Jeep Strokers

After the advice of Dino, SilverXJ and Torsqplit about the Bulltear pistons/long rods and avoiding the block decking, Here are my 2 options:

CJ7 with YJ 92 EFI:


Jeep 4.2L 3.895" stroke crank
Jeep 4.0L 6.125" rods
Custom Forged Bulltear Pistons 0.30 20cc
9.4:1 CR
68231-4 camshaft Compcams (already in my current stroker)
0631 head Exhaust polished.
Mopar/Victor 0.043" head gasket
0.0 deck
Mustang Ford Racing 24 pound Fuel Injector M-9593-AA302 with hesco adjustable FPR. (already in my current stroker)
99+ Intake with MAP sensor adjustable (from current stroker, may be the MAP sensor adjuster won't be necessary)
Standard 98 Block bored to 0.30
The second option is to bore the cylinders to 0.60. I know it is a crime, but 4.0 blocks are available in every junkyard here as a lot of XJ are imported to my country as Spare Parts.

Jeep 4.2L 3.895" stroke crank
Jeep 4.0L 6.125" rods
Custom Forged Bulltear Pistons 0.60 22cc
9.34:1 CR
68231-4 camshaft Compcams (already in my current stroker)
0631 head exhaust Polished
Mopar/Victor 0.043" head gasket
0.0 deck
Cloyes 9-3127 Double Roller Timing Chain.
Mustang Ford Racing 24 pound Fuel Injector M-9593-AA302 with hesco adjustable FPR. (already in my current stroker)
99+ Intake with MAP sensor adjustable (from current stroker, may be the MAP sensor adjuster won't be necessary)
Standard 98 Block bored to 0.60
Gas in my country is very cheap with a 95 RON rating, which Dino clarified it is like 91 US octane.

I can try to find another 98 block non standard bored so it wont hurt to bore it.

Final questions:

1.- Worth to port the head? should I change the dish of the pistons to keep CR?
2.- Bulltear pistons come with rings?
3.- Worth the investment on the 1.6 ratio roller rockers?
4.- I have (from a friend) brand new 4.0 rods casting 207, is that ok? I think I read this casting is not recommended for stroker application.

Any help appreciated guys, new and aftermarket parts in my country are not available so I have to import all this by myself. Any error I make can be a 2 months waiting. Junkyard is everywhere.

Looks like you have a good plan.
Porting the head is definitely a worthwhile exercise especially in a stroker. Done properly you could gain 15-20hp.
Definitely order your Bulltear pistons with rings. If Bulltear don't supply the rings, ask them to size the ring grooves for standard size rings.
The casting numbers on the 4.0L rods may have changed over the years but their anatomy is still the same, so yours will do fine.
When doing the SCR and DCR calculations, use 0 feet as the altitude so that the numbers will be for sea level air density.

Dino, thanks for the advices.

One question, why sea level?

I live in a city where altitude varies from 3200 feet to 0 feet. But sometimes I travel to other cities where altitude can reach 14.000 feet.

Shouldn't I consider this for CR? at sea level I get 9.94 CR with the dish I ordered in bulltear. should I run and change this?

I though using a number like 2000 feet would help.

lcolina wrote:Dino, thanks for the advices.

One question, why sea level?

You need to enter 0 feet to get the correct SCR. The DCR will, of course, go down as you ascend to higher elevations and the engine breathes thinner air but the SCR is fixed.
Bear in mind that you'll want your engine to run on 95 RON octane at sea level unless you don't mind adding octane booster.

Got it!!!! Thanks Dino.

We may want to have a discussion about altitudes effect on compression. If you intend to completely take into effect altitude, then you are changing from a static numbers point of view to an effective compression point of view. That being said, if you want to take into account altitude, it will change your effective SCR as well as your DCR. This means that you can get away with a higher number at a higher altitude. Another way to think about it is about the air that's actually being pulled into the engine. If the air is less dense, then the air being pulled into the engine will be less dense and compression will not be as much. You can validate this by doing cylinder compression tests. If you do them at a higher altitude they will be lower than they would be at sea level.

