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AMC Jeep 6-Cylinder Stroker Kits

Amc Stroker Kits
We Have You Covered !!

4.0L To A 4.5L Jeep Stroker Kit
(Click here)

The life and Ideas behind the 4.0 Jeep stroker conversion.

Have you ever been going up a hill in low gear just barely getting up it only to power out and find yourself stranded in the middle of a hill with no power steering or brakes to manipulate your way back down the hill? Well you are not the only one. Have you ever cussed your Jeep and wish that it just had a little more power? Once again you are not the only one.
 As engine builders we have customers in the shop all the time with engines from all sorts of different manufacturers that want just a little more power. Some time’s there is just not much that can be done without a major expense in Custom pistons, cams and or extensive machine work. Fortunately for you, if you own a 4.0L Jeep engine there are many economically based alterations that can be done to your engine to gain that extra bit of power you are looking for.
You have the normal power builders that are usually available to most any engine in the camshaft upgrade, a compression ratio change or basic port work on the cylinder head. But for the 4.0L Jeep engine the main power and torque builder you have available to you is the ability to make a lager cubic inch engine by installing a different crankshaft with a longer stroke into your 4.0L jeep engine.
The Factory 4.0L (242 cubic inches) engine uses a 87mm (3.425”) long stroke. The Factory 4.2L (258 cubic inches) was the predecessor to the 4.0L and was a well known combination for it amazing torque and hill climbing abilities. One of the main drawbacks to the 4.2L is that it is a carbureted engine and we all know that can cause problems for the serious off road enthusiast with the float bowl slosh from bouncing around.
As auto makers moved into the fuel injection era jeep designed a new inline 6 cylinder engine with fuel injection, a better head design, a header and an improved cam profile. They also changed around the bore and stroke combination of the lower end of the engine resulting in a slightly smaller cubic inch combination. The overall engine on parameters from the outside were the same as the original 4.2L and the basic blueprint of the block was kept the same as far as the journal and bore placement was concerned.
At the end of the day the new design had its good points and it bad points. On the dyno the new 4.0L made more torque than the 4.2L (220 ft lbs vs. 210 ft lbs), the only problem is that it took a higher rpm range in order to accomplish it (2500 vs 1800). For the off road enthusiasts this is not a very desirable trade off as most low end hill climbing is not done at 2500+rpm. So we have an engine now that has been designed more for fuel mileage and regular hwy operation than for bottom end grunt yet gives us the ability to go straight up or straight down and not mess up the ability of a carburetor to deliver the fuel to the engine. On Average with everything else being the same and just installing the stroker kit in to your engine with the factory cam etc. you can expect to see a 12-13% increase across the board in torque and horse power with the torque range coming in back down in the 1800-2000 rpm range depending on the rod combination that is used. With a appropriate camshaft change as well we can still have a pump gas every day driver that can deliver as much as a 25% increase in power.
At RPM Machine we have been building Stroker engine combinations for years. At the time in which I am writing this article I have personally been in the performance automotive engine industry for 26 years and as an avid engine enthusiast I have spent a majority of that time figuring out how to improve on what the factory has done without making major headaches by getting into a complete engine swap to a V/8 and even worse a swap to a different manufacturer engine (i.e. a Chevrolet into a Jeep).
On the following page we have put together several different combinations that will allow you to choose a kit that fits your budget and horsepower needs.
We have kits with cast pistons, hypereutectic coated pistons, std shelf stocking forged pistons and we can even put together high horse power/rpm kits with aftermarket H beam rods and custom forged pistons to accommodate higher compression ration’s and rpm needs.
If you have any questions on converting your jeep 4.0L to a stroker please give us a call and we will be glad to help you with your project.

Thanks for your business

RPM Machine


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RPM Machine-Performance Auto Parts
PO Box 281
Cedar Valley, Utah 84013
We carry parts from scat, je, wiseco, ross, crower, callies, eagle, cat, eagle
Most of our rotating assemblies include forged pistons
and 4340 steelcranks

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