9/10 header setups that I have built for motors in this displacement range ( around 3.5-3.8L) making power in the 6000-8500rpm range have all mostly been 1 7/8" at the head, and some stepping all the way to 2 1/8". The primary length and collector choke point is very critical as well. On 997 GT3 RS's I am running 1 7/8" off the head, stepped to 2 1/8" and I am still only using a 2 3/8" choke which makes the most power. going to a 2 1/2" choke loses almost 10whp.

With larger cams and more overlap, the closer to peak velocity in the primary pipe you get, the more the restriction will affect the power. Again, if the cylinder head is stock on the exhaust side, the head may be the choke point in flow. Large cams with stock heads may want a shorter primary length but a smaller diameter.

Yes I know honda, nissan, and porsche its not apples to apples comparison, but as far as engine dynamics are concerned the main specs of the motors can be very similar and a lot of information and configurations can be compared between them all.

 

The only cam timing change i see making a difference in the higher RPMs is going to be the exhaust cam timing.

When we first took the car to the dyno we were getting an intermittent crank sensor error which was disabling intake CVVT. So I disabled the code in the ECU. The only place power was affected was in the lower RPM ranges, by around 40 ft/lbs, with the losses tapering off about the 5k mark.

Retarding the exhaust cam a few degrees might make some more up top so long and the exhaust is up to the task.

 

In an earlier conversation w/ 1cockyz, he mentioned that the 380RS had 1.7" primaries on that 3.8L HR and the SuperSprints having 50mm primaries. That is nearly 2". He believed that the research done by SuperSprint showed no losses throughout the entire powerband.

 

The porsche had 48mm primaries and I was joking that even my miata has 1.7" primaries
There is a good article on racing beats web site about header developement

 

when you go to a stepped setup you can run a smaller primary pipe.

2 pipes with the same length but with the different diameters, the larger pipe will have more max flow potential. for the pipes to flow the same the smaller pipe will need higher velocity.... which will create a greater scavenging effect, jumping to the larger pipe increases flow potential.

you have to look at intake vs exhaust flow ratios in the cylinder head.

 

Perhaps we can do a test on our next set of headers and just start them straight off at 1 7/8", but already the step from 1 3/4" off of the head is a HUGE difference.

The 1 3/4" section does not last very long, and if we're not maxing them out at 340whp, I don't think you will either!

Space becomes a very big problem as we go much bigger as well, fitting 3x2" tubes through the drivers side of the engine will be very difficult!

We've tested 3 different size combinations so far on the engine, and I can tell you the racecar headers with 2" primaries DO have low rpm losses over the 1 5/8" to 1 3/4" coast fab headers.

Everything is about balance, not everyone is going to be running their engine at 7000rpm all day like I do The powerband for most people is realistically 5000-7000rpm.

Those 997 GT3's rev a lot more than we do, and are of significantly higher displacement, so i would imagine that's where the difference comes into play.

Unless the heads are ported, I can't imagine starting any larger would be of benefit. Of course I could be wrong!

 

your car is so far out of the box it doesn't really count anymore, lol.

imagine trying to do a set of FWD headers and then trying to keep the y pipe close to equal length. Our old headers were so poorly designed and flowed so unevenly we burned the electrodes out of 2 plugs at VIR.

i know your intake mod made good power, but what was your biggest power maker?i feel like I need a timeline and clifnotes for you mods, lol.

We Just started a new FWD build slated for a VQ35 Maybe with a Revup head and ECU twist.

 

^I have ported exhaust and intake runner and oversized valves. Those are the only two variables NEVER before seen in an NA build (Cosworth does feature the valves in their shop build) on this forum. I'm not that far out of the box. My numbers are almost identical to 1cockyz, powerband and peak.

I'm yet to modify my stock airbox, although I planned on fitting the larger velocity stack. I am installing the headers and then I will focus on what I want to do with the airbox and throttle body.

