STAGE WRITE

MY HARLEY HAD A FLAT BACK TYRE AND I RODE IT SLOWLY TO GLADSTONE IN POURING RAIN. MARK HARRIS, WHO RACES A LOW-SIX-SECOND BLOWN 41 WILLYS, OPENED UPHIS WORKSHOP TO FIX IT FOR ME

ONE of my friends asked for a cam recommendation for his 346-cube LS1 (bore 3.898in x stroke 3.622in).

I had new cams fitted to my 88ci twincam Harley (bore 3.750in x stroke 4.000in). If you get the calculator out, both engines have nearly identical cylinder sizes: 43.25ci for the small-block Chevy and 44ci for the V-twin Harley. Even though the camshafts for both engines were chosen for similar rpm ranges and street applications, the specs of each cam are quite different, and I thought it would be a good to delve into the reasons why here.

An engine doesnt know what brand name is on the tappet cover theyre basically air pumps with lots of variables: bore, stroke, compression, rod length, valve diameter, rocker ratio, head flow, port size, manifold length, exhaust pipe diameter and length. To get the ideal cam, you also need to know the weight, gearing, transmission, etc. These days computer software is available that can work out what is an optimum cam for your engine, or you can fill out a spec sheet and let a cam grinder select the right cam. tostroke ratio of 1.68:1. The Harley has really long rods by comparison 7.44in and a better 1.86:1 rod-to-stroke ratio.

The point Im trying to illustrate is that engines can have similar cylinder capacity yet require completely different camshafts to make power at around the same rpm.

Another area I thought Id look at is the exhaust pipes. So many V-twin owners get around with big-diameter, short, loud, single pipes. The best pipes for most street applications would be two-into-ones with a muffler as a collector, similar to four-into-one car extractors.

I put the LS1 346ci specs with a 226/234@.050in cam into the PipeMax software program, with the pipes at peak horsepower at 5500rpm and working from 3500 to 6000rpm, and it recommended a 1.563in primary diameter, 38 to 41in long, with a 2.89in-diameter, 21in-long collector.

Using the TC88 engine specs with the 236/240@.053in cam, the same program recommended an exhaust pipe with a 1.581in primary diameter and 41 to 42in long, with a 2.5in-diameter, 22in long collector. Both In the case of my bike, I put my trust in a Harley mechanic who recommended SE-204 cams for my stock 88. I have to admit I was very nervous about the narrow-lobe-centre, 236/240@.053-duration cams in my bike (Harley cams are measured at 0.053in) for street use. I thought they might be too big.

I think one of the main differences between the V8 and the V-twin is the heads, and, more importantly, valve size, runner length and port flow. The Harley has short runners with small 1.84in intake valves that only flow 20cfm@10in with .500in lift compared to the LS1 2.0in intake valves and flow of 135cfm@10in. The Harley needs comparatively more duration to fill the chambers, while the Chevy, with its bigger intake valves and high-flowing ports with long runners, needs less duration to fill the cylinders.

So I recommended a cam to my friend of around 226/234@.050in on a 112 lobe centre. The V8 has a higher 10.25:1 compression than the bikes 9:1, giving the small-block more torque. However I was very surprised at the rod- to-stroke ratios. The Chevy has 6.098in- long rods and a rod-tostroke engines have very similar exhaust pipe peak power at 5500rpm, which is a goal. A 1.563in inside-diameter primary 15/8in outside diameter, and on a Harley ordinary. However on a dyno I think the and horsepower would be quite noticeable baffled pipes that dump practically into Im going to use the last part of my Harris, who races a low-six-second blown riding my Harley back from Brisbane on just had a brand new back-tyre tube and it went flat at a place called Glenwood. split, so the mechanic behind the service Long, put a patch on it and said to take tube fitted at Maryborough. He said it on the patch again. Well, it made it as was pouring rain and I rode the bike slowly tyre to Gladstone.

Mark Harris had just come back from was unloading a bike at 5:30pm at his Davidson dealership when I limped in. workshop and fixed the back tyre for and I couldnt believe Id stumbled across its such a small world! We had a headed off into the rain to ride home. I thought exceptional service, and Id like to thank ONE of my friends asked for a cam recommendation for his 346-cube LS1 (bore 3.898in x stroke 3.622in).

