Hawk Talk

[Ghenghis]

Originally Posted by Ariel Red Hunter

This is very true. When I wrote about Joe Craig (the man who was very responsible for Norton's death-grip on TT and GP racing for 20 years), I didn't get very far into the intake system length part of his dissertation. He spent years on a dynomometer testing everything you can imagine. You might want to go back through this column, Hawk Talk, and read what he had to say. Understand, from 1928 to sometime in the first third of the fifties, this is all he did. He was an engine man, and he only worked on one type of engine, what came to be known as the Norton Manx. The Manx was a single cylinder engine made for racing, in 350cc and 500cc sizes. All air-cooled singles share a certain heritage. We can learn much from other successful designs. I am going to try to find the "intake and induction factors" part of his interview, and print it up this afternoon.

I'm looking forward to reading that! I was building my own engines for my hot rod cars back when I was 18, I've done lots of things wrong and some right, it's all a learning process that's kept me interested.

One of the biggest surprises came from something I didn't think would make much difference, not nearly as much as it did. I had a 94 Firebird and my buddy had a 94 Camaro, both had the LT1 engine. We had previously taken our cars to the 1/4 mile track and ran them in complete stock form. Rather than buying a cold air intake my buddy decided we would build our own. He found the largest diameter tubing that would fit under the hood, 4" truck pipe, it did require us to shave a little plastic off the edge of the top radiator mount to fit them. The tube had a 90 degree bend halfway through it's length which worked perfectly, it cleared all the components and stopped at the bottom of the engine compartment, we then fit K&N filters to the end of the tube. We also removed or cut a circular hole in the plastic cover/splash guard so they could pull fresh air from under the car.

Now it was time to test them at the track again. There could have been temperature/humidity variations from the last time we went but it had only been 2 weeks, so those will account for some but should be marginal. My Firebird gained 3/10's of a second consistently over many passes, a nice result I was extremely happy with. My buddy's Camaro "it had much lower mileage than my Firebird" gained .5 seconds on every single run he made. I know it sounds unreal, we hardly believed it ourselves, but the numbers don't lie. They were still 14 second cars, but now they were in the low 14's.

Proof that a long consistent diameter intake tube with a good filter works wonders. Not too many bends though, ours had a smooth 90 degree transition. To this day if I tell people that story they don't believe it.

[Ariel Red Hunter]

Originally Posted by Ghenghis

I'm looking forward to reading that! I was building my own engines for my hot rod cars back when I was 18, I've done lots of things wrong and some right, it's all a learning process that's kept me interested.

One of the biggest surprises came from something I didn't think would make much difference, not nearly as much as it did. I had a 94 Firebird and my buddy had a 94 Camaro, both had the LT1 engine. We had previously taken our cars to the 1/4 mile track and ran them in complete stock form. Rather than buying a cold air intake my buddy decided we would build our own. He found the largest diameter tubing that would fit under the hood, 4" truck pipe, it did require us to shave a little plastic off the edge of the top radiator mount to fit them. The tube had a 90 degree bend halfway through it's length which worked perfectly, it cleared all the components and stopped at the bottom of the engine compartment, we then fit K&N filters to the end of the tube. We also removed or cut a circular hole in the plastic cover/splash guard so they could pull fresh air from under the car.

Now it was time to test them at the track again. There could have been temperature/humidity variations from the last time we went but it had only been 2 weeks, so those will account for some but should be marginal. My Firebird gained 3/10's of a second consistently over many passes, a nice result I was extremely happy with. My buddy's Camaro "it had much lower mileage than my Firebird" gained .5 seconds on every single run he made. I know it sounds unreal, we hardly believed it ourselves, but the numbers don't lie. They were still 14 second cars, but now they were in the low 14's.

Proof that a long consistent diameter intake tube with a good filter works wonders. Not too many bends though, ours had a smooth 90 degree transition. To this day if I tell people that story they don't believe it.

I can well believe it, although I suspect you gained more from the cool air you were getting. Cooler air is more dense=more power.

[OUTERLIMITS]

Originally Posted by Ghenghis

I'll add a bit of info I read about intake spacer length. Says a lower geared quick revving motor does better with a shorter carb to head spacer length. The Hawk, mine at least, was geared far too low from the factory, it had 15/45 sprockets, I put a 17 on the front and I can tell zero difference in power, as in there was no loss of power, it made the bike far better to ride and greatly increased the top speed.

The 167FMM isn't a fast revving engine but it does make decent amounts of torque in it's mid range, so this is where we'd benefit most from our efforts to increase power, the 17/45 sprocket combo seems to do a good job of targeting this mid range power. My research says that a longer intake tube between the carb and head is exactly the type of setup you want for an engine that's a little slower revving. Since there is more mass of air/fuel flowing you get a better cylinder fill from that setup. Too long of a distance from carb to head and you'll get fuel pooling in the head. There's also some sciency bits, I'll quote them here:



Might be worth a shot to experiment with this. Also, the intake tube running up to the carb definitely benefits from keeping a uniform circumference throughout it's length. The Hawk airbox would seem to wreck any benefits gained from this as the tube opens up into a box. You'd be better off running the intake tube into the box and having a round style filter on the end of the tube, merely using the box to keep water/debris out, tossing aside the Hawk's lawn mower filter.

