More noob questions

[4wdparakeet]

Okay guys this is my first engine build for myself and I'm not a numbers guys. (my wife helps my 6th grade son with math homework) This is the stroker recipe I have chosen to build. To give you an idea of what the jeep is going to be used for. For probally the next year or so it will be a second DD. From that point it will become a trail rig. I want the motor to be able to pull double duty but would rather have it set up for the trail. I'm running 3.55's and 33's also.

4.6L Low-buck, low CR "rockcrawler"

Jeep 4.2L 3.895" stroke crank
Jeep 4.2L 5.875" rods
Silvolite UEM-2229 +0.030" bore pistons
Increase piston dish volume to 30cc
8.75:1 CR
Crane #750501 192/204 degree camshaft
Ported HO 1.91"/1.50" cylinder head
Mill block deck 0.035"
Mopar/Victor 0.043" head gasket
0.058" quench height
Ford 24lb/hr injectors with stock 39psi FPR for '87-'95 engines, stock injectors with stock 49psi FPR for '96 and later engines
234hp @ 4500rpm, 311lbft @ 3300rpm


I do plan on doing a few things different though and need some opinions on my changes and how it will affect my build.

1. I won't be dishing the pistons due to budget.... How will this affect my CR and octaine level selection.

2. I will be using a 89 head due to budget.... How will this affect the overall performance and should I home port it.

3. I am looking at going with a comp cams kit that has lifters (PN PART #CL68-115-4) 192/200 degree cam. But on the info page of the cam it says not for fuel injections. That's one of the part numbers on the page I got the recipe from. That's the page that quite a few people have linked noobs like myself too.

4. What would be the downside to running a 2.5" header to a flex pipe and then to a 2.25" reducer to my 2.25" pipe with no cat and Flowmaster 40 series untill I can afford to have it all piped with 2.5".

5. Is the stock valve train good for this combo or should I upgrade that also.

6. If I get a set of stock 4.0 +.030 pistons will that run me into issues or will it be alright.

I know these are noob questions that have probally been beat into the ground but I'm a horrible searcher. Thanks in advance for the help and opinions.


Parakeet

[4wdparakeet]

Somebody anybody???



Parakeet

[SilverXJ]

1) Run the numbers through the "Stroker CR Calculator" at the top of the page. As for octane requirements, I don't know of any cut and dry infor on it. You have the Dynamic compression which is just measurements on the pistons, head, gasket, stroke, etc, and the static compression which is the Dynamic compression applied to the cam selection. Those are the hard numbers. On top of that you have your piston composition material, quench, and head material that changed what octane is needed.

2) Polish the chamber in the head at least. What is the casting number on the head? It it isn't 0630/0721 then I suggest you discard it and find a 0721 (IIRC you need the sensor port on the back) and go with that. A P&N kit is like $60.. a good used head should be $90.

3) Don't know about that particular cam, but I have run the 68-231-4 on my 2000 XJ and it worked fine. Their fuel injection statement is just to cover their asses in case the computer throws a error. Don't get comp's springs as the have too much load. I suggest getting the Mopar Performance springs, retainers and locks if your stock springs can't handle the cam.

4) you will be fine until you can upgrade. And please run a cat.

5) See #3

6) You should be fine with stock 4.0L pistons (which are what most run with the 4.2L rods) as long as their dish fits your requirements. Or are you talking of used pistons?

[4wdparakeet]

I ran the numbers with a 58cc combustion chamber volume. I got a 11.51 SCR and 10.04DCR. The numbers I used are the bore at 3.905" (standard bore is 3.875+.030" over bored am I right in this thought), stroke is 3.895 ( that is the number for a 258 stroke but it should be the same since the crank and rods are out of a 258. and I right with this number), stock deck clearance( .0215), gasket height of .051, gasket bore of 4", and 0 dishing the pistions. The DCR number comes from a 5.875 rod length and the comp cams 68-231-4 numbers the calculator auto fills for you.

An 11.5:1 CR is way out of the question so based on this I will have to dish the pistons. Using the same numbers but dishing the pistons 20cc, I end up with a 9.24:1 SCR and an 8.09 DCR.

I have a feeling I'm missing something but I could be wrong. I don't want to run premium but it is what it is.

I will be running a high flow cat when I redo the exhaust but when the cat clogged the budget wasn't there to fix properly.

On the cam I would like something a little lumpy but not super aggressive. Where does the comp cam that you ran fall grand scheme of cams.

Parakeet

[SilverXJ]

You will be lucky is you could run pump gas on those numbers. Where you went wrong in the piston dish. A piston with a dish of 0 is a flat top piston. All 4.0L pistons that I know have a dish. IIRC there is a list in the FAQ of dish sizes.