In your case, you have a FWD drivetrain, so you're numbers are going to be a little inflated due to less drivetrain loss. Additionally, I wouldn't be too sure that putting cams in your car won't result in the exact powerband (w/ the power holding to redline) you achieved with the manifold and headers. For all you know, cams could just cause your motor's peak, which, like every single other NA w/ bolt-ons, is at 6250rpm, to be more pronounced, but still see the drop off to redline once you outflow the headers/manifold mods.

I am not discounting the work you did to the manifold, as you've really flattened out the torque curve in the midrange, but it turns down at the same spot everyone else's does. Your work is remarkable and nothing I'm qualified to do. A good contribution to the NA forum. Thanks!

I believe Sasha talks about the VE increase and TQ bubble and cause the HP peak w/ the non-rev manifold, etc here:

https://my350z.com/forum/8750067-post215.html

 

Awesome build man. Can't wait to go back to NJ and catch up with some of you guys. Sick builds and it definitely helps guys like me with stock revups looking to upgrade. I'm all about power in the high rpms and man did this thread teach me alot. Keep it coming.

Just thought of something here. With the Nismo Spec 2 heads, why not use those to raise the compression instead of building the block? It actually only gives a 12.0:1 compression ratio and you can run that on pump gas. With that run a Tomei cam, header, and test pipe setup, and I believe you'd make more power in a higher rpm. However I'd imagine there's flaws in that setup but I'm too stupid to find them. But to me it seems like it makes sense especially with the lower combustion chamber volume of the spec2 heads.

This is weird because the Nismo spec 2 heads are modified from the VQ30's. Here's what I found comparing the flows of stock heads, the Spec 2 heads, and the actual racecars GT300 heads. Mind you the GT300 car used these heads.
http://www.nismo.co.jp/en/products/c...inder_head.pdf

 

Nismo heads and tomei cams with tomei headers could net some serious power.

http://www.jdm-option.com/eng/featur...2/z33_v35.html

 

That's exactly where I grabbed the setup from. Most of the Nismo festival cars run that setup and make a lot of power. But they're ridiculous when it comes to setups such as Q45 tb swaps, dual intake plenums, and various other crazy setups not seen on the market.

My thing is, mix matching parts won't net you the same gains as parts from the same manufacturer, especially since they tune their parts to work with their own parts.

 

What benefit would you have in having a set of heads designed theoretically for high-rpm use if you don't have a block strong enough to withstand frequent high-rpm use?

 

Well let me define what I mean by higher rpms. Since most Z's really don't rev much higher than they do stock when built. A set of heads on a factory block, with a proper set of cams, headers, and tune will allow airflow upwards of 7000 rpm. Which for a revup as you know is the factory redline, and if the stock engine is capable of flowing those rpms then adding a modified top half should be a perfect match whether you have a built block or not.

However, you know a lot more than me.

 

my guess on using the vq30 castings with the smaller chambers is being able to use a piston with less of a dome, and as a byproduct, better swirl in the chamber, and/or less dome interfering with the swirl from the quench area. I bet piston dome design could find some power.

 

Another thing I found regarding the MREV2 and 5/16th spacer is, on a stock engine motordyne's dyno shows approximately 6hp loss from about 6600 rpm and on, and about the same 6tq loss from the 6600 rpm and on. Now that's on probably a stock engine, but that MREV2 and spacer are only designed to bring out low to mid powerange from dyno plots that I've seen. Why not port the stock Revup and make more power at the same rpm?

 

The stock revup is actually almost too big! It's MUCH bigger and a fair bit shorter than the non-revup plenum.

I agree that dome shape is a problem with high dome pistons (like the ones I run in my Z) and that making the head smaller would be the proper solution. I want VQ30 heads!

 

So then on a highly built application wouldn't you see more of a peak loss with the MREV2 because of lack of airflow? Another thing is. I wonder if those heads are modified to fit, or can we buy a set of used of vq30 heads, do some machine work, and swap them in?

 

if you want to drop some coin, a real machine shop/builder can weld material in and re-machine the chambers.

If i could see a picture ff some really high comp pistons i could make some suggestions.

 

Yes, the crossover is around 6500rpm iirc

 

I actually have an extra V2 revup motor. I got my original motor replaced, so the spare has only 4k on it. I bought the longblock in this car from SFR.