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1991 964 performance enhancements

Engine

Vehicle Information: Model: 964 c4; Year: 91; Body Type: Cabriolet; Total Mileage: 76600;

My 91 C4 runs great and I have done some low cost modifications to the car:1 Chip2 Secondary muffler removal3 K&N cone filterThe engine performs wonderfully with good compression in all cylinders and I hear no evidence of valve noise. I am very happy with the performance of the car with the exception of very low end lag, and am considering a couple modifications over the summer to improve responsiveness of the engine. Lightweight flywheel with the new chip to keep the engine idling. Question- do the chips for the flywheel mod also give the same benefits as the upgrade chip I am currently running or is it back to stock performance? Which flywheel kit would you recommend and whose chip?New valve springs, lifters and a valve job. Would also consider porting out the heads but have no idea if this would help my engine breathe better or mess with the emissions, have looked around but have not seen any mention of this being done to Porsche engine.I have read your comments about the upgrade to 3.8 liter cylinder heads and understand the upgrade to a more aggressive cam will likely cause emission failure, is this also true with just a cam upgrade? I assume so but since I am thinking about an upper rebuild I was considering a more agressive cam.Other questions- I recently (still waiting for them to arrive) orderd 18" sport design rims to replace my stock 16" design 90''s. Will the added weight of the wheels, and rubber F 225x40x18 R 265x35x18 effect my to the pavement horsepower, and will my speedometer read incorrectly?Am also considering a PS9 as opposed to lowering springs and stock struts. My mechanic said the setup will work with my new wheels but warns of shock tower problems with the springs as opposed to PS9, saying the chance of the struts bottoming out very high with the lowering springs. I want to lower my car but I really don''t want to spend 2K to do it.Any other upgrades I am not considering for my engine? I really don''t want to spend more than 3,500 on the engine upgrades this summer, but I really want that lag minimized.Thanks for all the help. I really commend PCA and you personally for this site.

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