2 1/2" vs 3" Exhaust and Diff Heat
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2004-2007 Cadillac CTS-V Performance Mods Discussion, 2 1/2" vs 3" Exhaust and Diff Heat in Cadillac CTS-V Series Forum - 2004 - 2007; Friday, August 6th, 2004 Since there seems to be a little debate on the which exhaust tubing size is best ...
  1. #1
    bbexhaust's Avatar
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    2 1/2" vs 3" Exhaust and Diff Heat

    Friday, August 6th, 2004

    Since there seems to be a little debate on the which exhaust tubing size is best for the new V-Series exhaust, I would like to express the development process at Billy Boat Performance Exhaust.

    When we first looked at what size to make the exhaust, we looked at 1) what size is the factory exhaust, and 2) we looked at our experience with the LS6 engine in the Corvette. Since the factory exhaust is already 2 1/2", I felt the performance gain long term (if we were to add computer mods or headers)would be limited. Our 3" exhaust for the Corvette has been very successful, so the attempt for the V-Series was a slightly milder version of that system.

    In my 18 years in the exhaust business I have never seen increasing the tube size increase exhaust temperature. In general, a larger tube and a free flowing system will reduce exhaust temp.

    The stock exhaust from the factory has only 3/4" clearance to the side of the diff and only 1" clearance to the halfshaft area. The B&B 3" system is designed with 1" to the side of the diff and 1 1/2" to the halfshaft area. I see no problem with increasing temp in these areas (it should actually go down), but here is what I have planned.

    Next week I will be doing a complete temperature test comparison between the factory exhaust and the 3" Billy Boat system. I will measure the exhaust temp at the tube at various points in the system, and I will measure the temp on the diff assembly, halfshaft area, and the driveshaft isolator. This way I will have concrete data to base my opinion.

    I would like to thank those on this board for their feedback. We are committed to building the best sounding and best performing exhaust for the CTS V. We are in the process of building the fixtures for the production exhaust systems, so I think we are on schedule to start shipping late next week.

    Thanks.


    Billy Boat
    President, Billy Boat Performance Exhaust

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    ssmith100 is offline Cadillac Owners Connoisseur
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    Re: 2 1/2" vs 3" Exhaust and Diff Heat

    Billy,

    Thanks for the update. Will be waiting patiently for my system to arrive.

    Shane

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    Re: 2 1/2" vs 3" Exhaust and Diff Heat

    Billy -

    Sounds like you will be plenty thorough. I personally don't think the 3" exhaust will show any detriments or excessive heat - but I suppose it is safest to test it first. Really looking forward to your system on my V. The BMR clearance issue should be easy to address, so, if in fact you start shipping late next week, well - I guess all I can say is again - you da man!

    Now, how can I hide that supercharger puchase from my wife! I'm sure she won't notice the car missing for a few weeks!

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    Re: 2 1/2" vs 3" Exhaust and Diff Heat

    Billy - what's the lastest on clearing the BMR kit?

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    Wink Re: 2 1/2" vs 3" Exhaust and Diff Heat

    Larger pipe diameter helps heat diffusion:

    It a simple matter of physics. The distance the exhaust travels from the cats to the differential has not changed, however the surface area of the exhaust system has increased due to the size of the pipes. This acts as a more efficient heat exchanger so less heat arrives at the pipes adjacent to the differential. The heat could be reduced by either extending the length of the exhaust run or by adding more surface area for a given length (larger diameter). The heat coming off of the pipes is commingled with the air flowing underneath the car, with the better heat exchange rate due to the larger pipe size, heat is further reduced at the differential when compared to 2.5" pipes.

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    globed70 is offline Cadillac Owners Enthusiast
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    Re: 2 1/2" vs 3" Exhaust and Diff Heat

    Kudos to Billy Boat for being one of the rare vendors who professionally responds to concerns in a timely matter.

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    GNSCOTT is offline Cadillac Owners Connoisseur
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    Re: 2 1/2" vs 3" Exhaust and Diff Heat

    He is absolutly correct (not that he needs me to tell him this). When you releive backpressure you lower EGT's. That is the point of going to a bigger exhaust. Now changing the programming on the ECM causes the car to run leaner and therefore can increase EGT's well above the factory norm. Not sure exactly why a CTSV would be prone to overheating? If it was close to being a problem, GM would have thrown heat sheilds on their exhaust.

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    Re: 2 1/2" vs 3" Exhaust and Diff Heat

    StealthV-

    Received my BMR kit today. It appears I only need to move the resonator 1 1/2" forward. Once I get the front of the system fixtured I plan to put it back on make the modification.

    Billy

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    Re: 2 1/2" vs 3" Exhaust and Diff Heat

    Quote Originally Posted by bbexhaust
    StealthV-

    Received my BMR kit today. It appears I only need to move the resonator 1 1/2" forward. Once I get the front of the system fixtured I plan to put it back on make the modification.

    Billy
    Thanks for accomodating the BMR kit. We appreciate you hard work!

