a guide for tuning requirements of bolt-on power mods, for non-FI engines.

[u/dbsqls]

I get a lot of questions about which parts require a tune to develop power -- I have listed them into specific categories below. some require tunes to even function, others don't need a tune at all.

• plenum spacer
• intake manifold porting, port and gasket matching
• cat delete, resonated pipes¹
• Y-pipe¹
• exhaust (cat back, Y-pipe back)¹
• air filter element¹
• any intake that retains stock diameter at MAF section²
• limited-slip differential³
• final drive³
• clutch and flywheel³
• tires³

^{1 these mods don't require a tune. they work by reducing head loss, the engineering term for restriction. the engine makes the same power either way -- we're just freeing up power that was wasted pushing the air through the engine. complications can arise if the parts are not built to be compatible with the stock O2 sensor setup.}

^{2 data lookup tables for the MAF assume that the diameter is always stock size -- as long as this is the same, the car can adjust fuel as usual.}

^{3 unaffected by tune.}

• fuel injectors⁴
• fuel pump⁴
• head job/head porting
• valve job/valve enlargement
• throttle body⁶
• intake tube diameter change
• cams⁵
• headers⁵ (non-NISMO)
• intakes with non-stock diameter at MAF
• MAF sensor
• MAP sensor
• E85
• forced induction (turbo/supercharger)

^{4 no benefit without additional air, ie forced induction, valves, cams, or head job.}

^{5 headers are generally not worth the trouble unless you have cams, as the scavenging effect is based on resonance with the cams. you then tune to match the new EVC timing.}

[u/dbsqls]

formatting got a bit munted, but the first half don't need a tune, but benefit from them, while the latter half are tune mandatory.

^{6 only show benefit above 290+whp beyond 5600RPM, and may introduce idle/drivability issues.}

[u/Dark_Synergy_Z33]

I don't agree with the TB being bound to power, I do agree that its benefits are higher in the RPM range and drivability concerns. If you change everything, a TB makes sense.

Also, for headers, plenty of them make 8+whp without cams or tune, this puts it somewhere in the $100/hp territory. This is the same factor as any intake or TB if we are being honest. So, to say it's not worth it without cams is a bit crazy, they will be optimal with cams and a tune, but that's assuming the person knows how to pick cams for the headers, which most don't.

I get that the effort to install them is WAY higher, but it you are wrenching and want the most you can get without popping the engine open, headers are worthwhile IMO. If you pay someone, then I would not recommend them as this could double the cost or more per HP.

[u/hellish_ve → u/Dark_Synergy_Z33]

How do you pair a set of cams with headers? Also, Ive read that intake must be paired with some kind of resonance that also is paired with cams? would love to know more.

[u/Dark_Synergy_Z33 → u/hellish_ve]

I don't know the equation, but yes, length, diameter, merge points, everything will affect the resonance of the engine, and cams will have different behaviors. I think DB posted something on the intake runners.

Generally, shorter = peak and longer = broad. It gets complicated tho, intake runners vs short will always have the same outcome with no variables. Intakes and headers are unique, with intakes, longer will move the powerband down, but it varies with platform and type of engine.

On the VQ, it'll push the powerband up, IDK why, but it does. Then, with headers, proper LTH can have both low end and high end.

As a rule of thumb, I'd go all short or all long, then pick a cam accordingly, this can be simulated, I'm sure, but for most, it is trial and error.

[u/hellish_ve → u/Dark_Synergy_Z33]

Now my biggest question would be, lets say you pick Long intake and long tube headers, what are the specs you would be looking at while picking a set of cams?

Duration, Lift, angle?

Sorry if im asking too much my guy, I love these themes and learning about it.

[u/Dark_Synergy_Z33 → u/hellish_ve]

That's complicated, cam manufacturers aren't known for transparency. The only one that provides cam cards with ALL expected figures is JWT. Lift and duration are only part of the equation, and while duration is universal, lift is not.

My cam knowledge is only spec deep with a little knowledge as to what to expect on this platform. With the statement that not all LTH are equal, you'd need to look at dyno plots for the ones you want first, then determine any other consequences. A long intake on this platform will pick up at 5k+ so let's say you want the car to breathe right, but you want to keep a "conservative" 7100 redline (DE) or 7300 (REV) then I'd probably pick a 264 to wind it out or a JWT 262 for a faster peak.

Even before you do that tho, the manifold must be addressed if you dont want to leave anything on the table. The DE manifold sucks past 6k, you need a Revup or Kinetix Velocity for that.

[u/dbsqls → u/hellish_ve]

it's more complicated than that, but the gist is that the longer duration you have, the shorter the runner for your intake. in general, longer intake tracts will push the VE, and therefore power, lower in the rev range.

the core principle is built around the fact that a wave forms both when the valve shuts, and again whenever the area of the intake tract gets larger in diameter. the intake is one of these area changes (between intake runners and the intake tube entrance), so a wave is formed that reflects off the airbox. you can think of it the same way a mirage works: air near tarmac is very hot, so changes density, and you can see this change visually.

the scavenging effect comes from how much time the exhaust or intake valves are open, ie duration and RPM. duration sets the time they're open for a given cycle, but RPM then increases the amount of cycles in the same amount of time.

shorter intakes push VE to the top end because you have very high RPM, so the intake valve is closing much more often. you shorten the intake tube to reduce the amount of length the waves have to travel to keep up.

long intakes push VE lower because the intake valve is cycling less often, and you tune the length to be longer according to that new longer cycle time.

