Retarding cam timing for better mpg?

E=mc2's picture

Every engine manufacturers setup is different....but I have info from someone who claims to have found that the cam timing on a Toy 1.5L engine was 11* retarded and he was reporting some pretty high mileage:

quoted...

"Its too soon to tell, and I've been doing too much highway mileage to say normal economy, but my last 3 tanks were- 41, 46, 29. More highway on the first 2 obviously. Highest I've ever seen was 49mpg, pure highway. And no, it wasn't a quirk fill-up, because it happened twice in the same day on the same trip. How you like them apples?

Oh, and btw, the last 3 trips, when on the highway, have been with 3 other "adults" (17-21) and my 1-year-old niece in the car."

Since he got the t-belt setup right...he now claims more power at lower rpms.

Before...he tended to rev it a lot....and with this car his highways revs were probably above 3K...maybe 3.5K.

I normally see around 32-34 mpg mixed with some mods with essentially the same car...though I did hit 47 mpg one day with a good tailwind.

The new EPA avgs for the car are...23 / 29

I tried advancing the cam timing by one tooth or 9* and the car lost power by 59%...as tested in 5th gear. I might have messed this "test" up by not pulling the dist and trying to reset it...though I thought I still had quite a bit of adjustment.

This engine...a 3AC ('83 to '88 Toyota)...has a 9 to 1 compression ratio and ignit timing is 5* BTDC standard.

With cam timing at OEM spec...the power can be upped with this engine by at least 20% though....by advancing the ignit.

The question?

Has anyone tried this on a stock engine and seen better mpg?

Obviously... the ignition timing would need to be set on the road to get it to run right.

Comments

Retarding cam timing for better mpg?

ssheen's picture

I have played with cam timing. Though I was doing it to move the power band, play with the EGTs. I know advanced it did not seem to help any. This on my 88 Daytona.

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Retarding cam timing for better mpg?

Pinhead's picture

I would tend to think it'd depend on the camshaft profile. An engine with a lot of intake duration (open early, close late) would probably gain MPG if you advanced the timing because it would reduce compression overlap and reversion.

Either way, I'd think PowreValvz would be a much better and more reliable/usable/drivable solution.

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Retarding cam timing for better mpg?

E=mc2's picture

A guy autocrossing the same Nissan 3.0L V6 I have...tended to retard the cam by maybe 4-5*. Car had poor response below 2K. He also did some intake/exhaust/mixture tuning for a final 33% HP gain.

One tooth and 9* retarded is probably too much...but must be livable cause it was driven that way a while with the guys 1.5L...he claimed it was at 11* retarded. A combo of one tooth off and belt looseness?

I have an extra cam gear...might get into trying to drill some extra indexing holes in it.

Misc info about the 3.0L V6...various...

"On my car with the gears at +3, midrange power increase was awesome but all power died by just over 5K. I'll be changing them to -3 over the winter."

"small advance brings the torque down, good for turbo cars who naturally peak at higher rpm...small to medium retard allows more air to enter and exhaust to leave on n/a cars improving efficiency"

"The cams from the VG30 (3.0L) are 114 lobe separation angle. These are very mild cams. The wild cams are 110, 108, even 106 in some cars. By decreasing the lobe separation angle you gain big power increases in the upper rpm range, of course, this, at the expense of torque."

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Retarding cam timing for better mpg?

mpgmike's picture

I know with Larry's Saturns, we had the cam timing too far advanced and too far retarded. It ran best overall with it close to the factory setting on his. We didn't get mileage numbers with the cams off, he drove down here to PA from IN to get the work done and time was at a premium.

I know on the Dodge 318s, advancing the cam seems to give it much better usable torque practically everywhere. I've done a couple ranging from 4* to 6*. Mileage didn't change that much.

Mike

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Retarding cam timing for better mpg?

E=mc2's picture

Might be possible that you could have a combo of poorer driveability and along with an increase in mpg?

Most cam timing mods are done for a power increase or maybe a torque increase at lower rpms?

Few have researched for mpg?

About the only way to find out would be to try it I guess.

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Retarding cam timing for better mpg?

paulorr1's picture

Hi guys,
I'm not a huge cam timing expert as I've never been involved in an indepth tuning project. I am an old school mopar man though. On single cam engines, like the 318, advancing the cam increases torque thru the entire RPM range by closing the intake sooner thus raising the dynamic compression from idle to max RPM. I would not think that retarding the intake timing would EVER help mpg but advancing the intake while retarding the exhaust would widen and flatten the torque curve.

