There She Blows

[Oilpan4]

It probably has a lot of ring gap from the factory. I run 0.015 top ring on my gx390 pressure washer, it runs wide open all the time.
I doubt a super charged go-kart would run much hotter than a pressure washer engine that goes WOT till it runs out of gas.

 

[bob58o]

It’s about the gap relative to diameter or circumference of the bore.

An 88mm bore gx390 with top ring gap of 0.015” is running at 0.0047” of gap per inch of bore.

I think a 212 has a 2.755” bore, not 2.835” as I said above.

Anyway

2.75” x 0.0045 = 12 thousandths of an inch gap

2.75” x 0.0055 = 15 thousandths

 

[Oilpan4]

I was going to look up the minimum for a a 212 but but it was chow time.
If you bought your 212 from the store it probably started life with a 20 to 30 thousands ring gap.

 

[bob58o]

Yep I’m pretty sure the bore, piston, and rings are all stock Hemi Predator 212 from Harbor Freight.

 

[bob58o]

I was reading through an older write up (maybe 2014) from ARC. I just skimmed it. It was talking about break it and cylinder shape and piston ring gaps. Let me find a link.

I think it says to set ring gaps to 0.004” or 0.005” and after break in after rings are seated, gap will be 0.008 to 0.009”.

Also think it says you can set ring gap to 0.001” and break in on 900 RPM electric break-in stand and end up with 0.004 or 0.005” end gap. They warn you (with 0.004” end gap) to make sure your engine is at operating temp before putting it under load.

This is for NA kart racing engines. It mentions Briggs in the article.

Does It Matter​

Posted by Carl Amundsen on 8th Oct 2014

Does It Matter

Does It Matter? A common sense approach to engine building.Historically, human nature has taught us two basic things about the question "Does It Matter ?"1 - If a problem exists, and we have the capability to correct it, we tell the world "It Does Matter".2 - If we don't have any interest or...

www.arcracing.com

 

[Oilpan4]

Man that's tight

 

[bob58o]

If the ring gap is 0.015” or larger as is, I won’t go any larger. I also will not get new rings to make it super tight (at least at first), unless the gap is currently around that 0.03” you mentioned.

 

[bob58o]

NR Racing…

GAB on GAP

Ring, Top, +.005'' BSP/Clone

We specialize in Honda GX120, GX160, GX200 and 6.5 Clone Performance for Karting, 1/4 Midget, Mini Bike, Mokai, Winch Boarding, Tractor Pulling, and Bar Stool Applications. Championship winning motors for QMA, USAC, BSP, AKRA, WKA, & ASN

www.nrracing.com

For an oversized file to fit set of rings…

“
This is a slightly oversized (file-to-fit) compression ring used in a standard bore, box stock clone engine. It is designed to close up the end gap on the compression ring since "stock" compression ring gaps are generally too wide.

Research has shown us that you want a minimum compression ring gap of .006". Any closer, and the rings will expand to close the gap completely during operation.”

 

[Oilpan4]

Yeah the rings too tight will grab the bore and try to stop the piston.

 

[65ShelbyClone]

And when ring ends butt they it can pull the top off the piston.

Cool project. I just saw two things of note:

1.) Your current configuration is draw-through. The throttle (carb) is on the blower inlet. When the throttle closes, pressure between it and the engine drops to engine vacuum. There won't be any pressure surge for the BOV to deal with, so it can be omitted. When the blower is trying to push air through a closed throttle (blow-through), that's when a BOV is needed.
2.) I think there is going to be a problem with fuel pooling in the intercooler. Draw-through setups aren't intercooled for that reason.

 

[bob58o]

I appreciate the input.

I just installed the 6500 rpm rev limiting coil was thinking about what happens when the spark stops. I was thinking flames out the exhaust.

Let me see how KISS I can make it. Carb, blower, intake port.

 

[bob58o]

I think EC carbs told me to set the gap the 0.015” so that’s where I set it.

 

[bob58o]

I guess a simpler set up might look like this.

Currently with this configuration, a 25mm OD 45 degree bend aluminum tube might complete the puzzle.

I will have to flip the blower around and get a shorter belt

 

[65ShelbyClone]

As an aside, some of the 1980s turbo F1 engines used two throttles; one on the engine and one on the turbo inlet. They worked in unison and the one on the turbo inlet both negated the need for a BOV and reduced turbo lag because the turbo was freewheeling in a relative vacuum rather than slowing rapidly from compressing air that would just be released by a BOV.

 

[bob58o]

Robot Cantina used two throttle bodies on his EFI supercharged 420. I think he was having issues with his plumbing getting sucked closed under vacuum

 

[Denny]

And when ring ends butt they it can pull the top off the piston.

Cool project. I just saw two things of note:

1.) Your current configuration is draw-through. The throttle (carb) is on the blower inlet. When the throttle closes, pressure between it and the engine drops to engine vacuum. There won't be any pressure surge for the BOV to deal with, so it can be omitted. When the blower is trying to push air through a closed throttle (blow-through), that's when a BOV is needed.
2.) I think there is going to be a problem with fuel pooling in the intercooler. Draw-through setups aren't intercooled for that reason.

Save your breath, I already tried to explain it to him and was told I’m wrong. The internet says so.

 

[bob58o]

Since I’ve been thinking about stuff … ignition timing.

I believe I tested this Kohler flywheel and IIRC it was firing around 19.5 degrees BTDC when installed straight up. I think I have it advanced another 5 degrees or so to fire 24 or 25 degrees BTDC.

I will probably go back to “straight up” timing. 19.5 degrees BTDC seems like an ok place to start?

 

[Oilpan4]

If you have a Honda UT2 ignition, set it really close to the magnet your timing will be about 20 degrees maybe a bit less and as rpms build some where around 4,000 rpm it will actually retard the timing. Which is what boosted engines want.

 

[bob58o]

Save your breath, I already tried to explain it to him and was told I’m wrong. The internet says so.

Denny, I don’t ever think I said you were wrong about anything. I wasn’t sure about the intercooler and was afraid of fuel pooling up.

I still think the BOV being used as a recirculating bypass valve could serve some function if I was able to get it to function how I wanted.

At first, the blower was going to be clutched on the TC jackshaft. In that case, I think it would be needed. If the blower spins with the crankshaft, it might only help with fuel efficiency.

I also think I remember some talk about the throttle blade being damaged in suck through under vacuum, but that might not be an issue with a little pump and a slide carb.

 

[bob58o]

Since my exhaust is so small the O2 sensor is a major restriction.

This spacer should give more freedom