20bfd3s

Hi
I am choosing right porting for my engine between PP and big street now.
please advice about advantages/disadvantages of each porting type.

From that I know about PP:

(advantages of PP)
1) more power and torque at high rpm

(disadvantages of PP)
1) engine have to be built to work at higher RPM. It is more comlicated and reliability will be less
2) poor idle and low end torque


I am going to run engine with 35psi of boost.

if we compare dyno charts of two engines, A is PP ported and B is big street at same boost then:

1) at that RPM engine A will start making more torque than B?
2) what will be torque difference at , for example, 9000rpm?


Just want to understand do I really need PP or not.

thanks!

bill Shurvinton

It's tempting to say that, if you need to ask you shouldn't be considering those boost levels. There are not many turbo rotaries running over 2 bar. Look at the dyno plots for ErnieT in this section.

But to cut a long story short, I have not seen any evidence that shows if a PP ever gets to the point of being a better choice for ultimate boosted power. Peter (Rice Racing) has tried both in similar enough setups to have an idea and IIRC he ended up unconvinced about a PP. The port does allow lots of air in, but lots of it goes straight out the exhaust again.

If you want to drive the car on the road, forget about the PP. For an out and out trailer queen racer then you could consider it.

20bfd3s

thanks for reply
this is a drag only car, not for street at all.

goal is to get around 1200whp with 3 rotors

just wanted to know if this is possible with big street port or restrictions are very significant.

if the difference just around 100whp then i am going to forget about PP and go with big street.

looks like this is so!

Cheesy

if you go PP you could run a 'short 20b'

peejay

Street port - kinda weak, kinda strong, WHAM HERE'S THE POWERBAND, oops time to shift.

Peripheral port - a little soggy, OH CRAP HERE'S THE POWER, WHEN WILL IT END ????

Street ports tend to be peaky and make good power only at high RPM. Peripheral ports make power *everywhere* once you're over about 2k. Below that, it's kinda "eh".

Now, the flip side.

Street port - driving around town and just driving it like a normal car, hey wow it braps a little bit at an idle, but it goes away so quickly when you touch the throttle.

Peripheral port - GOK GOK GOK GOK holy crap this thing barely runs in town GOK GOK GOK I have to drive it either at full throttle or with the clutch in GOK GOK GOK GOK because if I try to part-throttle it at low RPM it just bucks so hard I think I'll GOK GOK GOK break a U-joint or something.


If all you care about is power, PERIPHERAL PORT. It will make more power than the street port at ANY RPM you care to measure. If you have to drive it on the street (like, stop and go crawling city traffic) you might want to reconsider.

REVHED

Fuel injection really helps with the low rpm/light load drivability.

diabolical1

iTrader: (3)

personally, i think you answered your own question but in this case, yeah, i'd have to go with the peripheral port if it's going to be a dedicated racecar. not sure what to tell you about your 1200 WHP and 35 psi goals though except you should have some deep pockets.

Marcel Burkett

TRY a SEMI PP !! , You'll love it !!!!!

20bfd3s

yes I am going to run short 20b. but is there anything special about short 20B and PP?

I know about semi-PP.
one guy here built his car in Japan and dyno shown 677HP at 1.3 bar with semi-pp 13b...

http://www2u.biglobe.ne.jp/~fam/fammsg/index.html

but where can i get good semi-PP templates??
i think good template is a key...

also I think it is much more complicated to tune car with PP since free air partially goes to exhaust and changes AFR reading of wideband that might show lean while actually it is not so lean...


since i am building drag only car my working rpm area will be from 7000 to 8500.
i will be using th400 automatic transmission so there will be no pressure or rpm drops. thus i just dont care so much about power before 7000.

Yes, but what`s the exact difference? if it is 100HP then i`d like to keep steet port and run a little higher boost if needed. But if its 300HP or more...

enzo250

You won't see any real power till about 8k. Revving it to 8500 is not enough.
You'll need to go to at least 9500 maybe 10k.

z8cw

I know about semi-PP.
one guy here built his car in Japan and dyno shown 677HP at 1.3 bar with semi-pp 13b...


This is the highest HP I have ever heard of at less than 20 pounds of boost!!!!

GodSquadMandrake

It's not the pounds of boost that matters, it's the CFM.

20bfd3s

how about bridge porting? isnt it close to PP in flow?

why it is so unreliable in comparision with street?

Marcel Burkett

The bridge is close but the pp is better , since a round port will always flow more than the relatively small eyebrow shaped bridge port , the unreliability of the bridge is due to the bridge itself , to get a decent sized port , the bridge often ends up being very thin in size , this thinness often compramises the strength of the bridge and it sometimes breaks , destroying the motor in the process.

z8cw

I guess you don't need a turbo than since CFM...cubic feet per minute is a function of cubic inches of the combustion chamber, how efficient it can be filled and RPM.

CCarlisi

Mandeville told me P-Ports are at a disadvantage to street ports below 5,000rpms. However, he works primarily with N/A motors, so I'm not sure his opinion applies here.

peejay

Wellp...

I dunno, *mine* sure as hell was a lot stronger than any sideport engine at low RPM that I've ever driven. (I've never driven an N/A sideport 20B, but plenty 12A/13B stuff) And that's with an awful tune to boot. And that is taking into account that whenever anyone drives one of my sideport engines they say things like "DAMN this thing has a lot of lowend power"...

z8cw, it's semantics here, but generally CFM as regard to turbos is the CFM on the inlet side, since once you compress it beyond atmospheric, volume flow almost isn't important compared to mass flow. CFM is easier to deal with, since it doesn't change with weather conditions.

z8cw

Sure, the weight makes the difference thats why we like to compress the air and messure the pounds per minute. So I guess PSI is important than. Most turbos we typically run on our cars flow enough air for our engines, that is why most set-ups make very simialr HP....ie about 400 at 15 psi with a street port and the usual unrestricted flows, front to back. So the difference in establishing meaningful references for HP is PSI. I doubt that anyone here would post a, "I made 400hp at 25 PSI, blowing my engine because I put a little turbo on there that produced more heat than flow."

j9fd3s

iTrader: (3)

havent driven a pp motor yet, but the full bridge i drove had more lowend than my stock port gsl-se, from 2000 rpm. we even had 3 people in the bp car so the weight of the 2 cars were about the same....

Cheesy

well if you are going to run a short 20b pp is really the only choice otherwise the middle rotor will have very small ports ie no secondary ports

13btnos

iTrader: (1)

Not a 20B but a 13BPP turbo http://ausrotary.dntinternet.com/for...=77936&start=0

Quote from thread "Dyno today, 420HP at the tyres, slipping clutch and at only 7300rpm and 9psi boost! Made 9psi just over 3000rpm, so turbo is a little on the small side (currently GT42) for new target HP for this application so is going to be changed when the engine is run in."

420rwhp @ 9psi very impressive!

JBurer

I guess if you're drag racing it, you're not going to be too concerned with the power band.
However, trying to revv a turbocharged rotary out to 10-11k is pretty silly. You might get a couple of passes out of the motor before it needs to be overhauled - which means you'd better have some good financial backing!

20bfd3s

you`re right. i figured it out....
now choosing between semi-PP or full PP...

thanks!

z8cw

How about a full PP plus the primaries, anyone ever tried this?

20bfd3s

that might be not very good idea since not always bigger is better. there will be lower flow speed and probably it may cause some other disadvantages...