JimmyBlack

I've got a better question for you. Why does a standard Greddy produce <300whp at 12psi while most T3 and T4 rx8 turbos have documented 350whp at 12psi?

There are many ways to improve turbo efficiency, and depending on your exact turbo setup, some methods have large gains and minimal impact to spool. The best thing you can do to measure this is to record the rpm when target boost is hit, and record exhaust back pressure ratio (see my first build thread to see how to do this) before and after every change you make. The target is to reduce the EBPR at high rpm, while allowing the system to spool up at the lowest rpm. Here are some of the things that can be changed to work towards this:
- manifold design (incl. wastegate)
- turbine housing size and AR
- turbine/compressor wheel
- exhaust system
Depending on your turbo setup, some of these methods will barely impact spool at all while increasing performance significantly (exhaust system), while others will impact spool up enough that you may want to reverse the change. Needless to say, the changes that work for you won't necessarily work for your friend that has a turbo mustang.

We can't answer your question about larger AR for your friend - no idea what car he drives. If he drives an rx8 with a greddy turbo setup, then yes, a larger housing with larger AR would like provide much better max power, and would likely impact spool up to some degree. He'd also need to significantly modify his Greddy manifold or replace it to fit the T3 housing. The easier path would likely be to weld an external WG onto the back end of the Greddy manifold. External wastegates have no performance downside, and potentially significant upside, depending on the setup.

Ian_D

Jimmy, thanks. It is for an RX8 Greddy turbo, the one with the cracked snail.

Why less power on the RX8 Greddy? IMO simply down to space constraints for a low mount; there just isn't room for a bigger turbo. Greddy might also have been concerned over blowing too many engines with any greater power.

Intuitively I prefer replacing the turbo snail's T3 flange with a T25 one over fitting a T3 to the exhaust manifold. It seems easier and safer (if it all goes wrong, he can get another turbo snail but manifolds are not so easy to replace or repair). I'll have a closer look at my manifold later.

Also, I agree with your comment on fitting an external wastegate as far as theory goes, but I'm sceptical over fitting one here as:

• There is little room for one.
• Modifying the cast iron exhaust manifold to take one is difficult and any welds/modifications will be prone to failure.
• I'm concerned over protecting its diaphragm from burning out.

Of course, you could build a manifold to a completely new design (I'm watching your build with interest) or buy off-the-shelf (eg Esmiril's top mount kit), but that is all beyond my friend's skill and/or budget.

JimmyBlack

Ah, I see what you're looking to do with your friend's turbo now. No one has been able to prove whether the bottleneck in exhaust flow through the turbine housing is at the wastegate outlet or the wheel outlet (or even the right angle in the manifold immediately before the T25 flange). I suspect the excessive backpressure is caused by turbulence and squeeze of exhaust gas at the WG outlet just after it enters the turbine housing from the manifold, as after that point, as the gas carries on through the turbine housing to the wheel, there's only about half as much volume remaining, so it doesn't make much sense to me that this half volume of gas working it's way through the turbine wheel would be the cause of the excessive backpressure. This is why I think that welding a T25 flange onto the T3 turbo may not produce the results you're aiming for. I suspect it'll increase spool while doing little to nothing for top end. I could be completely wrong though... How would you like to be the guy that proves where the cause of backpressure in the Greddy system is?!

I agree that welding inconel is more durable than welding SS onto cast, though I've recently found that it can work quite well if you choose the correct filler rod that allows for the extreme temp changes. I'd still go with the eWG off the back of the Greddy manifold as the first option. It would have minimal negative impact on performance while potentially gaining a lot of top end performance. I've mocked it up on my car previously, and there's definitely room there if you use a 1 - 2" pipe shooting directly backwards from the end of the manifold into the WG inlet. If I can't get my T3 manifold working the way I like then I'll be doing this.

