tom9193

my '99 xj limited is getting up there in miles and im thinking my cylinder head is shot i was thinking about , what about a engine rebuild although the inline 6 4.0 engine is a great piece of machinery and was wondering if a normal rebuild would be best or i was reading up on stroker engines and still not sure if the pro's out weigh the con's... my rig is a daily driver but i have all the usual upgrades (bored T/B,flowmaster exhaust,2 1/5 inch exhaust pipe,hi performance cat,header,neon injectors,k&n fipk air intake and more) i don't do any wheeling i want to find out what is the cheapest way i could stroke my engine and get better performance but still be able to keep using regular octane fuel??

Agony Wagon

If you want to run 87, you'll probably want to keep DCR at no more than 8.0:1. Might be able to get away with a little higher, but it's a gamble. If you want a higher compression ratio, you'll probably need to run premium. If you want to stay on 87 for the money, you're probably better off just doing a rebuild.

There are all sorts of ways to build a stroker. Some ways cost more than others. Lots of info over on jeepstrokers.com. It's far more complicated of an issue than lift kits, so expect to spend hours and hours reading.

tom9193

i read on this website http://www.ajeepthing.com/stroker-motor.html
If the stock Jeep 4.0L 6.125" rods are used, expensive custom forged pistons with a shorter pin height than stock (1.380") are required to achieve zero deck clearance. Using longer rods does enable you to choose pistons with a larger dish volume than stock. These reduce the CR and allow the use of low octane fuel without detonation. You can also use a shorter duration camshaft for increased low-rev torque, and select the head gasket thickness required to achieve the desired 0.040"-0.060" quench height.

Agony Wagon

Yeah, there are ways you can achieve a certain compression. Dishing the pistons is one way. Gasket thickness, valve timing, and increasing the bore are others to increase or decrease compression. Decreasing quench, cooling the intake air, and polishing the chamber can reduce the likelihood of detonation a bit. But still, the dynamic compression ratio is the main determinant.
Unless you're going to drop $2000 on an aluminum head, detonation on 87 is much more likely to occur when DCR gets over 8.0:1, on U.S. gasoline blends, running near sea level atmospheric pressure.

BBuchta

How many miles are on the engine? I had a 97 with 230K on the clock and pulled it apart to do a stroker because I assumed it was worn out. All it needed was a valve job, the lower end was still within factory spec. I scrapped the stoker idea, replaced the valves, springs and did a mild port job around the valves and probably picked back up 10-20hp. Tossed in a new oil pump for cheap insurance wile I had the bottom end apart. If properly maintained, these engines last a long time.

tom9193

i got my xj when it had 70k miles i have taken very good care of my truck i have 125k+ miles , i have to get some tests done by my mechanic , i have the magical disappearing coolant and i've done all the tests i could do but im pretty sure my cylinder is cracked and if i have to replace the cylinder head i was toying around with the idea of maybe do a complete engine rebuild or a stroker..

BBuchta

Ahh well in that case I'd go with a new or used replacement head and have the block checked as well.

tom9193

yea but if im gonna have to rip half the engine apart why just fix it when i can make it better if i can...here is another link i found about strokers and can still use regular ocatne fuel and still get more power... i know its based on a yj but it still is the 4.0 liter engine... http://www.rockcrawler.com/techrepor...er40/index.asp

tyler_zj

I have a new crate that has 9.25:1 compression and I run 91oct but can run 89oct still fine

Agony Wagon

The compression ratios in that article are static, not dynamic.
When it says "The stock 4.0L HO has a compression ratio of 8.8:1 and Jeep recommends a minimum of 87 octane fuel," they're referring to static compression. The air in the chamber doesn't actually get compressed until the valves are fully closed. In the HO, this gives a compression ratio of about 7.5. I think the Renix engines are lower than that.

You'll also notice he states he is at 6000' altitude. That alone will drop his DCR by 1.0 or greater.

He's running 9.5 SCR and a .060 over-bore. Assuming he didn't change the cam, or the dish on the pistons, his DCR at 6000' would be about 8.0:1. If he drives down to sea level, that puts him at about 9.2:1, which would ping on 87 octane.

http://www.jeepstrokers.com/calculator/

Watch out for those compression ratios. You'll find most of the time people are talking about SCR. DCR calculation is a bit more involved. Use the handy link above to help you plan your stroker.

2001Classic

look into the 505performance.com stroker kits....they have 3 stages

Tom95YJ

Bad advice. Look up their reviews. Wrong parts shipped several months between order and shipping. They are well known to be bad.

Google the jeep strokers forum. And start reading.

tom9193

i have been checking out jeepstokers.com and its ALOT!! of reading!!!!some of it though i have no idea what is being explained(compressions,ratios,squelch etc. etc) i am far from a mechanic but i am good with my hands and usually find out and figure out how to fix my jeep as much as i can!! i love that feeling of taking care of my baby and doing it myself but i am very limited with tools,garage and knowledge..it seems like the majority of what is mentioned is the stroker engine it self and have not found anything yet about like i said is a rebuild with better than o.e.m parts more feasible for me financially or physically or a stroker

cleenrob

im kinda in the same boat. not sure if i want to stroke it or just rebuild it with a mild cam/ 99 intake/ and a ported and polished head. in addition to what ive got now

Jamie57

Here is a thought. If the crank and most internal parts of the 258 will fit the 242 (4.0) block why not just slap a HO head on it and the newer intake exhaust and MPFI? I mean it's already 16 cubic in bigger. Saves having to bore out the block and adding custom pistons. Is the 4.0 block that much stronger better faster whatever than the 258?
Can't you put the 4.0 cam in the 258?

I have a 99 block I was going to stroke by putting the 258 crank in and boring out 40 thou. It just hit me that I might as well just use the 258 with more cubic in and a newer head.
Is my reasoning flawed?

Oh and I want specific answers. Not my cousins wife knows a guy whose girlfriend once went out with a guy who was sure it wouldn't work but he never tried it crap.
If you have specific knowledge or can point us to a link on the web than chime in.