How to time cams for better gas mileage?

[NDB]

Can anybody explain how?

Thanks

[ghnl]

I suspect you'd get a lot more MPG by how you use your right foot than how you adjust a camshaft (or two).

[NDB]

i know that, but to make a large difference. like adjusting for a specified cruising speed or RPM. lets say 3000-3500 for the engine speed. i'm aware the idle could be effected. just curious.

[tiger0529]

What year is your Spider (carbs, spica, jetronic or motronic) and what MPG are you getting NOW?

[Salsero]

NDB,

Here in New Jersey, I always struggled to get my 78' Spider through the state emmissions test as it has twin Webbers. I leaned the carbs out as best I could with jetting and settings and still it would fail. What ultimately worked was eliminating valve overlap/scavenging (the slight moment when both valves are open at end of exhaust stroke and start of intake stroke) by advancing the exhaust cam and retarding the intake cam by approximately three widths of the timing marks on the cams/caps. After doing so, the car ran much leaner and I was able to pass the NJ emmissions test, however, as soon as I got home I readjusted the cams back to the factory setting as running too lean for extended periods can result in catastrophic failure not to mention the loss of performance due to the elimination of the scavenging effect. You might consider this strategy for enhanced fuel economy, perhaps not so aggressively, maybe one width of the timing mark on each cam and see what your result is before adjusting further. Ensure that your resecure all of the cams'/vernier wheels' lock nuts/cotter pins/etc after each adjustment to avoid anything coming apart in operation. Best of luck.

Salsero (Ed)
1978 Spider (Triple Black/the good sports car)
1969 E-Type(Silver+Cinnamon/the evil sport car)

[NDB]

83 spider L-jetronic

[Tifosi]

You can pick up 11 degrees on the intake cam by simply disconnecting the VVT solinoid. (provided yours is electronic and not the mechanical centerfuge version)

Well, 'pick up' is the wrong phrase. More like prevent an 11 degree advance, or, leave the cam 11 degrees retarded. However you want to look at it. :shrug:

That way it'll never kick into power mode and stay in the much 'softer' econo/closed loop (and better emissions) mode most all the time. There will still be a bit of open loop enrichment when you honk down on the throttle, but the intake cam won't kick over to the suck fuel degree index.

I suppose one could even disconnect the full throttle contact at the TPS also so that it didn't even get into an enrichment/open loop mode, but I'd imagine that would turn the car into a downright pig.

Well, actually, no 'imagine' about it, it would turn it into a pig. But hey, if it's mileage you're after, then sacrifices must be made, right?


Still, in a proper state of tune, you should be seeing milage in the upper 20's if not 30mpg range.

If you're not getting around that now, tinkering the cams is going to be far less benificial than an actual factual tune-up.

[Zunige]

Stock '83s and '84s will see mileage in the mid twenties only, while later cars yield better mpg... (This is also documented on the original window sticker.)

Best regards,

[ghnl]

Average driving (~ 50% secondary roads - 45-55 mph & ~ 50% highway - 65-75 mph speeds) gives me a pretty consistent 24-25 mpg. Steady Interstate driving (NC to NY/MA) was 33mpg. All with 'regular' octane gasoline.

[Tifosi]

I was as high as 27 city and 32 highway (in other words, about 29-30mpg average) before I got all antsy with performance mods.

[NDB]

well, i'll see what i'll be getting. i'll be driving 112 miles highway miles a day, so i'll get a pretty good idea what it gets. tinkering with stuff every fill up to see if anything changes.

[ghnl]

Make sure the Manifold Pressure Sensor (measures intake vacuum) is functioning. It is located under the trim panel behind the right side seat. If it is faulty (they've been known to leak) or its hose is cracked & leaking the ECU (computer) won't know to advance the igniton timing under cruise conditions. That'll reduce fuel economy.

[slyalfa]

try starting in 2nd and do not use 1st that can save a lot of gas in city.

[NDB]

i just drove from LA to Vegas with much luggage which primarily uphill as well and recorded 30 MPG. I'll see in a few days how it is since i will be driving more highway miles at a much lighter weight. i've read numerous of time from all those people with hybrids that are trying to set all their MPG records, that they allow hotter air into the intake among many other little tricks. figure, less density air, less fuel used, or hotter air, better fuel atomization. do you think adjusting the AFM spring for the flapper a little tighter is going to do anything? i've done a few mods already which don't necessarily help my gas mileage. i went from 26-27 before my mods/complete lookover and tune up. and then after, it dropped down to the low 20's. but that could also do with my heavy foot. i could definately feel a difference in power. but for the mean time, i'm more concerned with gas mileage right now. i'm running some goodyears which measure about an inch taller than stock at 25.2" in diameter. well, at least they were much taller than the tires that were on the car before. so i did this to reduce my RPM at highway speed so i could cruise at a higher speeds yet keep a lower RPM. i usually dont go above 3000 while shifting and cruise at 3000-3200.

[slyalfa]

Also pump up the tires as hard as you can, that can help. it might be just me but I think the headlight covers make a difference. and a hard top will also help with the drag some.
run as much timming advance as you can. changing the AFM should have no affect at cruise as you should be runing close loop with the NBO²

but it seems the spiders just do not get as good as MPG as the bigger Verde, seems strange.

try syn-oil all around that should also help some. rember to use the redline NS in the tranny.
every bit of drag adds up.