Advancing a cam and Gas mileage?

OK Update time and question time as well.

I hate how long it takes me to do any thing?

I finely got the van up running, I had to replace the water pump so I when deeper and replaced the timing chain, after all the van has 100K on it. (and a good thing it was a original chain and sloppy, the motor used to shake at 3000 plus now seems very smooth, only less willing to rev there.)

I went with a true roller performance timing set, and after debating with all I could find went with 4 digress advance.

Things seemed to work fine.

With the stock chip I seem to have more lower end off line power.
As I am still testing, I switched to a mileage tuned chip with power settings as well, and things looked good, but mileage?Gas mileage is down, I am getting readings of from 10 to 13 MPG down from the old readings of 16 to 18 MPG. (And very sadly not the 20 + I was hoping for?)

I have switched back to the stock chip and am hoping for better MPG.

The big question is: DID I mess things up advancing the cam?? Does/will advance a stock ?93 truck 350 cam cause such a drop in gas mileage??

All mileage test runs have been a run of around 60 miles range at around 70 MPH.

Another problem is either lack of fuel or that cam again?I can rev in first gear to 4500 and 5000 RPM smartly, and second does almost as well, but in third it seems to strain and almost hang up at 3000 plus and has a hard time going any higher, of course at this point I am hitting 80MPH so can not press on much longer.

So if it can rev to 5000 in first gear pulling the van, is things working normally?? I feel and know the gearing causes that drop in power in higher gears but from what I remember of drivng it last year it seems smother but straining more to rev.

Rich

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Comments

Advancing a cam and Gas mileage?

E=mc2's picture

Not so sure about this late model van...but I'm finding thru watching my O2 function...that too much pedal at all causes it to go into open loop. So if you are running a van (wind resistance) at higher speeds...you might not be going into closed loop at all?

You can monitor your O2 using a digital meter.

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Advancing a cam and Gas mileage?

racprops's picture

Good questions, I am asking if the changing of the cam could/would/does change the motors fuel mileage??

The van was getting around 16 to 18 MPG on the same road.

The thinking would be I should get more torque at lower RPMs and as I am doing around 2000 RPM at 70 MPH I should do better, unless the higher torque is made by a greater demand for fuel??

Rich

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Advancing a cam and Gas mileage?

BMac's picture

One thing you should watch when doing that is did you advance the cam or cam gear (retarding the cam)?

If you have more bottom end power then you must have done it correctly and should see more mpg. Now when you do that you should have moved your distributor to compensate or you now have too much timing and the computer will adjust accordingly.

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Advancing a cam and Gas mileage?

racprops's picture

Darn I can not remember for sure if I retimed it but I am fairly sure I did.

I have done these cam gear sets before, so I know I did indeed avance the cam.

On my other vans gas mileage was always bad so I never cared.

Rich

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Advancing a cam and Gas mileage?

BMac's picture

Then re-check the ignition timing.
The computer controls the timing on my Dak so I had to re-adjust the distributor to get it so spark correctly cause it was missing really bad at high vacuum, which also increased since I advanced the cam.
Make sure your ignition components are up to snuff!

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Advancing a cam and Gas mileage?

racprops's picture

I am fairly sure I would have retimed it.

The main question is has anyone advanced a cam and had a lost of mileage??

If that is normal, then I neeed to fix it.

If a lost of mileage is not normal and advanceing the cam gave better mileage than I need to figure what is not working.

Rich

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Advancing a cam and Gas mileage?

RoadWarrior's picture

Not sure what you meant by "I went with a true roller performance timing set, "

If you meant you went to roller rockers, did you end up with a change of rocker ratio and less valve lift?

Just thinking that the only time I've come across motors running out of breath like that is when the valve clearances have been really sloppy (resulting in low lift)

Also do you know where it made peak torque before? If it was only at 1500 rpm or something and you've nudged it back from that, then that might explain it. Generally when advancing the cam improves fuel economy, we're thinking about cams that peak in the 2-3K range or above.

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Advancing a cam and Gas mileage?

racprops's picture

Ture roller chain is the best type of chain.

Only the timing chain was changed no other enfine work other that the new water pump.

The engine is reated 300 FP @ 2800 RPM so mlowering that should have helps.

Rich

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Advancing a cam and Gas mileage?

BMac's picture

RoadWarrior wrote:

Not sure what you meant by "I went with a true roller performance timing set, "

He means a true roller chain not rockers.

If his cam was only a small profile stock type cam then it will run out of power in the upper rpm range but pushing a bus through the air will have an effect on it too.

