5.0 carb questions

97gtconv. · Aug 30, 2006

I'm asking some questions for my roomate and there's a couple q's that he would like to know. This is what he has...
1988 LX 5.0
306 with forged internals, gt40 heads w/bigger valves light port work, holley 4barrel 650 cfm, mallory ignition, holley blue pump, e303 cam, edlebrock rpm manifold, 373's, shorties, off-road h-pipe, Hawks racing 1.5 drop, Lakewood 50/50's out back and kyb non-adjustable up front.

1. What fuel pressure should he be running without the vacumm line on?
2. Is there a good way to show how to tune a Holley 650 4 barrel?
3. Is this a good matching engine?
4. Would 17x9 cobra r with 275/40-17's fit with spacer and some hammering on the fender well?
5. What would a be timing number for his engine?

I know there's alot of questions and data but he's a newbie with 5.0's and i really just deal with 4.6's

97gtconv. · Aug 30, 2006

anybody have anything?

trailblazr81 · Aug 31, 2006

Get a vacuum gauge to tune the carb. $15 from Napa
5-7 psi is good. Thats what the gauge on my fuel line to carb reads.
What type of carb? vacuum secondary, manual, double pump?
What compression you running?
Ive seen 275/40's out back on Fox's.

95GTAODE · Aug 31, 2006

Sounds like a nice set-up, very similar to mine.

Fuel Pressure- 6- 8 PSI, NO MORE!!! (No need to do any thing with vacumn lines- that only applies to FI cars.)

Timing- I recurved my dizzy so I get 20* advance in by 2800 RPM, and I run 16* Initial, for a total of 36*. He should shoot for the same thing.

I'm assuming the carb's a 650 DP?

Idle: With engine warm and timing set, set the floats until fuel is even with the bottom of the sight plug, then set the base idle to where you want it with the idle set screw on the throttle linkage. Attach a vacumn gauge to a manifold source, and adjust the idle mixture screws (located in each side of the primary metering block) until you achieve the maximum vacumn reading. (you will know when the vacumn peaks, then starts to drop off) Be sure to adjust each screw the same # of turns. If a vacumn gauge is not available, you can use the tach and adjust to the highest idle speed. Don't forget to re-set the base idle to where you want it.

WOT: If you feel a flat spot or slight heaitation during light acceleration, it needs a bigger pump shot, if it stumbles, then kick's in, you need a smaller shot. You can adjust the accelerator pump cam to a different hole and try again. If you run out of adjustment without curing the problem, you need a different colour pump cam.

Jetting: After a WOT run, shut it down and coast to a stop. Pull the plugs and ceck 'em- You are looking for a light tan colour... If it's rich(black, sooty), jet down, if it's lean (grey or white), jet up.

Go up and down in 2 jet size increments on both ends of the carb until you get it where you want it.

emeraldcoupe · Aug 31, 2006

95GTAODE said:
Sounds like a nice set-up, very similar to mine.

Fuel Pressure- 6- 8 PSI, NO MORE!!! (No need to do any thing with vacumn lines- that only applies to FI cars.)

Timing- I recurved my dizzy so I get 20* advance in by 2800 RPM, and I run 16* Initial, for a total of 36*. He should shoot for the same thing.

I'm assuming the carb's a 650 DP?

Idle: With engine warm and timing set, set the floats until fuel is even with the bottom of the sight plug, then set the base idle to where you want it with the idle set screw on the throttle linkage. Attach a vacumn gauge to a manifold source, and adjust the idle mixture screws (located in each side of the primary metering block) until you achieve the maximum vacumn reading. (you will know when the vacumn peaks, then starts to drop off) Be sure to adjust each screw the same # of turns. If a vacumn gauge is not available, you can use the tach and adjust to the highest idle speed. Don't forget to re-set the base idle to where you want it.

WOT: If you feel a flat spot or slight heaitation during light acceleration, it needs a bigger pump shot, if it stumbles, then kick's in, you need a smaller shot. You can adjust the accelerator pump cam to a different hole and try again. If you run out of adjustment without curing the problem, you need a different colour pump cam.

Jetting: After a WOT run, shut it down and coast to a stop. Pull the plugs and ceck 'em- You are looking for a light tan colour... If it's rich(black, sooty), jet down, if it's lean (grey or white), jet up.

