One big difference between 4" discussion here and with the Supra guys are that they AFIAK always dump the WG to atmosphere when going single/external wg.
Here most people find that too loud.
Going 4" after the wg ties in can somewhat compensate the disrupted flow when merging the different exhaust streams.

 

BTW, equal length is preferred but are also more sensitive to pipe length since they are tuned for a single rpm.

Mark I'll pm you some dimensions I have.

 

You guys crack me up! First it's "stock is the best", and now you guys want 4"! Seriously, there is no reason anyone should EVER be running a 4" on a 951, unless it has an ls1/lt1 and is making 800+hp. There is just no PERFORMANCE benefit whatsoever. Do it for the "bling" if you must. Hehe, I must confess I was recently rocking the 4" (not Lindsey's, custom from a "lister) but found it to be completely unnecessary for ANY 4 cylinder.

Disrupted exhaust flow from the wastegate tie in is minimal at best on 951's. Our cars tie the wastegate flow in far from the wastegate. Compare our cars to a conventional internal wastegated setup. Internally gated turbos have a much bigger issue with this. The wastegate flow merges at the exhaust housing which can cause tons of turbulence, and even backpressure on the turbine. There are many ways that the Japanese aftermarket has come up with to cure these issues, such as turbo "elbows" (some here call it the downpipe, the exhaust piece bolted to the turbo) that put a physical divider between the exhaust flow and wastegate flow. Basically it's 2 pipes instead of one, and they merge farther down like this In internally gated setups like that, there are actual performance gains to be had, though it is a complete non-issue on our cars.

 

Posts like that crack ME up
There IS a difference between venting the wg to the open or not. More so than 3" vs 4".
Just because there are "elbows" that creates less turbulence for internally wastegated turbos/cars doesn't mean that's the perfect solution.

There has been comparisions between these kind of configurations and where there is reduced back pressure there is more power to be had. BUT with that said, it isn't worth it for most of the cars, but don't be neglicant enough to think it is completely useless unless you have 800 hp.

The strangest part is that everyone is convinced a 3" exhaust is a great upgrade for a chipped or even stock car. But then all of a sudden you need 800 hp to make use of the "next step"

I've said it before... for those of you who think 3" with the wg tied in is perfectly enough for say 600hp, then why you don't get a 1.5" exhaust for your chipped car and enjoy the lighter weight...

 

Only if they were putting out 150hp....! Do the math.

Chris White

BTW - it you want my opinion - make it with SS oval tubing - now that would be cool.

 

Yes yes I know Chris... I admit that part was made to provoke.

But then let me rephrase and ask for the math were a 3" will have gains on a 300 hp car (compared to stock) but 4" won't have gains until 800 hp.

 

The 4" will make more noise scraping the ground...not a lot of clearance on a lowered car.
I don't think the gains will be noticable, I wouldn't bother with the 4"

Chris White

 

Thanks for clearing that up. I've been w/o a 951 for about 2 years now, so my under-car-clearance memories are fading.

 

http://www.burnsstainless.com/OvalTu...valtubing.html

would be nice.....excpet for the $40 a foot price!

 

i've actually seen dyno comparisons with wg dump to atmosphere vs. wg tie-in (both without a cat) and it made no difference on 951's.

thus, wg tie-in is preferred, unless you like to be ricer style.

 

4" - NO
3" - Perfect

Simple enough for me.

So, what did happen to the flex joint idea?
Are we talking about a flex in the header runners, or in the pipe going across to the turbo?...

 

Please let's just end this discussion... You just cannot generalize like that.
"it made no difference on 951's."

You have clearly no understanding of how this works. Dumping it to atm will reduce backpressure, that's a fact. In fact, besides other general sources, NZ951/Machtig did several tests on this, Ski did dyno pulls with/without wg tie-in or of it was 3" vs Lindsey 4" exhaust, Lindsey have done tests with their exhausts etc.

I'm not claiming you'll gain 30 hp on your average 951 just to dump to atm.

BUT with reduced backpressure you can make a more aggresive tune without risk for detonation. If you think of your engine as a complete system minimal backpressure is critical for maximum performance.

Yes I agree it's probably not worth the effort for most people here, but don't go around thinking stuff like this doesn't matter at all just because you don't tune for it or make use for when setting the specs for the rest of the engine.
If you at maximum will upgrade the turbo and get a MAF-kit then yes, thinking about big exhausts and/or wg-tie in or not is not really worthwhile.

For those who seek more performance than that, the above stuff is one of many things to consider.

Now back to topic. I hope further exhaust discussions of value for Mark can be made in his exhaust-thread.

 

I think the cost-benefit of a 4" system just isn't good enough. Higher costs, heavier, less clearance. I'll stick to my 3" for now. As for the oval tubing, isn't the factory exhaust using that sort of idea in the first place?

 

Yes, 3" with a flex-y should work just fine.

I'll verify pricing with my mfgr. Tomorrow.

Worst case: I may have to put a few thousand down to get the ball rolling with my mfgr as he said he was about 6 months behind unless I wanted to buy my way up in line. I don't mind buying my way in as long as I have deposits from what interested parties I have so I don't get stuck with 20k+ in parts. I need to order a min. of 30 to get this price....and from what interest I'm getting on this board, I can probably do that w/o too much stress. Also, I would dyno-test the prototype to ensure fitment, ease of installation, power/torque/spool to show results & would start next weekend.

If I had to ask this to ensure my $800 price (header + cross-under pipe), would $2-300 down from each interested party **** everyone off? Luckily I have a few weeks before the 928 stuff comes back from mfgring, so time will move quickly for this, & photos would be posted on a weekly basis until it ships out.

Let me know your thoughts. Mark.

 

So, what exactly is a flex-y?...

I couldn't possibly put $300 down right now to show my interest. Maybe in about a month's time when my tax refund gets here though.