Stroker- which rods?

[Squid4life]

Buying pistons for a slow "on the side" stroker build and need to buy pistons. What would a benefit of a 6" rod over a stock length rod be? Can get pistons for either, but not sure which rod would be better. I was considering the stock length because they could always be used in case plans change. Any reason to go 6" instead?

 

[DCVING 6]

Services

DLS has complete rotating assemblies with no guess work.

 

[Squid4life]

Yeah, I already talked to them. Don't have that kind of money right off. Found a good deal on pistons so I really need to know stock or 6" rod. Thanks for the input though!

 

[Jerryl]

Buying pistons for a slow "on the side" stroker build and need to buy pistons. What would a benefit of a 6" rod over a stock length rod be? Can get pistons for either, but not sure which rod would be better. I was considering the stock length because they could always be used in case plans change. Any reason to go 6" instead?

Here is a GREAT read
Hopefully, this will help you decide between performance and budget.
Rod Length article

 

[Squid4life]

Wow, lots of info there... Lot to digest. It makes good points on each length of rod, makes the decision difficult.

 

[DCVING 6]

What crank are you using?

 

[Squid4life]

Trying to decide on that, it all plays together... Either the one from TA or wait on DLS to get their kit together (still no rods). From what I see you can run either a stock length rod, or a 6" rod, and just need to change the pistons. Trying to decide which will be better, but I am swaying towards stock length rod to be able to use it in a stocker if I decide to change plans.

 

[gnxtc2]

I wouldn't buy anything until your block is machined. Too many variables when doing a stroker.

Billy T.
gnxtc2@aol.com

 

[Squid4life]

Still need to be machined for a stock rod length stroker? Haven't had much finding info...

 

[Nasty Wendy]

You need to know what combo you'll be running to make the best decision. The rpms you plan on spinning the engine is big factor. The longer the rod the faster the piston will travel and excessive piston speed will cause excelerated wear.

 

[Squid4life]

Best case scenario I will run a girdled 109, Champion irons, rev x roller from full throttle (210/215), RJC 70mm TB and plenum, maybe even champion intake. Not sure how high I will zing it, it will be my first non "stock based" 3.8 build. Don't want to rev any higher than I have to, like my stuff to last. Obvioulsy intend to upgrade to a bigger and better turbo as well.

Any suggestions, opinions, gut feelings, etc are very much appreciated.

 

[Jerryl]

........The longer the rod the faster the piston will travel and excessive piston speed will cause excelerated wear.

If; Speed = distance/time
Than my limited understanding, based on this formula, is that the mean piston speed is not affected by rod length as the stroke (travel distance) does not change with rod length.
Maybe there is a gap in my edumaction
Not trying to split hairs, just trying to understand.

 

[dr_frankenstein]

You wont notice much of a difference on a street engine. The rod wont be significantly longer than stock so the rod stroke ratio wont be affected enough for you to notice, About 1.7529 for the stock rod and 1.764 for the 6" long rod. A Rod Stroke Ratio of 1.75 is considered “ideal” by some respected engine builders, if the breathing is optimized for the design. The longer rod will help in turning the motor to a higher RPM more smoothly due to higher piston dwell time and the angularity of the rod. That is the main advantage of the length - the shorter the rod, the more stress on the cylinderwalls, wrist pin, piston and crank.

HOWEVER, you want to build a stroker engine, which changes around the rod stroke ratio significantly! using a 3.625 stroker crank and a 6" rod will give you a 1.655 rod stroke ratio and a 1.644 on a stock rod - which is less than favored by some- and is to our disadvantage in buick V6 world. the reason this hurts us is because of cylinder heads. As Jerry above posted about Rod Length - Shorther rod stroke ratios that fall into the 1.45 to 1.75 range tend to favor Large intake port volume vs. motor size- such as a nice Champion, TTA or Stage 2 head. Hmm.......? starting to see why buick engineers built the motor the way they did.

In My Honest Opinion, These are factors really only needed on a race engine where every little detail counts, Smokey Yunick once said that he threw a handful of different rod sizes at his stage 2 and never noticed much of a change in power. you may pick up 3 to 4 hundred rpm at the top end, but nuthing more than that warrents the expense of longer rods in the Buick V6 - its money better spent on porting, valve work, a well chosen cam, intake..... concentrate on BREATHING.:biggrin:

Good Luck.

