What do individual throttle bodies do for me?

FIntruder · Post by **FIntruder** » Mon Jul 24, 2006 6:14 pm

I can understand the benefit of port injection, each cylinder gets its own metered amout of fuel and the fuel doesn't have to travel as far as the intake air. What does a throttle body for each cylider do for and engine?
Easier to have shorter runners? Give folks a reason to buy syncronizing sticks? Looks cool?

TV Super Bee · Post by **TV Super Bee** » Mon Jul 24, 2006 10:27 pm

With a properly matched size, the throttle response would be quite "snappy", very quick off the line. Too large ITB's will be tricky to tune without surging. Yes, you would need to sync all of them without the benifit of a plenum between the TB and intake valve. I run dual mustang style 65mm TB's with a common plenum, so having them perfectly in sync is not as big a deal.

Ferret · Post by **Ferret** » Wed Jul 26, 2006 9:27 am

From what I read, most engines with "wild" camsahfts have problems with running at low RPM with a plenum chamber and ITB cures these problems.
Avner.

TV Super Bee · Post by **TV Super Bee** » Wed Jul 26, 2006 12:49 pm

My cam is 284 degrees duration and .484 inch lift. It would be considered medium/wild. It has a lopy idle needs a 2500 rpm stall and makes power up to 6000rpm. I could not get it to run on map dot AT ALL! At idle I have only 5hg's vacume. It made the map sensor go all over the place. I found that alpha-n works great for me with my dual 65mm TB's. With the accel bins set fairly low
v/s ms
5 4.5
3 2.7
1.5 1.2
0.7 0.5

I rev very fast with little throttle movement. I can't even hit the 25v/s that is the original upper setting. If you have a big cam and large TB's I would recomend this setting as a starting point.

Bernard Fife · Post by **Bernard Fife** » Wed Jul 26, 2006 12:59 pm

TV Super Bee,

I have a slightly bigger cam than that in my 406, and I can use MAPdot with no problem at all. I use a MAPdot threshold of ~80 kpa/sec.

My idle pulls about 38 to 42 kPa, so I'm surprised your is just 5 "hg (~67 kPa) - is the cam ground on a very narrow lobe displacement angle? If not, have you tried tuning the idle to minimize the kPa?

Lance.

TV Super Bee · Post by **TV Super Bee** » Wed Jul 26, 2006 4:28 pm

Lance,
5hg is at idle in drive gear (automatic), in neutral, Ihave 11hg of vacume. It is tuned for max vacume at idle in drive at aprox 900 rpm. Rpm rises to 1100 in neutral. I've tried various settings with map dot accel, every time the engine falls on its face. It may have something to due with the dual 65mm TB's dumping air into my plenum. With alpha-n, and low v/s settings it will get up and fly. My only problem with this set up is at high engine temps it will start to turn lean. sometimes above 18.0 ego. There is a air density compensation but, I'm not sure if I'm to move the % up or down for more or less fuel at a given temp. The megamanual does not specify. The default settings have the % decrease with temp (100%@160deg down to 80%@220deg).

jonfx4com · Post by **jonfx4com** » Fri Jul 28, 2006 2:20 pm

I run a 305deg cam with ITB's and use mapdot. It is ok if you use restrictors and a plenum to smooth the MAP but I'm sure that alphaN is the better way to go. Less work and probably better results in the end. On the more general question of what do ITB's get me?

Straight line of sight from the outside world to the back of the valve, instant throttle response, as near perfect gas flow as you will ever find.
If your going to spend money on the head don't waste it by saving money on the intake system. Of course for good maners in traffic, ease of tuning, a nice idle and good MPG they are often not the perfect choice.

You wont find many drag racers with less than one throttle plate per cylinder and it's not just coincedence they all go the same way.

Jon