It's running nice and cool, right or just a hair above the 155 degree mark on the gauge, not sure how accurate that is. I've got a 180 degree thermostat in it now but have a 160 thermostat handy that I'll pop in this weekend.

 

Toluene is an excellent octane booster and a main ingredient in alot of racing fuels. You can run up to 20% max, but 10% would probably do it. Slight re-jetting may be required
to bring it back to perfect.

 

Okay, so I removed the mechanical advance springs and fired it up, thinking this would give me the total mechanical advance number. Turns out, with no springs, it advances a total of 30 degrees. Seems a little high. I checked to see if the small rubber limiting bushing was installed and it is. So, I reinstalled the springs and backed down on the initial timing two more degrees to see it that helps. Sounds like my total mechanical advance is still a bit high according to the factory total of 26 degrees as explained by LeMans Pete above. I will try it where it is now, and back it down more if needed.

 

Stick to recommendations for Impala motors the L-46 is a 11:1 high compression Corvette motor and NO! it wasn't designed for crappy 91 octane fuel. You could try some GM top end cleaner to remove any carbon build up then retarded ignition timing or water injection. I've trained my wife to be ready to slowly release the clutch on her 70 LT-1 if it starts running on after shutdown due to our crappy 91 octane fuels.

 

You're on the right track.

 

Here we go again. My 70 L46 is 100% stock and never been apart. Everything is set exactly as it should be according to the factory. It has some miles on it so the only things I am unwilling to do is tear down a perfectly running motor to clean up some carbon build up or take the risk of using a top end cleaner.

I put in about 2-3 gallons of racing fuel along with 93 octane and problem solved.

Otherwise I can detune it to run on lower octane. What fun is that?

Until someone can show me a dyno comparing an L46 on 91 Octane versus 96-98 I am NOT buying that a bone stock L46 factory set up will run on 91 or even 93 octane without detonation or a loss of power.

Yes adjustments can be made, but NO way it runs the same. Dialing in to 26 degrees total advance will improve the situation.

When I put in that little bit of racing fuel the idle smooths out, it runs cooler, there is no detonation, and my seat of the pants knows the difference big time!

Bill

 

Why are you comparing fuel rated using RON vs. today's fuel that's rated in AKI?

 

Hey Bill,

Are you suggesting you get more power with a higher rated fuel?

Or maybe you have a mass spectrometer down your pants?

 

Oh good grief! Told you here we go again. Show me the numbers!

I agree that it will run on 91 octane. That is not the octane an L46 or 70 LT1 for that matter was designed to run on.

If someone has dyno numbers of an original L46 running on the correct octane versus a detuned version to run on lower octane I am all ears and eyes.

All I am saying is with an L46, it must be detuned to run on a lower octane. As a result there will be some loss of performance.

I am open to be proven wrong but I need to see the DYNO numbers. Lots of folks say it will run as intended with lower octane. No one has the numbers to back it up to date.

Feel free to come check mine out with 91 octane versus 96-98 octane. Different experience all together. Bring you timing light, dwell meter, or what ever else you think you need. Mine is bone stock and will not run as intended on todays 91 octane.

There may be an all original L46 out there running perfectly on todays 91 octane set up to exact factory specs with all factory equipment installed as it left GM. I have not seen it.




Bill

 

I only run 93 in my L46 as I had detonation issues with lower octanes. I have my ignition as close to spec as I am comfortable nothing. I have confirmed my motor configuration as stock.

I may not agree that anything higher than 93 will earn me any more "seat of the pants" power.

 

things like altitude factor in to the equation just like alcohol content and everything else. one car will run fine with one setup and another won't there are infinite variables. and no ,octane doesn't make more horsepower octane makes it possible to make more power.

 

Hey Bill,

Adding racing fuel or jet fuel or anything else like that will certainly take away the problem, but, I like to drive this car on long trips, and most gas stations along he way don't offer racing fuel. Suppose I want to jump in the car and take a drive up the Skyline drive for a day or so, no racing fuel there. The bottom line is, the car must be tuned to run on what is commonly available.

 

I completely understand. I am pretty confident you can get your L46 running pretty decent on 93 octane. 91 might be a little tougher.

You are on the right track. If I take a lot of timing out it helps significantly. I never tried 91 octane, just 93.

