How to build an NA engine...

[mrshin]

Nim: I'd love to check out some of those 26mm conrods! I might go see what my old model plane engine has in it...

[Nim]

Okay, so my test model of a 2JZ-GTE reaches maximum piston velocity at 74 degrees from TDC at a velocity of 32mps @ 6900rpm... which is actually 6,392 ft/min...??

[ed]

take 2/3 of that as the mean

[Nim]

Cool, so that's 4,261ft/min, or 21.646 mps.

Okay, all makes sense now.

EDIT: Mwahahah, the mighty B18C2 has a mean piston velocity of 5,092ft/min! The B18C7 in the Type R has a mean piston velocity of 5343 ft/min!

[ed]

dont forget, 5000ft/min is with high level lightweight componentry... ot stock rods and pistons etc

[Nim]

dont forget, 5000ft/min is with high level lightweight componentry... ot stock rods and pistons etc

I didn't think you thought so highly of Honda engines Ed.

[The Real Roadrunner]

iwhen 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.

its funny you mention all this, cause i seem to remember a certain 7m that didnt make much more power than stock

but then again you could be forgiven for starting with a poo motor from the beginning kinda like pissing into the wind.


cheers
linden

ps jjks

[RObErT_RaTh]

its funny you mention all this, cause i seem to remember a certain 7m that didnt make much more power than stock

but then again you could be forgiven for starting with a poo motor from the beginning kinda like pissing into the wind.

I'm about to begin this 'pissing into the wind' experience, should be interesting

Plus just cos it doesn't make big power doesn't mean it isn't a great engine, it sounds awesome, is solid as a rock, and revs hard with smooth acceleration! (I think )

[haison]

Me too.. decided to ditch the turbo stuff. I'm a perfectionist and I can see that costing a LOT of money with building a turbo engine..

[RObErT_RaTh]

Me too.. decided to ditch the turbo stuff. I'm a perfectionist and I can see that costing a LOT of money with building a turbo engine..

It'll cost money with either engine

(But you know that already )

[ed]

Plus just cos it doesn't make big power doesn't mean it isn't a great engine, it sounds awesome, is solid as a rock, and revs hard with smooth acceleration!

yep... it doesnt make numbers (not sure why!) but its impressive to drive. that said, it was my first attempt at a 'performance' build up (on a centrelink budget) as opposed to the simple 'put an engine back together' builds i had done in the past. im the first to admit i learnt a LOT in building it. hence the approach ive subsequently taken with the 1uz

i drove it again a few months ago, and shit me its a good thring to squeeze the pedal down on. incredibly responsive and solid. came away smiling even for 115rwkw or whatever it makes its quick

[brett_celicacoupe]

You plan to get around the frictional losses and extra mass how?

rev it out to 18,000+ rpm

the smaller you make the stroke the higher you can rev them and consequently, the more air/fuel you can burn in the engine. increase the number of cylinders for the same overall capacity and youll have to lower the bore/stroke.

these are probably all equivelent 'safe' piston speeds. if youve ever seen a honda CBR250 engine youll know how high they rev. 20000rpm is printed on the tacho. pistons, valves and rods are tiny.

5L V8 @ 6000rpm @100% VE = 2.5*6000 = 15000L/min
5L V16 @ 12000rpm @100% VE = 2.5*12000 = 30000l/min
5L V24 @ 18000rpm @100% VE = 2.5*18000 = 45000l/min

i couldnt be arsed converting to equivelent power output but by lowering the number of cylinders, the safe piston speed has been raised WRT engine rpm. that said there will be a increased amount of friction and inertia which will sap some power. i dont believe this will offset the higher rpm gains to give an overall power drop.

[Nim]

Brett, your model is quite achievable just based on piston speeds. Obviously there are more considerations, such as the clutch, flywheel, crank etc, but I'm gonna ignore them for the moment 'cuz I can.

I made up some models around a 5.0L engine with different cylinders and engine speeds. All use a 150mm conrod and a bore of 86mm (to keep the pistons the same size). The measurement of mps is taken from 73 degrees from TDC which is about the maximum velocity of the pistons.

5018cc 108mm stroke V8 @6000rpm = 36.08mps - 7,103 ft/min
5018cc 54mm stroke V16 @12000rpm = 34.188mps - 6,728 ft/min
5018cc 36mm stroke V24 @18000rpm = 33.59mps - 6,612 ft/min

Granted you could bore the V8 out a bit and reduce it's stroke, but then you'd be making the pistons heavier, so while the velocity would stay the same, the stress would not.

All of those also come in under the B18C5's max piston speed of 40.71mps - 8,015 ft/min. Of course, it has a bore of 81mm, so the piston will be a bit lighter.

[andylaurel]

This post made for a very interesting read.
Are there charts/tables available that spell out what intake/exhaust primary lengths and volumes for different displacement engines/RPM ranges?

[oldcorollas]

piston speed is a physical limit that is due to the connecting rod only. (and also piston mass and rod geometry etc).

hoe does piston acceleration change wqith the above two models? it is the piston acceleration that should be the limiting factor, combined with piston/rod mass, as that is the actual force through the rods.

for these high rpm, one main issue is valve train keeping up... for most engines, valve train is a significant limiting factor.

also.. rod and crank bearing speed. at some point, your nicely layer of oil on which the parts move is going to start shearing and getting all messy..

andy, for exhaust charst, look on bills page . doesn't give diameter tho. but is a good quick reference.