How to build an NA engine...

[Wedged'86]

I fully understand what you guys are saying. they need to be all done to have a decent effect. Don't worry. All i was saying is that it doesn't have to all be done in one hit does it? As long as it's all gonna get done.

Having said that it's probably better to do what i do and collect bits. Untill you look in your garage and do a stocktake and realise that you've completed the puzzle and then, like you said, do it all at one time.

[old_school_jap1]

300 ft/sec has been used as an optimum figure in pure race engines for many years. Production based race engines have compromised port designs and a theoretical 300 ft/sec may not be optimum due to other factors.

what does this roughly equate to in revs????

[oldcorollas]

unless you have one specific component that is bluntly inadequate because of some emissions or manufacturing process etc. to chase one 'bottle neck' after the other isnt rational, nor is it paying attention to the functioning system.

the only way id agree with your strategy stu, is if one were to take a part that was wholly inadequte for the engines design (as stated above) and replace it with the part the engine 'should have'. not to overstep it, and 'upgrade' that part to a higher level of function, as that can be just as useless as the underperforming part. i think mos' engine is a good example. its all 'just right'

i know im taking the hard line, but im trying to make a point

thast the point i was tryin to make

it's not a good thing to chase ones tail around in circles.. but many people spend thousands of dollars doing just that...

Old school: it's not to do with revs.. it's to do with port size and velocity... low revs, small engine.. small ports = 300ft/s
big engine big revs, big ports = 300ft/sec...

[Celica RA45]

i reckon i would have spent about 10k on development not 3 dollars like ed said ,but i started with a motor that TRD did a lot of work to and improved from there as well

[old_school_jap1]

i think $3M = $3 millon, lol.

can anyone answer my 1st question (page 1)????

[oldcorollas]

yes they will also experience a choke point, btu where the choke point is, is more difficult to determine.
this is because the air in plenum is pressurised, but there is going to be a balance between pressure and velocity in the runners....
higher velocity with lower pressure? lower velocity but maintaining higher pressure?

at the intake to the turbo, there is choke similar to NA... in that above a certain velocity, a restrictor will effectively cap the amount of air it can draw in (moving turbo closr to surge etc)...

[Nim]

piston speed is limited by two things, metal and aerodynamics. the generally agreed limit of instantaneous max velocity of a piston with current materials is about 5,000 ft/min.

This, however, can be represented in RPM. What's this in RPM with an 86mm stroke? Or even better, what's the calculation to figure it out?

I thought I had it figured out, but then realized that I was using constant velocity, and a piston doesn't have constant velocity. It accelerates smoothly up to top speed, then slows down smoothly at the top of the chamber, then speeds back up to top speed at half way, then slows back down again till BDC, repeat. And I have no idea how to calculate that kind of curve. I'm sure it has something to do with PI though. Bloody PI.

[rms]

Or even better, what's the calculation to figure it out?

And I have no idea how to calculate that kind of curve. I'm sure it has something to do with PI though. Bloody PI.

I dont know a simple way to calculate max piston velocity. It occurs somewhere around 90 - 110 deg ATDC depending on stroke and rod length.

Work out piston travel for every 1 deg crank rotation and the time of 1 deg rotation, taking into account con rod angularity change, this will show your max velocity and where it is in degrees.
You use trigonometry tables to do this.
You can use Excel to plot a nice sine curve.

Could never understand trig tables at school, found later they are used in engine, suspension, stress analysis, vehicle dynamics etc. Pretty handy numbers !

[Ben Wilson]

what does this roughly equate to in revs????

You really need to sit down and do some maths to work out the revs, it's dependant on the cylinder capacity..

For valve sizes, I use this formula (which isn't mine):

RPM = 23.275 * gas velocity * (valve diameter mm *.9)^2 / cc per cylinder

(halve the cc per cylinder for multi valve motors)

Gas velocity is in m/s (92m/s-300f/s) and the 0.9*valve diameter is to take into account the unavoidable restrictions around the valve seat.

[Andrew162]

great thread Ed.
page bookmarked.

[Nim]

I dont know a simple way to calculate max piston velocity. It occurs somewhere around 90 - 110 deg ATDC depending on stroke and rod length.

Work out piston travel for every 1 deg crank rotation and the time of 1 deg rotation, taking into account con rod angularity change, this will show your max velocity and where it is in degrees.
You use trigonometry tables to do this.
You can use Excel to plot a nice sine curve.

Could never understand trig tables at school, found later they are used in engine, suspension, stress analysis, vehicle dynamics etc. Pretty handy numbers !

BLAH! That sounds more complex than I can do. I'll have to ask my girlfriend.

I'm going to use the 2JZ as an example.
2JZ Conrod Length is 26.2mm right? Which would make the radius from the center of the crank to the middle of the conrod connection 16.8mm.

[ed]

not sure wtf those numbers are nim...

but anyway - save your head, go here for the maths

http://www.slowgt.com/Calc2.htm#PistSpeed

oh, and i miss wrote my original stetrment in the first post... now edited. the 5000fps (26MPS) is MEAN velocity limit not instantaneous max velocity. 2/3 of the intantaneous max velocity will give you your mean more or less

cheers
ed

[takai]

Cheers ed, ive been looking for that page for ages.

+rep if i could.....

[gianttomato]

http://www.slowgt.com/Calc2.htm#PistSpeed

Had that site years ago and lost it in the HD crash of 2005. Thanks again.

[Nim]

not sure wtf those numbers are nim...

but anyway - save your head, go here for the maths

http://www.slowgt.com/Calc2.htm#PistSpeed

oh, and i miss wrote my original stetrment in the first post... now edited. the 5000fps (26MPS) is MEAN velocity limit not instantaneous max velocity. 2/3 of the intantaneous max velocity will give you your mean more or less

cheers
ed

Aww, but I JUST figured out the maths for it! Damn.

And yeah I just noticed that my figures were way off. I got it from some site. Am I right in assuming it's actually 142mm for the conrod?