stroke

Reply

  #1  
Old 01-31-02, 02:34 PM
jd123
Visiting Guest
Posts: n/a
Question stroke

On stroking an engine. All they do is just ground the rod journal on the crank, to make it smaller, right? Then this in turn pulls the piston a little further down in the cylinder. But at tdc, the piston is a little further down in the cylinder with the same stock rods, but doesn,t that hurt compression? It doesn,t look to me like you gain anything. If there is more volumn in the cylinder, but it seems to me that the piston is already down further in the cylinder before the intake valve opens, so I don,t see that you gain anymore fuel. I guess there is something about this that I don,t understand? I didn,t mean to ask a question that would take all night to answer. But maybe you can shed some light on this. thanks
 
Sponsored Links
  #2  
Old 01-31-02, 04:19 PM
Joe_F
Visiting Guest
Posts: n/a
No engine rebuilding expert here, but I'll take a shot.

Ask anyone with a 383 stroker motor if they can leave a stock 350 or a 400 or even a midly modded one eating taillight dust .

Engine performance is about breathing, exhaust and fuel. All three must be in balance.

On a Pontiac 400 like my 79 Trans Am for example, 6X heads are used. These are originally 350 Pontiac heads. Putting them on a 400 lowers compression and hence emissions. You can port and polish them to flow like champs.

Same thing with getting the manifolds to Ram Air ones. Dport 400 manifolds all interchange from what I remember.

I believe you are using a 400 crank in a 350 to create a 383 stroker.
 
  #3  
Old 01-31-02, 05:26 PM
mooser1
Visiting Guest
Posts: n/a
jd, you have engine builders rolling in the aisles all across the country....whomever told you that all you do to "stroke" an engine is grind down the rod journals was severely pulling your leg......

Joe-F, this is one of the funniest ones yet!!!!!
 
  #4  
Old 01-31-02, 05:35 PM
cheese's Avatar
Forum Topic Moderator
Join Date: Jul 2001
Location: USA
Posts: 16,814
You can mildly change the stroke of the engine by grinding the crank journals. The way this is done is you offset the journal. Say you remove 30 thousandths from the rod journals...you increase the stoke by grinding 25 off the low side of the journal and only 5 or so off the top side. That makes your rod revolve 25 thousandths further away from the center of the crank. That also increases your compression. More than likely, this is what you're being told to do if it involves machining the crank.
 
  #5  
Old 01-31-02, 06:40 PM
mooser1
Visiting Guest
Posts: n/a
this just keeps getting better and better......maybe you guys should look for a "comedy" forum to post replies to......
 
  #6  
Old 01-31-02, 07:07 PM
Joe_F
Visiting Guest
Posts: n/a
Just remember that no one knows everything and no question is stupid .

That being said, we all learn and yes, sometimes picking up a book and figuring out what they're saying is a good thing .

Everyone starts somewhere .

I do agree there are some winners out there that proport to be "experts".
 
  #7  
Old 01-31-02, 08:25 PM
jd123
Visiting Guest
Posts: n/a
Question stroke

Hey mooser, I know that I don,t understand it, that is why I asked. If you have a better explaination than what has been posted, lets hear it. I,d like to learn. thanks
 
  #8  
Old 01-31-02, 09:41 PM
cheese's Avatar
Forum Topic Moderator
Join Date: Jul 2001
Location: USA
Posts: 16,814
Mooser...It's called turning a crank "on the high side". Before you laugh too much, ask a machine shop. It's common practice. Listen to the way I described it and you will realize that what I'm saying will in fact change the stroke of an engine. (that is if you understand the theory of operation of an internal combustion engine). I'm not claiming a drastic change, but it is a change, and it does change the compression ratio quite a bit. Imagine shaving 25 thousandths off the head deck.
 
  #9  
Old 01-31-02, 09:52 PM
Ron AKA
Visiting Guest
Posts: n/a
The only way to increase the stroke is to increase the distance from the center line of the crankshaft to the center line of the big end of the connecting rod. This distance is equal to 1/2 of the overall stroke. You could do this by buying a new crank, or possibly by grinding the journal area of the crank in an offset manner and then using a connecting rod with an undersized large end. Theoretically possible, but I'm not sure it is really practical.

