How to build an NA engine...

[ed]

i get enough emails and PM about this topic so i figured id bash out some principles of engine building that are both general in principle, and also specifically applicable to NA building...

firstly - engines are air pumps, pure and simple. air in, combustion, mechanical pump, air out. full stop.

ANYTHING that can improve the volume of air that gets in, through, and out (per unit of time) will make more power. be that with bigger capacity blocks, increased RPM, through increased density of air from a turbo, through harmoninc resonance tuning, or whatever... CFM = POWER

when it comes to NA engines, there is absolutely no room for the much heralded 'bolt on' modification... one item in an engine system just wont significantly modify the airflow of an engine to increase CFM in a way that will effect power in any appreciable manner. cams wont work without head work. head work wont work without rpm, rpm wont work without tuned manifold etc etc....

why? then engine is a SYSTEM, and the WHOLE engine must mork together as a tuned unit to move a given CFM. things need to be considered from the very start. how much power do you want to make? how much capacity do you have to work with. how many rpm are required to get the CFM through the cyls? how big do the ports have to be to sustain this CFM flow rate? how big does my throttle body need to be to sustain this flow rate. etc etc. forget the concept of a bottleneck.

NOT the other way around - ie "my ports can now flow 500CFM @ 28" and therefore my engine will make X power" bullshit. same goes for super bolt on intake pipes and expensive air filters. not one thing *makes* power - that mindset is just crap, and is designed to get you to buy stuff you dont need. i dont care who sells it or supports it. an engine from a manufacturer REALLY is about as good as it will get. give or take a bit of tweaking and tuning, youre stuck with what they built for you - and if youre not prepared to dive in and do it ALL from the very beginning, dont waste your money.

now, when deciding where to start planning your engine, there are some FUNDAMENTAL limits you need to work with. metal is not perfect. it fatigues and breaks. air is not perfect. it has friction and does like going too fast. fuel is not perfect. it likes to explode at the wrong time if treated badly.

piston speed is limited by two things, metal and aerodynamics. the generally agreed limit of mean piston speed of a piston with current materials is about 5,000 ft/min (which is about 26MPS). this can also be expressed in terms of the aerodynamic limit, with a figure of around 27MPS. the two basically tie in together nicely. some people think this is rubbish, and rev WAY higher, but the laws of exp diminishing returns and significantly decreased engine longevity will bite them in the arse. dont let unsustainable numbers fool you into believing in a design or product - use common sense.

rod stroke ratio can impact the velocity and acceleration profile of the piston, and should be taken into consideration. the fictional losses of a bad rod/stroke ratio are similarly important, especially at bad ratios like 1:1.6 and below. check out the following for specifics on rod:stroke: http://www.v-eight.com/tech_forum/viewtopic.php?t=110

air does not like travelling too fast - it tends to hit a point called a sonic choke. beyond this point is like pusing shit up hill, pointless and painful. head ports and valve sizes need to be determined specifically by how much CFM you expect your cyl volume and rpm to pull each cycle. the velocity at the throat of the port behind the valve face should not exceed mach 0.5. equally, the port velocity in the manifold and upper head port should be designed to sit around 300ft/s at peak operating conditions. see here for port velocity discussion: http://www.v-eight.com/tech_forum/viewtopic.php?t=148

note - the air in the intake is not flowing in a linear, continuous manner. its travelling like a sound wave due to the opening and closing of the valves. as such, the intake system can be tuned like an instrument to 'resonate' at a particular frequency... ie at a particular RPM. this tuned resonance can be used to increase the cyl filling during the open period of the valve as the air will be denser and will like to fill the cyl completely during a single cycle. this is what is referred to as the 'power band'. this power band depends on the cam and valve timing, the rpm, the intake temp, velocity, port length and dia, intake port entrance (bellmouth etc) port taper etc etc etc. each of these individual things needs to be optimised to work togther. the exhaust is basically the same as the intake, and follows the same priciples of harmonic optimisation. see here for a fuller discussion: https://dspace.lib.cranfield.ac.uk/b...7802-final.doc

throttle bodies do not define an engine, they just determine whats at the end of the intake runners... plenum or atmosphere (ie infinte plenum)

plenums are harmonic dampers, and also serve to feed air in equal volumes to each cyl. the volume required vaires depending on layout, but x3 the swept volume of the engine is a starting point. that said, consider that volume between you throttle body and the valve... goodbye throttel response - hence the ITB assembly... (plus they sound orsum). NA applications only? nope - your honour, the rb26dett

size of throttle is determined by flow. again, look for the magic 300ft/s regardless of where in teh system the throttle body is positioned.

air pummping losses occur EVERYWHERE. duct terminations, pipe transitions, curves, valves and port pockets, injector bosses etc. optimising the shapes of these adds up significantly. how do you plan to bring your runner into the plenum? bellmouth? how wide? what radius? internal taper? how will that effect your harmonic length and tuning?

do you begin to see why people get very frustrated when they spend big money on a single upgraded item for their NA engine, and it just doesnt seem to work? even multiple items, done over time dont seem to make a big impact over stock? then they quit NA and go turbo or SC as its cheaper and requires less thinking?

if you plan on building an NA engine, start with a CLEAN piece of paper. you are not modifying an engine. you are BUILDING your own engine, just within the limits of some solid things determined by what block and heads you decide to start with.

your engine will require COMPLETE and dedicated design to fulfill ONE goal and one goal only. you need to determine what this is and stick to it. build to this ONE end point and make EVERYTHING in the system compatible with that point. being sloppy will not yield anything, and will let the design down.