God bless,
Paul

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Retarding cam timing for better mpg?

gregersonke's picture

I think it depends on what you are doing.

If you got a high lift long duration cam. Advancing it will help the low end. The trick is however to tweak it to the setting which your powerband is most likely going to be. I do this on my zx2 with twin cams. If I want power down low I advance. If I want it up high I pull it back. I can only really tweak the intake since the exhaust is varible. But using .405 lift and I think it was a 242 duration I'd usually keep it at 2-4 degrees advance. The only downside is that it was really sensitive on the throttle response.

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Retarding cam timing for better mpg?

BMac's picture

I build an a$$kickin' 360 one time and advancing ghe cam 4* was common for an aftermarket cam for better torque which = better mpg. Well when I did this, I actually advanced the cam gear and not the cam, which means I actually retarded the cam.
My point is here, did he actually advance the cam, or the gear?
Learn from my dumba$$ mistake.

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Retarding cam timing for better mpg?

mpgmike's picture

Usage of the common nomenclature would dictate that "advancing" the cam would mean initiating cam opening and closing sequences earlier in relation to crankshaft events. Cam centerline is typically used to indicate when, in crankshaft degrees, these events are happening.

For example. I installed a high performance cam in a Dodge Spirit. The cam was to be installed at a 114* centerline. When I measured it, it was 118* ATDC. I had to "advance" the camshaft, in relation to the crank, to bring it back to 113* (it should have been 114* but it's a little tricky to adjust those and 113* was close enough).

Hope this helps,

Mike

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Retarding cam timing for better mpg?

racprops's picture

OK How about the good old 350 Chevy??

Specialy a 93 with flat tappet cam, in a van as per truck??

Need answer as next week I am replacing the water pump and plan on doing the timing chain and advancing it 4 egrees while it is torn down, as it has 100,000 on the OD.

Rich

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Retarding cam timing for better mpg?

E=mc2's picture

An interesting page showing torque and hp changes from varying different things, but for a particular engine:

http://www.billzilla.org/engvariable.html

My THEORY is that OEM engine designs are....guess what....are all different...so that variables are tweeked to different degrees amongst these choices and a few others not shown...putting some OEM setups into variable "corners" which can be easily taken advantage of?

An example would be a 3AC Tercel engine where you can gain over 20% in "power" simply by advancing the ignition...as per LaPointe.

Too bad there's not an output for mpg. Or for varying the ignit timing.

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Retarding cam timing for better mpg?

racprops's picture

I fear that little motor is too small to show much change.

Rich

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Retarding cam timing for better mpg?

E=mc2's picture

As fuel costs rise...we'll all be downsizing?

I doubt that engine displacement has a lot to do with % changes though. Probably has more to do with the OEM power output vs displacement?

His final HP peaks around 7.5K and 260 HP....not bad for a 2L 4 banger in a 1500 lb car.

http://www.billzilla.org/fraser.htm

Does anyone have a working copy of this program....the full version?

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Retarding cam timing for better mpg?

ssheen's picture

I am aiming for 300whp below 6k on my 2.2L. I think another built up head from Mike will help me reach that. Well, I want to do it at 18psi of boost or less. That is the challenge. :D

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Retarding cam timing for better mpg?

mpgmike's picture

Scott, that'll be a close one. I'm confident of my head work, and I'm confident we can blow away most other's numbers, but 300 WHEEL HP at 18 psi or less, it might be doable...come to think of it, I'd like to see if we can. I know Dez was getting something like 430 HP on 27 psi boost with one of my old heads.

Mike

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Retarding cam timing for better mpg?

ssheen's picture

Do I have more faith than you do?? :D

I would like to see lower than 18 psi and I would like to see it done on 87 octane.

I suspect around 220+ at 10-12psi currently. What you think your head will add? Need to go dyno and see where I am at now for sure. Then I can dyno after and you will have a before and after compare with only the head changing.

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Retarding cam timing for better mpg?

mpgmike's picture

I got it! Oversized valves! I haven't been doing the OS valves other than the +1s. That might be the key.

Mike

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Retarding cam timing for better mpg?

ssheen's picture

The only problem with that, is I would have do the metric mechanic mod to the new valves instead of use the stock ones they already did for me.

I have been wrestling that issue. We will have to talk about that more via PM perhaps.

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