There She Blows

[Denny]

The centerline is ground into the cam. No you can’t change that. But you can advance or retard them.

 

[bob58o]

And I had it backwards last time I mentioned it.

The 28.5mm intake valve has the 1.2 ratio rocker. Stock rocker on the exhaust. Also used two different length pushrods

My simulation software told me the exhaust / intake flow ratio was too high. I believe somebody recently mentioned using ratio rockers on the intake side only because the exhaust flows too much already (or is too large, or something along those lines).

Below is some of the info I was going off of when I used the 1.2 ratio on the intake.

“
The Intake Valve Mach # 'MACH #' is .604
at your 'Desired HP Peak RPM' of 6500 RPM.
This is somewhat high and indicates you will need more Intake Valve
Diameter, Valve Flow Efficiency or more intake cam profile
(larger Intake Duration, Tappet Lift or Rocker Arm Ratio).”



“
The % Exhaust to Intake Flow Capacity 'Total Exh/Int %' is 81.5 %.
This is somewhat high, and indicates you could be opening the
exhaust valve too early or you could improve performance by improving
intake valve flow and intake cam profile. The most common 'rule of
thumb' is to design for around 75% EXH/INT flow capability.”

 

[bob58o]

So what kind of carb should I use for this suck through set on E-85 with 28.5”mm intake valve?

Will a slide be an issue? (Will it get stuck?)

Will a butterfly carb be better?

If using E-85, Will a regular gasoline carb jetted fatter work (compared to one for methanol)?

Im sill struggling with how I would attach a gx390 style carb since Im limited with fabrication skills.

I guess I could use a gx200 to gx390 long adapter and cut the engine side flange off.

The flanges for stock style carbs always have that channel machined to allow air in. For some, It wouldn’t be too hard to make a new flange to replace the spigot on the pump. For me, a work around with off the shelf stuff seems more feasible. I think I could use some bolts instead of the intake studs to attach an air filter adapter. It’s been a while since I thought about how stock style carbs and air filter adapters work.

 

[bob58o]

Maybe I’ll try to message Flyin Hillbilly? This seems up his alley?

 

[Denny]

The blower should take care of any low flow for the intake. That’s kinda their whole intended purpose and reason for living. The biggest problem I see you having right now is every stupid theory you run into you try to build using it. The fact of the matter is not all things apply or are useful to what you are building. But you are just stubborn enough not to listen to experience. The long intake tract and blow through intercooler is costing you more power than you are making. You vaporize the fuel mix only to have it recondense in the cooler. Not good for making power. Not one bit! The long run also allows fuel to fall out of suspension. The distance between the carb and the blower introduces a lag time between open throttle and the hit.
If we were building 2 engines one by you and one by me I guarantee mine would make more power and be faster.

 

[65ShelbyClone]

Let’s see if the rings fit with about 0.016” gap now.

Im afraid I removed too much material and the gap that was 0.013” will now be 0.020”

If it's a little too loose, nobody would ever know. If it's too tight, everyone will know.

And what do y’all think about carb size?

My plan was to use a 30mm (which I have) with the blower, but had a 21 or 22mm on this engine when running NA. I probably have a 24mm around here somewhere. They are all basically the same carb with different sized Venturis bored though.

The carb should be sized for the power you intend to make. Engine displacement becomes a secondary factor with forced induction. I would probably be looking for at least 24mm if not 28-30. If you already have a 24, just try that first. A 25mm restrictor is enough for formula SAE cars to make 80+hp at the wheels.

While looking at the carb options and seeing the methanol ones, I remembered to start considering compression ratio.

After milling 0.035” off the head for an 18.4cc chamber and using the +0.020” connecting rod, the CR with a 0.040” gasket will still be around 10.4 : 1

Since the pulleys might deliver 11 psi of boost and the intake temps will be hot, I’m thinking alcohol is the answer.

Yeah, 10.4:1 with 11psi is a lot of squeeze for pump gas and a chamber that has effectively no quench. E85 would probably handle it.

Well PB blaster, a torch, a few pullers with clamps with a pipe wrench… I don’t think the supercharger pulley budged and now it’s damaged.

There’s a key in there. Maybe there’s a trick to getting this off.

Im ready to try to cut it off. I figure I might be able to use the dremel. Maybe an oscillating multi-tool. I’ve never used the one I have and not sure if they make a tool to cut through a pulley.

The one on my (genuine) AMR500 is a very close fit, but slides right off once the nut is removed.

1.) Will a slide be an issue? (Will it get stuck?)

2.) If using E-85, Will a regular gasoline carb jetted fatter work (compared to one for methanol)?

1.) I doubt it. Your blower can only pull on it as hard as the atmosphere pushes from the other side. It might be different if you were trying to push 11psi into it as a blow-through.

2.) It will take ~40% more fuel mass flow than gas, so make sure the carb can do that.

