I havn't done this yet - here's my plan

[MacaveliMC]

So, I have my '91 Wrangler sittin' on a 4-inch sus. lift with 33x12.5 AT's, and an engine with over 150k on it that is definitely lacking the power I would like. So I've decided to stroke it and here is my plan:

purchase a master rebuild kit with .030 over-sized pistons
grab a crank and connecting rods for the 258, probably new since there's not to many junk yards near me
grab this cam from cranecams - > http://cranecams.com/index.php?show=bro ... vl=2&prt=5

With this cam I'm pretty sure I need to shim the rocker arm bridges, though I don't really know what that is or how to do it, anyone know?

By the numbers this would bring the total displacement to 4.7L and a CR of about 9.5:1
Also, I am sticking with the stock HO fuel injectors and running 87 octane, any objections?

Most of my information I got from this article by Tony Lopez at rockcrawler.com
In fact I'm pretty much doing the exact same thing he did.

Any advice, or experience anyone could possibly share?

I'm also thinking about throwing on a cold-air intake, a bored-out throttle body, and maybe a Jet stage 1 chip eventually, as well as modifying the exhaust later.

[Flash]

Vary good article!

I couple thing i have disagreement with. First, having the piston lower in the bore then the 4.0L is not a good thing. yes it give you more valve to piston clearance(For the most part is not a issue) but make a bad quench motor (4.0L) even more so when stroked. 2nt, the compression is more like 9.7 with stock pistons.

Now with that said, will it work for you, as it did for him???????????

If you live at 6,000 feet or above, as he said he does, it can work just fine.............
If your at a low altitude, you had better plan on 91+ for this type of stroker.

There is a lot you can learn about the stroker build just buy doing some browsing in the FAQ section.
as well as several good threads on the many option you have.

After a while you will have the knowledge on how to build the stroker many different ways.
Then you can choose with one is right for you, and you budget!

The latest option is buying a KB piston that was designed for the 4.0/258 stroker......and it utilizes the longer 4.0L rod instead of the shorter 258 rods

Rome around the FAQ section for a while, you will have several more question
viewforum.php?f=27

P.S Welcome aboard


Flash

[John]

Interesting article, I have read it several times in the past. He built a motor for what he wanted it to do and where he wanted to do it. (High altitude) have you carefully considered what the important considerations for you might be. If it is to run regular grade gas for example. Recipe builds are ok if you understand the end product and it matches your needs. As Flash pointed out, dig around a bit and I will bet you have many more questions. Welcome to the site.
John

[Cheromaniac]

You can take a look at the stroker "recipes" that I put together on http://www.jeep4.0performance.4mg.com/stroker.html and also look at my own 4.6 stroker build-up on http://www.angelfire.com/my/fan/stroker.html

[MacaveliMC]

thanks for the info, and thanks cheromaniac for the recipes.

Flash - the info in the FAQ is very interesting. Especially the quench idea. I see what you mean, that my quench will be too big because the piston may be too far from the head.

But - I am failing to see how that effects your example of the Crane Cam that gets an 8.06:1 ratio.

Also, I had a hard time following your SCR and DCR calculations. It says you did, bore x bore x stroke but I see more than three numbers multiplied there (.7854 X Bore 3.895 X Bore 3.895 X stroke 3.875) what is the .7854??

finally, is there a quick and easy location I can find all the important specs for my own engine? Like, bore, stroke, head volume, head gasket, CC from flat top of piston and deck suffice, piston dish....all that good stuff.

[Flash]

See i now you would have more questions

unfortunately i don't have the time to answer your question right now...............but i will.
Bussy day and a racers meeting tonight.........


Flash

[Flash]

thanks for the info, and thanks cheromaniac for the recipes.

Flash - the info in the FAQ is very interesting. Especially the quench idea. I see what you mean, that my quench will be too big because the piston may be too far from the head.

But - I am failing to see how that effects your example of the Crane Cam that gets an 8.06:1 ratio.

