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914World.com _ 914World Garage _ Fuel/ignition settings for best gas mileage??
Posted by: Mueller Aug 15 2005, 05:10 PM
I "borrowed" the quote below from aircooled.net
With the fuel prices going up and up, I figured that was the kick in the @ss I need to get my 914 up and running as a daily driver....since my fuel and ignition can be set however I want with my laptop, I figure I should optimize my little 1.8 for being as frugal with the petrol as it could be right now 
| QUOTE |
It gets better! We give you the option of a vacuum advance on every unit except the basic model (single points are centrifugal only)! This means all you dual weber/dellorto guys can get another 4-5 mpg, AND the engine will pull harder off idle than ever before, and use less gas doing it (you can lessen the accellerator pump squirt, and idle jet size), while also running cooler! :-) The vacuum advance is FULLY ADJUSTABLE with a 3/32" allen key in the vacuum port to adjust the vacuum diaphragm, and you set it according to vacuum measurements you get from your carb(s). This means it doesn't matter what carb(s) you have, and it also doesn't matter what cam you are running! While other guys are running 32 degrees of full advance, you will be cruising around at 42 degrees on the highway, which optimizes mileage! It's important to know that the 32 degree setting is fine for full throttle, but at part throttle (cruise) you can use 42 degrees. If you are only running 32, your timing is retarded 10 degrees from optimal! Retarded timing creates MORE HEAT. This means you run cooler and use less gas if you have a properly working vacuum advance (VW put it on all their engines for a reason). All you need is a ported vacuum source ("ported" means the vacuum is coming from right above the throttle plate); do NOT run this to manifold or venturi vacuum!. Ported vacuum is 0 vacuum at idle, and 15-25" of vacuum at 3000 RPM and 1/8 - 1/2 throttle. |
Posted by: jkeyzer Aug 15 2005, 05:14 PM
gas mileage, engine life... gas mileage, engine life... hmm, which do i choose. 
just kidding mike.
at least you will get rid of those pesky carbon deposits (and valve seats too)
Posted by: Dr. Roger Aug 15 2005, 05:16 PM
absolutely true.
my dream car will have whatcha' got on yer ride, mike. have fun.
there is a fine line with that advance thing though. i experimented in high school auto shop with my parents van....
removed the engine cover so it was basically right next to me while driving it around. had a buddy playing with the timing and was driving at the same time. lots of learnin' and fun.
i still say people can go max advance under a particular circumstance as long as there is no ping. nice to read your posting.... 
Posted by: bd1308 Aug 15 2005, 05:17 PM
42 deg....is that even possible???
Posted by: Cap'n Krusty Aug 15 2005, 05:23 PM
| QUOTE (bd1308 @ Aug 15 2005, 03:17 PM) |
| 42 deg....is that even possible??? |
You DO realize that the vacuum advance on a bone stock 914 does, under certain conditions, go to 42 degrees, right? The mechanical advance goes to 28, or so, and the vacuum goes on from there. The Cap'n
Posted by: Mueller Aug 15 2005, 05:29 PM
| QUOTE (Cap'n Krusty @ Aug 15 2005, 04:23 PM) | ||
You DO realize that the vacuum advance on a bone stock 914 does, under certain conditions, go to 42 degrees, right? The mechanical advance goes to 28, or so, and the vacuum goes on from there. The Cap'n |
I "thought" you mentioned that once John, I guess I was not too crazy afterall
| QUOTE |
| i still say people can go max advance under a particular circumstance as long as there is no ping. nice to read your posting.... |
My wife starts working at the HD near your house in a few weeks, give me a good reason to come on over and check out your progress
Posted by: Dr. Roger Aug 15 2005, 05:47 PM
| QUOTE (Mueller @ Aug 15 2005, 03:29 PM) | ||
My wife starts working at the HD near your house in a few weeks, give me a good reason to come on over and check out your progress |
she's working at the HD? Harley Davidson? =-))) i didn't know you were hitched to a biker chick....
Posted by: bd1308 Aug 15 2005, 05:56 PM
| QUOTE (Cap'n Krusty @ Aug 15 2005, 05:23 PM) | ||
You DO realize that the vacuum advance on a bone stock 914 does, under certain conditions, go to 42 degrees, right? The mechanical advance goes to 28, or so, and the vacuum goes on from there. The Cap'n |
yeah but after 73, the vac advance port wasn't, in most cases, even available......
at least from my pelican reading....
Posted by: lapuwali Aug 15 2005, 05:58 PM
There's a point at every engine speed and every load point where the spark happens at exactly the right time. That point is going to vary depending on the exact engine, which is why your Link will allow you to alter ignition advance with engine speed and manifold pressure. Anything away from that point will give less power and use more gas.
