Forced induction 100cc

[Grumph]

This reminds me of an interesting discussion I was having. On the RC-31s (aka Hawk Gt, aka Bros650) the crank is pretty weak, and is prone to flying apart up near 100hp @10krpm. Now I've heard most of the crank stresses are from the centrifugal forces as it spins. So what I was wondering, if it is blown, and only revved to say 6krpm, will it be able to make more power with less chance of shredding cranks? Or will the extra power required for the blower make it snap earlier?

The answers are actually, yes, no and maybe....
When you boost a motor you increase the bearing loads from explosion pressure....But as has been correctly stated, most of the load on a crank is actually inertia (note spelling please). There is a point in the rev range where the inertia loads become greater than the loads from explosion pressure - called the crossover point. When boosted the effect is to raise the crossover point. This can in some cases be of great benefit to bearing life and crank longevity.
In the case of the RC31 I suspect that Hondas well known inability to finish cranks properly has more to do with their flying apart than anything else. A new RC31 crank with the oil galleries properly radiused, clearanced correctly, balanced correctly and probably with a smaller alternator rotor to raise it's natural frequency should last under race conditions.

[bogan]

The answers are actually, yes, no and maybe....
When you boost a motor you increase the bearing loads from explosion pressure....But as has been correctly stated, most of the load on a crank is actually inertia (note spelling please). There is a point in the rev range where the inertia loads become greater than the loads from explosion pressure - called the crossover point. When boosted the effect is to raise the crossover point. This can in some cases be of great benefit to bearing life and crank longevity.
In the case of the RC31 I suspect that Hondas well known inability to finish cranks properly has more to do with their flying apart than anything else. A new RC31 crank with the oil galleries properly radiused, clearanced correctly, balanced correctly and probably with a smaller alternator rotor to raise it's natural frequency should last under race conditions.

Crossover point eh, thats a good keyword to start some more research with.



You're probably right with the later, it just so happens Marine Crankshafts are doing a run of super strong billet cranks. Will have to make a shit-tonne of cash before I can pursue that option. Also noted, was that the clutch basket disintegrates, rods break, and small ends ovalise at those sort of power figure too.

[ducatilover]

Not to forget that a blower is stressing the crank in different directions to the combustion forces.
Look at bearings that have fucked out under blower use and bearing that have shat out from too much timing/why, all different areas of the bearings are rooted.
Snapped cranks are good fun

[ducatilover]

Crossover point eh, thats a good keyword to start some more research with.



You're probably right with the later, it just so happens Marine Crankshafts are doing a run of super strong billet cranks. Will have to make a shit-tonne of cash before I can pursue that option. Also noted, was that the clutch basket disintegrates, rods break, and small ends ovalise at those sort of power figure too.

Ouch.
And too much vibration and/or give. I'm glad mine never did that

[Grumph]

Looking at where that's broken, I'd say torsional vibration is the culprit.

We knew there was a problem with the Kawa 500 twins cranks which broke if you left the alternator rotor fitted and revved shit out of them.
I used the altenator boss to mount a lightweight ignition trigger on the motors I built and I never broke a crank - incl Tony McMurdo's one which got run harder than the others. Raised the naural resonance frequency of the crank above what was obviously a critical point.
Rods break if the bearings pick up cos the oil holes aren't done right by Honda....and stock Honda rods shouldn't be used at high power levels anyway. Don't people research history ? Honda rods have been going oval in the small ends since the CB750....

[speedpro]

Doing some simple maths(which I can't remember any more) on the forces inside an engine clearly show that in a regular engine the forces created in the power making process are dwarfed by the forces created when things turn or reciprocate quickly. Simple illustration - piston forces. bmep = 128psi but the "g" forces may be 6-8000 at peak. Multiply the g force by the piston mass and you see which value is the problem.

[Sketchy_Racer]

I tend to agree...as i've said earlier on here we finished up with .50mm clearance on rotors aprox 150mm long. The rotors are always hotter than the case as there's no good heat path away.
The classic sequence is run it, seize it, enlarge clearances, repeat sequence until it doesn't seize....
By the end of our sequence we had lost 2 psi but the bastard never seized again.

