301 Big Nasty

[Rat]

So I'm working on a 301cc Hemi Predator powered kart.
The engine refused to start at all, after noting the chain was too tight and removing it it starts first pull but only runs with 1/4 which floods it when you pop the throttle.

The owner said "Let's get stupid then" after filling him in on the details of what that means.

The plan is to stick a Keihin PWK on it, I'm figuring a 28mm and gut the gov out of it.

What I need to know is what weight the stock valve springs are, and if I'm going to need to put heavier in as well as if there are any billet parts I should advocate for.
Im probably going to push for a Dover Coil, and I've already found BMI has the ARC flywheel and Rod (+0.20)

I'm figuring conrod and flywheel for sure but it's not getting a cam or any major work, maybe a little port cleaning though

 

[panchothedog]

Stock springs are 30 lbs ( actually 29 ). But the valves are much bigger and heavier. 1st upgrade of springs is 50 lbs. Don't remember how much they were, but it wasn't much.

 

[Rat]

Stock springs are 30 lbs ( actually 29 ). But the valves are much bigger and heavier. 1st upgrade of springs is 50 lbs. Don't remember how much they were, but it wasn't much.

Yeah I say 50lbs that rate 95 at 0.95 lift, the only others I saw were 45lbs. This thing is most likely going to be beat on by a teen boy so the goal isn't so much hot rodding the baby big block as it is just making it reasonably blast proof.

So far it's a 100$ for a junky roller with a nearly new engine worth more than double that with an 18" long 1" ID straight pipe already on it.

The upgrade parts list so far is

Keihin PWK28 (air striker if possible)
Intake Stub for the clamp on carb
Billet Conrod
Billet flywheel
Dover Coil
Thinking I should push a 30 series because the Hilliard on it shows evidence of having been extremely hot.

The modification list so far is
port casting clean up
Gov removal

 

[Rat]

I should add the roller is pretty janky and may get scrapped if something better turns up for cheap because it's definitely a production cart someone hacked on and bodged back together. It has one all-thread tie rod, and both are way to short to even attempt aligning it at all.
Then theres the front tires that are 4" utility garden wagon tires that a few hardheadded newbs around here seem to think are safe.
Between the yak snot tires and bearing with more runout than the front of a severely neglected and abused 20 year old Craftsman mower, playing Russian Roulette is safer.

As is this thing is light enough that waking the engine up any significant amount is going to make it wheelie happy and probably able to flip pretty easily, so a roll cage is in the plans as well as some frame stiffening brace work.

I've seen a few decent full cage karts recently that would be far more ideal (a Murray, a couple Yerf Dogs, a couple Mancos, a bunch of random trash that ould still be a better starting point)

 

[Whitetrashrocker]

I took .040 off the head on mine. Could have went more. Ran a grinder in the ports and cleaned up the sharp edges and around the stem guides.

 

[Rat]

I took .040 off the head on mine. Could have went more. Ran a grinder in the ports and cleaned up the sharp edges and around the stem guides.

Dude, I've built small 2 strokes (72cc and 83cc) that would shame any 196cc ohc, and give most 212cc engines a hard run topping out in the 55-65 range; Port work is lowest priority of my concerns with this project I've been assigned.
This is going to be ridden by a teen boy that can't even keep a bone stock 196cc minibike running for more than a day so I'm stuck between not giving a sh★t about anything but getting paid, and not having this kid dead with a busted frame or a hunk of flywheel decapitating him

 

[Rat]

Stock springs are 30 lbs ( actually 29 ). But the valves are much bigger and heavier. 1st upgrade of springs is 50 lbs. Don't remember how much they were, but it wasn't much.

At 30 lbs are they even that easy to float? I was looking at the specs and it's the torque that's bonkers.

I've had a word with him, I think I need to take this to DM @panchothedog
He's decided that I am to go full out with it, cam and all and squeeze this thing for every bit it has to give.

 

[panchothedog]

For the big block parts, I'm sure you're aware they cost almost double of the small block stuff. For this reason, after bitting the bullet on the rod and flywheel,
I installed the " twister 250 " cam. About half the price of any of the dyno cams products. Very little difference in lift, but duration is 246 degrees on int. & exht.
Engine seemed extremely lazy in stock condition. Next time I fired it up I had done everything to it. Final modification ( and it was a good one ) was putting the heavy springs and light weight rollers in 40 series torque converter. Took engagement rpm from 1600 to 2600. Honestly felt like it had 5 or 6 more hp. This
difference was felt after all the engine mods.Kart will run 46-47 mph with me and one of my grandsons. 225lbs and 170lbs. It also leaps off the line from a dead stop. Faster then my other karts and mini bike.

 

[Rat]

For the big block parts, I'm sure you're aware they cost almost double of the small block stuff. For this reason, after bitting the bullet on the rod and flywheel,
I installed the " twister 250 " cam. About half the price of any of the dyno cams products. Very little difference in lift, but duration is 246 degrees on int. & exht.
Engine seemed extremely lazy in stock condition. Next time I fired it up I had done everything to it. Final modification ( and it was a good one ) was putting the heavy springs and light weight rollers in 40 series torque converter. Took engagement rpm from 1600 to 2600. Honestly felt like it had 5 or 6 more hp. This
difference was felt after all the engine mods.Kart will run 46-47 mph with me and one of my grandsons. 225lbs and 170lbs. It also leaps off the line from a dead stop. Faster then my other karts and mini bike.

Duely Noted; this is where I tell you this isn't being done on my dime and I've been advised to "Get Stupid".
It's being done with an open ended budget, and indefinite time-line for completion; the only prerequisite is squeeze it for everything it's going to give.
I know the head is where the power gets made... and the general idea is to make it break things

 

[panchothedog]

Mill and port the head, put on the heavier springs and install an aftermath cam. Is it a hemi or a wedge head. I'm sure you know that with the wedge head you can mill it much more as well as use a cam with more lift. With the billet rod and flywheel you shouldn't be breaking anything. You should be making horsepower.

 

[Rat]

Mill and port the head, put on the heavier springs and install an aftermath cam. Is it a hemi or a wedge head. I'm sure you know that with the wedge head you can mill it much more as well as use a cam with more lift. With the billet rod and flywheel you shouldn't be breaking anything. You should be making horsepower.

Hemi
Not going to mill the head, I'm not set up for that and I don't trust anyone to outsource it to.

Only porting I intend to do is basic; polish the exhaust, rough the intake up, and knock back sharp casting flash.

Breaking things was in reference to everything the engine is attached to, but mostly just sarcasm and hyperbole.

Tell me more about this cam.

I'm assuming the balance shaft needs to go bye-bye even if for no reason other than eliminating nominal parasitic drag.

The question is this: If the countershaft is supposed to buffer secondary vibrations, andbthe engine already shudders like a hard mounted Harley Evo... just how violently will it decide to shudder with a nasty cam and all the billet goods? I haven't been inside it yet but something seems amiss about how bad it shakes... could just be paranoid sonce I know a trash carb and fueling issues can cause that.

I know the billet rod will reduce some reciprocal mass (primary vibrations) while the flywheel will reduce rotational mass and potentially some vibrations caused my unavoidable imperfections in the iron.

 

[panchothedog]

The 301 doesn't have a balance shaft. Even though it's a big block, it is very much like a 212 internally. Mine is a hemi also and I only milled the head .030". The cam is called the Twister 250. It has a .250" lift. Stock lift is around .230", so it plays well with the hemi as for piston to valve clearance. Being the hemi it has the flat top piston, so better for C R. I bought the cam from OMB Warehouse. I think
NR racing also sells it. I don't think it's a real quality piece, but for the price I am very satisfied with it. Engine revs and feels real strong in the upper rpm range.

 

[Rat]

The 301 doesn't have a balance shaft. Even though it's a big block, it is very much like a 212 internally. Mine is a hemi also and I only milled the head .030". The cam is called the Twister 250. It has a .250" lift. Stock lift is around .230", so it plays well with the hemi as for piston to valve clearance. Being the hemi it has the flat top piston, so better for C R. I bought the cam from OMB Warehouse. I think
NR racing also sells it. I don't think it's a real quality piece, but for the price I am very satisfied with it. Engine revs and feels real strong in the upper rpm range.

I'd rather go with a potent cam that still starts up and idles without being too fussy, lumpy is fine as long as it holds. It's owner f★cks everything up about as quick as I can fix it so it's a revenge of the machines build.

The governor is getting tossed and it's getting a genuine Keihin PWK28 which will be sitting on a billet shorty manifold... dude said "Get stupid" so that's the angle, spin it as fast and hard as it will go and still make power without coming apart.

As the the mech, I want "Hold my beer and watch this" to end in severe disfigurement or death.

I know my major mechanical and fine tuning stuff, but cam cards are a blind spot... I'm not completely oblivious but I'm not particularly well versed either.

 

[Rat]

Got around to pulling the clutch... Hilliard aren't supposed to jingle.

I broke it down to find as I expected, less than zero tension on the weights. This thing supposedly ran like a missile but the clutch condition says it never reached full lock ever.

8hp/14ftlbs 301cc

13x5.0-6 rear tires
14t Clutch
60t Driven sprocket
4.2:1 (no wonder the clutch cooked the garter)

 

[Rat]

I took .040 off the head on mine. Could have went more. Ran a grinder in the ports and cleaned up the sharp edges and around the stem guides.

I got around to pulling it apart today and I've had good luck getting the head to seal bare when the decks are are as nice as this one is so instead of millwork I'll be leaving the 0.048" thick (measured at the fire ring) gasket out.

When it goes back together I'll be watching it for leaks and worst case scenario I'll need to get washers to toss washers under the head bolts and butter it with some Indian Head shellac if it leaks

 

[panchothedog]

What is Indian Head shellac? Have never heard of the product, or that term if it's slang for something. Copper Head gasket sealer.

 

[Rat]

What is Indian Head shellac? Have never heard of the product, or that term if it's slang for something. Copper Head gasket sealer.

It's made by Permatex now, idk maybe it always was.

I've used it on a couple heads that were a little chewed up after smoothing burs off. It says low temp, low pressure, but in my experience your cylinder head shouldn't be close 350° except MAYBE at and near the exhaust port, and if the surfaces are good there should be no pressure at all.

Either way with machined mating surfaces this pretty I doubt I'll have any issue bolting it up naked

 

[Rat]

The cam is called the Twister 250. It has a .250" lift. Stock lift is around .230", so it plays well with the hemi as for piston to valve clearance. Being the hemi it has the flat top piston, so better for C R. I bought the cam from OMB Warehouse.

What about a 275 cam?

Intake Exhaust
Open: 50.0 BTDC 88.5 BBDC
Close: 88.0 ABDC 50.0 ATDC
Lift: .276" .276"
C/L: 108.0 ATDC 110.0 BTDC
DUR @ 50: 239.5 Deg 238.8 Deg

I think
NR racing also sells it. I don't think it's a real quality piece, but for the price I am very satisfied with it. Engine revs and feels real strong in the upper rpm range.

It's an NR part, OMB happens to sell them, I found one with springs.

 

[panchothedog]

The 275 cam that you reference is probably a better cam. I just bought the twister cam because of the economical price. After laying out the money for the rod and flywheel, and the shop work on the head ( milling and porting ) it was time to put the brakes on a little as far as spending was concerned. Not sorry I bought it, but if it were someone's else's money, or funds were more plentiful, I would go for something like you are looking at.

 

[Rat]

The 275 cam that you reference is probably a better cam. I just bought the twister cam because of the economical price. After laying out the money for the rod and flywheel, and the shop work on the head ( milling and porting ) it was time to put the brakes on a little as far as spending was concerned. Not sorry I bought it, but if it were someone's else's money, or funds were more plentiful, I would go for something like you are looking at.

Ok
I was going to ask about a 308 cam but it says "pump gas not recommended" lmao

The 275 has a 6500 target rpm which is around the same as what I stuck in my 208... nice enough running cam