bogeypro

I just thinking of ways to up the hp and torque and still be NA. Seems to me that adding new cams and stuff would add small amounts of hp, but is it possible to add a different crank with a different stroke? I'm new to this so I don't know what all would be involved in adding a new crank. would you also have to add new cams or adjust the timing, etc...?

purePro5

Pulling the crank is very involved, and if you don't do it yourself, very expensive as well. Stroking the motor would be very beneficial. There is no replacement for displacement. he only thing that would net you more power on a consstent basis would be turbo. I would suggest the turbo oly because it is a cleaner install and there is much more tuneabiity. If you want to stay NA, then go with the pistons, manifold and cams. All ths wll cost you about half the price, but it will nt about half the hp. Your choice.

Bruce95fmla

Would be nice , but would not be worth the personal time or the money to pay someone to do it

carguycw

Stroker cranks are one of the oldest tricks in the book, but they come with some drawbacks. You don't mention what model of Protege you have, but the 2.0L FS-DE engine already has a low bore-to-stroke ratio for an automotive engine (83mm bore and 92mm stroke). Long strokes with small bores make for a very torquey engine, but have some problems that aren'y very obvious to a layman...

The first problem is the forces on the pistons and rods. Piston acceleration increases in a linear fashion with decreasing rod length and increases with the square of the stroke. In other words, if you decrease the rod length by half, you double the force, and doubling the stroke increases the force by a factor of 4. The deck height (distance from the crank centerline to head surface) of an engine is fixed, so if you lengthen the stroke, you have to decrease the rod length by the same amount to keep the pistons from popping out of the top of the block. Therefore, lengthening the stroke also decreases the rod length. What you get in the end is an engine that won't hold together at high rpm.

The second problem is piston area. Power output is largely dependent on the area of the tops of the pistons, which is limited by the bore, and a small bore also limits the size of the valves. Result? An engine that won't breathe at high rpm.

In order to make good POWER with a small engine, it needs to REV. You have to move lots of air through it. An engine with a small bore and long stroke will make good torque because of the leverage exerted on the crank by the longer stroke, plus the engine will breathe better at low rpm because the pistons move away from TDC faster, which pulls more air into the cylinder. (Long strokes also have better emissions and fit better into narrow FWD engine bays, but I won't get into that.) Unfortunately, these same factors turn into disadvantages when you try to spin the engine past 8,000 rpm. It won't breathe and it won't hold together. For POWER, you need a short stroke and large bore. The FS already isn't set up for good top-end power in this regard.

Bore/stroke of several 2.0L 4-cylinder engines, to give you an idea...
Nissan SR20DE: 86mm/86mm
Honda S2000 engine: 87mm/84mm
1956 Ferrari 500 Testarossa: 90mm/78mm*
Mazda FS-DE: 83mm/92mm

Notice a pattern?

* Yes, Ferrari HAS made cars with 2.0L inline 4-cylinder engines. No BS.

eeterp

Chris,

Where do you get your engine build up info?

carguycw

10+ years of reading car magazines and automotive-related books. There's no single source book that I can recommend. Sorry.

bogeypro

wow, thank you for the very informative response. You guys impress me more every day

carguycw

One more follow-up...

For some years now, many carmakers have been shifting to progressively longer-stroke and shorter-rod designs for economy car and truck engines. The reasons are detailed thoroughly in the link that Jesse posted. (Good link BTW! ) Designing an engine this way promotes good low-end torque, which is very important given Americans' love of automatic transmissions because automatics become more efficient (not to mention more pleasant to drive) when you apply more torque to them. Second, a long stroke/ short rod design promotes good cylinder filling and air/fuel mixing at low rpm, which is VERY important to meet modern emissions standards. Third, friction and rod angularity problems have become much more tolerable because modern metals can withstand more stress than older metals.

This has delivered in a generation of engines that are much closer to the point of diminishing returns when you start talking about increasing the stroke and decreasing the rod ratio. Before ~1980, small displacement engines were usually quite oversquare and had great rod ratios, which was done to maintain good top-end horsepower and low internal stresses. Back then, emissions were irrelevant, and automatic trannies were limited to 2-3 speeds and most people knew how to drive stick, so most small-engined cars were sold with manual trannies.

Example: my old 1971 Datsun 240Z had a bore/stroke of 83mm/73.7mm (1.13 ratio) and although I don't remember the exact rod ratio, it was ~2.2:1! However, compare this to the new Nissan QR25DE- a new Nissan engine with similar displacement and power output to the 240Z's L24- it has 4 cylinders rather than 6, with a bore/stroke of 89mm/100mm (0.89 ratio) and a rod ratio of around 1.3:1. Easy to see why an L24 will withstand 8,000 rpm with the stock bottom end, while the QR25DE has trouble approaching 6,500 rpm.

Bottom line: Stroker cranks used to be a good trick, but they don't really work on newer engines.

eeterp

That's fine, keep your secrets. LOL!!! I'm saving this thread in my engine info folder. What's the bore/stroke ratio of some of the 13,000 RPM bikes?

Got any pics of the 240Z?

arapau

After reading carguy's informative explanation of why our long stroke engine is not condusive to mods, would a shorter stroke crank and oversized pistons make the engine turn up higher? Seems like you can't really make a small displacement engine have low end torque and put out decent horsepower. I know Hondas don't have much low end torque, but I'd love to give up some of mine for another 1000 RPM and 160hp.
BTW that explanation of bore/stroke was the best I've ever seen- simple and clear.

eeterp

Yeah, I was wondering why you were a moderator on hondasociety....

BTW, I finished Maximum Boost (good read of course).

fastmov4

New reply to an old thread---it's amazing what good the "search" feature does! Oh, and Chris, you're awesome, buddy. A fountain of knowledge! Can I come study under you?

Anyways, I've been doing some research on several forums (probetalk.com, mazda626.net, alabamaprobeforum.org, and here) regarding increasing the displacement of the FS motor. My goal in upping displacement is to give a healthier baseline before going F/I (either a turbo setup or supercharger). HP goal is ~240-260 @ the crank @ the lowest possible boost setting. Torque goal is higher (hence why I want to go with more than 2.0L or displacement) @ ~260-280 lb-ft @ the crank.

Chris mentioned that, in increasing the stroke, you're going to seriously hamper the engine's ability to hold itself together at higher revs. Well, how about if you keep the engine's redline to about 6000-6500 RPM (like in the new SE-R)? The engine would be in a daily driver, so the car would rarely use power in the upper range of the tach. Performance between 3000 and 5000 RPM would really be the objective.

Since stroke is only one-half of the displacement equation, let's talk about the other half for a second: bore. How much could the FS be bored while still retaining cylinder wall integrity (aka not removing too much metal from between the cylinders)?

Also, I know that the World Challenge Protege5 teams were increasing displacement from the factory 2.0L to as much as 2.3-2.5Ls. Mind you, they were going for ultimate N/A performance, but certainly some of their tricks could be put to use in this application. Anybody have any links to any of the teams?

Thanks in advance for any help ya'll might be able to provide, and thanks for tolerating another NooB.

Chris