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GJF GJF is offline
Slantnose from HELL
 
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Join Date: Dec 2004
Posts: 801
It always amazes me to see people having a tough time with ITB's. It has always been a problem for many people to run engines with poor low speed velocity and get good response with ITB's. Understand that when using an engine with small displacement, the fuel cannot atomize and accel the engine if there is no velocity going to the ports. This senario in a small displacement engine with big ports, big valves, big ITB's, big cams and all trying to get to the powerband the car was intended to get to. This engine is basically a not gonna go anywhere til the car has some speed and the powerband is usable. This would be a perfect big track, in a feather weight car engine. In a short sprint course you might as well sit there and and just hold the steering wheel. Now that EFI has been affordable and used commonly the pressurized fuel injectors aide to atomize the fuel and help a little to get these little watch winders to ramp up a little faster. These engines were to fit a certain class and make the most power and still fit into the confines of the class.
Another problem with with ITB's is what I like to call the bigger is better why not go even bigger! syndrome. If you go too big on the size of the ITB it will hurt the port velocity as well. If you take the area of a single 80mm TB the area is about 7.75 and then take the area of 6 46mm ITBs it is about 15.42 that is more than double even 40mm is 11.61. ITB's come typically 40mm through 54mm for Porsche. If you put a set of 54mm on a turbo car and it is built for sprint then you just went backwards. If you are still running low compression ratios below 7.5 don't waste your time with ITB's you will suffer down low. It all depends on your build. Gabe's 3.8 will not have a problem with running ITB's as long as you keep them at a reasonable size, even running 40's there is still a sizable difference. The key when setting them up is to fire the engine with the ITB's open and equal all cylinders. Once that is done then there is only two adjustments. Linkage to the left bank and linkage to the right PERIOD............................................ ..... And also ITB's once sync'd they don't go out of sync unless something came loose. Once adjusted and tight that is it.

I run 96 lb injectors, (Sequential is a must)
13.5 AFR's is the lowest I can get it to run without losing injector control at idle
I run 8 at idle
my cars idles smooth and trouble free
starts on a dime, regardless what temp or how long it has been running
has zero driveability issues
On a side note the 96 lb injectors are good to support 1200HP I have been using them for a long time on different builds. On my car It can be turned up to that but it is not my goal to make that much power. My goal was to have the best all around power. It makes a little over 700 @1.5, that is more than enough for me. I usually keep it around 1.1-1.2 bar
It is all about matching components and having a proper tune.
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87 911 Carrera platform
Twin Garrett's, Big Valve, Xtreme Cylinder Heads, JB Racing cylinders and machine work, custom JE pistons, GT2 EVO cams, GT3 oil pump, modified 3.2L intake, 80mm TB, custom Intercooler, equal length headers, DFI, KEP Stage 2 custom twin disc, G50 custom gear set, LSD, Tilton trans pump, Fluidyne cooler

Last edited by GJF; 11-18-2009 at 12:09 PM.. Reason: edit
Old 11-18-2009, 12:03 PM
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