Ok well ive been asking around and people tell me that if i throw a 086 Head into a 2.4l that it would give me a compresion ratio of aprox 11:1.. the 2.4l comes originaly with 9.0:1 Compresion so that means that the head would raise it 2.0 ... What compression are the pistons on the 2.3? are the pistons 8:1 ? Because the compression of a 2.3l is 10:1 ... or is it that maybe i didnt get right info ? how much compression does a 086 head increase ? im thinking getting 10.5:1 pistons with 086 what would that bring my compression to ?

what you have to understand is that CC modify the compression. Displacement also play a role in it.

the 2.4 comes with 9.5:1 and 9.7:1 compression. not 9.0:1.

The 2.4 head have a combustion chamber of 61cc while the 2.3 head have a combustion chamber of 48cc.

The 2.4 have "flat top" pistons that have a DISH of 0.6CC witch gives 9.7:1 compression and piston with a DISH of 2.25cc witch give 9.5:1 compression.

The 2.3 Ho pistons have a DISH of 7.3cc to give 10:1 compression and the Lo pistons have a DISH of 11.5cc to give a 9.5:1 compression.

Now, by using the 2.3 head(48cc) with a 2.4 block/pistons combo, the compression goes up to 11.74:1 for the pistons with a 0.6cc dish and 11.4:1 for the 2.25cc dish pistons.

If you use a set of pistons that would give you 10.5:1 compression on a 2.4 with a 2.4 head and stock bore, you would need a 5.15cc DOME. Take that 5.15cc DOME and use it with the 2.3 head and you get 12.98:1 compression.

Don't forget, if you oversize your cylinder, the compression will be higher.



Gilles
2.3 Ho

Ok Great 12.98:1 WOW way to much ... I understood everything except for one thing.

" If you use a set of pistons that would give you 10.5:1 compression on a 2.4 with a 2.4 head and stock bore, you would need a 5.15cc DOME. """"Take that 5.15cc DOME and use it with the 2.3 head and you get 12.98:1 compression."""""

just so i can cross reference this what would get me 11:1 with the 2.3l head ? i tryed to use the calculator from Ross Pistons but it didnt work out to good. Basically im trying to get 11:1 with 2.3 head .. over bore the cylinders a bit. what size pistons would i have to order ? im sorry for my childish question but i dont want to make a mistake


Thanks alot you are Very Very help full Gilles i appriciate it and i know other people do as well.

To get 11:1 compression with the 2.4 block and 2.3 head, you need a :

Stock bore - 4.7cc DISH
0.010 over - 5.0cc DISH
0.020 over - 5.3cc DISH
0.030 over - 5.6cc DISH
0.040 over - 5.9cc DISH

I'd go with 0.030 over. It gives you a bit more displacement and you can still bore the cylinder to .040 if something happens. The machine shop can tell you tough. Ask them to mesure the bore of your cylinder and see if they are oval or if they are still round. If they are not oval (less than 0.001 difference), I would just put stock size back in with new rings.

If you want to calculate, use those number :

Bore (inches) 3.54 (That's stock size)
Stroke (inches) 3.7
Head (cc's) 48cc (2.3) 61cc (2.4)
Gasket Thickness (inches) 0.043
Deck Height (Put .0001 for zero deck) (inches) 0.0001
Dish or Valve Pocket [-] or Dome [+] (cc's) -0.6 (stock 99+ pistons)
Number of Cylinders 4

Don't forget that when you have a DISH, you have to put a " - " before the number otherwise it's a DOME.

Also, 12.98:1 compression is not too bad. I'm going with 12:1 on my 2.3.



Gilles
2.3 Ho

Ohhh MAN thanks that cleared up alot for me ... you think its possible to run 11:1 on 93oct ? or would i have to pull timing a little? Thanks again !!!!!!

11:1 would be fine on 91.



Gilles
2.3 Ho

one last question Im getting the 086 head port and polished would that change the head CC ? thanks and whats the highest compression i can on pump gas 93 oct?

