Brand new GRUBEE SkyHawk GT5B 69cc compared to GRUBEE SkyHawk GT5A 66

[Chainlube]

Transfers are scary to many because you can really kill the power if they are not right so many don't touch them, the shape, size and angles all have to work with the rest of the engine for best results.
The first and foremost important thing is the size or volume of both combined, they should be the same size as the carb used since they can't flow more than the carb let trough it makes no sense to be larger, this also effects velocity.
To find the true area of the transfers you need to measure the open height and width of each then use online calculator to get the equivalent dia this figure gets cut in half because it's doubled when considering the cross section of each, just as an example lets say we have a width of 22mm with a height of 10mm that's an equivalent dia of 15.9mm so best suited to a 16mm carb, this would be typical of a stock transfer port but will not support the use of a larger carb and so you have to increase the area for best results.
There is a whole lot more to trying to explain the shape, angles and correcting these but it has been covered here before and this reply is long all ready LOL so more to ponder.

Does that figure account for both transfers?

 

[Street Ryderz]

Does that figure account for both transfers?

Yes.

 

[Street Ryderz]

Picked up my new Grubee gt5b 69cc and some other goodies just to see what they look like, measure up so to speak, I got two 40mm cranks that are being used in this new engine, I'm going to balance and true them up, they are AF80 long rod (89mm) .
I got one of their hp heads it's a 6cc chamber with sort of a squish area, it doesn't go out to the bore so correcting it will increase the volume a bit, it's cast aluminum not cnc/mill cut and I was expecting it to be heavier than the common aftermarket heads but it's not really and has WAY more material and area for cooling over a stock head, super cheap price too!
The new Bofang carb which I though was going to be bigger dia bore but it's not, still not a bad looking carb for stock, it has the old speed carb cover and a much better clamp to hold it on to the intake with a o ring for sealing it up nice, the fuel inlet is different and the primer is on the bottom through the bowl.

 

[Street Ryderz]

The head,

 

[Street Ryderz]

So in looking at and measuring up this new engine it looks very good with lots of potential, first it comes with copper head gasket maybe .4 of a mm but I still have to double check that with digital caliper rather than the crude one I use to get the linear depth measurements for the port timings, the transfers are eyebrowed and partitioned A and B each side with the A having both walls angled toward the intake and the B needs it's wall closest to the exh port corrected for best results. The transfers are 32mm below the deck and the piston crown to deck has 3 mm clearance which in that stock configuration makes them 139 degrees of duration and with the exh port at 29mm below the deck and 158 degrees of duration leaves 9.53 degrees of blow down and the intake is 109.69 duration, not very impressive but easily corrected just decking away the 3mm and going for .7 squish clearance changes everything to exh 160.48, transfers 141.63, blow down 9.42, and intake 123.53 and now leaves room to alter the exh timing up to gain some more blow down.
The hardware is all grade 8.8 and the intake and exh port studs have been replaced with cap head Allen bolts, next I want to open it up and see the bearing bosses, crank shims and so on, it comes with all TZ electronics and I'll do the spark strength testing and timing soon with all the others hopefully in one video so more to come.

 

[digital_life]

Effin hard to get a picture down in the little port.

Hold the jug up above your head pointing to a light on your ceiling with the camera underneath it

 

[Mossy]

So in looking at and measuring up this new engine it looks very good with lots of potential, first it comes with copper head gasket maybe .4 of a mm but I still have to double check that with digital caliper rather than the crude one I use to get the linear depth measurements for the port timings, the transfers are eyebrowed and partitioned A and B each side with the A having both walls angled toward the intake and the B needs it's wall closest to the exh port corrected for best results. The transfers are 32mm below the deck and the piston crown to deck has 3 mm clearance which in that stock configuration makes them 139 degrees of duration and with the exh port at 29mm below the deck and 158 degrees of duration leaves 9.53 degrees of blow down and the intake is 109.69 duration, not very impressive but easily corrected just decking away the 3mm and going for .7 squish clearance changes everything to exh 160.48, transfers 141.63, blow down 9.42, and intake 123.53 and now leaves room to alter the exh timing up to gain some more blow down.
The hardware is all grade 8.8 and the intake and exh port studs have been replaced with cap head Allen bolts, next I want to open it up and see the bearing bosses, crank shims and so on, it comes with all TZ electronics and I'll do the spark strength testing and timing soon with all the others hopefully in one video so more to come.

Is that an open transfer G4 cylinder ?

 

[Street Ryderz]

Is that an open transfer G4 cylinder ?

Pretty much yes.

 

[Mossy]

Pretty much yes.

I'm wondering what the difference between the grubee 5 A&B the PK 80 and Zeda jugs are...

 

[Street Ryderz]

The listing for the new Bofeng speed carb is very misleading and I'm kinda disappointed but then again I should know better LOL, but would this not lead you to believe this is a 19mm carb?

BoFeng 2-Stroke High Performance Speed Carburetor 19mm

Compatible with GT5, GT2B, GT5A, GT2A, GT5B High-Performance Upgraded BoFeng Carburetor. Increase the speed of your engine by this SkyHawk tested and approved upgrade. A larger Jet than stock allows for optimization of the Air-Fuel mixture. Same dimensions as stock carburetor allow for direct...

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