lstvr

I am in the process of fitting Kinsler ITB's, i am restricted on space above them. I really need to run a trumpet straight out of the body just over an inch long.
Has anyone tried trumpets this short? The trumpets that come with them are around 4" long.

bug man nrg

do you have a pic of the space you have to work with?

SweetS10V8

iTrader: (4)

Length does matter, I hope you live at 5500+RPM.....Maybe such a liht car will help though.

lstvr

I had a clearer idea today, i have to take the trumpet stack from 90mm to 30mm. I will just have to see what happens!

Richard@WCCH

iTrader: (3)

Yikes!!! 30mm is really short! While the better breathing from the ITB stack will help as compared to a carb style intake, you're going to leave some torque on the table with the short stack length. The upper rpm range will work well though.....

Good luck,

Richard

lstvr

Here is an idea of what i am talking, the guy at Kinsler said i need 3 qtr's of the throat diameter as minimum clearance, throats are 55mm, so i need 41.25mm above the trumpet, i will try longer length when on the rolling road, just incase there are massive differences, but this length is easier to package. This is at the cardboard template stage, the base is now cut and box under construction.
The box volume will be in 12 ltrs plus, with two 4" cold air intakes.

With just the bodies on with no trumpets at all, this will idle down to 500rpms!!
Smooooth!

c5blkvette

Remember that your runner length is calculated from your intake valve, so what you are proposing may not be as bad as it seems (heck, what other choice do you have). Yes it is not ideal, but making them longer and then shrouding from the plenum is probably going to be just as bad. There are calculators/formulas on the web that can give you an idea of what RPMs are going to benefit from the pressure pulses for given runner lengths.

I would recommend the following course of action:
1. Dyno with the longer, or test a combination of runner lengths
2. Test your ideal packaged length and if you can live with the results then button it up.
3. If you cant live with the results, then either drop the motor (added benefit of lower center of gravity) or use a hood with more clearance (easier).

BTW. If you want to test how close you can put the plenum wall on top of the trumpets, use an aluminium plate with some adjustment screws and then adjust it down between dyno runs until you see a drop in peak HP.

lstvr

I have come to the conclusion i am going to have to power buldge it, so i will try the trumpets at around 60mm too, any more than this and the buldge will look a bit too hairy chest wig for my liking, plus the skuttle will need serious mods above this, i will try some plate and adjust it on some all thread, just to see if there is an optimum for plenum wall pulsing.
I will post my findings, will be in the next couple of weeks or so..

bug man nrg

you will need 50 mm from the top of your stacks .(air horns) to your air box to make this work for you .Short stacks are good for 7000 plus RPM but it will not help your low end power

lstvr

It sort of run out of puff at just over 6k, and the mid range was outrageous from 3-4K, so shoving peak power to nearer 7 would be desirable, but cam shunt was pissing me off, so was the main reason i bought these, if i get more power then thats a bonus too!

bug man nrg

Why did you not use a cross over set up ? this would have give you more room to play with on your runners or stacks .If you take a look at what BMW did there air box this might help you sort out what you need to do with this .

lstvr

Because these 10K throttle bodies came for less than 2k!

lstvr

Heres the progress so far, the top will not be completed until dyno testing, but this will be straight forward. I just have to decide how long i can go on the trumpets and still package.