BEAMS 3S build up... not NA

[oldcorollas]

i am also not sure... materials and processing has come a long way since the 4000ft/min average speeds of yesteryear (ok, maybe they still apply for V8's )...
F1 and the S2000 are around 5000ft/min average..

also remember that rods are only half the story. if the piston on the end is 300grams.. the rod will go to higher rpm than if it weighs 600grams. sometimes adding "lightness" is better than adding strength.

another part of the story is that it is all about cycles to failure. at 8000rpm, maybe you will have a few hundred thousand cycles, but at 9000, it might be a few thousand... even between one rod and the next from same factory, you can never be sure.

but this is Lindens thread.. so.. back on topic.

[Celica RA45]

ok auto pistons are 11to 1 comp and sit down the bore 1mm same as the manual motor bar the .5 increase in comp ,
they also use a deepish fly cut for clearence with the vvti mostly on the inlet and with a std 33cc combustion chamber most likely 9.5 would be your aim .
with some good strong rods and some special piston services in melb $1350a set
or toda at about 1200 a set with rings and pins but they are only 8.7 to 1 comp
on rod ratio mine works out to be 1.7 ratio and are good till 9000 rpm and weigh 575 grams each or my other ratio they weigh 475grams each with a 15 kilogram crank

[The Real Roadrunner]

but this is Lindens thread.. so.. back on topic.

its actually very much on topic as it gives me a better idea of exactly what to aim for so please let the discussion continue and anything else based around putting a good 3S combo together.

Glenn, what combo's of bore and stroke and different rod ratio's have you played with? if you dont mind sharing what sort of results have you had with them? i looked in your thread but the detail is very brief so i wasn't sure on exactly what you have played with.

cheers
linden

[jeffro ra28]

Hi,
Now i realise this is slightly veering from the topic but it may help You, Linden better choose your rods for practicality. Previously mentioned in this thread something about longer rods improving efficiency at TDC? This is a largly untrue statement. Rod length and angularity have very little real impact with the performance of an engine! Without junking up this thread to much that is all i will say. If you want an explanation i am happy to give one tho!

[The Real Roadrunner]

explain away, you are giving technical info and that is what this thread is about.

i stated the PS's to keep a technical side to the thread and am happy to have argeuments provided they are based on factual info (not i saw a mag article/read a website that said... kind of stuff )

i personally like longrod engines from both a reliability and performance perspective ie: not loading up the thrust side of the piston/bore and also keeping the piston at TDC longer for better homogenous burn.

but if i was to build a stroker then i dont have much of a choice and because i dont have a stupidly big budget i want to use as many off the shelf products as possible and if they need slight modifications then so be it.

cheers
linden

[dave368]

Hi,
If you want an explanation i am happy to give one tho!

Personally I'd be interested in the explaination. I was always of the understanding that a slightly longer rod would decrease piston velocity at TDC and BDC (change of direction) and therefore reduce load on the rod/piston combination. Whilst that may not increase performance itself, it does increase reliability as revs increase beyond the 8500rpm point. I must admit, I prefer the performance of a motor that has its rods safely inside the block, rather than the ones with them hanging out

I'm happy to hear another view though.

[Celica RA45]

TRD make longer rods by 8mm to 146mm so the motor can rev up to 8800 rpm std altezza 3sge has a red line at 7800 rpm with std rods of 138mm long

[Celica RA45]

and max power is at 8600 rpm

[The Real Roadrunner]

Glenn, did the auto have a different redline? i just can't think of any reason as to why they went for steel valves instead of the titanium ones fitted to a manual, also do they run a different cam profile?

cheers
linden

[jeffro ra28]

SOME reasons we give an engine a longer rod.
1. Results in less rod angularity
2. Which Results in a shorter ligther piston
3. Which results in a short skirt and less friction.
4. Results in less skirt side loading

To those unawares i will give an explanation.
Connecting rod angle is greatest when the crankshaft is at 90 degrees rotation.
Now At 90 degrees of crankshaft rotation, a short rod engine has greater rod angularity then does a long rod engine of the same capacity. This results in the piston having to be made taller and heaver because the rod does not reach as far up the piston. And gives the piston more skirt side loading

Longer rods leave the piston dwelling at TDC longer? YES
Does this improve performance? not to a measureable amount.

Its affect is next to nill. At 10 degrees ATDC (around the time when most pressure is present on piston on power stroke) the difference in your piston heights with a substantially longer rod would definantly be no more then .000015mm, in a short stroke motor like the 3sgte anyhow. Seems unbeleivable? Mock up an engine with two different rod lengths and test it for yourself. Now tell me how much longer the piston dwells at TDC? heaps isnt it
Even at 45 degrees crank rotation you would probably see a max of .25mm difference in piston depth between the two different rod lengths.
Those measurements are ballparks, obviously because stroke, rod length etc all change. But you would probably see less difference in distance of piston depth on a 3sgte with different rod lengths. The figures above are very safe to concerns of a 3sgte!

Yes TRD make longer rods, but i can tell you, they didnt do it to get the piston to dwell at TDC longer!

Regards
Jeff

[Celica RA45]

not sure on the different cams but i suppose .5 in the comp; bigger inlets by .5of a mm in titatium and dual vvti also the other differences are bigger buckets on the manual 33mm to the 31in the auto also on the inlet they have 6 cam bearing caps to your 5
but you would have to give me the cam shaft part no and then i could tell you all of my motors are manual and i have 1 fwd motor as well

[oldcorollas]

auto not expected to actually go to redline as much as the manual due to the autos shifting, and thus not as much benefit from the lighter valves?? so just a cost reducing exercise?

edit: re rod legnths...
on that calculator page things...
usign 86mm stroke
138mm rod = 7430 f/min peak
146 = 7393
150 = 7377
160 = 7343

93mm stroke
138= 8095
146= 8051
150= 8031
160= 7986

so.. longer rod does reduce peak piston speed, albeit marginally...

[whatthe?]

OC, I notice the question mark as a qualifier in your post above, but for modified engines (and the applications implied) do you think that those using autos aren't going to be revving the bejesus out of them?

[oldcorollas]

maybe i was reading it wrong (it is late...)... autos come with steel valves from factory, but manuals come with Ti valves? or did i get that ass backwards?

if that is the case.. i was thinking that the auto box is probabyl programmed to not allow the engine to use the last few hundred revs of the engine (to redline).. might be totally wrong tho

[whatthe?]

Once again, application dependant. Those of us who use modified autos have usually dispensed with the niceties associated with them (like pre-defined shift points) in favour of manualised shift converters and bogan shifters