Carburetor advice...

[Forrest39]

Aloha everybody!

Right now I'm getting about 11 MPG going down the road at 70 turning 2600 RPM. There is no choke and it runs a little fat anyway so I'm planning on replacing the Edlebrock carb with Holley 4160 600CFM unit. The engine is a 302 bored .030 over with Edlebrock performer RPM 6037 heads and 7122 cam. I'm after a little better fuel economy and cleaner plugs without trading up to a 5-speed. I'm hoping to improve to as close to 20 MPG as possible. I have a 2.88 rear end and 225/45-15 tires.

Yeah, I know..
... Slow down
... If you want good milage drive an Alpine (or honda)
... You didn't buy a spendy car just to bitch about gas prices did you?

So the usual digs aside, can anybody forward any experiences with these two carbs?

http://www.summitracing.com/parts/hly-0-80457s

Or this...

http://www.summitracing.com/parts/hly-0-1850s


Thanks in advance, -Kevin

 

[dlyle]

Didn't a track test of a stock Tiger return over 20 mpg while driving 100 mph? Seems to me even with a warmed up 302 you should be getting closer to 20 on the freeway.

 

[Jeff F]

I would expect that you can get much better than that. Rather than switch to something else (assuming that your existing carb is something reasonably street-able) I think your time and money would be better spend getting your existing carb setup properly. For a couple hundred bucks you can get an air-fuel gauge to install temporarily so you can see what is really going on. If you aren't comfortable doing it yourself you could always find a carb tuner guy and a dyno with a wideband. Anyone competent should be able to get it tuned up in a couple of hours.

Even if you get a new carb, it will still need to be jetted and setup for your particular engine.

 

[Warren]

Mods

I think that car has a 2.72 also hard to say if tachometer ever got sync'ed

Maliburevuen aka Gary had overseen most all the mods.

I have the same set of gears ring n pinion posi and stuff on the floor of the garage waiting to go in MK1A but now she's gone.

 

[chirodoc]

Edelbrock carb

Get an Edelbrock calibration kit which has jets and metering rods. Out of the box the carb is about 2-3 jet sizes too rich. Access an exhaust gas analizer or an A/F meter as Duke did for his 347. You should have less tuning problems with an Edelbrock Performer than the Holly 600 cfm.

 

[wag123]

Get an Edelbrock calibration kit which has jets and metering rods. Out of the box the carb is about 2-3 jet sizes too rich. Access an exhaust gas analizer or an A/F meter as Duke did for his 347. You should have less tuning problems with an Edelbrock Performer than the Holly 600 cfm.

+1
For the street, the AFB is better.

 

[0neoffive]

Somethin' Ain't Right

Aloha everybody!

Right now I'm getting about 11 MPG going down the road at 70 turning 2600 RPM. There is no choke and it runs a little fat anyway so I'm planning on replacing the Edlebrock carb with Holley 4160 600CFM unit. The engine is a 302 bored .030 over with Edlebrock performer RPM 6037 heads and 7122 cam. I'm after a little better fuel economy and cleaner plugs without trading up to a 5-speed. I'm hoping to improve to as close to 20 MPG as possible. I have a 2.88 rear end and 225/45-15 tires.

In a quick nut shell: Something's not right. You should be getting way better mpg with that pile of bolt-on equipment. . . . . .before swapping lots of parts around; check all the basic specs. The usual dizzy timing and cam timing (not easy) and down jet until the plugs are self cleaning. Go from there . . . .

 

[Forrest39]

Aloha everybody!

Right now I'm getting about 11 MPG going down the road at 70 turning 2600 RPM. There is no choke and it runs a little fat anyway so I'm planning on replacing the Edlebrock carb with Holley 4160 600CFM unit. The engine is a 302 bored .030 over with Edlebrock performer RPM 6037 heads and 7122 cam. I'm after a little better fuel economy and cleaner plugs without trading up to a 5-speed. I'm hoping to improve to as close to 20 MPG as possible. I have a 2.88 rear end and 225/45-15 tires.

In a quick nut shell: Something's not right. You should be getting way better mpg with that pile of bolt-on equipment. . . . . .before swapping lots of parts around; check all the basic specs. The usual dizzy timing and cam timing (not easy) and down jet until the plugs are self cleaning. Go from there . . . .

Good advice everybody, thanks!

This brings me to my next question... I have an MSD distributor with electronic ignition. It has no vacuum advance. I'm not sure how much advance I'm getting with this arrangement... Is it typical to have the vacuum. Removed?

