Nytsky's Engine Build

[MBS206]

yeah all running screamers!

So with the current discussion, not comparable.

We've been discussing with respect to plumbing back.

I asked NYTSKY if he was running screamer, hasn't yet responded, other wise you'd rule out the whole exhaust system and run a 3" for the whole system.

[NYTSKY]

It is plumbed in, but it is flanged so i can make it a screamer.

Last time on the old turbo we did a back to back run with and without it plumbed in and i actually lost power with the screamer due to the boost curve falling over.

Im going to have the screamer for Powercruise so ill throw it on the dyno for a power run to see if it makes any difference.

[juggernaut1]

some reading on the topic

http://www.calaisturbo.net/showthread.php?p=2383729

[NYTSKY]

Link doesnt work mate.

[MBS206]

It is plumbed in, but it is flanged so i can make it a screamer.

Last time on the old turbo we did a back to back run with and without it plumbed in and i actually lost power with the screamer due to the boost curve falling over.

Im going to have the screamer for Powercruise so ill throw it on the dyno for a power run to see if it makes any difference.

If it picks up power (And you can hold boost) then the dump/exhaust is being restrictive.

[MBS206]

What size waste gate are you running also?

[NYTSKY]

50mm

[MBS206]

50mm

I'd try a slightlysmaller gate too... around the 44mm mark.

http://www.skylinesaustralia.com/forums/ex...mp;hl=wastegate

That might help you keep boost up when running the screamer.

[TiTAN]

He is running a synchronic wastegate, they are designed a little differently to the regular kind you get from TIAL/HKS/ etc. though i didn't think he had any issues holding boost @ 25psi.

[MBS206]

He is running a synchronic wastegate, they are designed a little differently to the regular kind you get from TIAL/HKS/ etc. though i didn't think he had any issues holding boost @ 25psi.

Oh okay, didn't realise there was a difference... :S

Figured a 50mm gate when it opens 1mm has the same surface area opening as any other?

Have any more info on the synchronic?

he only had issues when he ran with the screamer on.

It is plumbed in, but it is flanged so i can make it a screamer.

Last time on the old turbo we did a back to back run with and without it plumbed in and i actually lost power with the screamer due to the boost curve falling over.

Im going to have the screamer for Powercruise so ill throw it on the dyno for a power run to see if it makes any difference.

[NYTSKY]

Had a chat to Adam again tonight.

And he said the dump and new cooler would be the best place to start.

I asked how many cars he had tuned making 400+ with a 3 inch dump and he said none.

Not saying there are not engines out there doing this. But if he says he has not seen one then there must be a reason.

[Cartman]

if it's still the original stainless manifold it isn't going to be an easy job to get it split properly. Its one with around 80mm of steel sheet between the merged runners and the flange so probably more dollars in custom work than it's worth. You'd basically have to remake half the manifold.

Even with a 6 boost or etm you'd have to chop off the merge collector and redo a fair chunk of manifold to get a decent result.

thinking about the 6boost and ETM manifolds i've seen it wouldnt be that hard actually, you'd simply mill the flange off and someone with great hand controll could use a 3mmbladeded 9" grinder to slice directly down the middle of the collector leaving 3 on either side providing that its in a spot to get away with doin so, than simple put in the devider and weld on the new flange! 

Edited February 6, 2010 by Cartman

[TiTAN]

The 50/50 split is going the wrong way beneath the flange for it to be a simple chop and weld job from memory.

Sell your current (ETM/6BOOST manifold) assuming you have one and they can make you a proper split pulse version to order.

Dave, will be interesting to see if the exhaust change and cooler change fix the issue, are you going to try them separately or just change both at once and see?

[NYTSKY]

Both at the same time.

[saliya]

Most of the dumps I've seen for 400+ have been 3.5" - 4"

And the outlet may be 3", but take a look at the big power builds, they all mouth out nearly instantly

I've not had this particular turbo in front of me; which is why I was asking about the outlet size.

In general, exhaust size changes should be kept gradual - no sharp steps if they can be avoided.

My exhaust-making friend's rule of thumb is about 6" of conical pipe per 1" of diameter change giving about a 5deg expansion angle.

There are a few other people stating similar things (the desirable angle seems to vary from 5deg to 12deg depending on who you talk to).

e.g. http://www.skylinesaustralia.com/forums/Ex...-T-t264202.html may be worth a read.

Cheers,

Saliya

[DRIFTER]

Both at the same time.

before power cruise?

[juggernaut1]

Link doesnt work mate.

Hmmmm works for me. Some important bits from the thread:

on some of the small testing we have done......

