Date: Mon, 13 Jan 1997 20:02:35 -0800 From: Mike West Subject: Choosing a Cam Shaft Mike. I read your reply to a camshaft question on the VW list and as you are obviously very knowledgable on the subject I hope you can help me. I have a stock 1600 Brazil engine in my bug and want to liven it up a bit. The only modifications so far is a Holley carb (copy of a downdraft Weber)and a 009 distributor, the only other planned mod is a free flow exhaust. My aim is to pull the torque peak as low as possible, for town driving, have reasonable fuel consumption at normal freeway speeds and to have a top speed of about 85 (VERY alert traffic cops here in Pasadena). Can you suggest a suitable cam profile?. I have asked several people who profess to know what they are talking about and have had a different answer from all of them. Many Thanks - - - - - - - - - - - - - - I got a couple three of these. So I assume there are a dozen more who won't even ask. The names have been changed to confuse everyone. :-) First you are wrong about me knowing about cam shafts. Six months ago I couldn't spell "cam". :-) I am an ex-engineer who is trying to be a mechanic and has the gall to drag a bunch of you along as I learn the trade. I do have a couple books tho and have read them in order to understand "what's haps" myself. One of the books is Bill Fishers "How to hot-rod a vw engine". That's where most of the data I feed you today comes from. Ok, we'll cover the question. You have a 1600 and want low end torque and 85 mph and good fuel economy. First let me say I hope it's a dual port, if it's not then get some on it. Biggest single item you can add for horse power and top end. Since you gave me no data on the car, I'll use mine. I have a '70 bug with a final drive pinion of 4.375 and a fourth gear of .88:1 . When it feels well, it does 73mph in third but the passengers start trying to eject. I still have to replace the "Jesus handle" from last time. :-) 85 mph is about my top end. I run out of air or the valves are floating. I think it's the valves. By the way this is a single port with the stock 30 pict 3. Part of the time this car has to "creep" up hills. The roads are so bad that only by getting it down to where it is actually going boom - boom with the pistons , can I make it up the hill. And then the majority of the time, it's just a trip to town and back. In town I get no mileage at all and I swear it's the damned 009 dizzy. OK we'll get back to cams. 85mph huh? Well rpm = mph X gear ratio X 336 divided by the tire diameter. Using my gear ratios (the lowest VW made) I have .88 X 4.375 = 3.85:1 So 85mph X3.85 X 336 /25 inches comes out to a little under 4400 rpm. I needed that number to get the next: CFM equal Liters times rpm divided by 56.64 . So 1.6 X 4400/56.64 is 124 CFM. Now we go look at Mr. Fishers "flow charts". For the dual port, I can get that from a stock cam at .300 lift. Gives 130 CFM on the intake. 92 on the exhaust but that's to give a bit of back pressure. The stock cam gives me a .320 lift actually. If I want to port and polish, you can get about 10% better flow. It's no secret that the VW engineers did their homework. The Carb will match the valves and the valves will match the CFM of the cylinder bore. The stock carb might be a little small to give economy. It's also a fact that anything you gain on top end with a cam, you lose on the bottom end. My recomendation is use the stock cam, until you put in bigger cylinders. Let's go look at my single port tho. The .300 lift only gets 94 CFM and the exhaust 93. Doesn't seem to be my valves at all, I've just run out of air. :-) Still, the fact is,I'm exceeding these flow readings by 25% if I can turn 85mph and 124 CFM. Not too shabby. :-) One step you haven't made that is a big hp gain is the extractor type exhaust. Good for about ten horses. Go down and buy this Bill Fisher book, He has a whole chapter on "bolt on horsepower". The only data I have on after-market cams is also in that book and it lists "Racer Brown" cams (is he still in the biz?) and the "Engle" cams. It starts at the 110 Engle and has a .429 lift with the 1.1 rocker. I could use some data, guys! hint, hint. :-) Also need flow data on the bigger valved heads. I hope I've answered the question and if you need more just give a yell. There are several hi-performance guys on the list here also. Actually running bigger bores and higher cams etc. They'll be glad to help too. west