I'll look into an Edlebrock calibration kit before swapping out the carb...

Cheers! -Kevin

 

[TigerBlue]

Vacuum Advance

We got near a 20 average on the round trip to Suni and the run to Monterey this year. The black Tiger was barely approaching 15 before some tuning.

I learned at a fix in that the cruise fuel air ratio was awful rich. Went to much smaller primary jets. (remember at cruise power you are driving a 2 bl carb. The secondaries are shut and power jets unused.) Lean? yes very, no problem.

I also discovered that my vacuum advance was disabled. Connecting it to the manifold vacuum port helped too and it idles cooler.

Specs? 260, performer carb Edelbrock 500, performer cam, intake 289 performer (not the performer RPM), Heads 289 HIPO compression only about 9:1. Posi 331 rear end Close R toploader. Yes 20 mpg at 70 - 75 and about 3,500 rpm!

Why? It works for me. I love the shift mechanism of the close ratio trans and the narrow gear spacing is great when you hurry through the gears. (Edit I am also stingy and relatively lazy.)

Rick

 

[Moondoggie]

Good advice everybody, thanks!

This brings me to my next question... I have an MSD distributor with electronic ignition. It has no vacuum advance. I'm not sure how much advance I'm getting with this arrangement... Is it typical to have the vacuum. Removed?

I'll look into an Edlebrock calibration kit before swapping out the carb...

Cheers! -Kevin

n,

If you want better mileage lose the MSD distributor it will eventually strand you on the highway anyways so it's just a matter of time. Pertronics makes a nice plug and play simple vacuum advance distributor for your 302 just make sure you know what cam you have so that you can get the right distributor gear on it. If you want to keep the mechanical distributor then look around for a K code dual point ford distributor ( good ones go for around $500) rebuild that and install a pertronics ignition module and you are good to go. Mechanical distributors are used mostly for racing and are fussy on street applications...just depends how serious you are about horsepower

Moondoggie

 

[TAH_Tiger]

We got near a 20 average on the round trip to Suni and the run to Monterey this year. The black Tiger was barely approaching 15 before some tuning.

I learned at a fix in that the cruise fuel air ratio was awful rich. Went to much smaller primary jets. (remember at cruise power you are driving a 2 bl carb. The secondaries are shut and power jets unused.) Lean? yes very, no problem.

I also discovered that my vacuum advance was disabled. Connecting it to the manifold vacuum port helped too and it idles cooler.

Specs? 260, performer carb Edelbrock 500, performer cam, intake 289 performer (not the performer RPM), Heads 289 HIPO compression only about 9:1. Posi 331 rear end Close R toploader. Yes 20 mpg at 70 - 75 and about 3,500 rpm!

Why? It works for me. I love the shift mechanism of the close ratio trans and the narrow gear spacing is great when you hurry through the gears. (Edit I am also stingy and relatively lazy.)

Rick

302 with petronic, Holley 600 ccm, 5 speed at
70 equals 24 mpg for me.

 

[TigerBlue]

More Advanced

More Advanced timing is key to better gas mileage. Does not replace mechanical advance present in all distributors. Low load cruise is high vacuum and you need an operating vacuum advance distributor for better gas mileage. WOT = no vacuum no vacuum advance just the mechanical. Total mech timing is not changed/should be the same with or without that vacuum pot.

PS Dawg Black Tiger has an MSD Dissy

Tuned the same one brand of distributor will deliver the same mileage and performance as any other

More facts and science for those with open minds on this subject: http://www.jeepforum.com/forum/f12/manifold-vs-ported-vacuum-994651/

 

[Forrest39]

302 with petronic, Holley 600 ccm, 5 speed at
70 equals 24 mpg for me.

That's great news!
To keep the data apples to apples as much as possible, could you please forward your specs for gearing and tire size? I'm hoping to put in a 5-speed but that may still be down the road a bit...
Cheers, -Kevin

 

[Forrest39]

More Advanced timing is key to better gas mileage. Does not replace mechanical advance present in all distributors. Low load cruise is high vacuum and you need an operating vacuum advance distributor for better gas mileage. WOT = no vacuum no vacuum advance just the mechanical. Total mech timing is not changed/should be the same with or without that vacuum pot.

