I myself have a Tial 40mm wastegate ready to go on my project. But I was wondering with the price differences of about $100, what are the differences between the two, performance wise. TIA

 

well in theory the 40mm can waste more exhaust gases so therefore it can regulate boost better. but when running high boost you actually want a smaller wastegate, cause you dont have to bleed off as much exhaust gasses. where as with low boost a 40mm or larger is optimal, cause you need to bleed off more. so id stick with the 40, if you need some money though sell it, there are plenty of people on here who use the 35-38mm and are fine on low to medium boost.

Landon

 

Also keep in mind that the valve in the 38mm doesn't appriciate race gas!!

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by newgsr &raquo;</TD></TR><TR><TD CLASS="quote">Also keep in mind that the valve in the 38mm doesn't appriciate race gas!!</TD></TR></TABLE>

please explain this more deeply.. thanks..

 

so for high boost say 20-30 lbs you want the 38mm?

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by Hella_JDM &raquo;</TD></TR><TR><TD CLASS="quote">so for high boost say 20-30 lbs you want the 38mm?</TD></TR></TABLE>

well in theory, but how much difference can 2mm make you know??? but yes you dont need a large wasetgate in a high boost situation.

Landon

 

cool thanks

 

so if smaller WGs are better for higher boost levels, 35 will be big enuf! wierd

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by z6 &raquo;</TD></TR><TR><TD CLASS="quote">so if smaller WGs are better for higher boost levels, 35 will be big enuf! wierd</TD></TR></TABLE>

i know it sounds funny, but it is true.

Landon

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by newgsr &raquo;</TD></TR><TR><TD CLASS="quote">Also keep in mind that the valve in the 38mm doesn't appriciate race gas!!</TD></TR></TABLE>

In regular usage (low boost) and that's not daily, I run 99 octane from VP Fuel. I intend to use race gas (C16) once in a while (to run high boost- around 19psi), will that be a problem if I use the 38 mm? Or is it advised to just go ahead with a 40 mm instead and be on the safe side?

 

Tial's standard 38mm valve is not intended for race gas. They do offer a race valve that will handle race gas but at a higher price.

 

Can anyone explain WHY it doesnt handle racegas?
What happens?

 

So the 40mm is fine with race gas?

 

Apparently race gas will kill the standard valve. The 40mm has the racing valve so no worries.

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by boosted_dc2 &raquo;</TD></TR><TR><TD CLASS="quote">

well in theory, but how much difference can 2mm make you know??? but yes you dont need a large wasetgate in a high boost situation.

Landon</TD></TR></TABLE>

I partially agree with what you are saying about the small gate for high boost. In theory that is how it is but I personally had a 35mm Tial and was trying to run 15 pounds (which is relativelly high boost). Even with the Lovefab manifold it would still creep to 18-19psi. I think it really depends on the turbo you are running. With my turbo, boost hit so hard that there was no chance for the wastegate to keep up. I would definatelly keep the 40mm in his case. You can't go too big but you can definatelly go to small.

-Ryan

 

it's weird how pretty much all the low boost factory turbo cars run tiny internal gates. I would guess about 25mm on most of them. The smaller gate/higher boost idea makes sense but in the real world I see the exact opposite.

 

Tial's website also supports the high boost/small gate theory. But the way I see it, I'm running a 40mm gate starting with low boost [.4 bar spring, with MBC I'm going to start around 9 psi], and I can swap in springs up to like 1 bar and with an MBC see twice that. I'm comfortable staying with my 40mm.

 

Now, this statement about running a smaller valve for higher boost is a bunch of crap...

When you run more boost, you pressurize the cylinders with more oxygen/fuel mixture...This will lead to larger quantities of Waste Gases...The need for evacuation of these gases require larger exits that will promote a more constant flow from the cylinder head and to the atmosphere...

Exhaust gases move in pulses, these pulses need to be amplified to keep from "stacking up" at the collector...To combat the stacking up and amplify the kinetic energy of the gases, we use larger passages, hence the 2.5" to 3" downpipe...Or, the 40 or 46mm wastegates...

In your mind, you are only seeing that boost numbers will go up therefore, the exhaust that passes through the gate will be less in quantity...This is not so, since, as the boost increases, so too does the Volume of Wasted gases...This requires a larger valve/gate to maintain the positive evacuation of the greater quantity of waste gases at a similar or more effeicient pace...

So, by using a smaller gate with Higher boost pressures, you will not move the additional waste gases out of the cylinder head leading to increased cylinder head temperatures, contaminated intake charge mixture, detonation, blown headgaskets, overheated turbochargers, and such...

Please do not continue to believe and repeat the statement that you have made, "Larger boost numbers means you are diverting less exhaust gases so you need a smaller gate," as this statement is completely false...

 

^^ wow, that's alot of writing and theory there.

in regard to the general statements about boost press related to wg size, it is a little too vague in its description, which is why it is only half right, but is also half wrong.

generally, i believe that the wg sizing is not dependent solely on boost pressure, which is what many statements have claims. the size of the snailshell also plays a part. for example. a large turbo, running large boost. using a small wg would work nicely, but take that large turbo and run only small amts of boost, and you'll need a larger wg. now on the other hand, if you have a tiny turbo that spools up instantly, you'll probably want a larger wg just to prevent overboost since it builds up pressure so quickly it can't bleed it off fast enough.

the whole concept is confusing since there is more than one factor to consider, and sometimes it even sounds backwards....lemme wait for a more respected member to step up and maybe they can make sense of my babble

-Alan

 

What are you talking about??? Spool time has little to do with the amount of exhaust gases you are producing...

