Sitting Bull

Hey Everybody,

I switched to an Edelbrock Performer 600 cfm carb from my hatched old QJet, which was going south on me. Problem is I've lost a lot of mpg

The QJet gave me 19.5 mpg around town and freeway. But the Performer is only giving me about 14 mpg.

I don't know what the precise jets and rods were in the Performer to begin with but the carb was a fresh rebuild from the local speed shop. Who does the rebuilds I don't know but I'm sure that the carb was reassembled with stock settings, rods- and jets-wise.

We have taken the jets down two sizes from stock and the rods are also one or perhaps two steps leaner. The altitude around here is 3500 ft. The engine parts are in my sig. It is basically a mild 305 pushing about one hp per cubic inch.

Can anybody give me a specific set of jets and rods to try with my setup? Surely the Performer carb is capable of coming fairly close to the QJet for mileage, can't it? I don't care if it can get 19.5 mpg but it must be able to get at least 18 mpg or so, shouldn't it???

All help is really appreciated

Sonix

iTrader: (1)

sorry, i'm of no help with respect to edelbrock carbs, I was just curious what went wrong with your q-jet that made you buy a new carb? sounds like an expensive solution....

Apeiron

You can keep going leaner on the cruise step on the rods until it starts to stumble. Have you tried shortening the pump shot? That can have a big impact on city mileage.

F-BIRD'88

Don't assume it has th4e stock baseline jetting. take the top off and look.

Here is the base calibration for the 1406 carb.

primary jet .098 sec jet .095 metering rod 7547 (.075x .047)

if this is what you have in your carb. you *can* do this adjustment working with the stock parts you should have.

You can switch the primary and secondary jets around.

this will lean out the primary cruise and power jetting a little
and richen the sec jetting.

see if this helps.

other wise you will need a calibration kit with some jets and rods to work with.

you need to verify what you have in there now.

Then lean out the primary jetting untill you find the lean limit. ( bog, surge) then go up 1or 2 size until the driveability comes back.
the primary jet and rod affects low cruise driving 25mph and better.
below that speed the idle circuit makes the car go.
the idle circuit is jetted by the idle feed restriction and idle air bleed.
Once you've dialed in the primary side jetting you can lean out the idle circuit with some thin wire in the idle feed restriction. (trial and error) again find the lean limit and go up a little. No drilling air bleeds or fruggin up the carb is required. if it does not work just remove the wire from the idle feed restriction.

nce you have found the lean limits and tell me the jet rod combo i will tell you the final rod jet combo to restore the power mode calibration. (proper combo of jet and rod major and minor step diameter)
need to know where you are now. and where the lean limit is. Do you have access to jets and rods?

here's your home work...there will be a test

Do you have a AFR guage to work with? or a o2 sensor and multi meter.

Onless you have this to work with the only way to find best mileage is to find the lean stumble limit and work up ( richer) optimum fuel mileage cruise AFR is between 15:1 and about 17.5:1 AFR How lean you can rundepends on cylinder to cylinder fuel distribution. Eventually one of the 8 cylinders will be too lean and misfire.

it is winter now. You always burn more gas during the winter... In July Aug you will be able to run leaner jetting.

contact

try putting in lighter, metering rod springs.
if the car runs just as good, or better,
something is wrong.

if the carb is a refugee from a speed shop,
more than likely, everthing has been
monkeyed with.

Sitting Bull

Well, the Qjet's choke wouldn't work much at all, sometimes it just died of fuel starvation under acceleration, and there were a few other annoyances, as well

When a carb gets this way and none of your mechanics can figure out its problems then it is time to let it go. I suppose there were flaws in certain mating surfaces or something along that line. Just one too many rebuilds ...

Sitting Bull

Actually, we did have the primaries leaned out to the point of stumbling. But it was mostly when the engine was cold. Anyway we put in the next step richer rods and that cured the stumbling. I also had the accelerator pump set for the richest shot but it just made the car too twitchy to enjoy much when driving at low rpm. So we moved it back to the lean shot and it is much more driveable now.

When are you coming back to Calgary? I was expecting you this summer, with your spare torque convertor ready to fit into the Sport Coupe

Sitting Bull

No, it is a quality rebuild. Everything is shiney and looks new. Just over $300 with gst and whatnot. That's why I bought it. I want a fairly pristine carb to work with from the start this time. My QJets had been through I don't know how many rebuilds and simply had reached the end of their road

Sitting Bull

Hey Russ,

Thanks for the write up! It might take me two or three weeks yet to get anything done on the Performer because my carb mechanic is pretty much tied up till new years. He does have the calibration kits for the 1406 carbs, though, so that will help a lot. I've bookmarked the How-to column and will review it thoroughly.

If you have any more ideas please let me know

And if the presense of the calibration kit allows you to make specific jet and rod suggestions, please do so right away.

F-BIRD'88

I recomend doing what I suggested above.

