i might get a new engine with 3mm seals and huge ports. are the big ports going to hurt my stock twins if i ran them at 15 psi ?
will they out flow the turbos at that boost level?

 

anyone?

 

I'm curious too. I've got an atkins stage II street port--someone warned me against running higher boost levels with the SP as well. Experts?

-BN

 

Nope, PM a member here "RTS3GEN". He's running a Pettit Dowelpinned Racemotor on stock twins without any problems (and he's been doing it for quite a while!).

 

thanks. anyone else?

 

Uh...wait a few months..and then I'll tell you. I'm getting a streetport with the stockers...why are you going with 3mm seals? Everything I've read say that's a bad idea, and it's junk..

 

so much for the ol' 15 psi rule, heh. Great question BTW, I always wondered myself. 13 psi on a street/race port and those turbos are working harder than 13 psi on a stock port. Still haven't been able to get compressor maps for these things.

 

ttt

 

I don't know that a larger port will necessarily "hurt" the twins, but if you go real large on the exhaust ports, the velocity will be lower, and spool-up performance will suffer... i think larger ports are more suited to mating with larger single turbos.

 

yeah what ptr said! yo should probably go single turbo w/ a port..

 

Its not going to hurt anything and depending on the port job can help. Its not going to HURT anything. Just make sure if you blew a apex seal in the old engine you need to take the turbine housings of the turbos and check the entire wheel to make sure its not damaged. If you blew an engine I'd say there is a 95% chance the turbine wheels are shot.

Porting is one of those thing that if done right can be soooo awsome, if done wrong can be sooooo bad. You arent going to want some giant exhaust port but some porting is fine.

STEPHEN

 

No...There are 5 or 6 locally here that run 15 psi on a LARGE streetport with the stock twins....BTW: I have been building rotaries for 20 years...

 

So basically the 15 psi stock twin rule is garbage since 15 psi on a large streetport is like 18 psi on a stock port?

 

I believe that was another "myth" of the FD world. However, as people have pointed out in various threads, the stock twins begin to loose efficiency at a certain point. Some people believe that over 15 PSI is that point, however I don't think anyone has come up with any hard facts.

I think everyone can agree that running the stock twins on extremely high boost will shorten their life span quicker than at normal boost levels.. That's about all we know for sure.

 

The stock hitatchi twins are not a serious power maker, the reason mazda went with the sequential twins was to try and eliminate any type of turbo lag as is the objective with most twin turbo methods. Running the car with stock twins on a streetport should do nothing to the turbos as the porting just allows more air/fuel to enter into the combustion chamber. You would only start effecting the turbos is if you started mucking around with the exhaust ports you would effect the flow of the exhaust through the turbo which will inevitably change spool up times.

 

What about opening up the intake port and polishing/leaving the exhaust port? Will that help with a twin turbo setup?

 

Should do.

The main reason your standard street port isn't as effective with twins as with singles is the stock exhaust manifold. Even if you port the exhaust side of the engine you still have that manifold as a chokepoint. You *should* see gains if you open up the intake side.

I'm still running stock ports though, so all my knowledge regarding porting is pure theory.

 

what about a half-bridge on stock twins?

 

Whats so bad about 3mm seals?

 

I had a large street port from IRP along with a PFC, 550 1300 injectors, intake, and 3in exhaust with ported waste gate on stock twins and made 320 rwhp on stock boost. PF supercars tuned it and the turbos spooled quick and hit really hard. I blew it due to my PFC setting being changed and need to have it rebuilt but i am going with the same port.

 

Just to bring this back...What do you guys constitute as a LARGE street port?

Any pics...?

 

Every shop has their own idea of a large port, in my opinion, the ITO port is large, anything less is normal/medium. There is no need to go anything near a large port on the stock twins, the stock ports can handle anything the stock twins can throw at them. Im not saying there isnt advantages to port work with the stock twins, but a large street port on stock twins is just wasted effort.

 

What some consider small I may consider large or vice versa. Thats why I was asking for pics BTW whats an ITO?

Well doesnt it all come down to physics? How much air flow the turbos flow to how much the port can flow?

In theory using the above forumula you should be able to match the flow for optimum results, no?

 

Judge ITO streetport is what I am referring to, search that user name and you should find several pics.

When most people port their engines, overlap is created between intake and exhaust. Some boost is lost thru the exhaust port and will cause in some applications less low end performance. Porting really depends on the application it is being used with, there are hundreds of dyno sheets on this forum showing cars with streetports on stock twins, and others on the stock port with the stock twins. Very very little top end power difference between the two on comparable healthy engines/setups with the same tuner is noticed.

I have seen several people claim between 360-375 rwhp on the stock port with stock twins around 16-17psi, most with street ports see pretty similar results. There are people here on the forum putting down 500+rwhp on the stock ports with relatively small turbos around 20-21 psi of boost.

The pic attached is my standard port, nothing large but slightly larger than what most shops consider a medium port. I tried finding pics of when I used the ito template for a customer but couldnt find them. With the ITO porting template you extend the closing edge of the port to it is near breaking into the water jacket behind it. A lot can be gained for the stock twins by simply cleaning up the factory casting marks in the ports and properly back cutting the opening edge of the port and cleaning all the casting from the "bowl" and intake runners creating less turbulence. The factory castings can be rather extreme at times as you can see in the pic of the primary port I am attaching.

 

here's the only compressor map on the twins that i have found. as you can see it is incomplete as to scale.

we can back into the X scale.... it takes 1.92 cubic feet of air to produce one rotary rear wheel hp. let's assume that the motor is making 385. two turbos so 385/2= 193 rwhp per turbo.
193 X 1.92= 371 CFM/14.471= 25.6 lbs/minute. that sounds about right to me re total air delivery on the X scale.



as far as porting...

the relationship between the exhaust and intake ports can have a major effect on the point at which a compressor cavitates. the amount of overlap can effect the output side force against the compressor.

when considering ports on a rotary there really is alot of confusion.. if you really want to understand what's going on you should study piston engine valve timing/camshaft dynamics.

that all said, messing w the stock turbosystem is putting lipstick on a pig. lots of EBP will cause high egts and kaboom. throw some AI at it please.

hc