Here is a brief write-up I did for a Cerokee e-mail list that discusses TB Spacers and the like...
Just wanted to pass on what sort of effect having a bored out throttle body can have on your engine performance. Yowza, Yowza, Yowza!
First a little background. My 98 Cherokee has previously had troubles running on 87 octane fuel. I have for the last 5.5 years been forced to buy 89 octane which is usually 10 cents/gallon more than the 87 octane. So I have had my eye on something that would alleviate my need to waste money on the higher grade gas, which was also allegedly yielded a lower mile per gallon than the 87 octane would.
So I started on my search for a miracle cure. I have heard that using a spark plug that works in a colder heat range would eliminate pinging, but I was unsure if there would be any other side effects introduced with such a solution. So I never pursued that avenue as a repair. I also noticed on Dirk's http://dpgoffroad.com/tech/default.htm
site that a cold air intake setup worked to eliminate his pre-ignition troubles. His application involved tying the cold air intake into a Safari Snorkel for fresh air scavenging. I liked the concept behind the setup and have always been a little jealous of the brothers "Gibson", Derek Paschal, Dora Fang and some of the other cool kids. So I emulated Dirk's setup with just a minor variation or two and created a new cold air intake for my XJ. Low and behold it actually worked just as Dirk said his did, I was finally back on 87 octane petro.
Then I decided I wanted to see if I could squeak a little more performance out of my freer breathing engine and purchased an inexpensive (IMO) cat-back exhaust from Dynomax for $100. This seemed to allow my jeep to hold highway speeds easier during long graded inclines. My transmission was no longer hunting for a way to keep my forward momentum at a constant rate. So once again another positive outcome, for a reasonable amount of money.
In my next piece of research I wanted to pursue a throttle body spacer and a bored out throttle body. I was sure I didn't want to buy a new, replacement throttle body like the ones offered from Turbo City or Rubicon Express. My reasoning was horsepower on the cheap and these products no longer were in my definition of cheap. So after spending a fair amount of time combing through the internet I had located two solid articles to base my decisions upon.
The first was from Jason West's Jeepin.com website. There he had two separate write-ups, one for a Poweraid throttle body spacer from Airaid. The other article was for a bored out throttle body from Jeepers & Creepers. He was most impressed with the result of the bored out throttle body. So I had a good testimony that the two items were worth pursuing.
So I knew I wanted a bored out throttle body, but I still didn't want to pay $110 dollars to Jeepers and Creepers for the luxury. So I looked up my next article from the man whom shares my first name, the thunder from down under... Marcus Ohms is pretty renowned on this list for his creative ways to improve an XJ on the cheap (http://go.jeep-xj.info/HowtoTBboring.htm
). So I studied his article on how he bored out a stock throttle body AND the Poweraid throttle body spacer. He too was ecstatic with the new found performance. So I went about deciding what tools would be necessary to bore it out, I had read of people using a sand paper flapper wheel, sanding drum, Dremel and a brake cylinder hone. Each method has its own positive and negatives.
Before I got too excited and bought a new tool or two I thought I would contact a machine shop to see how much it would cost. I have a large number of machine shops in my vicinity so I spoke with one that assures me that the work could be completed for under $50. I thought for that price I was game as surely the combination of tool purchase and time, plus the risk of screwing up would be greater than what the machine shop could offer me.
So $35.00 later I had a "Helix" throttle body spacer (I purchased the Helix brand because it was a natural aluminum color unlike that gussied up red one from Poweraid) and the lower portion of my stock throttle body punched out to 60mm, up from the stock 55mm. So the installation occurred this afternoon and I have had the opportunity to put 40 miles on the setup. And let me tell you I have certainly more responsive acceleration! Don't get me wrong, it isn't lightening in a bottle type of stuff, but it is certainly noticeable. Even with 32's and the stock 3.55's and the air conditioning pumping hard, I could still feel a significant difference.
So the long story short is that you can add me to the list of satisfied customers, big bang for $95! Your mileage will vary if you attempt this type of performance improvement depending upon your vehicles other performance upgrades.