Second Generation Chrysler

[86 century]

Re: Second Generation Chrysler

Ok
Thanks explaning that for me.

We have run N2o on a honda cr500(500cc two stroke dirtbike) worked well till the cases gave out.

 

[Frank Acampora]

Re: Second Generation Chrysler

Nope, Tater---It's just a standard Sears Craftsman 1/2 inch chuck drill press, floor model, 10 speed, with a 1/4 inch drive belt and 1/3 hp motor. I bought it in 1972, on sale, of course. I can only mill about .010 at a time so there is where the "damn near forever" came in. I really should get rid of it because the quill has the chuck taper ground just a bit off. This gives the Jacobs chuck about .020-.030 run-out at the jaws. That makes it very difficult to do precision drilling.

I wasn't considering racing exhaust since I don't intend to race the engine. But, in the future, that might be another custom project. What I am strongly considering are velocity stacks to tune the intake length.

For those who don't understand: An engine is an air pump. The more air you can move through it, the more fuel you can burn, and the more horsepower you can make. Air has mass. When a mass is moving, inertia tends to keep it moving. Thus, if the length of the air column is correct (for a given RPM), at that given rpm the air will tend to keep pushing into the crankcase (or possibly piling up at the reeds for the next induction stroke) after the piston stops creating vacuum. It is a mild supercharging effect. Think of the old 1970s Chrysler ram induction 413-426 engines with two four barrel carbs and either short ram manifolds for high speed or long ram manifolds for low speed torque. It really does work, but not as well as other methods of increasing airflow. Beach Boys, Shut Down: "He's hot with ram induction but it's understood--I've got a fuel injected engine sitting under my hood."

 

[86 century]

Re: Second Generation Chrysler

Frank
You have a better understanding of two strokes than I do could you explane why forced induction will not work.
Thank you

 

[Frank Acampora]

Re: Second Generation Chrysler

Bear with me--this will be long. If you mean supercharging by forced induction, then it is not that it won't work, but that unless the engine is designed for it correctly, it will not be efficient. On our outboard 2 cycle engines, because the bypass and exhaust ports are open at the same time, excess fuel/air will simply blow out the exhaust port. Thus: There is no reason to try to have the engine pump more than its capacity.

There are various designs of 2 cycle engines, but the design we know in outboards has several characteristics. because the ports are open for about 120 degrees, the bottom of the stroke is useless. Thus: An engine of 90 cubic inches could only move at 100% efficiency 60 cubic inches of air. Anything more is wasted. However, because a 2 cycle engine has one power stroke per cylinder per revolution and a 4 cycle has one per two revolutions the same sized 2 cycle will produce about 60% more power.

Now, the principle of supercharging is to force more air into a cylinder, thus making it appear bigger. The supercgarger most people think of on dragsters was originally made by GM for its 2 cycle BUS engines. However, these engines had bypass ports at the bottom of the cylinders and exhaust valves at the top. Thus, the cylinder could be overcharged. In fact, because of their design, these engines could not run without a supercharger.

Back up a bit. It takes horsepower to drive a supercharger. So, we take an engine that produces 200 horsepower and supercharge it. Now, (for example) it takes 100 horsepower to drive the supercharger so the engine only has 100 HP available. BUT---The supercharger can pack enough air into the cylinders to let the engine generate 400 horsepower. Thus: we have a net increase of 100 HP and the engine now makes 300.

OK--back to 2 cycle. It takes a certain amount of pressure to open the reed valves and this causes vacuum inside the crankcase. THUS: the two cycle engine will NEVER be able to injest its full capacity of air. NOW, if we supercharge to just enough psi to open the reed petals, then the engine can ingest its full amount of air and fully charge the cylinders. BUT: (and here is where I have no hard numbers, just conjecture) If it takes, for example, 100 horsepower to supercharge a 200 HP two cycle outboard and we can only just fill the cylinders, we will at best generate 100 HP more--so it is a wash. We spent all that money on equipment and made the engine much more complex just to have the same available horsepower generated using more fuel. That's not good economics.

 

[tater76]

Re: Second Generation Chrysler

Velocity stacks? do you have a pic or example? I have never heard of this, but I am guessing its the same principle as performance dual plane or single plane intake manifolds on cars? ie, you can tune the flow by changing the design to gain optimum performance?

