Out with the old,in with the new ( Again )

[john.p.clegg]

Gus
I agree,maybe it is the short runners,all the production angines seem to have lengthy inlet tracts,or is that purely for tuning?

"At 10 BTDC on the exhaust stroke the inlet valve is slightly open and there is a spark" ?


John

[elanman999]

John,
The big difference is that you are using a plenum, I and most (all?) of the others are using ITB's.
I can't speak for bike TB's but Jenvey DCOE TB's do keep their balance extremely well. I have not touched those on my Elan since they were installed 3 years ago.
Cheers
John

[PeterK]

Gus
I agree,maybe it is the short runners,all the production angines seem to have lengthy inlet tracts,or is that purely for tuning?

"At 10 BTDC on the exhaust stroke the inlet valve is slightly open and there is a spark" ?


John

Typical inlet tracks (measured from inlet valve to trumpet inlet) are 200mm plus, with over 300mm being often being touted as ideal - ideal here being most tractable at 'normal' revs. Your's look more like 100-150, so I would predict more peaky performance, with max power quite high up the Rev range.

My understanding is that you no longer have cam position sensing, so therefore you're running grouped injection rather than sequential. In that case, is there any real difference between your plenum set up to that on a TB set up ? In both situations, there's a puddle of fuel wetting the inlet tract a short distance from the inlet valve, and it is this cylinder that will be sparking at the 'wrong' time. The biggest difference that I can see is maybe that TB injectors will be up to 30mm further away from the inlet valve. Not much of a difference.

Alternatively, how much hot exhaust pulse into the plenum could the valve overlap be causing ?

Peter

[john.p.clegg]

Peter
You may have something there,initially there was an air leak on the plenum cover causing a really weak mixture ( melted the exhaust extractor coupling ) which could of caused the top end to be way too hot.

The last time I used this set-up I had a 420 cam with more overlap,am now running a 360 cam with less overlap,so in theory should be less likely

Before fitting the plenum/throttle body was running Individual Throttle Bodies with batch injection,never ran sequential injection.

The main difference is in the volume of the plenum ( explosive mixture ) running to all 4 cylinders wheras with ITBs you only have four small volumes?

I'm sure the humble mondeo has wasted spark,a plenum and a single throttle body?..and no explosions..

John

[PeterK]

Mondeo has its injectors almost at the valve. Pretty sure it runs sequential injection as Ford wouldn't fit a cam sendor if it didn't use it

For the grouped injection, the waste spark fires (almost) as the injector fires, so I would think that that would be the source of unwanted explosion, rather than the gaseous mixture in the plenum. Sure that any plenum explosion would soon follow though !
Peter

[Bud English]

My Zetec crate motor from Ford came with the complete FI system as used on the Focus and Escape here in the US. It's a single throttle body system and the runners from the plenum are really quite long (making it too bulky to use in the +2 as supplied). It may be that the considerable distance from the plenum to the open valve helps. But, according to info on the internet (that's a disclaimer), Ford uses sequential injection on this engine and that may make all the difference. The injector bosses in the stock manifold are mounted in the manifold flange and squirt directly on the back side of the inlet valves.

Having said that though, I haven't read anything about this problem on the many megasquirt or emerald mods out there running batch injection. I haven't got to the stage to know if I have a problem or not. Ignorance isn't bliss in this case.

[john.p.clegg]

Keep us posted Bud.

John