Hopefully I worded that so what I am trying to convey sounds like what I am actually thinking!:grin: How can one tell if the exhaust they are presently running on their vehicle is causing too much backpressure? For example: undercarbed shows vacuum being pulled at WOT. I'm looking for that type of test or something similar. The said vehicle is the Toro in my signature, still working some of the bugs out of this thing, although the old 425 seems to be running pretty good as it is!:beer
I don't know if this is in any way a valid method, but when my 225 just had a single 2" exhaust, the exhaust temp out of the tailpipe was very hot. You couldn't put your hand in the exhaust stream for very long. When I went to dual 2.25", the temp went down enough that I didn't have to worry about that anymore.
Simple enough to check for exhaust back pressure. Waekon sell a special tool for testing, as I write this there's one for sale on eBay. http://cgi.ebay.com/ebaymotors/ws/eBayISAPI.dll?ViewItem&item=2434754981&category=43989 But really, I wouldn't bother. Have a muffler shop weld in a nipple somewhere in front of the muffler. (One each side, for dual exhaust) Connect an ordinary fuel pump/vacuum gauge to it. Run a long hose to the inside of the car, and have someone watch the gauge as you drive. (make sure you use some hard acceleration!) downsides: 1) You'll have to plug the fittings when you're done. I'd have the shop weld in 1/8 pipe thread female fittings, which you can seal with a 1/8 pipe plug. To connect to the gauge for testing, screw in a 1/8 male pipe to hose barb connector. 2) Don't expect the hose to last very long, the heat is gonna kill it sooner or later. Figure about ten bucks in fittings and some hose, plus welding labor and buying a vacuum/pressure gauge if you don't already have one.
Hook up a vacuum gauge and accelerate under half throttle. Watch the needle and see if it drops. If it starts to drop after a few seconds its an indication that your exhaust is choking off the engines ability to breathe, and thus draw vacuum.
How to tell if your exhaust is too small The gauge in the exhaust is usually a good way to tell if you do not have enough exhaust. You should see no more than 2-3 pounds (at the max), if any more, you need more exhaust. You can put the O2 bung up at the collector by the either header. Then after you take the gauge out you can plug it or get a rich lean indicator to screw into its place. (If you don't have one) Then you will be making use of the bung you just drilled in the exhaust. Every hot rod that me or my buddy's have has a rich lean idicator on it. It makes it so much easier to tune carbs, especially 4500's. Blair :stmad: :stmad: :stmad:
