1098 C/R with 12G295..?
Turbo Mini Forums

Okay soo I finally found my mini to turbo!! 8-)

From what I know it has a standard 1098 bottom end at the moment, which I am going to be pulling down for a rebuild etc soon.

I am thinking of buying a 12G295 head to lower the C/R to somewhere around the 8.5-9.0 mark so I can run a reliable 10psi.

I have been reading about converting a 998 to 1098 by changing the rod & crank, and then you have to skim the 998 head so you get a decent NA C/R. So I'm thinking it'll work the other way... I think... Am I right guys.

Just to clarify -- By putting a 12G295 on my 1098 engine it will lower the compression ratio to somewhere around what I want??

..thats simply put.. there may be other mods to consider, but Im just making sure before I go and buy the head! :) Who knows, i'll probably find out im on drugs and im thinking like a crazy man!! Feel free to tell me tho..

Cheers,

Sam

You are right.

Your CR will all depend on your pistons. If they are flat topped then the CR may be a little on the high side. If dished, which I suspect they are, then you will be OK.

Best measure it all up and work it out.

If you are buying a 12G295, check that it has not already been heavily skimmed - most in the UK have.

Saul Bellow - "A great deal of intelligence can be invested in ignorance when the need for illusion is deep."
Stephen Hawking - "The greatest enemy of knowledge is not ignorance, it is the illusion of knowledge."

Shweeeet..

Yep my pistons are dished, no idea what cc though..

Hypatecs --



And this is the head, its apparently unmodified and from what my naked eye can tell, i think it is too --

Edited by spraycanmansam on 3rd Jun, 2007.

Measure the thickness of the head. It should be 2.75" it if has not been skimmed.

Do the pistons have a part number?

Saul Bellow - "A great deal of intelligence can be invested in ignorance when the need for illusion is deep."
Stephen Hawking - "The greatest enemy of knowledge is not ignorance, it is the illusion of knowledge."

perhaps if you measure down from the deck to the bottom of the chamber between the valves someone on here could tell you wether its skimmed or not ?

Medusa + injection = too much torque for the dyno ..https://youtu.be/qg5o0_tJxYM

Yep i would measure stuff If I had it on me! I only recently confirmed the pickup of my mini, and now im buying stuff like mad..

I mite see if i can get him to measure it for me.. so 2.75" face-to-face?

Um i did a quick search and I cant find the part number of the Hypatecs, but heres the link where I'm ordering them from if it helps --
http://www.minisport.com.au/prod26.htm

They're s'posed to be a fairly good piston and somewhat more reliable than the AE ones you guys have over there?

Yes 2.75" face to face.

I suggest you ask Minisport what is the cc of the dish, otherwise you are flying blind.

I think that the Hypatecs are marketed here as Mega pistons and they have a good reputation.

Saul Bellow - "A great deal of intelligence can be invested in ignorance when the need for illusion is deep."
Stephen Hawking - "The greatest enemy of knowledge is not ignorance, it is the illusion of knowledge."

I figure its somewhere around the 6-8cc mark.. dunno why! yes, ill have to email them..

Cheers :)

On 3rd of Jun, 2007 at 04:35pm spraycanmansam said:
I figure its somewhere around the 6-8cc mark.. dunno why! yes, ill have to email them..

Saul Bellow - "A great deal of intelligence can be invested in ignorance when the need for illusion is deep."
Stephen Hawking - "The greatest enemy of knowledge is not ignorance, it is the illusion of knowledge."

as std your 1098 should sport a 12g202 (ell me if im wrong)

this has a 26.1cc chamber, so a 12g295 (28.3cc) will add around 2cc..

out of curiosity and a bit o/t, are all 1098 pistons dished? werent std ones flat top?

"Turbo's make torque, and torque makes fun"

"did you know you can toast potato waffles?"

1098's were in the vast majority A series, there were a very small amount of A+ ones I believe. Anyway all the A series ones had dished pistons, as did all the bread and butter 998 A's

Yep they came out with the 202's as far as I know

I like the combustion chambers of the 295 better though..

IMHO i think that they'd be less prone to hot-spots.. bad for turbo! and I cant be stuffed modifying a 202

If your unsure of piston and chamber cc's, and want to check...

1. Get something flat like a CD
2. smear a ring of grease around the top of the piston (as thin as pos.)
3. Press CD down on top of piston
4. use a syringe with somehthing like oil or parafin (idealy) take note of how many cc's are in the syringe and squirt it into the centre of the CD until the liquid is level with CD.
5. Repeat method for head (making sure it is free from any carbon first)

This should get you a fairly accurate measurement of what the cc's are.

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www.fusionfabs.co.uk



1/4mile in 13.2sec @ 111 terminal on 15psi

I got an email back today for anyone who wants to know.. the dish is 7cc. I wasnt too far off..