Ian_D

Jimmy, thanks. I think everything along the exhaust gas route is restrictive. Bearing in mind that a rotary typically flows 20% more air than a piston engine for a given power, the exhaust manifold and turbo hot-side just aren't suited to free-flowing gasses and there isn't much you can do about it without throwing shed-loads of effort and/or money at it.

As an example of the costs of welding cast iron, I've just got a quote from a specialist for welding up the crack on that snail: £420 inc tax (say, US $530), excluding any machining. I'll have a look to see if there is a general welder near him who could have a go at welding a T25 flange on that new snail. If that's the sort of money I'll need to pay out just to get an external wastegate flange welded onto the manifold then I'm put off from the start.

More for others than you, see the images of my turbo on the exhaust manifold and the turbo on the car. I knew that the turbo was a tight fit, but I wasn't prepared for how tight it actually was. There also isn't much space between the turbine housing and the bodywork, but I think I can make space there by a bit of metal bashing, perhaps even cutting a section out and welding on a panel giving more clearance. I've not yet looked at the space I've got to play with at the compressor end, particularly as I also need to look at space to route the compressor inlet and outlet pipes; that may have to wait for a couple of days.

Brettus

iTrader: (2)

And yet .... I have a GT35r with a 1.01 AR exhaust housing down there

Ian_D

You've inspired me to try fitting the EFR 7670 I have in my loft. I'm sure it'll fit if I use a big enough hammer and remove the steering column.

I did also think of welding a T3 flange onto the manifolds mild steel flange but I don't have the height to play with, and it becomes unnecessary if I have to chop the snail to reduce the inlet length.

Ive sent a message to the snail seller to get its material spec. It may well turn out to be a cast steel that I can get welded more easily than cast iron.

Update: the snail is SG Iron with Nickel. That means lots of pre-heating and special care to get a good weld ie expensive. Even if money wasn't an object, I'm still wary of welding succumbing quickly to the temperatures and stresses involved. Overall, I'm close to a solution, but still falling short.

Brettus

iTrader: (2)

Would love to see someone do this . i suspect it would require some cutting and re-welding of the transmission tunnel to achieve though.

Ian_D

I'm not bothered over cutting and welding the tunnel. A turbo will sit ahead of the seats so I've got a fair amount of tunnel to play with.

I really do have a new EFR 7670 IWG in my loft. I also have a used Greddy TD07S 25g (EWG). I hadn't spent any time thinking of fitting these until my comment above, as I'd assumed that they'd be too big. I'll have a look tomorrow, more out of interest than any expectation of them being a practical option for me (my approach may be different to the norm as I'm preparing for this arrangement to be short-term; my Renesis may not have good compressions and I have a 13B REW and conversion kit ready to go in).

Thinking aloud, as to practical issues:

• I'm not bothered over cutting the transmission tunnel back as there is room and I have the welder and skills needed.
• I'm more concerned over the turbo housings' avoiding the exhaust manifold, which is designed to fit around the T618Z. I'll be in trouble if the turbo's CHRAs are a different length.
• My real concerns for fitment are the compressor inlet and outlets. For my RHD car, the steering column makes a barrier just where I'd like to run the pipes.
• Ideally, I'd like to avoid spending time and effort on bespoke designs such as Jimmy's exhaust manifold, and prefer to keep the existing kit as is so that I can sell it on when the Renesis goes bang. This means, for example keeping the T25 flange on the Greddy manifold, as I could remove the studs, weld a T4 flange to the T25 flange and port the hole.

Whilst I think of out-of-the-box solutions, I could also have a look at a rear-mount turbo . . . .

ps, with so much info and experience in NZ, perhaps I should come out to watch the British Lions tour . . .
pps. For US readers, there is a sport called Rugby where NZ has whupped everybody's asses for a long, long time. Every few years the 4 British nations combine to send a team to various places around the world, normally to make them happy by getting thrashed. This year, the Lions are going to NZ and have high hopes of doing well.
pps. USA does have a rugby team. They have pulled off a few surprises over the years.

Brettus

iTrader: (2)

I didn't clarify my comment earlier .... I don't have the greddy manifold anyore .


Sure ...have a "look" at it . Just don't do it .


Would be great to catch up Ian .... dooooo eeet !

Ian_D

My mate's now tearing his hair out trying to keep his costs down. He's worried about leakage through the gap under the wastegate flap if he leaves the crack as it is, he can't find a replacement Greddy T618Z turbine housing and doesn't want to risk cutting and welding that 12 cm2 turbine housing. There are plenty of T25 8 cm2 housings and he can get a 8 cm2 water-cooled turbo like the 20g here or the 60-1 here for less than the cost of welding and machining his existing turbine housing.

I've advised him that IMO an 8 cm2 housing will restrict the turbine more than the bigger turbine wheel will free it, and that's before we consider the needs of a bigger compressor wheel. I told him he could get away with machining the wastegate lip, but he's a little OCD over sorting things properly. I therefore agreed to consult the oracles here.

ps. I've enjoyed the beers he's bought me for helping, but I've now told him that he'll have to register and post here himself after I've got some answers for him.

dannobre

iTrader: (3)

Mostly because you are thinking about in the wrong way. Boost pressure has nothing to do with it really.....You are interested in the mass airflow that you get....

Pressure is a measurement of the restriction to airflow basically, so it really doesn't tell you much unless the system is constant...IE all the piping and other restrictions stay the same.

So 12 PSI on one system doesn't equal the flow of 12PSI on another.

I get 500HP out of 16PSI roughly so that really throws the pressure math off

JimmyBlack

(pretty sure that last line was aimed in Brettus' general direction...)

dannobre

iTrader: (3)

Not at all.....I don't "aim" things...if im shooting at you you will know 😎

Ian_D

Whilst not wanting to pack this thread out with side discussions, I thought I had to write something for the benefit of others who might read this.

• Mass air flow has everything to do with boost pressure. Boost pressure, whether at the turbo or MAF, is effectively synonymous with mass air flow in a given system, where mass air flow is proportional to total pressure (boost + ambient), regardless of how that boost is generated. There are some second order effect (for example, a lower efficiency compressor will generate that 12 psi at a higher temperature, which will feed into a lower air density in the engine's chambers/cylinders) but these are small in an efficient charge air system.
• You are conflating pressure losses with flow pressure in a turbo system. Sure, pressure differences indicate the restrictions in a system and they vary with mass air flow/boost pressure, but that has little to do with mass air flow from the turbo for a given system (there may be second order effects from higher temperature/lower density/higher volume/boundary layer effects but, again, these are too small to bother about).

For the original point: on the same engine, a Greddy turbo at x psi will produce the same power, give or take the odd bhp, as any other turbo at x psi, provided we measure that x psi at the same place (compressor outlet or inlet manifold). This assumes, of course, that the Greddy turbo can reach that x psi in the first place.

There are several reasons why the standard Greddy T618Z turbo makes less peak power than other turbos, whether Greddy hybrids or complete replacements, but IMO they all come down to higher boost pressures in the other turbos or the Greddy's not being able to maintain that x psi.

As an aside, I have seen a lot of wasted effort in power vs boost discussions because participants have bandied around boost pressures without realising they are different at the manifold and compressor outlet. I have also seen many people use compressor maps with manifold pressure instead of compressor pressure (manifold + pressure losses between turbo and manifold) and think that changing pressure ratio/boost pressure moves any point vertically rather than diagonally (remember, mass air flow is, for our purposes, proportional to boost pressure). It all gets so confusing . . . . .

dannobre

iTrader: (3)

That is all true....my very simplified point was you can't use boost pressure in different systems to equate to expected power output.

12 psi boost in 2 systems has very little to do with the amount of flow unless everything is the same in both

Brettus

iTrader: (2)

Something that has become apparent to me is that the exhaust ports on the Renesis engine become a severe bottleneck once there is enough mass airflow to produce approximately 400whp . You can improve airflow throughout the rest of the system by various means (as I have done) but all this does is reduce the boost pressure (and rpm) required to create that mass airflow . The underlying exhaust port restriction problem is still there no matter what you do .