PS Dawg Black Tiger has an MSD Dissy

Tuned the same one brand of distributor will deliver the same mileage and performance as any other

More facts and science for those with open minds on this subject: http://www.jeepforum.com/forum/f12/manifold-vs-ported-vacuum-994651/

Hmmmmm...
Looks like I need to shift priorities here a little. Before I start making carbeuretor changes, I should start with the ignition system.
I think I'll spin off a different thread for anybody looking for just ignition system opinions.

Thanks for all of the helpful responses!
-Kevin

 

[at the beach]

Kevin,

First, I did a 3,500 mile SUNI trip 5 years ago in one of our Tigers and averaged 24MPG. Most of the time we ran at 75MPH. I set the jetting using a wide band O2 sensor so at cruise we'd run at 15.5 to 1. (Hi-Po 289, Holley 4160 600 CFM with Vac. secondaries)

Second, Mike Michels started with my approach and then improved on it. He leaned the primaries 2 more jet sizes. (My guess is that he's near 17:1 at cruise.) I think he was in the 26 to 27 MPG range on his round trip to Monterey.

I know an all mechanical distributor is not optimum for MPG but I suspect your main problem is your jetting.

About distributors:
Both Mike and I run distributors with a vacuum advance canister. This is more sophisticated than the pure mechanical units. I set the distributor's mechanical advance to give about 35 degrees at full advance. (I set up the advance curve to be "all in" at about 2400 RPM (two of the thinnest wire springs out of an aftermarket spring kit usually does the trick). full manifold source)

Our small lightweight Tigers need less than fifty HP to cruise at 70MPH. My engines all make this at idle. So if you are at 3000, you're only using about a third of the power your engine is then producing. It's lightly loaded.

At low loads the engine produces high vacuum and the high vacuum will cause the vacuum advance cannister's diaphram to pull in more advance (up to about 10 or 12 degrees) than the mechanical alone. This extra (vacuum advance) timing improves the mileage. And don't worry, when you want performance and stomp on the gas vacuum drops so the cannister has no effect and the distributor reverts to being purely mechanical like a dual point.

Unless you are so stock that you still insist on using points, there is no performance advantage to an all mechanical dual point. Today, a properly set up Autolite vacuum advance distributor with a Pertronix 2,3 or with an HEI module will out perform any dual pointed dizzy for both raw horsepower and MPG.

Ford used the dual point design for a very limited amount of time and then never used it again. Any guess why Ford stopped using that design? Was it possible Ford engineers had a better idea?

About the Carb:
Holley says a 600CFM is too large for a 260-289-302.
My experience is that a 600 CFM Holley is OK on a Tiger that is properly jetted (like Mike's or ours) at sea level. However, tests with a wide band O2 meter have showed me that 600 CFM Holleys loose precision when at or above 5,000 feet. They still work but the thinner air does not allow them to operate as well as they do at lower altitudes. Above 5,000' I usually see the mixture too lean at idle and at lower revs and too rich at higher loads and RPMs. Road tests at elevations between 8 and 11-thousand feet (Beartooth Highway in Montana) show that just adding a little gas can open the carb's power valve circuit causing a massively rich condition. For most, these altitudes will never be a factor, but if I spent significant time above 5-thousand feet, I'd probably switch to a 450 CFM Holley (but those don't have a PCV valve port so that's something else to figure out).

I certainly prefer running a small 4 barrel instead of a 2 barrel. As Rick pointed out the majority of the time we are only running on the primary circuit. So you can jet the primaries very lean for MPG. Then as you get on the gas the (jetted richer) secondaries and perhaps the power valve circuits provide the needed mixture richening.

good luck

bt
at the beach

 

[michael-king]

Kevin,

First, I did a 3,500 mile SUNI trip 5 years ago in one of our Tigers and averaged 24MPG. Most of the time we ran at 75MPH. I set the jetting using a wide band O2 sensor so at cruise we'd run at 15.5 to 1. (Hi-Po 289, Holley 4160 600 CFM with Vac. secondaries)

Second, Mike Michels started with my approach and then improved on it. He leaned the primaries 2 more jet sizes. (My guess is that he's near 17:1 at cruise.) I think he was in the 26 to 27 MPG range on his round trip to Monterey.

I know an all mechanical distributor is not optimum for MPG but I suspect your main problem is your jetting.

About distributors:
Both Mike and I run distributors with a vacuum advance canister. This is more sophisticated than the pure mechanical units. I set the distributor's mechanical advance to give about 35 degrees at full advance. (I set up the advance curve to be "all in" at about 2400 RPM (two of the thinnest wire springs out of an aftermarket spring kit usually does the trick).)

