New to engine performance.

[bambam0417]

Im new to the site and am intruged with the idea of stroking a 4.0l. A Little backround, I have been working as an auto/heavy truck/ ariel lift mechanic for the last 7 years, but never got into engine perfornence. I have a 98 jeep cherokee with a strong running 4.0l with 154,000 miles. Ive done a little tinkering and have up graded fuel injectors, bored throttle body, replace my muffler with a flowmaster super 44 and converted my drums to disc brakes. Now Im not going to stroke the motor unless it dies and im going to rebuild it but I have some questions about this if I did build it. From doing some research i think my options seems to be a 4.2l crank and rods or 4.2l crank, 4.0l rods, and custom forged pistons. Now are these technically all the parts I need to stroke a 4.0? Now if I did end up rebuilding my engine I would obviously have the head and block freshened up bored .030 over, get a master rebuild kit, possibly a mild cam,a 4.2l crank and rods, and typical rebuild parts (water pump, theromstate, etc). From looking around people say they got their motor build for not much more then a typical rebuild would have cost them (estimating $2000), but I see some people spending $4000 to $5000. can a reliable stroker be built for alittle more then a typical rebuild? This would also be my DD so I would like to beable to run on regular gas 87 octane here. what is the highest compression ratio that I can run with regular? Like I said I'm new to engine performance and would like to learn/put that knowlege to good use someday.

[bambam0417]

sorry for some reason my computer posted this twice.

[Cheromaniac]

My advice is that you buy a decent complete junkyard 4.0 engine from a '96-'98 XJ, tear it down, gradually buy in the parts you'll need to rebuild it into a 4.6 stroker as your budget allows, hire a good machine shop to do the necessary prep work, reassemble the engine, and swap it into your Jeep when it's ready.
After you've run the stroker for a few thousand miles to make sure it's reliable, sell on your old 4.0 engine to recoup some of the cost. Hopefully the buyer will rebuild that into a 4.6 stroker and give it the second life it deserves.
That's exactly what I did 8 years ago on my XJ and here's my stroker parts list:

http://www.angelfire.com/my/fan/parts.html

I know parts were cheaper back then so it would cost more to replicate what I did but it does show you what's possible. The only thing I'd do differently if I was going to build another stroker is to keep the stock 4.0 rods and use Keith Black IC944 pistons instead of the 4.2 rod/677P piston combo.

[bambam0417]

My advice is that you buy a decent complete junkyard 4.0 engine from a '96-'98 XJ, tear it down, gradually buy in the parts you'll need to rebuild it into a 4.6 stroker as your budget allows, hire a good machine shop to do the necessary prep work, reassemble the engine, and swap it into your Jeep when it's ready.
After you've run the stroker for a few thousand miles to make sure it's reliable, sell on your old 4.0 engine to recoup some of the cost. Hopefully the buyer will rebuild that into a 4.6 stroker and give it the second life it deserves.
That's exactly what I did 8 years ago on my XJ and here's my stroker parts list:

http://www.angelfire.com/my/fan/parts.html

I know parts were cheaper back then so it would cost more to replicate what I did but it does show you what's possible. The only thing I'd do differently if I was going to build another stroker is to keep the stock 4.0 rods and use Keith Black IC944 pistons instead of the 4.2 rod/677P piston combo.

I do agree that buying a complete long block from a JY and rebuilding that motor is most likely what I would do. Nice write up on your parts list! how much of a power difference did you notice after going to a 4.6l? since this is where I would be looking to end up. Why would you perfer to run 4.0 rods and keith black IC944 pistions instead,is there any advantange over 4.2 rods and stock pistons? Also what octane gas do you run? Sorry about all the questions I like to pick people brain for information when I find something I am interested in.

[Cheromaniac]

I usually run 91 octane over here just to be on the safe side 'cause the outside temp. is 100+*F for six months of the year. During the cooler months the engine will run fine on 87 octane most of the time.
The 4.2 rod/Z677AP piston combination works fine but the 4.0 rod/IC944 piston combination is better. Quote from my site:

The 4.0L connecting rod/IC944 piston combination offers 155g less reciprocating mass than the 4.2L rod/677P piston combination (1275g v 1430g), thereby giving this engine a potentially higher rpm capability than the traditional "poor man's" stroker.

The power increase with the 4.6 stroker over my old 4.0 was very noticeable but the biggest difference was from idle-4000rpm. The stroker has incredible low rev grunt so I have to watch my speed very carefully to avoid collecting speeding tickets 'cause I can pootle along at 50mph in 5th gear with the tach at less than 1500rpm and hit 70mph before I know it. The Jeep feels much quicker than the dyno or 1/4 mile numbers would suggest. Driveability is excellent and the throttle response is neck-jerkingly sharp.

[bambam0417]

I usually run 91 octane over here just to be on the safe side 'cause the outside temp. is 100+*F for six months of the year. During the cooler months the engine will run fine on 87 octane most of the time.
The 4.2 rod/Z677AP piston combination works fine but the 4.0 rod/IC944 piston combination is better. Quote from my site:

The 4.0L connecting rod/IC944 piston combination offers 155g less reciprocating mass than the 4.2L rod/677P piston combination (1275g v 1430g), thereby giving this engine a potentially higher rpm capability than the traditional "poor man's" stroker.