A.j.

P.S. oh yea.......... go Navy.

 

[Squid4life]

Very good info, that is the kind of stuff I was looking for. It is odd how some things work in some engines and not so much in others...

Thank you so much for the edumacation.

 

[Nasty Wendy]

If; Speed = distance/time
Than my limited understanding, based on this formula, is that the mean piston speed is not affected by rod length as the stroke (travel distance) does not change with rod length.
Maybe there is a gap in my edumaction
Not trying to split hairs, just trying to understand.

Your calculation of speed is correct and its is why the avg. speed of the piston won't change when you calculate its travel from TDC back to TDC. It is after all the same distance regardless of rod length. Increased rod length does affect the dwell time. The longer the rod the longer the dwell time. The piston still has to get all the way around in the same amount of time so where does it make up for moving so slow for a longer period of time at the top and bottom of the stroke? Stroker motor pistons haul azz going up and down between dwells.

 

[dr_frankenstein]

Your calculation of speed is correct and its is why the avg. speed of the piston won't change when you calculate its travel from TDC back to TDC. It is after all the same distance regardless of rod length. Increased rod length does affect the dwell time. The longer the rod the longer the dwell time. The piston still has to get all the way around in the same amount of time so where does it make up for moving so slow for a longer period of time at the top and bottom of the stroke? Stroker motor pistons haul azz going up and down between dwells.

He is correct, and I correct myself, I meant Dwell not piston speed.:tongue:

A.j.

 

[1 quik6]

Yeah, I already talked to them. Don't have that kind of money right off. Found a good deal on pistons so I really need to know stock or 6" rod. Thanks for the input though!

I just got pinched in this problem with my 4.1L build. I understand you'd like to buy piece at a time but parts for our engines are really becoming hard to find. I was getting a CAT crank, with buick like rods, and custom pistons made especially for a TTA. Got the pistons made and my engine builder was "overly optimistic" on finding a crank. I then looked into the DLS crank and found the rods were on a long term backorder. I talked to DLS for a little while and found out the pistons wouldn't work with the DLS rods because they were made more like a Chevy rod (at least that is how I understood it) with a different pin size.

If you can buy a complete rotating assembly, do it. These parts are not plentiful and they all need to work together. I would not buy pistons without the rest.

My $.02

Eric

 

[Squid4life]

Yeah, I am slowly finding this out. If you find pistons on sale, they necessitate buying a more expensive set of rods, which don't work with the crank, etc. You are right, it is better to buy a kit, but now that is even hard to find. I am still looking into everything, and from some of the info, it seems stroker may not be worth it... I am still researching, reading, listening. We will see what happens. Maybe I should post a poll!?

 

[Alky V6]

How I understand it is, a shorter rod will accelerate piston speed at any given point thoughout its travel from top to bottom, and bottom to top for any given stroke dimension. And will increase cylinder wall side loading.
If you're using a cylinder head that is flow limited in relation to the cam, stroke, and target rpm, it's best to go with as long a rod as possible. You also get the advantage of less cylinder wall side loading.

My thinking is, selecting rpm range, stroke, cam, rod length should all be tied to the breathing ability of the head. You want to target a window of optimum intake port velocity for the head being employed. The stroke and camshaft specs will have the most affect on where the engine is going to peak taking the other variables into account. And, all selections should target the same end.

The first decisions that should be made before you start buying parts are,

1) What is my target hp level? The heads will usually be the limiting factor here, especially with cast iron heads and a long stroke, so all other decisions should revolve around the breathing ability of the heads.

2) What will be the operating rpm range of the engine? RPM = horsepower = money and maintenance time. How much am I willing to invest? If I'm trying to keep this budget, then I may have to revisit question one and lower my expectations.

 

[1 quik6]

I agree with the theory that a well built 3.8L can have as much horsepower as a Stroker. Shorter stroke = more RPM's. The reason I went with a 4.1L stroker 109 was for low end spool and torque. I am using this car on the street and I'm not as worried about high RPMs.

As for cost a stroker shouldn't cost a lot more if you are planning on replacing everything for strength anyways. The good steel cranks for standard stroke v6's are getting harder to find (and more expensive) again because of limited suppliers. You could re-use stock crank/rods but it won't be built to hold up with severe abuse/high horsepower.