I am no expert, but if you're changing the timing that much and it's not changing the sound at all then your advance curve likely isn't the issue and it's probably not timing-induced knock.

You sure it's just not something resonating at 3K? Heat shield, exhaust, something like that. Can you hear the sound at all if you rev the car in neutral? Engine trans mounts are good? Pulley's not hitting the body, engine's not hitting the sump guard?

Engine knock'll sound like rocks in a tin can typically. On my Spider it was kinda more of a crackly noise.

 

37° max advance is way to much. Go back to 32° like a standard car. You can then maybe increase to 34° but much more with pump gas won't give you more power. On a euro car we always put b7es in. I would do something like. Until 1200rpm 12° and then make a straight curve to 32° @4200rpm. The rest of the rpm stay @32°. If everything goes wel you can go to 34° max advance. But I doubt that it will make more hp.

 

Thanks for the comment. Most of the curves I've seen recommended say I can go higher but I think perhaps just as a test to see if the sound is still there I'll give your curve a try.

 

Not sure where you're getting that? The specifics of the curve are going to vary by year and engine, but Euro 2L GTVs were running 37-40 deg max advance. My '74 GTV engine is pretty much Euro spec and I'm having no issues with 36 max advance.

From the non-US 2000 GTV owner manual:

In any case he's having issues at 3K, and apparently he's tried advances between 25-34 degrees at that RPM. If there's no change in the sound across that range of curves then I can't see how the advance curve is the issue, right?

 

Not sure where you're getting that? The specifics of the curve are going to vary by year and engine, but Euro 2L GTVs were running 37-40 deg max advance. My '74 GTV engine is pretty much Euro spec and I'm having no issues with 36 max advance.

From the non-US 2000 GTV owner manual:

View attachment 1897777

In any case he's having issues at 3K, and apparently he's tried advances between 25-34 degrees at that RPM. If there's no change in the sound across that range of curves then I can't see how the advance curve is the issue, right?

I work 5 days a week on old italian cars. 75% are Alfa's. In the official manual that I have, it stated 32° max advance from 4200rpm. A 1600 or 1750 is stated 40°-43°.
Thats why. If there comes a car from another garage, in 90% of the cases the car ha too much advance. When I do my thing, everyone is happy with my adjustments. I don't say that a tuned engine doesn't require another ignition curve.

 

Lyle, my engine has a ping/rattle noise when going thru 3000 to 3500 rpm as well. I am attributing it to valve lash as I am a few thou fat on a couple of valves due to access to the right shims when I last adjusted them. I used my collection from the spare engine and the one in the car. I have double checked that it cannot be a timing chain rattle. Where did you land on your clearances? Funny that the sound is almost the same as wind noise at highway speed but comes in during acceleration. Also it seems associated with engine temp. not as noticeable at operating temps. I have been tempted to try to record the noise but figured it would not be discernable on the I phone mic.
Rusty

 

I have double checked that it cannot be a timing chain rattle.

If loose the top chain would typically make noise on decel when it slaps the valve cover. I dunno anything about the lower chain...I've never messed with that one.

 

By retarding AM you know 37 degrees may not be the issue. It still could be, with significant carbon build up or too hot a plug range. Different, seemingly identical engines can, develop detonation knock for different reasons. Next try one step cooler plug or a high rpm, WOT plug check. Then look into each chamber with a scope (or flashlight) watching for carbon build up on the partially open valve edges. Meanwhile, also look for something else that might also be causing a mechanical rattle.

 

Go back to your original advance curve and timing, then put in 5 gallons of 110 octane race gas and see if the noise goes away. I think you could be hearing the intake go in and out of resonance. If you still have the Alfa air cleaner ... temporarily put it back on and compare.

Also, you do not want any additional advance until after 200-300 RPM above your idle speed or it will never get a stable idle.

 

Go back to your original advance curve and timing, then put in 5 gallons of 110 octane race gas and see if the noise goes away. I think you could be hearing the intake go in and out of resonance. If you still have the Alfa air cleaner ... temporarily put it back on and compare.

Also, you do not want any additional advance until after 200-300 RPM above your idle speed or it will never get a stable idle.

I think you may be onto something with the intake, I've put back on the Spica air filter and will give it a drive later to see.

 

Bump up the fuel octane

 

I just filled up with 91 so I'll have to wait until ive emptied the tank to try this. There's a station not too far from home that has 94,96,98, and 101 so I may try that at some stage. What about an octane booster?

 

I work 5 days a week on old italian cars. 75% are Alfa's. In the official manual that I have, it stated 32° max advance from 4200rpm

On which cars? On the US SPICA cars, yes, max advance was limited to 25-31 degrees BTDC. They were terribly retarded for emissions purposes: they also ran 8 ATDC idle timing, which is kind of awful. The US manual also assumes min 91 RON which is 87 AKI (the octane number used in the US) so it's pretty conservative. With a more advanced curve you want to use 91 or 93 premium gas.

The pic above is from the Euro 2L manual where they didn't have to deal with emissions. I believe the "Wes Curve" above is what he puts on 123 Ignition units that he sells for US cars, if you advance the timing to more similar to the non-US specs you can get better performance.

Anyway you're missing the point by focusing on the max advance. He's not having the issue at max advance, he's having it at 3K RPM, and he's already varied the timing between 25-34 BTDC at that point. If he did that with no change in the sound then how can it be advance-induced knock?

I think you could be hearing the intake go in and out of resonance. If you still have the Alfa air cleaner ... temporarily put it back on and compare.

That sounds a lot more plausible. That or something else mechanically vibrating.

Also, you do not want any additional advance until after 200-300 RPM above your idle speed or it will never get a stable idle.

Nah. You don't want it idling in the middle of the ramp but you don't need that much of a gap. I set idle to ~1000 RPM and the ramp starts there and I've had zero issues with unstable idle. Below is what I think I currently have on the GTV.

 

Owner's manual says 87 AKI for a stock US '74. With a more aggressive timing map, yeah, you should definitely be running premium. The Euro 2L with 40 max advance just says "premium fuel recommended" though I don't see an octane spec.

Saffa, are you running higher compression than stock? I suppose it could be pre-ignition, which is very different from knock/detonation and would not be impacted by the ignition timing. That would be pretty bad. Preigntion could be caused by too hot plugs, carbon buildup, too high compression, too low octane, or running too hot.

If you're running stock compression and 91 octane gas then preignition seems unlikely. But again, not an expert, and I'm just guessing here without actually hearing the noise.

 

Okay, thanks everyone for the input here. I think perhaps I was getting a bit too paranoid reading about the dreaded ping. Today I put everything back as it was in my first post and reinstalled my Spica air filter. driving the car now I can't hear the rattle/ping I mentioned which makes me think that @4sfed may have been right!

 

As an aside... { He is ALWAYS right } You can ask how I know if you wish.

 

How do you know he is always right?….

 

As you get to know Jim, he will show you very specialized Alfa engineering projects you never imagined possible. Better still, they work well.

New or old, he has studied it to make it better.

Review his discussions on engine building for the fastest Alfa at Bonneville. Jim builds amazing stuff. I build Alfa oil pumps. Very good ones. Jim has built some considerably better. His engineering expertise keeps him thinking about things most never consider.

 

I am looking at other design cam followers there . any info on that?

 

Secret Jim Steck stuff. You need to call him for information. I remember he told me "expensive".