Fuel mileage

Ok guys, looking for advise. I have a 302 with a 4 barrel Holly Sniper. I just fueled up and did the math. 7 miles per gallon.

My stepson says it has too large an intake. He thinks going down to smaller size might help it run more efficiently. Is this unusual?  I mean I certainly didn’t buy the car for fuel mileage but 7 seems ridiculously low.

Ok, I'll try to help, but I'm not a Ford guy.  That shouldn't matter though because all wedge head motors like the SBF and SBC are actually very similar.

First, I'll need more info.

What is controlling timing?  An old school advance in the distributor or the Sniper EFI?  Or something else.

What is the EFI reporting as the actual air/fuel ratio?

What is your air/fuel target ratio?

Does the engine have a hotter cam?

What kind of heads?  Chamber shape makes a difference on timing.

What timing are you running now?  Is there a functioning vacuum advance?

What transmission?

What rear end ratio and tire size?

Be aware that the O2 sensor can be easily fooled by any leak, even a seemingly insignificant one, upstream or slightly downstream of the sensor.  If the sensor is getting extra air of any amount, it will skew the reading and the computer will attempt to correct the situation by adding fuel.

I'm on and off the computer during the day, so I may not be able to respond right away.

BTW - Intake SIZE shouldn't matter too much as to fuel economy.  The type of intake can.  A dual plane intake boosts low end torque as opposed to a single plane that ends to kill low end.  On a small engine like a 302, you need all the low end torque you can get.  A very oversize intake can hurt throttle response.

Also, my car originally had a 350 SBC and T5 5-speed with 3.00 rear gears.  When I got it, it would get about 7-8 MPG.  After some tuning and parts replacement, I got it up about 20-22.  Maybe I can help you.

Thanks Hotrod. The timing is set by the distributor I think. There is a vacuum advance and the Holly Sniper shows good air mixture numbers at idle. Like 1 or 2

I don’t know much about the heads but if it has a hotter cam than stock it’s mild. Rear is a 9” 3.55 posi trac. Transmission is a T5. Tires are 255/60/15 rear and 235/60/15 front running at 28psi

Currently I think it’s running a little rich as exhaust is a tad sooty.

Oh wow, good timing. Just 3 weeks ago i heard the whole story from a guy that installed one on a 302. Oh yeah, 7mpg is not normal. Possibly washing the cylinder walls with gas. He had to reprogram his 3 times. Seems he had residual voltage going to a pink switch (?) that kept the computer from saving changes when the key was switched off. Said he called Holy Tech Help at 1-866-464-6553 and got the info. They also have a good trouble guide on the site. Might be something as easy as that.
As far as it being too large, turns out that's a myth.
Engine Masters on Motor Trend TV did some episodes proving a naturally aspirated engines can only inhale so much air. Probably some way to view the episode on their web site.
Be interested in hearing what you find out. Am considering putting it on a mild 302.

Not sure we are on the same page about the air/fuel ratio.  1 or 2 sounds like the idle air counts (IAC).  The AF ratio should be a number around 10-14.  I'm not familiar with the Sniper 3.5 handheld settings since I program mine with my laptop.

Do you know what the timing is set to?  You should have 10-14 degrees initial at idle with the vacuum hose disconnected and plugged.  Total timing with everything reconnected and the engine revved to about  3000 RPM's should be around 32-34 degrees.   I like the vacuum advance hooked up to straight manifold vacuum, not ported.  The vacuum advance should be adding 10-12 degrees of advance when hooked up.  Timing is critical to getting good all around performance, including mileage.  Much more important than hitting the exact fuel jetting.

Study the Sniper manual to learn more about the info that is available to be displayed.  If your AF ratio is truly reading 1 or 2 then you have big troubles somewhere and it will take out your rings pretty quickly. I'm not ragging on you about studying the manual, just trying to get us talking the same language.

Hotrod wrote:Not sure we are on the same page about the air/fuel ratio.  1 or 2 sounds like the idle air counts (IAC).  The AF ratio should be a number around 10-14.  I'm not familiar with the Sniper 3.5 handheld settings since I program mine with my laptop.

