Lets talk Wankels

[rx7 mike]

Great thanks again ..I will try to email them

Michael.

[peejay]

Due to the power band of the Bridge and Peripheral port engine, you need a minimum of a 4.37 gear in the street. A Bridge or Peripheral port engine does not make any torque and are dogs and un-driveable at low RPM; they will tend to load up and kills plugs easily.

That's complete BS, like defining the length of a piece of string.

I drive my bridge ported car to the tune of about 1000mi/week. Power is a little soggy below 2000rpm but beyond that it really wakes up. Over 2000rpm, it's no contest stronger than any stocker, and this is with 6port end housings which close far too late to be useful. I think the spark plugs are 30,000mi old... FC-style trailing plugs in all four holes, had them out last week and the center electrodes were worn to points But it still runs great, never fouls or loads up or has any problems with starting. ( Look at what an undrivable dog it is)

My previous engine was even better. It made more torque at 3200 than most street ports do at peak. Difference was, it was a four port block.

I also used to have a peripheral port engine. Same thing, the powerband was a little soft below 2000 but then it came alive.

The trick to driving them on the street is less RPM and more load! My car would be loads better with the stock 3.91 gearing but as I use it in a lot of low speed competition, I went with 4.78 final drive so I can use three gears instead of two. I'm in fifth gear at anything over about 30mph.

Oh and the other trick is EFI! Carbs are fine but they are not good at drivability with finicky engines with next to no engine vacuum. I don't think my peripheral port would pull 15" vacuum at shut throttle/high RPM! It was a horrible pig with a carburetor, so I took it back out until I was ready to convert to EFI. Once that was ready, the engine went back in and it became a real dream to drive.

[nhrastocker]

Due to the power band of the Bridge and Peripheral port engine, you need a minimum of a 4.37 gear in the street. A Bridge or Peripheral port engine does not make any torque and are dogs and un-driveable at low RPM; they will tend to load up and kills plugs easily.

That's complete BS, like defining the length of a piece of string.
Oh and the other trick is EFI! Carbs are fine but they are not good at drivability with finick engines with next to no engine vacuum. I don't think my peripheral port would pull 15" vacuum at shut throttle/high RPM! It was a horrible pig with a carburetor, so I took it back out until I was ready to convert to EFI. Once that was ready, the engine went back in and it became a real dream@ to drive.

Hey Genius! If you re-read your post, you will see how many times you contradict yourself.
The discussion was based on a Weber IDA carburetor, not EFI. With the advent of EFI and electronic ignitin systems, you can have a driveable car. In the early days with carbs and points ignition, it was a different story, especially with a "J" style bridgeport.

[rx7 mike]

Guys......again thanks all for the responses but i was actually looking for a response around air flow / velocity through a weber carby , i enjoy the bp type engines but as we all know the dreaded kicking and bucking at low rpm ( as pointed out in the vid ) we all know their issues ....The business`s mentioned are not really interested unless buying something from them ( which is understandable ) so i will give a little info on my 12a bp ......
I had this 12a bp that was built from a guy about 800km away ( next state over ) and was a lucky dip as it ran well but had issues with the electrics as it would only put out about 115rwkw which was a little low so after going through it i found the ignition was playing up with the aftermarket coils as i ended up buring out a module so in went the std coils and the alternator arm stopped the dizzy turning more to advance it so i had to grind a little off and presto i had a little more advance ...back to the dyno and it went to 145rwkw @8700 rpm with a small 39mm choke on a 48mm ida weber. ( and same choke as original test )
I then studied at the local mechanical institute in dyno operation for 10 weeks and over a few nights we tuned it with 40mm chokes and power went to 154rwkw @8800 rpm ish with the lecturer ...with no/minimal loss of bottom end power or tq ........a year later while driving home a water hose cracked and did not see it so it cooked and rendered the plates a little blue so i re built it with another set of plates and slightly different ports mainly on the exhaust due to the short supply in the world of 74-75 rx2 12a rotor housings ( as they had small cracks in the exhaust port area due to the sleeves being removed to open them up to just a little larger than std 12a rx7 ports with sleeves ) see pic attached of latest porting with rx7 housings and sleeves intact.
This did more lower end tq ( from 3500-5500 ) but power was only at 140 rwkw @8500rpm ish ....... ( i tuned another mates rx2 race car with a 12a bp and 42mm chokes in the 48mm ida weber as a trial and the tq rose in the midrange which was a suprise as we had been told it would not work ...he had ignition issues as well so power was down a little ) i then used the same jetting in my 48mm ida weber with a similar result in the mid range while road testing but i did not remove them prior to racing and after a practice i checked the plugs and they were a little rich so i continued on with slightly bettering my times ...... my 48mm ida weber has a blockage in the idle circuit and does not idle well at all so I will be using the 51mm racing beat ida weber with this jetting and choke combo and try it at the dynos in a few weeks to see if there is a difference ( I will have to send the 48mm ida weber away for cleaning and rebuilding so i will use the 51mm racing beat and trial it from there .....................
So after all of that......by increasing the bore size on the carby but retaining the same choke size will velocity increase through the venturis ....just seeing if anybody has actually done this excersie before ?

Thanks for your patience

Michael

[nhrastocker]

Are you running a "J" port in the street?
Also, the exhaust port size is too big for a street application and is killing your bottom end.
The shape of your exhaust port is unconventional and alters the exhaust timing by moving to exhaust event too early.

Take a look at the Racing Beat exhaust size in their website and buy their templates and use as a baseline.
http://www.racingbeat.com/RX7-1975-1985/Porting-Tools.html

[rx7 mike]

I thought it would attract attention ...the port is well within the inner water seal just angled to improve flow ( work of art actually ) ...the exhaust port still retains the sleeve but is wider at the chrome surface than at the sleeve and looks like a funnel and the bottom is not ported down just leveled across ..the tq was actually up in the lower mid range to my suprise and the engine feels more tractable that the old engine and another suprise was the jetting is the same as the old 12a ......old 12a porting pics attached.

Porting down the exhaust ports on an BP NA engine has a negative effect on top end hp and the power stroke is shorter hence people often make good power using 13b gsl-se housings as the opening time is a little later........anyway that is what i have discovered over the years talking to dyno shops that specialize in this area but more are falling away now since the demand is lower these days for rotary engine.

michael...

[rx7 mike]

ok guys ...how about peoples experiences with different weber chokes and timing as a start.....

Michael....

[rx7 mike]

Tried the 51mm weber ida on the dyno and jetting needed to be changed a bit from the 48mm ida weber but still fell short of power , the throttle response was a little off as well ....

Next on the list is slightly larger choke in the 48 ida weber............

Michael...

[clutchdude]

How about a nitro blown rotary?

http://www.youtube.com/watch?v=lc4x2jogNI4

[rx7 mike]

Nice.....

[rx7 mike]

Update....

Tuning a mates 12a bp on the dyno and the operator could not get any power out of it ( this is the 2nd engine with limited ) found power in the split timing ( as it was out by miles ) now his is up to 150rwkw.....

looks like a different rotor recess in the 12a engines requires different tuning requirements ......Im going back to the dynos to do mine now

Michael...