Basics of a Budget Stoker

I know its probrably been asked a million times but what exactly is involved with doing the cheapo 4.2 crank stoker? i know the 4.0 rods are too long to use along with stock pistons so what do most do? 4.2 rods with 4.0 pistons? or 4.0 rods with some custom slugs? i've heard off alot of people having detonation problems with high compression and such but should'nt custom pistons solve the compression problem for the most part? Just looking for info for though experienced with this build up because i have an nice new disassembled short block 4.0 to start working with.

Eric

Most of the information about strokers comes from the Strokers group on Yahoo. By their informal definition, a "budget" stroker uses stock 4.2L rods and stock (or nearly stock) 4.0L pistons. This combination does increase compression ratio and requires 91 or 93 octane fuel, unless you have a non-HO with the knock sensor.

Using 4.0L rods requires custom pistons, and these can be manufactured with a pin height that corrects for the quench height and compression ratio. This is generally considered a better solution, but it is not the so-called "budget" stroker. Also, the custom pistons are forged, and those are noisy when cold. Some people find this objectionable, others don't.

Ok, i just thought of something, not sure if it would work but i'm gonna look into it. From what i've seen the cost for a set of forged pistons for the XJ is through the roof. Now here is my thought, i believe vette 350's or Ls1's, or some chevy 350 motor uses an exact 4" bore, now what if i could have the block on my 4.0 bored to an exact 4" and use a set of chevy pistons with the right pin height and dish for my application to set correct the quench and compression ratio? i know i could get some custom chevy pistons for alot cheaper thats why i ask and i've have alot more options too.

Thanx guys,

Eric

Check out the Stokers' group on Yahoo. This option has been thoroughly discussed, and largely discarded. It is not viable for a "budget" stroker because you can't reliably bore to 4.00". There are some 4" bore stroker engines running, but I believe they were sleeved after boring. The largest overbore you can go to without doing sonic testing and a bunch of other hi-tech racer tricks is generally .060"

thanx for the help eagle, do you or anyone else on here have a link for the strokers group on yahoo, i've looked but can't come up with anything.

thanx,

Eric

http://autos.groups.yahoo.com/group/strokers/

Bones :skull1:
#6

Here's a link to a site with very good stoker information:

http://www.jeep4.0performance.4mg.com/stroker.html

To me, from what I've recently learned, one of the best options for a budget stroker is to use the 4.2 crank and rods, and Keith Black Silvolite 4.0 pistons. These pistons can be machined to increase the dish size to an acceptable compression ratio. The injectors need to be larger, and machine work done and the right head gasket used to get a decent quench height, and a good valve job done. After that, everything else depends on what you want to get out of it and how much money you have/want to spend. A good cam, header, and larger throttle body are good ideas, and any other head work.

I just started looking into all of this, and hope to get a stroker into my rig before Moab, but it depends on a lot of things. More than likely it will be a winter project.

Eagle said:

Most of the information about strokers comes from the Strokers group on Yahoo. By their informal definition, a "budget" stroker uses stock 4.2L rods and stock (or nearly stock) 4.0L pistons. This combination does increase compression ratio and requires 91 or 93 octane fuel, unless you have a non-HO with the knock sensor.

Click to expand...

I dont want to disagree, just make a small point. You're right about swapping rods/pistons without doing any other machine work or mods will alter compression ratio. However, during any top end motor build, the compression ratio is what you ultimately build the motor around. Therefore, you would want to adjust this high CR back to an 'acceptable' level. You would do this by increasing the combustion chamber CC (volume). This can be done by either modifying the heads, dishing the pistons, or by simply running a taller head gasket. Just something to consider while building is that you can't just slap components together and run AV gas or TRICK racing fuel, there is a CORRECT way to build so that you get the extra flow & volumetric efficiency without making the motor 'race only'.

