TPI runner length calculations?
Thread Starter
Drifting
Joined: Nov 2001
Posts: 1,469
Likes: 6
From: 68 427 4.11s Roadster
TPI runner length calculations?
I'm trying to build my own but first I have to see how big and this means how to make.
I used a formula from http://www.grapeaperacing.com/GrapeApeRacing/ that shows how to calculate for length but after doing a reflection table it don't help much at all.
This is just a example and isn't real numbers.
12" long will reflect at 20, 19,18 and so on.
So will 5" and so will 22". The RPMs where reflection happens are spaced differently but this thing don't really help on length. You can literaly choose any length and it will reflect at a give rpm area but just a different RV value.
I would like to have 2 legnths. 1 long and 1 short on a valve for top end. Even if I do away with the short one sitill would like to know what the length is going to be best for me.
For me the formula ends up (265,000)/(rpm/reversion number)-1"
Maybe I did it wrong but I flipped it around so I could just find the RPM for each RV number with a set intake length. Reversion number is how many times it reflects. For 1 RV it might be 10', for 2 it goes down and so on.
So finally the question. Anyone know of anykind of info out there to determine this? Any other sites that tell you how to determine tuned runners?
I used a formula from http://www.grapeaperacing.com/GrapeApeRacing/ that shows how to calculate for length but after doing a reflection table it don't help much at all.
This is just a example and isn't real numbers.
12" long will reflect at 20, 19,18 and so on.
So will 5" and so will 22". The RPMs where reflection happens are spaced differently but this thing don't really help on length. You can literaly choose any length and it will reflect at a give rpm area but just a different RV value.
I would like to have 2 legnths. 1 long and 1 short on a valve for top end. Even if I do away with the short one sitill would like to know what the length is going to be best for me.
For me the formula ends up (265,000)/(rpm/reversion number)-1"
Maybe I did it wrong but I flipped it around so I could just find the RPM for each RV number with a set intake length. Reversion number is how many times it reflects. For 1 RV it might be 10', for 2 it goes down and so on.
So finally the question. Anyone know of anykind of info out there to determine this? Any other sites that tell you how to determine tuned runners?
Team Owner
Joined: Jul 1999
Posts: 65,492
Likes: 230
From: Orange Park Florida
Years ago I did a lot of reading and calculating on stereo loudspeaker engineering, among the solutions was a design known as 'bass reflex'.....largely unused today as it was very limited in the desired responses at various frequencies....and rather not smooth.....
this is related to your question in that it's a subject of resonance in the 'tuned' length of the induction tubes....
and the timing of the pulses, thing is....in a bass reflex enclosure the thing does not have any affect over 300-400 hz....mearly a factor of maybe 5x or so above the lowest tones they typically acheived....at ~80 hz.....
but a typical auto engine fires 5x par second at idle....600 rpm or so.....600 divide 60= 10 divide 2 for 2 cycle engine=5.....
but at 6000 rpm it's only 50 times/second....
buzzy little valves there....
trying to keep any really positive affect off the runners at a smooth overall performance level is nearly impossible....
due to length, all the ram/inversion affect is gone by roughly 2500 rpm or so....
That's why the later take offs of the TPI type systems just go with a short more open runner....LT1, etc....
GENE
this is related to your question in that it's a subject of resonance in the 'tuned' length of the induction tubes....
and the timing of the pulses, thing is....in a bass reflex enclosure the thing does not have any affect over 300-400 hz....mearly a factor of maybe 5x or so above the lowest tones they typically acheived....at ~80 hz.....
but a typical auto engine fires 5x par second at idle....600 rpm or so.....600 divide 60= 10 divide 2 for 2 cycle engine=5.....
but at 6000 rpm it's only 50 times/second....
buzzy little valves there....
trying to keep any really positive affect off the runners at a smooth overall performance level is nearly impossible....
due to length, all the ram/inversion affect is gone by roughly 2500 rpm or so....
That's why the later take offs of the TPI type systems just go with a short more open runner....LT1, etc....
GENE
Thread Starter
Drifting
Joined: Nov 2001
Posts: 1,469
Likes: 6
From: 68 427 4.11s Roadster
After completey confusing me 
I think we're talking about 2 different things.
Ram is different than tuning. Or at least this TPI or tuned port injection. Otherwise it should be called PI port injection.
The idea as I understand it is when the valve slams shut the air is still moving. Its pressure wave reflects off the valve and returns up the port. Hits the plenum and is sent back down the port again, I think this is a negative pressure now. It again hits the closed valve gets reflected back out and in again. If its timed right the positive reflection hits the valve just as it opens.
Its basicly the same thing that headers are supposed to do, except on intake you want the pressure wave and exhaust the negative wave.
I think the LT1 is still using this system other wise they wouldn't use long ports. Its much easier to make them short than it is to make them long. If you want short stick the plenum in the valley and the ports enter it from either side. Not wrap over the top of it but enter directly.
I think we're talking about 2 different things.Ram is different than tuning. Or at least this TPI or tuned port injection. Otherwise it should be called PI port injection.
The idea as I understand it is when the valve slams shut the air is still moving. Its pressure wave reflects off the valve and returns up the port. Hits the plenum and is sent back down the port again, I think this is a negative pressure now. It again hits the closed valve gets reflected back out and in again. If its timed right the positive reflection hits the valve just as it opens.
Its basicly the same thing that headers are supposed to do, except on intake you want the pressure wave and exhaust the negative wave.
I think the LT1 is still using this system other wise they wouldn't use long ports. Its much easier to make them short than it is to make them long. If you want short stick the plenum in the valley and the ports enter it from either side. Not wrap over the top of it but enter directly.
Pie ar round. Cornbread ar square.
Team Owner
Joined: Jul 1999
Posts: 65,492
Likes: 230
From: Orange Park Florida
Techno, it's not really two differant things in a physics sense, as the speaker moves back and forth, thereby affecting the pressures in the enclosure/box, and the only 'port' it can 'breathe' from is the long resonant tube, tuned for an octave lower than the speaker in the box....
sorta allmost the same thing as the engine, only the valve of course never allows any pressures to build from the suction side of the runner, of course, but the vacuum coming and going with induction sort of creates the same thing....
a column of air that is vibrating in it's motion which can be in sympathy or not with the piston/speaker-driver.....
but later engines have much shorter runners than a TPI setup...
GENE
sorta allmost the same thing as the engine, only the valve of course never allows any pressures to build from the suction side of the runner, of course, but the vacuum coming and going with induction sort of creates the same thing....
a column of air that is vibrating in it's motion which can be in sympathy or not with the piston/speaker-driver.....
but later engines have much shorter runners than a TPI setup...
GENE
