Manifold sizing question

[Gravy]

Ok, i've been looking around for some time, and found some answers to most of the odd questions i've had for a while, but there's one i looked for a little bit, and found mixed results for.

Car:
14b, stock almost everything but FMIC and exhaust were changed out

Problem was i had a stock 1g manifold and a tubular manifold for the GSX a while back. The stock 1g was... well you know how great those all are. The tubular had larger runners and looked like it would hold much more exhaust gas.

The difference i noticed with the two of them, is the stock manifold seemed to help out spool a lot, turbo spooled up quicker, didn't hit full boost as hard, but almost felt like it was dying off in the higher RPM range close to red line.

The other one had larger runners, it seemed to up the full boost point by about 4-500 rpm's and when it boosted it was more of a kick in the pants, held boost well all the way up to red line. Now to me this made sense to me from what i've read in the past but i want to get my facts right before i go assuming things on my Stealth in the future.

Did the smaller manifold give the gas less space for the exhaust to build in, and move the turbine wheel quicker giving the gas less space to expand into and releasing most of the energy in the exhaust housing? And if so, choke some in the higher rpm range due to the volume of air going though? Porting the stock 1g manifold only helped right before red line, other then that it was the same in every other way really.

And did the larger one give the exhaust more room to build up in, like a wave almost, to come in on the turbine wheel in higher volume causing a slower spool due to extra space needed to fill the pipes, and more of a volume going though to give it that extra "Kick" so to say?

I know most of this isn't very technical, and it's what i've kinda picked up from a few years of shifting through other people's posts, but on 5 hours of sleep and at almost 2 a.m. in the morning, i'm trying to get my thoughts down before sleep to see if i'm still on track, or if it's time to hit the books again. From what i remember, hot gas stores most of it's energy and releases it upon expanding, which it does in the turbine housing. I'll go more into where i'm going on this if people are confused.

Thanks in advance for reading my long, and probably hard to understand post, and thanks for any answers, constructive or otherwise.

[JET]

The main thing about exhaust manifolds is to keep the velocity of the exhaust gas up high. That is why the spool on the stock manifold was better. It probably had cracks in it, so that could have cost some top end. The larger manifold runner probably was hurting more than anything on a 14b. For what it sounds like your stealth is going to be, I would stick with the stock manifolds.

[Gravy]

The stock stealth manifolds will be staying on, had way to many people go with the TDO5 manifolds and experience more lag with the e16g's and even 14b's then when the stock manifolds are retained.

The stock 1g had no cracks in it, i checked it over several time and found no problems with any hairline cracks or major ones either.

[Pushit2.0]

boost creep will make the car feel faster up top.

~John

[Gravy]

Old car had a boost gauge, and it would actually fade a little around the top end. Going from holding 15 till about 5500 and then drop to 13 or 14 if i was lucky by red line. The larger manifold actually gave me boost creep a little until i ported out the turbine housing and wastegate port.

[Febo]

Josh Id rock the stocker mani's on your stealth, you dont have much exausht coming out of each bank to run the turbo's so like jet said you need the velocity of the gas to stay hi so when it hits the wheel it has some force behind it.

Also you are correct in thinking that the exhaust gas releases its energy on expansion, hence the reason the housings are shaped the way they are.

::I am a really bad speller

[JET]

Actually the exhaust gas isn't releasing any energy by expanding. It will cool and the velocity will go down(newton's gas law, PV=NRT). The reason for the high pressure before the turbine is the restriction that the turbine wheel/housing places on the exhaust. This restriction causes the increase in temps and decrease in velocity.

The gas cooling and slowing after the turbine helps to slow the exhaust and allow it to travel through the exhaust more efficiently. The other effect of the low pressure on the other side of the turbine is to help suck the exhaust gasses past the turbine wheel, because of the pressure differential.

[Gravy]

It dumps heat energy in the housing though, which would require heavier duty metal used there then in the exhaust beyond that point. But the heat i know bears no factor on the spooling of the turbo, but when it expands not only will it loose heat, but also some kinetic energy as well with the larger piping. That would explain some of the cracks, and maybe a less then ideal design by mitsu, but i don't' know enough to comment on that.

I will be using the stock piping, just have to weld an adapter plate onto the stock manifold and rock that out with the turbo on the adapter plate, can be had for about $10 from a few different places. Stock ones actually have run better with the Td05 turbo's on the stealths, they flow well enough for the 19t's some people run, and have even seen some guys with twin 20g's using the stock manifold with adapter plates, and plenty of extra room to fit them. Seen a few people say the after market tubular manifolds with the td04 flange of them say it actually hurts the spool up giving the car a tad more lag but still due to the turbo, fading in the higher rpm ranges is still there.

The idea behind this whole post was to figure out if the tubular, larger diameter, pipes would give me a better "kick" so to say then the stock one would. The size between the two isn't that much, and wouldn't be a huge deal but for an extra $200 i would still have to weld it up, but was wondering if it would be worth the trouble because i'll already have a slight disadvantage on the spool with only having 1.5l of displacement pushing the turbo instead of the 2.0(or more) that the td05 is use to seeing.

Also wanted to make sense of the reasoning, and not just read, "It will do this." and not know why it's doing it.

Thanks for all the responses so far.