1:13 comp ratio, ignition issue

[reuven]

Hi,
After building my tuned engine I tried some ignition systems, none fitted, I always had advanced ignition noises, the only thing that helped was using 110 octane.

I decided to make a test and weld the inside part of the distributor so it will not advance at all. I found the right point in which at low RPM it is advanced but not in a problematic way and in the high RPM 7000 to 8000 and more (in high gears) I dont hear any more the advanced noises.

If I will find a way to do the ignition map exactly as I want it to be off-course it would be better, but I found this as a good compromise.

Just to share ideas...

Reuven
Israel

[BlpltGTV]

13:1 compression is WAY high. The reason it pings on anything less than 110 octane is because the compression ratio is on the moon. If you weld the dizzy in place so it cant advance you loose the advance needed at higher rpm. Yes it will run, but it probably won't run correctly. If you use this engine on the street, I'd double your headgasket up to reduce the compression ratio.

Just a thought.

Will

[Greg Gordon]

The best way to deal with this is add water injection. Then you can run full timing without hearing the dreaded knock sound, and you will get all the power from your high compression ratio.

Greg Gordon,
hiperformancestore.com

[Alfar7]

13:1 is not so high that it should knock on 110 octane race gas. I would suspect cams with incorrect timing as the primary issue. Or cams with insufficient duration for that compression. As Greg said, some advance is necessary.
How did you build motor to get to 13 to 1?
What cams are you using? What are their profiles & timing events?

[reuven]

Cams are 11.3 mm high and 312 deg duration.
Pistons are 1:12.5 and the head was lowered a bit.

My idle is about 1500 rpm and the distributor is set to be very advanced at this rpm so it will be ok at high rpm. my biggest problem was the noises of the advanced ignition on the 5 gear when getting close to 200 km/h (about 120 miles/h) and higher.

At first I changed the springs inside the distributor to the strongest I could mount, it helped but did not solve the problem 100%.

Greg, can you tell me more about the water injection, how does it work and what do I need to install it.

[han]

They thing I would do is retarding the cams so that the filling is worse because off that part off mixture is pushed out again.

You now lower the presure in the camber, not in a way you would like but there is not match else you can do.

You can tray a thicker head gasket.


That will cosd some performance but not advansing is costing you more performance.


Han

[reuven]

Moving the cams is very dangerous because the valves are big and the head is low...

[papajam]

Other causes for engine pinging;

high coolant temperature
lean (weak) mixture
sparkplug heat range too hot

[reuven]

Quote:

Originally Posted by papajam Other causes for engine pinging; high coolant temperature lean (weak) mixture sparkplug heat range too hot

[Greg Gordon]

Reuven,

A water injection system is a powerful anti-knock device. It has a very similar effect to using higher octane fuel. If you use water injection, you probably won't need to retard your timing or lower your compression. Here is a short excerpt from a book I am working on:

"Injecting water into the engine’s intake system has an effect that’s very analogous to using higher-octane fuel. Just how much of an effect does it have? According to N.A.C.A., a lot. They came up with the following numbers. An engine normally requiring 100-octane fuel can operate satisfactorily on 80-octane fuel with a water/fuel ratio of .6:1. That same engine could be run on 88-octane with a .4:1 water/fuel ratio or 94-octane with a .2:1 ratio. If we assume that this effect will be the same with pump gas then 93-octane fuel with water injected at a .6/1 water fuel ratio will be effectively 116-octane!"

Now, that's just straight water. Water/Methanol is even more effective and under some conditions Water/Alcohol can be advantageous (not on an Alfa). I have data for all of that as well.

I use the "Coolingmist" brand system. They have an excellent system for high compression normally aspirated engines.

Greg Gordon

[reuven]

We have in Israel something called "TULUL", you mix it with the normal gas (max 99 octane in the gas stations in Israel) up to 30% and than it makes the octane of the mixture about 106 octane.

With 106 octane I can use the distributor with the strong springs with no pinging.

I will learn about the water injection, thanks for the info.

[5yearplan]

I'd definitely go with the water injection, it's cheaper (in the long run) than high octane gas, and you won't have to worry about compromising with the cams or timing, as it NEEDS to advance, or any headgasket funny business.

[reuven]

Here you can see and here the engine:

YouTube - Alfa Romeo Giulia Super Beautiful and Fast

[180OUT]

Reuven:

Here's an additional approach. Richard is right that race motors often run successfully with 110 octane gas. Increasing the overlap reduces the effective compression ratio. If you want to further reduce the compression ratio (not a bad ideal, I think) you can remove material from the combustion chamber itself. There are formulas which tell you how much volume relates to specific C/R's. Another approach, perhaps the easiest, is to have a thicker head gasket made of copper. There are limits to how thick you can make the copper gasket but I'd think you ought to be able to reduce the C/R by at least a point or point and a half. Combined with a little judicious releiving of the combustion chamber this ought to let you get a C/R that is more managable with what you are running.

A final thought. I don't know what kind of ignition you are using but a multifiring CD ignition like the MSD6 can have a significant effect on preignition. In one of David Vizard's tuning books he mentions that Otto cycle engines have a preignition moment at around 2500 RPM. The MSD6, firing over multiple crankshaft degreees at relatively low RPM's, is effective in better controlling the flame front (especially in an open chamber head) and, hence, preginition. This is, of course, 20 year old technology and a 3D mapped ignition like a Megajolt w/EDIS components would probably work even better. I tried the MSD6 appraoch, however, and it worked surprisingly well for me, although I wasn't running 13.1 compression.

[matsalleh76]

MSD sells an in-cockpit timing adjuster accessory box that works with their 6 series spark boxes allowing ~15deg of adv/ret adjustment. This cured my everyday around town hi-compression (12.5:1) knock although at the same time running a retarded spark reduced open road "playtime" performance.

For "playtime" dump a bit of toulene in with the petrol: it is available from most hardware or paint shops, is cheaper than petrol, and will give you a 2 or 3 point Octane boost and not harm anything in the fuel system.

Toulene is one of the components of normal petrol and the main component of over the counter Octain Boosters. Do a Google search and learn about the stuff.

Adding 15% toulene completely eliminated knocking on my car and with the MSD timing adjuster allows full advance throughout the entire rev range.

Regards,
bobf.