Bill

 

http://www.popularhotrodding.com/tec...s/viewall.html If your willing to remove heads, tighten quench to .040 with gasket, Remove all carbon, deshroud valves and open up the chambers a little. Polish all sharp edges. Thermal coating on chambers. A/F ratio as close to 12-12.5 to 1 across the board as possible. 165 thermostat. Heat shield for carb, cooler plugs, slower timing curve, less total timing, dropiming at detonation point with vac can or slower mech advance. lifter valley splash shield. Thinner oil will help cool internals 5W30 if your pressure will stay over 10 at idle and 10 PSI per 1000 RPM. All this can be done taking the heads off. Not a huge job.

 

Good point, and depending on the results of my compression & leak down test, it would be a good time to have new guides and valves put in.

I've put in the 160* thermostat and set timing at 26 degrees and she's running much better!

 

I've done all most the same, I did also cold plugs.
I did find out yesterday that I had the wrong stopper ring in my MSD 8571, it was the black. I did change it to the red, and a hard silver and light silver spring. (C in the MSD instructions)

That gives me 7-8 @1000rpm, and 28 @4700rpm.
I did set the timing to 7 in idle.

I do have a question, in Haynes it says:
Vacuum advance (crank degrees @ in Hg)
0 @ 7
15 @ 12

Can anyone explain what that means?

 

Thank you, you are correct re GM specs with full timing advance coming in at 5,000 rpm. Lars approach is based on typical use as it is most unlikely the average user is going to run 5,000 rpm. His tuning method is based on cruise speed and efficiency. Under Lars scenario the engine is running efficiently with the centrifugal “all in” advance at 2500/2800 rpm at 36*, you need to change the springs on the distributor weight to do this. It’s very easy to do, Lars explains. The result is, at 2500/2800 rpm you will now be at about 36* centrifugal plus about another 16* from the vacuum can for a total of 52*. At this rpm in top gear you will be running about 55/60 mph. If you haven’t read Lars paper it is really worth the time and has additional supporting information.
Stock Timing 1970 L46

A Initial timing @ idle 8* BTDC
B Vacuum advance 15* @ 12" Hg
C Centrifugal advance 0* @ 1000 rpm
D Centrifugal advance 10* @ 1700 rpm
E Centrifugal advance 26* @ 5000 rpm

Under this scenario max timing advance would occur @ 5,000 rpm and = A+B+E = 49* BTDC
With vacuum disconnected and plugged "all in" timing would = A + E = 34* @ 5000 rpm.

Lars timing for 1970 L46

B Vacuum advance 16*, “all in" 2" Hg below the inlet manifold reading when at idle rpm.
E Centrifugal advance 36* @ 2500/2800 rpm Needs to be "all in", distributor springs need to be changed.

Under this scenario max timing would occur @ 2500/2800 rpm and = B+E = 52* BTDC
With vacuum disconnected and plugged "all in" timing would = E = 36* @ 2500/2800 rpm.

In my case changing the vacuum can made a huge difference, I suspect it was original and had long since quit operating correctly. I’m running the cooler R43 plugs. I also changed the cooling thermostat to a lower value. I think the previous suggestion of blocking the crossover passageway under the carb is a good idea. I also removed the exhaust control valve at the right hand exhaust manifold and replaced it with a spacer. Anything which allows the engine to run cooler is going to help.

 

Excellent explanation in the article. Thank you.

The key is finding a machine shop to do the head work that REALLY knows what we are asking for on our cast iron heads..

It would seem to make more sense from a drivability point to put on a good set of aluminum heads rather then mess with the old cast iron heads. Have to believe there would be some additional power gains even with the stock L46 cam while eliminating the detonation issue.

Then you could clean up all that carbon build up while swapping heads.

Any suggestions on heads for just a head swap?

Bill

 

The distributor will rotate twice for each complete rotation of the crankshaft.

Hg is the measurement of vacuum, believe the scale is using inches of mercury .

0@7 = 0 advance of ignition timing at 7 inches of vacuum.
15@12 = 15 degrees of ignition timing at 12 inches of vacuum.

Typically to use this vacuum can you should see at least 14" of vacuum in your manifold at engine idle. It is important that the selected vacuum can is "all in" at idle rpm.

 

A lot of guys with L46 want to maintain originality. If your willing to make the jump to aluminum I would go AFR 180 65CC chamber, .015 Felpro 1094 head gasket. The combination of the aluminum head, fast burn chamber and .040 quench will run on premium, get full power @ 32 degrees initial timing instead of 36 and allow a much more aggressive advance curve. Likely give you 75 HP on top of the other benefits.