TedH

Prior to making the following adjustments to my 1980, I was averaging 15mpg:

Replaced 'DA' Secondary metering rods with leaner 'DR' rods
Replaced bargain suppression 8mm wires with custom 8mm Taylor Spiro Pro Wires
16 piece set of MSD 8mm 2-wire separators
Installed 2.5" crossover pipe in my 2.5" exhaust system
10W-30 oil/filter change (from 20w-50)

My latest fill-up shows that my average is now a whopping 18.6mpg.

As some may know, I am in pursuit of improved performance via tuning adjustments after a dissappointing dyno run which produced 220rwhp and 280rwtq numbers.

Assuming the improved mileage is a result of improved combusionl, is it safe to also assume that I can expect a performance improvement on the dyno? I am waiting for the tuner to repair his a/f monitor before I dyno it again.

For now, fingers crossed :cheers:


[Modified by TedH, 10:38 AM 5/15/2003]

cardo0

:cheers: Bravo Ted! Sounds like your the tune'n expert now. :D

LABulldog

Sounds like I need to follow your lead Ted. I'm a little bewildered, I would have thought the 700R4 alone would have added the 3+mpg and the tune-up would have added more. Anyway, as long as you're getting the better mpg, who am I to complain. Keep up the good work.

:steering: & :seeya

Chris O'

220 is dissapointing. I have a similar setup except for stock pistons and XE256 cam. I got 226rwhp so I would have thought you'd get 240 at least.

3.54 diff and TH700 must fry off the line! :yesnod: :cool:

TedH

I think the lack of tune (poor ignition wires perhaps) were negatively impacting engine efficiency; resulting in poor gas mileage.

I was very dissappointed back in 2002 after completing the 700R4 install to find mileage was poor. I expected the 18.6mpg 'out of the box'. No substitute for quality parts. Gives credence to 'total package' considerations.

74-Roadster

That sounds very good. The 700 may have done more than you think. With a stock L48, rebuilt carb and full tune-up, I'm still below 12 mpg. Hmmmm, think I'm still running a little rich?

TedH

Have you put it on the dyno recently? Most have an air/fuel meter that measures mixture under WOT. That will give you an accurate a/f reading.

My guess is that the combination of tuning changes all contributed to the gain in efficiency.

Can't wait to get it on the dyno to see if power has also improved. :smash:

TedH

What rear diff are you running?

With a stock L48 with 96K miles, TH350 and 3.08 gearing, I was pulling close to 17mpg. After my engine rebuild in '99 it dropped to around 15mpg. With the new gears and 700R4 it varied from 14-15mpg. So, my net gain after all of the rebuilds/replacements is about 1.6mpg. That's with 'spirited' city driving and some country cruising. I'm thinking 20mpg or better on the highway.

Chris O'

What about the vac advance? that costs about 5mpg if not working.

TedH

My vac advance is working fine.

Chris O'

You changed the secondaries but what about the primaries? Changing the secondaries won't affect economy. Economy and WOT don't go together. :p:

What jet/rod combo do you have? Is the power piston set correctly (about 2-2 1/2 turns out from bottom)? Plug colour?

TedH

My sig shows the primary jets/metering rod changes that were made prior to the last run that produced the 220/280 performance; we richened the primary circuit. Since the a/f ratio was fine on light/part throttle, we leaned only the secondaries. I am waiting to dyno again to see results of the secondary metering rod change.

cardo0

Forgot to ask, Ted did you make any timing changes? Any changes to vacuum advance (manifold or ported and canister rating), initial and total? How bout spring changes?
And to really annoy you what about plugs? :confused: Hotter? Colder? Bigger gap? :jester

isosceles

My L48 is pretty much stock except for true duals, TH350 and 3.55 rear. I tried 'nursing' it around town one week and barely got 13mpg. If I get on it a little around town it drops in the 10-11 mpg range. On the highway I have no problem getting 20mpg. At this rate, 3.6 mpg would be a 30% increase for me.
I'm saving for a 200r4!

Chris O'

Sorry dude - got sigs turned off!

I think I have 75 jets and 46 rods, CH secondaries. My economy is probably only slightly better. On a recent long trip I got 20mpg (Imp gal).

:cheers:

TedH

I run ALOT of initial advance. With this engine combination, I am able to run 25BTDC AT IDLE! By 1500rpm I am at 30BTDC and by 2500 I'm 'all in' at 35BTDC. ZERO detonation at any speed but I run PHillips 76 93octane religiously. That's a custom curve 'laid in' by a tuner so I'm not certain of the springs used but given the rate of advance, I'd guess medium. I don't know what he did to get the initial up to 25 but the engine loves it. My understanding is that I could retard the timing and gain gas mileage/reduce emissions but at the cost of power. I think I'll keep the power :smash: :smash: :smash:

The spark plugs are ACDelco R45TS (stock) gapped at factory setting of .045". Should I alter the gap or plug?

TedH

Lars setup the power piston so I defer to his judgement on that setting. The plugs are an 'off-white' grayish color with a hint of orange/tan. According to my chart, they are right where they need to be 'Normal'. Very limited carbon just 'south' of the threads of the base of the plug. Also, a 'hint' of motor oil on #7 spark plug which I am watching closely.

TedH

'80: 220rwhp/280rwtq, Restored stock dual-snorkel air cleaner with all new ducting and seals, K&N air filter, Lars-rebuilt/tuned q-jet carb ('74' main jet, '42' main metering rod, 'DR' secondary metering rods), Edelbrock Performer #3701 intake, Accel Perf Replacement HEI Distributor (re-curved), Taylor 8mm Spiro Pro Wires, MSD 2-wire 8mm Wire Separators (16), Crane 272H Energizer cam, DART 180cc Iron Eagle heads (72cc comb chamber, 2.02/1.60 valves, straight plug), Federal Mogul Flat top hypereutectic pistons w/ 4 valve reliefs - .020" overbore, Hedman #68301 Jet-Hot coated headers, custom 2.5" dual exhaust (no cat) w/ 2.5" crossover pipe, Dynomax Super Turbo mufflers, New cooling system, New vacuum systems, New/blueprinted diff with 3.54 spicer gears, Bow-Tie OD 700R4 with 1800rpm stall converter, Balance of drivetrain and suspension new or rebuilt.

NOTE: The 'DR' and 'CH' secondary metering rods are practically identical.


[Modified by TedH, 8:42 AM 5/16/2003]

Matt Gruber

Ted
keep an eye on spark plugs#5 and 7, as you go leaner these tend to overheat first.
if they are ok i would expect a power improvement. have you read my dyno tuning tips?(in profile & sig link)
:cheers:

cardo0

That's a very short advance curve Ted. Now your tuner may know best as my freinds with race only cars lock thier advance in at thirtysomething. But they run at full throttle for a 1/4 mile only.
I know when I tried to go from 8 to 15 degrees intial my shark slowed down. Just sounds like a lot room for experimentation. Do you have a spare distributor to recurve? I know youv'e read all of lar's Tech Tips on vacuum advance so won't go there.
If I remember right the coldest plug you can run without fouling/missing will make the most power. But coldest for around town driving as racing plugs can run much colder at constant high RPM. Wider gaps can be run with mutli/high power spark boxes (MSD etc.).
Looks like your going the right way on the carb. Nice work Ted. :thumbs: