Motors My Celica GT-Four Build Thread! - And Then There Were 4 (Update 25/08/20)

The QTP system is welded inline, it's a Y valve so when it's closed, the gasses go through the straight section to the rear section of the exhaust. When it's fully open, both ports of the Y are open but the exhaust gasses take the path of least resistance, which is straight out the now open port. When it's partially open, a percentage of the exhaust gas goes out the port and the rest continue on to the rear exhaust section. This is how the QTP gives you the ability to control the exhaust back pressure.

 

Yeah, and when exhaust gases go straight out an open port, especially one nice and close to the engine.... things get loud.... I'm talking about dragster loud, not the sort of thing that is allowed on the roads!

But when there is no Y intersection, just a valve in a pipe, then the valve can be positioned from partially closed for high restriction/low rpm, all the way to horizontal/practically no restriction/high rpm, which is great for maximizing street performance, especially when the street mode settings are dyno tuned to match.

For a Y valve to be streetable, it would mean something like the low restriction path bypassing one or more mufflers/resonators in the exhaust system, or just lead into a high flow resonator.
Either way, there would still have to be at least one resonator at the end of the loud/low restriction pipe for it to be road legal. If all you're going to have is a short pipe on the loud side of the Y valve, then it could only be used as a switch from street mode to track mode... I am assuming that open exhausts would no way be street legal over there!?

 

Nope, not allowed on public roads in populated areas. For a blast thorugh the hills on a Saturday night or Sunday afternoon though, a partially open valve would be fine on the street, without having it wide open and disturbing the wildlife at WOT

The maps are going to have to be valve position determind anyway. There'll be a massive increase in flow from having the exhaust vent through only the manifold and catalytic converter. The maps will be something like the following:

Lower HP street map @ closed valve
Lower HP street map @ semi-open valve
Lower HP street map @ fully open valve (just because I can)
Highest HP race map for race fuel & wide open valve
Highest HP race map for pump fuel & wide open valve
Highest HP race map for semi closed valve & pump fuel
Highest HP race map for closed valve & pump fuel

The bold map being the most powerful and also the loudest.

Open exhausts are not street legal here to the best of my knowledge. The exhaust must pass through a catalytic converter to meet emission level requirements and a muffler or silencer to keep the vehicle's engine noise at an aceptable decibel level. As I've said before though, on rural (probably mountain) roads on a weekend afternoon, nobody is going to hear it but the farmers and the livestock, and I won't have the exhaust fully open on public roads, no matter where it is. Obviously I wouldn't drive through town with the exhaust open either, or even partially open at anywhere near WOT. I think the design I've come up with is decent enough to meet my needs without being overly complicated. If the turbo-back system that I put on is good enough, it should be high flowing and tuned enough to produce a nice note and good performance even with the exhaust completely closed.

From browsing the GT4OC and 6GC forums over the past few weeks, I've gradually realised that I am designing a much more powerful and complex car than most of the owners vehicles on those sites... If and when all goes according to this plan that we're laying out, I will have one of the most powerful and best race prepped ST205's in the UK!

 

Just caught on to this thread. Looking at it to see where things go. Have a fun little track toy myself (03 Mitsubishi Evo VIII).

Are you going to be recirculating the wastegates or dumping them straight out?
Recirc is quieter but dumping will reduce backpressure and cause less turbulence in the exhaust flow.

 

Hate to burst your bubble Uni, but a completely open, unsilenced exhaust will really struggle to meet track noise requirements, cool though it is.

 

I just put on a straight through exhaust (but still with Cat) on a 1995 2.5L turbo diesel. The only difference is a solid throaty roar when on the motorway Most of the noise is engine noise aha. But yeah I agree with Krikkit, even tracks have noise restrictions now... If you're really wanting it then put an easily accessible bolt on high flow silencer for tracks and remove it if you're just mucking about in the deep countryside!

 

Dumping them straight out, more than likely through a couple of screamer pipes

I specifically asked about this on a couple of the other forums before I started discussing it as an option. Most people told me it would be fine for most tracks but that some of them would require the use of a more quiet full exhaust system... Have I been told wrong?

The only reason I want it is to increase exhaust flow and let the engine breathe more efficiently. Every little counts at the high end of the rev counter that I'll be at on track.

 

The rules are a bit loose and varied from track to track, a few people with track 106's have fallen foul of the rules. They seem to go from totally anal stewards who not only static measure your car but test it randomly at pit drive-bys, to places that don't even bother getting the meter out.

Just something to think about, but with several maps available it won't make much difference really. Come across a track with strict noise - use race map with restricted valve openings.

Noise for open/unsilenced exhausts seem to vary madly, I lost the backbox off my 106 and had to drive from M25-> home without it (damn rust!) and it was unbelievable how loud it was. Even through a pair of ear defenders, a pair of earplugs and two bobble hats to try and deaden the sound it was deafening.

 

Hmm, I'll have to just play it by ear (no pun intended) as far as the exhaust goes then. With the right maps I should be able to make it work in all situations, but it'd still be nice to be able to open it up at some track events. Maximum note + maximum flow = (maximum grin!)



