Stroker Engines
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4.0 engine torque curves

The torque curve of the engine in stock form was already broad and flat. The addition of some simple bolt-on performance modifications increased torque throughout the rev range, particularly at higher revs.
Maximum horsepower increased from 193hp @ 4850rpm to 235hp @ 5200rpm, and maximum torque from 239lbft @ 3500rpm to 269lbft @ 4000rpm. The torque curve is broader, with at least 242lbft (1.0lbft/ci) available from 1600rpm to 5100rpm. This translates into faster acceleration at any speed in any gear making passing manoeuvres safer. Gas mileage remained the same despite the higher HP/TQ outputs thus reflecting the engine's greater efficiency.


When 4.0 litres and 269lbft aren't enough...

There's no replacement for displacement so if you want even more torque, you need a bigger engine.
The 4.0L engine has a 3.411" stroke, 3.875" bore, 6 cylinders, and a displacement of 241.5ci (3956cc).
You can increase the displacement of your 4.0L engine by installing a stroker kit.
At the heart of the kit is the 3.895" stroke crankshaft that was used in the AMC/Jeep 258ci (4.2L) I6 engine.
On an engine with the standard 3.875" bore, the stroker crank increases displacement to 276ci (4517cc or 4.5L).
Add 30 thou or 60 thou overbore pistons and displacement is increased to 280ci (4587cc or 4.6L) and 284ci (4657cc or 4.7L) respectively.
Larger displacements will require custom parts. For a 4.8L stroker (4759cc or 290ci), 60 thou overbore pistons and a custom billet 3.98" stroke crank are required. If a custom billet 4.06" stroke crank is used, displacement is increased to 4.9L (4855cc or 296ci). The ultimate stroker would be a 5.0L version (5016cc or 306ci) with the block resleeved to accommodate 4.00" bore pistons and the aforementioned custom billet 4.06" stroke crank.
Here's some information on how you can build a stroker engine and the kits available.

Budget stroker build-ups

Robert Bryce built the world's first budget Jeep I-6 stroker engine, reusing as many stock components as possible in his assembly to keep cost to a minimum. The key to success was to keep it simple. Click on the image to the right to find out more.

Not to be outdone, I also jumped onto the stroker bandwagon and built the world's first "square" Jeep I-6 stroker engine with a bore and stroke of 3.895". It's identical to the 4.6L "poor man's" stroker shown below except that I used a Crane 753905 camshaft. I transformed a junkyard 4.0L short block plus a pile of parts into a rip-snorting torque monster with a displacement of 4563cc, hence I entitled my stroker story "From Junker to Stroker".
My stroker engine's producing a calculated 258hp @ 4850rpm and 320lbft @ 3500rpm. At least 278lbft (1.0lbft/ci) is available from 1500 to 4850rpm. The difference in performance over the old modified 4.0 is very noticeable, particularly from 1500-4000rpm where I need it most. Performance-wise, the stroker engine has hit the bullseye!

505 Performance stroker kit

505 Performance have introduced a range of stroker kits from mild to wild, including a 5.0L kit (actually 4855cc or 4.9L) with Ross Racing +0.060" forged pistons, Eagle 6.150" forged connecting rods, and a custom blueprinted 4.06" stroke crankshaft. They've also introduced a range of hydraulic flat tappet camshafts and they are the first company to introduce hydraulic roller tappet camshafts for the Jeep I6 engine.

Hesco stroker kit

Available for all Jeeps in .030 or .060 oversize. Click on the image to the right.
A Hesco 4.7 stroker dyno'ed 267hp @ 4700rpm and 332lbft @ 3400rpm at the flywheel. The specs of that engine are in this Yahoo Stroker Group message.

Another Hesco built 4.6 stroker did even better on the engine dyno, producing 269hp @ 4800rpm and 339lbft @ 3200rpm.
Other stroker kits


Other stroker kits worth mentioning are supplied by Speedomotive, RPM Machine, and Clegg Engine.
You can also get a complete 4.6L stroker longblock engine from Golen Engine Service

The Golen 4.6L stroker has been reviewed by JP magazine, producing 268hp @ 4900rpm and 324lbft @ 3900rpm on the engine dyno.

Limeyjeeper built the 4.0L engine from his '99 WJ into a 4.6L stroker engine using the Accurate Power stroker kit. It produced 210hp @ 4800rpm and 262lbft @ 3800rpm on the chassis dyno. Assuming a 20% drivetrain loss (RWD auto.), that's 263hp and 328lbft at the flywheel. Here's the link to Limeyjeeper's stroker story. 

Accurate Power and Jakes Racing Engines have ceased trading, while Clifford Performance continue to trade but no longer supply stroker kits.