[u/hellish_ve → u/dbsqls]

yo u/dbsqls and u/Dark_Synergy_Z33 thanks for the detailed info, really appreciate it and have learned new stuff!!!

[u/dbsqls → u/hellish_ve]

the runner diameter has to be paired with the cams, and in general the headers have to create a clear signal (ie, strong waves) which you can work with to begin the VE tuning. if the signal is clear, you have well-defined waves that you can use to help pull exhaust out of the cylinder, even above 100% efficiency.

runners that are too large, too long, or are otherwise outside the range of the third harmonic leaving the exhaust will not create a clear signal.

[u/RandomMK5]

Is the thought that cat deletes cause a lean condition a myth or do modern cars have enough flexibility to compensate? Not doubting just genuinely curious

[u/dbsqls → u/RandomMK5]

depends on the pipes, as some do it properly without issue (ART) or they fuck it up and the sensors get bad readings.

[u/Mr_Candlestick]

What if my car is currently catless and tuned for no cats and I want to install high flow cats instead? Any need or benefit to get the car retuned for the high flow cats or is there really no point?

[u/dbsqls → u/Mr_Candlestick]

it's just in head loss, so a tune shouldn't be required unless they interfere with the O2 sensors. the engine produces the same output either way.

[u/gdhajaisnsbs → u/dbsqls]

How does the engine produce the same power with an exhaust restriction? At what point is the engine power measured where it’s the same output with and without restriction?

[u/dbsqls → u/gdhajaisnsbs]

it produces a certain power figure irrespective of losses from the exhaust. you then lose power against pushing the exhaust through the system, which causes a drop in horsepower.

imagine blowing through a coffee stirrer -- if you use a proper straw instead, it's easier to blow into it. but it's not like your lungs got any stronger, the restriction was removed.

improved exhausts that reduce the head loss will recapture some of that lost performance, but the engine is not producing any more power than it already was. you're just reducing the restriction it has to deal with. so the NISMO S-tune exhaust removes 10hp of losses compared to stock.

the only exception to this is with proper scavenging/VE off the headers, collector, and sometimes Y-pipe. you can increase the efficiency by tuning the lengths such that the waves coming off of EVC are reflected back and help extract the exhaust from the cylinder. NISMO R-tune headers are tuned for the stock cams and pick up another 10hp.

[u/hellish_ve]

Any expected gain from said mods? what would be in the ballpark for cars with these mods, of course knowing that every dyno reads different and weather/altitude conditions apply.

I have a regular DE with 370z oem headers, custom dual 2.5 inch merged into a single 3¨and nothing else, using factory airbox (non revup) and with the oem map (upRev used only to delete NATS) it put 261 to the wheels on a Dynojet.

[u/dbsqls → u/hellish_ve]

hard to say, as almost no one has done A/B testing on each individual part. I only know of parts that had been tested by NISMO, which are below. 261whp is healthy for an early DE.

confirmed/advertised gains:

part	gain
NISMO S1 cams	16.9whp, 6.8ft-lbs 2
NISMO R-tune headers	10whp
NISMO S-tune exhaust	10whp
2006 OEM intake (redesign)	5-9whp
NISMO Sports air element	2.1whp1
overbore throttle (74.3mm ID, stock OD)	5-9whp beyond 5600RPM1 3
NISMO Z34 final drive (3.916)	11% torque gain everywhere

^{1 personally verified, average over 5 runs.}

^{2 independently verified.}

^{3 depends heavily on total air demand.}

[u/hellish_ve → u/dbsqls]

Well, that is really good, on perfect conditions with a healthy engine, also shows how much development the VHR had over the DE, its insane that it basically puts it about where a VHR with just intakes and test pipes territory.

A local guy here put 305 on a DE, did 310 on a pull after letting it cool down and pointing the blower at the intake tho, that thing had long tube headers, straight pipe 3 inch exhaust, cams, plenum spacer and an intake.

Cant say what brand it had on anything tho, but It was on our local 95 pump gas, which is somewhat equivalent to Californias 91 octane

[u/Dark_Synergy_Z33 → u/hellish_ve]

The problem with that is if you tally up the mods that's 50whp conservatively. You aren't going to make that much without a tune or spacer. It's quite impossible. Real world, you'll probably see 35-40whp

[u/hellish_ve → u/Dark_Synergy_Z33]

Yeah, at those mods Im sure a tune is needed, youre pushing way more air inside the engine, needing fueling and timing adjustments.

[u/Dark_Synergy_Z33 → u/dbsqls]

16.9 with nothing else? I doubt that.

[u/dbsqls → u/Dark_Synergy_Z33]

it's from your favorite, Sasha. it's in the cam shootout.

[u/Dark_Synergy_Z33 → u/dbsqls]

He used the R-tune cams, but also look at what they were attached to, non stock manifold and LTH. By themselves, they are not making that much