Also, I had a hard time following your SCR and DCR calculations. It says you did, bore x bore x stroke but I see more than three numbers multiplied there (.7854 X Bore 3.895 X Bore 3.895 X stroke 3.875) what is the .7854??

finally, is there a quick and easy location I can find all the important specs for my own engine? Like, bore, stroke, head volume, head gasket, CC from flat top of piston and deck suffice, piston dish....all that good stuff.

Well first of all The FAQ section will answer most of then questions but 4.0L standard bore is 3.875 and stroke is 3.41
the 258 crank that we us to stroke the 4.0L is 3.895( not the 3.875 stroke that i used in the example )Head cc is usually around 57-58cc as far as piston dish cc, cc from piston to top of deck........i don't know as they will vary between piston manufacturers but piston pin hight and dish cc is spelled out nicely in the FAQ section. If it is a stock or stroker crank, if you using the 258 rods or the 4.0L rods......if you are going to us the stock, custom, or stroker "KB" piston...........................................

OK, see if this helps
SCR (Static compression Ratio) is total volume at BDC ( Bottom Dead Center) Divided buy total volume at TDC (Top Dead Center) For an example if the volume at BDC was 700cc and the volume at TDC was 76cc the the compression ratio would be 9.2:1 9.2 times more volume at BDC then at TDC, Right?

NOW DCR (Dynamic Compression ratio) the eng has 9.2 SCR as the compression ratio is BDC by TDC right, Now what if you had a shorter stroke crank? but the TDC volume was the same, say your BDC Volume was now only 614cc and TDC the piston stop at the same height so TDC would still be 76cc now 76 Divided into 614=8.07:1 compression ratio.
Make sence so far?
Now, the piston can notstart to build compression until both valve are closed, Right! When Crane cam, closes its last valve(intake valve) there is only 3.14 inches left, of 3.895(stroker Crank) that is available (remember compression can not start to build or compress until both valves are closed)
The SCR of 9.2 has not changed but the DCR when down due to the valve closing ATDC(After Top Dead Center)
The Comp cam "IVC" is sooner there for builds more pressure or compression.(Piston has further to travel when both valves become closed on the compression stroke)


Bore 3.895 X Bore 3.895 X stroke 3.875 would give you a Square piston running down a Square Bore .7854 make the piston round instead of square! Make sence?

One more thing, in the upper right had area just below the Jeepstroker logo, is our stroker calulater, you can have a lot of fun punching different numbers in to see how it changes stroke, quench, compression ratios EXC.

If i lost ya some ware, let me know and i will try again

Flash

[MacaveliMC]

Flash - you said you were worried about the quench of the engine I described since the piston will end up lower in the bore, making the quench height bigger.

But you also still say that you use the 258 connecting rods to stroke the engine. How do you fix this quench height then? I couldn't really find a good way to do it in the compression FAQ.

Edit: Also, I was wondering what the rule was for moving from 87 octane to a higher octane gas based on DCR?

[John]

Quench can be adjusted by a few things, rod length, 258 or 4.0 rods. Gasket thickness for the head, around .043 - .052 is available. Machining, ie. .020 removed from deck of block. Piston selection, pin height.
John

[MacaveliMC]

I was under the impression that the 4.0 rods could not be used because they would impact the valves. Is there some way to remedy this? I know decking the block is one way, but that also increases compression. What exactly is pin height?

[Cheromaniac]

I was under the impression that the 4.0 rods could not be used because they would impact the valves. Is there some way to remedy this? I know decking the block is one way, but that also increases compression. What exactly is pin height?

Pin height (or compression height) is the height of the piston from the center of the piston pin to the top of the piston.
The 4.0 rods are 0.25" longer than the 258 rods (6.125" v 5.875").
Stock 4.0 pistons have a compression height of 1.601" and can only be used with 258 rods in a stroker, whereas KB944 pistons have a compression height of 1.353" and can be used with 4.0 rods in a stroker.
KB944 pistons used on 4.0 rods leaves the pistons 0.028" below the block deck at TDC. If you mill 0.020" from the block deck, the deck clearance is reduced to 0.008". Add the 0.043" Victor Reinz/Mopar performance head gasket and the quench height becomes 0.051". If you select the 0.020" overbore pistons, compression ratio comes in at 9.5:1. If you select 0.060" overbore pistons, compression ratio is slightly higher at 9.7:1.

