At the auto cross
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1983 Mustang
I bought the Mustang in 2002 and it was in pretty rough shape. True it is not my daily driver but the car has seen many long road trips countless laps at the Auto Cross and, unfortunately lots of time sitting in traffic on the Phoenix streets. The car carries Collector Car insurance to exempt it from emissions testing so there are usage restrictions placed on me by the insurance company. I have about 5000 miles on the current combination and drive it every weekend except when the thermometer gets above 100.
The car started off as a stock 5.0 making a whopping 175 HP. On the upside it had a four barrel carb and 5 speed transmission. The down side was about everything else including the 2.73 geared 7.5" rear axle. Performance was pretty dismal and I soon looked to build a more powerful motor.
Since the factory block was a flat tappet and I wanted a roller I sourced a newly rebuilt short block. It was .030 over and had ARP main studs, rod bolts, hyper pistons and a windage tray. This turned out to be a mistake but I'll get into that later.
Next I had to decide on a what I wanted for the top end. The route I chose is the same as many others have done. I did not want a lopey race car nor did I want to spend the money for aftermarket heads I sourced a set of GT-40 heads, a TFS1 cam, Stealth intake and rebuilt the factory carb. This provided a major seat of the pants improvement but the car was not fast by any means.
I played with the car for a while doing some small modifications and working on the body. The car was lowered slightly and received many suspension modifications to make it better suited for the Auto Cross. This worked well for all the street driving I was doing but eventually I got tired of the lack of real performance.
Through exhaustive research I came to realize that there was more to making power than the traditional bigger cam is better technique. This was a throw back to the days when hotrodders were modifying factory heads because there was not much else available. I saw that the OEM's were using big heads in the GM LSx and Ford Mod motors and these were ending up in everyday cars. I knew if Ford could use a 175cc head on a 4.6L motor that a typical 165cc head was too small for a 306. I looked for a cylinder head that was larger than normal and a cam that would compliment the heads. In the end I settled on a Canfield 195 and a custom cam. The cam had a tiny 214/228 @.050 duration with .600 lift (1.6 rockers). The lobe was very aggressive so a billet steel cam core was necessary. (5.0 HO engines are said to have a steel cam. The reality is they are a SADI core.) Valve train stability is always a concern so a double spring with 175#s on the seat and 460# on the nose was chosen along with Comp Cams 851-16 hydraulic roller lifters and roller rockers. I finished off the induction with a Vic Jr intake and a Holley 750HP carb.
I was told by many that this combination would be a dog on the street. It would have no low-end and would not rev past 5500 with that little cam. This turned out to be partly true but not for obvious reasons. The motor idled well and reved freely but made far less power than it should. I found that the shortblock had a problem as a leak down test showed 25% leakage that improved when oil was squirted into the cylinder. This was a tell tale sign that rings were not sealing. The motor cam out and was torn down and I found chrome rings had been installed, they never sealed. A quick bottle brush hone and a set of moly rings and the motor was back in the car.
Once the car was back on the road I was able to get a pretty decent street tune. The throttle response was instant and the car idled with 17" of vacuum. In normal driving the car was tame but when I opened it up the RPM's would rocket to 7000 and it felt like I hit it with a 200 shot.
The car started off as a stock 5.0 making a whopping 175 HP. On the upside it had a four barrel carb and 5 speed transmission. The down side was about everything else including the 2.73 geared 7.5" rear axle. Performance was pretty dismal and I soon looked to build a more powerful motor.
Since the factory block was a flat tappet and I wanted a roller I sourced a newly rebuilt short block. It was .030 over and had ARP main studs, rod bolts, hyper pistons and a windage tray. This turned out to be a mistake but I'll get into that later.
Next I had to decide on a what I wanted for the top end. The route I chose is the same as many others have done. I did not want a lopey race car nor did I want to spend the money for aftermarket heads I sourced a set of GT-40 heads, a TFS1 cam, Stealth intake and rebuilt the factory carb. This provided a major seat of the pants improvement but the car was not fast by any means.
I played with the car for a while doing some small modifications and working on the body. The car was lowered slightly and received many suspension modifications to make it better suited for the Auto Cross. This worked well for all the street driving I was doing but eventually I got tired of the lack of real performance.
Through exhaustive research I came to realize that there was more to making power than the traditional bigger cam is better technique. This was a throw back to the days when hotrodders were modifying factory heads because there was not much else available. I saw that the OEM's were using big heads in the GM LSx and Ford Mod motors and these were ending up in everyday cars. I knew if Ford could use a 175cc head on a 4.6L motor that a typical 165cc head was too small for a 306. I looked for a cylinder head that was larger than normal and a cam that would compliment the heads. In the end I settled on a Canfield 195 and a custom cam. The cam had a tiny 214/228 @.050 duration with .600 lift (1.6 rockers). The lobe was very aggressive so a billet steel cam core was necessary. (5.0 HO engines are said to have a steel cam. The reality is they are a SADI core.) Valve train stability is always a concern so a double spring with 175#s on the seat and 460# on the nose was chosen along with Comp Cams 851-16 hydraulic roller lifters and roller rockers. I finished off the induction with a Vic Jr intake and a Holley 750HP carb.
I was told by many that this combination would be a dog on the street. It would have no low-end and would not rev past 5500 with that little cam. This turned out to be partly true but not for obvious reasons. The motor idled well and reved freely but made far less power than it should. I found that the shortblock had a problem as a leak down test showed 25% leakage that improved when oil was squirted into the cylinder. This was a tell tale sign that rings were not sealing. The motor cam out and was torn down and I found chrome rings had been installed, they never sealed. A quick bottle brush hone and a set of moly rings and the motor was back in the car.
Once the car was back on the road I was able to get a pretty decent street tune. The throttle response was instant and the car idled with 17" of vacuum. In normal driving the car was tame but when I opened it up the RPM's would rocket to 7000 and it felt like I hit it with a 200 shot.
1983 Mustang GT