Injector sizing

Stroker engines require oversize injectors to provide adequate fuel and prevent pinging due to lean air/fuel mixtures. Click on the image to the right.
To calculate optimum injector size, use the following formula:

Injector flow rate (lb/hr) = [Expected HP x 0.5 (BSFC)] / [no. of cylinders x 0.8 (injector duty cycle)]

The actual injector flow rate from each injector depends on the fuel pressure (FP) in the injector rail. Most injectors have rated flows at 43.5psi fuel pressure. The actual flow rate from each injector is:

Actual injector flow rate = Rated injector flow rate at 43.5psi x square root of (FP/43.5)

Adjustable fuel pressure regulator

Fine tune your engine's fuel curve with a Hesco adjustable fuel pressure regulator (FPR). Click on the image to the left.
The fuel pressure can be adjusted to provide the optimum air/fuel ratio.
Part no. for the '87-'90 FPR is HES8790FR
Part no. for the '91-'95 FPR is HES9195FR

There is no adjustable FPR available for '96 and later engines.
Camshaft

Stroker engines need a longer duration than stock camshaft to maximise horsepower and torque. Click on the image to the right to go to the CompCams catalog. The aim is to produce maximum torque over as wide an rpm range as possible. Stroker engines built with a compression ratio (CR) of about 9.5:1 will derive maximum benefit from a midrange camshaft such as the CompCams 68-231-4 206/214 degree cam.
A stroker built to a CR of 8.8:1 that'll run with 87 octane fuel will benefit from a shorter duration dual-pattern cam such as the CompCams #68-115-4 192/200 degree cam for more low rev torque.
Long rods vs. short rods

NEW: Keith Black have come to the rescue of the budget stroker crowd with reasonably priced, off-the-shelf ICON forged pistons that can be used with the stock Jeep 4.0L 6.125" rods so there's little reason to use the 0.25" shorter 4.2L rods in a stroker build anymore. The pin height of these pistons is 1.353" so that leaves the deck clearance at 0.027" (quench height at 0.070" with 0.043" head gasket) in a standard deck height block, and the compression ratio at 9.2-9.4:1 (depending on bore size) if you use the IC944 pistons with a 21cc dish. If you mill 0.020" from the block deck to reduce the deck clearance (and quench height), the compression ratio will increase by 0.4:1.   

Stroker engine math

Here are some formulae, and how they apply to the stock Jeep 4.0L engine:

1. Deck height = Rod length + stroke/2 + piston pin height + deck clearance

9.453" = 6.125" + 1.705" + 1.601" + 0.022"

2. Combustion volume = Combustion chamber volume + head gasket volume + deck clearance volume + piston dish volume

84.6cc = 56.7cc + 10.5cc + 4.3cc + 13.1cc

3. Compression ratio (CR) = Cylinder volume/combustion volume + 1.0

CR = 660/84.6 + 1.0 = 7.80 + 1.0 = 8.80

4. Quench height = Deck clearance + compressed head gasket thickness

0.073" = 0.022" + 0.051"
Stroker combinations

I've outlined several stroker combinations from mild to wild below based on budget and desired horsepower levels. To get maximum benefit from the stroker engine you need a free-flow intake with an S&B or K&N cone filter, 62mm bored HO throttle body, header, high-flow cat, performance muffler and 2.5" exhaust piping.

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
CompCams 68-115-4 192/200 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 for '87-'95 engines, Accel 24lb/hr injectors for '96-'04 engines, '98 Chevy LS1 25.2lb/hr injectors for '05-'06 engines
240hp @ 4700rpm, 315lbft @ 3000rpm

4.6L "poor man's" stroker


Jeep 4.2L 3.895" stroke crank
Jeep 4.2L 5.875" rods
Sealed Power 677CP +0.020" bore pistons
9.25:1 CR
Stock 4.0 camshaft
Ported HO 1.91"/1.50" cylinder head
Mopar/Victor 0.043" head gasket
0.088" quench height
Ford 24lb/hr injectors for '87-'95 engines, Accel 24lb/hr injectors for '96-'04 engines, '98 Chevy LS1 25.2lb/hr injectors for '05-'06 engines
248hp @ 4900rpm, 306lbft @ 3250rpm ('87-'95 camshaft)
245hp @ 4800rpm, 315lbft @ 3000rpm ('96-'04 camshaft)

NEW: Modified "poor man's" stroker

Same as above except Jeep 4.0L 6.125" rods, Keith Black UEM-IC944-020 forged pistons, and 0.070" quench height. This is a great stroker build for a mild supercharger/turbo application with up to 6psi of boost. The 4.0L connecting rod/IC944 piston combination offers 155g less reciprocating mass than the 4.2L rod/677P piston combination (1275g v 1430g), thereby giving this engine a potentially higher rpm capability than the traditional "poor man's" stroker. 

