super chrager or stroker

Would I be better off stroking or super charging, I would really love more horse power that s what Im after, with decent gas milage

98_XJ_Classic said:

Would I be better off stroking or super charging, I would really love more horse power that s what Im after, with decent gas milage

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Bud, that's a wide open question!

Bear in mind that you have to burn more fuel to make more power, so you're going to lose some fuel mileage if you get a significant increase in power (superchargers require supplemental fuel delivery setups - they make your engine make more power by providing more air - which allows you to burn more fuel. Hmm...)

Stroking your engine increases displacement (increasing airflow thereby,) and generally results in a mild to moderate increase in compression ratio (increasing the thermal efficiency of the combustion process slightly. If you don't know anything about thermodynamics, just trust me. The groundwork for this was laid something like sixty years ago at MIT. I could tell you what books would explain this, but it's terribly dry!)

And, "more horsepower" is kinda open as well - there are two things that one could seek an improvement for (speaking generally) when one looks to increase the performance/output of the internal combustion engine:

Torque Output - this is the "low-end grunt," and for most engines this is what gets you moving off the line. Typical "torque peak" for our 242ci engine is around 2600-2700rpm crankshaft speed, and that's where you usually want to cruise (with a manual. Slightly higher with an auto, due to the action of the torque converter.)

Horsepower - this is the "high-end move," and it invariably peaks at 5252rpm or higher. Yes, that's right around the redline for our inline sixes - if you want high crankshaft speeds, install something with a shorter crankshaft to reduce harmonics (V8 engines can be balanced to spin 10Krpm all day. I6 engines have a couple of patches of harmonics to get through - the big one being 6000-7000rpm, and that one can break cranks!)

Generally, for light truck performance, you're after more torque than horsepower.

A supercharger will give you an increase throughout the RPM band, roughly equivalent to the percentage of boost you're running over one atmosphere (there are some losses due to air compression, drive losses, and that sort of thing. A good guideline would be 50% of an atmosphere of boost - ~7.35psi - would get you about a 42-45% increase in instant torque or power output.) Variables? You get a smaller percentage from a centrifugal supercharger than you do a positive displacement blower. Having a narrow belt (under an inch wide, or so) or one that is allowed to "slip" will also lose you boost points - that's why most of the big Roots blowers you've seen on rods have 3-4" wide belts with internal teeth (and matching teeth on the blower snout pully and crankshaft pully.) You have to set up supplemental fuel delivery - not only larger fuel injectors, but you have to modify the control system to respond to manifold pressures greater than one atmosphere, or add in a "piggyback" fuel controller.

Stroker pros? All you need is a crankshaft with a longer stroke (OEM is 3.44", AMC232 is 3.500", AMC258 is 3.895". Or an offset grind,) a shorter connecting rod, and larger fuel injectors (you need more fuel per pulse, but the manifold pressure range is the same - 0-1atm. If the injectors can deliver enough fuel and a bit more, the system will trim it with the HEGO feedback loop.)

With all that sort of thign in mind, I hope you understand the next statement - "Which is better for you? I can't tell you." I don't have enough information. I don't know what you're planning on doing with the thing. I don't know what your budget is. I don't know what your performance goals are, other than "more horsepower." And that doesn't really tell me anything...)

I'm not trying to dissuade you or obstruct you - more trying to help you understand why the question you're asking is not likely to get you a useful answer. Especially for a performance buildup - you need to have a goal in mind. Once you have a concrete goal, you can either do it all at once, or attack it piecewise. But, if you don't know where you're going, how will you know if you've gotten there?

if youre worried about MPG you may want to lean towards the super charger end, as it should only consume more gas while you are making boost. But you will probably also have to run a premium fuel to avoid pinging or detonation which will increase your fuel costs regardless of MPG.

Both! More Power Arrh! Arrh! Arrh!

I did a stroker and my mpg went up. Just make sure you build it right.

stroker, you can always blow it later.

smaller tires

wolfpackjeeper said:

stroker, you can always blow it later.

