Ever since Todd Miller told me that Karo uses a vortec 75mm TB, I have been thinking of something... Unfortunately, it would be harder to implement for manual transmissions, but...
An intake can only flow as much as the smallest cross sectional surface area (in this case, the intake piping). A larger throttle body will hurt low end air velocity, especially a 75mm one. And you will have "0" vacuum WELL BEFORE WOT. I have 2 3/4" OD piping, and it measures at 65.78 mm ID. What I was thinking: what if there was a separate 52mm throttle blade placed upstream in the intake piping which is smaller than the intake piping so that some air would pass by (equivalent of a 40mm TB at WOT) while the rest is obstructed. This throttle blade would be operated with the left foot (hence the difficulty for manuals) and would allow you to moderate for low end torque and top end horsepower at will. I was thinking about dissecting my old throttle body and seeing how it goes, but I thought I would get some constructive criticism from others first.
-
"Youth in Asia"...I don't see anything wrong with that.
Brian Whalen wrote: An intake can only flow as much as the smallest cross sectional surface area (in this case, the intake piping). A larger throttle body will hurt low end air velocity, especially a 75mm one. And you will have "0" vacuum WELL BEFORE WOT.
You oversimplifying intake airflow to reach your conclusions.
1st- as rpm increases, so does airflow. So even with a stock TB at low rpm it is also possible to "have "0" vacuum WELL BEFORE WOT".
2nd - the job of a TB is not to flow air into anything based on cross sectional area.
The job of the TB is to reduce airflow to reduce power output and also be large enough to keep the plenum full at WOT throughout the whole usable RPM band.
The plenum serves as a large reservoir (bucket) that dumps into the runners If you look at it in a one cylinder-one event, point of view, the valve will open and close long before any new air moves into the plenum through the TB.
As for other parts in the system, if your intake tubing is smaller than make it bigger. A tube on the opening of the TB should never be the small point.
Karo's 75mm TB is fed by a 100mm intake tube.
sig not found
Anyone have more specifics on Karo's TB set up? Like what he had to do to make a vortec T/B work on a J?
PSN ID: Phatchance249
Thanks Todd
The idea was based on utilizing the really large TB only when needed (higher rpm's), while reaping the benefits of higher velocity at lower rpm's (a cheap, psudo VTEC gimic if you will)...Oh well
protomec wrote:
As for other parts in the system, if your intake tubing is smaller than make it bigger. A tube on the opening of the TB should never be the small point.
Karo's 75mm TB is fed by a 100mm intake tube.
75mm would be way overkill for me...even 65mm would be, but if I were to go through the work to make the northstar TB work, I would want a way to limit it while still NA.
Regardless... If it's not going to work how I would suspect, then I'm not going to bother. Thanks again, Todd.
-
"Youth in Asia"...I don't see anything wrong with that.
I'm running a 65mm w/o any problems........ but I'm also not stock.
Karo's t/b was a GM unit, so all the sensors are the same (plug and play for a LD9), you just need to mod the HO intake to accept something that large..... mainly bore out the opening, and weld on a new flange (the t/b is a 3 bolt design)...... the throttle cable probably wasnt all that hard to make work.
SPD RCR Z -
'02 Z24 420whp
SLO GOAT -
'04 GTO 305whp
W41 BOI -
'78 Buick Opel Isuzu W41 Swap
I know that GM has a manifold that you can use on the eco's that will allow you to bolt up a ls1 TB to it... at least thats what i kinda remember reading... dont hold me to it... i think their like 72? can't remember for the life of me....
http://www.motortopia.com/cavyfreak442/cars
Best ET to Date: 14.251 @ 98.51 mph. 13's or Bust Baby!
Brian Whalen wrote:The idea was based on utilizing the really large TB only when needed (higher rpm's), while reaping the benefits of higher velocity at lower rpm's (a cheap, psudo VTEC gimic if you will)...Oh well
There are many motors that use this concept. My Audi has a secondary throttle plate, as well as secondary intake manifold runners (shorter for higher RPM), my SHOs also had secondary runners. IIRC, the rotary 13B has 3 seperate throttle plates in the TB.
fortune cookie say:
better a delay than a disaster.
Actually i was working on my dads 4.3l vortec and it looks like it would fit on a HO manifold it has all the same connections.. its 75mm though a little too big . im about to get another upper intake along with another throttle body and i will find out then