There's always water injection....or just get the rider to piss in the intake if you don't want the weight of a tank.

Okay, so I finished final assembly of the two lobe supercharger today, and here are the measurements.

Body Depth = 50.01mm
Drive Rotor length = 49.62mm
Driven Rotor length = 49.60mm

So for rotor end clearance I have got between 0.195mm and 2.05mm Which means that there would theoretically have to be a 200 degree difference in temperature difference between the rotor and housing before I need to worry about it seizing.

Body Diameter Driven side = 57.98mm
Body Diameter Drive side = 57.96mm (measured 57.00 when in the mill, but measured on a colder day and I think the housing has been stress relieved and moved a little.

Rotor Major Diameter = 57.59mm (both were the same size)

So again we are looking at 0.195mm clearance rotor to housing, and the same for rotor to rotor clearance.

For "technical" testing I have ran the charger at 3000Rpm for 30 minutes with marking blue on all surfaces and with the heat gun getting it up to around 100 degrees using the old spit test) and it didn't seize on me and upon pull down it would seem there is no contact which is good! Looks like it has sucked a bit of floating shit through it from my dust garage but only very very faint marks in the bearing blue.

You really want to have that injector spraying down before the valves. That way when it is picked up in the air stream it gets diverted onto the valves.

You also might want to to some spray pattern testing. Just apply fuel pressure and hook the injector up to 12V. If the spray is conical then no need to worry, but if the spray is flat then orient the injector so it sprays a horizontally. Injected machines can be quite picky with this; especially when starting.

Otherwise looking really good. Very impressed.

From what I have read, everything online (although to do with cars a injector is an injector) they recommend trying to get the injector to spray directly onto the intake valve as they suggest that the heat of the valve vaporises the fuel into and even finer mist before entering the combustion chamber. It looks like that is how the setup is on the GSXR600 racebike I have in the shed, I might pop the tank off and take a closer looks and see if they do it like that.

Haven't though about spray pattern testing, I'm going to take a punt and say that it is a flat sprat pattern as it has two holes about 50 microns in diameter.

Todays mission is to start porting the head to match up the throttle body, adapter plate and intake port.

Oh I got the PC talking to the ECU now, there is definitely something cool about plugging PC's into bucket racers. My friend who uses Motec engine management system popped in to take a look and is pretty impressed with the adjustability of the Ecotrons EFI kit. Can't wait to get it fired and start tuning it!

[Grumph]

Yep, those clearances will do as a start point. Good work.

Yes, by all means try and aim the injector stream at the back of the inlet valve. It might make all the difference thermally.

I seem to remember Gurney doing quite a bit of dyno research into injector placement on Chevys and finding that aiming at the back of the valve was significantly better.

[Yow Ling]

So for rotor end clearance I have got between 0.195mm and 2.05mm Which means that there would theoretically have to be a 200 degree difference in temperature difference between the rotor and housing before I need to worry about it seizing.

Clearancs like that sound like my kind of engineering

[Sketchy_Racer]

So the progress has been slow but lots of the little time consuming jobs have been taken care of, I have got the motor back together after porting the head and un shrouding the valves in the combustion chamber. I measured up the compression ratio and I am at 8.3:1 which is bone stock and the perfect number for me, can't believe how low the stock compression ratio is!

Had the valve seats cut as I smoked them with the grinder doing the ports, whoops. Pretty happy with how it has come out, The port arrangement is really shit but it will have to do.

I will get the cam looked at next but for now I just want to get the motor running without the charger at first.

Tonight I machined up a pulley and crank trigger on my little bench lathe, It's a pain in the ass coming from nice british colchester lathes trying to do accurate angles and diameters but with the use of a couple of Dial gauges I had one set on the cross slide and saddle to give me and accurate readout of the positions.

