peejay

CJ's PP idled at ~1500. I consider that to be "idle". Jeez, it's only 1500rpm. I dunno about you but even when driving the stockport I never see below 3k under any circumstances except sitting at a light.

Another thing with the streetport engine is how peaky it is. Torque peaks at 5500 or thereabouts and it falls off rapidly. Bridge/peripheral ports have a tabel-flat torque curve that simply does not fall off. It's not that they're peaky, it's that the simply don't lose torque as RPM goes up, so you can rev the **** out of them (and thus maintain the higher mechanical advantage of a lower gear) without losing acceleration.

Someone tried to prove how peaky a given PP engine was by supplying HP figures at various RPM levels. I did the math, and the 13B was putting out something like 150 or 175lb-ft of torque at every RPM point he called out. That's table flat, far from "peaky". When you have a flat torque curve like that, HP just keeps going up and up with RPM so it's advantageous to rev it to the mechanical limits of the engine.

My SP idled at 1500rpm under many conditions, and I loved every minute of it When it was fully warm it'd idle down to 600-900 (slow lope) but that didn't matter, the only time I'd drive in the city is with a cold engine...

My next engine *will* be a bridgey. I see no downsides.

PaulFitzwarryne

The NSU engine was designed for pp, but its port characteristics were not extreme.

Jeff20B

iTrader: (13)

Now I'm getting convinced to go bridgey. I've got to rebuild my 12A anyway. Why not?

peejay

Exactly. Why do people have to assume that peripheral port = "make the ports a fricking huge as possible and put a giant *** carb on it that doesn't start metering well until the tach needle twists off"?

REVHED

Peejay's right (as usual ). Here's an interesting graph. It's a comparison of VE between stock and peripheral port engines. VE is closely related to torque production so how the hell can that be considered peaky?

RICE RACING

Hey, that is my graph !!!

Peejay is a smart guy indeed.

PP's and BP's only real down side is lack of low load low speed fuel efficiency..... read bad economy below 4.5k rpm in a Mazda Rotary application.

Generaly above this engine speed they make more efficient power than a side ported engine, depending on what spped range the porting and manifolds are "tuned" for.

I can tell you from practacle experience that a 260bhp Peripheral Port 13B will get about 16mpg no matter how gently it is driven v's a 13B Turbo capable of well over double the BHP will get over 22mpg when driven with far less carefully. This is the real world facts, unfortunatley....I know from 6 years of PP daily driver experience !

They are a real rotary in my opinion, but they use a bit too much fuel for a daily driver. Drivability is almost the same (good) as a big street port.

RICE RACING

Paul, I was fortunate enought o drive a NSU Ro80 a few years back, this car made 135bhp at around 6000rpm. Same engine capacity as the R100 motor and the R100 made 105bhp at 7000rpm, another car which I have driven in std form.

the NSU does have alot more torque from 3000rpm onwards compared to the R100, but as in the case with more radical PP we use today it's BSFC of fuel efficiency is about 30 to 50% worse than the R100 side port engine at revs below 3000rpm and low loads (BMEP of less than half maximum IE, 95% of city driving situations!!!!!). I used to have a NSU rotor housing which was very interesting indeed to look at compared to what I am used to building v'small PP's which produce a very similar VE to the graph I posted, great for power, but unfortunatley not good for economy when the engine is not under much load. It is a fundamentel problem with the Peripheral port in a "pre mixed charged engine" In a stratified charged engine where the fuel is injected in the combustion chamber near the spark plug the Peripheral port is not a problem, in fact it is a benifit due to the massive amount of air it can flow.

WackyRotary

I find a simialer trait with my bridgey. Its milage stays in the 14-16mpg no matter how I drive it. As a result I drive it rather hard.

peejay

14-16mpg is right good in my opinion... I've had cars with less performance and worse economy

The only problems I would see are emissions performance and noise level. Emissions performance is a no-brainer, just swap a stock engine/emissions system back in the car every two years for the emissions test. (Good opportunity to freshen the engine at that time too) Noise level... well as I've said before, I used to drive an open-header 429 Ford on the street and managed to avoid trouble from anybody except my shop manager who told me to put mufflers on the beast or find employment elsewhere! (So I put two ratty, rusted hollow "turbo" mufflers on it to meet the letter of the demand )

851stgen12a

fortionatly All my cars are liscensed in a non-deq area.

I dunno I guess I will probobly go with a bridgey, seems like I have stired up a real bees nest with this one.