though you might like this srt-4 mod...

[Pirana]

SRT-4 modification (http://www.srtforums.com/forums/showthread.php?s=&threadid=20539&perpage=15&pagenumber=1)

[alexlitov]

That looks really nice!!!

[joka1]

damn!!!!!!

[Natey]

*picks up jaw from floor*

[traitorhound]

man that's wild

[Pirana]

if you read, it says should put 400whp with street gas, and 450whp with race gas. :eek:

[alexlitov]

Did anyone say skittle??

[traitorhound]

a skittle that'll eat you and taste yoru rainbow. ..then spit you out

[jred321]

unequal length runners on the manifold, but maybe due to space constraints. not bad

[Pirana]

I'am proof that that is not a big deal for the horsepower.

[jred321]

for horsepower yes, for longevity it is a bigger deal.

[DiscreetSpeed]

oh my, im way behind theyre power curve.....

[Pirana]

the 2004 SRT-4 increased power from 215 to 230. cool

[pdhaudio83]

nice. does it come with better than ZERO camber this year?! lol

[Pirana]

Hahaha, they did improve the suspension.

[scotthidley]

Equal length is overrated. It only helps spool up, and it makes a very small difference. Yes, it's nice to have, but the srt-4's packaging makes it hard to stuff a big turbo behind the engine. If longevity was an issue, I would think oem's would make it a point to have equal length, which I can't think of one that does. Also equal length needs to be calculated, not measured, as the equivalent flow length of a bend compared to a strait is much longer (a 90* bend = in strait length, 30 times the diameter of the pipe).

[jred321]

so how is having tons of exhaust back pressure at one cylinder (more than likely with exhaust blowing back into the cylinder) vs. almost none at another a good thing for the combustion process?

but looking at that design again after learning a bit more about exhaust manifold design, it's really not that bad w.r.t. this aspect (it looks like a lot of oem manifolds, which are generally not great designs but OK ones whose flaws become more apparent when you try to get more performance out of them), but the wastegate return to the exhaust should've been at a better angle so it won't disrupt exhaust flow as much.

[scotthidley]

I brought the wastegate design up to the engineer that works on it (I was talking to him after running him at a local drag strip), supposedly a new upgrade will reduce that. The wastegate only opens a few millimeters though, so the disruption isn't as bad as people think.

The exhaust isn't going to blow back into the cylinder. The valve closes, the pressure is going to go to the path of least resistance, which is the turbo. Regardless of length, that's going to happen on all setups. The equal length makes it so the exhaust pulses are even on the turbo (so it gets a steady push instead of jerky push, if you will). Not all oem manifolds are bad. The stock 2g dsm exhaust manifold is good for up to 600 hp. Yes equal length mani's are nice, but their one of the last things to want to upgrade if the current manifold isn't a restriction (assuming other upgrades on the car can still be done).

[pdhaudio83]

scott knows his stuff obviously :p

[jred321]

what if there is too much backpressure in one cylinder so that not all exhaust gas has left the manifold before the valve opens again? then won't it get sucked back in? that was one of the advantages i thought of having equal length runners, the fact that they will flow better by taking more advantage of the scavenging effect (like n/a headers) and thus create less back pressure. i could very easily be wrong though

and obviously scott knows his stuff, he's a elite dsmtalker :)

[Pirana]

Check the new HCI magazine, they show a SRT-4 build up with a T3/T04 turbo. An extra 95hp.

[scotthidley]

Lol about the elite talker. The scavenging is created by both intake and exhaust valves being open at the same time. Pressure before the turbine is good, because that is what makes the turbo spool. That's why when you port the turbine housing on a turbo, you don't want to make it larger, you just want to make as straight of a path with removing as little material as possible (and cleaning the casting flaws as well). Here's a little comparison of a ported 7 cm housing vs. a stock 6cm housing.

http://ffdet.com/members/scott/ceramic%20coating/7cm%20housing/7vs6.JPG

If you look at the 6:00 position of both housings, you can see how the bulge on the 7cm housing was eliminated.

So here's the trade off's with runner size / turbine housing size.

Larger = less restriction, more top end
Smaller = some restriction, faster spool up.

By having smaller runners, you force the exhaust to travel faster, in turn getting your faster spool up. So if your runners are the size of the ports on your head, and your losing power in top end (on a turbo bigger than the t25), it's time for a cam. If you have cams and still losing top end, it's time for head work, and maybe an intake manifold.

[jred321]

cool, good info. Thanks a lot!

[scotthidley]

Heh, I had to update my sig:P

[jred321]

lol