Who has High compression pistons?

[Kitika]

G'day I'm after some high compression pistons for a 1.3.
First question is there any difference between the 1324 and the 1298cc pistons? We are planning on using the 1324 crank with its accompanying rods in the 1298 block with the 1324's head as the 1324 block is abit suspect (I think that'll work out???).
I've seen on sammypro.com they sell 10.2 pistons (what is the stock compression supposed to be compared to that?) but is there any high comp pistons available in oz or from a different model that'll fit with ease? The pistons from sammy pro still retain the valve clearance notches so it stays non interference which is also a plus.

[built4thrashing]

From my experiance this is not a good idea.

I did a similar rebuild and used the 1298 pistons(flat tops) with the longer throw 1324 crank. Now it ran ok but i could not stop it from pinging even with 98 octane fuel and with timing set at 2 deg's. Tried using a different profile cam and no difference. If you are going to go straight gas or EFi it might be better but not recomended if staying carby.


1324 pistons are slightly dished
1324 crank has 1.5mm longer throw
1298 pistons are flat tops
1298 crank is 1.5mm shorter in throw.
conrods are the same
bearings and oil rings are the same
heads are the same.
stock cams are the same but i originally used a re-ground cam with more top end.


B4T

[Kitika]

My 1324 and 1298 pistons look the same and are both flat top? What was the final compression of your motor? It will be running gsx 750 carbs and a billet ground mid range cam.

[built4thrashing]

on my compression tester i came up with 210-230 in each cly. FSM states factory compression to be 180 after 7 cranks with oiled rings.

Just make sure you port , polish and CC your heads other wise ya gonna have probs with detonation.


B4T

[Kitika]

Was that before or after it had been broken in? My standard rebuilt 1298cc had just over 200psi per cyl before it was broken in fully. I have all the bits done at the machinists shop awaiting a quote and what he reckons is the best option.

[built4thrashing]

been driving about on this motor for the last 6 months and it has this compression now. Never checked it when it was freshly rebuilt but after 6 months of stuffing about with different fuels, carbys and timing it still has this compression.


B4T

[Kitika]

What type of compression are people running with shaved heads? And can they get it to run on 98 octane?
Are you in northern aus B4T? As in extra heat may have been contributing to the pinging? I'm thinking of just sticking with the standard compression for simplicity as it'll have plenty more power with the gsx carbs anyways.

[built4thrashing]

Im down here in melb so the heat doesnt exist in winter. Stick with stock compression but just ballance the bottom end as best you can and do some head work...port & pollish and maybe a bigger cam. Get some decent extractors and a high flow exhaust. And if it still aint enough then slap a small supercharger on it.


Quad carbs and a supercharger..... hmmmmm....that be a sweet setup.

B4T

[Kitika]

It'll have 4-1 extractors, high flow exhaust, a brand new billet midrange cam with port matched heads with the 38mm gsx carbs so I think it'll be pretty close to as good as it's gunna get for a 1.3. Would probably take it up a notch having higher compression but as it's gunna be a weekend car it probably won't need it for simplicities sake. See how I go its at the machine shop i'm just waiting for a call back about the pistons.

Dunno about forced induction and CV carbs would probably be better off with late model quad throttle bodies if you had the gear to tune them

[31zook]

i have shaved block, shaved head, high compression pistons, high lift cams, and $1100 worth of carby tuning timing and jetting recepts. This all is in a 1324cc G13A.... worth it??? not sure, but she can smoke first and 2nd on 205

[Kitika]

So what is your compression reading after all that? Do you have a torque or mid range cam?

[built4thrashing]

i have shaved block, shaved head, high compression pistons, high lift cams, and $1100 worth of carby tuning timing and jetting recepts. This all is in a 1324cc G13A.... worth it??? not sure, but she can smoke first and 2nd on 205

Is that on 205 width tyres? As mine with a stock motor will smoke the tyres in 1st with 31's.

[31zook]

it cost me $3500 to build, and i would have just bought a baleno motor if i got the chance again.... dunno what my compression is, and i have all my power between 1000rpm and 4000rpm.