Do you know what the timing is set to?  You should have 10-14 degrees initial at idle with the vacuum hose disconnected and plugged.  Total timing with everything reconnected and the engine revved to about  3000 RPM's should be around 32-34 degrees.   I like the vacuum advance hooked up to straight manifold vacuum, not ported.  The vacuum advance should be adding 10-12 degrees of advance when hooked up.  Timing is critical to getting good all around performance, including mileage.  Much more important than hitting the exact fuel jetting.

Study the Sniper manual to learn more about the info that is available to be displayed.  If your AF ratio is truly reading 1 or 2 then you have big troubles somewhere and it will take out your rings pretty quickly.  I'm not ragging on you about studying the manual, just trying to get us talking the same language.

Ok. I’m new to all this. Here’s a shot of the hand held

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No problem with being new.  Everyone is new at one time.

The 13.2 A/F (shown as AFR, A/F in your picture) ratio is not too bad at idle.  Certainly close enough for now.  The 134 coolant temp reading (CTS,F in the picture.  The F is for Fahrenheit) tells me the car was probably not warmed up when the picture was taken.

Drive the car, let it get up to temp and read the A/F ratio at cruise.  Then report back. No need for a picture since you will be driving.  If that's good as well, then we can move on to something else.

I'm going out on a limb and say I'll bet your timing is way off.  Do you have a timing light?  If not, can you borrow one?  Some auto parts stores like Orielly's have tool loner programs where you basically pay for the tool and when you return it, they refund the full amount.

Check that AFR at cruise and then we will move on.  Getting these thing sorted takes some time.  

BTW - Where in Florida are you?  We will be in Panama City Beach in November.

Also, a small engine like yours I would think should be capable of low to mid 20's on MPG in one of these cars.

Hotrod wrote:No problem with being new.  Everyone is new at one time.

The 13.2 A/F (shown as AFR, A/F in your picture) ratio is not too bad at idle.  Certainly close enough for now.  The 134 coolant temp reading (CTS,F in the picture.  The F is for Fahrenheit) tells me the car was probably not warmed up when the picture was taken.

Drive the car, let it get up to temp and read the A/F ratio at cruise.  Then report back. No need for a picture since you will be driving.  If that's good as well, then we can move on to something else.

I'm going out on a limb and say I'll bet your timing is way off.  Do you have a timing light?  If not, can you borrow one?  Some auto parts stores like Orielly's have tool loner programs where you basically pay for the tool and when you return it, they refund the full amount.

Check that AFR at cruise and then we will move on.  Getting these thing sorted takes some time.  

BTW - Where in Florida are you?  We will be in Panama City Beach in November.

Also, a small engine like yours I would think should be capable of low to mid 20's on MPG in one of these cars.  

My stepson who knows V8 engines way more than I tried to set the timing with a light. However it seems whoever installed the MSD distributor eliminated the timing mark indicating plate so he set it by ear and it improved the idle and throttle response but you are right we really don’t know what it’s set at.

For now until we figure out more I disabled the 4bbl linkage so it’s operating on 2 bbl. Hopefully Les wasted gas down the throat.

Pull #1 sparkplug and bump the engine over with a finger over the plug hole.  Obviously, the engine needs to be cool.  When you feel compression, you are close (only close) to top dead center on compression.  TDC will be 0 degrees as to timing.  There are aftermarket timing tabs that can be adapted to your engine or you can rig up a any kind of simple pointer that points to the timing mark on the harmonic balancer.  Once you have the engine close to TDC with the finger test, you may be able to see where the original tab was mounted.  If you know the year of the engine, you may be able to look up some pictures on setting timing to see what the timing tab actually looked like.

If you could actually look through the plug hole with a light, you could most likely see the piston come up to TDC.  Doubtful you could get into a position on a Sebring that allows you to look into the plug hole.

