Custom 208 Hemi

Rat

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First I need to clarify "Custom 212 Hemi"
It began as an LCT [Husqvarna Storm Force] 208cc winter spec engine.
I have since swapped it to a Hemi head so it can be ran while doing top end work to the original head.
The 212 Hemi it was pulled from was completely full of water when it was given to me, how it wasn't rusted solid is still beyond logic To me, but I tore it down cleaned it up and set it aside as spare parts because it's an older Hemi that seems to use mostly Non Hemi components (definitely has Non Hemi valve springs)

I'm trying to figure out what the ideal ignition timing change would be for it to squeeze more grunt out (Im probably pushing more power than I need but what's the fun in not going for more.

As it's I'm running:
a 24mm PWK copy with a short billet velocity stack,
full governor delete and case plug,
a +1mm forged conn rod and flat top piston (not a dished) to bump up compression
a cheater cam supposedly good for 6500 with gov delete alone,
stainless 5.5mm rods,
stainless lash caps and lifters,
hardened adjustable tappets,
and 22# springs.

I still need to get the automotive style spring seats and split keepers for it.
I am planning on putting the original head back on with the appropriate length stainless push rods eventually since it has about half the chamber size because more compression is always good (until it's not and you need race fuel to prevent predetonation)

Cam Specs
Intake
Open 30 Close 76
Lift 234
CL 112
Duration @ 050 > 220

Exhaust
Open 67 close 42
Lift 240
CL 105
Duration @ 050 > 223
 
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bob58o

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A longer connecting rod does not change displacement. A +0.040” rod doesn’t change the stroke of the engine. You have to change the crankshaft to change the stroke. I think some can do some type of shaping magic, but a longer rod can change angles and compression ratio and maybe some other things, but the stoke is still that of a 208cc displacement engine.
 

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A longer connecting rod does not change displacement. A +0.040” rod doesn’t change the stroke of the engine. You have to change the crankshaft to change the stroke. I think some can do some type of shaping magic, but a longer rod can change angles and compression ratio and maybe some other things, but the stoke is still that of a 208cc displacement engine.
Noted and I was half asleep when I posted. I know that a longer or shorter rod only changes the stroke relative to the position of swept bore, but does not actually change the amount of bore being swept aka displacement.

The 208 crank is beefier that the predator, and the rod swap was done specifically to increase compression just as the flat top piston was.
 
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Rat

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At what point would you be satisfied with the power?
I'm not NOT satisfied with the amount of power it already has, considering it only takes a flick to the throttle to yank the nose right off the ground.

2.50-18 motorcycle tires, Tav2, and 6.22 final drive (9/56)

I'm mostly just considering my options, it uses a 1/4" key unlike a predator 212, so it's probably not going to be easy to get an offset key for anyhow
 

bob58o

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When you say more grunt, I assume you want more on the lower end. It’s seems however you have enough grunt and want more scream.

ignition timing on these engines can really only be optimized for one specific RPM. If you want a boost at higher rpm, then you can try to advance it.

What size is the crankshaft of the 208cc? What is the diameter of the flywheel? With some measurements, some maths, and a file… you can make your own offset key. Or a degree wheel and piston stop and you can set timing without a key.
 

Rat

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When you say more grunt, I assume you want more on the lower end. It’s seems however you have enough grunt and want more scream.

ignition timing on these engines can really only be optimized for one specific RPM. If you want a boost at higher rpm, then you can try to advance it.

What size is the crankshaft of the 208cc? What is the diameter of the flywheel? With some measurements, some maths, and a file… you can make your own offset key. Or a degree wheel and piston stop and you can set timing without a key.
Ok yes definitely needs more scream, plenty of grunt.
The flywheel is 6⅝ like a Predator, but with a different taper angle.
I have no clue how to get the taper angle, but I do know it uses a 1/4" woodruff.

Being electric start and having had a key jump the keyway putting the flywheel back on which lead to some slip, I'm gonna pass on the keyless timing.

