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Super Coupe Club of America > SC Literature > CW Report on the SC Exhaust System

by Charles Warner

Blower Intake System Test Report


As we have learned a high flow exhaust system is critical for high performance, likewise a high flow intake system is needed for high output engines, particularly at higher RPM. This article documents the results of modification and tests of the intake system up stream of the blower.

Below are the engine specifications for the test vehicle. With the exception of the stock exhaust manifold, stock cats and the old style blower ('89-'93) this engine is quite stout and is a good platform to investigate additional performance modifications. Perhaps the items above can be featured in future articles.

  • Engine Specifications:
  • Ported and Chambered Heads
  • Ported Intake Manifold
  • Raised and Enlarged Blower Top (SCPI)
  • Old Style Blower 89-93(non- 'S')
  • 10% Overdrive Pulley
  • High Lift Cam with Stiffer Valve Springs
  • 38 Pound Injectors
  • 155 lph Fuel Pump
  • Stock 60mm Throttle Body
  • 71mm Auto Specialties Mass Air Sensor (NMS)
  • K&N Air "panel" Filter
  • 3 1/2 Inch Exhaust System with High How Mufflers
  • Ported Stock Exhaust Manifolds
  • Stock Cats

Test Report

Now to get on with the subject of this report, the diagram below illustrates the base line system including major components and the pressure drop associated with each. The base line system differs from stock in that it was previously modified to include a K&N panel filter, 71mm Mass Air Sensor (MAS), opened intake silencer and 3 1/2 inch inlet tube. All pressure measurements were taken at wide-open-throttle (WOT) and 6000 RPM's. As can be seen excessive restriction is evident in several areas including the stock throttle body (TB), MAS, and air filter with air box.

Total pressure drop through this system measured a whopping 1.85 PSI, as can be imagined a totally stock system would be more. The throttle body is by far the single largest restriction, however the combination of the MAS, air box, and filter add up to another .75 PSI drop which is also quite large.

Next, I installed a 70mm throttle body and 'moderately' ported and Extrude Honed Blower Plenum from SCPI. Boost pressure went up by 1 PSI and performance improved as well. The pressure drop across the throttle body decreased to .5 PSI while the pressure drop across the inlet plenum increased to .35 PSI as can be seen in the diagram below.

It should be noted that the stock intake plenum measures about 65mm and is larger then the stock 60mm throttle body. This is why very little pressure drop was measured across the blower plenum with a 60mm throttle body. The Ported Plenum increased the diameter to 70mm, the same as the 70mm throttle body, therefore the pressure drops tend to equalize. Although the larger throttle body and ported plenum did lower the pressure drop and improved performance, it is still too small for maximum performance. I recommend a 75mm throttle body (the largest available) and a "Max Port Plenum" to obtain even better performance.

Next a high flow 9 inch K&N cone filter was attached directly to the MAS. As you can see in the diagram below pressure drop was reduced to zero, however performance also decreased. Attributing the performance decrease to the engine breathing hot under hood air I tried several methods of mounting the cone filter in the finder well, but all attempts resulted in increased pressure drop in the additional tubing. The best solution I found is to mount the K&N cone filter directly to the MAS and route cool air to it via a 5 inch air duct concealed in the finder well. A "box" should be fabricated to fit over and cover the filter so hot air can't get to the inlet while idling.

These modifications improved performance dramatically. Back in March after the addition of the Enlarged Blower Top an acceleration run from 20 MPH to 55 MPH took 3.57 seconds. With the 70mm throttle body, Ported Blower Plenum, Cone Filter and Cold Air Duct this time was reduced to 3.28 seconds. Another .29 second improvement!

A Side Note

Last year when I decided to soup-up my bird I wrote a software model that simulates engine performance. This model takes into account engine displacement, RPM, volumetric efficiency, thermodynamic efficiency, boost pressure, power required to run the blower and calculates output HP, torque, total fuel consumption, fuel delivery per injector, and plots these parameters versus RPM. I used this model to size fuel injectors, fuel pump and other things such as the exhaust system to ensure they would be sufficient to meet my performance goals which was 360 HP. Well, while running this last set of performance tests I noticed the fuel pressure dropping off at higher rpm's and the engine stumbling a bit around 6000 RPM's, so I referred back to the software model to get a clue of what might be the cause. I updated the model's input parameters to reflect the latest changes and to my amazement I realized that I had exceeded my goal by a bunch. The simulation is calculating 402 HP at 5900 RPM's (plus or minus a few percent) while burning 163 liters per hour and the injectors are attempting to inject 41 pounds of fuel per hour per cylinder. This is all a bit much for my 155 lph fuel pump and 38 lb. injectors. Time to upgrade the fuel system and performance goals. How about 460 HP? That would take about 17 pounds of boost, a 190 lph fuel pump and 48 pound injectors and maybe alcohol injection to keep from detonating, but it would be fun.


A 70mm throttle body, ported blower plenum, K&N cone filter and cold air ducts are real power builders for the SC. However with a ported engine, high lift cam, large exhaust, overdrive pulleys and such the engine wants more air. A 75mm throttle body and 80mm MAS would improve performance even further. Also, you guys that have built your engine to this level should be running 190 lph fuel pumps and at least 42 lb. injectors.

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Document Last Modified: 07/29/04 03:33 AM
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