Stroker

	Stroker Engines
	Home Page \| Modifications \| Mod Diary \| Photos \| Intake \| Ram Air \| Homebrew FIPK \| Exhaust \| Tech Specs \| Ported Head \| Stroker \| Forced Induction \| Cooling \| Electronic \| Ignition \| Valvetrain \| Software \| Calculators \| Links \| Contact

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 short rod/ long rod and by RPM Machine 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 If you use the shorter Jeep 4.2L rods, cheap aftermarket cast aluminium or hypereutectic 4.0L pistons can be used but the result is a quench height higher than the stock 0.073". The quench height can be reduced by milling the block deck and installing a thinner head gasket but these measures increase the CR. In order to avoid detonation issues, the CR needs to be reduced again by increasing the combustion chamber volume and the piston dish volume. *For each 0.010" milled from the block deck (or taken from head gasket thickness) to reduce quench height, the combustion volume decreases by ~2.0ml and the CR increases by ~0.2*. If the stock Jeep 4.0L 6.125" rods are used, expensive custom forged pistons with a shorter pin height than stock (1.380") are required to achieve zero deck clearance, but these allow you to avoid milling the block deck and you can select the head gasket thickness required to achieve the desired 0.040"-0.050" quench height. You can also choose pistons with a larger dish volume than stock to reduce the CR and allow the use of low octane fuel without detonation. With a low CR, you can also use a shorter duration camshaft for increased low-rev torque in a naturally-aspirated engine or add forced induction for a further power boost.
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 seven 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 with stock 39psi FPR for '87-'95 engines, stock injectors with stock 49psi FPR for '96 and later 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 HO camshaft Ported HO 1.91"/1.50" cylinder head Mopar/Victor 0.043" head gasket 0.088" 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 248hp @ 4900rpm, 303lbft @ 3500rpm
4.6L low-buck stroker Jeep 4.2L 3.895" stroke crank Jeep 4.2L 5.875" rods Speed Pro H825CP +0.030" bore pistons 9.6:1 CR CompCams #68-231-4 206/214 degree camshaft Ported HO 1.91"/1.50" cylinder head Mopar/Victor 0.043" head gasket 0.081" quench height Ford 24lb/hr injectors with adjustable FPR or MAP adjuster for '87-'95 engines, Ford 24lb/hr injectors with stock 49psi FPR for '96 and later engines 264hp @ 4900rpm, 324lbft @ 3500rpm
	4.7L medium-buck stroker Jeep 4.2L 3.895" stroke crank Jeep 4.0L 6.125" rods Keith-Black Silvolite UEM-IC944 +0.060" bore pistons 9.6:1 CR CompCams 68-231-4 206/214 degree camshaft CNC ported HO 1.91"/1.50" cylinder head Mill block deck 0.020" Mopar/Victor 0.043" head gasket 0.051" 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 with stock 49psi FPR for '96 and later engines. 271hp @ 4900rpm, 333lbft @ 3500rpm 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 3.0" 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 3.0" 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