New 4.2L mini-stroker recipes

Newbies, and basic Stroker Recipes... Get started with your first stroker here!!
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Re: New 4.2L mini-stroker recipes

Post by Cheromaniac »

IH 392 wrote:That cam will work in your block, but you must retro the timing chain and possibly the cover too.
Did they say how much vacuum that cam generally produces??, according to two map sensors and my scan tool the OE OBDII cam only produces 12" :huh:
That doesn't sound right. The Crane 753905 cam produced 17" vacuum at idle in my stroker and my current '92 stock cam is surely producing more than that.
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Re: New 4.2L mini-stroker recipes

Post by IH 392 »

I never did put an actual vacuum gauge on it to see what it was?, I changed out the map sensor because it showed 12" on the scan tool and just shrugged my shoulders when the second one said the same thing?, I just kind of assume that's why it's had a, shall we say NOT! "stock" type idle quality from day one!?, and I know it was 100% OE, I ordered the Jeep and it had 3 miles on it when I took possession of it in March of '97.
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Re: New 4.2L mini-stroker recipes

Post by Knoxes »

I'm concerned about the quench on the mini recipe. It looks like it works perferctly if there isn't any decking. But my machine shop is advising to deck both the block and the head. He'll start at 0.002 and cut until it's flat. As it is, with the 2229 piston (just ordered), I think I'm looking at 9.456, so the quench will equal the thickness of the gasket. But if he takes off 0.01 total, I'm down to 0.03 quench. Any more than that, and it's getting too close. How do you address this?
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Re: New 4.2L mini-stroker recipes

Post by Cheromaniac »

Knoxes wrote:But if he takes off 0.01 total, I'm down to 0.03 quench. Any more than that, and it's getting too close. How do you address this?
A quench of 0.030" will probably still be OK but only just. You could try a thicker head gasket (OEM).
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Re: New 4.2L mini-stroker recipes

Post by Desertjr »

I know the naxja koth jeep runs a stroker and has a .028 quench. Richard aka goatman has a stroker in his chopped xj and runs a .026 I believe and somewhere in the 10s for compression on 91 Cali pump gas. These a reigned strokers but the quench cane tighter than .03x..how tight is the question..

I have the same option here. .038 quench with the stock .051 gasket or a .043 gasket giving me a .030. I'm building a mini stroker as well. Staying within 5400rpm & running the stock 96 cam with 1.7 rockers.
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Re: New 4.2L mini-stroker recipes

Post by IH 392 »

The "General" rule of thumb for a race engine quench is .040" for a 4" bore with .007" of skirt clearance on old school forged pistons, our engines are MUCH tighter than that, it wouldn't surprise me at all if an AMC/Jeep six didn't have any piston to head contact with as little as .010" quench with cast pistons.
The .040"-.045" is considered the MAXIMUM quench for a race engine and there is some hearsay that up to .0000" is acceptable!, this info is from the late great Smokey Yunick! :worship:
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Re: New 4.2L mini-stroker recipes

Post by sly-jeeper »

has anyone ever considered taking .011 or .012 off the top of h802's? or any others :idea:
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Re: New 4.2L mini-stroker recipes

Post by sly-jeeper »

im considering selling or trading my 258 crank and rods for a 232 and taking some off the top of my h802's :huh:
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Re: New 4.2L mini-stroker recipes

Post by torque062 »

Hey guys, I've decided to try out this mini-stroker on a 97 block for my 93 Cherokee. I plan on doing a .060" over bore and then using the 677AP060 pistons, stock 4.0 rods, .043" Mopar Performance head gasket, and the stock cam from the 97. With the 14cc dish in the pistons, 0.000 deck height, and a quench height at 0.043" that puts me at around 9.63:1 static and 8.25:1 DCR. Will this be ok to run 87 with no detonation? What kind of power should I expect to be making with that compression? Sorry for all the questions, but the 4.2L stroker doesnt seem to be covered very much.
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Re: New 4.2L mini-stroker recipes

Post by Cheromaniac »

torque062 wrote:Hey guys, I've decided to try out this mini-stroker on a 97 block for my 93 Cherokee. I plan on doing a .060" over bore and then using the 677AP060 pistons, stock 4.0 rods, .043" Mopar Performance head gasket, and the stock cam from the 97. With the 14cc dish in the pistons, 0.000 deck height, and a quench height at 0.043" that puts me at around 9.63:1 static and 8.25:1 DCR. Will this be ok to run 87 with no detonation? What kind of power should I expect to be making with that compression? Sorry for all the questions, but the 4.2L stroker doesnt seem to be covered very much.
With that rod/piston combination the pistons will be ~0.007" above the block which would leave the quench at 0.036" (good).
I've calculated your SCR at 9.78 and the DCR at 8.01. I doubt you'd be able to run 87 octane at sea level with that DCR though.
If you port your head, HP output could be in the 240-250 range.
The 4.2L mini-stroker concept is still fairly new and probably doesn't get much coverage 'cause the displacement increase over stock is small. However since the build cost is only a 232 crank more than that of a stock rebuild with oversize pistons, it might become an attractive option especially as 258 cranks are becoming increasingly scarce and expensive.
You could say that the 258 crank = Golddust, and the 232 crank = Stardust. ;)
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Re: New 4.2L mini-stroker recipes

