jimlab

It's not that hard to keep an engine alive that doesn't have enough power to hurt itself in the first place...

Of course naturally aspirated rotary engines last longer. They don't require turbocharging or have to strain to make a measly ~160 horsepower.

Jim Swantko

Why all the rotary hate?

jimlab

Maybe the fragility, noise, poor BSFC, and heat out-weigh the benefits of an artificially high and meaningless power-per-liter ratio.

2MCHPWR

iTrader: (2)

mine weighs 2730 with no PS, AC or ABS. it has 50.5% frt/49.5% rr weight distribution without me in it.

EJayCe996

Question, at what point does a N/A rotary "strain"?

KeloidJonesJr.

iTrader: (8)

Once you go rotary you won't go back. The purpose of RX-7's are their "rotary" engine. It's unique design gives it one of a kind performance seperating from the rest of pistons engines.

jimlab

At the point at which you have to resort to peripheral ports or bridgeports to try to make the peak horsepower an average V8 could make effortlessly at half the rpm...

Nihilanthic

So, according to you, the RX7 is nothing more than a gimmick?

Sorry, Id rather ditch the gimmick and keep the great bang/buck chassis.

capn

yeah, and a bad habit to catch fire and break parts, have poor gas mileage, barely pass smog testing, and have no torque.

yeah it definatly "seperates" the car performance wise.

JustinStrife

iTrader: (2)

One of a kind performance, as in no torque, no reliability, and sounds of a weed-eater?

DCrosby

Cutch has been baiting people for (years)?? has it been more that a year allreay clutch ??
Almost huh ???

EJayCe996

Well i guess i was looking for more of a "at what hp range" but since you say bridges and periphs the hp range is roughly 250-350 so effectively ~doubling hp, halving the lifespan and gas mileage... but then the same can be said for any other motor. It all just depends what the motor's base hp was in the beginning as to how much you'll be putting to the wheel when doubling the hp. Btw, I am in no way trying to justify one way or the other, just trying to pull more information. Like Nihil said, the 7s are a bang for the buck chassis, some want it more for power apps, others for more of a fun-factor basis. I got one because I felt like it'd be a fun car (and it is). When the rebuilds come are when I'll truly find out how "fun" this car is although I do have a lot of patience

88IntegraLS

Yep, same here.

88IntegraLS

I guess if you are prone to make decisions based on fashion rather than performance, that must be true! Keep posing.

Merc63

See, you're looking at it in a way of justifying low overall hp. The LS1 will make 350 hp STOCK, so putting it in the RX7 is like doubleing or tripling the hp WITHOUT the reliabilaty penalty that making a rotary make that much power incurrs. THAT'S the point.

Say I have a chassis that is exemplary in all areas: looks, ergonomics, balance, suspension layout, braking, and weight. I want 300-400 hp and similar levels of torque. Is the most logical method 1) spending a ton of money taking a tiny engine that makes low hp in stock form and modding it considerably to that hp level at the cost of reliability, or do I 2) use a larger displacement (but barely heavier) engine that makes those power levels in stock form, for less money and more overall reliability at that power level?

Yeah, your stock N/A will be fairly reliable (my last one made almost 110k before eating the rear rotor), but it does so at a distinct power disadvantage (hell, a stock N/A RX7 is slower in a straight line and slalom than a CRX Si of the same year... scary). And as we've found in doing dozens of these conversions, the only real advantage the rotary powered RX7 was supposed to have, it's "perfect" balance, is not negatively affected by pretty much any engine you can put in there, due to the layout of the chassis.



Trust me, the "fun factor" is still there. Handlig, balance, etc. it simply isn't saddled with low power. Many of us built our V8 cars after dealing with rotaries for many years (I owned and raced a bunch of rotary powered Mazdas and a couple other rotary cars). But we realize that the RX7 is vastly more than its engine.

EJayCe996

That is only half of what I was saying. Yes I was looking at it as an overall. But then I was also comparing to the "well a LSx is more reliable at xxxhp than a rotary." The rotary has already doubled its hp at xxxhp while the LSx is merely starting there. Now yes the "duh" factor is a motor designed at an already high hp is gonna be more reliable than one that had to be "extensively modded" to get there. I mean, I could turn around and say a Bugatti Veyron engine (don't know the spec code) at an estimated 1001 hp is more reliable than an LSx motor of the same output(of course I don't think any Veyron out there has over 5k miles on it, or a long-term test has been conducted to actually prove that) due to the fact the Bugatti's heart was designed for that hp. You've then almost gone 3-fold on that LSx's output.

