cylinder bore question

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cylinder bore question

Post by Exos »

Hi,

I'm new here, and somewhat new to engine building and specs. I plan on building a stroker with a '95 block I bought. Here's my plan:

258 crank
242 rods (6.125")
KB944 forged pistons 0.060 oversize, 21.73 cc dish

I aim for a 0.040-0.060 quench distance.

That's the base, not sure yet about the cam and other stuff. I may keep the stock cam and valve springs, if feasible.

I have two questions :

1- KB pistons say on their webpage that the piston to bore clearance should be .0040" - .0050". Does this mean I have to add this to my rebore size (3.875+0.060+0.0045=3.9395")? Or do I tell the machinist to bore to 3.935" (3.875+0.060)?

2- Is it possible to calculate deck clearance on paper, or is it better to wait for the pistons and do a test assembly with one piston?

Thanks.
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Re: cylinder bore question

Post by Mgardiner1 »

Any good machinist will tell you that they will not bore your block until they are holding the pistons in their hands. They do this so they can phisically measure the piston, and then add the "clearance" to it, this way they KNOW that the piston clearance is correct, rather then just go by paper specs.

You can calculate deck height on paper, however it will give you a range. If you check in the FAQ section, for instance, :1999 4.0 engine Deck height = 9.450 - 9.456 inch". so you can figure out your deck height, with a .006 margin. Its best to let the machinist measure things up with the pistons and all of your specs. I included a data sheet with mine that had rod length, compression height, and deck height, but he said he measured anyway to confirm my specs.
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Re: cylinder bore question

Post by IH 392 »

Mgardiner1 wrote:Any good machinist will tell you that they will not bore your block until they are holding the pistons in their hands. They do this so they can phisically measure the piston, and then add the "clearance" to it, this way they KNOW that the piston clearance is correct, rather then just go by paper specs.
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Re: cylinder bore question

Post by Exos »

Ok, thanks. That answers my questions.

I have one more about cams :

Can I keep my stock cam and valve springs, or should I buy a performance cam, like say a mopar purple? I know I won't buy a Crane with all the bad things I read about them... :shock:
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Re: cylinder bore question

Post by dwg86 »

Personally I would go with a performance cam. Your engine is going to be bigger so a bigger cam will help it breathe. As far as a mopar cam, the only ones left are the 228AB's. The 229AB and 230AB have been discontinued. As far as aftermarket cams go, my opinion would be to stay away from the big cam manufacturers, and have one custom ground from Reed, Engle, or some other smaller cam company. I like the ideal of picking my own specs to what's going to work for my build. I have built a lot of engines and have used cams from the bigger companies and from Reed. I have found the Reed cams right on when degreeing, and the finish on the lobes is better. I have also had better customer service from the smaller companies.
I went with an Engle cam for my stroker. They have new grinds made for the large AMC/Chrysler .904 diameter lifters. The new grind takes advantage of the large lifter. The lobe has a fast ramp that acts more like a roller. I went with a straight lift/duration: 214 [email protected] and 500 lift, with 3 degrees advance ground in to cam. I don't have my engine together yet, so I don't know it's going to perform. This is the first time I've used an Engle cam, but they have a good reputation.
I have a Reed cam in my 1979 Jeep CJ5 401 (228/232 dur @.050 and 512/518 lift, 10.5:1 compression). No problems, and will pin you to the seat when you stomp the skinny pedal. :rockout:
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Re: cylinder bore question

Post by jffffl »

Check your rod choice when using the KB 944 piston, I thought they were for use with the 4.0l rod,
not the 4.2l as you mention above. Please correct me if I'm wrong, as i have two sets of 4.2 rods,
and thinking of purchasing the KB 944 and a set of 4.0.
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Re: cylinder bore question

Post by SilverXJ »

jffffl wrote:Check your rod choice when using the KB 944 piston, I thought they were for use with the 4.0l rod,
not the 4.2l as you mention above.
They do, and from what I see in his first post he does. 242=4.0
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Re: cylinder bore question

Post by Exos »

I would like to keep filling up with regular pump gas (87 or 89? octane). What is the upper limit of CR and DCR that you can't go over?

Depending on my cam choice, my CR should be around 9.7:1 and DCR around 7.8:1. My quench distance should be between 0.040 and 0.050". I have cold air intake too, homemade but efficient.
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Re: cylinder bore question

Post by SilverXJ »

see here: viewtopic.php?f=15&t=528
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Re: cylinder bore question

Post by Exos »

OK, so I pretty confident I will run 87 octane with my setup, if quench is real close to 45 and DCR below 8.

Worst case scenario, I'll have to use "super".... no big deal.

thanks.
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Re: cylinder bore question

Post by Flash »

With DCR in the HIgh 7s, and quench in the 40esh............I'm pretty sure it will like the cheap stuff ;)

Just remember, what looks good on paper.......Isn't always reality when its all said and done.


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Re: cylinder bore question

Post by Exos »

Can't have the KB944"s until January... so it's "stay tuned" for the rest of the story...;)

I did not find a 258 , 12 CW crank yet either, so I'm waiting for this too.
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Re: cylinder bore question

Post by SilverXJ »

Sounds like what I went through. I gave up on the 12 weight and got a lighter one.
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Re: cylinder bore question

Post by Exos »

Found a 12 cw crank for 225$ CND including rod and main bearings. I'm going to pick it up this week or next. I will be removing my cylinder head tomorrow, and probly the pistons, rods and crank too. I'll try to post some pics soon.
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Re: cylinder bore question

Post by Exos »

Ok, another question comes to mind : After decking the block, and when all is ready to assemble, will I need stock length pushrods, or shorter ones? How do I measure the exact length I need? Is it OK to put shims under the bridges if my pushrods are too long?
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