Longrod question

[richwuest]

A friend of mine is building a 420 long rod engine. His crank is a stock stroke crank with long rods on it. His jugs have already been sleeved for a big bore piston and are MX ported for a stock stroke, stock rod motor. The question I have is with the Wiseco longrod style pistons, is there anything else that needs to be done? My understanding is that he should be set to go once he buys a set of the Wiseco pistons that are made for a long rod motor. The shop that we were at trying to have the jugs bored at said that since these jugs were ported for a standard rod motor that they may need the port timing modified and the deck height changed by shaving the top off the barrels to work with the long rod, even when using the long rod style Wiseco pistons. Are they wrong, or will these jugs need additional work done to them?

[sredish]

It is also my understanding that if you have portwork for stock stroke / stock rods, then your port timing will be affected if you modify to longer rods. I am not proficient in this category, but as I'm researching a long rod project, i've learned a few things.

[banshee370]

Actually a long rod does not change the stroke... So if you already have bigbore cyls then you would need to run blaster pistons or the 795(?) series wisecos.. Difference in them is that the pins are located 4mm lower than the stock pistons. (long rods are 4mm longer that stock)

Either way the porting may need to be changed some due to the long rods... You can actually run a little more exhaust duration than a stock crank. You can (depending on port timing now) run the porting the way it is but it will be on the conservative side.

My question is... Were the cyls ported prior to being re-sleeved? If so then the port timing will be way off... Since upon the installation of the BB sleeves they need to cut the cyls to accept the new sleeves. In doing so the port timing will be way off.....

[roosthrower]

I don't really see how the port timing would be any different with a bigger bore, but you can definitly go wider on the exhaust port with a larger bore. banshee370, care to explain how the timing would be effected by a bigger bore? I probably just don't know enough about big bore sleeves to really know how they effect port timing. also, it is my understanding that if you had +4mm rods and you are running a piston where the wristpin is located 4mm lower than a regular banshee piston, the port timing would be the same as it would be with a stock rod and piston combo. I am no expert in this field either though, but I thought I'd throw in my two pennies.

[banshee370]

roostthrower:

When replacing the sleeves you need to cut the cyls out to fit the new larger diameter liners. Now if the roofs of the transfers were flat, then not much would have to be altered, but most transfer angles are angled. Now off the top of my head I dont know the OD of the larger liners but a lot of your transfers are removed.... thus changing your port timing. Now remember you cant go too wide on your exhaust since there are water jackets on both sides... and you also dont want to go over a certain percentage of bore (not sure right now the max)

this link may explain some by the images http://macdizzy.com/cylinder_map6.htm

As for longer rods and diff pistons.... Yes your port timing would be back where it was.... but with the longer rods you can run a little more agressive porting since the long rods will gain a little torque (thrust angle on the crank) Thinking about it now... I think the long rods are 5mm longer than stock... Im confused now hehe

[superchicken]

you can run a little more agressive porting since the long rods will gain a little torque (thrust angle on the crank) Thinking about it now... I think the long rods are 5mm longer than stock... Im confused now hehe

u are correct

[roosthrower]

I was thinking that the longer rods were 5mm longer than stock as well, but I wasn't going to say nothing since I don't have a long rod setup. Also your not supposed to go any wider on the exhaust port than 70% of the bore. Wider will get you into excessive ring wear/snagging. There are ways to get around the water jackets and keeping your rings together though. Triple exhaust port is the ticket if you can afford it. If only yamaha would have kept the powervalves and bridged the exhaust port. I believe you can go wider on the exhaust port than the cylinder bore with a bridged exhaust port.

[banshee370]

Its been a long weekend... and my brain is about spent....... glad tomorrows monday/work. That way I dont have to think about anything.

Yes its 70% that you dont want to go over... and not only for piston/ring life but also overall performance.

Tripple exh isnt the golden ticket.... while it can help... its not the cure all.

Ahhhhhh all the "What ifs" If only Yamaha stepped up with a few things.... Imagine where the banshee would be today if they kept up w/ technology (as with the 4 strokes)

[FORMULASPEED]

I run a 65.5 bore with the wiseco 795 series , 5mm long rod, ported when its was a stock crank. It was a huge difference imop, I also ditched the single carb for 2 28mms, that couldnt of made that big of a differance. It loves the rs , and definately has some tourqe.

Your port timing will not be affected. PassionRE is a good person to ask,

he answered all my questions. Make sure your sleeves are matched to your

portwork.

Edited September 20, 2004 by FORMULASPEED

[sredish]

I also ditched the single carb for 2 28mms.

well, there's one roosthrower. i guess we'll see what happens.

 

we were just discussing earlier on another board the single vs. dual setup with the lr.

[FORMULASPEED]

I thought my quad was badass when it was the single carb.

But then my stock crank seperated, So I dumped in the LR

the 28s and +3 timing and a monster was born. It was a hole new machine

I even went from a 14 to 15 tooth front sprocket. It comes up more and pulls me in third from a low rev second I like it.

[Ducman]

Getting back to the original question: will the stock rod porting work? I believe that porting specifically for the long rod is necessary to make it run right even with the 795 series (long rod) pistons because when you decrease the angle between the rod and the piston it is makeing the piston stay at the top and bottom of the throw for a longer period of time (increases dwell time) and increases the speed that it is traveling in the middle of its throw. That is the reason that it needs incrased durration as someone else mentioned. It would probably work but will run like a much more mild port job than it would with a stock rod crank. Thats the way I understand it.

 

As for the duel carbs vs single I say single carb for mx, trail, or woods emphasis on smoother power, throttle responce, and midrange, duel carbs for sand and drag settups, emphasis more on top end.

[racer]

no, you will be ok duc. nothing happens at all to your ports. the longrod is an option that allows for a lower degree of rotation on the actual wristpin bearing itself. and the rods are 5mm longer, so the wristpins are 5mm higher in the pistion. nothing about your piston motion changes at all. the 4mm crank is a WHOLE diff. story and im sure that what the guys at your shop are thinking of. those do affect port timing and but like i said its a subject for a different day when youve got more money to spend on another new crank.

[roosthrower]

Getting back to the original question: will the stock rod porting work?  I believe that porting specifically for the long rod is necessary to make it run right even with the 795 series (long rod) pistons because when you decrease the angle between the rod and the piston it is makeing the piston stay at the top and bottom of the throw for a longer period of time (increases dwell time) and increases the speed that it is traveling in the middle of its throw.  That is the reason that it needs incrased durration as someone else mentioned.  It would probably work but will run like a much more mild port job than it would with a stock rod crank.  Thats the way I understand it.

 

As for the duel carbs vs single I say single carb for mx, trail, or woods emphasis on smoother power, throttle responce, and midrange, duel carbs for sand and drag settups, emphasis more on top end.

I never really thought about how the longer rod motor would stay at tdc and bdc longer than a shorter rod motor would. It all makes alot more sense now. Thanks for the your input Ducman. This place is starting to turn into planetsand with threads like this.

Edited September 20, 2004 by roosthrower

[banshee370]

Excellent post(s) Ducman/therail. Thank you for clearing some of that up. I apologize for the 4mm-5mm differences in the rods... Again it was a rough weekend.

As stated... you can run what ever porting the cyls already have... but with the longrods... you can go a little more agressive. I dont have all the techno mumbo-jumbo off the top of my head... since it was explained to me a long time ago.

 

Hope we helped roostthrower and sredish