Go up and down in 2 jet size increments on both ends of the carb until you get it where you want it.

good info. i was going to post the same thing

trailblazr81 · Aug 31, 2006

95GTAODE said:
Jetting: After a WOT run, shut it down and coast to a stop. Pull the plugs and ceck 'em- You are looking for a light tan colour... If it's rich(black, sooty), jet down, if it's lean (grey or white), jet up.

But be careful!!! She'll be hard to turn and stop with the motor off!!!

jeremey thomas · Aug 31, 2006

in all honesty the engine combo looks great however i have found in my experiences with 5.0 carbed engines what most people think is enough,is too much.i ran a holley 570cfm street avenger allthe way to 370.49 hp dynoe tuned at www.bieberfever.com.we tried a 670 street avenger first and all i could pull was 357.61hp.my combo was alittle more involved than his as i had afr185's for heads.and was using an edelbrock performer rpm air gap with a 1/2 phenolic carb spacer.trust me if he doesnt have the carb spacer tell him to pony up the extra 40 bucks.horsepower gain was minimal,but torque jumped from 390ftlbs to just over 415ftlbs.greatest 40 bucks i ever spent.

jeremey thomas · Aug 31, 2006

timing should be between 14 and 16 btdc.if he plans to spray it he need s to drop to 10 to 12 btdc. as far as the cobra r's go on my 90 vert i am running 275/40/17's on the rear with no problem,using bbk specific rate springs.as long as there is no passengers inthe rear he is fine.i have kids that like to ride so i am currently changing to motorsport b springs because with me my wife and 3 kids in the car i get minimal scrub.however 275's wont work in the front with the early 90 and down fenders.he will be limited to 255's on the front.

97gtconv. · Aug 31, 2006

Thanks for the great info. He said for compression it's pretty high as where he can't run anything less than 93. He estimates 10:1 and higher. He says the GT40-P heads were milled but doesn't know how much was takin off.

His carb is a Holley 650 SINGLE pumper. It won't idle less than 1K rpms... He's had trouble tweaking the Holley for awhile now and is probably getting ready to give up and get a Edlebrock 600.

Should he stay with the Edlebrock RPM and Holley 650 single pumper or go with Edlebrock 600 (p/n- 1406) with Edlebrock RPM Air Gap with spacer?????

And last what do u think he should put down hp and torque wise???

rd · Aug 31, 2006

My similar combo in an 82 shell runs high 12's on motor.

I have a Holley 600 List No 80457, the basic vacuum secondary Holley with a Ford kickdown for the C4.

Mine has a Rhodes 270 deg cam and Rhodes lifters, and will idle nicely at 600-800 all day. I do have a fairly loose 10 in converter, which makes idling easier.

The E cam may be a bit much, but this should still idle at 850 or less, easily.

If you are going for performance, I would stay with the Holley. Only prob is that is tuneable in every way, and if you get it off, you may not know where you went wrong.

My Holley 600 has 68 jets in front, original plate in the rear, and the lightest spring in the Holley spring kit in the secondary diaphram. That's about it for mods. I have about 6-8 deg basic timing, centrifugal advance only, with about 32 deg total, with the lightest springs in the Crane distributor kit installed. Timing is conservative becasuse it gets sprayed. Ignition is by a 1980 Duraspark.

I use a Holley mechanical fuel pump, and no regulator, yet. Shows 5-6 psi on the gage at the nitrous solenoid, and has handled the 100 shot just fine.

That setup should run real strong. I have iron Gt40's at present, and AFR's in the box awaiting installation.

I apprectiate the comment on the smaller carb being good up to much more power than I am making.

rd · Aug 31, 2006

Also note that float level in the carb, and the pickup in the tank, fuel lines, etc can affect the fuel flow. I have an original carbed style tank and pickup assembly, so I do not have the prob of the pump having to pull fuel up out of the top of the tank.

The stalling sounds like a low float level prob.

97gtconv. · Sep 1, 2006

the pickup tube is a cartech pickup tube. thanks

97gtconv. · Sep 1, 2006

for the great info

5.0 carb questions

97gtconv.

Member

97gtconv.

Member

trailblazr81

Member

95GTAODE

New Member

emeraldcoupe

trailblazr81

Member

jeremey thomas

New Member

jeremey thomas

New Member

97gtconv.

Member

rd

rd

97gtconv.

Member

97gtconv.

Member

Similar threads

5.0 carb questions

Member

Member

Member

New Member

Member

New Member

New Member

Member

Member

Member

Similar threads

Privacy & Transparency

Privacy & Transparency