another velocity stack question.

[AEeighty-six]

i will be getting my 20V ST tuned next week.

i plan to get velocity stacks for it.

should i get them before i get the motor tuned?
or is it alright to get them afterwards?

basically, would the motor run at its best if it was tuned with them?

and i know it has been asked before, but
what type of stacks should i get, length-wise?

i know this...
short stack = more power, higher rev
long stack = more torque, lower rev

but which would benefit more in a daily/weekend fun drift set-up?

[jondee86]

ITB's without stacks lose power.
ITB's with OEM bent stacks run OK at all rpm's.
ITB's with short (25 mm) stacks lose power everywhere except up high.
ITB's with longer stacks (75-80 mm) will work high and low, and may
even give a bit more power than OEM if you are lucky

My 2c worth

Cheers... jondee86

[ZDoman]

I would advise you to tune it only with the velocity stacks as they can change the cylinder "filling" as the length and shape changes of the velocity stack.

When I designed my stacks, I took a look on the original ones, they were ~120mm long. I wanted to have torque at mid rpms so I have 90mm long ones. But the best what you can buy is the technotoytuning 75mm.

[eight-six]

Does anyone have any hard facts on how much room you need in front of the stack? I have long stacks for my itbs (not fitted yet) which means the bell mouth opening will be close to the inner wing. Would this cause issues?

[gon]

it depends , the ONLY way to answer all these trumpet questions is on the dyno .
A Small room can actually be good due to enabling the reflection of sound waves . This can improve your performance when the frequency of the sound waves matches the length of the air travelling.

Although I do not disagree of what has been previously said in this post, I have to alert that the length of the trumpet is not the most important thing. The most important thing is the length of the inlet ( from the edge of the trumpet to the edge of the valve). As such the 20v ITB on a 20V engine can have a different optimum trumpet length than the 20V ITB on a 16V engine, due to the difference in length of the manifold connecting the itb's to the head, and also due to the difference in length from the edge of the head to the edge of the valve ( considering the 16v head VS the 20V head).

Once again it all depends on your engine.
Everything you think is good for your engine is only a guess until you do back to back testing.

[jondee86]

What he says ^^^ but in simple terms of airflow, a distance from
the wall of one bellmouth diameter would be plenty.

Cheers... jondee86

[XJS]

In a Circuit Driver magazine a while ago read an article from Dave Walker tuning K series Rover engines on dyno. He find on that particular example different lenght trumpets working best, the 1-4 shorter than 2-3. So i would mock up a blase plate, some diff lenght tubing and the bellmouthes, or gather a couple of different shape and lenght trumpet, and find out which one gives the most for the cams and ex. header in place.

[AEeighty-six]

alright. so i believe you are all saying this...

i should get velocity stacks before i get the motor tuned.

correct?

also.

where can i get air filters for the velocity stacks?
which kind work the best?

where could i find these? they look nice.
http://i18.photobucket.com/albums/b106/E...2b2223.jpg

[jondee86]

AEeighty-six Wrote:I should get velocity stacks before i get the motor tuned.

Correct? YES

Where can i get air filters for the velocity stacks? Which kind work the best?

These do... http://www.itgairfilters.com/content2.as...n=megaflow

Where could i find these?

At your nearest ITG sales outlet

Cheers... jondee86

[Diskovod]

Actually, comparing the length of the velocity stacks isn't quite accurate. The engine reflects on the WHOLE intake lengts - stack+ITBs+connector+intake port length... so that's it...

For 16V 4A-GE.
And if you want to gain something with (for example) stock cams with intake closing at 51 degrees at BDC, then the lengths would be:
for 5000 6000 7000 8000
cm 28,4 23,7 20,5 17,7
in 11,15 9,33 8,05 6,93

For 20V 4A-GE.
For stock cams with VVT engaged (closing intake valve @ 40 degs):
for 4000 5000 6000
cm 27,7 22,3 18,6
in 10,90 8,75 7,32

VVT turns off at 6500 so after this the intake valve closes @ 70 degs as usual:
for 7000 8000 9000
cm 28,1 24,2 21,7
in 11,04 9,52 8,54

As for all the minimum intake pipe (outside the head) for 20V equipped with VVT-i should be at least 11.9 cm (or 4.68 in).

happy tuning