Yep. Oversize headers have always been a good "marketing" tool, People think bigger is better and they show the peak power numbers and people think it is better. When the right size header willl make much more average torque over the powerband and especially in your driving rpm range. It's cheaper to make power with boost anyway. We already been through these discussions on several "generations" of different engine classifications. Those Coyote dyno graphs are showing that the larger header isn't making the torque as the smaller header up 500-600 rpm later in the graph and it is down 30 even 40 ft-lb of torque at that point.

 

The coyote is not the samr kind of v8 your dad grew up with. NA engines make power through fisplaemetand RPMs, these modern engines favor RPMs. I am doubting that you are finding dyno comparisons between headers that are showing a 30-40ft-lb loss. Even if they are, it doesn't matter as you would likely see that rpm once within the first couple seconds of WOT and it's all moot from there. Selecting headers is about matching them with your intake, cams and heads to make power where you want it. My coyote is built around living in the higher rpm range, in a 3000-3200lb car with a steeper final drive ratio, and 3600 stall. With everything dialed for 6000-9000rpm, my car will make less torque than it could, and I'll never notice it.

As for my IS350, it lacks the options for making more power and it's not worth ruining a good daily driver. Realistically the 1 3/4" headers will be ok, and I was being picky when I had my second headers custom made. I'd bet the largest split between them is less than 10hp. I still think the best route is to just leave the stock manifolds and go with 2.5" for the rest of the exhaust.

 

D, adding to you point, I was mildly impressed that at 7200 the 350 with F-Sport axleback and intake/airbox has a maf readings at +250 and does pretty fair hole shots taking many by surprise! At this point I have to say that the OS-Giken LSD is my favorite single modification to this chassis. You have to be pushing it past the limits of tires for traction nannies to kick in. Where without, all 4 tires are squealing through the corners and the nannies are attempting to fix stuff if not disabled. It really makes the platform handle well and puts down the power it has not wasting a drop... For me, no need for headers at this time with you confirming what I'm seeing from others that they just don't help until the very end of the curve. Maybe with some port and intake work, coupled with cams headers would allow it to move more air and put headers to use.


What is the Coyote in that weighs 3000lbs?

 

So the LSD is a big deal I see...

A 3000lb Coyote is probably stripped completely bare most of the interior, seats, door panels, windows replaced with lexan, body panels replaced with fiberglass. The cars are naturally heavy without weight reduction. Now an old school mustang 5.0 notchback could easily be 3000 lbs and could be lightened easily to 2800lbs with some creature comforts.

 

That's probably about as good as a na v6 is going to sound. I wonder how much of the difference is the H pipe instead of an x or y pipe setup that you would usually see on an IS350. I'd see if you have an exhaust shop nearby that you can talk to to see if they could make a custom exhaust for you using the same borla mufflers, maybe throw in a couple resonators to clean up any rasp.

 

Coyote is awesome. 3 changes and you are over 500rwhp ( headers and exhaust, tune and e85 ).

However that could also be done out of other 5.0 or close to 5.0 displacement engines that are pushrod.

The reason the Coyote makes the power:

1. High flowing cyllinder heads ( gen 3 coyote unported flow 320cfm peak cfm )
2. 12:1 compression
3. Tuned induction system
4. VVT gives good torque slightly off idle to mid range torque

A 5.0 Ford or 5.3 Chevy can make the 500rwhp and 400rwtq or thereabouts with the same changes as the Coyote:

1. High flowing cyllinder heads ( ported TFS 11r's or AFR's on the Ford or Twisted Wedge 215 or 225's on the LS over 300cfm @.500" and over 320cfm@.600" lift )
2. 11.5-12.5:1 compression
3. Tuned induction system ( Vic 5.0 EFI intake or Super victor converted to EFI or tunnel ram intake, or FAST 112 intake on the LS )
4. Good exhaust system ( 1 3/4" or 1 7/8" long tubes into 3" dual exhaust
5. Tune
6. It'll need a cam with over .600" lift to get it over the 300cfm range with a similar duration as the DOHC on the coyote.

Richard Holdener has a easy 500rwhp 5.3 build and Lykins motorsport has a 550HP engine 5.0 build ( 500rwhp ) .

The knowledge was always there to do this, it wasn't common because "everyone" didn't know.

 

So you are now accepting 1 7/8" primaries? That 5.3 had larger primaries with everything else just to barely pass 500hp on an engine dyno with no accessories. Take two cylinders away and it's making about what a fbo IS50 with light intake manifold work would make. Those aren't really impressive numbers, and at a glance would imply that 1 7/8" headers are fine to use if you are using that as an example of a proper setup for power. Comparable effort into a coyote would result in significantly better numbers considering that 5.3 is making what a stock gen 3 coyote would with exhaust and tune. I'm looking to put down something like 400ft-lbs and in the low 600hp range with my coyote.

I think it would be interesting to see what an IS350 would be like with a comparable amount of work done, but it just wouldn't be worth the hassle to do all that to compete with stock modern sport cars. I'd prefer a positive displacement blower and quiet exhaust if given the choice. It's a shame we don't have the hood clearance for something relatively cheap like a m112.

 

1 3/4" will have more torque on the street under 3500 rpm than the large 1 7/8" header and make 99.5% of the peak power. The 1 7/8" would be fine on dyno queen or a drag car. The 5.3 example was not the best but in the ball park. Its super easy on the platform. And yes remove 2 cylinders and its near a 2gr with a tune and bolt ons.