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Advancing a cam and Gas mileage?

racprops's picture

Well it is also a flat tapper type and rated 210 HPO at 4000 RPM so yes it is a smaller cam, a truck cam.

Rich

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Advancing a cam and Gas mileage?

BMac's picture

Well since it is a truck, you wouldn't normally drive it hard so mpg should pick up(pardon the pun).

Mine happens to have a cam that has RV type specs so advancing it would only help.

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Advancing a cam and Gas mileage?

racprops's picture

We all though that the factory cam came retarded, so that advancing it would make things better all over.

So far it is not looking good for mileage.

Rich

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Advancing a cam and Gas mileage?

BMac's picture

Put the dial indicators and degree wheel to it and degree it in.

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Advancing a cam and Gas mileage?

racprops's picture

Without the cam spects, how???

Friends, please let us return to the core question:

Has anyone else advanced a cam in say a Chevy truck (prefired) and after doing so did it effect the gas mileage in any way??

I am asking for facts, at lease personal facts, that before you got x amount of MPG and after you advanced your cam got New X amount of MPG be it better or worst.

I do not want to beat my self up trying all kind of fixes looking for a new problem to find it IS the advancing of the cam that took away my mileage.

Thanks.

Rich

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Advancing a cam and Gas mileage?

Spewn's picture

I'm not sure you'll find many people in the same boat as you. Most(probably 98%+?) people who buy adjustable cam gears do so for performance, and could care less/don't pay attention to their gas mileage. Even if there was a gain to be realised, most people wouldn't see it because they'd keep their foot in it that little bit extra.

Can't you set the cam back to the factory location, and see if mileage returns to normal?

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Advancing a cam and Gas mileage?

racprops's picture

On most hot rod sites i would agree with you, I thoght this place would know.

I talked with a company called AZ TPI and they feel it can hurt mileage...

Then again he felt I would have higher RPMs as well...

It is a major job to take it down to get in there and reset that gear.

I will just have to make other improvments just to get back where I started.

Darn it really made sense to do it, my spect was 2800 RPM for peak toqure so kicking it down to be close to my main cruse speed of 2000 RPM made total sense...

Oh well.

Rich

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Advancing a cam and Gas mileage?

manilow's picture

Pardon my asking - is yours a dual camshaft or single?

With a DOHC adjusting one camshaft (usually unlet) has an effect on the torque curve.

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Advancing a cam and Gas mileage?

racprops's picture

Single a Chevy 350.

Rich

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Advancing a cam and Gas mileage?

racprops's picture

Talked to tech suport at Comp Cams and was told the same thing, advanceing the cam will cut gas mileage and retarding the cam will make gas mileage.

Opps.

Rich

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Advancing a cam and Gas mileage?

E=mc2's picture

I advanced the cam by 9* (one tooth) and lost 37% power....did not test mpg.

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Advancing a cam and Gas mileage?

BMac's picture

racprops wrote:

Talked to tech suport at Comp Cams and was told the same thing, advanceing the cam will cut gas mileage and retarding the cam will make gas mileage.

Opps.

Rich

That doesn't make sense but I've heard it before.
Moving the hp and torque lower in the rpm band will let the engine not work as hard to get moving. More torque = less effort to move the vehicle.
You must have a small cam in there but I can't see it being a 350. Any engine I've built (small block Dodges) I've always bought RV type cams, 252 duration, and always advanced them 4 degrees with good results but like you said, I never checked them for mpg increase.

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Advancing a cam and Gas mileage?

racprops's picture

That is what I have heard for years, I have a 91 Caddy with a 305 rated with peak torque at 2200 RPM.

So advanceing the vans 2800 RPM cam made good sense...

Rich

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Advancing a cam and Gas mileage?

manilow's picture

Variable Valve Timing, among other interesting bits:

http://www.ford.com/en/innovation/design/performanceDesign/variableCamTi...

Ignition timing must be 'shiftable' too?

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Advancing a cam and Gas mileage?

racprops's picture

Great maybe, but still no answer..

Other than what I am seeing, a 17 MPG motor making 14 MPG after the change.

Rich

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Advancing a cam and Gas mileage?

manilow's picture

Okay, I read your post and earlier you said you'd fitted a 'mileage' chip - presumably one of those aftermarket eprom chip conversions. That, plus the new timing chain set sent your FE into a nosedive.

Then, you refitted the original chip? Still got poor driveability and poor FE?

