A few questions for building a trail-ridden Banshee...

[SLORYDER]

 

By your own accord you have never even ported a set of cylinders,by your previous post you are asking other peoples opinions on how to set up your motor, (which is cool),and now you are trying to tell someone to try all your ideas which you have not even tried yourself.What in a weeks time the student became the teacher.I think it is really cool that you want to build your own motor and that it intrests you,but should you really give out all this advice like you are a pro motor builder.Plus in this post you are saying not to listen to a pro motor builder if they pipe in and say you are wrong.

 

Like I said I have never ported 2 stroke cylinders, but have done a full rebuild of a four stroke engine including my own combustion chamber work and a full port and polish.

All one needs is a little intelligence and the right guidance and they can do anything they set their mind to.

You are much quicker to offer ridicule than guidance so if anything you are adding to the problem.

 

Actually blowit finally admitted I was right. And I still believe he is wrong because if you add a 2mm spacer and a 4mm crank your durations should be a few degrees more radical. A 4mm with a spacer no porting will run circles around a 4mm no spacer no porting.

 

I have yet to hear anyone tell me specifically why my plan won't work, just a bunch of people telling me I'm not a builder therefore have no right to state my opinion.

 

4mm crank

lower ports to top of piston

70-72% bore width on the exhaust

Raise exhaust 1mmIF blowit was right and durations are stock

raise the intake ports 3mm

Chamfer all ports

Bump compression

 

Probly under $700 with old crank exchange and a solid 60+ horsepower and a wider powerband than stock

 

I'm still waiting for someone to tell me why this won't work

 

The only problem I see is the spacer would add to the crank case volume a little but I believe the added duration would make up for it ten fold

Edited April 28, 2010 by SLORYDER

[blowit]

 

 

Actually blowit finally admitted I was right. And I still believe he is wrong because if you add a 2mm spacer and a 4mm crank your durations should be a few degrees more radical. A 4mm with a spacer no porting will run circles around a 4mm no spacer no porting.

 

 

 

I was looking specifically at the OP and the riding requirement. Adding a plate will most definitely not create the type of engine he is looking for. For the record though, adding the plate and a 4mm crank adds more than just a few degrees of timing and most certainly will NOT create a power band that would please the OP. I was not concerned about which would run circles around another, I was focusing on the engine requirement, just as I would do with any customer. Give them what they want, not what I want.

[AKheathen]

ok, i'll hit this in a few steps.....first, all this talk about "hp" and "amount of work @ given rpm".....let's disect that real quick.....hp, is actually torque x rpm (just stating the obvious for perspective) and what is needed is decent amount of torque across a wide range. with the no-spacer timings, the will definately be allot more torque, and start sooner, but adversely, taper off sooner, as well....with the "radical" timings, it will be less torque, but a t a higher rate (rpm) which translates into "hp" #'s that may matter most in drag, dune, and anywhere you are lookin to "do the most work" in a given time. when you are out in the trails, you are looking to move 4-500lbs at different rates of force, more than distance/time.....

ok, now for the timings setup.....one thing i have been stressin in the porting posts is getting the blow-down and transfer time-area right, as well as angles. simply out, the spacer leaves allot less to work with, and significantly increases the minimum rpm orientation on the porting, ads crankcase volume, which reduces "stuffing" and concequently less dynamic compression and power. it will also slightly increase signal delay to transfer/intake. the plate is also another weak point that will increase the likelyhood of movement and/or leaks......if you are gonna port, the plate is a huge waste of time, like throwing a lockup on a stock bike..... your "plan" may work to do a shade-tree job that will pull a bit, but not as good as just doin it right.

 

mikecheif- the search feature, and google are your best freinds.........you should read a.gbell, and 2stroke tuners' handbook first...not eveything in them is literal, or applies to banshee, but you will get 100x the idea of how 2 stroke flow, etc works. links to the books are pinned at the top of repais and mods....

 

bigblock- i was suggesting to make a trade for different pipes, as an idea....