3 Inch system, into 2 x 2.5 then 4 inch single at the end. Engine wouldn't make over 420 rwhp at about 15 deg timing at 7800 rpm at around 24 psi. (through an auto with 4200 converter)

Dropped the exhaust, still with the 3 inch dump pipe tho, could run an extra 7 deg timing (up to 22) and made 450 at 24psi. Now this was ok, except when we added gas, Power would spike to 490 then as the CFM increased power would always drop back to around 450 rwhp. This was with a 3 inch dump pipe, then increasing to 3.5 inch and exiting out the side of the car. It didnt seem to matter what we did with camshaft timing or anything else for that matter power always fell over hard.

So off to the drag strip, did what we needed to do with the car...... Afterwards a new full street exhaust was made, with a 4 inch dump and a full 3.5 inch system. This thing now makes more over all horse power than before with a 3 inch dump and side pipe but now makes more horse power the harder we rev the engine. Everything here has been done with a screamer pipe, So you could imagine the added stress with CFM having it plumbed back in.

So don't under estimate the need for size in the first 6 feet of your system, Especially if its heat wrapped __________________

and

The following excerpts are from Jay Kavanaugh, a turbosystems engineer at Garret, responding to a thread on Impreza.net regarding exhaust design and exhaust theory:

“Howdy,

This thread was brought to my attention by a friend of mine in hopes of shedding some light on the issue of exhaust size selection for turbocharged vehicles. Most of the facts have been covered already. FWIW I'm an turbocharger development engineer for Garrett Engine Boosting Systems.

N/A cars: As most of you know, the design of turbo exhaust systems runs counter to exhaust design for n/a vehicles. N/A cars utilize exhaust velocity (not backpressure) in the collector to aid in scavenging other cylinders during the blowdown process. It just so happens that to get the appropriate velocity, you have to squeeze down the diameter of the discharge of the collector (aka the exhaust), which also induces backpressure. The backpressure is an undesirable byproduct of the desire to have a certain degree of exhaust velocity. Go too big, and you lose velocity and its associated beneficial scavenging effect. Too small and the backpressure skyrockets, more than offsetting any gain made by scavenging. There is a happy medium here.

For turbo cars, you throw all that out the window. You want the exhaust velocity to be high upstream of the turbine (i.e. in the header). You'll notice that primaries of turbo headers are smaller diameter than those of an n/a car of two-thirds the horsepower. The idea is to get the exhaust velocity up quickly, to get the turbo spooling as early as possible. Here, getting the boost up early is a much more effective way to torque than playing with tuned primary lengths and scavenging. The scavenging effects are small compared to what you'd get if you just got boost sooner instead. You have a turbo; you want boost. Just don't go so small on the header's primary diameter that you choke off the high end.

Downstream of the turbine (aka the turboback exhaust), you want the least backpressure possible. No ifs, ands, or buts. Stick a Hoover on the tailpipe if you can. The general rule of "larger is better" (to the point of diminishing returns) of turboback exhausts is valid. Here, the idea is to minimize the pressure downstream of the turbine in order to make the most effective use of the pressure that is being generated upstream of the turbine. Remember, a turbine operates via a pressure ratio. For a given turbine inlet pressure, you will get the highest pressure ratio across the turbine when you have the lowest possible discharge pressure. This means the turbine is able to do the most amount of work possible (i.e. drive the compressor and make boost) with the available inlet pressure.

Again, less pressure downstream of the turbine is goodness. This approach minimizes the time-to-boost (maximizes boost response) and will improve engine VE throughout the rev range.

As for 2.5" vs. 3.0", the "best" turboback exhaust depends on the amount of flow, or horsepower. At 250 hp, 2.5" is fine. Going to 3" at this power level won't get you much, if anything, other than a louder exhaust note. 300 hp and you're definitely suboptimal with 2.5". For 400-450 hp, even 3" is on the small side.”

"As for the geometry of the exhaust at the turbine discharge, the most optimal configuration would be a gradual increase in diameter from the turbine's exducer to the desired exhaust diameter-- via a straight conical diffuser of 7-12° included angle (to minimize flow separation and skin friction losses) mounted right at the turbine discharge. Many turbochargers found in diesels have this diffuser section cast right into the turbine housing. A hyperbolic increase in diameter (like a trumpet snorkus) is theoretically ideal but I've never seen one in use (and doubt it would be measurably superior to a straight diffuser). The wastegate flow would be via a completely divorced (separated from the main turbine discharge flow) dumptube. Due the realities of packaging, cost, and emissions compliance this config is rarely possible on street cars. You will, however, see this type of layout on dedicated race vehicles.

A large "bellmouth" config which combines the turbine discharge and wastegate flow (without a divider between the two) is certainly better than the compromised stock routing, but not as effective as the above.

If an integrated exhaust (non-divorced wastegate flow) is required, keep the wastegate flow separate from the main turbine discharge flow for ~12-18" before reintroducing it. This will minimize the impact on turbine efficiency-- the introduction of the wastegate flow disrupts the flow field of the main turbine discharge flow.

Necking the exhaust down to a suboptimal diameter is never a good idea, but if it is necessary, doing it further downstream is better than doing it close to the turbine discharge since it will minimize the exhaust's contribution to backpressure. Better yet: don't neck down the exhaust at all.

Also, the temperature of the exhaust coming out of a cat is higher than the inlet temperature, due to the exothermic oxidation of unburned hydrocarbons in the cat. So the total heat loss (and density increase) of the gases as it travels down the exhaust is not as prominent as it seems.

Another thing to keep in mind is that cylinder scavenging takes place where the flows from separate cylinders merge (i.e. in the collector). There is no such thing as cylinder scavenging downstream of the turbine, and hence, no reason to desire high exhaust velocity here. You will only introduce unwanted backpressure.

Other things you can do (in addition to choosing an appropriate diameter) to minimize exhaust backpressure in a turboback exhaust are: avoid crush-bent tubes (use mandrel bends); avoid tight-radius turns (keep it as straight as possible); avoid step changes in diameter; avoid "cheated" radii (cuts that are non-perpendicular); use a high flow cat; use a straight-thru perforated core muffler... etc.”

"Comparing the two bellmouth designs, I've never seen either one so I can only speculate. But based on your description, and assuming neither of them have a divider wall/tongue between the turbine discharge and wg dump, I'd venture that you'd be hard pressed to measure a difference between the two. The more gradual taper intuitively appears more desirable, but it's likely that it's beyond the point of diminishing returns. Either one sounds like it will improve the wastegate's discharge coefficient over the stock config, which will constitute the single biggest difference. This will allow more control over boost creep. Neither is as optimal as the divorced wastegate flow arrangement, however.

There's more to it, though-- if a larger bellmouth is excessively large right at the turbine discharge (a large step diameter increase), there will be an unrecoverable dump loss that will contribute to backpressure. This is why a gradual increase in diameter, like the conical diffuser mentioned earlier, is desirable at the turbine discharge.

As for primary lengths on turbo headers, it is advantageous to use equal-length primaries to time the arrival of the pulses at the turbine equally and to keep cylinder reversion balanced across all cylinders. This will improve boost response and the engine's VE. Equal-length is often difficult to achieve due to tight packaging, fabrication difficulty, and the desire to have runners of the shortest possible length.”

"Here's a worked example (simplified) of how larger exhausts help turbo cars:

Say you have a turbo operating at a turbine pressure ratio (aka expansion ratio) of 1.8:1. You have a small turboback exhaust that contributes, say, 10 psig backpressure at the turbine discharge at redline. The total backpressure seen by the engine (upstream of the turbine) in this case is:

(14.5 +10)*1.8 = 44.1 psia = 29.6 psig total backpressure

o here, the turbine contributed 19.6 psig of backpressure to the total.

Now you slap on a proper low-backpressure, big turboback exhaust. Same turbo, same boost, etc. You measure 3 psig backpressure at the turbine discharge. In this case the engine sees just 17 psig total backpressure! And the turbine's contribution to the total backpressure is reduced to 14 psig (note: this is 5.6 psig lower than its contribution in the "small turboback" case).

So in the end, the engine saw a reduction in backpressure of 12.6 psig when you swapped turbobacks in this example. This reduction in backpressure is where all the engine's VE gains come from.

This is why larger exhausts make such big gains on nearly all stock turbo cars-- the turbine compounds the downstream backpressure via its expansion ratio. This is also why bigger turbos make more power at a given boost level-- they improve engine VE by operating at lower turbine expansion ratios for a given boost level.

As you can see, the backpressure penalty of running a too-small exhaust (like 2.5" for 350 hp) will vary depending on the match. At a given power level, a smaller turbo will generally be operating at a higher turbine pressure ratio and so will actually make the engine more sensitive to the backpressure downstream of the turbine than a larger turbine/turbo would.

Edited February 7, 2010 by juggernaut1

[MBS206]

Both at the same time.

If mine weren't so much of a pain in the ass to take off my car, I'd pull it off and lend it to you. It's a good plazmaman cooler. That way you could just do a test on it.

[T04GTR]

T04Z is a bit laggy for my liking.

And yes Simon got a great result.

I made 360 with the GT3076 at 23psi, so i only gained 30rwkw with the GT35 with 2 psi more boost.

Just doesnt sound right.

sounds on the money to me. i wouldnt get your hopes up to much. any rb25 making close to 400kw on a gt35 is very stout. hell my 26 only made 376 on 25pound with a t04z...

[T04GTR]

oh, with 3.5" ex no cat and screamer. but my dump pipe could of been better.