Stock jetting but everse the primary and sec jets.
This will result in the primary side being about 3 steps leaner than stock.

95 pri jet 7547 rod 98 sec jet.

heavyduty

Not totally on the subject..How do u know your getting near that much power out of your motor ? A properly tuned motor (unless it has a monster cam) should start up and idle on its own in a minute or so .....I just dont know how some of the people come up with the HP #'s they are speaking of.....305's are good motors but they are what they are 305's....takes more than a cam headers and some head work to jump from 150 HP to 300....and i dont know of any carbed motors that have excess of 300 HP getting 20 mpg even with over drive...Just my observation

Sitting Bull

heavy,

I used computer modeling and knowledgeable peoples' advice, and I think it is fairly close

MPG is my observed mileage around town and the freeways here. Not so unusual, five7kid gets about 18 in Denver.

heavyduty

Computer models are what they are ...computer models...I have and lucky and have the knowledge of Eddie Hill 's (top fuel world champion crew cheif) ...He just happens to have a speed shop..i have spoken at length with him on several occassoins about horsepower and such...300 naturally aspirated HP doesnt come that easy...the computer models and add in magazines have the fine print that many dont notice....most the motors are balances blueprinted and etc....not trying to be a smartbutt....but..throwing big cam or any other than stock cam intake headers and some ported heads are only worth so much HP...tell me how it takes a (maybe 150HP 305) and how those modes are worth 150 HP ....?... i have seen many many many people that just totally absolutely knew they had 250 or 300 HP put there hot rod on the dyno and got a really rude awakening....Now when ya hit the magic buttom and throw the giggle juice at it everyone smiles but the fords ...here is the link to my buddies speed shop i spoke of...he was Eddie Hill's (first guy to run in the 4"s) crew chief..http://www.autoshopmotorsports.com/

five7kid

iTrader: (14)

19.8 last fill-up. High 16's/low 17's more common, depending upon the amount of freeway included.

Never had it on a dyno, would be nice. Chevy High Performance magazine dyno'd their "My Generation Camaro" 350 with TES headers & single 3" muffler at 380. Their drag strip #'s were about the same as mine, but they had better gears - most of their problems were caused by the difference between the dyno headers and installed-in-car headers (the LG4 version of the TES have a big restriction at the EFE valve).

Say what you want about formulas and calculations, but drag strip conversions to HP have been shown to be more accurate than chassis dyno. Using the sig values, my current combo is putting down just under 300 RWHP, which, assuming 25% drivetrain loss, would be about 365 gross at the flywheel. The 305 was about 240/300 based on the same calculations (everything but the cam was the same on the 305 as is currently on the 350 - oh, the intake wasn't gasket matched on the 305, either).

Sitting Bull

heavy,

I think five7kid has largely answered your questions and I don't want to polute this thread with arguments about who says what and mine is better than yours, etc. Suffice to say that my observations and calculations are based upon gross engine hp, i.e., hp with no parasitic drag involved.

A lot of people are surprised to learn that the lowly LG4 engine will magically produce another 30 to 40 hp simply by giving it a set of headers and 3" exhaust pipe. That is how bad the LG4's exhaust was as it rolled off the line in your typical thirdgen.

Fast355

iTrader: (2)

My 305 is not carbed, but is very similar to Sitting Bull's and five7kid's. You would be suprised at how easy it is to get over 300 FWHP out of a 305 with old technology. I am at 278 RWHP on a Mustang Dyno with the old L82 grind(w/1.6:1 rockers), ported factory 305 TPI castings, a good Holley Projection intake, good 660 CFM TBI, 2 1/4" outlet cast iron manifolds, 2 1/4" into 3" Y-pipe, High Flow catalytic converter, Big Block 70 Series Flowmaster Single in Dual out muffler, all accessories, passes smog, and even had a 7 bladed clutch fan hanging on the waterpump.

That being said, you should be getting more than what you are getting in fuel mileage. My old 1406 would pull 16-17 MPG average on top of a performer RPM in my G20. That was in a highly tuned state though. Cruise A/F mixtures were around 16:1, idle about 14.2:1, and WOT about 12.4:1. I dropped a number on both the jet and metering rod, switched to a 8" power spring instead of 4", and finely tweaked the Idle Mixture until I got good off-idle respons and low emissions. Would pass smog with a little tweak to the timing. I will say however that I never exceeded the MPG a well tuned Q-Jet could deliver.

heavyduty

Hey i agree about my dang car getting better fuel mileage...i am open for suggestions...i say my avg is 13mpg in town and on the road...its about 900 ft altitude here ...my plugs look good..actually a tad lean ..they look like new..snow white...and i have 2400 miles on the rebuild...it runs great ....just hope the fuel deal gets better

Sitting Bull

OK all,

Here is what was and what now is-

When we pulled apart what I have in the Performer, it turned out that we had 92 primary jets and 6842 primary rods. Secondary jets were 95.

