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I apologize in advance, but I have just been unable to find this information. I basically want a simple yes or no as to whether I'm thinking about this right.
Below is what I'm potentially planning on:
0.020" over
4.2 Crank/Rods
0.010" decking of block
stock overbore pistons
stock head gasket
According to my calc's (or the spreadsheet I have anyways) this results in:
9.51:1 CR
0.0905 Quench
4.6L/276 cu in.
What I'm leary about is the quench. I don't fully understand what's "good" or "bad" and if what I'm planning on is going to cause problems. Ideally I would like to run this on 87 but don't have a problem running 89 or 91 if I have to.
I know that I could get pistons with increased dish vol. to drop the CR and go with the performance head gasket to get the quench closer to stock, but my question is do I need to or will what I have planned work okay?
Honsetly I am not sure, mine is an Accurate Power kit (before they went out of business) I think it is lke 9.5:1 or maybe even a bit higher as I know they decked the block pretty far on mine.
Sounds like you are building a fairly "stockish" type engine. If that's the case build it for cheap and run mid grade or premium fuel. You either have to give up some CR or quench to get away with not spending money on custom parts.
You could use a thinner head gasket to get some quench back but you would have to open up the combustion chamber a bit. I got 3 cc's with a mild clean-up and with out altering the shape of the CC too much.
It all depends on how deep your pockets are.
Ryan can you elaborate on this? I just got my 4.0 mopar performance head gasket, which I believe is thinner than stock, although I don't know how much. I am porting/polishing the head and was planning on keeping the shortblock stock because this is a short term engine anyway. Did I forget something? Or will I have to run 89 octane instead of 87 now?
Well, I will have to talk to the shop who is assembling it to see what they are planning on for pistons. I was planning on the stock-style Speed-Pros for 0.020" over which I believe have a 13cc dish volume. I am trying to avoid having to have a lot of extra machine work done because more machining = more $$$
my brothers 4.7 has custom pistons to keep the CR 8.8 and run regular gas with no detonation. here is info on the engine we built:
http://www.jeepsunlimited.com/forums...hlight=stroker
The stock compressed head gasket is something like 0.043, the one we used was special order and was 0.052 (IIRC - going off memory). Not that big of a difference in the big scheme of things but enough to make a difference if you are already dealing with higher CR's than you want - like on the stroker engine in the OP. I was basically saying that you could use a thinner head gsket to get the quench measurement down closer to stock and then remove some material in the combustion chamber to help lower the CR.
In your case is sounds like the minimal difference in HG thickness will be made up for if you just polish and deburr the combustion chamber. I'm sure 87 octane will be fine in your engine.
Hope that helps.
I just got off of the phone with a Keith Black tech, tell me if this sounds any better than my original configuration.
258 crank
4.0 rods
0.030" over
0.010" decking of block
stock head gasket
KB 2229030 pistons
This results in a CR of 9.2:1 and quench of +.002 over stock. I'm thinking this is the better route, the only bitch is I've already bought the 4.2 rods
Well, as they always do, plans changed again. Been thinking and reading all afternoon and it just doesn't make sense to spend the money to put this together and have the quench so bad that I get horrible knock. I'm a little disappointed that I already bought the 4.2 connecting rods sense I've decided to go the KB forged piston route and 4.0 rods, but should be able to sell them for about what I paid for them.
My final setup is going to be:
-258 4CW crank
-stock 4.0 connecting rods
-KB944 pistons (21.7 cc dish & 1.353 comp. height), no more than 0.030" over depending on what the shop says upon gaging the block
-0.020" decking of block
-Comp Cams X4250H-13 cam
This should result in good CR and quench numbers
CR: 9.35:1
Quench: 0.0605" (0.012" above stock)
This is going to cost me a bit more since the forged pistons are about $75 each but in the end I think it will be more reliable and run better with less worry of knock.
That sounds like a pretty good build. We just went through all of this CR and quench stuff with my stroker, so I'm fairly new to this, but here's what I learned with mine.
I did the "poor man's" stroker like is outlined on Dino's 4.0 website. Basically consisted of 4.2 crank and rods, Sealed Power 802 pistons dished to 18cc's, thin Victor Reniz head gasket (~.038"). My final numbers were SCR 9.25:1, DCR 7.96:1, and quench height of .081". The motor ran ok on the 87 octane fuel that was in the tank before the rebuild. I have been running 89 (mid) in it ever sense with no pinging at all.
You should look at your dynamic compression ratio (DCR) more than your static (SCR) because that factors in the opening and closing of the exhaust ports. You can't create compression in the cylinder until the exhaust port is closed.
Jeepstrokers.com is a forum dedicated to builds like yours. They helped me out a lot.
Last edited by rradford9; 03-23-2009 at 09:27 PM.
Did you get a price on the KB944's? My 4.7L is a 96 NVH block 4.2 crank and rods. .060 over Speed Pro pistons my piston to deck clearance is .055" my compressed head gasket thickness is .046"(stock Mopar MLS gasket). Right now I'm still running the old style fuel system with a pressure regulator and have the regulators vacuum line off till I get the right injectors but right now I'm not getting any pinging or anything running 87 octane since that is what I filled it with before the engine swap.
Pics and more info on jeepstrokers.com under Stroker basics
http://http://www.jeepstrokers.com/forum/viewtopic.php?f=15&t=651
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