Given that the cam sprocket may have not been aligned properly but that you have no way of finding out short of stripping things down the next question is:

Did you set the distributor right - if this was removed during the install?

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Advancing a cam and Gas mileage?

racprops's picture

I have returned to the factory chip to see if that inproves thing, will know when I get gas.

Chip is a custom tune done for me and is second tuneto be done after doing a tail pipe test with a sensor and meter.

I am fairly sure I retimed it as I have done enought work to know I had to do that.

The New chip being leaner felt harder to get off line, old chip feels better in take offs but runs a little roughter...

I was very carefull in relaining the slightly moved timing marks on the cam gears.

Motor seems to be doing what I exspected, more power off line and in lower RPMs, but that is a by the seat feeling.

As it feels better off line I exspected better mileage.

As one guy said, get more power, how? By using with more gas, simple...

Live and learn.

Rich

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Advancing a cam and Gas mileage?

racprops's picture

Well todays test run gave better mileage, perhaps i just needed to break the timing chain in, I get a reading of 17.4 MPG.

More as it comes along.

Rich

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Advancing the cam...

whitevette's picture

racprops wrote:

Without the cam spects, how???

Friends, please let us return to the core question:

Has anyone else advanced a cam in say a Chevy truck (prefired) and after doing so did it effect the gas mileage in any way??

I am asking for facts, at lease personal facts, that before you got x amount of MPG and after you advanced your cam got New X amount of MPG be it better or worst.

I do not want to beat my self up trying all kind of fixes looking for a new problem to find it IS the advancing of the cam that took away my mileage.

Thanks.

Rich

Hi, Rich!
Whitevette, here. Let me chime in ; you pick & choose.
First, by installing a new chain...you eliminated a lot of slack, which means you advanced the cam(back to OEM specs). On top of this, you advanced the cam some more. More advance.
What happens to the power curve when the cam is advanced? Low end power (torque) drops( the intake opens sooner, bleeding pressure...or the lack of it). High end power is increased... apart from what happens to the torque curve. Lower torque means less MPG ; higher power has to be made somewhere...MPG drops. Thus, advancing the cam is great for revs / HP but you pay the price in MPG!
Besides, you advanced a bunch of degrees! I won't go there...this is a different argument! Hope this helps. -Ted Hart / CHEMbustion

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Advancing a cam and Gas mileage?

automotivebreath's picture

Whitevette,
My view of advancing the cam is opposite. Advancing the cam closes the
intake valve sooner to capture more of the charge at low RPM. This is
normally associated with improvements in low RPM performance.

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Both right

markweatherill's picture

Advancing the intake cam timing will do both - opens the intake valve sooner, and also closes it sooner. :D

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Advancing a cam and Gas mileage?

racprops's picture

That is what I have always been told: advance lowers the power curve and thus gives more low end power.

Retarding it moves the power curve up in rpms giving more RPMs.

And again I was told that stock cams in stock cars etc come retarded for better smog, and after market moters come stight up.

And as my vans manual says the motor makes 300 Ft pounds at 2800 RPM and that I cruse at 2200 to 2500, it seems a good idea to lower the power curve.

AND If lowering the power curve gives more off line and pulling power power it should use less gas.

My only guess is the key, more power still means (in this case too) more gas to make it.

Funny as well uis I have a 91 Caddy Fleetwood that runs a 305 that is cammed for 2200 RPM Toque and it gets 18 MPG totaly stock.

Now what when wrong??

Rich

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Advancing a cam and Gas mileage?

manilow's picture

Rich, I read your garage and it said the distributor had been replaced.

Did you set the dizzie gear incorrectly, by chance? Or could it have been the wrong spec dizzie?

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Advancing a cam and Gas mileage?

diamondlarry's picture

Quote:

My only guess is the key, more power still means (in this case too) more gas to make it.

That's not necessarily so. Mike has told me numerous times that if you can get that power increase by making the combustion process more efficient that you won't need more fuel. A good example of that for me is my Saturn SL2. Mike is familiar with how stock turbo-Dodge cars run(~150 hp) and, after driving my car when we were done with the head mods, he said that the SL2 was running stronger and the car is getting much better than the EPA with my son now driving it.

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Advancing a cam and Gas mileage?

racprops's picture

Well is seems I did not make a improvement, I made a change so in this case it was not good.

I will have to put it back.

Anyone live in Phoenix, I could use some help.

Rich

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Advancing a cam and Gas mileage?

