Of octane and knock

T

typhoon

New Member
Has anyone played with fuel enrichment to get rid of knock on a 10.5 engine, instead of retarding timing?
The reason I ask is my engine is ALMOST free of knock at 6 degrees btdc idle, but will knock mildly under load from about 3000 rpm on. I did screw the jets out a little towards teh rich side, and it did help, but it is winter here, and the knock will only get worse as it heats up.
I don't want to kill of base timing, as it gives a fair bit of low end torque, so my options are enrich fueling in the knock range, recurve distributor or constantly run an octane booster.
I know it's easy to just say retard base timing, but I bought a 10.5 compression engine for the performance, and by golly, I want the performance!
So, what is the best way to enrich HIF carbs in the uper midrange under load, but keep reasonable economy the rest of the time, or will it not cure the knock, and I should recurve the distributor?
Is it worth also playing with cooler spark plugs, or is a bit of all the options above the way to go?

Regards, Andrew.
 
Andrew,
in the early part of 2004 another additive has recently been added to the approved list although it has been on sale since the virtual disappearance of leaded petrol.
TetraBOOST (a genuine lead additive) contains tetraethyl lead in a solution of aromatic hydrocarbons and, as an additive, it falls outside the EU regulations and is sold with all fuel tax and duty paid.
However it is only available mail order of 8 x 945millilitre bottles at a time but can be used at various dosages to produce a range of fuels equivalent to leaded petrol from three star to five star plus.
100 millilitres of TetraBOOST added to 11.5 litres of standard 95 octane unleaded will produce 11.6 litres of 4 star 97 octane fuel and 100 millilitres of TetraBOOST added to 11.5 litres of super 97 octane unleaded will produce 11.6 litres of 4 star 99 octane fuel and 100 millilitres of TetraBOOST added to 11.5 litres of Shell Optimax 98 octane unleaded will produce 11.6 litres of 5 star 100 octane fuel.
This is fantastic news for all owners of early, high compression, four and eight cylinder Rover engines and is probably the route I would take and recommend.
Regards, John
 
Does enrichening the mixture solve anything ? Surely the problems with normal unleaded are -

1 Not enough octanes - hence the knock effect
2 Not enough lead - hence the risk to your valves and seats
 
An over rich mixture can reduce combustion temperatures, and help reduce knock.
Whish is why my engine never knocks when cold with choke.

Regards, Andrew.
 
In my opinion, since your problem is lower octane you should use an octane booster.
Rich mixture may mask the problem, but remember that engines were designed to run with a specified fuel/air ratio.

Too rich mixture will result in a rough engine, excessive emissions, loss of power, carbon built-up and whatever comes next. Plus the fact that fuel consumption will increase (and we are talking about a V8 here!) up to the point that it will be more economical to have bought the octane booster in the first place!
Last but not least higher octane fuels have significantly better characteristics that result in better power and MPG.

Do you still want to rich your carbs?
 
How about a device that only retards the timing under full throttle conditions ?
There are devices that do this for Nitrous oxide installations, so I guess the same could be applied here.
Or some way of modifying the ignition advance curve would probably be better than over-fuelling.
 
That's actually rather a good idea! I have a feeling that is how "knoick sensors" work on modern engines. Is that an invitation for the electronically stimulated (definitely not me - I like to be able to see what the electrics are doing!) to put a modern engine management system on a 10.5:1 P6? Does a Range Rover P38 have such a set up?

Chris
 
The distributor can be made to retard timing, although not by sensing knock. It's fairly straightforward to take out some mechanical advance from the top end of the curve, which still leaves proper low rpm advance.
This is one option I was looking at. You can get ignition retard boxes, but they usually sense boost or similar for turboed engines.
I agree that teh main issue is octane, I'd just like to find an option that works with premium fuels available today, and that will retain maximum driveability/ power.
I am wondering if teh fact that my engine will not knock at full throttle when not fully warmed up is pointing to intake air heating up or similar? I may also play with manifold insulation. Does teh heater coolant supply run through the manifold?

Regards, Andrew.
 
That's exactly how knock sensors work, the ignition / engine management system detects the knock and retards the ignition, depending on how clever the system is it will remember the setting and permanently retard the ignition under the same load/speed conditions.

That's why when you switch to optimax type fuels on modern cars you need to re-set the ecu so that it will re-adjust to the improved octane rating and the engine will produce optimum power. In theory you would have the engine fully re-mapped whenever you change fuel type, but that's a bit extreme ! :D
 
When you say it doesn't knock when not fully warmed up, is the choke still on ?
If the choke is on then the mixture is rich, but if the choke is off then you could be right, obviously we all know about the fuel vapourisation problems on the v8, this usually only affects the car after the engine is turned off and the carbs heat up, but running heat will have an effect on fuel temperature and hence fuel density. Plus the carbs have bi-metal mixture adjusting strips in the float chambers to compensate for fuel temperature, so that's another potential variable.

You've also got the possibility that wear in the carb pistons is preventing them from lifting as high as they would when new.

In fear of being stoned to death at our next regional meeting I would suggest binning the carbs and distributor and fitting a new fully mapped engine management system :) Then you can have the exact fuel / advance settings you need.
 
No stoning from me, I can't hurl things that far! :p
And yes, the car does not ping when it is not up to full operating temperature, and has no choke on.
However, I did stumble across a fully programmeable ignition kit last night, one that allows full mapping throughout teh rev range, and has teh ability to use knock sensor and manifold vacuum input. The only problem is it is a kit, and requires soldering etc, which I can do, but haven't done on such a scale before.
For under $200 Au, it looks the way to go, with an electronic distributor of course. It has a handheld programming box as an accessory, and can be adjusted on the fly!
My other option is LP gas, but it's a big outlay and frankly for the kilometres the car does, overkill!
http://www.siliconchip.com.au/cms/A_108521/article.html
http://www.jaycar.com.au/product....TID=347
http://www.jaycar.com.au/product....TID=347

Sorry about the long links, I have no idea how to wrap them smaller.
Regards, Andrew.

EDIT: Look at that, it automatically wrapped! Clever webmaster!
 
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