I have been scratching my head over backpressure for the VQ's. I did a search on this subject only not to find a specific thread that addressed this issue for me.

I run a N/A G for starters (for now), but my issue falls well into my forced induction plans as well as most of the guys/gals here.

Example: 3.0 Inline 6 Toyota Supra running a street legal HF Cat and 3" single exhaust. Putting down like 600 Wheel. THIS IS JUST MY EXAMPLE.

Now place the 3.5 VQ running a similar set up as the SUPRA EXAMPE above but running dual 3". What is the advantage or, perceived to me, disadvantage of running dual exhaust???

From the dyno and street results that I have seen. Every VQ running similar set ups, be it N/A or dual....the single seems to be putting down more HP to the wheels.

So does the VQ need a specific amount of back pressure to remain at optimal efficiency?

Your thoughts gentleman and ladies?

Single exhaust FTW?

 

im pretty sure that back pressure sucks for fi. resistance(back pressure) against the turbo will not let it spool as quick. i would also run a true dual exhaust maybe with a h-pipe.3" all the way back.

 

My problem is that Supras has just a slightly smaller engine than ours, yet "in general" put our higher numbers. Yes we are getting there with the VQ, but not one Supra I have seen has or needs dual exhaust.

Am I wrong here. Guys with N/A VQ motors are losing HP with dual exhaust, test pipes and headers. VS those with a more restrictive exhaust set up.

Just ideas, that I am throwing out there. I love the look of duals and find our cars looking odd with single exhaust, but the performance is my bottom line.

 

The inline engine design will compliment running a single exhaust, and the VQ design is much more suited for a dual setup.
Physically look at both engines and see the difference on intake/exhaust for the two. Should make perfect sense when you see them.
Pretty much all the big number Z guys are running a twin turbo setup with dual exhaust while Supra guys are running a big single turbo with single exhaust.
Difference between an inline and V.

 

I agree with you on the differences of the line vs the V. But air mass is air mass..18PSI is 18PSI.. Mass... be it intake or exhaust (per liter) should be ruffly the same? We seem to have more flow with a true dual 3" than a single Supra 3", so we should put down bigger numbers if my thinking is right?

Again, not saying I am right at all. Just scratching the head trying to get my head around why the true dual 3" set ups die at the top end. I am thinking because of back pressure?


And I am comparing apples to oranges with N/A vs FI set ups also. Im sure its less forgiving on the FI side of the house as far as loss of top end HP, but still yet we have not justified the dual set up as a advantage???
Thanks for the input.

 

One turbo, better to run a single exhaust. Two turbos, better to run dual exhaust.

Turbo setups make power with no backpressure. NA setups make power with a small amount of backpressure. Superchargers fall somewhere inbetween.

Simple enough?

On a supra, even with a TT setup, the turbos are mounted on the same side of the motor so the exhaust can be merged even on a TT setup. On a 350z, a TT setup has one turbo on each side of the motor (exhaust manifold), so it's easier and better to run two pipes back.

However, I do think that dual 3" pipes are overkill for 95% of the built cars out there. The 350z community seems to be fond of doing everything overkill for the power levels achieved.

 

LOL, thanks man! thats what I was looking for....

OVERKILL is the perfect word. Doesnt hurt as much as it helps, but its popular.

Thanks!

 

The thing is with the Supra is that it only has a single header so I would think spliting the exhaust into a dual exhaust would cause unnecessary restriction. I don't know for sure, but that's what I'd guess. We have 2 headers so with a true dual exhaust would be doin the same thing as the single on the Supra. Supra: 1 header, single exhaust & VQ35: Dual header, dual exhaust.

 

According to Corky Bell a true dual 2.5" exhaust should be able to flow in excess of 900 bhp (ref Maximum Boost, p. 133). He also states that most modern catalytic converters contribute less than 2 psi to the total back pressure in the exhaust (deemed acceptable but not really put into context of the rest of the system). Anyway, the general rule of thumb in turbo systems, as stated above, applies: minimize backpressure to maximize horsepower.

EDIT: Even for NA motors, backpressure is not "good" but a necessary evil in order to maximize exhaust velocity.

 

Ok...so look at a supra that's running 18psi....How much power you think it's putting down? 570/580...maybe close to 600? And a Z at 18psi with a dual turbo power?? Well, I'm not exact on this but you see guys like alberto and eagle running mid 500 to low 600 with 15psi, so the numbers can't be that far off. Z's numbers will probably be higher in a psi to psi matchup.

You just won't see Z guys pushing 25-30 psi on a block like the Supra guys can, which is why they have huge numbers.

 

Why not? I think eventually there will most definitely be guys pushing 25lbs and running 9's.

 

When they start making VQ's bottom ends with different metal maybe...

 

Back pressure is not ideal in any setup and not necessary. A well designed free flowing exhaust is the best exhaust.

 

Has nothing to do with the metal. The boost limit has to do with controlling detonation on this motor on pump gas. Move to race gas and/or W/M injection and you can pump the boost up for some insane power levels already.

 

18 psi is not 18 psi......volume is a very important factor that most people forget about.

an extreme example would be thus:

18 psi on a 1.8L Honda at 8000 rpm versus 18 psi on a 10L BigBlock V8 at 8000 rpm.......do you think that it takes the same volume of air to create 18 psi on the honda as it does on the big block? NO WAY!!!!

 

not true....intake/exaust resonance is VERY important,big exaust on small motor destroys power band and usually causes poor idle and driveability problems.although misused often it's where the term TUNED exaust comes from.

 

+1 Turbo size/flow, motor/setup efficiency, etc etc etc the list goes on forever


As far as exhaust is concerned, as everyone said the inline-motor single-turbo Supra setups lend themselves nicely to single exhausts. The Z most typically has twin turbos on opposite sides of the motor which makes dual exhaust ideal.

Dual 3" exhaust flows only slightly more than the supra-standard 4" single. For bigger-turbo supras 4.5 and 5" exhaust are more common now, both of which outflow dual 3".

 

Agreed but my question was on a 3.0L and a 3.5L not 1.8 to 10L.

 

We we say ideal are we referring to installation and air flow or are we saying effeciency?

One 5" has less volume than two 3" (3+3) being 6. I no I am being picky here, trust me...I just want to learn.

So I guess with a cross pipe from one side of the manifold to the the other, the amount of usable air flow is not enough for a VQ to run single exhaust effeciently?

But if going dual exhaust, to equate to the Supra 5"....wouldnt that be dual 2.5's for the VQ?

Thanks for taking the time for my off the wall questions in advance.

 

I don't feel this is 100% true. The reason Z guys usually run twin turbos is there is physically no room in the engine bay for a large single. We run single turbos on both our 350z and Toyota Supra. Z put down 1016rwhp and the Supra puts down the same. Both of these are through automatic transmissions.

350z 1016rwhp Dyno Thread