sohc 12valve piston discussion

[Sundance 6g72]

piston on the right is a 93 piston, on the left is 99 piston
(or so im told!) Notice the difference in height between the top ring and middle ring. also notice the difference in height between the top of the piston and the top of the ring



notice thering gap difference. the bigger gap is on the 99 piston. other piston is a 93 piston



left 99, right 93. 93 appears to be stronger by its shape. possibly a heavier piston.




now piston on the left has an unknown year (it belonged in bobbys daytona before he switched to 10:1 pistons) Im asking him on FB for the year right now





from what i know, the 93 piston and the piston from bobby look to be 8.5:1 pistons and should be stronger in theory due to ring placement. I melted one of my 93 pistons on 10psi but i also spiked 13:1 afr and ran more timing that i had in the past. Add a capped off stock rear manifold to the mix and you get higher egt on cyl 1 and 3. (piston one is what melted!)

i could have avoided ruining that piston with a high flowing rear manifold potentially BUT should have made sure the tune was good in the first place.






So whats the deal? the 99 pistons have the Mitsubishi symbol on them, those are said to mean they are the 8.9:1 pistons. My 93 pistons are said to also be 8.9:1 but looks like we have some possible mis information? Maybe my 93 are 8.9:1 and the 99 pistons are actually the rumored 9.3:1 (or something like that)

can someone get pictures of the 10:1 pistons as well? There are two 10:1 blocks locally here but i dont have the money to buy those just to get pictures :{

---------- Post added at 02:35 PM ---------- Previous post was at 02:34 PM ----------

keep in mind i have not actually measured anything! But its pretty clear that the 99 pistons have the bigger gap just by looking at them. all other differences are also visable to the naked eye.


EDIT: 10:1 piston pics!

[Juggy]

the older 3.0L piston i believe was 8.85:1, the 98+ pistons were 9.1?? :1

the newer design piston got a small bump im compression, which raised hp from 140 to 150.
anything from 1998 and up is the newer designed piston

[Ondonti]

Your motor must not be original, OR, 1994 is the actual changeover year for pistons. I already noted these piston differences years ago on TD and that the larger ringland piston would theoretically be better if you had larger ring gaps. That said, All the original 3.0 "boosted" blowup motors 8-10 years ago were all older early circa 1990 motors.

The compression difference between those pistons is 8.85:1 (oldschool) and 8.9:1 (new small skirt style).

Ring gaps can only be measured in the bore. Mitsubishi has a huge tolerance so its really difficult to say that ring gaps ever changed. One motor can be huge, one can be small, its all in spec.

The chrome rings I ordered were for the modern thin ring 3.0 piston. 1.2mm top ring is better for revs. 1.5mm ring is very thick for 8000 rpms. Power could drop off simply because the ring will not behave at that RPM.

[Sundance 6g72]

my 1993 motor is 100% original. I know this because my dad is the first and only owner in its entire existence.

and yes, i stated a few facts that your self told me, just so i could get them down "on paper" for everyone.

im kinda excited that i probably have 8.5:1 due to slightly lower comp. and a stronger piston.

But like the first reply says, compression was raised anything 98 and up.. did you ever have a 98+ motor, Brent? I dont know how to check if one piston would make more compression than the other.

[Force Fed Mopar]

Brent, what are the specs on the 7.5 pistons you bought for the Duster?

[Ondonti]

Somewhere in paperwork. .96 overbore I believe. 1.2 1.5 and 3.0mm rings. OEm style dish, just extra deep. Valve pockets that had to be flycut because I had oversized valves. I removed enough head chamber that it dropped compression down near 7.

[c2xejk]

Joe, do you have a scale to weigh the two pistons? The '99 looks like it might be a lot lighter which would be good for reving...

[Sundance 6g72]

^ my thoughts exactly. Ill make sure to weigh them when i do a weight difference for the valve train parts. I have to get ahold of a scale that measures such light things.... only person i know who would have that is some pot head kids.. lol no joke. Plenty of them around here shouldnt be too tough >.<

[Force Fed Mopar]

Post office sells a small scale cheap.

[Ondonti]

I will say it again, that is not a 99' piston since the same piston came in 1994 K based cars. That is the standard replacement 8.9:1 piston. 8.85 is the beefy large ring piston. The only motor I have ever seen with 8.85:1 pistons was the late 80's 3.0 slider motor that was in the trunk of my Duster when I bought it. 8.9 pistons are also the only pistons I have ever broke (my 8.85 motor was not really usable, but that is what Joe broke).

[Sundance 6g72]

I will say it again, that is not a 99' piston since the same piston came in 1994 K based cars. That is the standard replacement 8.9:1 piston. 8.85 is the beefy large ring piston. The only motor I have ever seen with 8.85:1 pistons was the late 80's 3.0 slider motor that was in the trunk of my Duster when I bought it. 8.9 pistons are also the only pistons I have ever broke (my 8.85 motor was not really usable, but that is what Joe broke).

i thought the motor said 94 until a guy pointed out that it says 99.. i looked at the writing again and it said 1999 (the last 9 could be argued as a 4 but im almost positive it was a 9.)

how can i check the block for a build date or a vin number?


what i am 100% sure of is that the piston i broke is without a doubt a 93 piston. Have yet to hear from bobby what year pistons he sent me. I asked for 8.9:1 and he sent me what he thought was 8.9:1.. im assuming he has a year that we assumed was the switchover year.

[Ondonti]

Well like I said, if it started in 1994 then its not a new design and the compression level is 8.9. The older piston looks the same as the 80's slider pistons.

[paduster]

I got some 10:1 piston pics on my Facebook if u wanna post them here I still can't figure out how to attach pics on this site.

[Sundance 6g72]

right click the picture when your viewing it and click "copy image location" and then when making your post click on the insert image button (third from the last) and paste your link

[paduster]

Yea only have my phone right now computer getting worked on

[Ondonti]

PADUSTER's pics from facebook.







https://fbcdn-sphotos-a.akamaihd.net...57723221_n.jpg

If you hit refresh on your flash style picture, it reverts to a normal website view. THen you can right click and copy the image link. THen hit the picture button on here and paste the link "FROM URL" and upload. I prefer to never upload pictures here, just hotlink. Your mobile folder is public so hotlinking seems to work.

[paduster]

Thanks

[Sundance 6g72]

hotlinking seems to always work from facebook no matter what. lol so much for safe and secure. not that i care but some people do.

ill put those pics in the main post

They look like the 8.9:1 pistons but have the extra valve cut for the exhaust valve. I wonder how strong they are on 93pump with boost. probebly a dumb idea to not use e85 with a "high compression" piston. e85 dosnt care though.

[Ondonti]

Not sure about 93 octane. I might try it in the future on the 10:1's. Good way to keep power down.

[paduster]

Well I got e85 near me and 93 so when I build this I will find out