Really happy with how the pulley/trigger turned out, even got the electrics making a spark tonight! It's tempting to fire it up but I will wait until I get the exhaust at least!.

Anyway nothing to exciting but here are a couple of pics of the progress.



Also got a dash from lascom motorsport, it looks pretty sweet, does two temp readings, thinking one for the motor and one for the supercharger also can piggy back onto the 02 sensor so I can see what that is doing.

http://www.koso.com.tw/products-deta...lang=en&id=308

That's all for now!

[TZ350]

I will get the cam looked at next but for now I just want to get the motor running without the charger at first.

My sons Toyota Turbo had no overlap at all. What is your plans for cam timing?

[Grumph]

Do you have the std Longshit cam figures ?

Turbos are a whole different deal re cam timing...in this motor IMO a fair amount of overlap is desirable to give a blow - through period to cool off the valves....

[speights_bud]

Really happy with how the pulley/trigger turned out, even got the electrics making a spark tonight!

So how does the wiring diagram work out? given the funky colors and your high pressure bag end?

[Sketchy_Racer]

My sons Toyota Turbo had no overlap at all. What is your plans for cam timing?

The cam is stock at the moment and would appear that is has absolutely no overlap at all but in saying that I have not put the DTI to measure it. I will start with this and look to change it to optimise it later.

Do you have the std Longshit cam figures ?

Turbos are a whole different deal re cam timing...in this motor IMO a fair amount of overlap is desirable to give a blow - through period to cool off the valves....

Funny you should mention that, everything I have read has suggested that valve overlap is no good in supercharged engines as it just chucks the boost pressure out the exhaust but my thoughts are along the lines of valve cooling also that if the correct amount of overlap is used you can exhale more exhaust gasses so that you end up with a better volumetric efficiency to over come the lost boost energy out the exhaust. Cam's are $30 each so it will be something to easily try out later on.

So how does the wiring diagram work out? given the funky colors and your high pressure bag end?

The wiring off the end of the crank was easy as in the end, I used the stock hall effect sensor and put the whole inner rotor kit aside as it's pulse per rev was to noisy and gave the ecu the shits.

However the rest of the wiring is a farken nightmare I am certainly no auto sparky but everything works as it should so far. In theory if I put fuel in the tank it would run now without the supercharger but I need to finish the exhaust.

[Sketchy_Racer]

So a small update, still boring stuff at the moment but I am getting close to fire it up!

I have finished all the wiring for now, It's ok but certainly not great I will probably redo the whole wiring loom once everything is working just to tidy it up.
My dash arrived today so that went on with a temp sensor on the head of the motor and one in the supercharger. The temp probes are easy to mount as they are M5 threaded so all I had to do was drill and tap a hole and screw them in. They are super sensitive also which is good. The dash is set up to flash an alarm at me if either of the temps go over 100 degree but that is adjustable and also the shift light is set a 10000 RPM at the moment.

I am happy with the dash it is neat and tidy and has everything I need to know while the engine is running.

I have just purchased two handle bar switches, one for ignition and one for map selection so I can trial two different maps in one session which is cool.

I have cut the stainless steel sheet for the plenum now and have taped it into place to check fitment. It looks like it will work ok, it has a volume just shy of 1500cc at the moment which is very large but it is much easier to make it smaller than to make it larger so I thought I would start there. Piping is just radiator hose which should work ok, it can handle boiling water up to 1 Bar so I am sure it can handle hot air to the same.

I am still waiting for the guy off trademe to send my blow off valve, apparently it takes over a week to post something from auckland to wellington.

I have also been doing so study on the tuning software and how to use it. The more I play with it the more I like it.

Next on the list is exhaust design - what's the go with that? I have never done an exhaust for a diesel before. Does supercharging make a difference to design?

Anyway here are some photos and one from an odd ball job at work today, It's a wood splitter, the joker snapped the end off it so I had to make a new one, The screw was machined with a 12mm ballnose end mill using the rotary axis to turn the job as the cutter moved longitudinal to the rotary axis.



Cheers,

-Sketchy