You're right about swapping rods/pistons without doing any other machine work or mods will alter compression ratio. However, during any top end motor build, the compression ratio is what you ultimately build the motor around. Therefore, you would want to adjust this high CR back to an 'acceptable' level. You would do this by increasing the combustion chamber CC (volume). This can be done by either modifying the heads, dishing the pistons, or by simply running a taller head gasket. Just something to consider while building is that you can't just slap components together and run AV gas or TRICK racing fuel, there is a CORRECT way to build so that you get the extra flow & volumetric efficiency without making the motor 'race only'.

Click to expand...

While I agree with most of this in theory the problem is there isn't much alteration that can be done to the 4.0 as it is a quench compliant design. By the time you deck the block to bring the 4.2 rod stroker into quench the CR is unacceptable. Too high of a CR OR not being in quench on the 4.0 block will cause pre-detonation problems. That is why there is so much discussion on the stroker board about pistons, heads, CR, quench, and unfortunately PING.
Yes you can open up the chamber size on the head but not much and the cost of doing it right will start to off set the whole "budget" goal. A thicker head gasket isn't much of an option either. IIRC there is only the .045 and .060 thickness gaskets available out there and most 4.0's already run the .060's. What Goatman eluded to is that there is a set of HE pistons with enough thickness on top that they can be dished out more to try to keep the CR acceptable and the engine in quench on a budget.

We aren't driving Chevy's with small blocks (well most of us aren't thank god) so the supply of aftermarket and specialty parts is very limited. The idea of a budget stroker is more complex than one would think on the surface because of the CR vs. Quench issues. If it was easy the strokers group wouldn't be over 2.5 years old and still going strong.


Oh, and the term "Budget Stroker"... It is a relative term. By the time you figure up the cost of the stroker once you get it dialed in and running properly you won't have much of a budget left. But that’s my own little
:soapbox:

Bones :skull1:
#6

vintagespeed said:

I dont want to disagree, just make a small point. You're right about swapping rods/pistons without doing any other machine work or mods will alter compression ratio. However, during any top end motor build, the compression ratio is what you ultimately build the motor around. Therefore, you would want to adjust this high CR back to an 'acceptable' level. You would do this by increasing the combustion chamber CC (volume). This can be done by either modifying the heads, dishing the pistons, or by simply running a taller head gasket. Just something to consider while building is that you can't just slap components together and run AV gas or TRICK racing fuel, there is a CORRECT way to build so that you get the extra flow & volumetric efficiency without making the motor 'race only'.

Click to expand...

You're missing the point, but that's probably because you haven't been following the stroker engine build group for several years. The original question was about a "budget" stroker. A "budget" stroker is made by using a 4.0L block, 4.2L cank and rods, and off-the-shelf 4.0L replacement pistons. As a direct result of minor variations between the engines, this combination results in the top of the piston sitting higher in the block at TDC than a stock 4.0L, with a resultant high compression ratio.

Since most engine rebuilds require minor decking of the head (and maybe the block) to straighten/flatten them, this only makes to condition worse. There's only so much you can dish out the pistons, and the 4.0L heads don't have that much material to remove that you can substantially enlarge the combustion chamber.

Your screen name suggests race experience, but the "budget" stroker is not a race engine. It is specifically not a "designed" engine, it's a kludge. In fact it is slapped together out of stock components from two engines that happen to be enough alike that rods and cranks can be interchanged. That's why there is a compression ratio problem, and it's a problem that we've been debating for several years. There are work-arounds, all discussed in extensive and excruciating detail on the strokers' group, but in addressing the question please keep in mind the intent of the petitioner.

D*mn Eagle...

You and I are starting to think a lot alike....

It is really scary!
:shiver: :scared:


Bones :skull1:
#6

Even worse -- we're starting to write alike.

REALLY scary

We'll thanks guys. You're right, my experience is not directly with quench-restricted designs like the 4.0L and I need to study up on it. I am considering a stroker (aren't we all?) and once the damn thing is back on the trail I'll spend some time dwelling on it. I appreciate you not ripping me a new one, being a newbie to I suppose I should wait until my pubes grow in to comment on anything. LOL.