[MacaveliMC]

Cheromaniac - thanks for that awesome explanation! I understand that much more now. Am I correct to assume you are talking about static compression ratios? You must be since you didn't mention a cam I'm guessing.

Is there an easy way to determine how far the piston has traveled up from BDC when the intake valve closes? I noticed in the compression FAQ says the number was obtained from either the stroker calc or some other calc, but I don't see anything on the stroker calc about those numbers.

So far I get what everything is on the stroker calculator except these terms: Plaining head, & Custom piston (cc).

[Flash]

Cheromaniac - thanks for that awesome explanation! I understand that much more now. Am I correct to assume you are talking about static compression ratios? You must be since you didn't mention a cam I'm guessing.

Is there an easy way to determine how far the piston has traveled up from BDC when the intake valve closes? I noticed in the compression FAQ says the number was obtained from either the stroker calc or some other calc, but I don't see anything on the stroker calc about those numbers.
I don't believe our stroker calculator has provision for DCR. I did a search on the INTERNET for DCR calculators and found one that you down load to you computer..........thats were the Inch's of stroke, before valve closes came from.
Most DCR calc. just need the input of the IVC spec to do the figures. Mine will tell me have far up the bore (in inches) it has travel when i put the IVC spec in.
So far I get what everything is on the stroker calculator except these terms: Plaining head, & Custom piston (cc).

Plaining head = resurfacing the head and how many .000" of a inch has been taken off.
Wether its Custom or stock piston, the calc. needs this info to get the compression ratio right(SCR)
Most of the piston Dish cc are in the piston FAQ section

Make sure you understand "regular compression ratio" or SCR before you get to deep into DCR.
As far as DCR go's , it takes a few time before the light comes on completely At least it had to be explained to me a few time before i real got it and understood it.


Flash.

[MacaveliMC]

Flash I'm pretty sure I understand the difference between SCR and DCR.

SCR is purely the mechanical difference. The total chamber size when the piston is at BDC divided by the chamber size when it is at TDC.

DCR uses the size of the chamber at the point when the intake valve closes. Since the intake valve closes so many degrees after the piston passes BDC and starts
to head back up, the chamber size is going to be smaller, so you are dividing a smaller number by the size of the chamber when the piston is at TDC. This way, by choosing your cam, you can create a smaller DCR even if your SCR is pretty big.

What I do not understand is how to calculate how far the piston has traveled back up, based on so many degrees past BDC. Take this quote from the compression FAQ:

"Lets start with a Comp cam 68-231-4 cam with a Intake Valve Closed (IVC) Spec on 56*........that means that the the piston will travel from BDC up .612" or just over a 1/2 inch, before the valve close....."

What I want to know, is how did you get .612"??? What is the calculation?

Also, just out of curiosity, how come the stroker calc has the stock piston dish volume set at -13 when the piston FAQ says it's -13.5?

[Flash]

Here is a DCR Calc that you can play with on the internet!
http://www.wallaceracing.com/dynamic-cr.php

And here is the one, that i down loaded on to my computer(as thats the only way it works) and was able to come up with the numbers
http://www.empirenet.com/pkelley2/DynamicCR.html
Scroll down to the bottom and you will find this

DCR FAQ's, the answer to your question could be here.

DCR Calculator with VB6 Runtime files 1.55 MB

DCR Calculator without VB6 Runtime files 423 KB

there is quite a bit of reading there, but it start to get real deep.

The first one has a space for Altitude input............its kinda fun to see just how high altitude afects DCR as well and Low.

I down loaded the first one on the list as i didn't know if my computer had VB6 runtime files

As far as the calc go with stock piston cc.....there was a clarification change just recently that changed the cc on a couple piston..................the calc was designed before the change...........you can change it to what ever you want so it not to big of a deal.



any ways this one will convert IVC spec in to piston travel distance in inches.

O and SCR and DCR you have a good understanding.........but its about to get a lot clearer as you start to play with the 2 calc. that i gave you links to above

Take your time have some fun with both DCR calc. It will start to make a lot more sence once you have punch some numbers in


Flash