I didn't say you lose the fun factor, but what you've said here says to me that you didn't feel the car had enough power, and thus dipped into that so-called "power application" side of my comparison. The guys still with rotaries (turbo of course or 20b N/As) but have over 350hp (my opinion of the upperline of "useful streetable hp" for just about any non-supercar) also fall into this category. I also know that with all the extensive modding to get 2 rotor rotaries in the 400+ range usually calls for a larger everything in the engine bay, thus making the motor as a whole weigh a little more than an LSx in some instances.

stilettoman

iTrader: (1)

I agree with what EJayCe996 is saying. Personally, I think the Bugatti is a ridiculous car - at least the Pagani, Koenigsegg, and Spyker are using a production based engine. The most impressive car of the bunch to me is the C6 Corvette - you have to spend six times the money to get anything that will beat it. And how many time in your life would you be in a situation where the acceleration, cornering, or stopping ability of a C6 Vette is not adequate???

My V8 powered 1st gen is, to me, just a low budget Vette. It will never corner like a late model Vette, and is not as fast, though it probably stops about as well after I did the brake upgrade. But there is some satisfaction in making a purse from a sow's ear, and having something a bit different that you created yourself. For me that is a large part of the motivation.

Nihilanthic

I just want a fast, but well-handling car without stipulations, conditions, gimmicks, or a high price.

Honestly, if I wasnt swapping a rx7, Id probably be turbocharging a miata and figuring out how to sit in it (Im 6' tall, long limbs).

GtoRx7

iTrader: (5)

Torque is a only a 1D of measurement, hell my 1/2" impact gun has 1000ft-lbs of torque, but it wont beat anything in the quarter. You need to provide torque for a period of time, to create hp. Horsepower is the ONLY thing that provides WORK. Race a car with a diesel engine, 650ft-lbs/ 255hp versus a exact same car/ weight but with a engine with 215 ft-lbs/ 265hp (optimal gearing for both) and tell me who would win? Hell hitch them up to pull some weight, who would win then? If you think 650ft-lbs would win you'd be wrong again. Torque is a means, not a end. Higher torque with the same hp is more stressful on drivetrain componets, which needs to have heavier, beefier pieces to hold together longer. This adds weight. A engineer at Mazda would have never used the RX-7 tranny/rear end in a production car if its engine produced 400ft-lbs of torque.

jimlab

Do you write dialog for a soap operas in your spare time?

Actually, horsepower is only a calculation of work over time, derived from torque and rpm.

horsepower = torque * rpm / 5252

Torque is what actually moves the car by producing thrust at the contact patch. Is it time for a Physics refresher course?

f = ma

A 10 horsepower "advantage" isn't going to save the car with low torque. At any given rpm, the diesel-powered car would have a higher wheel speed thanks to a torque and gearing advantage, and would easily blow the doors off the 265 horsepower car if the weights were the same.

Real world example...

My wife's Ford Escape Limited's 3.0L V6 produces 200 horsepower @ 6,000 rpm and 193 lb-ft. of torque @ 4,850 rpm, and weighs 3,492 lbs. My Lincoln Town Car's 4.6L V8 produces 205 horsepower @ 4,250 rpm and 280 lb-ft. of torque @ 3,000 rpm. It weighs a hair over 4,000 lbs. With the 5 horsepower "advantage" offset by 500 extra pounds of weight, which do you think is faster and why?

A: The Town Car is faster. It has a much broader and more powerful torque curve and a 3.07:1 differential helps turn it into higher wheel speed at any given rpm. More wheel speed means more ground covered per unit of time.

Want to bet? Put your 3-rotor in a 1-ton Ford 4x4 and let me know how well it tows.

Then again, if the rotary engine reliably produced 400 lb-ft. of torque and was able to pass emissions while doing it, the RX-7 might still be in production...

88IntegraLS

Ah the classic peak horsepower rotard rebuttal. Without knowing the exact integral of the horsepower vs. rpm function of each engine and their respective gearshift points, it's all bench racing.

Rotaries blow, and that can be proven.

JustinStrife

iTrader: (2)

I don't even have to burn you when everyone else does such a good job.

You might think torque doesn't make a difference, but as a Corvette owner with 350hp and 360ft/lb torque at my disposal via a V8, I can wax many a car where it counts.

Now why am I interested in RX7's if I love the LS1? Cause the FD is the prettiest car made in my opinion, with the C5 coming up a close 2nd. So why not get the best of both worlds? Take what I truely love about the C5(the drivetain), and put it in the body that's the best? The ultimate car for me.

