DOHC EFI modification underway

[spud69]

That looks really nice Matt, its a good pulling engine the dohc and will suit the roadster really well. Been out in a couple of Sierra with the same engine and they pull very well. It's just the size and weight of the engine that puts some people off.

For me i would keep the intake as short as poss with a nice cone filter on for that nice induction roar, i've always believed that for production cars the long runners and air boxes is to prevent any induction roar - not really what we want....

Well Done....AndyH

[davidimurray]

Generally - you cannot make extra power/torque by tuning runner lengths, but you can move the position of the peak on the performance curves. The theory is that as the valve closes a reflected wave is produced back up the intake. When this wave meets a large volume change it is again reflected. If you can time this reflected wave with the normal pressure wave generated by the inlet stroke and the addition of the two provides an extra charge of air into the system - hence a peak. The same applies to exhaust system. If you look for Helmholtz or organ pipe theory you can do the quite simple maths behind it. Generally, the longer the runners, the lower down the RPM range your peak will be,

To get more power you need to increase the volumetric efficiency (VE) of your engine. Hopefully I'm not teaching people to suck eggs, but the VE is the relationship between the cylinder volume and the actual amount of fuel/air mix you can get in there. You can only burn as much fuel as you have air for, so you need to get more air in the engine. You can do this with a turbo and have a VE greater than 1. You can also improve the efficiency of the your intake system so that their are less frictional losses for the air coming in - in its simplest form porting, but the same principal should apply to your intake system as well.

Now of course when you really get into it, the two affects above actually combine. As your losses are based around the air velocity travelling through the system, but you have to size your diameter for a particular velocity. So in an ideal world you would have variable length and diameter intake runners!!

[Enoch]

Lambos have variable length inlet pipes.
Thought you should know

[twinturbo]

Originally Posted by davidimurray

So in an ideal world you would have variable length and diameter intake runners!!

Which have been used on many cars over the last 15 years.. ( cosworth BOB, 2.0 16V DOHC ( ford ). etc...

Can't remember which way round it is but short/long is good for power/torque.

TT

[alga]

Short = less friction = more top power
Long = resonance down low = more low end torque

[mark]

Originally Posted by Enoch

Lambos have variable length inlet pipes.
Thought you should know

As do loads of bmws and the st170 engine im currently putting in my roadster!

The variable runner intake will be going on ebay rather than my car though

[davidimurray]

And quite a few motorbikes do now.

I'm not particulalry up with the latest fancy engines - but most of these inlet systems I've seen are 2 or 3 stage discrete systems, i.e. not truly variable. Does anyone know if any cars use a fully variable system?

[Wynand]

Originally Posted by davidimurray

Generally - you cannot make extra power/torque by tuning runner lengths, but you can move the position of the peak on the performance curves. ..........Generally, the longer the runners, the lower down the RPM range your peak will be,

As your losses are based around the air velocity travelling through the system, but you have to size your diameter for a particular velocity. So in an ideal world you would have variable length and diameter intake runners!!

I beg to differ.

Shorter runners will result in LOWER rpm HP whereas the longer runners will make HP in Higher rpm range.
IOW, for a town car shorter runners would be ideal and for racing engines longer runners would be more suitable. Ever wondered why racing engines have such beautiful long curved runner to inlets?

Basically an ideal plenum for a car to be used in town a good plenum design would be;

Plenum volume: 80 - 100% of engine volumetric capacity - normally aspired engines.
Runner lengths: anything from 200 - 300mm - measured from valve seat edge to runner inlet at plenum.
Runner diameter: 110 - 120% of inlet valve diameter.

General shape of plenum: Round or oval tapered down from TB - taper starts between 1st and 2nd intake from TB and runs well past last intake. Minimum diameter at the narrowest end of plenum must be about 1.5 times the diameter of the runners.

Just my 2 cents worth

[snapper]

907 on Locostbuilders can fabricate and TIG, does lots of great work to a fantastic standard, my recommendation

[rapidtornado]

Happy days, engine out of the Sierra and into my chassis. Bit of a pig though as my garage door height prevented me from hoisting the engine high enough to clear the frame so had to lift up rear end of the chassis by about a metre just to shoe horn it in. I was hoping that I could have lifted the chassis over the engine but due to it's width it just wouldn't go. I'll stick some pics up after of the engine in it's new little home (well until I get the engine mounts made anyway)



Now time for a brew and a sit on a radiator as I'm frozen through!

Later folks