[bigblockbanshee]

That's cool on the pipes. I guess I was just being stubborn and bull-headed. I'm trying to work out a trade locally with a couple of guys on either some FMFs or Pro Circuits.

[SLORYDER]

I was looking specifically at the OP and the riding requirement. Adding a plate will most definitely not create the type of engine he is looking for. For the record though, adding the plate and a 4mm crank adds more than just a few degrees of timing and most certainly will NOT create a power band that would please the OP. I was not concerned about which would run circles around another, I was focusing on the engine requirement, just as I would do with any customer. Give them what they want, not what I want.

First you said that the crank/spacer would result in stock port timing, now you say that the timing would be more radical..Do you have any clue what it would put the timing at? If you do please share as I am very curious...

 

Op stated that he really wants a 421 cub. The powerband created by port timings depressed from stock will definately not be satisfying if that is the what is desiring. I took it literally perhaps he meant he just wishes he had money for a project like that...

[bigblockbanshee]

Op stated that he really wants a 421 cub. I took it literally perhaps he meant he just wishes he had money for a project like that...

 

Bingo, guess I should've made myself more clear...

Edited April 28, 2010 by bigblockbanshee

[SLORYDER]

simply out, the spacer leaves allot less to work with, and significantly increases the minimum rpm orientation on the porting, ads crankcase volume, which reduces "stuffing" and concequently less dynamic compression and power. it will also slightly increase signal delay to transfer/intake. the plate is also another weak point that will increase the likelyhood of movement and/or leaks......if you are gonna port, the plate is a huge waste of time, like throwing a lockup on a stock bike..... your "plan" may work to do a shade-tree job that will pull a bit, but not as good as just doin it right.

 

 

 

Heathen,

 

If a performance oriented engine (some trails, more duning and dragging) is what you are after, then IMO a 4mm with a spacer is the most economical way to go.

Theory:

This is assuming the plate gives you around 124 transfer, 190 exhaust.

If you have pipes such as T-5's just the durations gained from the spacer and the displacement gained from the stroke I would guesstimate a gain of around 12-14hp, as compared to 5-7 on the bottom end and a loss on top with crank no spacer.

From this point you can raise your exhaust port another mm or so and widen to about 75% and you will have gained I'd say another 8 or so hp in the upper mid range, and lose a couple hp down low.

So 20+ hp gain from buying the crank, porting it yourself which most anybody can do as you don't have to touch the transfer roofs AT ALL. Yes if you were looking to NOT use a spacer, buy the crank and send it to a builder he could port it for you and get maybe 5 more hp than you did but you'll pay 300 or so plus shipping; the additional crankcase volume would be compensated for 20 fold by the extra free hp you got out of your engine.

 

And about the air leak from the spacer-c'mon you gave the same non'leaking case and jug surfaces you did BEFORE the spacer, and two brand new shiny surfaces and gaskets to add. If it was not leaking before it will not leak after.

 

You can call it shadetree all you want but there are just ZERO reasons not to go for it as long as you know where to cut

[SLORYDER]

Bingo, guess I should've made myself more clear...

 

Gotcha

[SD1026]

to be honest if you want a huge bill then do it up 4mil stroker blaster pistons port work and so on. but if you keep stock crank get it true and welded , mild trail port,timing plate,t5's,set of 30's ,head,and put money into your suspension that is a solid trail banshee.but i would say do your suspension first no point in power if you cant get it to the ground or control it . more control harder and longer you will stay on that throttle instead of letting off.pm sleeper06 he built my motor

Edited April 28, 2010 by SD1026

[okbeast]

What a mess of a thread. If you want a 4mil cub I say do that

 

But in all reality, just get it ported for the 4mil.

[blowit]

 

 

 

This is assuming the plate gives you around 124 transfer, 190 exhaust.

 

 

 

I cannot remember the exact figures off the cuff, but those numbers are not quite accurate. I apologize if I misled you or anyone else regarding any timings of a particular setup. The plate can certainly work for some things.