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:yap: thats hilarious...sorry!!

strok'in is for little boys.........gettin blowed is for men?

kboyts said:

if youre worried about MPG you may want to lean towards the super charger end, as it should only consume more gas while you are making boost. But you will probably also have to run a premium fuel to avoid pinging or detonation which will increase your fuel costs regardless of MPG.

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True - but a supercharger is always making boost. It's a "string driven thing" - the engine is turning? The supercharger is turning.

Stroke it and supercharge it. Let us know your progress.

You can also put a clutch similar to a AC compressor clutch on the supercharger. The new motors where they are going for fuel economy are smaller motors that are supercharged.

i've seen a picture of a pro-charger for 2000-2200. but i never saved the website.
one of these days i'll get my stroker finished.

5-90 said:

True - but a supercharger is always making boost. It's a "string driven thing" - the engine is turning? The supercharger is turning.

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Doesn't matter what the supercharger is doing. Manifold pressure is what matters to the engine/fuel.


Stroking the engine will give a small amount of torque and horsepower, and also lower the rpm where both are at their peak.

Supercharging will ad a LOT of torque and horsepower. If you're using a roots/twin screw type blower, you can expect big gains in torque almost right from idle to wherever you shift. When making boost you're going to increase fuel consumption, and you'll always be running premium fuel. Engine temps will increase too.

If you're only running 5 or 6 psi, it's possible that you could get by with 87 octane fuel, and a water/methanol injection kit.

winterbeater said:

You can also put a clutch similar to a AC compressor clutch on the supercharger. The new motors where they are going for fuel economy are smaller motors that are supercharged.

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Any supercharged motor I have had experiance with would barely run without the blower belt. Maybe on a very low boost application with a centrifugal supercharger. But at that point there is not an advantage of a blower. I do not think a motor tuned for a supercharger is going to do better on gas without the blower turning. In most cases you would get better milage with the blower because you do not have to use as much throttle. Now all fuel milage goes out the window when you floor it. You sure you have not been watching to much MadMax.

squirrel80 said:

Any supercharged motor I have had experiance with would barely run without the blower belt. Maybe on a very low boost application with a centrifugal supercharger. But at that point there is not an advantage of a blower. I do not think a motor tuned for a supercharger is going to do better on gas without the blower turning. In most cases you would get better milage with the blower because you do not have to use as much throttle. Now all fuel milage goes out the window when you floor it. You sure you have not been watching to much MadMax.

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It's true. I would think without the impeller turning, and heavy throttle usage, you would be seeing vacuum at the manifold. Engine would run like shit.

5-90 said:

True - but a supercharger is always making boost. It's a "string driven thing" - the engine is turning? The supercharger is turning.

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not true. The supercharger will have a bypass valve that is vacuum operated. It only makes boost when you are hard on the throttle.

My previous car had an Eaton M45 (small I know but it was a 2 liter engine) roots style blower. I could drive it all day long without seeing boost if I wanted to. The bypass valve rediects some of the excess pressure outside of the intake manifold instead of pressurizing the manifold and making boost.

kboyts said:

not true. The supercharger will have a bypass valve that is vacuum operated. It only makes boost when you are hard on the throttle.

My previous car had an Eaton M45 (small I know but it was a 2 liter engine) roots style blower. I could drive it all day long without seeing boost if I wanted to. The bypass valve rediects some of the excess pressure outside of the intake manifold instead of pressurizing the manifold and making boost.

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Well, technically he's sort of correct. The impeller is always making positive pressure, but positive displacement blowers like the eatons/whipples will have an internal bypass. Centrifugals like my Novi2000 have to have a bypass after the discharge somewhere. They're open as long as the intake manifold is seeing some amount of vacuum.

I just made my own turbo kit for my 4.0 in the Jeep. gas milage went up and well, on 35's and 4.56's i embarassed an Eclipse one night driving home. the 4.0 has a low-ish compression raito, 8.8:1 which makes it nice for forced induction. I run 7 PSI and its plenty.