Ron
 
  #10  
Old 02-01-02, 10:26 AM
cheese's Avatar
Forum Topic Moderator
Join Date: Jul 2001
Location: USA
Posts: 16,814
Yes Ron. The stroke is the amount of up and down movement of the piston. This is created, and changed only by placing the rod journal farther away from the crank journal. Grinding the crank as I mentioned earlier in an offset manner (taking more metal off the inside of the jornal, and less off the outside) places the rod journal farther away from the crank journal...thus increasing stroke. It isn't enough to amount to much, the compression is changed though. You use oversized bearings, rather than rods with smaller bores. This is only a way to sneak a tad more power from your engine rather than make a "stroker" out of it. Joe mentions using a 400 crank in a 350 engine to make the 383 stroker...this is true, but other things will have to be changed to keep the piston from rising above the block deck. This is also common procedure.
 
  #11  
Old 02-04-02, 07:41 PM
Visiting Guest
Posts: n/a
ok after laughing my a$$ off to stock ya change the stroke...(crank)...or ya can go with longer rods...or....we could go on for a long time... i have a 383 "stroker"...(350 with a 400 crank) a 331 (350 with a 327 crank)...both are two different strokers....but here is the key ...don`t let anyone tell ya that you have to stoke a motor to make it run...i have a 350 with the original stroke putting out mid 700`s hp at the flywheel...the stroke combos just didn`t produce the needed output for the mentioned motor...if ya have any q?? e-mail me and i`ll try to give ya different combos that work well within several budgets....
 
  #12  
Old 02-05-02, 08:02 PM
cheese's Avatar
Forum Topic Moderator
Join Date: Jul 2001
Location: USA
Posts: 16,814
Are you saying longer rods will increase the stroke? If the original poster was told the stroke can be changed by machining the crank, this is the only way it can be done. What's funny about it? Am I wrong? No, I don't claim that it makes a performance engine, or changes the stroke much. Machine shops and racers in my area do this regularly, since it costs little more than just grinding the crank normally. If I am mis-informed, I would like to be enlightened. TY
 
  #13  
Old 02-06-02, 12:09 AM
knuckles
Visiting Guest
Posts: n/a
Post

Doyle:

You said "ok after laughing my a$$ off to stock ya change the stroke...(crank)...or ya can go with longer rods...i have a 383 "stroker"...(350 with a 400 crank) a 331 (350 with a 327 crank)...both are two different strokers....but here is the key ...don`t let anyone tell ya that you have to stoke a motor to make it run...i have a 350 with the original stroke putting out mid 700`s hp at the flywheel
..."


1. Increasing the length of the connecting rod does not increase the stroke. Stroke is the distance from the center of the main journal to the center of the rod journal X 2. The ONLY way to increase stroke is to increase the distance between the center of the rod journal and the center of the main journal. This can be accomplished by offset grinding a stock crankshaft, or installing an aftermarket crankshaft, or modifying a stock crankshaft from a larger displacement stock engine.

2. A stock 350 Chevy engine has a 4.00" and a stroke of 3.48". A stock 327 has a 4.00" bore and a 3.25" stroke. So, using the formula for the volume of a cylinder, we can see that a 350 block (4.00" bore) with a 327 crank (3.25" stroke) yields 326.7264 cubic inches, or 327 rounded off to the nearest whole number.

There are 2 ways to achieve 331 cubic inches on a small block Chevy engine using basically stock parts. The first is to bore a 327 block to 4.030" and use the stock crank. The second is to install a 400 crank in a 305 block.

3. A 700HP 350 CI Chevy engine is nowhere near stock and certainly not practical for street use, even with feedback EFI. A long stroke engine such as the 383 (.030" over 350 block with 400 crank) makes a nice torquey street engine.

Next time you might want to engage your brain before you engage your keyboard.

Cheese:

Offset grinding is commonplace, but becoming less popular due to the relatively recent availability of new, "low cost" performance crankshafts.

Longer connecting rods do not increase stroke, but can increase performance in some applications. For example, a stock small block Chevy rod measures 5.7" from center to center (except the small block 400, which uses a 5.565" rod). Rods measuring 6.00" center to center will increase both torque and throttle response on *most* small block Chevy engine combinations due to the fact that longer rods expose the piston to the high cylinder pressure in the combustion chamber for a greater amount of time than short rods.

If you want to learn more about performance engines and engine building in general, I suggest you read the book "How to Build Max Performance Chevy Small Blocks on a Budget" by David Vizard. It should be available from your local bookstore. If not, Amazon.com sells it for $13.26 + shipping.
 
Reply

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off


Thread Tools
Search this Thread
Display Modes