookshelf in my office.

[lgoodson@pacbell.net]

My LT1 /T56 is getting 11 to 14 on the road and off mostly on. I will pull a plug and see what they look like. It is turning 2000RPM's at 70 MPH. Still trying to verify the speedo calibration. Using a Cable X converter. This could be a problem and also the rear diff ratio.

[Sparks280zt]

OK a bit of an update:

 

I have made some longer highway trips and used 6th gear on them, the miles listed below are all highway miles, here are the results:

 

Trip 1:80 miles: 17 mpg with AC on whole trip

 

Trip 2:80 miles: 19 mpg with no AC

 

Trip 3: 150 miles: 21.45 mpg no AC

 

Trip 4: 150 miles: 21.35 mpg no AC

 

I made trips 3 and 4 today, so I was feeling pretty good. I haven't done anything to the car other than using 6th gear on the highway.

 

BUT:

 

I made one more trip

 

Trip 6: 30 miles, ALL CITY MILES, ................8.8 mpg. I wasn't babying it, but I sure as heck wasn't beating on it.

 

What would cause such great highway mpg, and poor city?

[Pyro]

what is your ignition timing (initial, max mechanical, max vacuum advance).

 

have you tried jetting down the carb until it complains? the jet back up a few sizes?