My "stroker" plans

[W_A_Watson_II]

OK, after a lot of reading and some help from others here and else where, I think I have a set of plans (recipe) for my engine overhaul and re-build for my 1993 Jeep YJ (http://jeep.wawii.com/93YJ.htm).

□ - Jeep 4.2L 3.895" stroke crank
□ - Jeep 4.0L 6.125" rods
□ - ICON Performance Pistons IC944 +0.030" (3.905" bore)
□ - 9.57:1 SCR & 8.28 DCR
□ - 1999-2004 OEM camshaft
□ - Ported HO 1.91"/1.50" cylinder head
□ - Mill block deck 0.0?" to achieve a 9.4295 Deck Height
□ - Mopar Performance 0.043" head gasket
□ - 0.050" quench height (0.009" deck clearance)
□ - 2.5" exhaust
□ - Ford 24lb/hr injectors with stock 39psi FPR
□ - ? hp @ ? rpm, ? ft.lbs @ ? rpm

I'm looking to get a good low cost, and low RPM High Torque engine for the YJ's off road fun, while still running 87 octane gas. The YJ has an Automatic, that will have to be rebuilt as well. Yes, I'll be replacing axles as well after all this, but not immediately.

When I run the above info through the Stroker Compression Ratio Calculator I get the following:

Your Data:
Cylinders: 6
Bore: 3.905"
Stroke: 3.895"
Combustion Chamber: 58cc
Deck Clearance: 0.009"
Gasket Thickness: 0.041"
Gasket Bore: 4.0"
Dome/Dish/Valve Relief: 21cc
Connecting Rod Length: 6.125"
Cam Intake Duration: 253.3 degrees
Cam Lobe Separation Angle: 107.3 degrees
Advance or Retard: 0 degrees

Your Calculated Results:
Cubic Inches: 279.89
Liters: 4.57
Static Compression Ratio: 9.57:1
Dynamic Compression Ratio: 8.26:1
Quench: 0.005
Intake Valve Closing Angle: 53.95

As I understand the stock 4.0L spec's, the Deck Height was between 9.450"-9.456", however I've seen some state 9.429"-9.435". Not sure which is correct, so I set my Deck mill plan in the recipe to get the lowest of the two specification's range. This concerns me some as I'm worried about the CR and 87 octane fuel. If the large rang is correct I could increase the deck height by 0.02". This will lower the CR to 9.21 SCR & 7.95 DCR with a Quench of 0.07".

Comments, concerns or suggestions are all appreciated.
Will

[Retlaw01XJ]

It's a fairly standard build, and a good one!
You have a bit more compression than my build, and I wouldn't guarantee you'll be able to run on 87 octane, unless you're at a higher altitude than me (400 ft). I'd like to hear more opinions.
My '01 build is similar.... A mild Crower 44243 cam and 0.020" cut off the deck (pistons are 0.013" down) and I'm near 9.3 SCR and 7.7 DCR.

The late cams use a retention plate to keep the cam from moving back and forth. I believe you can modify your older block to accept it. (?)
The newer cams also require a standard 'link' type timing chain since the roller chains only fit the older cams/timing sprockets.

[W_A_Watson_II]

Thanks Walt, I'll look in to the cams. I appreciate the feedback.

If the Deck Height Specifications I have are right that the 93 block factory height is between 9.450 & 9.456, then I'll be able to keep the CR at 7.95:1 DCR. Here is a drawing of that recipe:

[casual]

I doubt it will run on 87oct..You can & should polish the valve faces, chambers & piston tops though..keep you quench as tight as possible! That will help prevent detenation..but with the DCR that high I doubt it will run happily on 87oct.

I should be around 9.3:1 static & 7.25:1 dynamic. I'll have a .040" quench height, & I'm polishing my chambers & pistons tops & valve faces. I should be able to get away with 87oct but I still worry..hece why I polished the chambers & pistons tops & valves!

[W_A_Watson_II]

Thanks Casual,

So with raising the neck height and upping my Quench to 0.070", the SCR goes down to 9.21:1 and the DCR goes to 7.95:1. I'd read (somewhere) that as long as the DCR was at 8:1 or lower 87 octane should be good. But I like the polishing idea as insurance.

Thanks,
Will

[casual]

The bigger the quench the more chance of detenation.

Kep the quench as tight as possible..as close to .045" as possible! If you need lower compression, you should dish your pistons. Also when polising the cumbustion chambers they will get slightly bigger...try to do very minor porting just to get the chambers from around 58cc up to maybe 60cc or so..that will also help drop the compression some..polish will keep the heat in, and smoothing out any rough edges, sharp edges will help prevent detenation!

Honestly I don't think it willrun on 87oct unless its around 7.5:1 DCR. But again idk everything thes is..hell maybe I can get away with more compression myself. I guess I just wanted to play it safe!

[Cheromaniac]

As I understand the stock 4.0L spec's, the Deck Height was between 9.450"-9.456", however I've seen some state 9.429"-9.435". Not sure which is correct, so I set my Deck mill plan in the recipe to get the lowest of the two specification's range. This concerns me some as I'm worried about the CR and 87 octane fuel. If the large rang is correct I could increase the deck height by 0.02". This will lower the CR to 9.21 SCR & 7.95 DCR with a Quench of 0.07".