I had new cams fitted to my 88ci twincam Harley (bore 3.750in x stroke 4.000in). If you get the calculator out, both engines have nearly identical cylinder sizes: 43.25ci for the small-block Chevy and 44ci for the V-twin Harley. Even though the camshafts for both engines were chosen for similar rpm ranges and street applications, the specs of each cam are quite different, and I thought it would be a good to delve into the reasons why here.

An engine doesnt know what brand name is on the tappet cover theyre basically air pumps with lots of variables: bore, stroke, compression, rod length, valve diameter, rocker ratio, head flow, port size, manifold length, exhaust pipe diameter and length. To get the ideal cam, you also need to know the weight, gearing, transmission, etc. These days computer software is available that can work out what is an optimum cam for your engine, or you can fill out a spec sheet and let a cam grinder select the right cam. tostroke ratio of 1.68:1. The Harley has really long rods by comparison 7.44in and a better 1.86:1 rod-to-stroke ratio.

The point Im trying to illustrate is that engines can have similar cylinder capacity yet require completely different camshafts to make power at around the same rpm.

Another area I thought Id look at is the exhaust pipes. So many V-twin owners get around with big-diameter, short, loud, single pipes. The best pipes for most street applications would be two-into-ones with a muffler as a collector, similar to four-into-one car extractors.

I put the LS1 346ci specs with a 226/234@.050in cam into the PipeMax software program, with the pipes at peak horsepower at 5500rpm and working from 3500 to 6000rpm, and it recommended a 1.563in primary diameter, 38 to 41in long, with a 2.89in-diameter, 21in-long collector.

Using the TC88 engine specs with the 236/240@.053in cam, the same program recommended an exhaust pipe with a 1.581in primary diameter and 41 to 42in long, with a 2.5in-diameter, 22in long collector. Both In the case of my bike, I put my trust in a Harley mechanic who recommended SE-204 cams for my stock 88. I have to admit I was very nervous about the narrow-lobe-centre, 236/240@.053-duration cams in my bike (Harley cams are measured at 0.053in) for street use. I thought they might be too big.

I think one of the main differences between the V8 and the V-twin is the heads, and, more importantly, valve size, runner length and port flow. The Harley has short runners with small 1.84in intake valves that only flow 20cfm@10in with .500in lift compared to the LS1 2.0in intake valves and flow of 135cfm@10in. The Harley needs comparatively more duration to fill the chambers, while the Chevy, with its bigger intake valves and high-flowing ports with long runners, needs less duration to fill the cylinders.

So I recommended a cam to my friend of around 226/234@.050in on a 112 lobe centre. The V8 has a higher 10.25:1 compression than the bikes 9:1, giving the small-block more torque. However I was very surprised at the rod- to-stroke ratios. The Chevy has 6.098in- long rods and a rod-tostroke engines have very similar exhaust pipe requirements to make peak power at 5500rpm, which is a practical street rpm goal. A 1.563in inside-diameter primary would be around 15/8in outside diameter, and on a Harley would look very ordinary. However on a dyno I think the difference in torque and horsepower would be quite noticeable over short 2in baffled pipes that dump practically into the ground.

Im going to use the last part of my column to thank Mark Harris, who races a low-six-second blown 41 Willys. I was riding my Harley back from Brisbane on a public holiday. Id just had a brand new back-tyre tube liner fitted to my bike, and it went flat at a place called Glenwood. The tube had split, so the mechanic behind the service station there, David Long, put a patch on it and said to take it easy and get a new tube fitted at Maryborough. He said it would most likely split on the patch again. Well, it made it as far as Miriam Vale. It was pouring rain and I rode the bike slowly with a flat back tyre to Gladstone.

Mark Harris had just come back from Agnes Waters and was unloading a bike at 5:30pm at his Harbour City Harley- Davidson dealership when I limped in. He opened up the workshop and fixed the back tyre for me. We got talking, and I couldnt believe Id stumbled across another drag racer its such a small world! We had a good chat and then I headed off into the rain to ride home. I thought that was pretty exceptional service, and Id like to thank him for his help.