The power increase with the 4.6 stroker over my old 4.0 was very noticeable but the biggest difference was from idle-4000rpm. The stroker has incredible low rev grunt so I have to watch my speed very carefully to avoid collecting speeding tickets 'cause I can pootle along at 50mph in 5th gear with the tach at less than 1500rpm and hit 70mph before I know it. The Jeep feels much quicker than the dyno or 1/4 mile numbers would suggest. Driveability is excellent and the throttle response is neck-jerkingly sharp.

Im in new jersey so it is in the 90s for a mounth or two during the summer so I guess octane issue shouldnt worry me. Im reading that alot of 4.0 stroker failures seem more to be due to aftermarket cams, lifter, and valve spring combination. From reading this i would probably just stick with the 4.0 cam and valve springs. The rev limit would be at stock engine spec which I think is roughly 5300rpm. I very rarely get it over 4000rpm so im not to much concerned with being able to increase my rev limit being the valve would still float at the stock rev limit. not that I would total exclude the 4.0 rods and piston combination. Also I read some stuff about the pistons in that combination wearing faster if they arent given time to warm up some. have you heard anything about this?

[amcinstaller]

its because its a forged piston. they need a little more heat and time to expand the skirts properly. also, youll have piston slap when you first start it on a cold morning. not much to worry about if you just treat it right.

[bambam0417]

its because its a forged piston. they need a little more heat and time to expand the skirts properly. also, youll have piston slap when you first start it on a cold morning. not much to worry about if you just treat it right.

I know the 4.0s in general are known for piston slap, mine does it now. If I used the 4.2 rods and new stock 4.0 pistons do you think this could still be a problem? Also Keith Black IC944 pistons are forged aluminum. what metal is the stock piston made of?

[SilverXJ]

its because its a forged piston. they need a little more heat and time to expand the skirts properly. also, youll have piston slap when you first start it on a cold morning. not much to worry about if you just treat it right.

The KB944s are 4032 alloy. They only need .003" on a street engine. Minimal noise. Maybe for the first two minutes. However, ANY engine shouldn't be driven hard when cold.

I don't remember what year it was but the 4.0L switched from cast to a hypereutectic piston (more silicon).

[amcinstaller]

i must have been thinking of another piston. i remember reading it here. oh well

[bambam0417]

its because its a forged piston. they need a little more heat and time to expand the skirts properly. also, youll have piston slap when you first start it on a cold morning. not much to worry about if you just treat it right.

The KB944s are 4032 alloy. They only need .003" on a street engine. Minimal noise. Maybe for the first two minutes. However, ANY engine shouldn't be driven hard when cold.

I don't remember what year it was but the 4.0L switched from cast to a hypereutectic piston (more silicon).

Yea I let mine warm up until the noise goes away, roughly a min or to depending on engine temp. but would lover to have an engine with no piston slap.

[604rail_king]

There's cast, hyperutectic, forged 4032, forged 6018 ... And likely more depending on application. What this means is they are all made from different metal compositions and therefore have different expansion/contraction rates. They also have different strengths and weights. Some pistons you can machine for a tighter fit and others need more clearance to allow for metal to expand under heat and even boost

The kb944 are forged 4032 which allow for tighter cleaned and less likely to have audio able slap. Much like cast or hypers

[Cheromaniac]

its because its a forged piston. they need a little more heat and time to expand the skirts properly. also, youll have piston slap when you first start it on a cold morning. not much to worry about if you just treat it right.

Yeah, just drive gently from a cold start and don't start revving the engine until it's reached normal operating temp.

I don't remember what year it was but the 4.0L switched from cast to a hypereutectic piston (more silicon).

Chrysler changed to lighter weight pistons in 1996 (not sure if they were hypereutectic) and they seem to be more prone to breaking at the skirts.

My old 4.0 had a little cold start piston slap but in my stroker it's virtually non-existent (4.2 rods, cast 677P pistons).

[SilverXJ]

its because its a forged piston. they need a little more heat and time to expand the skirts properly. also, youll have piston slap when you first start it on a cold morning. not much to worry about if you just treat it right.

Yeah, just drive gently from a cold start and don't start revving the engine until it's reached normal operating temp.

Mine has very little piston slap noise and usually goes away in a minute or less. This is with KB944s w/ .003" piston to wall clearance. Its usually noticable in the winter, and hardly on warmer days. However, I usually drive it easy until the oil is warmed up a good deal.

I don't remember what year it was but the 4.0L switched from cast to a hypereutectic piston (more silicon).

Chrysler changed to lighter weight pistons in 1996 (not sure if they were hypereutectic) and they seem to be more prone to breaking at the skirts.

My old 4.0 had a little cold start piston slap but in my stroker it's virtually non-existent (4.2 rods, cast 677P pistons).

1996 was the year they changed to hypers as well. They are more brittle than straight cast (hypers are cast as well) due to the higher silicon content, but they allow for a tighter piston to wall clearance. My 1995 ZJ has some piston slap all the time.

[Cheromaniac]

1996 was the year they changed to hypers as well. They are more brittle than straight cast (hypers are cast as well) due to the higher silicon content

There's no doubt that hypereutectic pistons are more brittle than cast or forged. I've seen a hyper piston on a Jeep engine shatter like glass and fill the oil pan with fragments. Not a pretty sight. However most modern engines use hyper pistons because the piston-to-bore clearances can be kept tighter, reducing oil consumption and hydrocarbon emissions.