YES - forced induction engines follow these exact same priciples, but the effect of reaching for the bleed valve and upping the boost simply outweighs the fine nuances and cumulative tuning effects of these outlined parameters. that said, the 'properly done' FI engine is actually HARDER to design as integration of the turbo pressure map into the above design get very headache prone, very quickly.

stop, think, read, design, recalculate, rethink....

[old_school_jap1]

ultra schweet man. never heard bout that sonic choke effect before. am i right in thinkin forced induction motors will experience it at the same point????

[ed]

am i right in thinkin forced induction motors will experience it at the same point????

short answer - i dont know

long answer - http://www.v-eight.com/tech_forum/viewtopic.php?t=268

[Billzilla]

Excellent post.

[Mos]

when it comes to NA engines, there is absolutely no room for the much heralded 'bolt on' modification... one item in an engine system just wont significantly modify the airflow of an engine to increase CFM in a way that will effect power in any appreciable manner. cams wont work without head work. head work wont work without rpm, rpm wont work without tuned manifold etc etc....

Can I bolt your entire intake manifold on (my injectors) to see what difference it makes? Should only take half hr or so to retune for peak power
(And you'll have a more effective base map too )

Mos.

[Jorrs]

sweet post mate..
im gonna print it out.

[MWP]

when it comes to NA engines, there is absolutely no room for the much heralded 'bolt on' modification...

Didnt think i would hear such a rather silly comment from you.

When going to the extremes like you are, sure that statement is correct.
For the avg joe however, bolting on a set of "stage 2 cams" would make gains that he is probably quite happy with.
Same goes with extractors, ECU "chipping", CAI's, exst work, etc, etc.

We are not all chasing that insane uber expensive NA engine you are.

[oldcorollas]

what he means is.. depending on the components that are there, a single change, or a couple of changes, will nto give a good effect or much effect..

for example, a short 4-1 exhaust manifold and short ITB's, with a small duration cam...

sure it might be better than stock.. but you are wasting effort to do those things and not match them..

it's like taking half a trumpet and half a saxaphone and trying to make it resonate properly... to make a muscial instrument (air instrument.. in this case, car engine) work properly at the right frequencies, each part has to be the right size, shape and length

[gianttomato]

But I got 20 more rwkW when I bolted the cold air intake to my auto CA18DE S13?

Riddle me this Dr Ed......

[ed]

Didnt think i would hear such a rather silly comment from you....uber expensive NA engine...

i do want to clarify - im not talking about twaeks and fiddling to improve performance ~10%. im talking about building an NA engine that makes numbers

for the money and effort people tend to invest in single bolt on upgrades in search of a performing NA engine, they are generally disappointed, and wonder why the gains dont come in leaps and bounds. these parts are generally not cheap, and ive spoken with quite a number of people whove spent quite a chunk of cash, and are left wondering. find me someone who has spent considerable money on 'stage 2 cams' and all the associated labour and costs (new timing belt, reshimming, assembly lube and new engine oil etc) who 6 months later isnt a bit *meh* about the whole thing... esp when they see their mates turbo dyno graphs hitting the top of the page with a lot less

anything significant and markedly effective for an NA engine IS uber expensive or time consuming (or both)

[ed]

Can I bolt your entire intake manifold on (my injectors) to see what difference it makes? Should only take half hr or so to retune for peak power
(And you'll have a more effective base map too )

Mos.

yes, but ill make you use my injectors

[gianttomato]

when it comes to NA engines, there is absolutely no room for the much heralded 'bolt on' modification....

Interesting. The ITB's and extractors I bolted on to my 2JZ fattened up the torque, gave me plenty more midrange and bumped up peak power (both in quantity and also put it 1100 rpm further up the rev range.

General extreme comments can be a bit tricky to defend. Also things like 5000 ft/min and 300 ft/sec are guides, albeit good guides.

Other things to consider are frictional losses ( a 5 litre V16 just can't quite make the same power as a 5 litre V8) and those of momentum/reciprocating mass (Stu, you know the right engineering lingo) - clearly a donk with osmium conrods and 50 kilo crank will blow harder than a fag at a glory hole.

But otherwise, I like the post. Brave, given the kids nowadays just want a big fuck off turbo.

[RObErT_RaTh]

A good read guaranteed

I somehow feel like I pushed you to this with my PM's, sorry

[Ben Wilson]

From a general package point of veiw, Ed is 100% right. On the other hand, a lot of factory motors (particularly older ones), have one or two parts which really restrict* them. These motors can benefit from 'bolt ons' like inlet and exhaust.

* Often put in place for noise or emissions purposes.

[ed]

Interesting. The ITB's and extractors I bolted on to my 2JZ fattened up the torque, gave me plenty more midrange and bumped up peak power (both in quantity and also put it 1100 rpm further up the rev range.

much like erols itbs/manifold and extractors bolted onto his stock 1uz block/heads and cams

and dave, how much did your itbs/manifold/extractors/motec cost? much the same as erols 50mm slides and manifold, cosworth extractors, and his m800....

you realise the significance that having atleast some of the system tuned to one operating parameter, but its dumbed down by the stock head tuning character. if youd spent that money, and didnt have plans to integrate the ported head and cams, would you be happy with your $:hp ratio?

now... tell me exactly how much power those same itbs and extarctors SHOULD make once you sort the head and cams to work together in the system...

erol went from 320hp to 530 hp for example with the exact same intake and exhaust components on each occasion, but sorted out the bits bolted between them