Ian_D

1. Can anyone confirm the A/R of the standard T618Z compressor housing (AFAIK its 0.60 for the standard 18g compressor housing, but Greddy might have changed that)? I did a quick measurement on my compressor housing and came up with an A/R of 0.69, considerably higher than the 0.60 of the standard 18g housing; this might be my measuring, but I think it's more that the housing has a larger A/R to get higher flow, as is the case with the turbine housing.
2. I can find no information on the Kinugawa, or indeed any other, 18g billet wheels and they may have no real design effort behind them. Has anyone seen anything or have views on them?

Perhaps as a wider issue to the first question, I haven't seen a summary of the standard T618Z. My understanding is that:
1. The T618Z is, in effect, a marriage of the TD05 18g cold side (18 and g are Greddy codes for the 50.6/68 wheel and style/number of blades respectively) with a TD06 oil-cooled housing and a TD06 10 cm2 hot side.
2. The compressor wheel is a 55 trim.
3. Standard A/Rs are 0.60 for the TD05 18g compressor housing and 0.73 for the TD06 10 cm2 turbine housing.
Have I got anything wrong?

ps 400 rwhp from a Renesis? How the other half live.

dannobre

iTrader: (3)

I didn't live there....not for very long at least

The exhaust flow issue became apparent very early on for me...and the REW just seemed like an easier way to get around that barrier

Zachary Verge

I need a new turbine housing for my kit, there is a crack where the wastegate is, unless a high temp jb weld woupd work. I've been scouring the internet for a replacement, even ordered one and the inner diameter didnt fit over the turbine.

StealthTL

iTrader: (1)

there is a crack where the wastegate is

How big is the crack?

Is it in the housing, letting gas escape, or just inside by the wastegate port?

Many, many turbos crack around that port, the Subaru IHI models on the STI models are USUALLY cracked there, it's no big deal.


.

Ian_D

You won't find a new replacement housing with the 10 cm2 A/R and T25 flange of the RX8's Greddy. You can get a T25 8 cm2 easily enough, but that doesn't suit us, and the odd 10 cm2 T3 flange, but that is awkward and expensive to modify.

The only repair is by welding. However, welding the ductile cast iron (FCD with Nickel) is a specialist job requiring expensive rods and controlled heating and cooling, which make it expensive. Your average welding shop can't do it.

The general action is to ignore such cracks.

Read the last few pages of this thread where there is some discussion on a crack that I'm dealing with. Post up an image of yours so we can see it.

Didn't fit? What are the wheel exducer and inducer dimensions, A/R and flange of the one you got? If its wheel housing is smaller then you can get it machined; if it's larger you could fit a larger wheel, with a bigger wheel on the front too (machine existing or get new housing). JB weld or any glues will melt and burn in seconds at the red-hot temperatures involved.

dirtyDEE

Hi Everyone!

Would runing lean eat up the apex seals and everything involved ? before installed my greddy kit - compression was at 7.5. (250)

about 1.5 month later after the install engine stalls and doesnt start. all the seals after a quick inspection seem to be in place. 1st section shows 2 low compression numbers, second section doesn't show compression. Motor seemed to use oil, and oil injectors were fine. i also premixed often. however there was a problem of running lean for a little while. i am curious to see your suggestions.

RotaryMachineRx

iTrader: (1)

If you have low compression then you have low compression, I don't know what you are asking?

Of course running lean while under boost will kill your engine... if you have to ask that I feel like you didn't have much business boosting this engine.... or any engine...

NotAPreppie

Lean begets pre-ignition and heat.
Pre-ignition and heat beget low compression.

So, yes, you probably killed your engine by not fixing whatever caused it to run lean.

9krpmrx8

iTrader: (46)

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