I've been in your same situation.  Let me tell you, the ONLY person who can deny warranty work is the regional manager for Toyota.   Your warranty is with Toyota and not an individual dealer.  The individual dealers have absolutely no authority to deny warranty work.  Another thing to keep in mind is that a dealer will actually lose money on big warranty jobs like turbos and engines.  Because Toyota low balls the time estimate to replace such items and the dealer still has to pay the mechanic working on the car.So if the mechanic is a putz, and takes twice as long as Toyota thinks it should take to repair the car, the dealer has to make up the difference. It's in the dealers best interest to deny all warranty work, so they try it every chance they can get. Here's what you need to do.  Demand to talk to the area service manager. Since you left the exhaust and BOV on the car, come clean and don't deny you had these two things on the car.  Ask him why the warranty was denied, and try to convince him to honor the warranty because you don't buy his argument.  If this doesn't work, tell him you will need the arbitration papers laid out in the warranty manual.  This will get his attention.  He will now have to fill out a denial of warranty statement and other paperwork, which means work for him, and Toyota will have to prepare a case and pay the bill for an arbitrator.  This takes time, energy and money on their part.  This is a business, so they will handle the decision based on good business sense.  If it is a small claim, and they have to spend more money defending their position that it would take to fix the car, they'll just fix the car.  In your case, it will probably still take more money to fix the car.  But you're not through yet.  The warranty manual specifically states that the proper procedure is to try and handle it through arbitration.  If you don't like the resolution, then you can seek a court judgment.  Don't threaten to sue!  That's a big mistake!  Don't immediately take it to court!  That's another big mistake!  The first thing the toyota lawyers are going to say to the judge is that the situation could have been handled through arbitration, but YOU didn't follow procedure and now you are wasting the courts time and the taxpayers dollars.  The judge won't like that.  You'll lose the case. Arbitration can take up to 3 months, so in the mean time you will be without your car.  That's ok, because if the arbitration goes in your favor, claim you had to rent a car for three months and you want reimbursed for the expenses.  This is perfectly legitimate.  The arbitrator won't have a problem with that.  Toyota also knows this, so all of a sudden the defense of their case, in case they lose is getting very expensive.  It might be easier to just fix the damn car and avoid all this.  If they still aren't persuaded, try your luck at arbitration.  Toyota will have to prove the mods made the engine fail.  A certified toyota mechanics testimony will carry more weight than your "opinion" in arbitration, so you will need an "expert" witness statement to contradict the toyota statement.  Who better than Greddy to give you this.  They have a vested interest.  If word gets out that their exhausts  or BOV's void warranty, that would be bad business for them, so they will want to help you defend your position.  Besides, every Greddy part has a E.O. exemption number which is given by the government, which says that the part doesn't void the emissions warranty plain and simple.  If you could get your car to run, would it pass emissions testing with a whole in a piston or two?  I think not and the engine is covered by the emissions warranty.  This has teeth!, and toyota knows that. If for some reason, arbitration doesn't go in your favor, take it to court. Lawyers are very, very expensive.  Especially the top notch kind of firms that Toyota hires to defend them.  Like $300 per hour.  To defend a case in court will be extremely expensive compared to replacing the engine.  Get my drift?  But they can sue you to cover their lawyers fees.  No judge or jury is going to reward toyota with lawyers fees unless this is a blatant case of gold digging and you appear your just trying to make some quick cash. I know all this because I just settled with toyota over a set of blown turbos earlier this year.  Toyota and the local dealership wound up spending close to $20,000(my lawyer got to be friends with the lawyer from toyota so this is a quote from the toyota attorney) to defend the case.  Needless to say, the turbos got replaced   under warranty. Bottom line, you have a very good case and an excellent chance to win.  Be persistent and don't make stupid threats like "I'll sue".   Follow the procedure in the warranty manual and help toyota understand how much it will cost them to defend the case instead of just fixing the car.  They will use scare tactics and try to force you to crumble. As soon as they figure out your in it for the long haul, they'll be the ones who crumble.