Long Rod Crank With No Added Stroke

[Ducman]

I was looking at the goodies in the Banshee Superstore , flirting with the idea of building my own 4mm stroker motor, trying to figure out what would be the least expensive way to do it and should I do it myself or wait and have a builder do it later on when I can afford to drop a little more dough and/or get some porting at the same time.

Anyway, I see they sell a crank that has a stock stroke but uses "long rods". What the hell is the point of this? The piston would travel the same distance stroke but now you would have to either use a stroker plate or the wiseco stroker or blaster pistons due to the added length of the rods right? I thought the only reason to use long rods was so you could use the wiseco stroker pistons and not need a stroker plate when using a stroker crank. With stock rods and a stroker crank you would have to use a stroker plate otherwise the pistons would go past the top of the cylindar and the stock rods are too short for use with the stroker pistons right?. You choose the length of the rod based on the added length of the stoke if you want to use the stroker pistons and not have to use a stroker plate right? Or is there some benifit to using the stroker piston and/or long rod that I am not seeing? I can't emagine that a piston made for an air cooled Blaster would be as light weight and work as well as a piston designed for use in a watercooled banshee cylendar. Can someone tell me if I'm thinking along the correct lines and what the benifits of the long rod and/or long rod piston are?

 

Also is there less expensive ways to obtain a 4mm stroker crank like having the stock one out of my shee rebuilt, or e-bay, but yet something you can trust and isn't just a cheap P.O.S hack job. These rookie questions are probably a good argument get the engine done by a reputable engine builder but I think it would be more satisfying and economical to do it myself and a great project for next winter.

[PlaynSand]

Ducman, I am not an expert on this but here is what I sorta remember.

 

The long rod is used to decrease side load on piston skirt and increase dwell time

piston is at TDC.

I think the main reason the are used is to increase engine life and reliabilty by reducing side loads on pistons.

If more stroke is added to the crankshaft and the rod length is left the same the rod ratio is increased to extremes which causes excessive side loading on pistons and cylinders shortening engine life and increasing the chance of breaking or scouring.

 

In theory a long rod engine will last longer and make more power due to decreased piston side loading.

 

 

May some of the experts will chime in and help me out.

[H300F]

the pistons you are talking about are not made for the stroke of a stroker crank, they are made for the long rods of a long rod crank and go by the name 795 series.

 

and you can do a stroker crank yourself as far as dropping it in your cases. the cheapest way would be to buy a wiseco +4 stroker reg or long rod (H129) and put it in your cases. but you will need to send your cylinders out to be ported to run correctly.

[H300F]

and playnsand has it right. and i have heard a longrod makes alittle more torque but the regular rod revs up alittle faster.

[rebelbanshee2]

The rod has nothing to do with making up for the stroke. A stroker plate or cut head is needed for a stroker no way of getting around it. Like they said the long rod is just to make things last longer and supposably makes the power curve broader. The wiseco 795 pistons are now used to compensate for the long rod instead of blaster pistons now.

[Ducman]

I thought it might have something to do with the piston and rod interaction. Now that I think about it, it makes sense because with a longer rod the angle between the piston and/or cylender centerline and the CL of the rod is less with the longer rod and with a longer stroke the angle would increse even more. Don't know why that didn't compute before.

 

But I thought that I read in one of the adds that you could use the stock pistons in a stroker but then you would need the stroker plate with a thickness depending on the rod length, but if you use the 795 series pistons and the correct length rod then you didn't need the stroker plate? Isn't the stroker plate just to position the cylenders so that the piston comes just to the top of the cylendar; so the piston doesn't go too far up and hit the head or when its at TDC it's too far down and effectively lowers the compression ratio and combustion geometry? Isnt the distance fron the wrist pin CL on the 795 series to the top of the piston less than on the stock piston?

 

I'm so glad that I can ask these complicated questions and their are people out there that can answer them. The learning curve must be steeeep for the people without computers and BHQ! Thanks!

[brugal]

I just learned something reading this today to...

[.]

That's what playnsand was getting at. If you use the 795 series pistons and the correct rod, you could get away with not having to mod the head or run a plate, but the sideload on the pistons would be greater, and decrease engine life dramatically.

 

Even worse if you used a stock piston, and even a shorter rod. It'd rev out hella fast though.

 

Best setup to run is a LR stoker (the LR will decrease the added sideload) and 795 series pistons with a head mod done or you could run the plate. You dont need to do porting right away if you you just blew a crank and dont have the money for porting, but it is recommended and wont run to its potential until you do get the portwork done. This is for a standard lr stroker, when you start getting in the higher mm strokers you get into a whole new book of rules

[Oilsmoke]

So how do you use a Long rod, Stock stroke crank assembly? With or without the 795 piston, if so do you need a plate or custom cut dome so to you don't change the port timming?

I think this the Crank that Ducman Question started from.

I wonder about this myself because i trying to plan a High rev shee to go with my Shearer pipe that can handle the extra RPM's that the pipe will let the motor make.

It's like 11,000+ @peakHP.

[H300F]

for a longrod stock stroke you need to have the 795 pistons or a spacer plate under. 795 pistons lowwer the pistons or spacer plate raises the cylinders.

[Ducman]

Ok, I'm pretty sure I'm starting to understand. Without the stroker plate you just cant use long enough rods to make a big enough difference. The 795 pistons will allow for a longer rod but not long enough. Thats why you need both a plate AND the 795 pistons. The stroker plate under the cylenders is probaly the easiest way to make the stroke length work out and the thickness can be varried based on the lenth of rods you choose. The longer stroke changes the porting intake/exhaust flow dynamics so I can see why you would need porting and it might run weird without it. Even with just the long rod and no added stroke the piston speed would be different durring the stroke than with the stock rods and change the port dynamics.

 

With the stroker crank, long rods, and correct stroker plate you don't need any special head work or special domes for a aftermarket cool head right? Just the correct dome size to yeild the desired compression just like on a stock motor?

 

So what rod length is best to use with a 4mm stroker crank? Would it be up to the engine builder doing the portwork to match the stroke or are there some sort of guidelines or engine power tradeoffs for going longer or shorter? Do you pick the rod lenght first and match the porting or pick the rod based on the porting. The O'l chicken VS Egg.

[MULLET~BOY]

i don't like spacer plates of any kind i have a 370 lr and used the spacer plate with stock pistions i wasn't able to find studs long enough to work correctly and i had problems with gaskets blowing out just a bad experince over all

[H300F]

wiseco stroker cranks come with regular rods or long rods. they are both set lengths and you cant order special lengths.

 

and im using a spacer plate on mine with no problems.