There are some spacers on the market to make that length effectively a bit longer. Would probably have to experiment to see what would work on the Hawk. Maybe that could solve two problems in that it seems like most of the pictures I've seen of the carb to air box boot that it's just a little short. There is what looks like a little groove in the air box boot that should normally fit into the wall of the air box, but in most pics I've seen the groove is on the outside the the mounting area just heavily slathered with sealant.

[Ghenghis]

Originally Posted by Ariel Red Hunter

I can well believe it, although I suspect you gained more from the cool air you were getting. Cooler air is more dense=more power.

Exactly. But our self-made CAI's performed far better than any manufacturer model I'd used previously.

[Ghenghis]

Originally Posted by OUTERLIMITS

There are some spacers on the market to make that length effectively a bit longer. Would probably have to experiment to see what would work on the Hawk. Maybe that could solve two problems in that it seems like most of the pictures I've seen of the carb to air box boot that it's just a little short. There is what looks like a little groove in the air box boot that should normally fit into the wall of the air box, but in most pics I've seen the groove is on the outside the the mounting area just heavily slathered with sealant.

Yep, you can easily tell that was kind of a last minute fix. I like to imagine hearing that design conversation as a nearby observer, lots of fast gibberish I cannot understand, yet anyone would notice the tension in their voices, then an engineer walks in with a tube of black sealant, everyone nods their heads in approval...

[OUTERLIMITS]

Originally Posted by Ghenghis

Yep, you can easily tell that was kind of a last minute fix. I like to imagine hearing that design conversation as a nearby observer, lots of fast gibberish I cannot understand, yet anyone would notice the tension in their voices, then an engineer walks in with a tube of black sealant, everyone nods their heads in approval...

Yeah so maybe the proper fix is the one someone here did with a metal tube that connected to the carb via a rubber tube with clamps and then just clamped on a Uni pod filter inside the air box. You would still apply sealant around the air box joint, but at least having a perfect seal there would really not be all that important with a pod filter clamped to the tube. Plus those pod filters are pretty efficient and have a lot of surface area. I'm a huge fan of foam filters and Maxima FFT filter oil. The clean side of the filter in the air box tube has always been super clean on all my bikes when it has come time to clean the filter and I ride in a lot of dust.

[Ghenghis]

Originally Posted by OUTERLIMITS

Yeah so maybe the proper fix is the one someone here did with a metal tube that connected to the carb via a rubber tube with clamps and then just clamped on a Uni pod filter inside the air box. You would still apply sealant around the air box joint, but at least having a perfect seal there would really not be all that important with a pod filter clamped to the tube. Plus those pod filters are pretty efficient and have a lot of surface area. I'm a huge fan of foam filters and Maxima FFT filter oil. The clean side of the filter in the air box tube has always been super clean on all my bikes when it has come time to clean the filter and I ride in a lot of dust.

Yes, this is exactly what I'm going to do. Allows you to keep the dynamics of a straight tube, or at least as straight as possible, sound control as it's enclosed in the airbox, which also keeps it out of the elements.

[OUTERLIMITS]

Does anyone know what the stock stator is rated at? I'm hearing the TT250 is 300 watts, which sounds like a lot, but I thought the two bikes had very similar engines save for the counter balancer on the TT.

[Merlin]

Originally Posted by OUTERLIMITS

Does anyone know what the stock stator is rated at? I'm hearing the TT250 is 300 watts, which sounds like a lot, but I thought the two bikes had very similar engines save for the counter balancer on the TT.

If I remember right its 180 watts. I would love to upgrade my stator to a 300 watt ver if I could find the right part.

[OUTERLIMITS]

Originally Posted by Merlin

If I remember right its 180 watts. I would love to upgrade my stator to a 300 watt ver if I could find the right part.

Sounds like plenty for a bike this size. I know people want to power big lights and heated grips and all, but even a DRZ400 only has about 150. If it's a true 180, that seems pretty good. I'm guessing the 300 that the TT250 is claiming might be a little speculative.

[Merlin]

The 300 watts stator would let me run a 100 watt transceiver. (Long term plans)

[Ariel Red Hunter]