We changed the primary jets from 92 to 89. And that is all we changed. Both the primary rods and secondary jets were left unchanged at 6842 and 95 respectively.

So, I shall drive it like this for a while and see what we come up with for mpg

MaxxMitchell

iTrader: (4)

LOL bringing it back from the dead. Any updates on tuning and mpg?

Sitting Bull

Well, I haven't been feeling too good lately so there is only a little to report. The jets on the main side are now 89s and at present the Camaro is giving me about 15.5 mpg around town.

So a definite improvement but still not up to my old QJet's standards. Perhaps with the milder weather it'll work even better

Sitting Bull

OK, here is the latest. 371 kilometers using 48 litres of fuel.

... Equals 18.2 miles per gallon. Pretty darned good ...

But this carb certainly appears to be weather sensitive.

Tobias05

Yeah, my idle will change by a couple hundred RPM from day to day due to weather.

...Would changing out the accelerator nozzle to, say a .23 help you out any without handicapping your performance? .28 is stock for the 1406.

Sitting Bull

Good question ... I don't know

If I can save up a couple hundred dollars I'm going to see if I can get this engine dyno-tuned. Will let everyone know what happens

Tobias05

good luck, interested in your results once you make it to the dyno!

Rustydawg

Sitting Bull, with the 371 Kms travelled and 48 Litres burned from this fillup I calculate 21.8 miles/Imperial gallon - which is pretty darned good for one of our carburated fossils. No reason not to try and get it better, of course... Is your figure using U.S. Gallons?

I just searched for some metric conversion pages to confirm my 'correction factor' to convert from litres and Km to MPG. Working with 4.54 litres to an imperial gallon and 1.609 Km to a mile, multiply your Km per litre figure by 2.82 and you get miles per Imperial gallon.

For comparison purposes, I just filled up my recently acquired Taurus wagon (3.8 litre EFI V6, Auto O/D, approx 3500 lbs) and got 24 Miles/gallon mixed city & highway. To think you were doing even better with the Q-jet... Must be that thin Cowtown air!

Sitting Bull

Hey Rusty,

Yeah, I'm using US gallons for the standard because 9 out of 10 people on the board are Americans.

But it truly is tempting to use imperial gallons and just freak everyone out with our wild British mpgs, isn't it

SteelTownMadDog

iTrader: (2)

Amazing how you guys are getting just 40 RWHP less than me with your 305s with stock heads and mild flat tappet cam vs my 355 w/ roller cam and Trick Flow heads. </sarcasm>

From the parts you have in your sig, you're no where near 300 HP in my EXPERIENCE. I would say between 230-250 on a cold day.

BTW, I had a Performer 1411 750cfm on my 355 before I switched awhile back, and was getting almost 23 MPG US (or 27 Imp) on the highway. But I am getting better mileage now with the street/strip prepped QJet. It's just plain logic when you consider the size of the primaries on a QJet vs any other squarebore carb.

Sitting Bull

Hmm, I don't have stock heads and I've repeated quite often that my 300 hp estimation is based on hp with no parasitic drag at all. Anyway, this is a thread on carbs, not hp, so let's keep to the topic

84z28350

Whats up with all the "**** up the rope" contests...

Who really cares if the HP he claims is 100% accurate or not? boo hoo.

Ive put my engine through a couple of modeling programs and they come up with anywhere from 380-420hp and 415-490ft/lb torque. Though i highly doubt its anywhere near that!

But anyways, this thread is about edeljunk errr i mean edelbrock carbs not whose digital engine simulation is more accurate.

So keep the EDELBROCK CARB replys coming, ill be starting to tune mine soon!

RLZ28

I have a 1406 as well, I had to calibrate mine to the higher altitude I live in. 6,000 Ft. If you purchased from a local speed shop you may not have received a manual on the carb. Below is a link to the owners manual on edlebrock carbs. Has the calibration charts in there. This may help.

http://www.edelbrock.com/automotive_...ers_manual.pdf

sleeper84

iTrader: (1)

guys, you probably really dont care....but i've been working on Q-jets since i was 14, my dad was a g-m trained mechanic and we've only happend upon 2 of them that we couldn't get to run after rebuilding (one cracked body and one that someone had re-drilled the secondary rod openings on) the Q-jet is w/o a doubt, the best street/performance carb you can get.... the Edelbrock/Carter carbs are alright (i vastly prefer a holley to them though), but the Q-jet was designed to be a more versitile carb, being used on anything from a 4.3V6 to 454's... a little knoledge of the carb, and a g-m parts guide w/ the primary spring rates, rod sizes and jet bores, and a little help from Edelbrock (they sell some nice aftermarket stuff for Q-jets) or a g-m parts manager, and you'll have the ultimate carb for anything on the road....

Sitting Bull

Well, some really exciting news this time!

299 kms using 39 litres equals ... 18.06 miles per gallon

The last post here was in error (3 am delusions ) and this is the correct mpg. Seems to be settling right in on the 18 mpg range.