I made the original post simply to inform folks that reasonably priced custom pop-ups were available for the somewhat rare 3.8" bore. The follow-up question about the intent for using pop-ups is a good one. The short answer is if I use heads with bigger chambers I'd need pop-ups to keep the compression ratio about where it is now, allowing it to run without problems on the lower octane fuels we have today.
Here's the long winded explanation, some of which was contained in my earlier posts in this thread: As I mentioned earlier, I'm thinking about building a new street motor for one of our Tigers. I'm not afraid of experimenting. I don't plan on copying a known formula. I'm thinking about a frugal solution that meets my needs, not one that satisfies someone else. My thinking is tailored to my intended use. It is not a cookie cutter solution to impose on everyone else.
I use my Tigers. Thousands of spectators see our SCF race Tiger run every year. And we drive our street Tigers. In the past we've driven 3500 miles in ten days. Our Tigers are not garage queens that are trailered to events or occasionally carefully driven to a "cars and coffee" and then immediately garaged afterwards. My Tigers have the warts and patina that comes from this type of use. I know Duke is an owner who also uses his Tiger like we do but he seems to have found an anti-wart potion to protect his Tiger. (I think his secret is a lot more effort.)
For my uses on that particular Tiger, excellent MPG coupled with reasonable pep are my goals. I think decreasing the cubes to 260 would help the MPG. Stroking will not give me the mileage I want so it's not even worth me considering because it's not germane to my quest for better mileage. It's not a viable option for this use.
One of our Tigers has a 5-speed with a .62 OD. The OD cuts the revs by over a third. This helps mileage and makes it easier to talk/shout to my wife while rolling down the highway. It gets good mileage, in part due to the T-5 we installed for less than a thousand dollars, including the cost of the tranny. Frugal. The mileage in this Tiger is already about what Duke hopes to eventually get with his combination of stroker and TKO. That's great mileage but I'm greedy - I want more MPG. Moondoggie's greedy - he says he wants the stroker HP to crush replica Cobras. It's a trade off and my personal choice is to opt for mileage in this particular use. (Of course our race Tiger is a bit of a different situation with it's normal MPG at about 4!)
Anyway, I've been thinking about how to make the motor more efficient to further increase mileage while simultaineously increasing its output by a hundred or more horsepower. I don't know if it can be done much less if I have the skill to spec a suitable combination of components. My budget for this project is only $2-thousand dollars. Again Frugal. (This is also about the cost of the tires we destroy at Monterey each August. Not Frugal.)
To increase efficiency, I'll probably use a more modern Ford cast iron head head to improve combustion and breathing. I bought a set of modern heads to play with for a bit over $100. However these heads have much bigger combustion chambers. The pop-ups would be used to regain, not increase compression. (I love compression but I am limited by the fuel available today not to mention what may be available in the future.)
The additional benefit of using a light-weight custom piston is to decrease the stress on the rotating parts of the engine. I think this would increase reliability of the bottom end so much I could keep the stock crank and rods without worry, even with a major horsepower increase. Again, frugal.
About worry: Duke seemed worried about me using a "rare" (tiger 260) block. Over the years I've collected a half dozen of them. I might well use one of them. They are certainly "seasoned", but aren't we all?
bt
at the beach