If you feel you can detect knock well enough by ear, then go ahead a fool with lots of advance in certain areas. Experimentation of this kind is easy with a fully programmable setup, so EXPERIMENT! Overadvanced or overretarded engines can run hot, so I'd rig up a CHT if you haven't already. Use ping and CHT to find the safest operating range. For best economy, you really only need to tune the fairly narrow range of MAP/rpm where cruising takes place.
Posted by: lapuwali Aug 15 2005, 06:00 PM
| QUOTE (bd1308 @ Aug 15 2005, 03:56 PM) | ||||
yeah but after 73, the vac advance port wasn't, in most cases, even available...... at least from my pelican reading.... |
Huh? All stock 914s had vacuum distributors. Some used manifold pressure to alter BOTH advance and retard.
Posted by: bd1308 Aug 15 2005, 06:01 PM
i was talking about vaccuum advance only.....
i realize the retard was used in all years.
Posted by: rhodyguy Aug 15 2005, 06:54 PM
for great fuel cost savings per week use public transportation. mileage smileage. so If you get that much better on the mpg you're saving what on an average tankful. 3 or 4 bucks? i didn't check, but my guess is i got in at least the very high 20's on the way home from the cruise last weekend. steady throttle, no highjinxs.
k
Posted by: cnavarro Aug 15 2005, 07:02 PM
Total advance aside, what target a/f ratio are you aiming for? I've set up more than one Nickies engine with 13.8-14 without any ill effects of heat. But I wouldn't experiment with leaning it out and upping the advance- one at a time please :-)
Posted by: Dr. Roger Aug 15 2005, 07:33 PM
13.8 to 14.2 to 1......... air to fuel ratio........
there is a effect of an explosion vs. a controlled burn.
case in point.
when i fire my potatoe cannon, if i use too much starter fluid it just pops out the end. barely....
when i give it just the smallest of squirts of starter fluid and fire it, it blows that spud so far, it goes out of sight!
engines need that controlled burn effect. any more lean and power detiorates very quickly. 
Posted by: Mueller Aug 15 2005, 07:53 PM
| QUOTE (rhodyguy @ Aug 15 2005, 05:54 PM) |
| for great fuel cost savings per week use public transportation. mileage smileage. so If you get that much better on the mpg you're saving what on an average tankful. 3 or 4 bucks? i didn't check, but my guess is i got in at least the very high 20's on the way home from the cruise last weekend. steady throttle, no highjinxs. k |
it would take me about 4 hours each way with public transit
Posted by: Jake Raby Aug 15 2005, 07:56 PM
I could write for days on this one- I won't even try.
There are no standards for this- EVERY engine is different and ITS ALL DEPENDANT UPON THE COMBO and your climate/elevation...
Don't attempt any of this until you have EGT, CHT, AFR gauges in your car- you can't make any observations until you are able to monitor/log the changes that adjustments make.
Every change has an equal reaction and you HAVE to remember that first and foremost.
Posted by: Andyrew Aug 15 2005, 08:53 PM
So what could you do to a sbc with an electronic dizzy, and FI (holley pro jet..)
Just learning great stuff with this new toy!!!
GL mike...
YOu know you need it
Posted by: scott thacher Aug 16 2005, 12:16 AM
28 + mpg at 80 + mph 
Posted by: Jake Raby Aug 16 2005, 12:25 AM
I beat that in my 912E..... 
TIV powered..
Posted by: airsix Aug 16 2005, 10:21 AM
As always, the Cap'n is correct.
On my PEFI I have an rpm-based (ie. mechanical equivalent) max of 27 degrees. I have a vacuum-based table that is independent of the rpm-based table. The vacuum-based curve is set for a max of 12 degrees. These two tables combine to give a total max advance of 39 degrees under high-rpm/high-vacuum conditions (highway cruise for example). This is very similar to the stock advance curve (ok, a hair more conservative). I think what aircooled.net is trying to say is that if you don't have any vacuum advance you are always going to have sucky gas mileage. I'll add that you'll also always have a big flat spot from 2,400- 2,700rpm.
While we're on the subject... I played with seemingly infinite ignition advance settings since it's so easy to type them into the laptop. After extensive testing I found that there is a real sweet spot that works better than anything else I tried -- The stock advance curve. (note: I have stock cam and compression. YMMV)
-Ben M.
Posted by: redshift Aug 16 2005, 12:13 PM
| QUOTE (rogergrubb @ Aug 15 2005, 09:33 PM) |
| case in point. when i fire my potatoe cannon, if i use too much starter fluid it just pops out the end. barely.... |
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