4.6L low-buck stroker

Jeep 4.2L 3.895" stroke crank
Jeep 4.0L 6.125" rods
Keith Black UEM-IC944-030 pistons
9.6:1 CR
CompCams 68-231-4 206/214 degree camshaft
Ported HO 1.91"/1.50" cylinder head
Mill block deck 0.020"
Mopar/Victor 0.043" head gasket
0.050" quench height
Ford 24lb/hr injectors with adjustable FPR or MAP adjuster for '87-'95 engines, Ford 24lb/hr injectors for '96-'04 engines, '99-'00 Chevy LS1 26.2lb/hr injectors for '05-'06 engines
264hp @ 4900rpm, 324lbft @ 3500rpm

NEW: Propane Conversion Special

Same as above except for Keith Black IC945-030 pistons
Mill block deck 0.030"
0.040" quench height
10.9:1 CR
262hp
 @ 4900rpm, 319lbft @ 3500rpm

If you all thought that the old AMC 232 I6 crankshafts were only destined for scrapheap oblivion, think again. There are plenty of them around and with a 3.500" stroke, you can use them to convert a stock 4.0L engine into a 4.2L mini-stroker. While it doesn't have the displacement of an AMC 258 crank-based stroker, the 258 cranks are becoming increasingly scarce and expensive so a mini-stroker offers a low cost alternative to more HP/TQ:

4.2L Milder mini-stroker

AMC 232 3.500" stroke crank
Jeep 4.0L 6.125" rods
Silvolite UEM-2229 +0.060" bore pistons
Increase piston dish volume to 23cc
8.8:1 CR
CompCams 68-115-4 192/200 degree camshaft
Ported HO 1.91"/1.50" cylinder head
Mopar/Victor 0.043" head gasket
0.040" quench height
Ford 24lb/hr injectors for '87-'95 engines, Accel 24lb/hr injectors for '96-'04 engines, '98 Chevy LS1 25.2lb/hr injectors for '05-'06 engines 
241hp @ 5000rpm, 294lbft @ 3000rpm

4.2L Wilder mini-stroker


AMC 232 3.500" stroke crank
Jeep 4.0L 6.125" rods
Silvolite UEM-2229 +0.060" bore pistons
10.0:1 CR
CompCams 68-235-4 210/218 degree camshaft
Ported HO 1.91"/1.50" cylinder head
Mopar/Victor 0.043" head gasket
0.040" quench height
Ford 24lb/hr injectors with adjustable FPR or MAP adjuster for '87-'95 engines, Ford 24lb/hr injectors for '96-'04 engines, '99-'00 Chevy LS1 26.2lb/hr injectors for '05-'06 engines
270hp @ 5300rpm, 306lbft @ 4000rpm

4.7L medium-buck stroker

Jeep 4.2L crank offset-ground to 3.915" stroke
Jeep 4.0L 6.125" rods
Keith-Black UEM-IC944-060 pistons
10.0:1 CR
CompCams 68-235-4 210/218 degree camshaft
CNC ported HO 1.91"/1.50" cylinder head
Mill block deck 0.018"
Mopar/Victor 0.043" head gasket
0.043" quench height
Flometrics F&B 68mm billet TB
Accel 26lb/hr injectors with adjustable FPR or MAP adjuster for '87-'95 engines, Accel 26lb/hr injectors for '96-'04 engines, '01-'02 Chevy LS1/LS6 28.6lb/hr injectors for '05-'06 engines
281hp @ 5000rpm, 337lbft @ 3700rpm

4.8L high-buck stroker

Custom billet 3.98" stroke crank
Eagle forged 6.15" rods
Custom forged +0.060" bore pistons, 24cc dish, 1.315" compression height
10.0:1 CR
505 Performance 267/282-14HRK hydraulic roller camshaft
Hesco aluminium cylinder head
Mopar/Victor 0.043" head gasket
0.043" quench height
Flometrics F&B 68mm billet TB
Dual 2.25" exhaust system
Custom PCM programming
319hp @ 5300rpm, 362lbft @ 3900rpm

4.9L high-buck stroker

Custom billet 4.06" stroker crank
Eagle forged 6.15" rods
Custom forged +0.060" bore pistons, 17cc dish, 1.275" compression height  
11.0:1 CR
505 Performance 273/273-14HR hydraulic roller camshaft
Hesco aluminium cylinder head
Mopar/Victor 0.043" head gasket
0.043" quench height
Flometrics F&B 68mm billet TB
Dual 2.25" exhaust system
Custom PCM programming
328hp @ 5200rpm, 379lbft @ 3900rpm

5.0L very high-buck stroker

Same as above except: 

Block resleeved to 4.00" bore diameter
Custom forged 4.00" bore pistons, 16cc dish, 1.275" compression height  
11.5:1 CR
505 Performance 281/281-14HR hydraulic roller camshaft
344hp @ 5300rpm, 384lbft @ 4000rpm