You have to realize that the VOLUME of the intake air determines the VOLUME of the exhaust gases...

If you are producing enough volume for 500HP then you need at least a 40mm Valve to maintain a healthy tune...

If you are producing a 350HP setup, then a 35mm Gate is good enough...

Its not the specific amount of boost, but the VOLUME of Gases you are trying to evacuate...

Maybe I didn't come right out and say that in my first post but I was hoping that people who are posting on this forum can figure that out for themselves...

Again, When you increase the Volume of Intake Air, you will Increase the Volume of Exhaust Waste Gases...Therefore, you need to increase the diameter of the gate that the larger Quantity of Exhaust Gases has to pass through...Or else suffer the consequences I stated in my first post...

 

And it only takes me 3 minutes to type any of this, that includes the theory...Maybe you should come over to http://www.nasioc.com and speak to some of the more "intelligent" engine enthusiasts...Oh and since you have a 1st Gen Impreza, don't forget to check out http://www.rs25.com

 

i don't know if the above is an insult or not, but i'm a member of both those boards and i find the seasoned honda FI people more intelligent than the subaru crowd. that's why i'm getting rid of my impreza to build another turbo honda. and my impreza isn't first gen, impreza's have been around for longer than just 2.5RS's and WRXs.

First you tell me spool time has little to do with amount of gas made.
Then you say volume of exhaust air is dependent on volume of intake air.
Well then, what do you think determines the amt of intake air?
Maybe some "forced" induction would increase the amt of air taken in substantially, which in result would increase the amount of exhaust air.
I don't know if you even read my post, because the only point you made is that it's not about the specific amount of boost. i never said it was only about amt of boost. in fact, my post specifically stated it wasn't about just boost pressure. i said it was a combination of boost pressure and turbine size. now go on and tell me that boost pressure and turbine size aren't related at all to amount of air taken in.

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by Kwuaymaikrup &raquo;</TD></TR><TR><TD CLASS="quote">

I partially agree with what you are saying about the small gate for high boost. In theory that is how it is but I personally had a 35mm Tial and was trying to run 15 pounds (which is relativelly high boost). Even with the Lovefab manifold it would still creep to 18-19psi. I think it really depends on the turbo you are running. With my turbo, boost hit so hard that there was no chance for the wastegate to keep up. I would definatelly keep the 40mm in his case. You can't go too big but you can definatelly go to small.

-Ryan</TD></TR></TABLE>

well IMO 15 psi is not high boost at all, im refering to like 23+.

think about this, with the drag mani for instance the boost creep is generally on low boost (7-15psi). but the people who run them at 25 psi never seem to have creep issues. thats because they dont need to waste as much. thats aslo why a cure for the drag creep issue is to port the number 1 runner. thats opening up the path for the wasted gas. the drag mani is not a good design by any means, im just using that as an example.

Sunrise City Rider

your statement about volume of intake affects volume of exhaust gasses is true. but your statement about needing to get rid of the gasses is wrong. you NEED those gasses to keep the compresor pushing the high amounts of boost.

a 350 hp setup a 35mm is good enough?? thats just what people want good enough. why do you think tial made a replacement that fits the 35mm flange but is a 38mm gate??? because the 35 is not GOOD ENOUGH for todays setups. when people are running turbos that flow ALLOT of air, and are only running 7 psi then they really need to have a wastegate that is effecient. and guess what a 35mm is not good enough, it works yes but a 38 is better and a 40 is even better than that.

Landon

 

Much Good Info keep it coming!

 

Well, I do know that a larger valve is always better than a smaller valve...You need to move the gases out, thats the bottom line...Its not used to spool the turbo anymore than is neccessary...Once the charge is burned, it needs to go...Thats it...It will spool the turbo at the rate it spools the turbo, no matter the size of the gate...A larger gate will not slow the spool of the turbocharger so use a larger gate if you can afford to do so...

I was just ribbin you with the Subie Love crack...But, you will be amazed by the amount of smarties that own Subarus...At least when it was more of a cult car and not the "in" car to own...

Look, I'm saying this once and for all...The need for a larger gate is neccessary when you are moving more exhaust gases out of the combustion chamber...Same as when you have Oversized Valves, Larger Ports, Longer Duration Cams...The problem with a smaller gate is the stacking up of the larger quantities of exhaust gases in the collector as a result of the above mods...I'm not stating anything that isn't known to the gate manufacturers and any turbo engine builder...Look at what your'e saying and what is actually being used...Its obvious that your theory is inverted and the reciprocal of it is indeed correct...

You should realize this as a fact and not an opinion or theory...You need a larger door for bigger people, you need a larger gate for a bigger blast of exhaust gases...If you don't have that bigger door, the gases will slow down and you will experience many problems as I stated earlier...

Backpressure begins at the exit of the exhaust port and you need to maintain velocity at all costs to reap the greatest benefits of your setup...Hence, keeping the exhaust flow moving in a positive fashion...