 

[Frank Acampora]

Re: Second Generation Chrysler

No photos but if you look up old school hot rods, they were common. The principle is more like a high rise manifold. They do go by various names but velocity stacks are simply trumpet shaped pipes that are bolted to the top, or in my case, the front of the carbs. They are cut to the correct length to enhance performance at a given RPM range. They can be tuned by figuring the wavelength of that frequency and since it is too long, an even segment it used--like 1/4 wave. For example only: 5000 RPM corresponds to 83 cycles per second. If an 83 cps wave is 5 feet long, a 1/4 wave pipe would be 1 1/4 feet long. ---Too long for our use so we go to 1/8 wave which would be 8 inches. Of course, unless I could custom bend some to wrap around the block, the engine cover will not fit over them.

Very similar to tuning a pipe organ pipe or a CB radio antenna. (Ooooh! That one is showing my age) Don't ask for specifics because before I do it I will need to study.

 

[droach77]

Re: Second Generation Chrysler

Not trying to jack your thread frank...Herman Munster had velocity stacks on his hot rod.... I am sure most people can fit the image to his hot rod machine.

dave

 

[wolfie-uk]

Re: Second Generation Chrysler

a very similer idea was used by Volvo when they made outboards, i have varying length trumpets to improve air intake, in the photo are the standard ones for everyday use.

 

[tater76]

Re: Second Generation Chrysler

Ha! Munsters Rod!! LOL!! Love the visual there droach. I guess I kind of get the principle, but is it really worth the effort? and if it is, what about building a set that is adjustable? Kind of like a set of three progressively smaller pipes that fit inside one another? this way they could be adjusted very easily, slid in or out for the desired performance, then set with a set screw? Just a thought.

 

[Faztbullet]

Re: Second Generation Chrysler

Velocity stacks are more for looks than performance on a 2 stroke, the only thing they do is straighten out the air flow into carb making a smoother transition thru carb. They will add about 2-4 CFM to flow and this proven on flow bench testing. The best way to increase hp cheaply is to make engine produce more crankcase vacuum. The lower the vacuum the faster the intake charge and quantity. Remember that 90% of of intake charge is pushed thru engine intake due to atmospheric pressure (14+psi) to fill the crankcase void and remainder due to crankcase vacuum, thats the reason the 1" spacer plate on a V-6 increases bottom end and mid range torque as the reeds are moved away from crankcase and increases the crankcase CC's. When I drag raced in the 80"s we had a STOCK 200hp turbocharged Mercury that made on the dyno 295hp at crankshaft at 5psi boost. It pushed a 17ft Hydra-sport Areostar bass boat hull @ 106 in 1/4 mile turning a 34 pitch cleaver at 6800rpm. Also on a crossflow you are limited to how much you can shave off the head as piston will hit top of chamber, to increase PSI on a crossflow you make the chamber area smaller....

 

[wolfie-uk]

Re: Second Generation Chrysler

so if i move the reeds away from the crankcase i will improve the lower end performance, what effect though on top end ?

 

[Frank Acampora]

Re: Second Generation Chrysler

No, Wolf. You don't want to move the reeds away as this will increase crankcase volume. Since we are trying to increase air pumping, this will be detrimental. We always (through "packing") try to minimise crankcase volume.
You want to either move the carbs or add pipes to them. Just like on your Volvo. Typically, with the Chrysler super stock auto engines, the pipes were made for a desired RPM band. Long pipes--long wavelenght--low frequency--enhanced low speed torque. Short pipes. better top end performance. Increase in low end should not appreciably affect top end performance.

 

[Faztbullet]

Re: Second Generation Chrysler

if i move the reeds away from the crankcase i will improve the lower end performance, what effect though on top end ?

Yes.... and top end may increase just a little. A 2 stroke works way different than a super stock 4 stroke. The more air/fuel you can put in crankcase the more you pack the cylinder intake charge, a the crankcase does not completely empty itself on the intake stroke. Thats also on of the reason the re-circulation system on the "hot rod" 2 stokes dumps to a common area and engine burn ups the excessive at WOT. For example a late 80ish early 90's Force 40/50 2 cylinder are exactly the same engine except for decals and carb. The smaller venturi on the 40 carb reduces the volume the engine can "inhale" vs the 50hp carb which flow mores air /fuel thus a 10hp increase.