I hate to keep digressing away from the OP, but I want to make sure that we are all on the same page. If we feel we should discuss further then we should bring it up in the calculator thread that I will bump.

The static compression ratio is always fixed. After all the size of the chambers, piston dishes, head gasket bores, deck clearance, and bore/stroke doesn't change with altitude so neither can the SCR. The only thing that changes is the air density and consequently the cylinder pressure, thus affecting the dynamic compression ratio.
You'd preferably want to build the engine to a dynamic compression ratio for the altitude that you live at but keep in mind that if you descend to lower altitudes, detonation may become an issue unless you have access to higher octane gas.

Finally my pistons arrive to my country and now I am worried.

They sent the specifications information like this (image):


My concerns are:
1.- Head Type 232/258. Is this ok? My head is 0631 for 242.
2.- Rod: 6.000 (it is supposed to be 6.123"). The compression height seems to ok.
3.- Stroke 4.000 (it should be 3.895)
4.- The displacement says 4.8L.
5.- No rings were included as I requested. Are the groove sizes specified in the document ok?

Thank you guys.

BTW, the order notes were:

The notes I added to my order were:

"I want to build a 4.7L Stroker with following specs:

4.0 Block (53020569) bored to 3.935 (0.60)
Head 0630. (assumed 58cc Combustion Chamber, please confirm)
4.2L Crankshaft.
4.0L connecting rods.
Comp Cams 68-231-4 (Intake Duration= 250, Lobe Separation Angle=111, Advance or retard=4).
Victor Reinz 0.043" Head Gasket.

I want 0.0 deck clearance so I need the pistons to have 1.380 compression height, please confirm this, and the pin compatible with 4.0 connecting rods.

I am pointing to have 9.6 SCR@ 1600 feet. I live in a city where altitude varies from 0 to 3200 feet so I am assuming this SCR will be OK for both. No problem with premium fuel. Any recommendation here is highly appreciated as I am not an expert in engines.

Desired pistons should be (please suggest or correct anything you consider):

Custom forged +0.060" bore pistons, compression height 1.380", dish volume 20cc".

After Dino's correction about altitude the SCR will be 9.94 with 0.043 Gasket or 9.77 with 0.051". I checked with a local friend and I will be ok here with that SCR.

Doing a little reading, as long as the compression height is 1.380 I will be fine right? This is te number I should care.

The heads are swappable so I should be fine too.

Would these rings be ok? or should I point to something with more performance?

http://www.summitracing.com/int/parts/s ... /overview/

Yes, if its the pin height and bore you want you will be fine.

Thank you my friend.

Hi guys,

I am facing a new problem with my project.

I lost the wire locks sent by Bulltear (please don't ask how), but I was told by them that I do not need it as the 4.0 connecting rods are press fit.

Turns out that the machinist tested the pin in the stock 4.0 rods I have (stock brand new). They fit tight, but no need to press fit. The machinist said I need to use the wire locks.

I can order a new set of wire locks (part# 927-072-WL or 927x073 SLX). The pin diameter is supposed to be according to Racetec (manufacturer) 0.927" or 23.55 mm, but my concern is if it would be ok to have a floating setup in rods that are supposed to be press fit.

I saw the FAQ for connecting rods and I am curious if I really have 242 rods or in fact I have 232 rods as the casting is 207 and not 544 as stated by the following table:

You can not just float a steel piston pin in a cast rod. The rods need to be bushed.

SilverXJ wrote:You can not just float a steel piston pin in a cast rod. The rods need to be bushed.

That't is good news because it is easier for me to make the bushings here instead of importing any other solutions.

However, should I assume Racetec made a mistake in the diameter of the pins? Or it is still possible my stock rods are the issue?

Thanks.

Leo.