Our small lightweight Tigers need less than fifty HP to cruise at 70MPH. My engines all make this at idle. So if you are at 3000, you're only using about a third of the power your engine is then producing. It's lightly loaded.

At low loads the engine produces high vacuum and the high vacuum will cause the vacuum advance cannister's diaphram to pull in more advance (up to about 10 or 12 degrees) than the mechanical alone. This extra (vacuum advance) timing improves the mileage. And don't worry, when you want performance and stomp on the gas vacuum drops so the cannister has no effect and the distributor reverts to being purely mechanical like a dual point.

Unless you are so stock that you still insist on using points, there is no performance advantage to an all mechanical dual point. Today, a properly set up Autolite vacuum advance distributor with a Pertronix 2,3 or with an HEI module will out perform any dual pointed dizzy for both raw horsepower and MPG.

Ford used the dual point design for a very limited amount of time and then never used it again. Any guess why Ford stopped using that design? Was it possible Ford engineers had a better idea?

About the Carb:
Holley says a 600CFM is too large for a 260-289-302.
My experience is that a 600 CFM Holley is OK on a Tiger that is properly jetted (like Mike's or ours) at sea level. However, tests with a wide band O2 meter have showed me that 600 CFM Holleys loose precision when at or above 5,000 feet. They still work but the thinner air does not allow them to operate as well as they do at lower altitudes. Above 5,000' I usually see the mixture too lean at idle and at lower revs and too rich at higher loads and RPMs. Road tests at elevations between 8 and 11-thousand feet (Beartooth Highway in Montana) show that just adding a little gas can open the carb's power valve circuit causing a massively rich condition. For most, these altitudes will never be a factor, but if I spent significant time above 5-thousand feet, I'd probably switch to a 450 CFM Holley (but those don't have a PCV valve port so that's something else to figure out).

I certainly prefer running a small 4 barrel instead of a 2 barrel. As Rick pointed out the majority of the time we are only running on the primary circuit. So you can jet the primaries very lean for MPG. Then as you get on the gas the (jetted richer) secondaries and perhaps the power valve circuits provide the needed mixture richening.

good luck

bt
at the beach

One of the most useful and descriptive posts.. we should save it as a locked post or in a tech section.

 

[ToyTrainGuy]

Aloha everybody!

Right now I'm getting about 11 MPG going down the road at 70 turning 2600 RPM. There is no choke and it runs a little fat anyway so I'm planning on replacing the Edlebrock carb with Holley 4160 600CFM unit. The engine is a 302 bored .030 over with Edlebrock performer RPM 6037 heads and 7122 cam. I'm after a little better fuel economy and cleaner plugs without trading up to a 5-speed. I'm hoping to improve to as close to 20 MPG as possible. I have a 2.88 rear end and 225/45-15 tires.

Yeah, I know..
... Slow down
... If you want good milage drive an Alpine (or honda)
... You didn't buy a spendy car just to bitch about gas prices did you?

So the usual digs aside, can anybody forward any experiences with these two carbs?

http://www.summitracing.com/parts/hly-0-80457s

Or this...

http://www.summitracing.com/parts/hly-0-1850s


Thanks in advance, -Kevin

I agree with most comments here that there is something really amis here, as you should be getting much better mileage with you combo.

My combo is a Dynoed 275hp original 289 with 289HP heads, properly jetted 600 cfm Holley, vacuum advance Pertronics distributor (like Moondoggie suggested), 3:31 rear with a 0.64 5th gear. Driving to SUNI, I got just under 24 mpg. I think the light foot on the pedal also contributed greatly....

 

[Maliburevue]

Craig's Engine

Kevin,

Craig's engine came with the Edelbrock 600 CFM carb. The air/fuel ratio was never measured and should have been.

Also, some mechanic Craig took the car to, replaced the distributor. Why, I don't know, so who knows how it was setup.

Gary

 

[Jeff F]

Looks like I need to shift priorities here a little. Before I start making carbeuretor changes, I should start with the ignition system.

I don't think so. If your plugs are fouled, you are waaaaaay off. Fix the carb first.

 

[Moondoggie]

Kevin,


Also, some mechanic Craig took the car to, replaced the distributor. Why, I don't know, so who knows how it was setup.

Gary

Kevin,

You need to find out what cam is in that motor so that you can get the right
distributor gear...bronze, steel, or cast iron !!! The wrong gear WILL wipe out your cam in short order.

Moondoggie