Who Wants To Know The Ideal Runner Length For An Engine?

[jacobs53 0]

I have been using 4 stroke head for over 3 months now, and I have finally found out how to obtain the best runner lengths for both inlet and exhaust. Im going to post these up

 

What engines do you need information for???

 

I need the following spec..

 

RPM where max power is produced (not max permitted speed!)

bore

stroke

CR

 

and thats it! seems so easy from your seat but I have to compute all this information to obtain the ideal lengths.... I wonder how far off the mi16 inlet and gti6 inlet are from being perfect?

 

I was testing this on the 206gti engine and the inlet runner needed to be 247mm long!!! to obtain approx. 267bhp at 9000rpm. And the exhaust needed to be 290 - 330mm long.

 

lee

[nick 3]

247mm is roughly 10" which at a guess is about the same as an Mi inlet.

 

So sounds about right.

 

Nick

[Rippthrough 98]

Surely you need the cam specs. to do it accurately? As otherwise the pulse might arrive too early/late with low overlap cams?

 

Anyway:

 

6600rpm

75 bore

77 stroke

10.4:1

 

 

-Phillip

Edited November 21, 2006 by Rippthrough

[smckeown 1]

6625rpm

83 bore

88 stroke

11.25:1

Edited November 21, 2006 by smckeown

[jacobs53 0]

well thats what I first thought about the cam timing..... but aparently the cam is does not alter the lengths by much at all!!! considering the application is racing use.

 

second though supply me with valve size for inlet and exhaust... sorry forgot this one!!!

 

lee

Edited November 21, 2006 by jacobs53

[James_R 3]

interested in the GTi-6

 

inlet -34.1mm inlets

Exhaust - 30.6mm

 

7000

86.5

88

12:1

 

And

 

6700

83

88

11.5:1

 

thanks

[petert 554]

36.5mm inlet

30.0mm exhaust

7500

86.5mm bore

86mm stroke

11.8:1

[Sandy 189]

It's not something you can model accurately, there's far more variables than that at work. Trial and error produces suprising results.

[Higgy 0]

Is '4 stroke head' a simulation program?

 

I used Dynomation while doing Formula Student, christ, thats nearly 5 yeaars ago!!

(you can input cam profiles in etc).

 

On your runner length does that include the actual distance from the cylinder head port to the back of the valve?

 

Higgy.

[stevec205gti 0]

I'd be quite interested in learning how you did this - I spent a fair amount of time looking for ideal inlet runner lengths for my home cooked injection manfold for a triumph spitfire, and it was a complete minefield!!! There was all sorts of things like deciding which reflected pulse you wanted to use.........

[C_W 3 1 Cars]

Surely you can't know what rpm max power is produced at since the runners will affect this

[bennett418 1 1 Cars]

The way i know it as, short = more low rpm power

long = more high rpm power

 

I could explain this more but am going on my lunch!

[B1ack_Mi16 67]

The way i know it as, short = more low rpm power

long = more high rpm power

 

I could explain this more but am going on my lunch!

 

It really is the other way around.

[smckeown 1]

well thats what I first thought about the cam timing..... but aparently the cam is does not alter the lengths by much at all!!! considering the application is racing use.

 

second though supply me with valve size for inlet and exhaust... sorry forgot this one!!!

 

lee

 

any update on this ?

[Faz85 0]

There is no single optimal runner length for best performance, there is only a compromise since there is many different variables which come into play once the revs climb. Thats where variable length runners and variable resonance induction come in, which i think VAG were one of the first to employ, but the system is also used on the pug 3.0 V6 also IIRC

[jacobs53 0]

sorry i completly forgot! Il check it out tomorrow

 

lee

[jacobs53 0]

inlet -34.1mm inlets

Exhaust - 30.6mm

 

7000

86.5

88

12:1

 

Assuming a exhaust manifold diameter of 38mm and inlet diameter of 40mm. Also stem diameter of 7mm

 

Intake pipe length (from back of valve to end of runner) 324mm. This is tuning for the secondary ramming pulse.

 

exhaust pipe length (assuming 4 - 1 ) 918mm for each runner from the start of the cylinder head. Then collector length 1106mm with a diameter of 66mm

 

 

6700

83

88

11.5:1

 

Intake pipe length (from back of valve to end of runner) 338mm. This is tuning for the secondary ramming pulse.

 

exhaust pipe length (assuming 4 - 1 ) 963mm for each runner from the start of the cylinder head. Then collector length 1156mm with a diameter of 66mm

 

To create a accurate simulation I will also need the following

 

1) Valve Stem Dia.

2) Both Manifold Dia.

 

lee