c3_dk

Also what I've did also:
160F
Cold plugs
8 + 12 degrees, no vacuum.

Detonation comes:
On a hot day.
Giving full gas.
"pulling" in 4th gear, or speeding up from 40-50mph in 4th gear.

Gordonm

What is your total advance. Initial advance does not mean much.

c3_dk

8 degrees in idle (700rpm), 12 degrees advance @ 2800rpm, so total @ 2800rpm = 20 degrees. No vaccum.

Mike Ward

Max is 20* BTDC?

Either it's not detonation or there's something else really really wrong. More octane won't help.

Revi

Something isn't adding up quite right. 20* at 2800 is low and you shouldn't be getting any detonation. Are your weights/springs still advancing past 2800rpm?

Also, at full throttle you shouldn't be getting any vacuum advance. Unless the vacuum can on the distributor isn't backing off all of the way, which will give you too much timing.

Get a dail back timing light, disconnect vacuum, measure your timing at idle, 1000rpm, 2000rpm, 3000rpm, 4000rpm, 5000rpm, etc.. What you are looking for is when the mechanical advance stops advancing.

Example,
700rpm - 8*
2000rpm - 22*
3000rpm - 30*
4000rpm - 36*
5000rpm - 40*
6000rpm - 40*

In the example above the mechanical timing is still advancing past 3000rpm, it doesn't max out until 5000rpm. (You do not want that to happen.)

Your goal is to find the perfect balance of weights/springs so you get the maximum of 36* timing around 2800-3000rpm. The mechanical weights should be at their stops at this point.

Example of my L-46,
750rpm - 10*
2000rpm - 28*
3000rpm - 36*
4000rpm - 36*
5000rpm - 36*
6000rpm - 36*

c3_dk

All advancing stops @ 2800rpm.
I did set it to 36 degrees @ 2800rpm, and took 2 of every time I heard detonation. (Lars told me to)
Lars also told me, that I would never get my engine to run 11:1 without detonation. With the quality of gas I can get today.

Revi

If you started at 36*@2800rpm and had to back the timing off to 20*@2800rpm you have way bigger problems as Mike Ward has indicated.

While the L-46 is advertised as 11:1 compression, actual production engines were less. Most likely in the 10.5:1 range or so due to manufacturing tolerences.

Do you know the actual compression of your engine or just what someone has told you? Has it been moded at all? Has the harmonic balancer slipped? Your timing numbers and detonation don't add up.

You may want to pull the #1 spark plug, bring the piston to TDC and see where the timing mark is in comparison to the timing tab. It should be around 8* BTDC if everything is aligned properly. If the timing mark is 15*-25* BTDC the balancer needs corrected.

c3_dk

It is.
Engine is 0.030, std L46 heads, 0.020 head gasket, L46 cam, "factory" 3cc (2.6cc) TRW dome 0.030 piston, 0.025 down the hole.
This gives me 11:1 or a bit more.

http://www.jeepstrokers.com/calculator/

c3_dk

BTW no and no

Revi

My L-46 is .030 over, stock heads (but ported), stock pistons, .025 down the hole, forget head gasket thickness off the top of my head, Comp Cam XE262, and I'm at 10.4:1. Runs fine on 93 oct.

In the past I could coax just a bit of transient detonation at times in 4th gear if I floored it at a lower rpm, but nothing consistant. I believe I'm right on the hairy edge of what 93 oct (and my timing) can handle and any deviation in gas quality from station to station causes the problem. I could bump the timing down 2* and the problem goes away.

Again, your timing numbers just don't make sense. There doesn't seem to be any possible way to get detonation at that low of a timing setting. Have you tried disconnecting the vacuum advance and just drive around with mechanical timing to see what happens?

Mike Ward

FWIW- the quality of gas today is superior to that of the 60s and 70s in many, many ways. With the exception of low RVP numbers that might lead to vapour lock or percolation in hot weather, it's a far better product. Best thing that ever happened was getting rid of the lead.

Many people are unaware of the octane rating system change-over here in the 70s and think that the anti-detonation properties are lower.

Whooops- we've hijacked again.

c3_dk

A small rubber plug in both ends.

Thanks for the update/info.
Lars told me, if I what to run full advancing (52 degrees), then I need min. 104 octane EU gas.

I agree I've hijacked, let's stop here.........

rvazquez

Congrats on the new project David, I followed your Sparty project from beginning to end and am looking forward to this one.
Regards
Roy

AllC34Me

I think I'll start another thread later on the 350/360. This one has gotten side tracked.
David

1974ta

The L46 compression with cast iron heads makes it a real challenge to get it to run on pump gas.

I have a 70 L46 bone stock and original and have gone through EVERYTHING suggested on the board that says it should run on 93 octane.

Bottom line is that if set up as it was from the factory it will run much better with a little more octane. My L46 detonates with 93 octane and basically runs terrible. I can retard the timing and it will sort of run on pump gas. Add 5 gallons of 110 Sunoco and the car runs like it was supposed too. Idles perfect and winds up to the red line flawlessly.

While it is reasonable to think some L46 motors will run well on 93 octane, they will run best with a little more octane IMHO.

I would love to see a dyno chart of an L46 "tuned" to run on 93 octane and an L46 "factory tuned" running a bit higher octane.

I have had some good folks say the L46 should run on 93 octane. I just wish one of them was closer because I would love to learn what they know. It is a source of great frustration as 110 octane gas is not easy to come by and limits road trips.

Now if you really want to have some fun, run a 50/50 mix of 110 and 93 octane in your L46!

Bill

LeMans Pete

Hey Bill,

That statement would ring true for most motors, right?. If you bump that octane level up, you have the potential to bump that timing up. My L46 ran fine on 93 for a few years until it was time to tear it down. But, I will still be installing a thicker head gasket to bring that compression down.

Revi

Mike Ward

If the engine is able to run the recommended 36-38* advance and does not detonate, raising the octane level to run more advance will probably be counter productive.

LeMans Pete

True, but the L46 does not operate at 36-38° from factory, nor is it meant to. If you want to put 110 octane in your car so you can operate at that curve, well by all means do. But the car was designed to run at 26° with pump gas.

Don Rickles

David,

Wow, You're a lucky guy! JT is a hell of a guy!!! Hope everything is OK?
I know he has been working on and collecting parts a LONG time for this project.

Good luck, I'll be waiting to see your progress!