Wednesday, January 19, 2011

Febuary 2011 Modified Tech Feature with Powerhouse Racing!

Toyota Exhaust Test Rear View

3-Inch Vs. 3.5-inch Exhaust Test - Tech

Today, Bigger Is Always Better.
January 19, 2011
By Pablo Mazlumian
Photography by Pablo Mazlumian
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Toyota Exhaust Test Rear View
For modified turbocharged cars pushing 300 to 600 whp, the most common exhaust size seems to be 3-inch. Some big-turbo cars use 4 inches at the expense of increased noise and decreased ground clearances, which is enough to deter many away from the larger-diameter piping. With piping sizing becoming more diverse, the option to go to a 3.5-inch diameter is now a viable choice. Experts say a 3-inch exhaust is fine for sub-800-whp levels like our Toyota Supra test car, but how much is being left on the table?
Toyota Exhaust Test Exhausts
The 3-inch exhaust (left)... 
   
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3.5-inch Exhaust Test (Downpipe back)
Modified by KC in Kansas City was kind enough to build our 3.5-inch exhaust and let us perform our testing on its Dynojet 424x, with pump fuel maps with methanol injection. Using 304 stainless tubing and a 3.5-inch, free-flow muffler (including a 5-inch tip from MagnaFlow), MKC fabricated the entire exhaust system from the existing 3-inch downpipe on the car.
Toyota Exhaust Test Installing
Surprisingly, the 3.5-inch... 
   
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3.5-inch Downpipe Test (Full Exhaust)
Fabricating a custom downpipe on a Supra with the engine still in the car is a tedious and costly job. And while there are a few outfits with 4-inch setups, 3.5-inch is almost nonexistent. Fortunately, our friends at Powerhouse Racing (PHR) in Texas sell a 3.5-inch downpipe and mid-pipe specifically for HKS-style manifolds, the same used on our SP turbo kit.
Toyota Exhaust Test Parts
Setting the boost back up to 29 psi, the larger 3.5-inch system started to expose the octane limits of our engine with pump fuel still coursing through its veins. At 764 whp, the AEM EMS pulled a couple of degrees of timing up top, limiting the gains to 30 whp at 6100 rpm. Still, compared to our first baseline, our total gain was now up to 70 whp at 6100 rpm with the full 3.5-inch exhaust. With a couple gallons of race fuel in the mix, surely we could have clipped the 775-whp mark.
Toyota Exhaust Test Downpipe Midpipe
The PHR 3.5-inch downpipe... 
   
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Toyota Exhaust Test Downpipe Midpipe
The PHR 3.5-inch downpipe and mid-pipe combo is a true 3.5-inch system with 3.5-inch V-band clamps. Adding the downpipe to our new 3.5-inch exhaust netted us another 52 whp and 30 whp in peak gains over our 3-inch downpipe.

Toyota Exhaust Test Parts
Toyota Exhaust Test Close Up
Toyota Exhaust Test Dyno
All told, at our mid-range... 
   
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Toyota Exhaust Test Dyno
All told, at our mid-range 19-psi boost level we gained a whopping 103 whp with a 200-rpm improvement in spool-up.
Toyota Exhaust Test Dyno
At high boost, our total gain... 
   
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Toyota Exhaust Test Dyno
At high boost, our total gain equated to 70 whp at 6100 rpm, but easily could've been higher with a bit more octane over our pump fuel/methanol delivery.
80-120 MPH DYNO ACCELERATION, FOURTH GEAR

BASELINE 3.5" EXHAUST 3.5 DP/EXH*
19 psi 2.54 seconds 2.54 seconds 2.24 seconds
29 psi 2.00 seconds 1.88 seconds 1.84 seconds

*8 degrees (F) hotter that day

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