 

[bman1bpm]

Re: Second Generation Chrysler

always learn something reading Franks' Posts!

 

[Frank Acampora]

Re: Second Generation Chrysler



Here we have the first phase of assembly. First photo shows me using a sharp tool to scribe the ground flat, checking for cap alignment. Second shows assembly oil (TCW-3) and my 1/4 inch driver with a six inch extension and a 1/4 by 12 point socket. This is to snug the rod cap bolts. They will be torqued later.

Third photo shows the pistons (through the bypass ports) and the relation of the new piston ports to the cylinder ports.

Fourth photo shows all the pistons and con rods assembled. You can see the inter-crankcase seals right next to the two center bearings. If you look closely, you can also see the crankcase "packing" slugs in the bypasses. Some Chrysler and early Force engines had them. Later force engines eliminated them as a cost saving. They don't really reduce the volume that much and I really don't know if they had any effect. BUT--- this block came with them so I will use them.

Last photo is a close-up (too close) of one of the two ground flats on the big end of the con rod.

Strange: They never upload in the same order as I put them.

 

[Justinde]

Re: Second Generation Chrysler

What sort of displacement (cc's or ci's will do) id this engine and how much power will she have- should I swap you a great 1988 125 Force for this donk?

Looks great mate, cant wait to see a youtube vid of it!

 

[Frank Acampora]

Re: Second Generation Chrysler

3.3125 bore by 2.80 stroke for a 72 cubic inch displacement or about 1.2 liters. Understand that these engines were rated at the powerhead and did not account for power loss through the water pump and lower unit. If it performs as well as the last 90 I ported, I expect it to deliver a good solid 90 at the prop. If it is better, maybe 100 HP at the prop. Since I do not have a dynamometer my results will be based upon RPM and speed delivered on my test boat. The test boat is a 1971 deep vee, 15 foot Glastron V153. This boat has had about 5 different engines on it ranging from an old '67 Chrysler 55 to the current Chrysler 105 so I have quite a number of speed and prop comparisons on it. I just threw in the last photo to make you jealous. Before you ask---Yes, she dyed her hair black and was the model for the mermaid. LOL

 

[Frank Acampora]

Re: Second Generation Chrysler



Sigh! I think I might just be going crazy! Who else would do this? Again, a bridgeport mill would make my life a LOT easier BUT--I don't have one.

Well, the easy part is done--all the bolt holes are drilled. Now comes the difficult part: Shaping the water flow ports and cutting out the inside. All for a couple of extra cubic inches exhaust chamber volume. The Machine shop wanted $300 to cut it on the water jet so I said no thank you. That is too much to invest for a part that is experimental and may--in fact most likely will--have no effect on performance.

 

[Pauloski]

Re: Second Generation Chrysler

Enjoying your thread Frank. You have so much knowledge stored in your head. Great you are downloading some of it into the computer so we can all learn more. Keep the pics coming and as someone said a vid on youtube when finished would be great. Cheers, Paul

 

[Frank Acampora]

Re: Second Generation Chrysler



Here is the finished product ready to be installed on the engine. This 1/2 inch thick aluminum plate gives 17 cubic inches more volume to the exhaust chamber. Cost: 40 bucks for the aluminum, 7 bucks for cutting blades, 8 bucks for a dremel carbide bit I broke. The rest were tools I already had---assorted end mills and cutting burrs.

Royal PITA to make this part. Aluminum clogs the bits, drills, and blades. I would not recommend trying unless you have good drill press and a bunch of end mills, and a Dremel with carbide bits. also use plenty of cutting oil.

If it does have a performance gain, the next one will be made by the machine shop. Mind you: The only reason I am increasing the exhaust chamber volume is because the engine will be recreational, non-racing. Chrysler did increase the 45 to 55 with a similar spacer plate on the 55 to increase volume and lower backpressure. However, the 55 had a greater cubic inch displacement and a larger carb in addition to the plate. SO----This is an experiment that may not work. But for 50-60 bucks in parts, its worth a try.