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    Re: 2 1/2" vs 3" Exhaust and Diff Heat

    Guys say what you think may be the case. The truth of the matter is that the concern/warning of increased heat by the rear diff was "brought up" by GM Engineers. Which means, IF they decide that the larger tubing caused a heat build up near the rear diff which led to it's failure, they will NOT cover the repair. There will be no arguing it.

    A similar situation is with GM not covering any repairs on the suspension/drivetrain on it's SUVs if the vehicle has any wheel/tire combo larger than 20". Their engineers determined that they were seeing alot of repairs and that a majority of these SUVs had wheels that were larger than 20". They therefore made the decision. They stopped at 20" since they now offer 20" wheels in their accessary catalog. I have had several of my customers run into this at their dealerships.

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    Re: 2 1/2" vs 3" Exhaust and Diff Heat

    5CTRVET,

    I don't think will have to worry about "GM engineers" not covering our differential warranties. Obviously you haven't seen my dealerships drive line tech. Had a long conversation with a guy at Borla yesterday about the heat issue. Was checking if they were going to make an exhaust. His exact quote on the phone to me was "the 3" will dissapate heat better and should not be an issue unless the exhaust is basically sitting on the rear differential. If that's the case it won't matter if it's 2" or 4", it could have problems. My honest oppinion is that Corsa kind of dropped the ball on this one with having a long delay and not keeping us up to date. I for one was one of the people getting the run around on the phone. They missed quite a few sales in just some of the guys here alone. I'll be purchasing the B&B. If it matters, the last exhaust I bought ..........Corsa.

    Shane

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    Re: 2 1/2" vs 3" Exhaust and Diff Heat

    ssmith100,

    I also have B&B systems on two of my current vehicles and have had Corsa's on several of my past vehicles.

    I am not trying to argue whether 3" tubing is better or not, all I am saying is GM has made a cautionary statement specifically mentioning a 3" exhaust causing heat build up in the rear diff. How can you argue this? It's fact.

    Like I said, this came from GM and no matter what B&B, Borla, Corsa, or anybody else says, if GM feels that there is a large number of failures and those cars have larger than approved exhaust systems, they could decide not to cover the repair. It has been done in the past and will continue. GM is not in the car business to lose money. Think about it...GM approved which system to be a dealer installed option? Which means it is covered by their warranty if installed by the dealer. Which exhaust did GM put on the C5 Pace Car? What exhaust shows up on most, if not all, of Moss's creations/concepts? Also, both Mallett and Lingenfelter use Corsa's system. Why? Both of their tuning packages create alot more power than stock but are able to breathe just fine. They didn't see a need to use 3" tubing.

    I agree, Corsa dragged it's heels a bit. I have always gotten straight forward information from Jim Jr either in person or via email. Did this cost them some of the business form this forum, probably but they did what they did for a reason and in the long run they'll sell just as many systems.

    My customers tried to argue that the 22-26" wheels were actually lighter than the oem wheels but IT DID NOT MATTER TO GM...they had made the decision and were not going to back off of it. Every single one of them had to pay for the repairs. By the way, I did not sell them the wheels/tires. I only sold them accessories.

    Bill

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    Smile Re: 2 1/2" vs 3" Exhaust and Diff Heat

    5CTRVET,

    I hear what you are saying and you have a point for owners whose primary concerns are about their warranties. However, using that line of logic NO mods can be done to a car without the approval from corporate. A car enthusiast would have to wait till the end of all manufacturer warranties before he did anything to a car. So, I guess if your a car nut, you just take your chances.

  15. #14
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    Re: 2 1/2" vs 3" Exhaust and Diff Heat

    Geno,

    That is not entirely true. A vehicle owner can perform what ever modifications they want but it one of those mods can be proven (and proven is used very loosely) to be the cause of the failure, the dealer/manufacturer can deny coverage of the repair. I deal with this all the time since I own a truck accessory & cap shop. We also do spray-on bedliners and technically by getting one done, the truck owner has voided his paint/rust through warranty but only for the bed & tailgate of the truck. If the hood started to peel, that would be under warranty (given the 3 yr/36,000 mi period). But since GM has already made note of the possiblity of a 3" system leading to a possible failure of the rear diff, they put the dealers and owners on notice. I would bet money that someone with a Corsa system that experienced a rear diff failure would not have a difficult time getting it covered (given that the failure was not due to 6000 rpm clutch drops/extreme wheel hop, etc). Where as someone with a 3" system would be fighting an uphill battle that they would most likely lose. Would this happen, who knows but I would hate to be the one that does find out first hand!

    Just like all of those unfortunate people that installed a CAI system with a reuseable filter, only to have their MAF go haywire. It was determined that the oil coming off the filter fouled the MAF wires/sensors and therefore was not covered under warranty.

    I am not trying to persuade anyone either way. All of my vehicles get way modified and I know that I am running the risk that if something goes wrong, it may not be covered. But that is a risk I am willing to make in order to make the vehicle look and/or perform the way I want it too.

    Bill

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    Re: 2 1/2" vs 3" Exhaust and Diff Heat

    If going from 2.5" to 3.0" exhaust is going to destroy the rear end in our V's, then we got a rear diff that is marginal in its design for the V. Oh yeah, some already seem to have that.

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