Grubbe GT5 from the case up ....

[mew905]

On another note i confermed at the dax website that the dax f80 is a 40mm stroke 1 pc crank with a 110mm con rod and the top end from the dax motor i built is what i am running on this build

No offense to dax as a dealer, he's really good for his service, but his information tends to be off. For example his 50cc 11hp engine listed he lists the peak torque as more, at a higher RPM, than HP (I think he listed 11hp @ 10500 and 11.5 ft/lb @ 11000). Which is impossible as HP is a function of torque x rpm /5252 (using the numbers I mentioned, that would make 24hp @ 11000, so unless power spikes radically, and he didn't list the right number, or the information is wrong). He also lists his balanced bottom ends as "hand drilled", which it was discovered they werent, they just happened to be straighter and rounder from the factory, and better balanced. Best practice is to measure it yourself. I am interested to know if it actually is 40mm

 

[hsvmick]

g'day all f80, DAX ,are 40 mm strokes and both use A type piston's and yes you call the super rat right which also is 40mm ,the rod's sure no where near quality as the GT-5 38mm rod's with a B type piston but we all like the 40mm ?????
gt-5 engines i use for my bike builds to sell cause they are super to warranty and i dont get throw backs but to say this i use myself on my own bike's a thin built crappy looking 40mm stroke rod so each to their own i guess 2mm makes a differ or does it is my question now

 

[rogergendron1]

let mw know what you think about my port map ... all measurements taken from the jug deck to the port roofs and floors on a surface plate with a digital vernia.

old top end race jug from my 38mm stroke top end race bike

jug over all hight ...80.75mm
exhaust port roof...22.95mm from deck
exh prt flr...41.88mm
exh prt hight...18.93mm (19mm)
exh prt width...25.25mm
transfer port roof...32mm
open transfer ports no floor #s
intake port roof...43.35
int prt floor ...61.25
int prt hight...17.9 (18mm)
int prt width...24.5

new jug for 38mm stroker... shooting for a strong midrange and top end

jug over all hight...80.67
exhaust port roof...27mm from deck
exh prt floor...42.48
exh prt hight...15.48
exh prt width...27.55
transfer port roof...31mm from deck
trsf prt floor...42.83
trsf prt hight...11.83
intake port roof...43.52mm from deck
int prt floor...57.83
int prt hight...14.31
int prt width...23.03mm

ok let me know what you think about the new jugs port map

here is a video of the jugs and what i have going on with them, i plan to deck the jug as soon as the piston comes in so the port hights will change a little bit depending on how mutch i take off the jug but judging by the over all hight it should not be by mutch.

......

 

[rogergendron1]

well the vid is uploading now lol the phone died in the middle of the upload..

anyway i went with the tried and true gordon jennings aproach with the exhaust port and made it 60% of the bore diamiter, he said that it can be safley widended to 62% of the bore witch would be 28mm i went with 27mm wide and only raised it a little bit to keep as mutch dynamic compression and blow down as possable to maintain a broad power band

let me know what you guys think about the port map any ideas will be apresiated and taken into consideration

especialy on the intake port, i lowered it a good bit and widended it a little but i a not shure how mutch more i should go for maximum power all around without the low end and idle suffering from reberberation and blowback through the carb ???? 100 deg intake 110 deg ???? the race jug was over 120 and low end was non existant LOL

 

[rogergendron1]

her is the video...

https://www.youtube.com/watch?v=m_4NaUL2Jcg

i am also thinking about ether addding jb weld to the transfer port openings to reangle them to the rear of the chamber away from the exhaust port or picking up a right angle tool and just cutting them out to thee proper angle cause i am not to shure about the jb weld over time in those ports under heat but i would like to here from someone who has done it before and what the results were,...

 

[66sub]

g'day all f80, DAX ,are 40 mm strokes and both use A type piston's and yes you call the super rat right which also is 40mm ,the rod's sure no where near quality as the GT-5 38mm rod's with a B type piston but we all like the 40mm ?????
gt-5 engines i use for my bike builds to sell cause they are super to warranty and i dont get throw backs but to say this i use myself on my own bike's a thin built crappy looking 40mm stroke rod so each to their own i guess 2mm makes a differ or does it is my question now

the real deal thanks. have u witnessed the sloppy crank phenonamon where the crank walks side to side? i think it is the way the factories do it when 6mm headbolts are used. ????

 

[rogergendron1]

I have seen the poor cranks on the 40mm strokers and they are thinner and not shimmed like the grubee gt5 38mm is the grubee crank is rod is a lot thicker and well made and the needle bearinhs look better too

thats why i build the grubee motors now even though they are an odd bnck , its worth it to have a rock solid motor and i feel like they rev higher out the box and are a bit better balanced

anyway my piston did come in but i missed delovery so i am picking it up at the post office today and i will bolt down the jug and take some measurements

 

[rogergendron1]

Also gonna make a degree wheel and give u guys the port time openings in deg and mabey you can help me correct them further from where they are

 

[Theon]

Port timings in deg will make a lot more sense.

 

[66sub]

ex height at 24mm get u a 7500rpm peak/ lowend will suffer alot. pipe needa 1 1/8" inlet maybe too as the port looks terribly shaped/ very tall.

****ing logout here ****

 

[66sub]

i dont go wider than 24mm/0.95" or the piston gets sloppy loose. i like 0.90" then smoothed. stock is i think 0.85 for reference.

 

[66sub]

the midrange cyl needs a pipe and fairly stock ports. the height sounded great.
----
peak power between 5600- 5800 would be sublime. more or less and not so much fun.

 

[rogergendron1]

24 was the old exh hight

the new jug has the exhauat roof at 27mm down from the deck and 27.55 wide
and the intake is 23+ mm wide

Picking up the piston today so i will get some deg measurments soon

 

[66sub]

im just adding reference. 27mm is my midrange target. i had a long post that was lost due to logout. it sounds reallllllly wide. let us know if it lasts.

 

[rogergendron1]

Yeh as mutch mid as possable lol i went 27.5 down and 60 as wide as the bore

 

[rogergendron1]

I am wondering about intake duration though how much is too mutch before i start loosing low end via blow back ?

 

[66sub]

piston port? single speed? aircraft slingshot? hot clutch?

 

[66sub]

i run 4 petal reed. i tame mine down however. perhaps my heights are little better than reference only

 

[rogergendron1]

Piston port sinfgle speed 40t rear on a 26in tire

also its a 65.9 cc with a 6cc head going on so uncorrected comp is like 11.98:1
With the exhaust port closing 27mm down then olny the last 2.7cm is actuall compresable stroke so

corrected comp would be like 8.8:1 with the hight of the exhaist roof and a 6cc chamber

rought estamate could be lower or a bit hogher depending on x chamber tunned length

 

[66sub]

thats my prefered trail gearing exactly. lifts my front end so i can just chill.....and roost