4.0 Stoker's. Whats the real deal?

After researching the web extensively for the last couple of weeks I haven't found any conclusive evidence that in can be a DIY build up with used parts. There are a number of sites where guys have done this but after checking further most admit to more than a few problems, detonation, overheating, piston slap, or the need to run high octane fuel ( which I definately want to avoid). Even the Accurate Power has a few detractors, mostly about noise from piston slap or the chance that some wont run on 87 octane fuel. Other than that AP seems to have a very high number of customers. Has anyone here built a stroker and found it to be worth the trouble and expense and has it performed as expected? I've tried the e-groups site but found it to be a frustrating experience without much luck (probably due to my not being computer friendly). TC

I have 800 miles (3 weeks) on a so called Budget stroker.
90 4.0block (.060) and head and 85 258 crank and rods.
With Sterling 525P? pistons and no block or head milling CR is 9.1 and it is running hapily on 87 octane. FM9076PT head gasket (.065).
With a comp Cams 235-4 Extreme Energy cam it makes good power - haven't g-teched it yet but will shortly.

The cost is similar to a 4.0 rebuild, $1400 or so.
If you want more high end power a cam and headwork, etc will add $ and performance.
I'll tell you that while a 4.0 will cruise at 75 - 80 MPH this 4.7 will cruise as fast as the road allows.

Bob Salemi from the North Atlantic chapter has about 1000 miles on his new stroker. He is still "dialing it in," but the basic problem seems to have been distributor indexing rather than any fundamental problem with the stroker recipe.

There are two ways to go: (1) use the 258 crank and rods with production pistons, and deal with compression/detonation issues; (2) use the 258 crank with 4.0L rods, and get custom pistons.

Andreas Ritterbusch has the best running of the option (1) engines. He found a production piston with enough thickness at the top that he was able to machine out a larger dish to reduce compression back to a managable level. Bob Salemi's engine also uses the 258 rods, but I don't know what he runs for pistons. The "piston slap" you refer to with the custom pistons isn't that much of a problem. It is a result of the pistons being custom (low production) forgings rather than hypereutectic slugs like the OEM pistons. The forged slugs expand a bit more than hypereutectic, so they are machined with more clearance when cold. The noise goes away once the engine warms up. "Stroker" from the North Atlantic chapter has been running an Accurate Power stroker for two or three years, and it hasn't been a problem for him.

Building a stroker is no more complicated than doing a stock rebuild. When I need to rebuild my '88, that's the way I plan to go.

Mine definatly likes the 93 octane best. I would guess my compression is around 9.4:1. But boy does it make nice power.

any comparison of gas mileage between the two?

i may be the exception to the rule here but.....
I dont really care to run 87 octane in any vehicle i drive, i have run and always ran 93 octane.... As for gas mileage.....when the needle goes to E i fill it up....


I have had my motor from AP for 2+ years now with no problem, except when i put it together i didn't install a new cam gear on the dist. and it wiped out my cam...MY FAULT, not AP's, other than that, i beat the snot out of it and it runs GREAT.

Motor Specs

Also Mike at AP did talk me out of going with a bigger, than what i have, cam because of having to deal with engine codes and such.

If you have any ?'s e-mail me... [email protected]

HTH
STROKER

The 258 crank/rod combo with the 4.0 pistons seems to be the most common approach, yours is one of the very few that didn't have the detonition problems on 87 octane that I've heard of. I think it's sometimes just plain luck and probably has a lot to do with the variations from head to head. Are the Sterling pistons specifically for the 4.0 or a different application that has the proper specs? Is the pin hight higher than the standard 4.0 piston? I'll be using the smaller Comp cam or the Crane 901 to keep the torque down low, I rarely ever go above 4000 rpm.
The Accurate Power kit seems to be well thought out and addresses most of the problems, it's just the 1400 bucks plus injectors that I balked at. I wonder if I might be better off biting the bullet and save myself problems down the road.
Eagle, is the Sterling piston that rsalemi mentioned the one you were refering to? I'd be nice to find the proper piston, after all the 258 cranks and rods are a dime a dozen.
Stroker, I see you're using 30lb injectors instead of the 24 lb ones that I thought most were running, did they come with those or did you step up?
Thanks gang, I'm trying to talk myself into this but my money tree hasen't bloomed for a while. TC

Mike sold them to me, he said he tried all different injectors and found them to work best with the ecu and they provide good fuel delivery...i think sometimes too much, but thats ok...

