I'm planning to build a fully divided twin wastegate manifold for my new Precision Billet 6765 turbo and I had some doubts about it.

Since I put a lot of abuse on my car and had previous cracking problems on my old manifold, I was going to use 321 stainless for this one since its supposed to be better? Would 2" diameter piping be a good size?

Now about ideal wastegate positioning. I was thinking about doing something similiar to full-race's where the wastegates are just before the flange like below. Seems the simplest to do and I believe will work. However, they are at a 90 bend so I'm not sure if its ideal. Would putting them coming off a bend be better?



And the last question is what wastegates to use. I have a brand new in box Synapsy 50mm gate. I could just buy another one and use that but would it be too big using 2 of them? I know I can use the little insert to make them a little smaller but I'm not sure.

Anyway, I plan to run this thing between 20 and 25 PSi all the time but I might venture close to 30 PSi out of curiosity at some point . Wonder what type of power and response I'm going to be making at these boost levels with this turbo and setup ^_^

thewird

 

2" id is too large a diameter for your purpose it will only induce lag unless your running a seriously ported engine. Run the gates at or off the first bend if possible, if not, run them in a direct flow path at least, if not, then run them as shown in the pic. 321 is pointless unless you plan to support the turbo with a brace as it will be 16 gauge, use 304/316 schedule 10 it will be more than fine. Running two 50mm gates is fine.

~S~

 

what size ID would you recommend for a streetport with a gt4202 t6 rear end, smaller or 2" because of the t6?

 

So 1.75" for the runners then? I took a guess from pictures that 2" is the size. I never actually measured mine though lol. According to that mcmaster site, the closest thing would be a 1.682" inner diameter piping. What's the inner diameter on the 500r manifold?

Why wouldn't you go with 321 stainless? Isn't it a stronger material that is even more tolerant to heat? Or does the added weight not allow it to support its own weight + the turbo? Is the 316 schedule 10 what you use? I'm gonna try running an air duct at the turbo/manifold this year too so maybe it won't be so bad. Plus no more turbo blankets haha.

thewird

 

Running T6 would use 2" runners it mates up perfectly to the turbine inlets and will flow well with the larger ports most would have with a t6 framed turbo.

~S~

 

Your runners should be 44mm id, using 44mm tubing with T4 framed housings will give better fitment as well as better response.

321 has a higher resistance to intergranular corrosion from running at sustained elevated temperatures, a big reason is due to the addition of titanium. All three stainless steels mainly used 304/316/321 all effectively handle essentially 1600 degrees. Is 321 superior to 304 or 316 for this reason? Sure. Have I noticed any difference whatsoever in longevity from one type to another? Not yet almost ten years and I don't know how many manifolds later I have seen little to no difference. What you do gain is being able to make a manifold out of thinner material so it weighs less. You absolutely will have to back purge 321 16ga if you want to make it worthwhile especially if your not good at welding thin wall stainless. However you will also need to add a support to now brace the turbo as .060 wall will not support it. Versus a well made 304/316 manifold with .120 wall will, so savings on weight overall will be minimal. Your essentially making up for lower resistance to intergranular corrosion by running thicker heavier duty walls. .120+/- versus .060 +/-

I wouldn't run a turbo blanket in your app, nor would I wrap the manifold.

~S~

 

Why do you say that? I am running a thin wall 321 stainless manifold and i just wrapped it. I am also planning on running a blanket and am curious why you would advise against it. I have been running without a support on the turbo for quite some time and it still has not cracked, but i also don't drive it on the street and i run methanol.

 

why are 2" too big -lagy- and 44mm id fine for the mani tubing (leaving fitment aside)? Please explain.

 

Sean knows what I'm doing with the car. I need the manifold to withstand roughly 30 minutes of WOT between 5,000 and 8,500 RPM at 1,800F+ continuous EGTs preturbo, as well as regular street driving with a lot of mileage. Its not just for pulls down a strip

Thanks for your help Sean, got all my questions sorted . I never wrapped the manifold, only the downpipe. Can't wait to get the car together with the new stuff

thewird

 

That's why.

~S~

 

It is more application driven than a set or given rule. For his application 50mm will hurt him more than help. You'll get higher velocity out of 44mm runners as compared to 50mm runners. What I have noticed is better crisper response with 44mm runners on T4 framed turbo's. We have made more hp on 44mm runners on a RE street ported block, 4202 T4 than any circuit or street car will ever need. 44mm runners are more than capable without causing much restriction. If your running large exhaust ports and a heavy breathing engine 50mm runners will work fine, mating them to fit a T4 inlet though requires more work and at that point the T4 will become a restriction.

~S~

 

^ Good info, thanks

I was also wondering about some info I read but could never verify. Short runners are responsive but have peaky power, and long runners have a better peak powerband and midrange? Is that true? I was thinking of doing something in the middle.

thewird

 

my experience is more piston engine based. Applying the same logic, even the 50mm seemed small. One rotor would corespond to 3 cylinders of a 1.3 liter engine and even the 60HP engine of my tiny Peugeot has a 50mm exhaust. I understand that going bigger diameter on a rotary causes fitting problems to the turbo but I would have thought that the bigger step on the joint between exhaust manifold and exhaust port would help particularly on the peripheral exhaust ports of the rx7 engines.
Maybe the bahaviour you described is the reason why turbos tend to make more HP with T6 housing than with T4 housings keeping A/R constant.
Thank you for explaining.

 

why would you say not to wrap the manifold? i'm in the going single process and just wrapped it. should i remove mine? thanks

 

Longevity, It can lead to a warped and cracked manifolds, especially under hard use.

thewird

 

If your car is street driven and wont be doing prolonged sprints on the track wrapping it will be fine. It's when you start getting into sustained high temperature lapping that it keeps too much heat in for normal stainless steels to handle over a long life span. You will need inconel at that point. All three stainless grades are good for roughly 1600 deg. This is why you see places like burns stainless recommend only inconel for rotaries. They are looking at it from a purely racing standpoint. That said in the all the years we've been making manifolds I have had one failure that was with a customer who coated it, wrapped it, then ran very high EGT's due to tuning issues and literally blew a hole through the side of the manifold. Even he acknowledged it was his fault and offered to pay for a new manifold. We see some that get very minor cracks on some of track cars manifold inlet ports. We found this is due to the grinding down of the weld there to smooth it out leaving some parts of the inner weld thin it has never once caused a manifold failure as it is not even remotely a weak point. The runner inlets are welded both inside and out for a total of five passes (we now do things a bit differently to help avoid that issue). All that has ever needed to be done is clean up that area put some material down where it was ground a bit too thin and your done ten minutes at most.

Methanol drag cars are a different beast all together, the cars run so cool it's not a issue.


~S~

 

i do plan to do road racing, but i also am going to have AI with 50/50 water meth. complicates it a little. hehe it will be mostly street driven however. should i just get rid of the wrap?

 

Yes, get rid of it. Running AI helps egts but its not the same as running purely on an alcohol. If your road racing get rid of it. It doesn't really provide that much of a benifit anyway.

thewird

 

So would 44mm runners work well with a s475 t4?

 

43-45mm tubing fits well to a divided T4, if your running undivided and large port work you could run the 50mm tubing and collect them at the flange.

~S~

 

and what schedule metal piping would you recommend for these manifolds?

 

^304 schedule 10 is what seems to be popular.

 

Schedule 10 is plenty fine.

~S~