 

[bob58o]

The blower should take care of any low flow for the intake. That’s kinda their whole intended purpose and reason for living. The biggest problem I see you having right now is every stupid theory you run into you try to build using it. The fact of the matter is not all things apply or are useful to what you are building. But you are just stubborn enough not to listen to experience. The long intake tract and blow through intercooler is costing you more power than you are making. You vaporize the fuel mix only to have it recondense in the cooler. Not good for making power. Not one bit! The long run also allows fuel to fall out of suspension. The distance between the carb and the blower introduces a lag time between open throttle and the hit.
If we were building 2 engines one by you and one by me I guarantee mine would make more power and be faster.

We got rid of the intercooler.
We got rid of the BOV.
And we greatly shortened the intake runner length. Who says I don’t listen to experience?

 

[Denny]

Now mount the blower closer to the head. And the carb above that!

 

[bob58o]

The previous carb that was working on this engine when last running was a PWK style 21mm with #32 pilot jet and main jet drilled to 2.05mm.
2.05mm
0.080"
205 Keihin Jet Size
170 Mikuni size

 

[bob58o]

If it's a little too loose, nobody would ever know. If it's too tight, everyone will know.



The carb should be sized for the power you intend to make. Engine displacement becomes a secondary factor with forced induction. I would probably be looking for at least 24mm if not 28-30. If you already have a 24, just try that first. A 25mm restrictor is enough for formula SAE cars to make 80+hp at the wheels.



Yeah, 10.4:1 with 11psi is a lot of squeeze for pump gas and a chamber that has effectively no quench. E85 would probably handle it.



The one on my (genuine) AMR500 is a very close fit, but slides right off once the nut is removed.



1.) I doubt it. Your blower can only pull on it as hard as the atmosphere pushes from the other side. It might be different if you were trying to push 11psi into it as a blow-through.

2.) It will take ~40% more fuel mass flow than gas, so make sure the carb can do that.

I already have a 30mm as well. It’s what I had for a 420cc engine. The 45mm UNI filter fit on the 48mm air horn of the carb with a little hot water to loosen it up. These carbs have a “power jet” which when the pressure drop in the air horn is enough it pulls fuel from the bowl and sprays it before the venturi/slide. I usually just replace the small fuel line with vacuum caps, but this is an option to dump more fuel at WOT I think. I’m not sure how this circuit really works. I always have just capped it and adjusted the main jet.

 

[65ShelbyClone]

Power jets are pretty much a two-stroke thing. I only ever knew of Lectron carbs having them, but I don't play with a lot of two-smokes.

 

[bob58o]

I suppose it’s time to start putting stuff back together. I had a BP6ES spark plug in the head and I guess I should go 1 heat range colder, which for NGK I believe would be BP7ES.

I had a few laying around. See it’s not hoarding if you eventually use it.

 

[bob58o]

No clue on their accuracy but one of my best Harbor Freight purchases was the set of 3 TQ wrenches for $9.99 each.

Not sure where others get a 1/4” drive TQ wrench for the rod bolts or how much they cost. I guess the Jungle site probably has cheap ones available now.

The ARC rod bolts got 175 inch pounds.
Side cover studs 210 inch pounds
Head studs 220 inch lbs
M14 spark plug with washer in aluminum head 228 inch lbs (19 ft lbs)

 

[Denny]

Always wondered who made this one. View attachment 139847

Bob, that is how you want your engine and blower to be. Nice and close to the intake port just after the carb. That will give you the lowest intake temperature, keep fuel suspended and best throttle response.
What did you ever do with your mini bike and granddaddy?

 

[bob58o]

Sold one mini bike. One got stolen. Granddaddy buggy was given to the nephews, then it got sold.

 

[bob58o]

Going to have to test this version first. I’ve gone too far to turn back now. Might dream up some sort of water line wrapping the intake going to a radiator. If you won’t let me have an intercooler. Lol

 

[bob58o]

I tested this Kohler flywheel before with a straight up key and the timing light and got around 19.5* BTDC. I used a 5* key to try to get closer to 24.5* in the NA version.

Now I tried using the same key flipped around. Hopefully the flywheel didn’t spin on the shaft while I ugga dugga’d the nut.

I think this is where it fires, and it seems to line up with one of two timing mark I made before. I don’t remember what they mark.

Makes me think the flywheel spun and I’m back to the 19.5 BTDC instead of 14.5, which is where I wanted to be.

 

[Denny]

I might not sweat the timing too much until you get it running. But that’s just me.

 

[bob58o]

Coil on backwards, forgot flywheel fan and pull start thing… Somebody memory is going…

Well TDC should be set with this degree wheel held together with toothpicks and tape and a piston stop.

Using my understanding of when a spark plug fires by relationship of coil to magnet, I think it is only 10* BTDC.

 

[bob58o]

I might not sweat the timing too much until you get it running. But that’s just me.

Well I got to put timing somewhere to try to get it going.

It seems like my ignition timing is now about 10 degrees before top dead center. Since there’s no vacuum or mechanical advance and low rpm’s actually have more advance than higher rpm’s, do you think 10 BTDC may be a reasonable place to attempt to start and then tune from there?

This set up might give me 10 BTDC at 3k rpm and 8 BTDC around 5500 rpm.

Boost will be constant with a roots style blower (more or less)

Full 11 psi the whole range, I think.

10.4 : 1 CR
Torque cam
11 psi boost
E85