4g61t.org

i have been looking for some pistons for my 88 mirage with a g32b engine, i found some online that said they were for my engine but found out when i got them that they were not the same. the pistons i bought are for the non turbo engine, the seem to look and have the same measurements as my stock piston except for the dish in the top of the piston. my stock pistons have about a quarter inch deep dish in them, and the ones i got online is less than half of that.
has anyone had this problem before or any experiance using non turbo pistons in their engine? i know if i use the non turbo pistons with less dish i will raise my compression ratio but i am wondering if it will hurt anything? and if it is ok to use the new pistons will i have to modify anything to compensate for the higher compression?
i appreciate any kind of help, thanks.

Do you have a way to monitor air fuel ratios and alter them if needed? I am honestly not sure if changes to the AFR will be needed due to an increase in compression ratio. BUT an increase in combustion chamber temperatures will definitely occur as a result of increasing the pressure in said chamber. Do you happen to know what the total change in compression ratio or combustion chamber pressure will be?

On previous builds, I have utilized a NA 4g63 with a 9:1 CR with a turbo ECU, stock 14b turbo and stock 450cc/min injectors to no ill effect. I actually observed the typical extremely rich AFR situation that the stock ECU likes to be at when at WOT. BUT the difference in CR between the turbo and NA 4g63 is 1.2;1 (7.8:1 for the turbo engine, 9:1 for the NA).

no i do not have any way to monitor the air fuel ratio or any way to alter it. but according to the online ad the turbo ratio is 7.6:1 and the non turbo is supposed to be 8.5:1. i hope this helps.

OK as far as my understanding of the issue is concerned with the increased compression will come an increased chance of detonation meaning that you are likely to experience engine knock. I don't think that you will have any change to the fuel air mixture as the total amount of air and fuel drawn into the engine will not change only the pressure it is under.

I would think that there would be two ways to combat this detonation, by going to a higher octane fuel and perhaps reducing the pressure from the turbo.

You could always lengthen the waste gate rod to decrease the pressure from the turbo but if you had to use the pistons that you purchased I would suggest that you start with the higher octane and see how it works out. If you experience knock you could then begin to increase the length of the wastegate rod to reduce the pressure until the engine stops knocking.

I suppose that the other concern would be to make sure that the bottom end of the connecting rod works with the crank that is in our G32BT engines...

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84 Turbo
Intercooled

i went and measured the the difference in the depth of the dish in the two pistons and my original piston is dished about 3/16 deeper than the non turbo pistons i bought. the pistons i bought are ITM and was wondering if anyone has any experiance with them?