Ohh and ive messes around with the ross piston calculator and i found that the pistons on a 2.3 are 7.5cc dish stock bore im i right ?

around 7.3 7.5 cc for the Ho pistons. The Lo are 11.5cc

you should be able to run 12:1 with 93 octane no problem. At least I will.



Gilles
2.3 Ho

also, a port and polish is in the PORT, not the combustion chamber. You can modify the combustion chamber but it's dangerous with a 086 head.



Gilles
2.3 Ho

hurmmm whats the difference between a Dome, Dish or valve pocket.. is a DOME a flat top and Dish a piston with valve pockets or deep for the valves not to hit the piston ? and how deep does it have to be so that the HO cams (.410) lift wont hit the piston? is there a minimum required because like yall stated before the ho pistons are 7.4 - 7.5 cc ?

A dome is a dome, A dish is a dish and valve pockets are valve pockets.

You can have a dome with valves pockets, a dish with valves pockets and a flat top with valves pockets.

A dome is the opposite of a dish. The dish is a lower spot on the pistons and a dome, well, it's a dome.

A flat top stay a flat top.

A dish will have -X cc, a flat top as 0cc and a dome will have +X cc.

The dish/dome is not the only thing you have to look for when you want valves clearance. The desing of the head is a big thing to understand. Like on the 2.4, the valves head are a bit higher than on the 2.3 so you can use more lift on a 2.4 than on a 2.3 head(that's using the same block and pistons).

There's a minimum distance between the valves and the pistons that you want. Better be safe than sorry. It all depend on what you build and what you use. Like I'll be using a set of 12.0:1 compression ratio Wiseco pistons. They will have a DOME top with valves reliefs.



Gilles
2.3 Ho

Great info guys! Not to jack your thread, but how much would upping the compression ratio help?....performancewise?



2004 Cavalier
13.2@105........
Mods...
BFG Drag Radials
Saab Turbo kit
2.5 exhaust, w/cutout
Spec Stage 2+ Clutch

You say that your going to run 12:1 with 93 oct ... how is that possible ? my understanding and what ive heard around is that 12:1 would need race gas or Time retarding .. if not please educate me on how your going to run 12:1 if you dont mind please. im only going 11:1 because of Gas perposes theres not a track around here for miles and no were to get race gas and shoot if i can use 93 with 12:1 compression .. 12:1 it is. I order my 086 head already so just a matter of time before i order my pistons and hopefully you can help me out . later Thanks.

On the 2.4 it's alot easier than on a 2.3.

The 2.4 run 9.7:1 stock on 87. So going with 12:1 with 93 octane is really easy. Alot less chance of detonation compare to my W41. The timming the 2.4 has is not high so you can run it no problem.

I'll be running 12:1 with bigger cams with a modify Scx ecm on 93 octane. My cams have more overlap than stock Ho/W41 so it will help there. I'll also be running alky injection as a precaution. My timming on the W41 will not be reduce. If anything, it will be advance.

I can get race gas here easily so it's not a problem if I ever want to convert. I'll be running alot of alchool before going to race gas. Even tough it would smell so nice



Gilles
2.3 Ho

So this 12:1 engine your building is it still Streetable ? can you drive it acros town to the grocery store ? seems like everyone wants to run the same thing. im gong to run the 086 head with the HO cams because they seem perfect for a nitrous application . Im going to run Hptuners software so im pretty sure its going to be Easy to run 93 oct on 12:1 compression. how do you think my auto tranny is going to like it ?

You'll have an idle like a V8 The tranny will take it. it's not compression that break tranny.

Yes it's a street car that will see the stripp alot of times. I'll drive it in town for sure. Nothing's better than being at the stop light in town and everybody that walk by your car are like



Gilles
2.3 Ho

I love the sound of a Cammed V8... Loopinn.. I sometimes hear my dad's mustang waiting to see if it turns off hopefully i get some 8.5's at the 1/8 or better... and low 8's with 75 shot .... Hopefully it turns out good cause all my buddys are awaiting the Slow Cavy.... they say i wont break the 8's that if im lucky ill get 9.2 all motor......