Ok all, i finally got around to taking pictures and testing my new ideas for turbo porting. I coudnt be happier with the results....

The turbo is an upgraded 1989 - 1991 model. It has been upgraded with a 60 series compressor wheel from Turbonetics.

The Problem:

As with Blue TII, i ran into the problem of serious boost spike problems when using a large compressor wheel with a stock exhaust housing on a Turbo 2. Blue TII tried standard wastegate porting with no real results. I started thinking about i and decided to pull my turbo apart (i was having boost spike problems too) and analyze what could be improved over standard wastegate porting to combat this problem.

The Analysis:

Wastgate porting does a great job of helping to control boost spike, but it is limited by the fact that you can only machine so much out of the turbo housing before you start causing the material to be too thin, or have leaks where the flapper seals the two holes. But what if you could nearly DOUBLE the wastgate flow over the current porting practice without any drawbacks? Sure enough, you can. The problem lies within the back plate on the turbo itself. When you shine a flashlight in it and lift the flapper while the back plate is on the turbo, you will see that the flapper bottoms out on the back plate. My idea was to machine the back plate in conjuntion with standard wastegate porting to see if i could raise the boost control threashold.

The Work:

After doing a standard port job on my turbo, i started machining the back plate. I removed 1/2 of the material where the wastegate flapper opens, and continued a "trough" to the large opening where the downpipe connects. I then radiused the opening to the downpipe to aid in reduced turbulence where the wastegate exhaust meets the turbo exhaust. This took a bit of time to get right, patience is key.

The Result:

I found that my boost is ROCK SOLID at 11 psi on my upgraded turbo. No added lag over a the stock or stage 1 (standard porting) port. Durability has not been a problem so far. I removed the plate and checked it at 1000 miles and it has no signs of wear or cracking. I would like to go higher on boost, but i cannot support any more because of lack of fuel. I will update this thread when i find out more with regards to higher boost......

Graham

 

Well, i guess ill have to reduce the size of my pics again, they are 135k each but the forum now has a 100k limit (i thought it used to be 200k, but maybe im wrong). Ill add pics when i get home.

Graham

 

Hum, why did no body respond to this!

Pics man!

James

 

Agreed, pics! If you can't resize them or host, send them to me and I'll resize and host them for you:

ddub114@comcast.net

Just let me know which pic corresponds to which paragraph if you do.

 

yea, i need pics to get a better idea of this. Sounds awesome though.

 

To add on to this idea.....

Could you.....

Basicly cut a hole in the metal plate that lets the wastegate flapper come thru it...almost having the flapper perpindicular to the holes.

Then just weld a plate over the hole so it is sealed?

James

 

No new ideas here. I suggested this to a buddy of mine some time ago (dcee) and it worked great.

DCEE was having boost creep problems with his s5 hybrid boost creeping on his high compression 4 port. Basically I suggested he port the hell out of it, place a divider between his turbine outlet and wastegate, punch a big azz hole behind his wastegate flapper on the back plate so it opens further, then weld on a seperate wastegate tube and merge it into his downpipe. He did a great job of it and it worked, BUT after this mod he had a low boost problem....... The spring in the wastegate diaphram was now being over come and forced open by exhaust pressure. Quick fix, he installed a stiffer spring and has been boosting controllably for ver a year or two.

http://www.cardomain.com/memberpage/390773/2

https://www.rx7club.com/forum/showth...hreadid=155100

https://www.rx7club.com/showthread.p...highlight=dcee


~Mike..............

 

I do remember all that work....

Thanks for the links. Here is one link that goes straight to pictures of the work he did.

http://www.cardomain.com/memberpage/390773/2

Was wondering with that pipe in the way how hard it is to tighten the DP nuts. They are already a major pain in the *** to begin with.

However, if you don't can't do the fab work do you think you could just do what I suggested?

James

 

........

 

wow thats something new to me. I wonder if you could of just made a full back system from there and have True dual from right there. I think that would be intresting. just me 2 cents though

 

Um...how could this be a true dual? For a True Dual setup you would need one pipe for each exhaust port. Since you have a turbo connecting the two ports, it's not True Dual.

Not to mention, what the guy has is an extra pipe for the wastegate, that would hardly be worth it's own exhaust system. It'd be a waste of time and weight.

 

I posted a picture of the turbo porting on my "for sale" ad on my car, look on second post and you will see what im talking about! (i dont think rx7club lets upload the same picture 2 times)


https://www.rx7club.com/showthread.php?t=376056

 

Looks good man! Nice work!

What did you use to remove the metal?

 

I just might have to do that when I get started on mine again.

 

Tools used:

Milling Machine

Die Grinder with various carbide cutting bits

 

so how much is that backing plate preventing the flapper door from opening??? it looks like you machined it down pretty deep.

does this mean the flapper is opening less than half swing at most

 

Seperating the wastegate exhaust so the flapper can open more is OVERKILL.

Just grind into the backing plate about 1/4 the way through so the flapper can open more.
*hint* use whiteout on the backing plate as a grinding guide. Wipe some on then place the backing plate in place and move the flapper arm hard to slap the flapper against the backing plate to mark the paint. Grind. Repeat as necessay.

-Ryan

 

have you done this? i think grinding the back-plate would do more than actually porting out the wastegate holes... especially if the flapper is opening less than halfway at most...

 

yes i have. u should do both, port the holes and mod the back plate. stop typing and get grinding.

 

Jacobcartmill:

Yes i did machine it relatively deep, about 1/2 thickness for the trough. Then i radiused the edge that meets the turbine exhaust outlet for smoother airflow.

If you want to see just WHY i decided to do such an extensive job, try this:

Pull off your back plate on your turbo and disconnect the wastegate actuator. Now lay a straight edge across the back of the turbo so that the wastgate flapper will open and hit it. Now you can see how far the flapper actually opens! Try it and you will see why i decided to port the wastegate AND machine the back plate!

Graham

 

yeah i took my turbo off last night and did my best to do some porting, but i didnt have a long enough burr bit so i couldnt really get in there far enough to to the best job... and i also found out that its going to take some kind of drill press to dig into that 1/4 inch steel backing plate, as i got nowhere trying to grind on it... i guess i'll just have to wait a few days and try again

 

What type of bits are you using? You HAVE to use carbide bits (about 30 -45 bucks each) to cut through anything. I used a milling machine to cut the backplate and a carbide porting bit to radius the edge

 

why dont u just get a bigger turbo, and upgrade from there.
or do what i did, 502 twin turbo in an rx7. come play ladies! lol

 

The RX-7 is just a car. What makes it truly different and special is the engine.

I think you may have forgotten that simple fact.

For those who keep it what it is supposed to be. Thank you.

James

 

That's not why you do it! Seperating the turbine and wastegate flows eliminates the significant turbulence caused by the two streams mixing, which increases both flows, plus it provides a less restrictive path for the wastegate gases. These two factors reduce boost creep and increase power.

Having the flapper open further is only of limited benefit. Once the wastegate port is uncovered you can only move the flap back so far before flow stops increasing. Think of covering a hole in a bucket of water with your finger. If you move your finger half an inch away from the hole water starts flowing out. If you then move it another half inch away does the flow increse? Nope. Also you have to remember that the flap's movement is limited by the wastegate actuator. It's rod can only extend outwards so far, plus it will only open further if boost increases, which is what we're trying to avoid.