A downpipe is the section of exhaust which comes directly off of the turbine. The factory downpipe on the 3rd generation Supra Turbo is very restrictive and is a horsepower and torque sucker of power. This 3" diameter HKS downpipe replaces the pre-cat and uses a mandrel bent tubing to offer superior exhaust gas energy flow and therefore creates horsepower!! 20HP gains have been noted with this modification alone!! This bolts up to your factory exhaust or any aftermarket 3rd generation Supra exhaust system like those offered by HKS and GReddy.

This DP can be used with your factory exhaust, aftermarket cat-back exhaust or with our test-pipe for total CAT elimination.

Inset picture shows the HKS DP installed on the car with the flex pipe very apparent. Photo compliments of Paul S.!

Benefits of a down pipe

Reduced turbo lag (turbo spools up quicker)

Increase in boost (1-2psi in boost means power)

Reduction in EGT (exhaust gas temps drop with free flow)

We had a good question via email the other day regarding down pipes and pre-cats. Here is the question and answer from SupraStore.com from a Texas MK3 Supra owner.

Hi,

I recently purchased a 89 MKIII Turbo with approx. 50,000 original miles. When I had it inspected here in Dallas(I purchased it out of state) it passed with "zero" emission. I have added a HKS Turbo 75MM catback and Blitz SUS Air Filter since the inspection. As you know, this car has a "pre-cat" built into the stock downpipe and a secondary catalytic converter. Currently, I am thinking about replacing the "pre-cat" stock downpipe with a performance(HKS, AMS) 75MM downpipe.

However, I am worried about my car passing the emission inspection test here in Texas if I replace the "pre-cat". In Dallas, the emission testing is done via a probe being placed inside the tailpipe. Is the "pre-cat" or secondary catalytic converter the main source for reducing the emissions on the MKIII Supra? Surely, SOGI Members and other numerous MKIII owners that have websites listing their 75MM downpipe modification have faced this same situation. Any response or advice concerning this problem will be appreciated.

ANSWER:

While we are not Texas emissions experts, nor do we have access to their data and requirements in testing, we can inform you the main purpose of the pre-cat is for cold weather emissions (aka cold start). The pre-cat is required for the cars to meet the US emissions testing of the manufacturers prior to entering the US market. The pre-cat helps absorb the oversupply of hydrocarbons on cold starts. Since you test your car HOT, the pre-cat should have no bearing on tail pipe emission testing. Off Road Use Only