I would recommend that you measure the diameter of the harmonic balancer and buy a timing tape for that diameter.  They are really cheap. It will have the balancer broken down into degrees.  Put zero on the tape directly over the TDC mark on the balancer.  With the tape, all you need is a simple wire pointer.  

Absolute way to find TDC is to use a piston stop screwed into the plug hole.  The engine is rolled BY HAND until the piston is stopped by the piston stop.  Mark the balancer and then rotate the engine the opposite direction until it stops.  Mark the balancer again and the center distance between the 2 marks is actual TDC.

One other suggestion is to see if you borrow or rent a diagnostic camera. It will have a tiny camera and light on a flexible probe along with a small display.

This could be snaked into the plug hole to watch #1 piston. The piston will dwell slightly at TDC. Knowing that should be plenty close enough for tuning/

Thanks guys. You’ve convinced me I need to put the timing thing to rest once and for all. I’ve ordered a TDC gauge and the Harmonic Balancer Tape. We will nail down the timing and then go from there.

Update. Got a TDC gauge. Properly set the timing at around 6 degrees base timing. Also fuel cooling mods have eliminated vapor lock. The car is now getting a tad better than 15 mpg

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Much better. Was the TDC mark on the balancer off?

Hotrod wrote:Much better.  Was the TDC mark on the balancer off?

We had to make our own mark. Where the original mark is ended up behind the water pump at TDC. There is no indicator plate so we marked the block and had a programmable light. We got it dialed in. It was 4 or 5 degrees off. Runs so much better and with cooler fuel it’s almost right. I still think the Sniper needs a tweak but it’s livable

You could try bumping the timing up a little, say to 10 -12 degrees and try it.  Some engines have "lazy" combustion chambers and respond well to more timing.  The factory settings are usually so the car can pass emission testing.  Nothing wrong with experimenting with more base timing.  Being an open car, you should be able to hear any timing rattle or pinging easily.  Back off at least 2 if you hear any.

You also said earlier that the exhaust was sooty.  With the car warmed up, you should be seeing AFR's in the high 13's at cruise and you could experiment into the 14's.  14.7 to 1 is considered the "perfect" fuel/air ratio, but most engines run better at less than that.  14.7 is used by the factories to improve emissions.  You can adjust the target fuel table to get what you want.

I will say that my experience with my Sebring is that mid 20's on MPG seems to be about all I can get whether carbed or fuel injected.  I am still playing around with my tuning too, but can't seem to crack about 23 on a good day.  Probably has something to do with the way I drive it!

After this last adjustment the exhaust is way less sooty. Smells perfect too

Well, great news. Now that the car is more reliable with the fuel cooled off, I ventured out of town yesterday. Did 116 miles of mostly highway driving and it took 7.2 gallons. That’s right at 16 mpg. I can definitely live with that! The adventure continues.

Took the car from home to Tallahassee for a motorcycle gathering. My bike group didn’t mind a car tagging along. Driving at relaxed speeds in 5th gear I’m getting 22 mph now.

Thanks everyone for all the suggestions. Better timing definitely helped. Cooling the fuel was also crucial. And highway driving in top gear proved to up the numbers as well. I think I’m at its best right now.

Chilling gasoline increases power. Heating gasoline reduces power and increases MPG. . Old intake manifolds had exhaust ported through to warm everything.
32 BTDC spark advance at cruising RPM

Ok, today was the first time I ventured out on the freeway. She did great. 70mph is a tic under 2,000 rpms in 5th gear. 105 mile trip and right at 18 mph and most of those miles were 70mph. I was very pleased. Engine temp stayed at 172 the whole time and it was a really nice drive.

Nice job Hotrod! You're still the tuning wizard around here ;P

I'm just glad I can help. It doesn't always work out, but this time it did. Hope he enjoys the car more now.

Hotrod wrote:I'm just glad I can help.  It doesn't always work out, but this time it did.  Hope he enjoys the car more now.

Yes, thanks a bunch Hotrod and anyone else that replied. The car is everything you could wish for now