 

I too may be mislead in the build if the OP is asking about a trail bike and then wanting a 421 (drag port) cub. To the OP, the cubs are near full drag spec out of the box so they should be reserved for more wide open riding or drag racing. It is just fine to ask though. Hopefully that will help you. If you want a trail bike, staying with your stock cylinders is the best bet. PM if you would like and I can lay down a setup for you that will work great.

 

 

Slo, you may think I am trying to insult you but I am trying to get you to grab that calculator and figure it out. You need to learn it if you want to port. I never had anyone hold my hand in the learning process and I firmly believe that level of learning solidifies the foundation of tuning.

 

Brandon

[SLORYDER]

I cannot remember the exact figures off the cuff, but those numbers are not quite accurate. I apologize if I misled you or anyone else regarding any timings of a particular setup. The plate can certainly work for some things.

 

I too may be mislead in the build if the OP is asking about a trail bike and then wanting a 421 (drag port) cub. To the OP, the cubs are near full drag spec out of the box so they should be reserved for more wide open riding or drag racing. It is just fine to ask though. Hopefully that will help you. If you want a trail bike, staying with your stock cylinders is the best bet. PM if you would like and I can lay down a setup for you that will work great.

 

 

Slo, you may think I am trying to insult you but I am trying to get you to grab that calculator and figure it out. You need to learn it if you want to port. I never had anyone hold my hand in the learning process and I firmly believe that level of learning solidifies the foundation of tuning.

 

Brandon

 

 

You know you're alright B

 

I really don't know for sure, I don't really have a scientiffic means of doing it right now, just a ruler and a compass....I came up with like 136/ 195 but that doesn't seem right..

I you give ma a formula I would be happy to try and figure it out, even though my math is rusty at best...

[blowit]

You know you're alright B

 

I really don't know for sure, I don't really have a scientiffic means of doing it right now, just a ruler and a compass....I came up with like 136/ 195 but that doesn't seem right..

I you give ma a formula I would be happy to try and figure it out, even though my math is rusty at best...

 

 

The formula in Gram Bell books will work great. I recommend inputting that in an excel format and working it from there. I would start with ONLY the stock porting because you know what it is. Work your math until that calc comes out where is is supposed to. What gets tricky is the odd deck clearances for strokers. We use (-) for above deck.

 

It is very important that you grasp the timing concepts. I promise that once you do, a LOT of other things will fall into place and make sense like rod angles, piston speed, etc.

 

Hint here is rod angle and stroke have a LOT to do with port time area at a given angle. The change of port timing with a stroker is not a linear equation. Ie, there is no equation that says (example) .500mm up = 5 degrees of timing. That response is not linear.

 

Beat your head on the floor if you must, then go get some Advil and work the numbers. If you cannot work the numbers, engine building is only a guess. I don't guess at anything!!

 

 

Brandon

[RagunCajun]

If you dont ride fast trails, i would personally spend the money on better suspension so it makes the ride more enjoyable.

 

I have a 4mil playbike on race gas with all the goodies. Has tons of power and yet im on stock garbage suspension. I know it's not what you asked but if i had to do it over again, id do suspension before stroking it.

 

As for cubs and other drag cylinders, you really need to ride one to fully understand how they make power. It's like a 125 dirtbike but worse. It's nothing then MASSIVE power. Basically gonna throw the front end of your bike up if it hooks. Terrible for anything but WOT. I would do a cub set up in a heartbeat but i refuse to have a playbike with a drag ported type of power band feel.

[SLORYDER]

I don't guess at anything!!

 

 

Brandon

 

I try not to either.

I have a good method problem is I don't have a protractor handy.

 

I will also add that my ghetto fabulous ideas will work IF you have the knowledge understanding AND foresight to make every cut and calculate every angle duration ect correctly. It is not something that anyone can do, but, like I said if you have the right guidance I believe something like what I explain can be done by almost anyone.

I know I've made some dumb (apparently) topics but rest assured I was probably trying to get something out of it that I couldn't have got by asking directly. And I believe I have done a fair job.

 

In a woods or play application where max performance doesn't matter I wouldn't hesitate to try something myself, but make no mistake if I wanted something competitive I would definately send my engine to a builder.