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Auto Racing/About Exhaust please

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Expert: - 11/30/2007


Question
QUESTION: Hi, I have a stock 1997 jeep cherokee 6-inline 4.0L engine.
I want to make my engine breathe well :) so it will be faster.. What should I do to my exhaust pipe and tail pipe ?? increase diameter or decrease ? I want to do it in a welding garage.. Thanks.

ANSWER: Enlarge it by 1/8"  or about 3 mm.

---------- FOLLOW-UP ----------

QUESTION: You mean exhaust pipe or tail pipe or both?

And please I have one more question about suspension, I want to lower my ride by cutting the spring, how many ring should I cut to not damage my shock?

Answer
OK,  I don't usually answer questions that are not related to actual race cars.  Jeeps are not and never will be, race cars.

AS to my previous answer, increase the size of the entire exhaust system.

As to lowering the car, your suspension was designed by a highly trained team of automotive engineers. Lowering the vehicle can create steering , handling and control problems that are dangerous. Cutting coils off springs USUALLY causes damage to the chassis over time. Don't' do it.  

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Dan Liddy

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Anything concerning race cars, 20 years competition experience, Senior Competition Driver Instructor , car builder, mechanic, welding, fabrication, tuning , engine modifications, set up, suspension design. Specializing in Datsun/Nissan products. Please submit questions about RACE CARS ONLY. No street cars, no video game scenarios Thank you.

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I have been racing for 20 years, I have been the Central Florida SCCA Regional Championship points for 5 years running, and won the championship in my class 2 times. During my first start in the 60's I won many solo awards and the State Championship Drags. I serve as a senior instructor for SCCA, and have taught in Mercedes AMG events at Daytona, and Dodge Viper Days at Sebring International. I have been in the thick of the competition for all of my career. At one time or another I have driven race cars at speeds nearing 195 MPH. It's quite a ride !

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