The Comp Cam 68-231-4 is the best all around cam that I have run though Desktop Dyno. While the software isn't good for true numbers it is good for comparison. Idle is good, smooth. Good power through the RPM, Torque doesn't end early either. I like it. You don't want a lumpy cam. They usually hurt performance more than help it.

[4wdparakeet]

With the right dish cc's numbers and stock deck height I'm showing an almost 9.9:1 DCR. That sounds better but still seems higher than what would allow me to run 87 oct gas. Maybe it's just me but I think I may still be off somewhere.


Parakeet

[rradford9]

I'll hop in here and try to help you...I was in your shoes a few months ago and everyone here helped a lot in my build.

The first thing I'll say is: Do not go cheap! Its fine to have a low budget, I did (1000 for parts) but make sure you're getting QUALITY stuff or you'll be rebuilding again sooner than you'd like.

The stroker recipe you picked is pretty good to fit the needs you described. I'd try to stick as close to it as possible, but a little variation is ok. To use the CR calc on here you need to get some firm numbers for certain parts like gasket height, piston pin height, and cam specs. If you'll post some of those #'s I'll do some of the math for you and run it through the calc. I know for me, the .0215 stock deck clearance # was way off from my actual deck clearance so that completely screwed up my numbers at first.

Dishing your pistons is fairly cheap. PM oletshot. He does great work and his prices are very reasonable. I'm not sure how much dishing you can do to the stock pistons. I'd recommend using Sealed Power +.030 pistons. IIRC, the price from Falcon was only about $20 a piston! I know that oletshot said he could dish the Sealed Power 802's out to 20cc's.

[4wdparakeet]

So I called Falcon Global about pistons today and they had the H802cp for $16.89 a piston the H825CP was $26.48. Both pistons were for years newer than the block I'm using. Both are a cast piston. The only difference that he could give me were the rings were metric/sae. According to the Availble Piston FAQ both have a 15.5cc dish.

Will either one of these work in my 89 block with 258 crank and rods? Obviously I would like to see the $17 price tag but if it won't work...


Once again thanks for all the help


Parakeet

[rradford9]

The year of your block shouldn't matter as they were all the same dimensions. The H802CP's should work fine, thats what I used in my build.

[SilverXJ]

The year of your block won't matter which pistons you use. Just be sure to get the correct rings for the pistons you purchase (metric/standard)

[4wdparakeet]

Okay I've decided on pistons. I will be getting the SP802CP. These have the 15.5cc dish to them as they sit. I ran the numbers through the CR calculator and this is what I got.

Bore: 3.905
Stroke: 3.895
Combustion Chamber: 58cc
Deck Clearance: 0.035
Gasket Thickness: .051
Gasket Bore: 4
Dish Value: 15.5cc
Piston Ring Height: 1.592
Connecting Rod Height: 5.875
Cam intake Duration: 250
Cam lobe seperation: 111
Advance: 4

There are the numbers I got.

SCR: 9.41:1
DCR: 8.24:1
Quench: .086

What do you guys think? To much compression still? Would I be in premium territory or just close?


Parakeet

[dwg86]

It would be better to get the quench lower. I would send the pistons to oletshot to get dished and zero deck the block. My stock 4.0 has spark knock. I have to run 89. I can't remember what the stock quench is...somewhere around .080? Stock compression 8.8:1.

[4wdparakeet]

I just ran the same numbers except zero deck and 20cc dish.

That changed my compression to 9.64:1 SCR , 8.43:1 DCR and quench of .051.

I would like the compression a little lower. According to a post earlier in the thread the SP pistons can only be dished to 20cc.


Parakeet

[rradford9]

I just ran the same numbers except zero deck and 20cc dish.

That changed my compression to 9.64:1 SCR , 8.43:1 DCR and quench of .051.

I would like the compression a little lower. According to a post earlier in the thread the SP pistons can only be dished to 20cc.


Parakeet

You can remove a little material from the combustion chamber to increase the cc's and get your CR lower. Also, your cam choice can help lower the DCR, which really, is more important than the SCR since compression in the cylinders can't actually start until the exhaust port is closed.

And I know everyone on here pushes for the ideal .040 to .050 quench height, but mine ended up being ~ .081. I have a lower CR though at 9.20:1 and 7.96:1. You may have to make some trade offs between getting that ideal quench and your CR goal.

[4wdparakeet]

I was looking at the recipe and it shows all the low buck strokers have a .080 quench. It's not untill you get into the bigger strokers that the quench get's closer to .045. Are there alot of stroker builds that have .080 quench without issues. I'm would really like to be around 9.5:1 SCR.

How does the cam selection affect the DCR and what do you guys recommend based on the numbers I've given above. The last set of numbers I have posted.


Parakeet