Dale T.'s picture

You did fine by advancing your cam, This opens the valves a little earlier and gives you more power on the low end where you want it on a street vehicle. you would retard it for more top end power. This is an old racers trick. As for raising mileage it is small. Advance your timing 2 degrees from stock. Add a home made PCV jar (look in Welcome and introductions under "How To Make A PCV Jar like Condensator for directions) if carbed add a carb enhancer . Make sure you have clean filters and your carb is in good working order, or rebuild it. This will make a big difference. Dale

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Advancing a cam and Gas mileage?

racprops's picture

That was my understanding...

But I lost 4 MPG and it also seems to be running hotter than normal as well.

Rich

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Advancing a cam and Gas mileage?

2fords's picture

I've got no personal experience to say one way or the other, but my understanding has always been that even though retarding a cam is generallly known to shift the powerband up slightly, it makes it more efficient since the exhaust valve starts to open later and the combustion gasses have more time to act on the piston. Also, the overlap occurs slightly more on the intake stroke (compared to advanced, or straight up), when there is a negative pressure in the combustion chamber, creating a bit of an EGR effect and preheating the mixture.

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Advancing a cam and Gas mileage?

racprops's picture

Now I need to find a local machinic to redo the cam for me.

Rich

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Advancing a cam and Gas mileage?

E=mc2's picture

racprops wrote:

Now I need to find a local machinic to redo the cam for me.Rich

BIG DIFFERENCE between a 2007 vehicle and the older ones? With the later models engine management is more controlled.

ECU is probably in limp mode? Can't handle the valve timing change...out of expected parameters?

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Advancing a cam and Gas mileage?

Dale T.'s picture

4 degrees ether way will not cause you to over heat as well as loose mileage. There is something else wrong. As some one else said earlier they retarded cam timing for emissions. The other thing is if you get the timing chain off 1 tooth this is around 20 degrees not 9. Do you have a vacuum leak or plugged exhaust? Did some vacuum lines get mixed up? What year and model vehicle, What motor and fuel system? Dale

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Advancing a cam and Gas mileage?

E=mc2's picture

Dale T. wrote:

The other thing is if you get the timing chain off 1 tooth this is around 20 degrees not 9.

Generally it is 9* at the cam? Count the number of teeth on the cam gear and divide by 360*?

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Advancing a cam and Gas mileage?

racprops's picture

I got a true roller chain with the 3 possion gear, one 4 degrees advance, one stright up and the third 4 degrees retared.

I used the 4 degrees advance setting.

It only seems to run a little hotter, from 190 to around 200 220...

Rich

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Advancing a cam and Gas mileage?

racprops's picture

OK here is a update:

I lost the fuel pump a while ago, so everything stopped for a couple of months.

At last I got the fuel pump replaced. The repair shop tested it and I was right it was bad?

But when they restarted the Van with the new fuel pump in, they said that it was running very badly and had to trouble shoot it and found that my MAP sensor has shorted!!

I was a bit of a unbeliever, after all as far as I could tell it was running very well and seemly had nothing wrong other that the fuel delivery failure.

But having little chores I said OK replace it.
Well what a improvement!!!

My brakes work again!!!

Brakes????

Yes brakes, for the past year I have had poor brakes, I could not get them anywhere near lockup even using both feet. I was getting ready to replace the Vacuum Booster with a Hydroboost system as I could find nothing wrong with the booster.

It seems I had almost no engine vacuum to work the booster.

Yet to my seat of the pants, it seemed to be running very well. (other than low gas mileage?)

Talking with both the guy who replaced the fuel pump and the sensor and other automotive experts, I find that they all agree that the computer had been compensating for the failing sensor, and had done so much that my timing had been pulled back so far to more or less kill any engine vacuum.

George who replaced the sensor said it was bearly operating and when he replaced it it cleared right up, he feels the system was running of the tables within the computer adn more or less limp home mode.

Unbelievable (to me anyway) I am totally blown away that a system could compensate so much that it totally hid this malfunction to me. And did so while making it seem to be running so well, in fact the engine is now much harsher to my feelings, but it also makes more power and pulls stronger.

I am eager to pull some mileage runs to see what this repair and dynamic change has done for the gas mileage.

I may not have to retime the cam after all. (replaced timing chain, advanced it 4 degrees, lost 4 MPG, feared I would have to undo this change to recover my lost MPG?)

Reactions??

Rich

PS I now am wondering if there is any way to get a comperhenstive testing to find such problems, I now know how far a system like this can be running glass smooth and be hidding a major problem, so now feel I need to test it before making any changes.

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