Port/Carb Question

[quadsrus1]

Hey fellas i found a guy around here that does port work, he said he can get the blasty to rev at 13000 RPM'S. He can trench cases, but what gets me is he said he can bore my stock carb, to open it up another 3-4mm. What do you think about this fellas?????

 

[Awk08]

13,000 rpms ???? he's whack, run away !!!!
and think about the wall thickness of a carb, is there 3-4mm extra ???? run away !!!!

 

[Prime]

13000!!??? Is he nuts? And yes the carb can be bored. I wouldn't trust that guy at all though.

 

[brandoz28]

it's something that can and has been done for a while, usually they will only go about 2mm. depending on the cost, a good used carb may be about the same amount of scratch.


and as for revving to 13,000rpm....I wanna see/hear it. the piston speed is getting pretty crazy at that point.

 

[quadsrus1]

And this is why i love this forum i almost fell for it HAHAHA i knew i should ask

 

[01BLAST3R]

agreed^^^^^^^^^

 

[sicivicdude]

it's something that can and has been done for a while, usually they will only go about 2mm. depending on the cost, a good used carb may be about the same amount of scratch.


and as for revving to 13,000rpm....I wanna see/hear it. the piston speed is getting pretty crazy at that point.

At about 4k FPS aluminum and steel like to get pretty close. On a blaster crank that's about 11k rpm.

 

[brandoz28]

At about 4k FPS aluminum and steel like to get pretty close. On a blaster crank that's about 11k rpm.

thanks, i was too lazy to do the math again lol

 

[quadsrus1]

OK but now my next question is what if it was piped with a good pipe he really talked like he knew what he was talking about.

 

[brandoz28]

the problem is that 13K rpm with even a stock stroke blaster crank is going to push the thing past speeds that it can actually handle. long story short.


BOOM

 

[sicivicdude]

OK but now my next question is what if it was piped with a good pipe he really talked like he knew what he was talking about.

It's not about the particular setup (carb and pipe setup). It's about the fact that oil cannot lubricate when the piston is moving too fast and it the piston generates too much heat by friction and will gall to the cylinder liner.

At 13k rpm, the piston would last about a minute before it destroyed itself.

 

[quadsrus1]

Damn ok just wondering i guess ill be staying away from this guy

 

[Awk08]

he really talked like he knew what he was talking about.

so did adolf hitler, jim jones, and goerge w. bush !!!!!!!!

 

[quadsrus1]

so did adolf hitler, jim jones, and goerge w. bush !!!!!!!!

Yea yea yea AWK you always tryna bust my bubble LOL

 

[Larry's Shee]

Is his name Anus Kennedy by chance?????? Lot of factors limit rpms of stock design, oil isn't one of them. 6oo street bikes run 13-14,000rpm, Formula-1 runs 17-18,000. If this guy could make one spin that fast AND live, the path to his door would look like the Grand Canyon.

 

[sicivicdude]

Is his name Anus Kennedy by chance?????? Lot of factors limit rpms of stock design, oil isn't one of them. 6oo street bikes run 13-14,000rpm, Formula-1 runs 17-18,000. If this guy could make one spin that fast AND live, the path to his door would look like the Grand Canyon.

Engines that can turn that sort of RPM have several major differences.

First off, you won't find one that turns more than 8k-10k that's not liquid cooled. Taking away heat is a MAJOR problem at high RPM's

Second, these are all 4 strokes with pistons WITHOUT full skirts. Schnuerle ported 2 strokes by design have to have full piston exhaust side piston skirt that does not uncover the exhaust port at TDC. The engines that turn 18k rpm have two or three ring lands and then a tiny patch of piston at the front and back to act as their thrust surface. Those tiny surfaces have a LOT of load on them but they're smaller meaning the oil film has less area to cover.

High rpm 4 strokes also have oil jets aimed into the bottom of the piston from below. This serves two purposes. First, the oil spraying in the bottom of the piston cools it from below (referring back to the heat mentioned earlier) and also the oil splashing around is likely to coat the cylinder walls even at high RPM's where windage wouldn't normally allow oil spray to stay against the cylinder wall to coat it thoroughly.

Also, those extremely high rpm engines are generally VERYYYYYYY over square. A CBR600RR engine (for example) has 4 cylinders at 67mm bore but each piston only moves 42.5mm (less than 2" total stroke TDC to BDC) resulting in an engine where the crankshaft is moving VERRRRRRRYYYYYYYY fast but the piston isn't moving that fast. 2 stroke engines can't be but so oversquare because port timing and area have a certain amount of diminishing returns because of port area versus stroke versus scavenging efficiency versus transfer velocity. A 67mm more 42.5 mm blaster engine would starve at high rpm's anyway....

Also, 2 strokes engines have to rely solely on windage oiling. The exhaust side thrust surface specifically is starved for incoming oil spray AND is hotter than the intake side. At super high piston speeds, the oil film on the exhaust port side will break down first resulting in high wear on that side allowing the piston to slap breaking down the oil film further. Bad news!

 

[Budget_Blaster]

Id say this falls back on the age old "BELIVE NONE OF WHAT YOU HEAR AND HALF OF WHAT YOU SEE".

Dude may in fact know his sh*t but hes really "CHURCHING" it up in my opinion.

BTW what are his credentials?Shop owner?HiPo builder?Are there any of these engines for you to see and hear?Whats his claimed combo for these rpms?

Theres alot of things i would have asked while my bull sh*t meter metered this guys claims.

If you want the carb modded id first check with KOR if he doesnt do it id check into RB hes done a bunch of guys carbs on KDX RIDER.NET and his work on the kdx heads and carbs is pretty impressive.

But if you mod the carb buy a new better one and then send that off not the stocker.

 

['00 WO-YA!]

Wow, 13,000, that's nothin! I know a guy that can do this kind of work but he's also a black-ops ninja, rock n roller, iron chef, moto-cross superstar!

 

[Paulie B]

If you could even rev it that high, it won't have enough torque to move. The powerband would hit like a slege hammer for about 1000 rpms then quit.