Sterling 525P Pistons

The Sterling pistons are produced by Federal Mogul and were ordered from Northern Auto Parts - they are a replacement piston for the 4.0
They have a slightly shorter compression height and with the shorter 258 rod ended up .055 down in the unmachined block. The head was not milled; measures 58.6 CC (on the high end of spec) and with the .065 FM headgasket calculate out to 9.1 to 1 CR.
The quench is out of the supposed spec; but the engine doesn't seem to care.
Again; this is an automatic and doesn't load the engine like a stick - 1300 RPM is about as low as it gets.
So far this thing acts just like the 4.0 - idles fine, same 195 degrees, no problems (except the mis-indexed dist (which I was informed by Jeep Techs even sometimes happens with stock production cams!)

It appears that if you keep the CR down you can run 87 octane - some early strokers were assembled at 10-1 because they milled the head and block and those have problems on low octane fuel.

Is this the absolute best setup - probably not.
But my next one has the heavy crank, 2000 stiffened block, 7120 ported head with Ls1 valves, and probably forged pistons and 4.0 rods. (about 1/2 way done now!)

I'm doin' a stroker right now--- and I looked into it just like you--- and I found Accurate Power was the best way to go. Rather than look around for parts and not know for sure if its gonna work--- Mike over there sent me everything I needed for just over $1400 shipped.

Still a LOT of money--- but I expect it to be worth it.

I have full coverage of everything I'm going on my webpage.
As you can see its been a LONG project--- I've just been doin' it in my spare time. I have 2 other vehicles too.

Project 4.6L

Sounds like the higher cc head with the .065 gasket was the right combo, sounds like a sweet motor.
Steve it looks like you're about ready to drop it in, let us know how it works out. I'm really surprised that there aren't a lot of Dyno charts out there on the 4.0 as plentiful and popular as it is.
Eagle, I reread you're post, I see that you mentioned you didn't know if the pistons were the same in both build ups. my bad.
The one thing that seems to be consistant with all the sucessfull strokers is that they make tons of torque in the low and mid-range.... exactly what I'mlooking for. Thanks. TC

Yes! Did you see my desktop dyno screen shot on my web page? My Stroker should top out just over 320 ft lbs around 3k rpm... at ALL times between 2k rpm and 5k rpm it makes at LEAST 300 ft lbs. MmMmmmmMMmMm torque

Re: Sterling 525P Pistons

rsalemi said:

The Sterling pistons are produced by Federal Mogul and were ordered from Northern Auto Parts - they are a replacement piston for the 4.0
They have a slightly shorter compression height and with the shorter 258 rod ended up .055 down in the unmachined block. The head was not milled; measures 58.6 CC (on the high end of spec) and with the .065 FM headgasket calculate out to 9.1 to 1 CR.
The quench is out of the supposed spec; but the engine doesn't seem to care.

Click to expand...

The chamber is outside the questionable zone for poor quench. It should work good.

One misunderstanding about quench is that it's useful importance is more where not to build chamber clearance, rather than a magic number for what works. There is a narrow clearance range where the chamber promotes detonation: a range from ~0.065" to ~0.110".

Run less clearance, less the 0.065", and you prevent detonation by not having enough clearance volume in the perimeter to sustain combustion, and gain some power and emissions benefit from the charge turburlence of compressing all the charge to a centralized location in the chamber. The need for tight perimeter quench clearance becomes more critical, demands a tighter clearance, as the compression is raised higher. The step from the perimeter quench band needs to be distinct between it and the resulting chamber (sometimes hard to accomplish with an irregular piston dome).

Run more clearance, more than 0.110", and you prevent detonation by not allowing the charge volume to experience the localized high pressure regions that promote detonation. You may lose a little turburlence, and you lose the emissions benefit of the more tightly controlled charge density at ignition, but not much power in the rpm ranges we operate the 4.6L six. Real power loss is not that great for a 9:1 compression ratio engine.

Where you have to be careful with quench, is the 10:1+ engines with poor clearance volume (~0.070-0.100") and where the three dimensional chamber shape has irregular sharp edges to develop hot spots and detonation. This is where the perimeter quench clearance has to be idealized and compared to the irregular chamber/piston clearance. Some chamber shapes have no perimeter quench band and can be a detonation problem (some of the older AMC six chambers for example). Lucky for us, most modern engines use flat top or dished pistons that prevent this piston dome interference problem by design.

Large bore engines suffer the most power loss from designing on the wide side of the poor quench range because it is simply more difficult to efficiently light a large chamber with a single plug (the old Chrysler hemi's used dual plugs to overcome the drawback of the large hemi clearance volume). If you are building an open chambered late 60's or early 70's BBC or BBF into a high performance package, with irregular pop up pistons, be aware of the quench trade-off. The Chrysler hemi of the same age avoided the problem with a fairly smooth high compression piston dome (sometimes it's better to be good by chance, rather than over-engineer the design with misunderstood concepts).