6A12 RPM? More mods...

[spetz]

So, just been talking to the engine builder and going to take a different path to what I was plannig

Initially never planned to do cams, now I might be

But, the problem is how many rpm can the 6A12 handle?

The problem I am facing is bolt kit for the rods. The pistons will be cryoed, and teflon coated, conrods will be shotpeened, polished and cryoed. From talking to the engine builder this will increase strength by roughly 30%
The engine will be assembled and cc'd and heads modified to get around 10.8:1 compression ratio and all other specs taken from it to make some custom cams to work on the engine with the mods it will have

It seems with a ARP bolt kit, and those mods to the internals with valve springs and cams etc the engine can go to 9000-9500rpm
But are there ARP bolt kits available for this engine??

[Bennoz]

Should be, bolts are generic in sizes. Could try my tuner at Croyon Racing Developments on 02 9648 4264. He's always got plenty in stock. Just need to provide him the old nuts & bolts to match them up.

[droidy]

What sort of pistons are you usind spetz??

[SG]

would changing the lower and upper cams to higher torque points mean in first gear u'll be up to like 4.5/5k before u can get into second? imagine that in slow traffic

[Bennoz]

Voiced my opinion on the needlessness of going higher rpm on cams grinds for more power before, but I certainly dont mind being proved wrong

[spetz]

The pistons are stock Droidy but with polishing, shotpeening, crack testing, and cryogenically treating the rods + molybednum coating and cryo treating the pistons they usually get around 30% more strength

Not a huge deal but with some higher lift cams those 1000 or so extra rpm will come in handy

MIVEC probably wont kick in until about 6800rpm or so but then rev out to 9000-9500rpm or so

Now... the gearbox

[droidy]

sweet dude- with the "right" gearbox, gonna be fast

[spetz]

haha you know what the right gearbox is

The problem even that gearbox was not designed for 9500rpm shifts
But I am sure tough synchro's are easy to find for it

[MADFTO]

Right gearbox is gonna be tough, until you know what your torque curves will be. (of course you should be planning what your cam changes will do to your torque curve)

My gear box mating knowledge isn't that great so I'm throwing ideas out here to get my knowledge fixed up (I haven't googled this yet so I could be corrected doing when doing my research).


Higher RPM cars need closer ratio boxes, because of the multiplier effect. (The revs will drop faster at higher revs essentially)

This shortening can be offset by (I always get this wrong) decreasing the final drive ratio to get a higher top speed but there is a limit to this.

[spetz]

I am not playing with final drive ratio because from 1st to 2nd it will still fall out of the MIVEC range

Regardless all the mods done to the car are just increasing top end power, so short ratio is the way to go

I hope my peak torque will be around 7000-7500rpm


On a downside I am unsure if pistons can/will be cryo'd
Checking for custom forged 11.5:1 but might be out of price range

[Nacho]

How much are those pistons a pop?

[Storm]

Here they are in the states for $600 US but I dont know what the shipping or exchange rate is.

http://www.sfxperformance.com/parts/TUSM6A12.htm

Arashi

[spetz]

Yeah but the compression ratio is 8.5:1 as you can see
Which is really only suited for turbo spec

[SG]

on a different note, i had a look around the stx performance site and found some underdrive pulleys...
http://www.sfxperformance.com/parts/UNO020910102.htm

anyone know if they'll fit? seems to fit the 3000gt dohc motor from '92 to '96

[spetz]

I doubt they would fit

I heard this is just a myth though that underdriving stuff works

ie. With the alternator, sure it is spinning at a lower speed, but it needs more effort to spin as the current draw from it is higher if that makes sense

[SG]

it does work... having a lighter and smaller gear means the motor has slightly less load in order to turn it, but as you said all the accessories get less power, power steering, air con, alternator, etc. dont know what happens with the alternator...though your probly right.

if you google u see heaps of people's response about how much faster the car revs up after fitting it and that the top end doesnt wanna die off quite as easy. sounds like a good mod if it fits.

[SG]

ah well, confirmed by Mitsiman that it doesn't fit
i was probly wishin a bit much there...

[Storm]

Spetz, why are you needing forged pistons if you aren't going down the forced induction route? Surely standard ones will hold up to about 280 BHP?

Or do you have a secret mod you aint letting on about

[spetz]

No everything is in the open besides the gearbox combo simply because that isn't a definite yet (if it will fit) and I don't wanna be one of those "I am getting this done, and that done" and then not actually do it.

The forged internals aren't so much for hp, or boost, but to make that kind of power I would need plenty of revs. More than the stock internals can cope with I would say
Basically, with cams, if peak power will be around 8800rpm, then the engine must be able to safely rev to that revrange

Anyway I don't know what is going on
At this stage there are too many issues:
Can't find rod bolts
Might not be able to cryo the pistons
Not enough money for forgies

I'll probably still cryo the rods, shotpeen them, and cryo the crank, but just for reliabilities sake. Without strengthening every single recorporating part inside the engine, I am not game enough to raise the rev limiter

Regardless though, the engine is dummy assembled, to check CR, clearances and a whole list of info needed so that I can send it off to camshaft company, alone with dyno figures after it is put together, and they will tell me what, if any cams will work
From then on, if I can get say at least 15-20kw more power from cams without raising rev limiter, I'll take my stock ones out and get some custom billet cams made up

Regardless none of this is definite yet