Post by torque062 »

Cheromaniac wrote:
torque062 wrote:Hey guys, I've decided to try out this mini-stroker on a 97 block for my 93 Cherokee. I plan on doing a .060" over bore and then using the 677AP060 pistons, stock 4.0 rods, .043" Mopar Performance head gasket, and the stock cam from the 97. With the 14cc dish in the pistons, 0.000 deck height, and a quench height at 0.043" that puts me at around 9.63:1 static and 8.25:1 DCR. Will this be ok to run 87 with no detonation? What kind of power should I expect to be making with that compression? Sorry for all the questions, but the 4.2L stroker doesnt seem to be covered very much.
With that rod/piston combination the pistons will be ~0.007" above the block which would leave the quench at 0.036" (good).
I've calculated your SCR at 9.78 and the DCR at 8.01. I doubt you'd be able to run 87 octane at sea level with that DCR though.
If you port your head, HP output could be in the 240-250 range.
The 4.2L mini-stroker concept is still fairly new and probably doesn't get much coverage 'cause the displacement increase over stock is small. However since the build cost is only a 232 crank more than that of a stock rebuild with oversize pistons, it might become an attractive option especially as 258 cranks are becoming increasingly scarce and expensive.
You could say that the 258 crank = Golddust, and the 232 crank = Stardust. ;)
Lol, thank you. But I'm not sure where I went wrong calculating the deck height. Who knows, I have punched the numbers on the calulator so many times I'm sure it wasnt my first mistake.

I'll probably do some very minor porting to the head. Mainly just smoothing the surface since I'm no performance engine machinist. I'm not even sure if the rods and pistons are going to be balanced since its not going to be a high revver. I kinda planned on running 91 (which I hope it should be able to) since its what, $3-4 more per fill up? I guess I was more curious as to whether or not I'd be able to.

I'm also not sure if it would be worth going to a slightly thicker head gasket since the quench is still so low. I actually havent even started any machining yet either. I want to make sure I have done everything correctly on paper first. The engine is just going in a weekend rig that really doesnt (ever) see action above 4000 RPM because its an XJ with 8" of lift and no sway bars so I wanted to build it for more low end torque, which is why I am sticking with the 97 camshaft.
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Re: New 4.2L mini-stroker recipes

Post by Cheromaniac »

torque062 wrote: Lol, thank you. But I'm not sure where I went wrong calculating the deck height. Who knows, I have punched the numbers on the calulator so many times I'm sure it wasnt my first mistake.

I used deck height 9.453", rod length 6.125", piston compression height 1.585", stroke/2 1.750", 0.043" head gasket, 57cc chambers, ICA 60.9* for '97 cam
torque062 wrote: I'll probably do some very minor porting to the head. Mainly just smoothing the surface since I'm no performance engine machinist.
Just concentrate on pocket porting the valve bowls/throats and smoothing the valve guide bosses into a teardrop shape. That's where you'll see the biggest flow gains.
torque062 wrote: I'm not even sure if the rods and pistons are going to be balanced since its not going to be a high revver.
The pistons will already be balanced for weight so just make sure the rods are also balanced to within 1g. The idea is to make the engine run smoother and be more refined at higher rpm. It doesn't take much work and it'll be worth it.
torque062 wrote: I kinda planned on running 91 (which I hope it should be able to) since its what, $3-4 more per fill up? I guess I was more curious as to whether or not I'd be able to.
Shouldn't be a problem.
torque062 wrote: I'm also not sure if it would be worth going to a slightly thicker head gasket since the quench is still so low.
A 0.036" quench will be absolutely fine.
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Re: New 4.2L mini-stroker recipes

Post by Cheromaniac »

Karyl1Matt wrote:if you are kind enough to tell me something about the california vehicle inspection.
I live 9500 miles away from CA so that might be a bit difficult. ;)
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Re: New 4.2L mini-stroker recipes

Post by jpradcliffe »

Hey there Cheromaniac, what springs do i use in the wilder ministoker with that cam on a 1996 4.0 head?
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Re: New 4.2L mini-stroker recipes

Post by Cheromaniac »

Depends. If you upgrade to larger diameter LS1 valves, you could also use LS1 springs.
Otherwise the Mopar Performance P4529242 springs are the way to go.
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