Hi everyone. I'm having a bit of an issue where I'm having around 4 psi of boost build with my wastegate wired open, whereas the seller of my turbo kit says with the wastegate wired open, I should only be seeing 1 or 2 psi of boost. They recommend porting the wastegate and making a channel toward the wastegate hole, which I did both of these things. However, I am still seeing 4 psi of boost with the wastegate wired open, when I shouldn't be. I'm afraid to port out the hole any more in fear of going too far as I have it ported out almost as much as I safely could.

I noticed the wastegate flapper seems to open only a very small amount (video attached). Is this normal, or is the wastegate not opening up enough causing my issues? I can grind out a divot behind the flapper for it to open more if needed, but not sure if that would help at all. What do you guys say?

 

If the gap between the fully open valve and its seat is <1/4 the diameter of the hole, it is opening far enough. Less than 1/4 -> worth grinding that divot. Some other possible causes of your problem are:
- turbine/turbine housing too small. With the wastegate closed, does the boost start very early in the rpm range?
- timing retarded.
- E85 or E100 fuel generates greater exhaust gas volume. Harder to control boost. Try a bigger turbine or housing.

 

I will have to measure the hole and then the gap of the fully open valve and the seat, didn't even think of doing that. Sounds like a good thing to check!

I actually have not run the car with the wastegate closed since I have a tuning appointment set up soon, and I'm too nervous of hurting something by running on wastegate pressure with a tune that I put together myself. I don't trust myself too much with Megasquirt yet, lol. So, I did set base timing when I was first setting up the car to 10 degrees (its a NB Miata), but then I didn't touch anything with timing after that was set. Running 93 octane here.

 

So, I ended up having to buy a new turbo (cheap, chinese T3 turbo) due to overporting the wastegate hole. Trying not to do that again, I'm taking it slow with my porting. So, I have ported the wastegate hole to 26mm, as well as carved out a little air channel based on what I've read elsewhere. However, I'm hitting 10 psi at redline with the wastegate wired open! I'm thinking maybe the wastegate flapper door is just way too close and it needs to open more? Can this cause such a high amount of boost with the wastegate wired open? Attached is a picture of the channel and the sealing area of the wastegate flapper (greased outline). According to where I bought the turbo from, it is an A/R .48 50 trim, if that makes any difference. Anyone have any idea why I'm getting such high boost even with the wastegate wired open? I have a tuning appointment Wednesday, so just want to hopefully get everything dialed by then.
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Something doesn't sound right but to continue with the porting blend the hole opening into the direction of the exhaust flow. Smooth the transition of the exhaust flow so it can smoothly exit the hole when the flapper opens. That groove should be doing this but try and make the entire hole as smooth transition.

If you can I would try removing the muffler to free up the exhaust pressure in case that is a restriction .

ks

 

Thanks! Do you mean something like beveling the inner edge of the wastegate hole? I can also try removing the muffler and see what happens there as well.

 

Yes, bevel the inner part of the hole but only from one direction to allow the exhaust to flow easily into and out of the hole.

ks

 

A lot of things going on here.
1. What size is the engine? How much NA power should it make?
2. What size DP, what does the rest of the exhaust look like?
3. That flapper doesn't seem to open very far compared to a stock Ford T3 or Buick T3. Are you able to run a traditional looking outlet?
4. That is a fairly small A/R housing for most engines. It's made to make boost early and easy. Seems to be doing that.

 

If its making 10 psi wide open, then the gate opening is just too small imo. It's not a new problem with internal gates, especially when you see a small external gate is 12+ mm larger with a better flow path. Add an external gate, and be done.

 

1.) The engine is a 1.8L BP Mazda engine in a Miata. NA, the Miata should make around 130-140 hp.
2.) The downpipe is a 3 inch bellmouth downpipe, to a 3 inch straight through, catless midpipe, to a big magnaflow muffler that I plan on changing to something smaller in the future.
3.) I can try and make some more space behind where the flapper hits the back of the V-Band housing/flange area, since I've seen people do that on Miata forums.

This is the turbo that came with the kit I purchased for my Miata, and the vendor is fairly well known, so not sure about much else about the turbo other than its a .48 A/R and 50 trim journal bearing, T3 replica. New to turbos, so learning as I go!

An external gate would be great, no doubt. Just have to figure out how to do that with my setup.

 

One other thing to think about is that if you're untuned, and your ign timing is super conservative, that can cause creep issues.

 

- Radius the entry to that hole you see in Post #4 first photo. The groove won't help.
- 10 psi is not too bad. I would assume that is close to your target boost. Take it to the tuner - tuning will probably sort it. If the problem is still there after tuning, put a bigger turbine housing on it. Next size is probably A/R = 0.63
- Less muffler restriction = more boost. If you put a more restrictive muffler on it that will help your problem.

 

Have you considered putting and external gate on it and just leaving internal gate unhooked.
Would have been cheaper than a new turbo.

 

Spotted a mistake in post #2 where I said "If the gap between the fully open valve and its seat is <1/4 the diameter of the hole, it is opening far enough."
Apolpogies. The valve lift should be > (greater than) 1/4 x diameter of seat, not < (less than).

 

Thanks for all the suggestions guys! So, I made the channel larger that goes toward the wastegate hole, and also made a little bit of a divot for the wastegate door to sit a little further. At redline, the max I'm getting now is around 4 psi, which I can live with. I'm untuned, so will see what the tuner says tomorrow as well. There are a few rattles from the intercooler piping hitting, but thats okay for now, at least the 10 psi is now 4!