Are KB's worth it?

[jimmydaux]

Hey guys quick question. Ive been lurking this forum for quite a while planning my stroker.

Im trying to decide which pistons to go with so I can figure out what needs to be done with my block. I plan on going 40 or 60 over, and would like to get quench into an ideal realm. So my question is this,,

If I plan to deck my block for flatness and could easily have it cut down to get good quench regardless of my pisont/rod combo, Is the benefit of using the stock 4.0 rods worth the added cost of purchasing KB's or Custom pistons? I have the set of rods out of my 98 as well as a a set from a 4.2 so sourcing is not an issue. Im not too concerned about doing a super budget build but would like to keep it reasonable. Deciding where my piston is going to end up in the bore seems to be my next step so I can get work started on the block.


When I pulled my 98 donor motor apart it looked almost brand new with 212k miles on it. Is there any way to tell if it has been rebuilt. I looked at the bearings and didnt see any markings that indicated they were oversized. The crank looked flawless, and the piston walls still had most of the crosshatch bore lines. The cam had zero markings on it.

Would I be able to reuse the lifters, pushrods, rocker arms and mounting hardware? I do plan on using an aftermarket camshaft. Eventually id like to go to roller rockers but not anytime soon.

Thanks for your help in advance. I will try to keep my questions to a minimum through this build.


Jeremy

[dwg86]

Go to http://www.bulltear.com You can have custom pistons made for $475.00. I do believe that's cheaper than the KB's, and you can get what ever compression and deck height you want.

[jimmydaux]

Yeah ive found that there are some decent priced custom pistons out there, but they are still quite a bit more expensive than a set of off the shelf silvolites or sealed power. When trying to keep the budget lean, is it worth it to incur the added cost of custom slugs?

[jimmydaux]

No insight on this? Any help would really be appreciated. I'd really like to get things under way and this is proving to be a hanging point.

Jeremy

[Exos]

I'm no professional builder, but KB's are good stuff according to me... besides the fact that they came with wrong instructions.

Oh, and don't reuse your lifters if you change your cam!

[jimmydaux]

So KB's with 4.0 rods or Cheaper off the shelf pistons with 4.2 rods? Is the first combo worth the extra $300+?

[shawnxj]

i'm actually in the same boat as jimmy. looks at the recipes from dino's page is an extra 13 hp worth the extra money?

[SilverXJ]

The longer 4.0L rod will give you the benefit of more piston skirt in the cylinder which reduces piston rock at the bottom of the stroke. The KBs are also forged which will give you a stronger piston verses the 4.2L rods/ hyper pistons. That will give you more resistance to piston failure from pre detonation (ping and knock) than a hyper or cast piston. The longer rod is also said to give you more torque, but I am not sure I believe that. The draw back is you have to run more piston to cylinder clearance, which will give you a noisy start up in cold weather until the pistons heat up and expand (5 minutes at most). However, the newer KB944 pistons are made from 4032 alloy which means you can run less piston to wall clearance than the prsvious 2618 alloy they used. Its something like .004" vs .0025" on the clearance. The only other draw back is that if you want a very good quench you have to have the block decked with the KB pistons as they usually sit .030" down in the bore. The other alternative is to look into bull tear (http://www.bulltear.com/catalog/index.php) which is offering decent priced custom pistons for the 4.0L rod and longer rods (eagle and I think they also sell a longer rod).

[gonridnu]

I agree with Silver. When you look at the overall cost of building an engine it is not a significant cost difference for the benefits he cited as well as.

1. Better rod to stroke ratio reduces side loading
2. Lighter piston by about 100+ grams
3. Designed with correct dish to achieve a tight quench and reasonable compression ratio. As I understand it the short rod engines cannot achieve a good quench number without dishing the piston AND decking which all costs $.
4. Forged pistons have higher thermal conductivity than hypereutectics reducing the chance for for detonation because they run cooler.
5. KB/Icon pistons feature a gas accumulator groove between the 1st and second compression rings that is designed to help equalize the pressure and provide a better ring seal

To me personally building an engine and installing it is a huge investment of time and money. I cannot make a financial decision or determine the value of something for somebody else, however I believe the benefits vs. additional cost to be "worth it".

Just make sure you get the blue instruction sheet...LOL

[jimmydaux]

Silver and Gonridnu,,, thanks a million for your post. I knew there was a wealth of information out there that was just waiting to be tapped. Thank you for the input. I guess a few hundred isnt too much to spare to build the motor the right way. If I dont have to deck the block, that would offset a fair amount of that cost as well. Guess its time to get it to the machine shop to see what work has to be done on it.

Jeremy

[gonridnu]

I had to deck my block .027" to get near zero deck....the shop I'm borrowing charges $85 and we are on the west coast which tends to be more expensive than back east.

[lafrad]

Just a slight correction... Rod length will never change how much stroke the piston will travel... The piston will come out into the crankcase the same amount with ANY rod... given the 4.2L stroke crankshaft.

All of the other comments seem spot on.

[gradon]

No correction needed-no one said the longer rod made for a longer stroke, but that it made for a better rod-to-stroke ratio, which helps reduce side loading of the piston on the thrust side of the piston(less friction).

[gonridnu]

I think it was in reference to the stock style pistons having a longer skirt than the KB's....

[shawnxj]

so would you do the kb's over the bulltear pistons? i have a 99 engine that's gonna be turned into a stroker to put into my 88 cherokee. i haven't decided if i'm gonna do a stand alone fuel injection setup or go put an obd2 setup yet but will have to decide soon because i'm about to start getting into the build in the next month. also would you use the stock rods and just have them cleaned, destressed, and shot peened or would you go with a new set of eagle rods. what's the benefit of a floating wrist pin compared to a pressed fit other then not having to have the pistons installed by a machine shop? my bugdet for this build just increased dramatically because i got a new job so now instead of doing a 4.6 poorman's stroker i'm thinking of doing a 4.7.