About measuring boost

A customer recently asked me about the level of boost he’s been seeing on his Techco supercharged mustang. Concerned about the numbers he was seeing, he was wondering if there’s a more accurate way to read it. He’s using an aftermarket boost gauge Tee’d into the the vac/boost line that connects to the fuel pressure sensor. Here are some notes about reading boost… Inside the Techco Supercharger Diagram
Inside the Techco Supercharger Diagram

  • Generally, with the base 7psi Mustang kit, you’ll see 6psi for most of the RPM range and near redline it’ll creep up to 7.
  • The published boost levels were recorded at sea level in Anaheim, CA. If I remember correctly, you’ll lose about 0.5 psi for every 1000 ft elevation.
  • All lot of the time, aftermarket automotive boost gauges are not calibrated accurately. Get a GOOD pressure gauge from SnapOn, Craftsman, etc. One that goes up to 20psi or 50psi or something (you can’t acurately read low pressure levels on the ones that go up to 150-200psi). Hook both gauges up to a single air line with a regulator and make sure both gauges are reading the same. Depending on the boost gauge/sensor, some you have to calibrate.
  • Make sure your SC belt is fairly tight
  • Every once in a while, there’s a problem that people run into with the by-pass valve operation. When the by-pass butterfly shaft slips in the linkage, the boost levels will substantially drop. Here’s a link to a post about checking the bypass valve for proper operation
  • As for the boost reference location, it shouldn’t make TOO much of a difference where you hook it up. I think the line that goes to the fuel pressure sensor is hooked up to a single runner. This usually causes some fast pressure fluctuation caused by the intake valves opening and closing. For PCM use, filters are applied to the voltage which smooth it out. For a mechanical pressure gauge, you MAY see smoother values hooking up to the bypass vac/boost line because it’s derived from the intercooler housing which is common for all runners. Additionally, you may see SLIGHTLY higher boost values from the bypass valve’s pressure reference port because it is hot air. There’s a slight pressure drop after the air cools from the intercoolers. Below is a diagram I made. I think the bypass pressure reference port is actually where we measured the pressure back at Techco but don’t quote me on that because I’m not 100%.

Checking bypass valve on Techco SC for proper operation

Every once in a while I get a complaint of a Techco supercharged car not nearly making the boost numbers you’re supposed to see. It can be several different things but every once in a while the linkage for the bypass valve slips which prevents the bypass valve from closing entirely. Here is an email I wrote to someone on how to check it.

Check supercharger bypass valve for correct operation. You’ll need to remove the front intercooler cover (part that says TECHCO) and then remove the intercooler cores. You’ll see the bypass valve blade in there. Now turn the bypass valve from the outside of the housing by pushing forward or pulling back the bypass valve linkage. When the linkage is all the way toward the front of the car, the bypass valve blade should be open. When the linkage is all the way toward the back of the car, the bypass valve blade should be completely closed. If the valve blade doesn’t operate EXACTLY like I said, the bypass valve linkage slipped on the bypass valve blade shaft. Readjust and retighten set screw (it needs to be fairly tight so it doesn’t slip again).


Dodge/Chrysler 5.7 & 6.1 Techco Supercharger Installation Manual



Ford Mustang 4.6L Techco Supercharger Installation Manual

For those that need the installation manual…



Cog Drive System in the works for Techco SC!

It looks like there are enough people interested in a cog drive system for their Techco Superchargers that I’m pricing out the rest of the development costs. As soon as I get an accurate price ready (another week), I’ll let everyone know how much it will cost for a cog drive pulley setup and the sizes I’ll offer. The cog pulleys will be made out of high quality aluminum and adhere to highly accurate machining. The cog pulleys will allow you to run a more relaxed belt for less parasitic losses, less stress on the bearings, as well as the guarantee you won’t have belt slip issues. Perfect for 10+ psi applications. It will be available for both Dodge and Ford applications. Free free to leave any comments or suggestions about the system.


10psi Dodge Magnum with Techco SC

I’m currently working with a customer to get his car running perfectly after he upgraded from Techco’s stock pulleys for more boost. Currently, he’s running 10psi on a STOCK block. I generally don’t recommend more than 8psi on the stock bottom end but if you want more, go for it. haha.

We’ve run into some road blocks here and there but so far have been able to overcome every one of them. Besides the pulley change we also needed to do the following

  • Replaced heat plugs LZTR7AIX-13 (factory gap of .050) with LTR7IX-11 (factory gap of .044) to prevent misfires under high boost pressures
  • Adjusted the boost-a-pump for adequate fuel supply.
  • Recalculated Volumetric Efficiency for ALL Manifold Pressure/RPM points for an oem-like flawless calibration
  • Currently looking into fuel supply as the injector duty cycle is beyond it’s limits

This car was already fast with the base kit but it’ll seriously kick some ass as soon as we’re done with the final touches on the calibration.