The Service Department
THE SERVICE DEPARTMENT
GORDON H. JENNINGS
HOP-UP?
I have a 1960 Ducati which has 98 cubic centimeters, and I am interested in getting more speed out of it. Could you tell me how to accomplish this? Money is a problem. Also, do you recommend boring out the cylinder to obtain more cubic centimeters?
Tony Gardner Los Angeles, Calif.
As a matter of policy, I never recommend that anyone modify any engine; it is an expensive pasttime and does not often yield the expected results. However, most motorcyclists (and I must include myself in this group) have some kind of a peculiar compulsion to get into an engine’s internals and fiddle things about. It is a lot of fun, but when it is done right there is a considerable expense involved — and when it is done wrong the engine suffers a power loss. In either case, there is almost always a loss of reliability. One cannot expect to second-guess professional engineers without paying a penalty. The only exception to this rule is in the case of hand-finishing. Mass produced motorcycles, like all other assembly-line products, are not put together with as much tender-loving-care as some owners are willing to supply. The ambitious, and skilled, individual can, therefore, improve an engine over its stock condition by such things as polishing the ports and carefully matching of port and manifold openings. Go much further and you must plan on spending some money — and you have already stated that money is, in your case, a problem. This being true, over-boring the cylinder is quite out of the question: to do so — even if you could get the job done free of charge — would commit you to the expense of a new piston and rings. Probably, the engine could most easily be stretched by using parts from the 125cc Ducati. I suggest that you inquire ' into the matter further at the nearest Ducati dealer. You might even find — as many have — that in the end, the cheapest and most satisfactory means of getting improved performance is to simply buy a more powerful bike.
TEMPERATURE?
/ have a question: is there presently on the market, or to your knowledge has anyone ever hooked up a temperature gauge to a cycle engine to guard against overheating? 1 am especially interested, as 1 plan some modifications for the drag strip and I would like some kind of warning system other than the old trial and error methods.
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A friend suggested adapting an aircrafttype cylinder head temperature gauge, with the heating element next to the base of the spark plug — a critical temperature location.
What is your opinion of this? Does it sound feasible?
If anyone has experimented with this, l would appreciate a letter from them very much.
Billy J. Goodsell
Box 22, 2015 Comm. Sq.
Randolph AFB, Tex.
The basic idea of an engine temperature gauge not only sounds feasible, but is an excellent idea. The only thing to be decided is the location, and kind of heat sensing device to use. This year, the Corvair (an automobile, you should excuse the expression) with the supercharged engine has a cylinder head temperature gauge, and this offers a possibility for a reasonably inexpensive conversion. Also, there are similar devices made for the Volkswagen, and we understand that these have a sensing element that fits, like a washer, under a spark plug. Very good results, from the standpoint of safeguarding the engine, have been had from oil temperature gauges. These are available in a wide variety from automotive (that word again) accessory firms. The oil temperature sensing element could be placed in the oil supply — either in the engine sump or, in instances where the' dry-sump system is employed, in the storage tank — or located in the return flow from the cylinder head. It seems to me that the latter positioning would be prefenable: thus located, it would give an instant indication of changes in cylinder head and valve-gear temperature. Also, it would reflect, broadly, the temperature of the engine as a whole.
RAM TUNING, A DETAIL
One question about intake and exhaust ram tuning: does the time for the sonic wave to reach its maximum value remain constant with changes in engine speed and if so, should this time be expressed in terms of crankshaft degrees, or fractions of seconds? Waldo E. Burdick, Jr. Olean, N.Y.
The exact rate of wave buildup varies not only with engine speed, but with valve timing and several other factors. However, for practical purposes, we may consider it as constant at all engine speeds — once we determine what it is for a particular engine. But, whatever it is, in all calculations always remember that time is the important factor. The waves bounding back and forth in the pipes are very little affected by crankspeed. What does affect the waves substantially is temperature. In the intake pipes, and just over the normal range of temperatures, the wave speed may vary from slightly under 1100 feet per second (a warm day, gasoline for fuel) to perhaps 1400 feet per minute or slightly more (cool day, alcohol fuel). Any good high school-level physics book will have a section dealing with wave speeds, in gases (like air) at varying temperatures and densities, and if the exact temperature of the air in the intake duct is known, the wave speed may be calculated with great accuracy. And, of course, the same thing applies to the exhaust.
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FEEL THAT POWER?
7 own an Allstate 250, which has an advertised 14.5 bhp. I would like to know what changes 1 could make in the engine to raise the power to over 15 bhp to make the machine legal for freeway riding. I have experimented by filling the head with ¡reliare and have created a squish area over the front piston. I also polished the intake port slightly and belled out the inlet sides of the transfer ports. The overall results have not been startling; in fact, 1 can’t feel the difference. If 1 can get an increase in power, and have it certified on a dynamometer, I can carry the certification card and ride the freeway.
James E. Korley Moffett Field, Calif.
Good luck with that dyno. You will probably get the extra power, but if you think the state of California is going to yield to mere logic (if that were so, they wouldn’t have such a stupid law in the first place) you had better think again.
As for being able to feel a power increase; you can’t. This is a mistake often made: people go to great lengths with an engine and expect to feel the difference with the seat of their pants. In actuality, only when there is a vast improvement can one feel it.
This is the reason we go to such lengths to get performance data for our road tests. We have learned that one’s senses cannot be trusted. For anyone who is doing hopup work, we would recommend some work with a stop-watch as part of the procedure. Otherwise, it is all too easy to delude one’s self into thinking that great things are happening when the engine is simply running badly, or to overlook a real improvement when it occurs. •
