Stroker crank questions

[user-612937456]

Need opinions on changing to stoker crankshafts in general.
Not answers to questions, but what questions needs to be ask to help make an informed decision.
If you Stroke any engine What question comes to mind?
What Questions do you ask if you are considering Stroking your current engine?
How should I consider what Kind of racing or street application are you building the engine for?

Some ideas I Think of are below, see where I am going? Asking some of the members here can contribute with some other ideas or expand on the points I bring up?

2015-09-02_19-43-00.jpg

Increase displacement in proportion to efficiency. If you just stroke the engine with no other changes you get an average 8-12% Hp change for the increase cubes? EXAMPLE 350 cube = 1.3 Hp per cube or 455 HP, 383 cube = 1.22 Hp per cube or 467 HP Now I understand the rate of torque change is a different but its just a talking point.

1. What other changes need to be done to get an equal HP increase per cube?

2. For a given application changing stroke, how do you figure whats the most efficient Damper size, Cam change, Valve train differences, Induction, Carb size?

3. What application Specific connecting rod do I use for best results and efficiency? There are a lot of different lengths and several different architectural designs.

4. What kind of material and stroke increase is needed for a specific application?

[Keyboardmechanic]

At what point should deck height be considered a limiting factor?

[pdq67]

The limiting factor for, "deck height", (i.e., pin distance to the top of the piston flat), is if the pin can't go any higher using a given rod, even though an oil ring support is used. Remember, the piston can only go a, "skosh" out of the top of the block and it is probably best to use the .025", stock, "down in the hole", quench distance... Or use zero....

That said, make sure that your rod/deck height combination is such that the pin bosses of the pistons clear the counterweights at bottom dead center.

Or if not, then you either have to change everything OR cam-cut the crank counterweights for the needed clearance at bottom dead center or make a flat where the pin bosses hit on the crank.

Doing this usually means that you will probably have to have heavy-metal installed in the crank which adds cost to the rotating assembly.

All is good IF you choose the correct pin height and rod length.. If not, then ----- And I went through this when I made my 496" engine using thumb rods. I flat missed it when the Salesman told me to use 6.385" long rods and, "correct", pistons, everything would have worked great. No h-m and no machining.

Been there, done that.

pdq67

PS., and I was just laying in bed thinking about stuffing a 4.5" crank in a stock 502", .030" over block to make a 9.8" tall, 571"/572" engine..

pdq67

[digger]

The limiting factor for, "deck height", (i.e., pin distance to the top of the piston flat), is if the pin can't go any higher using a given rod, even though an oil ring support is used. Remember, the piston can only go a, "skosh" out of the top of the block and it is probably best to use the .025", stock, "down in the hole", quench distance... Or use zero....

That said, make sure that your rod/deck height combination is such that the pin bosses of the pistons clear the counterweights at bottom dead center.

Or if not, then you either have to change everything OR cam-cut the crank counterweights for the needed clearance at bottom dead center or make a flat where the pin bosses hit on the crank.

Doing this usually means that you will probably have to have heavy-metal installed in the crank which adds cost to the rotating assembly.

All is good IF you choose the correct pin height and rod length.. If not, then ----- And I went through this when I made my 496" engine using thumb rods. I flat missed it when the Salesman told me to use 6.385" long rods and, "correct", pistons, everything would have worked great. No h-m and no machining.

Been there, done that.

pdq67

PS., and I was just laying in bed thinking about stuffing a 4.5" crank in a stock 502", .030" over block to make a 9.8" tall, 571"/572" engine..

pdq67

also the length of the cylinder matters, no use pulling the piston too far down at BDC that it isnt supported sufficiently well

[pdq67]

Good point, digger!

I didn't have that problem.

pdq67

[Keyboardmechanic]

The limiting factor for, "deck height", (i.e., pin distance to the top of the piston flat), is if the pin can't go any higher using a given rod, even though an oil ring support is used. Remember, the piston can only go a, "skosh" out of the top of the block and it is probably best to use the .025", stock, "down in the hole", quench distance... Or use zero....

That said, make sure that your rod/deck height combination is such that the pin bosses of the pistons clear the counterweights at bottom dead center.

Or if not, then you either have to change everything OR cam-cut the crank counterweights for the needed clearance at bottom dead center or make a flat where the pin bosses hit on the crank.

Doing this usually means that you will probably have to have heavy-metal installed in the crank which adds cost to the rotating assembly.

All is good IF you choose the correct pin height and rod length.. If not, then ----- And I went through this when I made my 496" engine using thumb rods. I flat missed it when the Salesman told me to use 6.385" long rods and, "correct", pistons, everything would have worked great. No h-m and no machining.

Been there, done that.

pdq67

PS., and I was just laying in bed thinking about stuffing a 4.5" crank in a stock 502", .030" over block to make a 9.8" tall, 571"/572" engine..

pdq67

Yeah I've been thinking about my "ultimate" sbc build, and starting to make parts lists, one thing I have been debating is weither I should grab as much stroke as possible, I've seen quite a few big small blocks "living" on the street in recent years (unlike some of the older 427 400 nickel block builds where I've heard of everything from warped walls to cracked webbing), But I'm still debating sb vs bb build simply because of deck height, and many other factors. Either way, the author of this post was looking for questions to ask when you start a stroker build and I figured this would make a good one

[user-612937456]

the author of this post was looking for questions to ask when you start a stroker build and I figured this would make a good one

