Quote:
Originally posted by 91GTturbo
Chris,
I don't nor am trying to start a flame war here, but with 8:1 he can run 10-12 lbs of boost on pump gas easily. I'm just adding heads to mine and I'm going to be running 8-10 lbs on pump gas with 9:1. Why do you say so low? With 8:1 unless he's making some big hp on motor, the thing want get out of it's own way.
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The driver I worked for last season (2000) builds exotic race engines and tests them at his dyno and out at Willow Springs, and I've tagged along several times to learn what I could. What I learned from him regarding boost pretty much echoed what I was taught in my engines class at the local cc when I was preparing for my ASE Engine Repair and my ASE Engine Performance Certification exams, and that was that pump gas is not safe beyond 6 pounds of sustained boost in a stock small block Ford with 9:1 pistons. In fact, this is a widely accepted standard. There are different options available that can alter these numbers, but for a general guideline, 9:1 compression and pump gas can safely handle no more than 6 pounds of boost. That doesn't mean that you can't run more and not have a problem, it is only a recommendation of how much boost can be added without increasing the chances of detonation to an unacceptable level. For my customers, I will not install any combinations that will result in more than 6 pounds of boost if I know they have a stock bottom end with 9:1 or higher compression, without having them first sign a warranty release that becomes effective the first minute after they take possession of the vehicle. This hasn't caused a problem yet, as my customers trust my recommendations. I know I've got books around here that repeat what I'm saying, and if you like, when I have time, I'll dig through and find one or two for you if you would feel better about this by seeing it in writing.
I know that there are many people who regularly run 8-10 psi with 9:1 compression on pump gas, but they tend to be the ones that have the failures you hear about. I won't make a recommendation that has a high chance of failure. It doesn't help me and it doesn't help the customer, so why bother.
Quote:
POSTED by srv1:
hey Chris, what would be an accurate tool or gauge in measuring boost? i never hear much on the accuracy of gauges, so what do you know or recommend? i think most of us would like to know, smarty pants! j/k
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As far as an accurate method of measuring boost, the dyno was the best, but since it's difficult to carry one around in your trunk, a quality boost/vacuum gauge that is hardlined to an isolated manifold vacuum source is the best bet. Boost-only gauges, meaning those that do not also measure vacuum, are the worst, and almost always read higher boost than is actually being produced. The factory boost gauges are often off by 50% or more. Most forced air engines produce less boost than the owner thinks they do. I had a customer with a turbo T-Bird who claimed to have 10 pounds of boost "all the time". It actually never exceeded 5 psi, and even that was rare. He wasn't happy to hear that, and preferred the exagerated numbers, but then, he was that kind of guy. He liked exagerated HP numbers, too.
Take care,
-Chris