BEAMS 3S build up... not NA

[Mos]

the piston travels lower down the bore therefore proding more torque.

Huh? What do you mean? It will travel down the bore by the same amount regardless of rod length. The only difference is the speed and acceleration curve - the displacement will still be the same - it's fixed by the stroke.

Mos.

[jeffro ra28]

while i do believe there isn't much of a difference, there still is one and if you calc the 8000rpm rotations down to milliseconds the piston does still stay at TDC for longer and travels lower down the bore therefore proding more torque.

Just to be picky. I dare say it would be more close to a division of a nanosecond.

as stated im just a fabricator and no maths genius but i have the ability to think about things in "outside the box" ways.

Likewise. im just a 19 yo fitter machinist that likes to call myself an engine builder

I beleive the gains would be more from the less friction, ligther pistons, and improved revving capabilities more then anything. But then i spose it comes down to the purpose and use of the engine? It certainly would be more reliable and longer lasting with a longer rod. BUT does it need to be revved that much harder to gain the full advantage of a longer rod?

Regards
Jeff

[Mos]

Just to be picky. I dare say it would be more close to a division of a nanosecond.

8000rpm is 20.8333 microseconds per degree of rotation, so you'd be looking at divisions of a millisecond (or multiples of tens of microseconds)(or multiples of ten thousands of nanoseconds).

Mos.

[Joshstix]

Huh? What do you mean? It will travel down the bore by the same amount regardless of rod length. The only difference is the speed and acceleration curve - the displacement will still be the same - it's fixed by the stroke.

Mos.

I assume Linden missed an S in that comment and it was meant to say the piston will travel slower down the bore.

[jeffro ra28]

8000rpm is 20.8333 microseconds per degree of rotation, so you'd be looking at divisions of a millisecond (or multiples of tens of microseconds)(or multiples of ten thousands of nanoseconds).

Mos.

My guessing hasnt been to good id better stop.
So would it be correct to say that with a 146mm rod it would take 20.8333 mircoseconds more time for the piston to travel to the same point in the bore at 10 degrees atdc then with the 138mm rod?

[Mos]

I assume Linden missed an S in that comment and it was meant to say the piston will travel slower down the bore.

But that's not entirely accurate either. The only difference will be the velocity and acceleration curve. They can't travel any slower on average. Lower peak velocities with longer rods just means it has to accelerate more in a different portion of the stroke to be able to make up the length of the stroke in the same time.
I'd like to run some calcs for piston acceleration, but can't do that now. I'd be interested to see the peak acceleration between different length of rod.
(There's more I wanted to add in response but don't have the time now).
Mos.

[Mos]

My guessing hasnt been to good id better stop.
So would it be correct to say that with a longer rod it would take 20.8333 mircoseconds more time for the piston to travel to the same point in the bore at 10 degrees atdc then with the shorter rod?

20.8333uS per degree, so 10 degrees is 208.333uS, or 0.2mS.
This isn't a guessing game

Mos.

[oldcorollas]

Mos, this page does both velocity and acceleration
http://www.andersonperformance.net/piston22.xls

[The Real Roadrunner]

I assume Linden missed an S in that comment and it was meant to say the piston will travel slower down the bore.

yes i missed the S in front of the "lower" ie it will take more time to get the same distance down the bore till the 90deg atdc therefore more of the burn will be completed by this stage,
and yes i understand it won't be by much but it's still something.

cheers
linden

[Celica RA45]

if i have 146mm rod with a 48mm big end and i machine it down to 45mm bigend wont the rod be longer to accomodate the 1.5mm taken off the crank

[Joshstix]

The effective rod length is the distance between the centres. Unless the crank is offset ground to change the stroke the change in rod length doesn't do anything really.

[oldcorollas]

acceleration of piston.
(edit: shit.. thats 4000rpm.. stupid V8 based programs )

86mm stroke, 138mm rod, 4000rpm (8000rpm)
TDC = 3843m/s/s, (15372)
BDC= 2062m/s/s, (8250)

86mm stroke, 146mm rod
TDC = 3793m/s/s, (15172)
BDC= 2086m/s/s, (8345)

86mm stroke, 160mm rod
TDC = 3717m/s/s, (14870)
BDC= 2143m/s/s, (8572)

max accel is at TDC and BDC

so... lengthening rod decreases acceleration at top dead centre.. which is good cos rod is in tension.
lengthening rod increases aceleration at bottom dead centre.. but this is ok cos the accel is just over half that of TDC, and is in compression, so much less of a worry.....


average piston speed is same, as it has to go same distance in same time, but the acceleration curve is different, with less accel at top of bore, and more accel at bottom of bore (but less actual accel at bottom of bore)

HTH

[Wildsupra]

this better not be going into a jza80!!!! or you have stolen my idea, if it is i'l let it slide this time round i guess

Looking forward to the outcome, im currently installing a beams 3s into my ex g.f's RA28 celica, only N/A so not as exciting as yours, but should go sweet in the Celica even in stock ish form

Matty

[JustenGT8]

I think a few Japs have beat you to that idea Matty, not to mention Saffo over your way

BEAMs RA28 will be sweet.

What's your donor car Linden?

[Wildsupra]

I think a few Japs have beat you to that idea Matty, not to mention Saffo over your way

BEAMs RA28 will be sweet.

What's your donor car Linden?

Japs dont count

Who is saffo?? you say he is over my way??