Correct the intention of this post is to Help me and others to logically think and plan the build out from the inception. Its so easy and tempting to start buying parts for the ultimate build and midways through the build start rethinking your previous decisions. I have seen many post asking advise and after several post the member that started the post responsdes "I already have this rod length and piston height. I was planning on a 300 shot of Nitrous and you say I do not have aqueduct piston stability?" I want to help myself and others understand the questions needed to properly analyze and engineer the basics of the rotating assembly. Understanding that there is no one size fits all short block. There is a logical way to select the components that are spot on for the expected end product. Not too much or too little but just right for proportionally budget efficiency( David Vizards catch phrase not mine. No plagiarism here ). Parts of this line of questioning may find its way to the New Scatt rotating assembly Module in the David Vizards Seminars that I contribute to so many thanks for what ever you can add to the little I knowledge my tiny brain can absorb

[wyrmrider]

gvx
what motor and block?
any idea of a ball park compression ratio
do you want to run forever or tear down every week?
that said
I'd first check with all the rotating assembly vendors and see what they have then see what problems with each combination
we know that rod bolts hit cams and then blocks
that pistons come too far out of the block so we shorten compression height
then come too far out of the bottom of the block so we go to a longer rod with an even shorter compression height
easy to do with a 440 chrysler where you have 2+ inches of compression height to start with
less easy with a small block chevy or ford
the problems with each brand of short block are well known
do you want the oil ring through the pin bore with a support rail? if not then limit
do you want to run very expensive very narrow rings? or off the shelf rings?
are you willing to regrind the crank to a smaller journal to get a smaller dia rod big end to clear the cam
at some point an aftermarket block starts to look pretty good
I've done 4 1/4 stroke in a stock block 327 chevy- would not recommend it- but they (2) actually did not have the tear it down every week problem (after the initial first time out thrash)
IMHO anything over 3 3/4 stroke in a stock block sbc is hardly worth it and gets progressively harder 3 7/8 and 3 15/16 --4" head flow is going to determine horsepower

[user-612937456]

I think the key #1 question is What is the purpose of the for the build mild street DD, Hot street, Street strip, Max effort street/strip, the different Drag strip classes, Several Dirt classes, Different Asphalt oval classes, Different Road course classes, Different Desert/ endurance racing classes, Standing Mile, Bonneville top speed classes, Mud racing classes, Various Hill climbing classes, .....? This is Just a few to speak of.

Nothing bugs me more that When someone comes in the shop or post on line somewhere and says I need you to build an engine expecting me to read there mind! Or Will this cam work in my "Trefidy". and I got this aluminum intake or cam that my buddy gave me it should save me some money. I digress LOL

Why I want this to be the 1st question that needs to be settled although its harder (to down right difficult) for some.

Now its time for the 2nd Question What power-plant platform? (Ford, Chevy, Dodge, or any other) Then the base engine

[rfoll]

And then there is always " I want X amount of horsepower 383" or whatever. Usage information is always primary when building anything. It dictates every thing else.

[MadBill]

.. pistons come too far out of the block so we shorten compression height
then come too far out of the bottom of the block so we go to a longer rod with an even shorter compression height
easy to do with a 440 chrysler where you have 2+ inches of compression height to start with
less easy with a small block chevy or ford...

Lots to consider for sure, but the rod length doesn't affect the 'dangle' out the bottom; it's only the stroke, overall piston height and bore length.

[wyrmrider]

you sure bill?
say I have a 3 3/4 stroke and a 5.7 rod and my piston comes out of the bottom of the block .5
I go to a 6" rod and shorten the piston .300 at tdc
since the pin is .300 further up the piston the skirt now is now only .200 out of the block
1.5 ch to 1.2 ch

[MadBill]

That only works if the piston height changes, but typically it's just the pin location that moves. Let's say the piston is 2.5" high crown to skirt, the stroke is 3.5" and the bore is 5.0" long. At TDC, the top of the piston is at zero, so the bottom is down 2.5". Now we turn the crank to BDC and so the piston moves down by 3.5". Since 2.5 + 3.5 = 6.0, it's left hanging out the bottom by 1.0" no matter what the rod length.

[In-Tech]

That only works if the piston height changes, but typically it's just the pin location that moves. Let's say the piston is 2.5" high crown to skirt, the stroke is 3.5" and the bore is 5.0" long. At TDC, the top of the piston is at zero, so the bottom is down 2.5". Now we turn the crank to BDC and so the piston moves down by 3.5". Since 2.5 + 3.5 = 6.0, it's left hanging out the bottom by 1.0" no matter what the rod length.

I was gonna do this after your first stroke rod comment a couple posts back.

What custom piston company is going to leave the overall length of a piston the same after moving the pin height a substantial amount. But heck, I don't make pistons so since there are a few of the good guys here that can comment, I am all ears.

[MadBill]

Skirt lengths are not a fixed dimension below the pin centerline and for performance pistons in general the trend is to shorter. I have a Ford D3 Mahle paperweight here that is 2" total height with a 1.2" CH and a 0.8" skirt. Next to it is an Arias that is over 3" with a 1.7" CH and a 1.4" skirt and a pin boss column tall enough to permit ~ +/- 0.200" CH variation.

Many custom piston castings/forgings are designed to accommodate a range of compression heights, so it is by no means certain that a shorter CH equals a shorter piston. My point is that it's the piston height that directly determines if and by how much it comes out of the bore at BDC and that this number may or may not be affected by rod length.
This one for example is unlikely to overhang the bore regardless of stroke..