The correct block deck height is 9.450-9.456". The 0.020" lower figure that you saw on keith Black's IC944 piston spec page assumes that the block deck will be milled by 0.020". If you don't mill the block deck the deck clearance will be ~0.027", quench will be ~0.070", and the SCR will be ~9.2:1. The DCR will be lower than the figure you quoted because the stock '96-'04 cam was ground with 7 degrees of retard.

[W_A_Watson_II]

Thanks Guys for all the insight, knowledge and help.

So both the “poor man’s” and “modified poor man’s” require above 87 octane, but on the “poor man’s” you might get away with it with some polishing, etc...

Sounds like I should just bite the bullet and decide to go with 89 or better octane fuel. If that’s the case I wonder if I should go ahead and do the low-buck stroker and accept the slightly higher RPM peek for torque.

Thank You!
Will

[Cheromaniac]

Sounds like I should just bite the bullet and decide to go with 89 or better octane fuel. If that’s the case I wonder if I should go ahead and do the low-buck stroker and accept the slightly higher RPM peek for torque.

Depends on your budget. The low buck stroker has an aftermarket cam and requires upgraded valve springs/retainers/locks, adding ~$300 to the cost compared to the poor man's.

[W_A_Watson_II]

Cheromaniac,

Ah, guess I missed the need for upgraded valve springs/retainers/locks. However I'd planed on a new Cam, so the cost is OK. After a little more reading/research I'm guessing the "low-buck" recipe will defiantly require 93 octane, but I guess to play you have to pay. Any thing else I should be cautious for or planning?

4.6L low-buck stroker - for my 1993 YJ
279.89 cu.in (4.59L)
Jeep 4.2L 3.895" stroke crank (Scat 942010)
Jeep 4.0L 6.125" rods (Mopar 53020126)
Keith Black UEM-IC944-030 pistons (1.353" Pin Height, 21.0cc Dish)
9.6:1 CR (9.57 SCR & 8.35 DCR)
CompCams 68-231-4 206/214 degree camshaft (Part: K68-231-4)
52º Intake closing angle
Ported HO 1.91"/1.50" cylinder head (58cc Chamber)
Mill block deck 0.020" (9.4295" Deck Height to achieve 0.050" quench height. Based on head gasket compressing to 0.041")
Mopar/Victor 0.043" head gasket (Mopar P4529242)
0.050" quench height
Ford 24lb/hr injectors with adjustable FPR (Part no. FMS-M9593-A302 & Hesco HES9195FR)
62-68mm Throttle Body, Stock is 60mm necked to 56mm (BBK 1724 or Fastman or F&B Flometrics 1X86J)
93 octane fuel
264hp @ 4900rpm, 324lbft @ 3500rpm

Again Thanks!
Will

[casual]

I'll toss this out for ya...out here in Ca 87oct has ethynol in it. I'm pretty certain our 91oct doesn't. Ethynol robs mileage...and to be honest you'd probably get better mileag on the higher octane cause it can be tued slightly leaner without pinging or detenation!

Also out here 87oct is going for around 3.99-4.03 per gallon. Premium or 91oct is 4.13-4.15 per gallon. My gas tank will hold 25 gallons after I did the gojeep.com mod to it. So its effectively 2.50 more per tank..shoot I think I just talked myself into using premium gas as well lol.
I could leave my piston dish at 11.5 cc vs dishing them out to 16..and just run on 91 octane lol.

[casual]

Dino can you do a 9.7:1 SCR & a 7.4:1 DCR on 91 octane?

[Retlaw01XJ]

Will, you could use a bigger cam and keep the same static CR but reduce the Dynamic CR.
There are some grinds out there (Crower, Schneider) without a lot of valve lift..... you could still use low cost stock springs and retainers

[W_A_Watson_II]

Casual Good point on the fuel, that indeed might just be the ticket.

Retlaw01XJ, how does those cams effect the torque level and curve?

Thanks,
Will

[casual]

Ya bud, don't stress yourself fighting for 87oct..cause even if you do everything, chances are you will still probably deonate and need to do more preventative things to make it run on 87oct. And it will get worse mileage on 87oct, cause it will need to run richer to not detonate. The higher octane buns colder so it cnbe run leaner thus more mileage!
Just do everything like you were, polish chambers ect ect & run it on premium. It litterally dollars more per tank. Comparing the lowest regular gas price here to the highest premium price, theres a 21cent difference. 21 cents x 25 gallons = $5.25more per tank of gas. I feel up almost ever 2 weeks..probably 1 1/2 weeks. Doing the math it will cost me an extra 190 bucks roughly per year. Thats going off of 20000 miles & the current .21cent difference!
That extra 200 bucks a year..if that much is far worth the added performance & mileage!

Just to add more fuel to the fire. My current stock motor with 100% bolt ons..header, exhuast, throttle body, injectors, intake heat sheild, 2.5" high flow downpipe..litterally every bolt on minus a cam. I'mrunning it on 91oct. I have a Apexi SAFC II. Its got 2 maps tuned, 1 for 87oct & 1 for 91. I'm gtting better mileage wth my 91octane tune because its tuned leaner without knocking giving better mileage. So even with the extra few pennies, honestly its averging out better than buying 87oct.
Currently 286k on my original 4.0, 5speed, 3.55 gears on 31's & a 3" lift. And I have hella 500's on my roof which is causing some drag..but I'm getting 18 in the city & 22-23 highway. More even if I can draft safely. So 18/22...my jeep wasn't even rated for that from the factory, its a 1988. Thats also with a lift & lights & tires
it does work out to be better in the end...so keep the extra compression, get your quench height tighter & have some fun