What are the best ways of combating detonation?

Mapping a friends engine at the mo, but have had to remove alot of ignition advance to get rid of the detonation.

Down to about 13 deg @ 0.5 bar under load.

I think most of this is due to the poor chamber design he now has after fitting a decomp plate (no more squish).

I know that backing off the advance moves the ignition event back in the cycle and lowers the post ignition cylinder pressures which in turn prevents post ignition gases from igniting on their own after the spark.
I was just wondering if there are any other methods of reducing det that i could use?*

The ACTs are already pretty low and the engine also runs at a decent temp.

Would water injection give me any det protection other than cooling the charge?

I realise stu might not want to give away his secrets, so one for the home mappers really.

Any suggestions welcome.

Cheers,

DC.



* bar removing the plate and rebuilding with some dished pistons and/or careful enlarging of combustion chamber. Not my engine so can't open it up.

 

What AFR are you running?

Fuel is a pretty good Det surpressant!

 

your options are:

a bit more fuel...

lower the boost....

drop the act....

back off the ignition.

Its best to run as much ign as you can even if it means dropping the boost.

Alex

 

Currently running 12:1 at that point in the map.

 

Pretty much forget about running any more fuel then!

Looks like the options are pretty minimal!

What CR is it?
Can you do anything about that?

 

I would not recommend using WI as a det suppressent, as if / when water runs out / jet gets blocked - engine goes BANG.

 

could say same about fuel injectors tho surely? and idve thought, providing you got a decent setup, no greater risk?

 

Itsmeagain, its ok if there is some sort of warning i guess?

But most people with WI dont know its run out!

 

CR is a knats cock under 8.7:1.

Would like to be running 10psi in the end. I have dialed out all the det so far at 7 psi but it just seemed like quite a low advance figure for that boost/cr setup.

Do you think the lack of squish makes that much difference?

Not sure that shed loads of fuel is the best way to combat det / run an engine. Our local so called tuner once showed me a RR printout of his cossie running 9:1 afr and seemed to think it was fueling great!

 

8.7:1 isnt exactly high compression, so thats lil strange.

GTST skylines are 9.5:1 as standard and ive seen them running 1.5bar no problems on pump fuel

Gotta be down to huge squish area surely? Prob would work better without the decomp plate!

 

Ok... aprt from the running out aspect, does it do anything to help suppress det apart from cool the charge?

I have monitored the ACTs on this engine and as far as i can remember they were pretty good.

 

Thats what i mean. Would love to see an ignition map from a car that spec.

Think it must be the lack of squish that encourages the det?

 

I run 11psi on a 10.5:1 engine, that has cast pistons

 

I know its obvious...

but what engine is this?

Alex

 

I'll wager that Mike means you shouldn't really utilise WI as a normal means to reduce det' when mapping - ideally, WI should be the last resort, a safeguard to combat high charge air temp's (yes that's CAT's not ACT's ).

I.e. WI shouldn't be kicking in whilst driving around normally.....

Another option is higher octane fuel, but again this is a compromise, unless you have easy access to run it all the time (or dual maps)

If you can't reduce det' to an acceptable level, then something is amiss (as you've already said) - do you really want to map a 'compromised' engine??

 

how old is the fuel in the tank?

 

Fresh optimax, so not that.

 

What engine and what management?

 

BMW 318 is

Megasquirt!

 

There's a knowledgable chap who knows his BMW's on here and a couple of users with Megasquirt experience also. Maybe edit the post title and add BMW 318 & Megasquirt.

 

Cheers Billabong.

This is my fourth MS install/mapping. So pretty familiar with the MS kit.

But being my fourth engine to map, still on a steep learning curve where mapping is concerned!

 

I know both systems


Its not an ideal engine to turbocharge, your porbably finding the limits of the combustion design.

Alex

 

can you upload the maps?

 

You have changed the spark plug heat range havent you?

 

Stu, that sounds MUCH more likely than chamber design and squish at such low levels of boost!

 

Stu,

So what your saying is the plug electrodes are running too hot and in turn causing the detonation?

So simply trying a cooler running plug may help?

Will give this a try at the weekend. Dial some of the advance back in and let you know the results.

Thanks,

DC.

 

Keep us posted, very interesting topic

 

Will do. Should have a chance to re map on sat.

Chap is putting a new clutch in it as we speak. Last mapping session, as we started pulling the fuelling map closer to ideal the worn clutch started deciding it couldn't cope with the new found torque!

 

New plugs puchased! Gone from NGK 7s to 9s.

Two steps cooler. Hope it works.

 

NGK 7s on 7psi at 10.5:1.... Detonation or not, that could have killed her stone dead.

 

Keep going Doug

Silly question but who's beemer is it?

Stu - Thought Doug said it was around 8.7:1

 

Smit,

A friend of mine. Not sure you know him.

If you are down the pub (sorry, truck stop ) next Wed i will try and bring it along. Will take you for a spin if yer fancy it?

Yep 8.7:1, but been doing some research i think Stu is right about the heat range of the old plugs. Way out!

 

Doh.... didnt read deeply enough to realise it was decompressed

 

Eye, but with an aluminium plate!

Chap bought it from Ferriday. I was a bit worried about it so had a chat with Mike something un pronouncable from ferriday and he seemed to think it should work as an extension of the head and hold the cylinder pressures ok.

Seems to be holding up ok so far...

Still loose any decent squish the piston/head design had though!

DC.

 

I'm on nights next week Doug so won't be up the trucky

Be there the week after though as i'm on 2-10

Got a picture of the turbo conversion, sounds kinda funky

 

Squish is of course very important, but its not the end of the world at those power levels.

Lots of people on big (well ish relative to cossies!) power vauxhall engines use 1.9mm gaskets to lower the CR and seem to get away with it just fine.

Obvously taking some metal out without ruining the squish would be better, but i personally dont think its that causing the problem.

 

Is it using a eurpean 323 TD manifold?

 

Nope. Custom tubular exhaust manifold and modided stock inlet.

Surely a 323 would be a six pot? Or did Europe get a four pot version?

 

I havent quoted myself before....

A decomression plate is a bodge!

Thats why your getting det, very bad combustion chamber design. You've change the attributes of the CChamber completely, things like squish, flame front and end gasses are now completely different to the original design.

Alex

 

sorry mate, wasnt paying attention, thought it was a 6 pot engine, i just saw bmw and my mind refused to admit any less number of cylinders