If the 106 was that loud, the GT4 will be ridiculous! I saw a video on Youtube of an untuned one with a QTP open fully - will try and find it now

[edit]

Courtesy of Batman722 on 6GC.net;

 

Looked like in that first video he is running a bit rich... 10 or so AFR.

Don't forget that a turbo will act like a bit of a muffler. With the evo (2.0L) I run no cat and 3" or 76mm all the way to just a bullet muffler and have no issues with police or track sound problems. As long as you route the dump tubes downward to bounce it off the ground and into the car to muffle them a bit, those won't be much louder than a harley full out either.

If you really want to open her up for a track, jack it up and take the exhaust off at the cat/test pipe and put a small bullet muffler there with a turn down after it to keep the exhaust actually off the car. Lose the weight of the back half of the exhaust system. Personally don't like the QTP as they seem to overly complicate things.

 

How is it that you think the QTP system complicates things? From what I've seen, read and heard they do nothing but simplify opening up your exhaust for the track and allowing it to be closed or partially open the rest of the time. I still may just resort to completely removing the rear section of the exhaust for track days, although given the concerns that have been raised regarding acceptable noise levels at tracks, I may need that muffler that you mentioned.

Here's a small update... that if I'm honest is not really related to this project... but sort of is. That makes no sense, but bear with me

A while back in this thread, I mentioned that I'd made a small purchase. I believe MV joked about it being a TRD sticker at the time Well, it wasn't a sticker! It was this:



The story behind this; My intention to date has been to buy the engine for my car and have it built before I actually own the car. I know that the engine is going to be the most expensive part of this build so I may as well get it out of the way first, and I also know that right now I have the space to work on and store an engine but not really enough space to store and work on a whole car. So, I started looking at 3SGTE engines. I also looked at a few valve and cam covers to get ideas for what I'd like mine to look like, and whilst I was looking at engines and 3SGTE parts on eBay one evening, I saw this valve cover. It was a freakin' steal, so I bought it! Now, the problem is that I didn't really look at what it was all that carefully. It was listed as a 3rd gen 3SGTE engine cover, but the image of it was pretty low-res and I didn't look at the type of cover much, I just made sure it wasn't beyond brightening up and hit "buy it now" before someone else beat me to it.

It only arrived earlier this week because the seller forgot about it due to an illness, the Christmas period and a holiday, but I don't mind - I'm just glad it arrived eventually. Now, here's the interesting part. The reason this doesn't really relate to my project is because this is the valve cover from a '91-'92 MKII MR2 Turbo, with a 2nd gen/rev2 3SGTE engine. It's what the MR2 boys refer to as an "early valve cover" because the appearance is a little different to the one on the late rev2 engine, even though both covers will fit the newer later head just fine.

Here's a picture of one from TurboMR2.com that was fully restored for the rebuild of a later gen 2 MR2 3SGTE, in the fantastically detailled article "rebuilding the 3SGTE":



Some of the MR2 owners actually seem to prefer this older design of valve cover for their engines.

So, I've got myself what you might call a "loosely related microproject" - restoring this valve cover to it's original (or better) condition so I can either sell it to an MR2 owner to use in an engine rebuild, or mount on the wall of my workshop

Updates coming soon

 

Mmm... Nice! Get your eye in, eh? A weekend in some paint stripper, some crackle paint and a new piece of hose will get that looking awesome.

 

Oh yessir, awesome weekend project And of course I know I'm going to have to do another one of these in the not too distant future! I edited the post above to include a picture of the one I saw on TurboMR2.com. That's how mint they can look

 

That looks pretty bloody good, but I much prefer crackle paint on cam covers than gloss finishes.

 

Not 100% sure what colour/finish I want to do it in yet, but I've made a start at the prep. I removed all the oil baffles, gaskets and liquid sealer/gasket from the underside and started to clean it up:



The guys on GT4OC are not convinced this is an MR2 valve cover. Note the difference in the breather pipe in the two pictures in my post above. My breather pipe is straight (mostly ) but the one on the finished MR2 cover is bent at 90 degrees. They're thinking it may be off a Celica 185RC. Still waiting on confirmation.

 

Do a nice job and that's a small detail someone will work around to make fit.

 

Glad to see you're getting somewhere with this! Little necro posting here, but oh well. I've just re-read the whole thread, it's making me want to 'build' a car now :/

Made any more progress on this yet mate?

 

Awesome, thanks for looking and bumping it up again, it needed an update anyway! I've been making slow progress. Obviously I haven't bought anything yet (other than the valve cover) but I've been getting well geared up for when I do start buying. The plan is still to build the engine first and chassis second, so I've been sourcing engine machine shops and have been in touch with one place that has been very helpful and has said they can achieve what I'm after on the block, head and inlet manifold.

I'll post an update at the weekend with some pictures and progress on the valve cover

 

That settles it. I am definitely going to get an EVO / MR2 when I leave uni.

I know zilch about cars (well, engines) tbh; this whole thread has been one big learning experience. My dad has an old Westfield so I might poke about that a bit during the summer, it needs a bit of cleaning up so I might see if I can persuade my dad to see if we could make a small project of it.

 

Just to give this thread another tickle, it might be worth getting in touch with these guys about a cage - they run a race series (and build a spec car for £5500) of T200's, so they must make or buy their cages!