By the time I finally found the book, I was tired out enough to have to go to bed. You guys can laugh, but some day you too will be pushing toward your 80th birthday, so BACK OFF. Anyway, Joe makes the observation that the exhaust and intake are inter related. So I'm going to start there with his statement. "In a racing engine, the exhaust gases must be discharged so that the piston works against the minimum possible gas pressure. The kinetic energy of the gas must be utilized in such a manner as to produce the maximum negative pressure in the cylinder towards and at the end of the exhaust stroke. Use can thus be made of a large valve overlap to get the inlet gas column moving in readiness for the next filling stroke. It has been established that the combination of exhaust pipe length and diameter is important in achieving the best possible results, and that no one combination is equally efficient over the whole speed range of the engine." Kinda sad, huh? Jeez, Joe, are you trying to tell me this is not going to be easy? That I might have to do that most dreaded of all work, THINK? I'm horrified! "Usually a long pipe of small diameter is good for power at low rpm, while a short pipe of larger diameter is better for power at high rpm. It is necessary to compromise with a pipe diameter and length that will give the best results at the most used part of the engine speed range." Think about that statement the next time you look at the inside of the head pipe. See those sloppy welds in there? Look at all that bubble gum. Any wonder that a new exhaust system really makes a difference? So now I'm going to quote the question, put forth by the tech editor of The Motor Cycle magazine, which will help yu get in the flow of what Joe says: 'Is it not true that considerable induction pipe length and long valve opening periods are necessary in order to make full use of the phenomenon you have just described?' I'm going to pull out the answer for the 348cc engine, as it is closer to what we are using here. "In the 348cc Manx engine, the diameter of the inlet port is 1 1/8th inches, and the length from the mouth of the carburettor to the middle of the intake valve is 10 and 3/8s inches." In other parts of this article he talks about a 1 degree widening of the whole inlet tract as improving power even a little bit more, but that is easy to over do. And for your information, when I first read this article, 62 (I think) years ago, I thought aha, I'll just make a trumpet 4 inches long, and I will be Golden. Didn't work. Couldn't get the carb tuned right. So I made a spacer 4 inches long and my carb problems were over.
So, hopefully you guys can see how this whole thing is inter related. Ideally, you make or buy a free flowing exhaust system that has at least some extractor effect. Then adding an inlet pipe to move the carburetor farther from the head. When you find the right length, there will be a positive pressure wave of intake gas at the valve, just when it is opening. The time for all of this to occur is very short, so even an 1/8th of an inch in the length of the pipe will make a difference. You could purposely make it too long and then shorten it in 1/16 inch steps, until you find the sweet spot.

[Ariel Red Hunter]

Designing a good push rod engine, one that runs easy and tirelessly is much more difficult than designing an overhead cam engine. And Honda really did a job when they came up with this little number. Thanks to new aluminum alloys and much refined foundry technique, and modern machine tools, these are really magnificent little engines. Yes, if I was in charge of engine development over there, I'd build a thousand of these lil' darlins' stroked out to 240-250cc, and send them over here to see if American riders can tear them up. I'd send them a hundred at a time to RPS, with spare engines in the event one blew up. Before they left China I'd have tried to wear out a few on a dyno. I'd send them as soon as the first ones passed the dyno test. Then turn them loose on the American public. And see what you guys do to them. Be fun, huh?

[pete]

Only had one push rod motor MK3 Weslake..
was a great motor till the OHC motors came along
Jawa/Godden/GM... then it could no longer holds
it's end up...


..

[Ghenghis]

I've been reading more about intake runner length, air flow, air velocity, and how surface texture affects air flow. There are plenty of opinions out there, you've got to weed through them all.

One bit that had a contradiction to our thinking on intake runner length between the carb and valve may be plausible. This supposed highly reliable/intelligent source stated that the distance between the carb and intake valve and it's benefit from shockwave resonance had little to do with making more power until an engine reached 6500 rpm. Total length of the air intake system had more effect on an engine revving under 6500 rpm. The reason for this was air velocity, as air travels through a round tube it experiences less drag at the center of the pipe, so a longer tube will experience greater air velocity overall. The outer air near the walls acts as a bearing to reduce drag, at subsonic intake speeds you want a rough finish as this provides a more efficient laminar flow across it's surface, this would also keep fuel from attaching to surfaces along the intake since it will also ride along above this air bearing and stay suspended in the intake flow. Reducing any irregularities or mismatched surfaces after the carburetor will result in not only the best flow but a uniform air fuel charge on each cylinder fill.

I'd guess this is why all my old Holley carburetors released fuel into the air stream at the center.

If you decide to do any porting on the intake port do not touch the floor of the port unless it's to add texture to the surface or remove blemishes, lowering the port floor will slow down the incoming charge. Unshrouding the port ceiling around the intake valve stem will raise the efficiency of the total valve face area. If you could see from inside the cylinder looking up as the intake valve opened you'd see the intake charge coming in mostly from one side of the valve because of uneven flow above it's face in the intake port on most stock setups. This makes it harder to fill the cylinder, so power is reduced.

Some people dimpled their entire intake like the surface of a golf ball. Dimples on a golf ball are there to reduce it's wake as it moves through the air so they fly straight, a large wake causes irregular turbulence causing a sphere to change direction. Jury is out on that method, unsure if you'd see any difference over roughing up the intake surface, intake air isn't exactly moving around a sphere. I suppose you could dimple your choke plate...

Combustion chamber and exhaust ports do see a benefit from being polished or smooth, it reduces hot spots and resists carbon buildup, also, supersonic moving airflow is more efficient along a smooth surface. Keeping the heat in your exhaust flow results in a higher velocity which has a scavenging effect on the next exhaust cycle. Wrap those exhaust pipes and smooth out those burrs!

I'm tired now.