History Part IV
The Story of the Ultimate Nova continued
To make a very long story short for now, things went sharply downhill after the intercooler installation. At the track, the car would pop and buck the entire run. The plugs were white, dangerously lean, so we went to full 108 jets square. Not only was the car lean, but we were having horrible backsurge problems with the blower, which was later cured by the installation of a surge valve (a part ATI forgot to mention was needed). Lets recap everything here. For those who have read the ATI story, this may sound familiar... because its the same content :)
As you know we are running a 1200br blower which was specified for our engine having provided the manufacturer with our engine build data. At the time we purchased the 1200br the blower manufacture's advertising brochures stated that the P600, the 1200br's little brother, was capable of producing more than enough boost. We opted for the 1200 for the sake of insurance and future engine development.
Being unfamiliar with centrifugal supercharger applications we would experience several problems. Upon installing the unit and connecting the boost gauge below the carb plates, it appeared that the gauge wasn't functioning correctly. We then called the manufacture and they advised that the boost signal to the gauge should be derived from the hat above the carburetor. We then connected the gauge in this fashion and it appeared that the reading was more inline with what we would expect, more boost. However, we didn't see the level of boost expected and the gauge appeared to be confused by altitude and barometer changes. Consequently, the boost gauge (sadly enough) was ignored as we were eager to move on and confident that it was no more than a gauge application problem. We were confident that the manufacture's claims regarding boost, minus 20% for altitude, was indeed available.
The assumption that we had 10lbs of boost (with a 12lb pulley at altitude) would loom large in the events to follow. Upon going to the dragstrip the unknown lack of boost would prompt several actions related to the fuel system. The car would lean out, pop and lay down, under WOT which led to increasing the jet sizes, bowl extensions, larger fuel pump, larger fuel pressure regulator, larger needle and seats, 5/8ths fuel line, fuel cell, and a Jacobs accuvolt ahead of the fuel pump. After all of this the car did not lay down and the 1/4 mile ET's improved only slightly.
Continuing on, we considered that part of the problem could be with ignition timing. We are running a MSD 6BTM boost sensitive timing master ignition system. Again, the dial out of timing is relative to the pounds of boost delivered to the 6BTM module. Unfortunately, we dialed out 8° of timing under the assumption the supercharger was putting out 10lbs of boost. In running 118 octane the effect of dialing out 4-10° made very little change in the cars performance.
Again, we are anxious to move on with our goal of going into the 10's with a 4000lb car/driver combination at 5300 ft elevation. We installed a special order Spearco intercooler with the thought that it could have some influence on the popping and laying down by supplying the engine with cooler air. Also, no doubt the cars performance should improve with 8lbs of cold boost as opposed to 10lbs of hot boost(altitude corrected). At the track with this combination the car's performance was basically the same as it was without the intercooler. We returned to Farmington and removed the intercooler system.
By this time, as you can imagine, this is getting to be a little more than frustrating. The preceding paragraph represents several trips to the dragstrip, a 400 mile round trip, and several unmentioned trials that didn't prove out. While my dad was plumbing in a mechanics boost gauge I went to the internet for information. The test my dad performed verified that the supercharger was only putting out between 4-4.5 lbs of pressure running the car through the gears at WOT. I learned from the web (thanks Julio Don) that the boost gauge signal must be connected below the carb plates and gained other information which was not provided by the blower manufacture. Remember, this was a initial question put forth to the supercharger technical people with a different and unfortunately incorrect response. Upon connecting the car's boost gauge in the correct manner the gauge worked correctly at WOT and both gauges verified 4-4.5lbs of actual boost.
Now things are painfully clear as follows:
- The low readings on the fuel pressure gauge, again which we sadly ignored, was actually a result of the blower's inability to produce the expected and advertised pounds of boost to the fuel pressure regulator.
- The boost gauge, connected to the carb hat, per the blower manufacturer resulted in erratic boost readings due to pressure build up at part throttle above the carb plates. At WOT the boost readings, were dismissed again faithfully following the blower manufacturers advertising claims.
- The absence of significant changes in ET's, resulting from dialing out varying amounts of ignition timing, was actually a result of the blower's inability to produce the expected and advertised pounds of boost to the 6BTM ignition module. The engine, at such low boost and 118 octane, likely did not need any dial out of timing advance.
- The fuel system probably only needed a higher output fuel pump to prevent the engine from laying down, and the remainder of the problems were actually a result of the blower's inability to produce the expected and advertised pounds of boost.
- The failure of the intercooler to improve performance over hot boost runs was actually a result of the blower's inability to produce the expected and advertised pounds of boost.
- In consulting with Spearco on the proven lack of performance gains with the intercooler installation, they indicated that it sounds like the blower is a mismatch for the engine and an intercooler installation.
So here we were, with a blower that was too small, and a fuel system that could not even handle 4 pounds of boost. After much grief with ATI, we struck out on our own and decided on a new course of action.
On to Part V