GtoRx7

iTrader: (5)

You can have all the torque you want, and it wont move anything! Torque is a force, as you well know, and for it to do WORK it must have rpms, At the very second it moves .000000001rpms it is turned into HORSEPOWER!
Here is how I understand my example: Using real world Tq x rpm/ 5252.
I used two engines that are real engines. The first is a Caterpillar
engine out of a Ford 650. The second is a near stock FD engine. The Cat produces its peak HP at 2000rpms, and its torque is the same from 900 rpms to 2000rpms. A FD rew, has 216ft-lbs from 2500-6500 rpms (rough est.) So keep the trannys the same gearing, and just change the rear end to achieve the same speed in each gear. So first gear tranny is 3.40 with a rear end of 1.26 for the diesels, and a rear end of 4.10 for the REW, would produce 466 wheel rpm for BOTH. Do some quick math and the REW has 3011 ft-lbs and 267 hp @ 466 rpms. The Cat would have 2,784 ft-lbs and have 247 hp @ 466rpms. Do further math and you'll see the FD has a broader wheel hp also. So who would win? Yeah My 3-rotor would out-tow the cat engine like a bitch if we are geared for the same speed in each gear. But have my 3-rotor geared the same as cat motor wouldnt be fair, as I would go 4.25 times faster in each gear. So why do Diesels have so much torque? To last longer, by having less RPMS, and longer clutch life. Need further proof? http://www.yawpower.com/tqvshp.html

So to me, torque is a means, not a end, higher torque is higher stress on axles, rear end componets, and trannys. To do it "engineered" properly, these componets would need to be larger and heavier, add to the fact torque most likely is coming from displacement, and the engine may or may not be heavier as well. This is why in racing class worlds, the rotary did very well, low torque and weight, high hp, and was reliable, = one very light chassis. The rotary is near all cast iron, and has cast iron turbos, it will way the same with over 1000hp in a drag car, the LS1 is n/a non-turbo all-aluminum, it wont get much lighter, ever. Put turbo's on it to make 1000hp and it will weigh more no? Need a cast iron block for that? Oh yeah more weight yet. And Jimlab, good to hear from you again.

jimlab

I've read the article before. Have you? You should have stopped here...

With this same information, we can also calculate the acceleration rate of the vehicle, but first we need to consider Newton’s second law of motion, which states that "Acceleration is proportional to force." and "Acceleration is inversely proportional to Mass." This law is normally stated more simply as "Force equals mass times acceleration." or F=MA. If we rewrite this to solve for acceleration, we get A=F/M. To find the rate of acceleration for a vehicle, we simply divide the force (In lbs. at the tire contact patch.) by the mass (Total weight of the vehicle in lbs.)

No mention of horsepower there. Why? Because torque is a twisting force, and rate of acceleration is determined by force at the contact patch. Not horsepower.

Let’s calculate the acceleration rate of a 1st. gen. RX-7. The engine has a torque peak of 100-ft.-lbs. In fourth gear, the ratio is 1 to 1, and so the torque at the output shaft is also 100-ft.-lbs. The ring and pinion ratio is 3.909 to 1, and so the torque at the rear axle will be (100 times 3.909) 390.9-ft.-lbs. The tire diameter is 24 inches, and so the lever length (Distance from the center of the axle to the ground.) is 12 inches, or one foot. The resulting force at the tire contact patch will be (390.9-ft.-lbs. of torque divided by lever length of one foot.) 390.9-lbs. of force. The total vehicle weight with a driver is 2600 lbs., and so the acceleration rate in G’s (The force of gravity.) will be force (390.9) divided by mass (2600) which equals .15 G’s.

Again, no mention of horsepower. A vehicle's acceleration curve follows the engine's torque curve, not the horsepower curve. Peak acceleration in each gear is achieved at the torque peak, not the horsepower peak.

Which just indicates to me that you don't really understand the math involved. That's OK, not many people do.

I hate to break it to you, but you can't have higher horsepower without also having higher torque. At any rpm.

GtoRx7

iTrader: (5)

Alright, that all makes perfect sense, but how is it, I broke down TWO completely different engines, and to make them both equal in speed per gear, THE REAR TIRE TORQUE NEARLY IS THE SAME, so how would the higher torque motor accelerate ANY faster than the Lower torque engine, if the FT-lbs at the tire are higher on the low torque, higher HP car? Its the horsepower that is still providing the motion, as FT-lbs has no reference to motion, no? Please enlighten me. Because it seems to me we are both right and dont realize it yet.