Topic: Conrod length

[peterlm844]

Longer rods

I’m in the process of figuring out what to do with the engine on my upcoming 350four racer.
I spend last night with a mate brainstorming and I think we just about got it right now. But there are a few questions we still need an answer on.

Conrod length. What are the consequences of making new LONGER conrods (apart from balancing the crank again)? The length will be needed for our design and Piston/Head setup. Will the engine loose torque with longer rods? We are talking 12mm – 15 mm.

We will need to find the right pistons for the beast. Does anyone know of a good on-line source where we can browse pistons in the range of 47 – 49 mm?

Regards

Pete

[Sam Green Racing]

Peter, Why do you want longer rods ? also, the crank shaft ballance is done without the rods.

Look at the videos in this link.  http://www.john-sleath.com/crank.htm

Sam.

[classic bike tuner]

Longer rods

I’m in the process of figuring out what to do with the engine on my upcoming 350four racer.
I spend last night with a mate brainstorming and I think we just about got it right now. But there are a few questions we still need an answer on.

Conrod length. What are the consequences of making new LONGER conrods (apart from balancing the crank again)? The length will be needed for our design and Piston/Head setup. Will the engine loose torque with longer rods? We are talking 12mm – 15 mm.

We will need to find the right pistons for the beast. Does anyone know of a good on-line source where we can browse pistons in the range of 47 – 49 mm?

Regards

Pete

hallo pete   cbx 550  [MA7]  can be make fit these are shorter than stock  [103,5mm]  15mm ppin
 cb 550 sc nighthawk  [ ME4]  about the same as cbx but longer than stock [111,5mm] 15mm ppin
both have same much stronger bolts

yamaha xj 550 rods  are 1mm longer  than stock   15mm ppin
these can be used for fitting cb 500 or 550 pistons in a 350 /400

build 1 engine 350cc with honda  pistons on stock rods 
pistons used  GB5 or GB0 47,5mm [dont now wich] much lieghter than stock
you need to lower the cilinder block  and shorten the liners
replaced the rod bolts for kvo types  13213-KVO-000

gerrit

[Howell]

Longer rods

I’m in the process of figuring out what to do with the engine on my upcoming 350four racer.
I spend last night with a mate brainstorming and I think we just about got it right now. But there are a few questions we still need an answer on.

Conrod length. What are the consequences of making new LONGER conrods (apart from balancing the crank again)? The length will be needed for our design and Piston/Head setup. Will the engine loose torque with longer rods? We are talking 12mm – 15 mm.

We will need to find the right pistons for the beast. Does anyone know of a good on-line source where we can browse pistons in the range of 47 – 49 mm?

Regards

Pete

hallo pete   cbx 550  [MA7]  can be make fit these are shorter than stock  [103,5mm]  15mm ppin
 cb 550 sc nighthawk  [ ME4]  about the same as cbx but longer than stock [111,5mm] 15mm ppin
both have same much stronger bolts

yamaha xj 550 rods  are 1mm longer  than stock   15mm ppin
these can be used for fitting cb 500 or 550 pistons in a 350 /400

build 1 engine 350cc with honda  pistons on stock rods 
pistons used  GB5 or GB0 47,5mm [dont now wich] much lieghter than stock
you need to lower the cilinder block  and shorten the liners
replaced the rod bolts for kvo types  13213-KVO-000

gerrit

And this man Gerrit knows it !!!

[turboguzzi]

amazing memory indeed!

[peterlm844]

Engine characteristics
Thank you for your replies. But maybe I did not quite put my question right.

Will my (Or any other) engine change behaviors with longer conrods? Assuming that the compression ratio and the conrod/piston weight remains the same.

The reason for this question is that we got to small compressors that we are thinking about squeezing into the frame under the carbs. They could be driven by the drive to the starter(Who needs that anyway).
The downside is that the carbs will have to be replaced, and we will most likely have to raise the cylinders with about 15 mm (Plus cutting some of the cooling fins) in order to get space to the compressors.

The idea is to make new conrods or to get piston with a longer length from the pinhole to the top crown. Making new rods should not be a big problem. My mate has a machine shop and I run a wire EDM and a diesinker on my job.

But the big concern is how the engine is going to react on the mods.

Regards

Pete

[turboguzzi]

dig into any v8 tuning rod length discussion on the net and you'll find plenty of opinions. these guys have plenty of choice

due to structure of separate cyl blocks of most older bikes, rod length to stroke is above 2 while nowadays more compact engines run at less than 2:1.

theory says that longer rods "dwell" more near TDC, so for all I know, drag racers tend to short rods, supposedly better accelration.

on the other hand, longer rods put less side load on the piston mid stroke but also weigth more.

told you its fishy....

[simon#42]

im no great four stroke expert but two stroke rods have got longer over the years , aprilia gp 250  rods started out at 110mm then went to 113 and finished up at 115mm
[ for a 54.5 stroke ]  as the last of the works bikes made 119 hp i guess they knew what they where doing .  i have always thought it was as tg said , long rods dwell more near tdc .

[turboguzzi]

makes sense to me simon, maybe longer rods ease the side loads when the 2-str pisotn glides over the ports?

peter, just to give you an idea how complex this subject is, see this topic. there are some heavy tunning hitters in that forum,

http://speedtalk.com/forum/viewtopic.php?f=1&t=406

if you reach any conclusions let us know....

[754]

 To be clear, you are attemting to supercharge..?.. is that what you are saying?
 cheaper to make pistons than rods, in a lot of cases..

[classic bike tuner]

we build one engine [cb 500] with shorter rods   there was no difference in output with the longer rods [gsxr1000] 

its better to go for longer rods  and keep the piston pin as close as possible to the top of the piston