The exhaust is 1"od at the flange to make the manifold connection fit between the studs, but the rest is all 1" ID till you get to the baffle which has a 1" od core and a 2¼ shell... it's all in house fab work
 

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If you want to file a key, measure the diameter (or circumference) of the crankshaft at the back of the keyway (closest to the engine).
Divide circumference by 360 degrees.
Multiply by how many degrees you want to advance.
File that much off.

If the diameter at the back of the keyway is 1” for example.

1” x 3.1416 = 3.1416” circumference
3.1416” / 360 = 0.0087” per degree

If wanting to advance 8 degrees…

8 x 0.0087” = 0.0696”

Filing 70 thousandths off the top part of the key would advance the flywheel 8 degrees (if the diameter of the crankshaft at this location happened to be one inch).
 

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Rat

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If you want to file a key, measure the diameter (or circumference) of the crankshaft at the back of the keyway (closest to the engine).
Divide circumference by 360 degrees.
Multiply by how many degrees you want to advance.
File that much off.

If the diameter at the back of the keyway is 1” for example.

1” x 3.1416 = 3.1416” circumference
3.1416” / 360 = 0.0087” per degree

If wanting to advance 8 degrees…

8 x 0.0087” = 0.0696”

Filing 70 thousandths off the top part of the key would advance the flywheel 8 degrees (if the diameter of the crankshaft at this location happened to be one inch).
Seems simple enough, but I think I'm going to leave well enough alone.

I'd ask about final ratio, but...

1. That's a different topic entirely;

and 2. I'm in the mountains now so any changes have a huge impact on the load the tav2 will be dealing with.

I was running a 10t on the jackshaft output to the 56t when I discovered the nose was easy to pull up from a dead stop... as you can well imagine swapping to the 9t output (5.6:1 to 6.22:1) just made it even easier.

It's not one of those things that is super easy to do by accident, although the discovery was. I though damn sure for a moment the bike was going to end up riding me (more than 2ft off the ground)

I recently acquired a genuine PWK 36 Air Striker... any thoughts on that?
Im thinking it migh be too much carb even for a high compression 208cc... but I knocked together an intake for it anyway.
 

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I like the 24mm PWK style carbs for 212cc’s

As for overall ratio, assuming you are talking about “gear ratio,”

low gear for 30 series TC with 6” driven unit is around 2.7 :1

So if sprocket ratio is 6.2 :1 multiply that by 2.7 =
16.7 :1.

high gear (overdrive) with 6” driven is 0.9 :1

6.2 x 0.9 = 5.6 :1
 

Rat

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I like the 24mm PWK style carbs for 212cc’s

As for overall ratio, assuming you are talking about “gear ratio,”

low gear for 30 series TC with 6” driven unit is around 2.7 :1

So if sprocket ratio is 6.2 :1 multiply that by 2.7 =
16.7 :1.

high gear (overdrive) with 6” driven is 0.9 :1

6.2 x 0.9 = 5.6 :1
Yes gear aka final drive ratio.
56÷10= 5.6:1 final drive
56÷9= 6.22 final

I run #415 chain and am not beyond shaving a #41 sprocket until it fits safely in a ProTaper PT415MX chain. I'm comfortable with the current gear ratio but my only alternative sprockets at this time are as follows: 27, 36, 38, 44, 48, and 60.

The "Koso" 24mm PWK short body copy I have is definitely proving itself after a shaky start dialing it in for altitude changes. I had it dialed in really nice at 940ft avg ele, and moved to 2100ft avg ele, then developed an intake leak while retuning only to crack another header as I got it closer. It runs real nice on the current set up which is why I decided to back off modifying the ignition timing.
 
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Rat

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34mm is the ideal size for a 390.
Yeah there's a formula I came across that indicates a 26mm carb is pretty much the ideal largest size

sqr rt (Displacement) ×2 = ideal nominal size [round as needed to nearest available size]
 
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